Tesis Doc o al
Ingenie ía de Telecomunicación
G id aul s de ec ion and con ol
o powe con e e s o dis ibu ed
gene a ion sys ems
Au o : Jesús Muñoz-C uzado Alba
Di ec o es: Edua do Gal án Díez y Juan Manuel Ca asco
Solís
Ingenie ía de Elec ónica
Escuela Técnica Supe io de Ingenie ía
Uni e sidad de Se illa
Se illa, 2016
Tesis Doc o al
Ingenie ía de Telecomunicación
G id aul s de ec ion and con ol o powe con e e s o
dis ibu ed gene a ion sys ems
Au o :
Jesús Muñoz-C uzado Alba
Di ec o es:
Edua do Gal án Díez y Juan Manuel Ca asco Solís
Ca ed á ico y Ca ed á ico
Ingenie ía de Elec ónica
Escuela Técnica Supe io de Ingenie ía
Uni e sidad de Se illa
2016
Tesis Doc o al: G id aul s de ec ion and con ol o powe con e e s o dis ibu ed gen-
e a ion sys ems
Au o : Jesús Muñoz-C uzado Alba
Di ec o es: Edua do Gal án Díez y Juan Manuel Ca asco Solís
El ibunal nomb ado pa a juzga la Tesis a iba indicada, compues o po los siguien es
doc o es:
P esiden e:
Vocales:
Sec e a io:
acue dan o o ga le la cali icación de:
El Sec e a io del T ibunal
Fecha:
A C is ina y Elena
VIII Resumen
bles si uaciones de islanding. Una si uación de islanding se puede p oduci cuando al
desconec a una pa e de la ed, la sub ed es an e queda ene gizada po que se dan los
siguien es dos ac o es: la p oducción y el consumo o al en la sub ed son ap oximada-
men e iguales; y que la ecuencia de esonancia de la sub ed en es as condiciones es á
den o del ango de ope ación de la ecuencia de ed del sis ema. Po lo an o, se ha desa -
ollado una nue a écnica an i-islanding que mejo a signi ica i amen e las p es aciones
en e a o as p esen es en la li e a u a. En e las en ajas del nue o mé odo es án que se
puede aplica en cualquie pun o de abajo, in oduce meno es pe u baciones al sis ema,
su zona de no de ección es nula, y conse a un buen iempo de de ección de si uaciones
de islanding.
Po o o lado, el con ol de con e ido es de po encia en e a al as de ensión ha sido
a ado ampliamen e en la li e a u a. G an pa e de la in es igación en es e campo es á
cen ada en el con ol du an e la al a en sí misma. Sin emba go, el ansi o io en el inicio
de la al a suele se mucho más ápido que la ecuencia de con ol del sis ema, lo que
puede lle a a una posible si uación de ines abilidad en la que la máquina obse e un
pico de co ien e po encima de los lími es de segu idad pe mi idos. A endiendo a es a
p oblemá ica, se ha desa ollado un nue o mé odo que igile y con ole que no se alcancen
los alo es de segu idad lími e es ablecidos, e i ando posibles a e ías y desconexiones
indeseadas en el caso que el con olado de co ien e no u iese iempo de ac ua .
Todas las apo aciones han sido alidadas expe imen almen e con máquinas indus i-
ales come ciales de g an po encia en ins alaciones eales en a ios países.
Con en s
Abs ac V
Resumen VII
1 In oduc ion 1
1.1 P elimina y conside a ions 1
1.1.1 F equency excu sions 4
1.1.2 Vol age excu sions 4
1.1.3 Vol age sags and phase-jumps 6
1.1.4 Islanding cases 10
1.2 Objec i es 11
2 Con ibu ions o An i-Islanding me hods 13
2.1 Con ibu ion desc ip ion 13
2.2 P oposed me hod: Q- d oop an i-islanding algo i hm 15
2.2.1 Analysis o Q- d oop cu e 15
2.2.2 Q- co ela ion me hod 17
2.3 Resul s 19
2.3.1 Simula ions 19
AI uning me hod 21
2.3.2 Me hod esponse e alua ion 22
Compa a i e es s wi h o he me hods 24
2.3.3 Expe imen al es esul s 25
Tes bench UL and IEC esul s 25
2.3.4 Beha iou in a eal Indus ial Sola Powe Plan 27
2.4 Conclusions 28
3 Con ibu ions o ol age sags compensa ion echniques 29
3.1 Con ibu ion desc ip ion 29
3.2 P oposed me hod 30
3.2.1 Powe Con e e Con ol S a egy 30
IX
XCon en s
3.2.2 Fas P edic i e Peak Cu en Sa u a ion Me hod 31
3.2.3 Du y Signal Upda ing Imp o emen Me hod 32
3.3 Resul s 36
3.3.1 Simula ions 36
3.3.2 Expe imen al Valida ion 40
3.3.3 Model Valida ion 43
3.4 Conclusions 45
4 Conclusions 47
Appendix A New Low Dis o ion Q- D oop Plus Co ela ion An i-Islanding
De ec ion Me hod o Powe Con e e s in Dis ibu ed Gene a ion Sys ems 49
Appendix B A New Fas Peak Cu en Con olle o T ansien Vol age
Faul s o Powe Con e e s 59
Appendix C A New Fas Peak Cu en Con olle o T ansien Vol age
Faul s o Powe Con e e s 83
Appendix D PV solu ions o g id se ices in Sou h A ica 91
Appendix E Sys em and me hod o peak cu en con ol o a powe con-
e e exchanging powe wi h he g id 93
Lis o Figu es 121
Lis o Tables 123
Bibliog aphy 125
1 In oduc ion
1.1 P elimina y conside a ions
The objec i e o he elec ic powe g id is o p o ide a physical link o deli e he
powe ene gy p oduced by supplie s o he inal consume s. The elec ic powe
g id is made o gene a ion plan s, dis ibu ion lines links, subs a ions, and consume s’
poin s [1]. The elec ic g id scheme is di ided in o wo pa s clea ly di e en ia ed: he
ansmission g id; and he dis ibu ion g id [2]. Fig. 1.1 shows a ypical s uc u e o
an elec ic powe g id. In one hand, he ansmission g id usually is made o high and
e y high ol age links, only he la ges gene a ion plan s and consume s a e connec ed
o i di ec ly. Fo example, he mal and nuclea powe plan s and e y la ge acili ies
a e connec ed o he ansmission g id di ec ly. On he o he hand, he dis ibu ion g id
is made o low ol age links, and i is esponsible o connec he g id he consume s’
subs a ions and small size gene a ion plan s, like pho o ol aic and wind- u bine a ms.
In pa icula , he enewable ene gy plan s (REPs) p oduc ion has g ow h signi ican ly
in he las yea s [3–5], inc easing no ably hei pene a ion ac o [6–9]. Fig. 1.2 shows he
e olu ion o pho o ol aic (case a) and wind- u bine (case b) echnologies powe ins alled
. Bo h cases ha e an exponen ial endency in he las yea s. This is possible due o he
p og essi e cos educ ion and he e iciency imp o emen o e he used echnology.
1
2Chap e 1. In oduc ion
Figu e 1.1 Elec ic powe g id scheme: (yellow/ ed) ansmission g id; (g een) dis i-
bu ion g id [10].
(a) (b)
Figu e 1.2 Wo ldwide ins alled powe e olu ion o wo ep esen a i e REPs echnolo-
gies: (a) pho o ol aic ins alled powe ; (b) wind ins alled powe [4].
1.1 P elimina y conside a ions 3
The e o e, he elec ic powe g id model showed in ig. 1.1 is changing by wo ways. In
one hand, pas REPs we e o small size; consequen ly hey we e connec ed di ec ly o he
dis ibu ion g id wi h small Dis ibu ed Gene a o s (DGs). Howe e , ecen REPs ha e
g ow h in size by joining a bigge numbe o DGs on he same plan ; he e o e, new plan s
a e connec ed o he ansmission g id di ec ly. On he o he hand, he inc emen on he
numbe o REPs has inc eased signi ican ly he amoun o powe gene a ion inside he
dis ibu ion g id. Nowadays, his issue induces ha elec ic powe g ids ha e o conside
he concep s o sma g ids [11].
REPs inc emen has led o a signi ican de elopmen o new in e na ional legisla ion
ela ed o equi emen s o REPs o be connec ed o a speci ic elec ic powe g id [12–
24]. Fig. 1.3 shows how he numbe o coun ies wi h REPs legisla ion has g ow h las
10 yea s, om ew coun ies wi h legisla ion o be p esen almos in e e y coun y [4].
Nowadays, new REPs mus help he elec ic powe g id o i s secu i y, s abili y, and e-
co e y. The objec i e is ha he elec ic powe g id will be obus enough unde he new
condi ions. Requisi es imposed by he g id codes o he local u ili y g id a e known as
minimum echnical equi emen s (MTRs), and REPs mus comply wi h hem o be au-
ho ized o he connec ion o he elec ic powe g id.
(a) (b)
Figu e 1.3 REPs ins alla ion in e na ional legisla ion e olu ion: (a) Coun ies wi h eg-
ula o y legisla ion abou REPs in 2005; (b) Coun ies wi h egula o y legis-
la ion abou REPs in 2015 [4].
MTRs egula e a lo o di e en aspec s ela i e o he gene a ion plan s wo king: o-
al ha monic dis o ion (THD) h esholds; g ounding and isola ion uni aul s; beha iou
agains ex e nal condi ions (dus , humidi y, e c.); beha iou agains elec ic powe g id
aul s; and o he ones. Speci ically, he beha iou agains elec ic powe g id aul s has
had a signi ican ele ance in las yea s. The g ow h o he pene a ion ac o o REPs in
he elec ic powe g id becomes he beha iou agains g id aul s c i ical.
Main aul ypes s udied by he MTRs a e he ol age and equency excu sions; ol age
sags and phase-jumps; and islanding cases.
4Chap e 1. In oduc ion
1.1.1 F equency excu sions
F equency excu sions a e ela ed o de ia ions o he measu ed g id equency espec
wi h i s nominal alue. The uni wo king ope a ing ange de ines one o mo e iming s eps
wi h an associa ed equency h eshold each one. I he measu ed equency eaches an
e o h eshold con inuously du ing a p ede ined ime, he gene a o will p oduce a con-
olled disconnec ion om he elec ic powe g id. Unde and o e equencies h esholds
a e de ined. This p o ec ion is known as he equency ide h ough (FRT) o he uni .
Once he equency g id condi ions a e e-es ablished inside he wo king ope a ing ange
he DG e-connec s o he elec ic powe g id.
A equency egula ion (FR) ac ion could be equi ed oo. FR echniques de ine a d oop
cu e o be applied o e he ac i e powe e e ence. The objec i e is o help he sys em
eco e y o he nominal g id equency.
Table 1.1 shows FR and FRT equi emen s o some o he mos ep esen a i e in e -
na ional g id codes [12,14,16,17,22,23]. The e a e impo an di e ences be ween he
g id codes. FRT equi emen s could a y om only one h eshold, as he I alian g id code
[14], o cases wi h se e al h esholds, as he Sou h-A ican g id code [16], wi h up o i e
de ined unde - equency excu sions s eps.
FR echniques ha e s ong di e ences be ween hem, oo. Ge man and I alian leg-
isla ions [14,17] desc ibe he classical d oop cu e. FR ac ions begin when a s a ing
equency is eached (Ge man code: 50.2Hz). Then a d oop gain educes he ac i e ou -
pu powe o he plan . Consequen ly, he ac i e ou pu powe du ing he aul is lowe
han he ac i e ou pu powe p e ious o he beginning o he aul condi ion (PM). How-
e e , i he equency is es o ed pa ially, he d oop ac o emains on his lowes alue.
The d oop ac o is cancelled only when he equency eco e s o nea ly he nominal g id
equency alue (Ge man code: 50.05Hz).
Pue o Rico, Mexico and Sou h A ica equi emen s [16,22,23] look alike o o e -
equencies, bu es ablish special equi emen s o unde - equencies. The main di e -
ences o o e - equencies aul s beha iou a e he de ined hys e esis cu es, and he d oop
gain is ela ed o he nominal ou pu powe o he plan (Pn), ins ead o PM. Howe e , o
unde - equencies an ex a ese e o powe o an ene gy s o age sys em (ESS) is equi ed,
in o de o inc ease he maximum a ailable powe o he plan (Pa a) when necessa y.
Finally, Chilean code [23] is simila o Ge man legisla ion, bu FR eco e y is no so
ab up . Howe e he es o a ion is pe o med wi h he same equency amp han down-
wa ds, only i is imed o a maximum o 0.2p.u./min.
1.1.2 Vol age excu sions
Vol age excu sions a e egula ed wi h a wo king ope a ing ange also, bu ela ed o he
AC ou pu ol age. Simila ly o he equency case, se e al ol age s eps could be de ined.
O a maximum allowed ol age sag p o ile could be de ined by he g id code.
Apa om he ol age h esholds, a ol age con olle could be used o e-es ablish he
nominal ol age. The injec ion o eac i e powe o he g id usually changes signi ican ly
he g id ol age. The con olle usually is e e ed o he plan poin o common coupling
(PCC) ol age [16,17,22], bu he e a e also cases e e ed o he DGs local ol age
1.1 P elimina y conside a ions 5
Table 1.1 REPs equency egula ion MTRs e iew. Ge man associa ion o ene gy and
wa e indus ies: BDEW; Elec o echnical I alian Commi ee: CEI; Na ional
ene gy egula o o Sou h-A ica: NERSA; Elec ici y ede al commission:
CFE; Pue o Rico Elec ic Powe Au ho i y: PREPA; Na ional Commission
o Ene gy: CNE..
Coun y FRT FR
Ge many
(BDWE)
T (s)
(Hz)
0.0
50.0
47.5
60.0
51.5
1.0
PM
(Hz)
1.0
0.6
50.0
50.05
50.2 51.2
I alia
(CEI)
T (s)
(Hz)
0.0
50.0
47.5
60.0
51.5
1.0
PM
(Hz)
1.0
0.0
50.0 50.3 51.5
Sou h-A ica
(NERSA)
T (s)
(Hz)
0.0
50.0
47.5
47.0
51.0
52.0
60.0
48.0
49.0
51.5
0.2 10.04.0 6.0
46.0
PM
(Hz)
Pa a
1
50.0 52.0
2
3
5
Pmin
6
Mexico
(CFE)
T (s)
(Hz)
0.0
60.0
57.5
62.0
600.0
58.0
58.8
62.5
5.0
61.2
0.1
ΔP/ Pn
(Hz)
0.1
49.75
50.0
52.5
-1.0
Pue o Rico
(PREPA)
T (s)
(Hz)
0.0
60.0
57.5
56.5
61.5
62.5
10.0 30.0
ΔP/ Pn
(Hz)
0.1
59.7
60.0
59.988 60.3
60.012
-0.1
Chile
(CNE)
T (s)
(Hz)
0.0
50.0
47.5
47.0
52.0
150.0
48.0
49.0
51.5
15.0
PM
(Hz)
1.0
0.0
50.0 50.2 1
6Chap e 1. In oduc ion
[14].Table 1.2 sums up main ea u es o some o he mo e ep esen a i e MTRs ela ed
o ol age egula ion sys ems (VRS) wi h eac i e powe injec ion equi emen s.
Table 1.2 REPs ol age egula ion MTRs e iew. Ge man associa ion o ene gy and
wa e indus ies: BDEW; Pue o Rico Elec ic Powe Au ho i y: PREPA;
Na ional ene gy egula o o Sou h-A ica: NERSA; Elec o echnical I alian
Commi ee: CEI.
Coun y Ge many Pue o Rico Sou h-A ica I aly
S anda d BDEW PREPA NERSA CEI
Con ol ype Open loop Close loop Open loop Open loop
Re e ence ype cos φ/ex e n Q ex e n Q ex e n Q P e-de ined cu es
Measu e poin PCC PCC PCC DG ou pu
Response ime 10s1s30sN/D
1.1.3 Vol age sags and phase-jumps
Vol age sags and phase-jumps MTRs de ine he DG beha iou in o de o help he sys em
eco e y om he ansien aul condi ion. Mo eo e , MTRs poin ou he se e es g id
aul s ha he DGs mus bea wi hou p oducing he disconnec ion om he elec ic powe
g id. Table 1.3 and 1.4 show wo impo an equi emen s ela ed o ol age ansien
aul s o ecen and ep esen a i e MTRs [12–17,22,24]: maximum allowed ol age sag
p o iles; and he ac i e and eac i e cu en injec ion equi emen s du ing he aul .
Vol age sag p o iles a e di e en o each g id code; howe e some guidelines could be
es ablished. Fi s , a alley ime is se wi h a ela ed admissible minimum ol age module,
he alue usually is ze o o nea o i . I he aul eaches he e o p o ile, he in e e
is allowed o disconnec . The alley ime could las en h o seconds. And a second
pa de ines a maximum eco e y slope o he ol age sag, in o de o p e en he uni
disconnec ion.
Fo example, he Ge man p o ile [17], an impo an e e ence o new MTRs, has wo
de ined alleys ha p e en he ol age module d ops he speci ied limi . A ze o- ol age
ansien aul is equi ed o 0.15s, and hen ol ages below 0.3p.u.a e no allowed un il
0.6s. A e he alley, a amp eco e y o 0.9sis de ined. Recen legisla ion imposes a
ze o- ol age aul oo, like Pue o Rican o Jo danian legisla ion [22,24]. Howe e , o he
legisla ion is imposing smalle ol age sag magni ude equi emen s, bu longe in ime,
o example Chilean and Romanian g id codes [12,13].
Mo eo e , ecen MTRs some imes add also a ansien o e - ol age p o ile, like Sou h-
A ican case [16].
Then, some equi emen s a e imposed o e he powe gene a ion du ing he ol age
excu sion, in o de o help he sys em s abili y. An injec ion o eac i e cu en (Iq) is
always equi ed. Olde g id codes, like Spanish o I alian legisla ion [14,15], usually
equi e gene a ing he maximum possible capaci i e cu en . Howe e , mos ecen g id
1.1 P elimina y conside a ions 7
codes usually equi e a d oop cu e be ween capaci y cu en he ol age sag dep h, in
o de o p o ide a so ene eco e y [12,16,22,24].
14 Chap e 2. Con ibu ions o An i-Islanding me hods
DG
DG
DG
G id
RLC
PC C
PDG + jQDG
PL oad + jQL oad
ΔP + jΔQ
Powe
Con e e
Powe
Con e e
Powe
Con e e
Figu e 2.1 Island con igu a ion case..
as,
1
Z=1
R+1
jωL+jωC
Pload =V2
PCC
R
Qload =V2
PCC
ωL−1
ωC
x(2.2)
So, i ∆Po ∆Qa e di e en om ze o when an island happens, acco ding o Eq. 2.2,
nex beha iou will be expec ed [27,28]. On he one hand, i ∆P>0, he ol age will
d op o sa is y he equa ion. And i he imbalance is lowe han ze o, he ol age will ise.
On he o he hand, i ∆Q>0, he equency will d op. And, i he imbalance is lowe
han ze o, he equency will ise.
I bo h ∆Pand ∆Qwe e small, he island could no be de ec ed by p o ec ion h esholds,
and he sys em would emain ene gized inde ini ely. AI me hods y o de ec island cases
o s op he DG.
AI me hods can be classi ied in o wo g oups: local me hods applied inside Dis ibu ed
Gene a o s (DGs), o emo e me hods applied a he Poin o Common Coupling (PCC)
[29]. Which can be u he di ided in o wo unc ional ca ego ies, passi e and ac i e
me hods. Passi e me hods a e based on measu es o he sys em and communica ions,
bu hese do no add any dis u bance o he g id. On he con a y, ac i e me hods add a
dis u bance in o de o check a possible island case.
In emo e me hods, he PCC elays communica e wi h he DGs o ip in he p esence
o an isola ed ne wo k wo king as an island [30], o hey in oduce ex a elemen s in he
PCC in o de o o ce he sys em ou o he equilib ium esonan poin . Remo e me hods
a e highly e ec i e, bu hey a e also e y expensi e.
Local me hods a e based on a ailable elec ic in o ma ion and hei de i ed indexes
om ol age and cu en signals.
On he one hand, passi e local me hods do no ha e nega i e e ec s, and hey a e
usually cheap and easy o implemen . Un o una ely, i he s able esonan poin is inside
he h esholds es ablished by passi e p o ec ions, he island could no be de ec ed. The
egion whe e a me hod is no able o de ec an island is called he Non De ec ion Zone
2.2 P oposed me hod: Q- d oop an i-islanding algo i hm 15
(NDZ). Passi e me hods ha e a high NDZ, so hey usually a e complemen ed wi h an
ac i e me hod.
Some o he mos common passi e me hods a e ela ed o equency and ol age h esh-
olds. The O e F equency P o ec ion (OFP), and he Unde F equency P o ec ion (UFP)
de ine he equency ope a ion ange o he DG. Beyond hese limi s he DG is discon-
nec ed. In he same way, he O e Vol age P o ec ion (OVP), and he Unde Vol age
P o ec ion (UVP) de ine he ol age ope a ion ange o he DG.
On he o he hand, ac i e local me hods in en ionally in oduce dis u bances a he ou -
pu o he DG o de e mine i hey a ec he ol age, equency, o impedance pa ame e s,
in which case i is assumed ha he g id has been disconnec ed and he in e e is isola ed
om he load.
Some de eloped ac i e echniques can be poin ed ou : Impedance Measu emen [31,
32], Ha monic Injec ion [33–35] o me hods based on posi i e eedback dis u bance schemes.
The la e ype is e y popula because i injec s a li le dis u bance in s eady s a e ope a-
ion, and when he island happens, he dis u bance will ise ab up ly o ge ou he DG o
passi e p o ec ions h esholds.
The e a e di e en ypes o dis u bances among posi i e eedback me hods like F e-
quency D i , Sliding Mode F equency Shi (SMS) [36], Sandia Vol age Shi (SVS),
o based on eac i e powe dis u bances [37–39], among o he s [40]. The p oposed Q-
co ela ion me hod belongs o he la e ca ego y.
These me hods a e capable o educing he NDZ. Howe e , all o hem in oduce small
dis u bances, hus incu ing in losses and p oducing ha monics in he g id. In o de o e-
duce hese p oblems, di e en solu ions ha e been p oposed; o ins ance, me hods based
on co ela ion be ween elec ic measu es. Co ela ion coe icien s ha e been used la ely
and discussed in ecen publica ions [41–44] o check he s a e o he ne wo k.
The p oposed Q- co ela ion me hod has a good clea ing ime esponse, a ze o NDZ,
and p oduces e y low dis u bances in s eady s a e ope a ion. Fu he mo e, he me hod
has an easy implemen a ion and uning. The p oposed echnique allows ha ing ze o dis-
u bance du ing long equency excu sions.
2.2 P oposed me hod: Q- d oop an i-islanding algo i hm
2.2.1 Analysis o Q- d oop cu e
The e is a ela ionship be ween he eac i e powe in he island subsys em and he s able
equency ope a ion poin (see Fig. 2.2). Fo a load esona ing a 60Hz and wi h he
DGs eac i e powe e e ence se o ze o, he equency will emain wi hin he equency
h esholds ( a- c). Consequen ly, he aul will no be de ec ed.
E en hough he ela ionship be ween eac i e powe and equency is non-linea , i
could be linea ized in a small ange ( a- c) [39]. Fig. 2.2 shows h ee esonan equen-
cies d awn wi h dash lines ( d, b, and e), each one o a di e en esonan load. The
solid line deno ed by Q e ep esen s he DG eac i e powe injec ion. The Q e cu e is
independen o he equency, so i is ep esen ed as a ho izon al line. Bo h exp essions
mus be sa is ied simul aneously in hei in e sec ion, because he DG´s eac i e powe
16 Chap e 2. Con ibu ions o An i-Islanding me hods
59
61
−1.5
−1
−0.5
0
0.5
1
1.5 x 104
F equency (Hz)
Reac i e Powe
−
Resonan cu e C
Resonan cu e E
Resonan cu e D
Q e +
b
a
d c e
Figu e 2.2 Q- d oop cu e and IOP example. Resonan RLC cu es (dash lines) and
DG Q e cu e (solid line)..
(solid line) mus be consumed by he load (dash line) o become a s able sys em. The
in e sec ion be ween he DG and he load cu e will be deno ed as he Island Ope a ing
Poin (IOP). The s able equency ( IOP) o his subsys em is gi en by Eq. 2.3 [39].
Q es( ) = −2P e Q ( − 0)
0
QDG( ) = Q e ) IOP = 0− 0Q e
2P e Q
(2.3)
whe e 0is he nominal g id equency, P e is he DG ac i e powe injec ion, and Q
ep esen s he quali y ac o . Fo he passi e OFP/UFP AI me hod, any load cu e wi h
an IOP be ween poin s dand e o ms he NDZ.
I a small posi i e change in equency +happens o e b, he DG eac i e powe
(solid line) will be g ea e han he load eac i e powe (dash line). Then, he equency
will s a o d op in o de o inc ease he load eac i e powe . So, a he end, he sys em
will e u n o poin b om c. A simila easoning could be done o a small nega i e
change −. In conclusion, bis a s able IOP.
Posi i e eedback me hods add a in o de o make he sys em uns able. Fo example,
i he e was an island, he IOP could be b. I a posi i e dis u bance we e added o e
2.2 P oposed me hod: Q- d oop an i-islanding algo i hm 17
Q e , he ho izon al line would go up, and he IOP would mo e ac oss he esonan load
cu e owa ds a. In he nex algo i hm s ep, a new dis u bance o eac i e powe could
be calcula ed wi h he new IOP poin . A posi i e eedback AI me hod will ha e a g ea e
dis u bance alue in a han in b, so he IOP will mo e s ep a e s ep owa ds d. Once
UFP is eached, he uni will be disconnec ed.
2.2.2 Q- co ela ion me hod
Fig. 3.2 shows a classical con e e DG con ol block scheme. The con olle is di ided
in o he ollowing laye s:
P e SP
Q e SP
Pmax
Pmin
P e ’
Q e
P e
Qmin
Qmax
Id e
Iq e
Cu en
con olle
P e sa lim calcula ion
Q e sa lim calcula ion
High le el
Low le el
Middle le el
Middle le el
IGBT D i e
Sys em
RST/
DQ0
Idq
Ha dwa e
le el
I s Du y Con ol
V s
Vdc
Q- co ela ion AI
+
Figu e 2.3 Simpli ied con ol block scheme o a dis ibu ed gene a o (DG) powe con-
e e .
•High le el con olle : The highe le el con ol is in cha ge o gene a ing he app o-
p ia e ac i e and eac i e powe e e ences p o ided o he lowe le el con olle s.
The pu pose is o b ing he in e e o he desi ed objec i e: maximize he ac i e
powe gene a ion, and help he u ili y g id wi h he eac i e powe injec ion.
•Middle le el con olle : The middle le el con olle is in cha ge o se ing he
con ol ac ions in o de o ollow he highe le el con ol e e ences based on he
in o ma ion p o ided by he a ailable senso s. Mo eo e , sa e y ea u es a e also
conside ed, modi ying he con olle s ac ions in unc ion o ope a ing cons ain s
such as empe a u e and o e ol ages. The p oposed AI me hod is inside his laye .
•Low le el con olle : The low le el con olle includes he inne cu en con ol
loop o he ou pu cu en s.
18 Chap e 2. Con ibu ions o An i-Islanding me hods
ΔQ
Δ
x+
T(x)
QAI
Z-1
-
+
kmem
kpΔ
Cmem Qmem
QΔ
Δ ΔQ
Figu e 2.4 AI Q- co ela ion con ol scheme..
•Ha dwa e le el con olle : The ha dwa e in e ace, which p o ides he swi ching
pulses o he powe con e e semiconduc o s.
The a o emen ioned me hod o con olling he powe con e e includes an AI de ec-
ion algo i hm oge he wi h he passi e p o ec ion gi en by OFP/UFP h esholds. Fig.
2.4 shows he AI con ol block scheme. Upon islanding condi ions, he ac i e p o ec ion
will gene a e a dis u bance in o de o each he passi e p o ec ion limi s. Once any limi
is eached, he powe con e e will be disconnec ed om he u ili y g id.
The algo i hm modi ies he o al eac i e powe based on he measu ed g id equency.
The me hod is based on he posi i e eedback p inciple like o he known echniques [37–
40,45]. Howe e , his me hod does no educe he powe ac o quali y, and i wo ks
p ope ly i he powe ac o e e ence is no he uni y.
The dis u bance algo i hm ou pu (QAI) is calcula ed in wo pa s clea ly di e en ia ed.
Fi s , a new dis u bance alue is calcula ed wi h a p opo ional gain con olle in unc ion
o he equency a e change. This con olle is uned wi h a pa ame e called Kp∆ :
Q∆ =Kp∆ ·∆ (2.4)
Secondly, he las ime s ep ou pu (QAIi−1) is co ec ed in unc ion o he e olu ion
o he sys em in his pe iod. A weigh coe icien is calcula ed wi h he c oss-co ela ion
unc ion be ween equency and eac i e powe inc emen signals, and scaled by he ac o
Kmem. The ime window o he signals in ol ed in he c oss-co ela ion unc ion mus be
high enough o emo e noise om co ela ion be ween he signals. And he ime s ep o
he algo i hm mus be la ge enough so he sys em could each he IOP s able poin .
Cmem =Kmem ·(∆ ?∆Q)i(2.5)
The c oss-co ela ion ou pu is passed in o a simple uzzy logic unc ion called T(x)
desc ibed in Fig. 2.5. T(Cmem)is a memo y ac o o decide i he dis u bance mus be
hold o o go en.
On he one hand, i Cmem gi es a low alue, he e will no be a ela ionship be ween Q
and and he DG will emain connec ed o he g id. So QAIi−1mus be lowe ed in o de
o educe he pe u ba ion injec ed o he g id. Then he ou pu gi es a co ec ion ac o
o blowe han he uni . This alue mus be low enough o emo e he pe u ba ion in a
2.3 Resul s 19
Cmem
T(Cmem)
1
o b
b0b1
-b0
-b1
Figu e 2.5 T(x) uzzy logic unc ion. b0and b1a e he uzzy ule limi s o Cmem o
de e mine a g id connec ed case (Cmem <b0), o an island case (Cmem >b1)..
easonable ime, bu mus be high enough o allow he pe u ba ion emaining along he
ime window o he c oss-co ela ion o de ec an island phenomenon.
On he o he hand, i he Cmem gi es a high alue, he e will be a ela ionship be ween
Qand and he DG could be in island. The co ec ion ac o ou pu mus be he uni
in o de o hold QAIi−1 alue. While b0and b1a e he h esholds ha se he DG sys em
ei he on island o g id connec ed wo king mode. No ice ha he alue o b0mus be
highe han Cmem in g id connec ed mode (Cmem has a esidual alue due o noise), and
lowe han Cmem when wo king in island mode. Finally, b1is se in o de o ensu e a
smoo h ansi ion be ween wo king s a es, based on he accumula ed noise p obabili y
cu e.
As a esul , Eq. 2.6 gi es he co ec ed pe u ba ion alue (Qmem).
Qmem =T(Cmem)·QAIi−1(2.6)
Then, QAI ou pu (Eq. 2.7) is es ima ed by sub ac ing Eq. 2.6 and 2.4.
QAI =Qmem −Q∆ (2.7)
Finally, he calcula ed alue (QAI) is added o he e e ence se poin (Qsp) in o de o
s ablish he eac i e powe e e ence (Q e ), o be p o ided by he in e e , Eq. 2.8.
Q e =Qsp +QAI (2.8)
No ice ha his inno a i e echnique p o ides ze o mean dis u bance, leading o ze o
a e age e o , u he educing losses and ha monics.
2.3 Resul s
2.3.1 Simula ions
The p oposed me hod has been alida ed ia simula ion wi h he elec ic ansien powe
ool EMTDC/PSCAD. The es ci cui shown in Fig. 2.1 has been used acco ding o
20 Chap e 2. Con ibu ions o An i-Islanding me hods
IEC and UL legisla ion [18–21], implemen ing a de ailed wo-le el in e e in he powe
con e e s age and he con olle scheme depic ed in Fig. ??.
The simula ion pa ame e s can be summa ized as ollows:
•Subsys em ac i e powe : PDG =Pload =600kW.
•Con e e cu en con ol: kpD=0.05,kiD=5,
kpQ=0.05,kiQ=5.
•Subsys em eac i e powe : QDG =Qload =0kVa .
•Quali y ac o : Q = [1,2.5].
•G id ol age and limi s: Vn=240V,OVP =1.1p.u.,UVP =0.85p.u.
•G id equency and limi s: n=60Hz,
OFP =63.5Hz/0.1ms,63Hz/50ms,60.5Hz/0.16s,
UFP =56.5Hz/0.1ms,57Hz/160ms,59.8Hz/0.3s.
•Maximum disconnec ion ime: 1s o IEC, and 2s o UL.
•Me hod con olle : Kp∆ = [5·104,5·105],
Kmem = [10−6,10−3].
•Time s ep: 5ms.
•Co ela ion window: N=20 samples.
•T(x)is de ined as: o b=0.95,b0=6.5·10−6, and b1=6.0·10−6
Con ol pa ame e s and elec ic sizing o he DG has been selec ed acco ding o an
indus ial high powe in e e . AI sampling ime (5ms) equi es a slowe dynamic han
he lowe le el con olle . The pu pose is o each he IOP be o e he nex con ol s ep.
The co ela ion window has been adjus ed o mee IEC and UL clea ing ime equi e-
men s, and a he same ime il e ing he noise om measu emen s. T(x)pa ame e s
ha e been se expe imen ally in unc ion o analog boa d misma ching, equency PLL
con igu a ion and equency g id oscilla ions.
OFP/UFP and OVP/UVP a e selec ed based on legisla ion [21] and u ili y g id equi e-
men s. Acco dingly, he e a e h ee di e en equency e o limi s. I he equency
eaches he i s h eshold (63.5Hz o OFP and 56.5Hz o UFP), he uni will be discon-
nec ed immedia ely. On he con a y, he second and hi d h esholds need o be exceeded
mo e han a pe iod o ime be o e doing he uni disconnec ion (50ms o e 63Hz and
160ms o e 60.5Hz o OFP, and 160ms unde 57Hz and 300ms unde 59.8Hz o UFP).
2.3 Resul s 21
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
QAI (kVA )
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−125
0
125
Time
(
s
)
Case c
Case b
Case a
Case d
Figu e 2.6 Q e simula ion esul s o se e al Kp∆ alues: 5·104(a), 7.5·104(b), 105
(c), and 5·105(d). Island wo king mode is igge ed a 1.5s..
AI uning me hod
Two expe imen s ha e been pe o med o ge an app op ia e uning o he me hod. In all
cases, an island has been i ed a 1.5sins an , and he esul ing clea ing ime has been
measu ed.
Fi s , some simula ions ha e been epea ed o se e al alues o Kp∆ . Fig. 2.6 shows
he dis u bance esponse (QAI) added in island condi ion. The simula ion has been pa ame ized
wi h a quali y ac o Q =2.5(wo s case scena io in o de o comply [18–21]). Kmem is
se o 6·10−5allowing a good beha iou wi h he selec ed b0and b1 alues. In case a,
he con olle gain is oo low (5·104), hen he dis u bance g adien will no be enough
o mo e he sys em ou o he s abiliza ion, and he island will no be de ec ed. Case b
se s he gain o a highe alue (7.5·104), and as esul , he island is de ec ed be o e he 1s
clea ing ime equi emen . The igu e shows how he eac i e powe mo es ou o ins a-
bili y a e he 1.5s igge . Once he in e e has s opped, he eac i e powe e e ence
d ops o ze o. Case cse s he gain o a highe alue again (105), ge ing a lowe clea -
ing ime esul . Howe e , case dshows ha i he gain was excessi ely high (5·105), an
oscilla ion o e he eac i e powe ou pu would appea in s eady s a e ope a ion. This
oscilla ion is due o he inhe en oscilla ions p esen ed in a PLL equency. So, he powe
con e e ou pu quali y would dec ease.
Fig. 2.7 shows simula ion esul s o a ange o alues o Kmem be ween 10−6and 10−3
o de e mine memo y ac o in luence. In his case, again Q =2.5, and Kp∆ =105ha e
been se in he simula ion.
Case ashows ha low memo y ac o s (10−6) will inc ease he numbe o non de ec ed
aul s. This is because he c oss-co ela ion measu es a e ne e high enough o hold he
pe u ba ion. Cases band cshow how aising he memo y ac o , he sys em could de ec
22 Chap e 2. Con ibu ions o An i-Islanding me hods
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
Time (s)
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
QAI (kVA )
Case a
Case d
Case c
Case b
Figu e 2.7 Q e simula ion esul s o se e al Kmem alues: 10−6(a), 10−5(b), 6·10−5
(c), and 10−3(d). Island wo king mode is igge ed a 1.5s..
as e he island condi ion and hold he eac i e powe e e ence pe u ba ion. Ne e he-
less, case dshows ha oo high memo y ac o s (10−3) could de e io a e he s eady s a e
esponse, o e en lead he sys em o ins abili y.
2.3.2 Me hod esponse e alua ion
Di e en simula ion es s ha e been pe o med o e alua e he e ec i eness o he p o-
posed me hod o se e al Q . Acco ding o p e ious sec ion, pa ame e s ha e been se o
Kp∆ =105, and Kmem =6·10−5.
Fig. 2.8 shows he me hod beha iou agains an island wo king condi ion. The Q
ac o has been se o 2.5and he b eake has been igge ed a 1.5sin o de o isola e he
sys em and wo k in island mode. The uppe g aphic shows he o al appa en powe in
he PCC, wi h ze o powe consump ion du ing he island case. The second cu e is he
RMS con e e ol age, emaining cons an du ing island phenomenon un il he con e e
disconnec ion. The hi d cu e shows he ou pu ac i e powe o he con e e , poin ing
ou he con e e disconnec ion when he island has been de ec ed. The ou h plo shows
he ou pu eac i e powe cu e and i s e olu ion a e he island e en . Finally, he bo -
om cu e shows he g id equency measu e ipping he OFP h eshold, and i ing he
disconnec ion uni .
Subsequen ly, he me hod clea ing ime was e alua ed by a se o simula ion es s. The
p oposed scena ios co e h ee di e en Q (1,1.75, and 2.5) o h ee di e en powe
le els (0.33p.u.,0.66p.u., and 1.00p.u.).
In island wo king s a e he equency s ep con ol de ia ion depends on he p e ious
Q e de ia ion, as a esul clea ing imes may depend on ini ial condi ions. Be o e en e -
ing he islanding wo king mode, Q e was se in ela ion wi h equency de ia ions, so
2.3 Resul s 23
1 1,5 2 2,5
−10
0
10
kVA
SPCC
1 1,5 2 2,5
0
100
200
300
V
V ms
1 1,5 2 2,5
0
500
kW
PDG
1 1,5 2 2,5
−100
0
100
kVA
QDG
1 1,5 2 2,5
55
60
65
Hz
Time (s)
FDG
Figu e 2.8 AQ =2.5island. PCC appa en powe , DG RMS ol age, DG ac i e powe ,
DG eac i e powe and DG equency espec i ely. Island wo king mode is
igge ed a 1.75s..
Table 2.1 Min./Max. Clea ing ime e alua ion o Q- co ela ion me hod (ms).
P(p.u.)Q =1p.u.Q =1.75p.u.Q =2.5p.u.
0.33 39.6/45.0 41.8/59.5 50.0/60.2
0.66 62.9/65.2 77.4/85.2 94.8/110.3
1.00 98.7/164.0 81.3/172.7 123.5/216.9
e o s in he equency measu es and esonan oscilla ions would change he ini ial condi-
ions. To cope wi h his e ec all cases ha e been epea ed en imes, opening he b eake
a di e en ins an s o look o he wo s case. All esul s a e shown in Tab. 2.1. No ice
ha in all cases he island clea ing ime o 1swas me , p o ing he capabili y o comply
wi h code equi emen s [19].
Finally, a es has been pe o med o e alua e he me hod beha iou in s eady s a e
ope a ion. Tab. 2.2 shows he ou pu eac i e powe esponse espec o he ins alla ion
wi hou he AI me hod, o se e al ac i e powe alues. ∆σQ, and ∆µQpoin ou he
inc emen o he s anda d de ia ion and he mean o he ou pu eac i e powe espec i ely.
Resul s show a small inc emen in he mean and s anda d de ia ion alues o he measu ed
30 Chap e 3. Con ibu ions o ol age sags compensa ion echniques
The e is much esea ch on powe con e e con olle s du ing g id aul condi ions [55–
60], bu un o una ely, he e is no enough analysis abou he uncon olled beginning o he
aul . A as peak cu en con ol (FPCC) me hod has been p oposed o help he con e e
con ol limi ing he o e -cu en peak a he beginning o he aul . Consequen ly, ha d-
wa e and so wa e cu en p o ec ion could be a oided, imp o ing he MTRs compliance.
Fu he , lowe peak cu en educes insula ed ga e bipola ansis o s (IGBTs)’ deg ada-
ion and unexpec ed disconnec ions om he g id o he powe con e e s, so mean ime
be ween ailu es (MTBF) inc eases.
3.2 P oposed me hod
3.2.1 Powe Con e e Con ol S a egy
A wo-le el h ee-phase opology has been selec ed o he s udy. Indus ial high-powe
g id- ie con e e s usually use a single-s age in e e opology, wi h an LC ou pu il e
[61,62].
Fig. 3.2 shows a classical DG con e e con ol block scheme. The con olle is di-
ided in o ou laye s. The highes le el con olle gene a es he app op ia e e e ences
o he middle con olle . The middle le el con olle eac s by modi ying he esponse as
a unc ion o he en i onmen agen s, which could limi he in e e capabili y. Typically,
special ol age sag con ol will be placed a his laye . Then, he low le el con olle in-
cludes he inne cu en con ol loop ha se s he in e e con ol ac ions ollowing he
e e ences. Finally, he ha dwa e le el con olle ansla es he con ol signals o he phys-
ical pulses o he con e e .
P e SP
Q e SP
Pmax
Pmin
P e ’
Q e
P e
Qmin
Qmax
Id e
Iq e
Cu en
con olle
P e sa lim calcula ion
Q e sa lim calcula ion
High le el
L ow le el
Middle le el
Middle le el
F PPC S
I G B T D i e
Sys em
DSUI
RST /
DQ0
Idq
Ha dwa e
le el
I s
Du y C on ol
V s
V dc
Figu e 3.2 Simpli ied con ol block scheme o a dis ibu ed gene a o (DG) powe con-
e e .
3.2 P oposed me hod 31
The p oposed FPCC will be imp o ed wi h wo indi idual ac ions. G ay boxes in Fig.
3.2 show whe e hese ac ions ake place. On he one hand, in he lowe le el, he du y
cycle con ol signal is sa u a ed wi h a heo e ical cu en limi , called he as p edic-
i e peak cu en sa u a ion (FPPCS) me hod. On he o he hand, a he ha dwa e le el,
he delay o du y con ol signal upda ing is educed wi hou modi ying pulse wid h mod-
ula ion (PWM) swi ching equency wi h a echnique deno ed as du y signal upda ing
imp o emen (DSUI).
3.2.2 Fas P edic i e Peak Cu en Sa u a ion Me hod
Fig. 3.3 shows a simpli ied single-line model o he con e e as an ideal con olled ol -
age sou ce. This model has been widely p esen ed in he li e a u e [63]. The con e e
ou pu line- o-line ol age (VgRS,VgST) is de ined by an impedance (Zsc) and a g id ol -
age sou ce. The measu ed ol age could be used o build up an equi alen ol age sou ce
model (VnR,VnS,VnT) connec ed o he i ual neu al poin o he con e e model (no ed
by he dashed lines in Fig. 3.3).
Eq. (3.1) shows he ela ionship o he induc o ol age (VL) wi h he ol age sou ce
model o Fig. 3.3 and wi h he di e en ial equa ion o an induc o :
VL=DVdc
2−Vn
LdIL
d
(3.1)
whe e Vdc is he DC-link ol age, Vnis he g id ol age, Dis he DG du y con ol signal
in he ange o [−1,1],Lis he induc i e alue o he il e alue and ILis he cu en
ac oss he induc ance. Since he con olle is execu ed pe iodically a a ixed equency
Fs, Equa ion (3.1) could be disc e ized, and Dwould be gi en by Eq. (3.2):
Dk=2L(ILk+1−ILk)Fs+Vnk
Vdck
(3.2)
DRVdc/2
LC
Zsc
ILR
VLR
LC
Zsc
VgRS
ILS
VLS
LC
Zsc
VgST
ILT
VLT
DSVdc/2
DTVdc/2
VnR
VnS
VnT
Figu e 3.3 Simpli ied in e e ol age sou ce model.
32 Chap e 3. Con ibu ions o ol age sags compensa ion echniques
Eq. (3.2) gi es he ela ionship be ween IL ime e olu ion and he con ol signal alue.
Consequen ly, he cu en measu emen on he nex s ep con ol could be p edic ed. Im-
posing a con ol law es ic ion wi h a maximum cu en h eshold IFPPCS, Eq. (3.3) se s
a heo e ical maximum con ol signal:
DmaxRk=2L(IFPPCS−IRk)Fs+Vgk
Vdck
DmaxSk=2L(IFPPCS−ISk)Fs+Vgk
Vdck
DmaxTk=2L(IFPPCS−ITk)Fs+Vgk
Vdck
(3.3)
whe e DmaxRk,DmaxSkand DmaxTka e he maximum du y allowed con ol signals o he
de ined IFPPCS in each phase and IRk,ISkand ITka e he measu ed cu en s o he h ee
phases a he kins an .
3.2.3 Du y Signal Upda ing Imp o emen Me hod
Typically, PWM echniques upda e only hei con ol signals in he alleys and peaks o
he iangula ca ie , T0and T2 espec i ely (see Figu e 3.4), gua an eeing non-desi able
i ing, he swi ching equency emaining cons an and a oiding ex a powe losses [64].
Fig. 3.4 shows a ypical delay added in a powe con e e con olle . I he con ol
p ocesso needs he compu a ional ime (Tc) since he las sampling ime (T0), hen an
addi ional delay o Tmwill be inse ed be o e he ac ion will be execu ed, because he
con ol signal can only be upda ed in he peaks and he alleys. The p oposed echnique
upda es he con ol signal a T1wi h some es ic ions. Then, only Tcdelay happens, and
he peak cu en unde aul y condi ions will d op.
T0T1T2
Con ol
delay Modula ion
delay
PWM ca ie
Du y con ol
signal
Tc
Tm
Figu e 3.4 Typical delay added in a powe con e e con olle . The measu es a e aken
a T0, bu Tcis needed o calcula e he nex con ol signal. Finally, he con ol
signal is upda ed and applied a T2. Pulse wid h modula ion: PWM.
As an example, Fig. 3.5 shows all ou possible cases in he up-slope PWM ca ie
semi-cycle, bu simila cases could be exposed in he down-slope semi-cycle. On he one
hand, du ing he up-slope, i he p e ious con ol signal (D0) is g ea e han he iangula
ca ie alue a T1, no ex a ansi ion is gua an eed, and he new con ol signal (D1)
3.2 P oposed me hod 33
could be upda ed wi hou any addi ional swi ching in he semi-cycle (Cases c and d in
Figu e 3.5). On he o he hand, i D0is lowe han he iangula ca ie a T1, a leas h ee
ansi ions may occu i D1is upda ed a T1: he i s one belongs o he D0le el; a second
ansi ion happens a T1; and a hi d ansi ion will happen a he D1le el. Consequen ly,
he con ol signal will be upda ed in he nex alley o peak o a oid ex a swi ching (Case
a in Fig. 3.5). Finally, Case b does no p oduce any ex a-swi ching, bu nei he modi ies
he con ol ou pu .
T1
D0
D1
T0T2
aT1
D0
D1
T0T2
b
T1
D1
D0
T0T2
cT1
D1
D0
T0T2
d
Figu e 3.5 All ou possible du y upda ing cases in he ising PWM semi-cycle. The
con ol signal could be upda ed a T1in Cases c and d, bu mus be upda ed
a T2in Cases a and b..
G aphically, Fig. 3.6 shows an example o PWM signals gene a ed in Cases a and c. In
Case c, he du y signal is upda ed (blue line) wi hou p oducing ex a swi ching, educing
he on s a e o he semiconduc o . Howe e , in Case a, he con ol signal mus be upda ed
in T2(solid blue line); o he wise, wo swi ching e en s will happen (do ed ed line).
Following he same s eps, along he modula ion down-slope cycle, i D0is lowe han
he modula ion alue a T1, he con ol signal could be upda ed wi hou any change in he
swi ching equency. Fig. 3.7 shows all ou possible cases on he down-slope semi-cycle.
Fo una ely, no all cases a e ele an wi h espec o cu en aul s. The e o e, a s udy
could be made o de e mine he e ec i eness o he imp o emen in hese special cases.
The e a e wo aul condi ions: a posi i e and a nega i e o e -cu en peak. F om he e, he
up-slope case will be analyzed, bu a simila easoning could be done o he down-slope
semi-cycle.
34 Chap e 3. Con ibu ions o ol age sags compensa ion echniques
T1
D0
D1
T0T2
a
0
PWM
1
T1
D1
D0
T0T2
c
0
1
Figu e 3.6 PWM signals gene a ed wi h Cases a and c o he ising PWM semi-cycle.
The ed do ed line poin s ou possible mal unc ioning wi h wo swi chings
in he same semi-cycle i he p oposed ule is no applied. The blue line
poin s ou PWM signals gene a ed wi h he du y signal upda ing imp o e-
men (DSUI) me hod..
T1
D0
T0T2
aT1
D0
D1
T0T2
b
T1
D1
D0
T0T2
cT1
D0
D1
T0T2
d
D1
Figu e 3.7 All ou possible du y upda ing cases in he alling PWM semi-cycle. The
con ol signal could be upda ed a T1in Cases a and b, bu mus be upda ed
a T2in Cases c and d..
3.2 P oposed me hod 35
Acco ding o Eq. (3.2), a ins an k= 1, he wo s o e -cu en peak (IL0) would happen
i he cu en peak aul was add up o e he maximum cu en alue modula ed. Conse-
quen ly, D0is expec ed o be posi i e and big enough. In addi ion, i a dange ous peak
cu en happened, he con olle would ha e o d op IL o a sa e y egion. Acco ding o
Eq. (3.2), o ake down IL1,D1will be e y low. The e o e, i a posi i e o e -cu en peak
happens, Case c o Fig. 3.5 is expec ed.
As p e iously men ioned, his is one o he allowed cases o e esh he con ol signal,
so he o e -cu en peak will be educed.
A simila easoning could be made wi h a nega i e o e -cu en aul . On he one hand,
now, D0is expec ed o be nega i e and big enough. On he o he hand, om Eq. (3.2),
he D1expec ed alue will be e y high. Consequen ly, i a nega i e o e -cu en peak
happens, Case a o d o Fig. 3.5 is expec ed. I Case d happens, he con ol signal will be
upda ed, and he o e -cu en peak will be educed. Un o una ely, i Case a happens, he
me hod will no ac in his semi-cycle.
Fig. 3.5 poin s ou ha Tcin luences he e ec i eness o he me hod. I Tcis o ced o
ze o, all con ol s eps will be in he c and d cases, so i is impo an o ha e a small delay
Tc o sho he measu ed peak cu en in mos si ua ions.
Finally, one mo e ac ion could be pe o med o educe he o e -cu en peak. A aul
happening in semi-cycle kwill be measu ed a he beginning o he nex semi-cycle k+1,
and he con ol ac ion will be placed a T1in he bes case o a he beginning o k+2in
he wo s case. The e o e, he maximum delay could be 2Tso Ts+Tc.
I Tcis ela i ely sho , a new con ol s ep could be done a he middle o he semi-
cycle. This con ol signal will be applied wi h he same ules as he o he s, so in a gene al
way, i will be placed a he inal pa o he semi-cycle. In his case, i a aul happens a
he middle o he semi-cycle k0, i will be measu ed a he beginning o he nex con ol
s ep k0+1, and he con ol ac ion will be placed a T1in he bes case o a he beginning
o k0+2in he wo s case. The e o e, he maximum delay could be Tso 0.5·Ts+Tc.
Assuming VLcons an in a sho pe iod o ime du ing he aul condi ion:
IL=1
LZVLd −→ ∆IL=VL
L·Tdelay (3.4)
whe e ∆ILis he expec ed inc emen on he peak cu en induced by he aul and Tdelay is
he ime necessa y o con ol he aul . The e o e, acco ding o Eq. (3.4), he peak cu en
will be educed in:
PImax =
VL
L·1.5Ts
VL
L·2Ts
=0.75 p.u.
PImin =limTc→0
VL
L·(0.5Ts+Tc)
VL
L·Ts+Tc
=0.5p.u.
(3.5)
whe e PIis he p opo ion o he peak cu en educed wi h he imp o emen (be ween
50% and 75%).
36 Chap e 3. Con ibu ions o ol age sags compensa ion echniques
3.3 Resul s
3.3.1 Simula ions
A high powe indus ial PV sola in e e has been modeled o es FPCC. Howe e , sim-
ila esul s could be ob ained wi h o he applica ions. Simula ions had been pe o med
wi h he elec ic ansien powe ool EMTDC/PSCAD V4.2. Figu e 3.8 shows a de ailed
desc ip ion o he simula ion. The simula ion includes:
•Sola panel ield model.
•De ailed comme cial wo-le el h ee-phase g id- ie in e e ; he in e e ac s as he
de ice unde es (DUT) o he simula ion.
•Medium ol age ans o me .
•POI wi h he u ili y g id.
•Va iable pa allel impedance load o pe o m ol age sags and phase-jumps.
Elec ic g id
23kV 60Hz
DUT
AC
DC
600 kVA
23kV/240V
PV Panel
Resis i e
load
Fo phase
jumps
Induc i e
load
o ol age
sags
POI
Figu e 3.8 De ailed simula ion scheme o es FPCC..
The PV panels ha e been modeled acco ding o he diode model [?]. Tes condi ions
ha e been se o each maximum powe . The main pa ame e s o he comme cial wo-
le el h ee-phase g id- ie in e e a e summa ized in Table 3.1. Nominal alues, inne
cu en con ol PIDs, swi ching equency, so wa e p o ec ions and he FPCC se up a e
de ailed.
3.3 Resul s 37
Table 3.1 G id- ied in e e se up..
Pa ame e Value Pa ame e Value
Nominal ac i e powe PDG 500 kW O e -cu en so wa e p o ec ion SP 1.3p.u./0.1ms
Nominal ou pu cu en In1202 AO e -cu en ha dwa e p o ec ion HP 1.4p.u.
Nominal g id ol age Vn240 VAc i e cu en con ol kpD=0.05
kiD=5
FPPCS limi IFPPCS 1.05 p.u. Reac i e cu en con ol kpQ=0.05
kiQ=5
Delay con ol ime Tc0.6p.u. PWM equency PWM 1980 Hz
The POI is simula ed wi h an ideal h ee-phase ol age sou ce a VL= 23 kV and =
60 Hz, wi h a sho ci cui powe (Ssc) o 500 MVA.
Two ypes o aul s ha e been analyzed a ull powe . The wo s cases desc ibed in he
in e na ional legisla ion [12–18,22,24] ha e been selec ed. The sys em will be es ed
agains symme ic and asymme ic ol age sags and phase-jump aul s. Fig. 3.9 shows
line- o-line ol ages o he deepes aul s o each ype used o es he sys em. Case a shows
a h ee-phase ol age aul wi h ze o emaining ol age. Case b shows an asymme ic
ol age aul wi h wo phases o e lapped. Case c shows a h ee-phase 45◦ ol age phase-
jump. Finally, Case d shows he same phase-jump o only one phase.
Fig. 3.10 and 3.11 show he ansien powe con e e esponse agains a 45◦ h ee-
phase jump dis u bance and a 0.0p.u. h ee-phase dip ol age, espec i ely, i ed a 0.00
s. Fo bo h igu es, (a) shows he ansien beha io o one phase ol age (Vg). Fig. 3.10b
shows he phase (θ) ansien o 45◦and Fig. 3.11b he ol age module (m) ansien o
0.0p.u., du ing he aul . Cases c o e show wo cu es i each one; he solid line cu e
ep esen s he e olu ion o he sys em wi h a classical app oach (CA), and he dashed
line cu e ep esen s he e olu ion o he sys em wi h FPCC. Cases c o e show he du y
signal con ol (D), he s ack ou pu cu en (IL) and he con e e ou pu cu en (Iou ),
espec i ely. No e ha so wa e p o ec ion (SP) and ha dwa e p o ec ion (HP) h esholds
a e poin ed ou o e Case d and how, wi h he FPCC ac i e, he h eshold is no eached.
As a esul , he uni emains connec ed. The Iou peak is educed, oo, bu addi ional
emaining peaks appea in he con e e ou pu due o he line capaci o il e .
38 Chap e 3. Con ibu ions o ol age sags compensa ion echniques
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(a)
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(b)
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(c)
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(d)
Figu e 3.9 Line- o-line h ee-phase g id ol age o all ypes o aul s es ed. (a) Th ee-
phase ze o- ol age aul ; (b) asymme ic ze o- ol age aul ; (c) h ee-phase
45◦ ol age phase-jump and (d) mono-phase 45◦ ol age phase-jump..
3.3 Resul s 39
−1.0
0.0
1.0
Vg (p.u.)
−45
0
θ (º)
0.0
0.5
1.0
D (p.u.)
CA
FPCC
HP
SP
−1.0
−0.8
IL (p.u.)
CA
FPCC
−0.03 0.02 −0.01 0.00 0.01 0.02
−1.5
−1.0
−0.5
Iou (p.u.)
Time (s)
CA
FPCC
Figu e 3.10 DG esponse agains a 45◦phase-jump aul wi h he classical app oach
(CA) and FPCC echniques. (a) G id ol age; (b) phase; (c) du y con ol
signal; (d) s ack cu en and (e) con e e cu en ou pu ..
−1.0
0.0
1.0
Vg (p.u.)
0.0
0.5
1.0
m (p.u.)
0.0
0.5
1.0
D (p.u.)
CA
FPCC
HP
SP
−1.0
−0.8
IL (p.u.)
CA
FPCC
−0.03 0.02 −0.01 0.00 0.01 0.02
−1.5
−1.0
−0.5
Iou (p.u.)
Time (s)
CA
FPCC
Figu e 3.11 DG esponse agains a 0.00 p.u. h ee-phase dip ol age wi h he classical
app oach (CA) and as peak cu en (FPCC) echniques. (a) G id ol age;
(b) module; (c) du y con ol signal; (d) s ack cu en and (e) con e e cu -
en ou pu ..
46 Chap e 3. Con ibu ions o ol age sags compensa ion echniques
powe sola powe con e e has been pe o med wi h excellen esul s. The ela ionship
be ween simula ion and expe imen al esul s is consis en , so he models used ha e p o en
hei e icacy.
Peak cu en s o all ypes o aul s ( ol age sags and phase jumps) ha e been educed,
a oiding c i ical h esholds. Se e e aul s cause la ge peaks cu en s han small aul s
unde a classical con ol echnique. Howe e , peak cu en s do no inc ease in he same
way wi h he FPCC echnique. The inc emen o peak cu en magni udes is la e wi h
FPCC han wi h a classical app oach. Consequen ly, he ange o ole ance agains aul s
is inc eased.
No e ha he FPCC h eshold is se o 1.05 p.u. o all es s. Resul s show peak cu en s
be ween 1.12 p.u. and 1.24 p.u. The e o e, he con ol h eshold has been passed only
0.07–0.17 p.u. The e o e, he e iciency o he me hod has been measu ed.
The ou pu cu en o he con e e is g ea e han he s ack ou pu cu en signi ican ly.
This is due o he ene gy sa ed in he AC capaci o s o he ou pu il e o he con e e .
The peak cu en componen due o AC capaci o s is no educed wi h FPCC, because i is
no con olled by he con e e . The e o , he ou pu cu en o he con e e is g ea e han
he s ack cu en ou pu . Howe e , he mos c i ical componen s agains peak cu en s a e
IGBTs, so he ex a cu en added by he capaci o s does no inc ease he isk o ailu e.
Finally, he main ad an ages o FPCC a e summa ized in he nex sen ences:
•The peak cu en has been educed be ween 0.4p.u. and 0.7p.u. o he wo s
cases.
•The me hod helps o comply wi h in e na ional MTRs.
•The me hod p e en s he uni om ipping by o e -cu en , educing p oduc ion
losses and helping he g id eco e om he aul .
•Reducing peak cu en s p e en s uni damage. Consequen ly, he MTBF o he
uni s is longe .
•The me hod does no need any addi ional ha dwa e, so i is e y inexpensi e and
easy o implemen in exis ing uni s.
4 Conclusions
REPs p oduc ion has g ow h signi ican ly in he las yea s, inc easing no ably hei pen-
e a ion ac o . The e o e, he elec ic powe g id model is changing o a dis ibu ed gen-
e a ion scena io. Consequen ly, mo e exigen g id codes ha e been de eloped o DGs.
Mos impo an changes o MTRs a e ela ed o g id aul s, because DGs help is c ucial
o he g id sys em eco e y om he aul .
This wo k con ibu ions help o a be e de ec ion and con ol o elec ic powe g id
aul s by DG powe con e e s. Conclusions ob ained om his wo k could be sum up in
he ollowing s eps:
•In e na ional legisla ion MTRs ha e been s udied, conside ing hei e olu ion om
las decade. The pu pose is o de ec he endencies and equisi es o u ili y g ids
wo ldwide. Mos ecen changes added o cu en legisla ion ha e been compa ed
wi h mos ep esen a i e laws, as Ge man g id code. The e o e, he u u e e olu ion
o g id codes wo ldwide has been poin ed ou .
•Li e a u e con ol echniques abou MTRs ha e been s udied. Li e a u e con ibu-
ions abou de ec ion and con ol o di e en g id aul s ypes iden i y weak poin s
and he ad an ages o each solu ion o he p oblem.
•De ec ion and con ol echniques o g id aul s ha e been de eloped. Two ema k-
able p oblems abou he de ec ion and con ol o g id aul s a e islanding cases and
ol age sags. Some con ol echniques o bo h g id aul ypes ha e been p oposed
o imp o e he DG esponse beha iou .
•Resea ch abou ansien ol age aul s has led o a new echnique o imp o e he
ansien beha iou a he beginning o he aul . The me hod educes he ini ial
peak cu en , so i p e en s he uni om ipping by o e -cu en and possible dam-
age. Consequen ly, he MTBF o he uni s is longe . Mo eo e , he me hod needs
only so wa e ac ions, so a cheap e o i o e exis ing uni s could be made o .
•Resea ch abou islanding condi ions has led o a new ac i e an i-islanding ech-
nique. The p oposed me hod imp o es he esponse o he sys em compa ed o
47
48 Chap e 4. Conclusions
p e ious li e a u e me hods. The me hod has a low clea ing ime, could wo k a
any se -poin , shows a ze o NDZ, and p oduces e y li le dis u bances in he g id.
•P oposed con ol echniques ha e been alida ed by simula ion and expe imen
esul s. All g id aul cases could be analysed wi h he beha iou o he sys em
in a simula ion en i onmen . La e alida ion wi h labo a o y expe imen al es s
checks he models and he p oposed echniques.
•P oposed con ol echniques ha e been es ed on eal indus ial powe plan s. The
s ep om a con olled labo a o y es o a eal comme cial p oduc ins alled wo ld-
wide is he p oo o he de eloped con ol echniques use ulness. Pa icula ly, elec-
ic g id aul s ha e a complex and wide casuis ic, he e o e he me hods obus ness
ha e been p o ed oo.
Appendix A
New Low Dis o ion Q- D oop Plus
Co ela ion An i-Islanding De ec ion
Me hod o Powe Con e e s in
Dis ibu ed Gene a ion Sys ems
49
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 1
New Low Dis o ion Q- D oop Plus Co ela ion
An i-Islanding De ec ion Me hod o Powe
Con e e s in Dis ibu ed Gene a ion Sys ems
Jes´
us Mu˜
noz-C uzado-Alba, Ja ie Villegas-N´
u˜
nez, Jos´
e Albe o Vi e-F ´
ıas, J.M. Ca asco, Membe , IEEE,
and Edua do Gal ´
an-D´
ıez Membe , IEEE
Abs ac —A new ac i e Q- d oop an i-islanding algo i hm is
p oposed. The me hod is based on equency and eac i e powe
c oss-co ela ion measu es. The p oposed con ol echnique is
in ended o ul il ecen and u u e g id code equi emen s.
The algo i hm looks o a ze o non-de ec ion zone, adding low
dis u bances, wo king wi h long equency excu sions and non-
dependency o he powe ac o se poin . The me hod was e i ied
using a se o simula ion models de eloped in PSCAD en i-
onmen . The es s show esul s o se e al quali y ac o s and
di e en ac i e powe le els. Also, a compa a i e agains o he
an i-islanding me hods is p esen ed. Expe imen al and simula ion
es s p o ide u he insigh on he con olle s pe o mance unde
di e en wo king condi ions, conside ing se e al quali y ac o s
and ac i e powe le els. Mo eo e , i s pe o mance is assessed
compa ing he p oposed con olle beha io agains s a e-o - he-
a an i-islanding me hods.
Index Te ms—An i-Islanding (AI), Q- d oop, c oss-co ela ion
ac o , posi i e eedback con ol, dis ibu ed gene a o s (DGs),
non-de ec ion zone (NDZ), pho o ol aic sys ems.
I. INTRODUCTION
ELECTRIC powe is ypically p oduced a a wide ange
o gene a ion plan s and dis ibu ed h ough a a ie y o
ansmission g ids [3]. In case o a aul o abno mal line
ope a ion, he b eake on a line can be opened and a speci ic
sec ion o he g id can be isola ed. I he gene a o s inside
his sec ion emain connec ed a e he aul , an island wo king
condi ion will appea . In o de o p o ec he ene gy gene a ion
s a ions and he elec ical ne wo k om his phenomenon,
di e en An i-Islanding (AI) echniques ha e been ecen ly
p oposed. Fig. 1 shows he main a ailable ca ego ies o AI
de ec ion me hods.
AI me hods can be classi ied in o wo g oups: local me-
hods applied inside Dis ibu ed Gene a o s (DGs), o emo e
me hods applied a he Poin o Common Coupling (PCC) [4].
Which can be u he di ided in o wo unc ional ca ego ies,
Manusc ip ecei ed July 9, 2014; e ised Oc obe 13, 2014 and Decembe
10, 2014; accep ed Janua y 22, 2015.
Copy igh (c) 2015 IEEE. Pe sonal use o his ma e ial is pe mi ed.
Howe e , pe mission o use his ma e ial o any o he pu poses mus be
ob ained om he IEEE by sending a eques o [email p o ec ed].
This wo k was suppo ed by GPTech Spain (www.g eenpowe .es) and he
Elec onic Enginee ing Depa men o he Uni e si y o Se ille.
J. Munoz-C uzado Alba, J. Villegas Nunez and J.A. Vi e
F ias a e wi h he R&D Depa men o GPTech, A . Ca-
mas N28, Bollullos de la Mi acion, 41100 Spain. (e-mail:
jmunoz@g eenpowe .es; j illegas@g eenpowe .es; ja i e@g eenpowe .es)
E. Gal an Diez and J.M. Ca asco Solis a e wi h Se ille Uni e si y.(e-mail:
egal [email p o ec ed]; [email p o ec ed])
passi e and ac i e me hods. Passi e me hods a e based on
measu es o he sys em and communica ions, bu hese do
no add any dis u bance o he g id. On he con a y, ac i e
me hods add a dis u bance in o de o check a possible island
case.
In emo e me hods, he PCC elays communica e wi h he
DGs o ip in he p esence o an isola ed ne wo k wo king
as an island [5], o hey in oduce ex a elemen s in he PCC
in o de o o ce he sys em ou o he equilib ium esonan
poin . Remo e me hods a e highly e ec i e, bu hey a e also
e y expensi e.
Local me hods a e based on a ailable elec ic in o ma ion
and hei de i ed indexes om ol age and cu en signals.
On he one hand, passi e local me hods do no ha e nega i e
e ec s, and hey a e usually cheap and easy o implemen .
Un o una ely, i he s able esonan poin is inside he h es-
holds es ablished by passi e p o ec ions, he island could no
be de ec ed. The egion whe e a me hod is no able o de ec
an island is called he Non De ec ion Zone (NDZ). Passi e
me hods ha e a high NDZ, so hey usually a e complemen ed
wi h an ac i e me hod.
Some o he mos common passi e me hods a e ela ed
o equency and ol age h esholds. The O e F equency
P o ec ion (OFP), and he Unde F equency P o ec ion (UFP)
de ine he equency ope a ion ange o he DG. Beyond hese
limi s he DG is disconnec ed. In he same way, he O e
Vol age P o ec ion (OVP), and he Unde Vol age P o ec ion
(UVP) de ine he ol age ope a ion ange o he DG.
On he o he hand, ac i e local me hods in en ionally in-
oduce dis u bances a he ou pu o he DG o de e mine i
hey a ec he ol age, equency, o impedance pa ame e s, in
which case i is assumed ha he g id has been disconnec ed
and he in e e is isola ed om he load.
Some de eloped ac i e echniques can be poin ed ou :
Impedance Measu emen [6]-[7], Ha monic Injec ion [8]-[10]
o me hods based on posi i e eedback dis u bance schemes.
The la e ype is e y popula because i injec s a li le
dis u bance in s eady s a e ope a ion, and when he island
happens, he dis u bance will ise ab up ly o ge ou he DG
o passi e p o ec ions h esholds.
The e a e di e en ypes o dis u bances among posi i e
eedback me hods like F equency D i , Sliding Mode F e-
quency Shi (SMS) [11], Sandia Vol age Shi (SVS), o based
on eac i e powe dis u bances [12]-[14], among o he s [15].
The p oposed Q- co ela ion me hod belongs o he la e
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 2
AI me hods
L ocal R emo e
Passi e
Ac i e
Passi e
Z in PCC
C ommunica ions
R adio
MW
PL C
Fibe
Op ic
F equency
V ol age
Phase V ol age
T HD
Z measu e
Ac i e
Ha monics
V ol age
F equency
Posi i e eedback
Phase
QQ- co ela ion
SMS
Sandia V ol age
Sandia F equency
Fig. 1. AI me hods classi ica ion.
DG
DG
DG
G id
RLC
PC C
PDG + jQDG
PLoad + jQLoad
ΔP + jΔQ
Powe
Con e e
Powe
Con e e
Powe
Con e e
Fig. 2. Island con igu a ion case.
ca ego y.
These me hods a e capable o educing he NDZ. Howe e ,
all o hem in oduce small dis u bances, hus incu ing in
losses and p oducing ha monics in he g id. In o de o
educe hese p oblems, di e en solu ions ha e been p oposed;
o ins ance, me hods based on co ela ion be ween elec ic
measu es. Co ela ion coe icien s ha e been used la ely and
discussed in ecen publica ions [16]-[18] o check he s a e o
he ne wo k.
The p oposed Q- co ela ion me hod has a good clea ing
ime esponse, a ze o NDZ, and p oduces e y low dis u -
bances in s eady s a e ope a ion. Fu he mo e, he me hod has
an easy implemen a ion and uning. The p oposed echnique
allows ha ing ze o dis u bance du ing long equency excu -
sions.
This manusc ip is o ganized as ollows, Sec ion II explains
he basis o he Q- d oop cu e and he p oposed me hod.
Sec ion III and IV show simula ion and expe imen al esul s
espec i ely. Finally, conclusions a e gi en in Sec ion V.
II. Q-F CORRELATION METHOD
A. The island phenomenon
Fig. 2 shows a simpli ied schema ic o a possible island
case. The sys em unde s udy can be composed by one o
mo e DGs p o iding ene gy o he u ili y g id, and di e en
ypes o loads. Loads and DGs a e connec ed o he u ili y g id
ac oss a common link, he PCC. Typically, a powe con e e
is needed in he DGs ou pu , in o de o connec hem o he
elec ic g id.
An islanding elec ic phenomenon will happen i he b eake
in he PCC is opened. A e ha , he g id loses comple e
con ol capabili y on he isola ed ne wo k. When a disconnec-
ion happens due o scheduled main enance o aul , s anda ds
[19]-[22] o ce all DGs o s op gene a ing ene gy. DGs mus
be disconnec ed in o de o p e en haza ds o people ge ing
access o an ene gized line, and damage o he cus ome and
u ili y g id equipmen [23].
When he PCC b eake in Fig. 2 is swi ched on, and he
u ili y is connec ed, PDG+jQDG lows om he DGs o PCC,
and Pload +jQload lows om PCC o he load. Summing
powe lows a PCC,
∆P=Pload −PDG ∆Q=Qload −QDG (1)
Eq. 1 shows he powe low om he u ili y in o PCC. I
he PCC b eake is disconnec ed, he sys em will be isola ed
om he es o he g id, so ∆Pand ∆Qwill be o ced o be
ze o. The load is modelled as a pa allel esonan RLC ank.
Ce ainly, in he eal wo ld he si ua ion is mo e complica ed.
Howe e , expe imen al es esul s and heo e ical e idence
[19] show ha his simple model should wo k well in he
p edic ion o wo s -case islanding es condi ions.The load
admi ance and powe could be o mula ed as,
1
Z=1
R+1
jωL +jωC (Pload =V2
P CC
R
Qload =V2
P CC
ωL−1
ωC
(2)
So, i ∆Po ∆Qa e di e en om ze o when an island
happens, acco ding o Eq. 2, nex beha iou will be expec ed
[24]-[25]. On he one hand, i ∆P > 0, he ol age will d op
o sa is y he equa ion. And i he imbalance is lowe han
ze o, he ol age will ise. On he o he hand, i ∆Q > 0, he
equency will d op. And, i he imbalance is lowe han ze o,
he equency will ise.
I bo h ∆Pand ∆Qwe e small, he island could no be
de ec ed by passi e me hods because p o ec ion h esholds
would no be eached, and he sys em would emain ene gized
inde ini ely.
The p oposed ac i e me hod se s he equency ou he
OFP/UFP h eshold o cause he DG disconnec ion. Acco ding
o Eq. 2, he algo i hm adds a dis u bance o e he DG eac i e
powe e e ence o mo e he equency.
B. Analysis o Q- d oop cu e
The e is a ela ionship be ween he eac i e powe in he
island subsys em and he s able equency ope a ion poin
(see Fig. 3). Fo a load esona ing a 60Hz and wi h he
DGs eac i e powe e e ence se o ze o, he equency will
emain wi hin he equency h esholds ( a- c). Consequen ly,
he aul will no be de ec ed.
E en hough he ela ionship be ween eac i e powe and
equency is non-linea , i could be linea ized in a small ange
( a- c) [14]. Fig. 3 shows h ee esonan equencies d awn
wi h dash lines ( d, b, and e), each one o a di e en
esonan load. The solid line deno ed by Q e ep esen s he
DG eac i e powe injec ion. The Q e cu e is independen
o he equency, so i is ep esen ed as a ho izon al line.
Bo h exp essions mus be sa is ied simul aneously in hei
in e sec ion, because he DGs eac i e powe (solid line) mus
be consumed by he load (dash line) o become a s able sys em.
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 3
59 61
−1.5
−1
−0.5
0
0.5
1
1.5x 104
F equency (Hz)
Reac i e Powe
Resonan cu e C
Resonan cu e E
Q e
b
a
d c e
Resonan cu e D
+
−
Fig. 3. Q- d oop cu e and IOP example. Resonan RLC cu es (dash
lines) and DG Q e cu e (solid line).
The in e sec ion be ween he DG and he load cu e will
be deno ed as he Island Ope a ing Poin (IOP). The s able
equency ( IOP ) o his subsys em is gi en by Eq. 3 [14].
Q es( ) = −2P e Q ( − 0)
0
QDG( ) = Q e ) IOP = 0− 0Q e
2P e Q
(3)
whe e 0is he nominal g id equency, P e is he DG ac i e
powe injec ion, and Q ep esen s he quali y ac o . Fo he
passi e OFP/UFP AI me hod, any load cu e wi h an IOP
be ween poin s dand e o ms he NDZ.
I a small posi i e change in equency +happens o e
b, he DG eac i e powe (solid line) will be g ea e han he
load eac i e powe (dash line). Then, he equency will s a
o d op in o de o inc ease he load eac i e powe . So, a
he end, he sys em will e u n o poin b om c. A simila
easoning could be done o a small nega i e change −. In
conclusion, bis a s able IOP.
Posi i e eedback me hods add a dis u bance in o de o
make he sys em uns able. Fo example, i he e was an island,
he IOP could be b. I a posi i e dis u bance we e added o e
Q e , he ho izon al line would go up, and he IOP would
mo e ac oss he esonan load cu e owa ds a. In he nex
algo i hm s ep, a new dis u bance o eac i e powe could be
calcula ed wi h he new IOP poin . A posi i e eedback AI
me hod will ha e a g ea e dis u bance alue in a han in b,
so he IOP will mo e s ep a e s ep owa ds d. Once UFP
is eached, he uni will be disconnec ed.
C. P oposed AI Q- co ela ion me hod
Fig. 4 shows a classical con e e DG con ol block scheme.
The con olle is di ided in o he ollowing laye s:
•High le el con olle : The highe le el con ol is in
cha ge o gene a ing he app op ia e ac i e and eac i e
powe e e ences p o ided o he lowe le el con olle s.
The pu pose is o b ing he in e e o he desi ed
objec i e: maximize he ac i e powe gene a ion, and help
he u ili y g id wi h he eac i e powe injec ion.
•Middle le el con olle : The middle le el con olle
is in cha ge o se ing he con ol ac ions in o de o
ollow he highe le el con ol e e ences based on he
Q e SP
Pmax
Pmin
P e ’
Du y
Con ol
An i islanding
me hod
+
+
QA I
Q e
P e
Qmin
Qmax
Id e
Iq e
Cu en
con olle
Idq
P e sa lim calcula ion
Q e sa lim calcula ion
P e SP
High le el
L ow le el
Middle le el
Middle le el
I G BT D i e
Sys em
Fig. 4. Simpli ied con ol block o a DG powe con e e .
ΔQ
Δ
x+
T(x)
QAI
Z-1
-
+
kmem
kpΔ
Cmem Qmem
QΔ
Δ ΔQ
Fig. 5. AI Q- co ela ion con ol scheme.
in o ma ion p o ided by he a ailable senso s. Mo eo e ,
sa e y ea u es a e also conside ed, modi ying he con-
olle s ac ions in unc ion o ope a ing cons ain s such
as empe a u e and o e ol ages.
•Low le el con olle : Finally, he low le el con olle
includes a PI con olle o he ou pu cu en s, and he
ha dwa e in e ace, which p o ides he swi ching pulses
o he powe con e e semiconduc o s.
The a o emen ioned me hod o con olling he powe con-
e e includes an AI de ec ion algo i hm oge he wi h he
passi e p o ec ion gi en by OFP/UFP h esholds. Fig. 5 shows
he AI con ol block scheme. This algo i hm is pa o he
middle laye con olle . Upon islanding condi ions, he ac i e
p o ec ion will gene a e a dis u bance in o de o each he
passi e p o ec ion limi s. Once any limi is eached, he powe
con e e will be disconnec ed om he u ili y g id.
The algo i hm modi ies he o al eac i e powe based on he
measu ed g id equency. The me hod is based on he posi i e
eedback p inciple like o he known echniques [12]-[15], [26].
Howe e , his me hod does no educe he powe ac o quali y,
and i wo ks p ope ly i he powe ac o e e ence is no he
uni y.
The dis u bance algo i hm ou pu (QAI) is calcula ed in wo
pa s clea ly di e en ia ed. Fi s , a new dis u bance alue is
calcula ed wi h a p opo ional gain con olle in unc ion o
he equency a e change. This con olle is uned wi h a
pa ame e called Kp∆ :
Q∆ =Kp∆ ·∆ (4)
Secondly, he las ime s ep ou pu (QAIi−1) is co ec ed in
unc ion o he e olu ion o he sys em in his pe iod. A weigh
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 4
Cmem
T (C mem)
1
o b
b0b1
-b0
-b1
Fig. 6. T(x) uzzy logic unc ion. b0and b1a e he uzzy ule limi s o
Cmem o de e mine a g id connec ed case (Cmem < b0), o an island case
(Cmem > b1).
coe icien is calcula ed wi h he c oss-co ela ion unc ion
be ween equency and eac i e powe inc emen signals, and
scaled by he ac o Kmem. The ime window o he signals
in ol ed in he c oss-co ela ion unc ion mus be high enough
o emo e noise om co ela ion be ween he signals. And he
ime s ep o he algo i hm mus be la ge enough so he sys em
could each he IOP s able poin .
Cmem =Kmem ·(∆ ⋆ ∆Q)i(5)
The c oss-co ela ion ou pu is passed in o a simple uzzy
logic unc ion called T(x)desc ibed in Fig. 6. T(Cmem)is
a memo y ac o o decide i he dis u bance mus be hold o
o go en.
On he one hand, i Cmem gi es a low alue, he e will
no be a ela ionship be ween Qand and he DG will
emain connec ed o he g id. So QAIi−1mus be lowe ed
in o de o educe he pe u ba ion injec ed o he g id. Then
he ou pu gi es a co ec ion ac o o blowe han he uni .
This alue mus be low enough o emo e he pe u ba ion
in a easonable ime, bu mus be high enough o allow he
pe u ba ion emaining along he ime window o he c oss-
co ela ion o de ec an island phenomenon.
On he o he hand, i he Cmem gi es a high alue, he e
will be a ela ionship be ween Qand and he DG could be in
island. The co ec ion ac o ou pu mus be he uni in o de
o hold QAIi−1 alue. While b0and b1a e he h esholds ha
se he DG sys em ei he on island o g id connec ed wo king
mode. No ice ha he alue o b0mus be highe han Cmem
in g id connec ed mode (Cmem has a esidual alue due o
noise), and lowe han Cmem when wo king in island mode.
Finally, b1is se in o de o ensu e a smoo h ansi ion be ween
wo king s a es, based on he accumula ed noise p obabili y
cu e.
As a esul , Eq. 6 gi es he co ec ed pe u ba ion alue
(Qmem).
Qmem =T(Cmem)·QAIi−1(6)
Then, QAI ou pu (Eq. 7) is es ima ed by sub ac ing Eq. 6
and 4.
QAI =Qmem −Q∆ (7)
Finally, he calcula ed alue (QAI) is added o he e e ence
se poin (Qsp) in o de o s ablish he eac i e powe e e ence
(Q e ), o be p o ided by he in e e , Eq. 8.
Q e =Qsp +QAI (8)
No ice ha his inno a i e echnique p o ides ze o mean
dis u bance, leading o ze o a e age e o , u he educing
losses and ha monics.
0 0.2 0.4 0.6 0.8 1
60
61
62
63
64
65
Psp (p.u.)
max (Hz)
Q =2.5
Q =5.0
Q =10
Q =25
Q =100
lim
Fig. 7. NDZ (ba ed a ea) in unc ion o Psp and Q− .
D. Q- co ela ion me hod NDZ
The pe u ba ion o he p oposed me hod is based on he
Q- d oop cu e. Eq. 3 gi es an exp ession o he equency
eached o a ce ain amoun o eac i e powe injec ed. The
absolu e maximum alue o eac i e powe (|Qmax|) would
es ablish a maximum equency alue ( max) gi en by he
ollowing exp ession:
max = 0(1 + |Qmax|
2PspQ
)(9)
whe e Psp is he ac i e powe se poin o he con e e . Then,
he e will be a NDZ i max is lowe han he OFP h eshold
( lim). Acco ding o [22] he limi is se o 60.5Hz.
Fig. 7 shows he me hod NDZ in unc ion o Psp and Q .
To de e mine he eac i e powe capabili y o he con e e , a
Powe Fac o (PF) o 0.95 has been conside ed as a ypical
alue [27].
NDZ is de e mined by he egion unde he lim h eshold.
Values o max in his zone a e due o e y high Q alues
(abo e Q = 20) compa ed o maximum legisla ion alues
equi ed o de ec AI (1[19] and 2.5[21]). Ne e heless, he
NDZ could be educed.
A powe con e e capabili y cu e is desc ibed by a cons-
an maximum appa en powe alue, independen ly o ac i e
and eac i e powe se poin s desi ed (Psp and Qsp). So, i
he equi ed Psp oge he wi h he equi ed Qsp a e ou o
he capabili y cu e, a p io i y ule mus be chosen o comply
wi h only one o he wo equi emen s.
The p oposed me hod does no injec any signi ican QAI in
s eady s a e ope a ion, because he memo y ac o in oduced
a oids i . So, a p io i y ule o QAI o e Psp could be se
wi hou incu ing in powe p oduc ion losses, unlike o he Q−
[14] and Reac i e Powe Con ol (RPC) [28] me hods. Then,
Qmax in Eq. 9 will be cons an and Psp will end o ze o,
leading max o in ini y.
Mo eo e , acco ding o Eq. 2, he e would be a quad a ic
ela ionship be ween VP CC and Psp. The e o e, i Psp became
ze o in an island case, he ol age could be educed o ze o,
and he UVP h eshold would be also igge ed.
In conclusion, he expec ed NDZ will be ze o.
III. SIMULATIONS
The p oposed me hod has been alida ed ia simula ion wi h
he elec ic ansien powe ool EMTDC/PSCAD. The es
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 5
ci cui shown in Fig. 2 has been used acco ding o IEC and
UL legisla ion [19]-[22], implemen ing a de ailed wo-le el
in e e in he powe con e e s age and he con olle scheme
depic ed in Fig. 4.
The simula ion pa ame e s can be summa ized as ollows:
•Subsys em ac i e powe : PDG =Pload = 600kW .
•Con e e cu en con ol: kpD= 0.05,kiD= 5,
kpQ= 0.05,kiQ= 5.
•Subsys em eac i e powe : QDG =Qload = 0kV a .
•Quali y ac o : Q = [1,2.5].
•G id ol age and limi s: Vn= 240V,OV P = 1.1p.u.,
UV P = 0.85p.u.
•G id equency and limi s: n= 60Hz,
OFP = 63.5Hz/0.1ms, 63Hz/50ms, 60.5Hz/0.16s,
UF P = 56.5Hz/0.1ms, 57Hz/160ms, 59.8Hz/0.3s.
•Maximum disconnec ion ime: 1s o IEC, and 2s o UL.
•Me hod con olle : Kp∆ = [5 ·104,5·105],
Kmem = [10−6,10−3].
•Time s ep: 5ms.
•Co ela ion window: N= 20 samples.
•T(x)is de ined as: o b= 0.95,b0= 6.5·10−6, and
b1= 6.0·10−6
Con ol pa ame e s and elec ic sizing o he DG has been
selec ed acco ding o an indus ial high powe in e e . AI
sampling ime (5ms) equi es a slowe dynamic han he lowe
le el con olle . The pu pose is o each he IOP be o e he
nex con ol s ep.
The co ela ion window has been adjus ed o mee IEC and
UL clea ing ime equi emen s, and a he same ime il e ing
he noise om measu emen s. T(x)pa ame e s ha e been
se expe imen ally in unc ion o analog boa d misma ching,
equency PLL con igu a ion and equency g id oscilla ions.
OFP/UFP and OVP/UVP a e selec ed based on legisla ion
[21] and u ili y g id equi emen s. Acco dingly, he e a e h ee
di e en equency e o limi s. I he equency eaches he
i s h eshold (63.5Hz o OFP and 56.5Hz o UFP), he
uni will be disconnec ed immedia ely. On he con a y, he
second and hi d h esholds need o be exceeded mo e han
a pe iod o ime be o e doing he uni disconnec ion (50ms
o e 63Hz and 160ms o e 60.5Hz o OFP, and 160ms
unde 57Hz and 300ms unde 59.8Hz o UFP).
A. AI uning me hod
Two expe imen s ha e been pe o med o ge an app op ia e
uning o he me hod. In all cases, an island has been i ed
a 1.5sins an , and he esul ing clea ing ime has been
measu ed.
Fi s , some simula ions ha e been epea ed o se e al
alues o Kp∆ . Fig. 8 shows he dis u bance esponse
(QAI) added in island condi ion. The simula ion has been
pa ame ized wi h a quali y ac o Q = 2.5(wo s case
scena io in o de o comply [19]-[22]). Kmem is se o 6·10−5
allowing a good beha iou wi h he selec ed b0and b1 alues.
In case a, he con olle gain is oo low (5·104), hen he
dis u bance g adien will no be enough o mo e he sys em ou
o he s abiliza ion, and he island will no be de ec ed. Case
bse s he gain o a highe alue (7.5·104), and as esul , he
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
QAI (kVA )
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−125
0
125
Time (s)
Case c
Case b
Case a
Case d
Fig. 8. Q e simula ion esul s o se e al Kp∆ alues: 5·104(a), 7.5·104
(b), 105(c), and 5·105(d). Island wo king mode is igge ed a 1.5s.
island is de ec ed be o e he 1sclea ing ime equi emen . The
igu e shows how he eac i e powe mo es ou o ins abili y
a e he 1.5s igge . Once he in e e has s opped, he
eac i e powe e e ence d ops o ze o. Case cse s he gain
o a highe alue again (105), ge ing a lowe clea ing ime
esul . Howe e , case dshows ha i he gain was excessi ely
high (5·105), an oscilla ion o e he eac i e powe ou pu
would appea in s eady s a e ope a ion. This oscilla ion is due
o he inhe en oscilla ions p esen ed in a PLL equency. So,
he powe con e e ou pu quali y would dec ease.
Fig. 9 shows simula ion esul s o a ange o alues o
Kmem be ween 10−6and 10−3 o de e mine memo y ac o
in luence. In his case, again Q = 2.5, and Kp∆ = 105ha e
been se in he simula ion.
Case ashows ha low memo y ac o s (10−6) will inc ease
he numbe o non de ec ed aul s. This is because he c oss-
co ela ion measu es a e ne e high enough o hold he pe -
u ba ion. Cases band cshow how aising he memo y ac o ,
he sys em could de ec as e he island condi ion and hold
he eac i e powe e e ence pe u ba ion. Ne e heless, case d
shows ha oo high memo y ac o s (10−3) could de e io a e
he s eady s a e esponse, o e en lead he sys em o ins abili y.
B. Me hod esponse e alua ion
Di e en simula ion es s ha e been pe o med o e alua e
he e ec i eness o he p oposed me hod o se e al Q .
Acco ding o p e ious sec ion, pa ame e s ha e been se o
Kp∆ = 105, and Kmem = 6 ·10−5.
Fig. 10 shows he me hod beha iou agains an island
wo king condi ion. The Q ac o has been se o 2.5and
he b eake has been igge ed a 1.5sin o de o isola e he
sys em and wo k in island mode. The uppe g aphic shows he
o al appa en powe in he PCC, wi h ze o powe consump ion
du ing he island case. The second cu e is he RMS con e e
ol age, emaining cons an du ing island phenomenon un il
he con e e disconnec ion. The hi d cu e shows he ou pu
ac i e powe o he con e e , poin ing ou he con e e
disconnec ion when he island has been de ec ed. The ou h
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 6
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
Time (s)
1 1.25 1.5 1.75 2 2.25 2.5
−50
0
50
QAI (kVA )
Case a
Case d
Case c
Case b
Fig. 9. Q e simula ion esul s o se e al Kmem alues: 10−6(a), 10−5
(b), 6·10−5(c), and 10−3(d). Island wo king mode is igge ed a 1.5s.
1 1,5 2 2,5
−10
0
10
kVA
SPCC
1 1,5 2 2,5
0
100
200
300
V
V ms
1 1,5 2 2,5
0
500
kW
PDG
1 1,5 2 2,5
−100
0
100
kVA
QDG
1 1,5 2 2,5
55
60
65
Hz
Time (s)
FDG
Fig. 10. A Q = 2.5island. PCC appa en powe , DG RMS ol age,
DG ac i e powe , DG eac i e powe and DG equency espec i ely. Island
wo king mode is igge ed a 1.75s.
plo shows he ou pu eac i e powe cu e and i s e olu ion
a e he island e en . Finally, he bo om cu e shows he g id
equency measu e ipping he OFP h eshold, and i ing he
disconnec ion uni .
Subsequen ly, he me hod clea ing ime was e alua ed by
a se o simula ion es s. The p oposed scena ios co e h ee
di e en Q (1,1.75, and 2.5) o h ee di e en powe le els
(0.33p.u.,0.66p.u., and 1.00p.u.).
In island wo king s a e he equency s ep con ol de ia ion
depends on he p e ious Q e de ia ion, as a esul clea ing
imes may depend on ini ial condi ions. Be o e en e ing he
islanding wo king mode, Q e was se in ela ion wi h e-
quency de ia ions, so e o s in he equency measu es and
esonan oscilla ions would change he ini ial condi ions. To
cope wi h his e ec all cases ha e been epea ed en imes,
TABLE I
MIN./MAX. CLEARING TIME EVALUATION FOR Q-F CORRELATION
METHOD (ms)
P(p.u.)Q = 1p.u. Q = 1.75p.u. Q = 2.5p.u.
0.33 39.6/45.0 41.8/59.5 50.0/60.2
0.66 62.9/65.2 77.4/85.2 94.8/110.3
1.00 98.7/164.0 81.3/172.7 123.5/216.9
TABLE II
SIMULATION RESULTS OF REACTIVE POWER PERTURBATION IN STEADY
STATE OPERATION
P(p.u.) 0.0 0.2 0.4 0.6 0.8 1.0
∆σQ(%) 0.01 0.03 0.03 0.05 0.03 0.04
∆µQ(%) 0.04 0.09 0.07 0.05 0.12 0.14
opening he b eake a di e en ins an s o look o he wo s
case. All esul s a e shown in Tab. I. No ice ha in all cases
he island clea ing ime o 1swas me , p o ing he capabili y
o comply wi h code equi emen s [19].
Finally, a es has been pe o med o e alua e he me hod
beha iou in s eady s a e ope a ion. Tab. II shows he ou pu
eac i e powe esponse espec o he ins alla ion wi hou he
AI me hod, o se e al ac i e powe alues. ∆σQ, and ∆µQ
poin ou he inc emen o he s anda d de ia ion and he mean
o he ou pu eac i e powe espec i ely. Resul s show a small
inc emen in he mean and s anda d de ia ion alues o he
measu ed ou pu eac i e powe o e e y ac i e powe le el.
Since he pe u ba ion is added o he eac i e powe e-
e ence, i could be achie ed independen ly o he in e e
ope a ing poin , o he sola panel a ay con igu a ion.
C. Compa a i e es s wi h o he me hods
P e ious sec ions ha e widely shown he me hod beha iou
pe o mance unde se e al wo king condi ions and commonly
used ope a ing poin s. Howe e , a compa a i e analysis o
he con olle esponse wi h o he me hods desc ibed in he
li e a u e is equi ed. Two classical me hods and h ee ecen
published me hods ha e been selec ed o his pu pose. Fou o
he me hods selec ed a e based on he eac i e powe injec ion
in o de o do an easy compa ison. A i h me hod based on
ha monic injec ion has been selec ed in o de o compa e he
me hod wi h di e en ypes o con ol echniques, p o iding
u he insigh on he con olle s ad an ages and d awbacks.
The main ea u es o he selec ed ac i e AI me hods o
be compa ed, a e summa ized in Tab. III. Tes s ha e been
done wi h he same DG and con igu a ion. All es s ha e been
pe o med a P= 600kW and Q = 2.5. A p e ious measu e
o he sys em in s eady s a e ope a ion wi hou any AI me hod
has been done in o de o calcula e he inc emen s o he AI
pe u ba ion co ec ly. Finally, island simula ions ha e been
epea ed en imes wi h di e en igge ing ins an s.
The analysed me hods ha e been es ed wi h he ollowing
pa ame e iza ion:
•Q- co .:Kp∆ = 105;Kmem = 6 ·10−5.
•SMS:θm= 25◦.
•Q- :K1=−0.1;K2= 6.
Ene gies 2015,xx 3
Table 1. MTRs e iew o VRT capabili ies PV plan s (A)
Coun y Ge many Pue o Rico
S anda d BDWE PREPA
VRT
p o ile
VPCC (p.u.)
T (s)
1.00
0.90
0.30
0.0 0.15 0.60 1.50 3.00
VPCC (p.u.)
T (s)
1.00
0.90
0.00
0.0 0.6 3.0
1.15
1.25
1.30
1.40
0.15 1.0
Iq
VRT
ΔIQ (p.u.)
V (p.u.)
1.00
1.11.2
-1.00
0.50.0 0.9
ΔIQ (p.u.)
V (p.u.)
1.00
-1.00
V1
0.0 0.85
IdVRT 0 0
Reco e y ime 5s5s
Phase Jump N/D N/D
Coun y Sou h A ica Spain
S anda d NERSA REE
VRT
p o ile
VPCC (p.u.)
T (s)
1.00
0.90
0.00
0.0 0.15 2.0 20.0
0.80
1.10
1.20
VPCC (p.u.)
T (s)
1.00
0.80
0.20
0.0 0.5 1.0 15.0
0.95
Iq
VRT
ΔIQ (p.u.)
V (p.u.)
1.00
1.1 1.2
-1.00
0.50.0 0.9
IQ (p.u.)
V (p.u.)
1.00
0.90
0.00 0.5 0.85
-1.00
IdVRT P e ious aul Id0
Reco e y ime 5sN/D
Phase Jump Up o 40◦N/D
Ene gies 2015,xx 4
Table 2. MTRs e iew o VRT capabili ies PV plan s (B)
Coun y Chile I aly
S anda d CNE CEI
VRT
p o ile
VPCC (p.u.)
T (s)
1.00
0.80
0.10
0.0 T2+0.02 1.0
VPCC (p.u.)
T (s)
1.00
0.85
0.00
0.0 0.2 0.4
0.40
1.10
Iq
VRT
ΔIQ (p.u.)
V (p.u.)
1.00
1.11.2
-1.00
0.50.0 0.9
IQ (p.u.)
V (p.u.)
1.00
0.00 0.9
-1.00
IdVRT P e ious aul Id0
Reco e y ime N/D N/D
Phase Jump N/D N/D
Coun y Jo dan Romania
S anda d ERC TRANSELECTRICA
VRT
p o ile
VPCC (p.u.)
T (s)
1.00
0.90
0.00
0.0 0.25 1.5 180
0.80
1.10
1.20
60
VPCC (p.u.)
T (s)
1.00
0.90
0.00
0.0 0.625 3.0
0.15
1.10
Iq
VRT
ΔIQ (p.u.)
V (p.u.)
1.20
-0.4
1.2
-1.00
0.40.0
IQ (p.u.)
V (p.u.)
1.00
0.00 0.9
-1.00
IdVRT 0 0
Reco e y ime 60s350ms
Phase Jump N/D N/D
Ene gies 2015,xx 5
−1.0
0.0
1.0
Vg (p.u.)
1.72 1.73 1.74 1.75 1.76 1.77
−2.0
−1.0
0.0
1.0
2.0
IL (p.u.)
Time (s)
Figu e 1. Example o peak cu en aul unde a se e e low ol age excu sion. (a) T ansien
low ol age p o ile; (b) S ack con e e ou pu cu en s, uncon olled peak cu en s ma ked
wi h g een ci cles.
be a oided, imp o ing he MTRs compliance. Fu he , lowe peak cu en educes IGBTs deg ada ion
and unexpec ed disconnec ions om he g id o he powe con e e s, so Mean Time Be ween Failu es
(MTBF) inc eases.
This manusc ip is o ganized as ollows; Sec ion II analyses in de ail he p oposed me hod heo y.
Sec ions III and IV show es esul s. Discussions a e gi en in Sec ion V. Finally, he Ma e ials and
Me hods used a e poin ed ou in Sec ion VI.
2. FPCC me hod
2.1. Powe con e e con ol s a egy
Two le el h ee-phase opology has been selec ed o he s udy. Indus ial high-powe g id- ie
con e e s usually use single s age in e e opology, wi h a LC ou pu il e [20]-[21].
Fig. 2shows a classical DG con e e con ol block scheme. The con olle is di ided in o ou laye s.
The highes le el con olle gene a es he app op ia e e e ences o he middle con olle . Middle le el
con olle eac s modi ying he esponse in unc ion o en i onmen s agen s ha could limi he in e e
capabili y. Typically, special ol age sag con ol will be placed in his laye . Then, low le el con olle
includes he inne cu en con ol loop ha se he in e e con ol ac ions ollowing he e e ences.
Finally, ha dwa e le el con olle ansla es he con ol signals o he physical pulses o he con e e .
The p oposed FPCC will be imp o ed wi h wo indi idual ac ions. G ay boxes in Fig. 2show whe e
hese ac ions ake place. On he one hand, in he lowe le el, he du y cycle con ol signal is sa u a ed
wi h a heo e ical cu en limi called Fas P edic i e Peak Cu en Sa u a ion (FPPCS) me hod. On he
o he hand, in he ha dwa e le el, delay o du y con ol signal upda ing is educed wi hou modi ying
PWM swi ching equency wi h a echnique deno ed as Du y Signal Upda ing Imp o emen (DSUI).
Ene gies 2015,xx 6
P e SP
Q e SP
Pmax
Pmin
P e ’
Q e
P e
Qmin
Qmax
Id e
Iq e
Cu en
con olle
P e sa lim calcula ion
Q e sa lim calcula ion
High le el
L ow le el
Middle le el
Middle le el
F PPC S
I G BT D i e
Sys em
DSUI
RST/
DQ0
Idq
Ha dwa e
le el
I s
Du y Con ol
V s
V dc
Figu e 2. Simpli ied con ol block scheme o a DG powe con e e .
DRVdc/2
LC
Zsc
ILR
VLR
LC
Zsc
VgRS
ILS
VLS
LC
Zsc
VgST
ILT
VLT
DSVdc/2
DTVdc/2
VnR
VnS
VnT
Figu e 3. Simpli ied in e e ol age sou ce model.
2.2. FPPCS me hod
Fig. 3shows a simpli ied single-line model o he con e e as an ideal con olled ol age sou ce.
This model has been widely p esen ed in li e a u e [22]. The con e e ou pu line- o-line ol age (VgRS,
VgST ) is de ined by an impedance (Zsc) and a g id ol age sou ce. The measu ed ol age could be used
o build up an equi alen ol age sou ce model (VnR,VnS,VnT ) connec ed o he i ual neu al poin o
he con e e model (no ed by he dash-lines in Fig. 3).
Ene gies 2015,xx 7
Eq. 1shows he ela ionship o he induc o ol age (VL) wi h he ol age sou ce model o Fig. 3, and
wi h he di e en ial equa ion o an induc o :
VL=(DVdc
2−Vn
LdIL
d
(1)
whe e Vdc is he DC-Link ol age, Vnis he g id ol age, Dis he DG du y con ol signal in a ange o
[−1,1],Lis he induc i e alue o he il e alue and ILis he cu en ac oss he induc ance. Since he
con olle is execu ed pe iodically a a ixed equency Fs, Eq. 1could be disc e ized, and Dwould be
gi en by Eq. 2:
Dk= 2L(ILk+1 −ILk)Fs+Vnk
Vdck
(2)
Eq. 2gi es a ela ionship be ween IL ime e olu ion, and he con ol signal alue. Consequen ly,
cu en measu emen on nex s ep con ol could be p edic ed. Imposing a con ol law es ic ion wi h a
maximum cu en h eshold IFPP CS, Eq. 3se a heo e ical maximum con ol signal:
DmaxRk= 2L(IF P P CS −IRk)Fs+Vgk
Vdck
DmaxSk= 2L(IF P P CS −ISk)Fs+Vgk
Vdck
DmaxTk= 2L(IF P P CS −ITk)Fs+Vgk
Vdck
(3)
whe e DmaxRk,DmaxSkand DmaxTka e he maximum du y allowed con ol signals o he de ined
IFP P CS in each phase, and IRk,ISkand ITka e he measu ed cu en s o he h ee phases a he k
ins an .
2.3. DSUI me hod
Typically, Pulse Wid h Modula ion (PWM) echniques upda e only hei con ol signals in he alleys
and peaks o he iangula ca ie , T0and T2 espec i ely (see Fig. 4), gua an eeing non-desi able i ing,
emaining cons an he swi ching equency, and a oiding ex a powe losses [23].
Fig. 4shows a ypical delay added in a powe con e e con olle . I he con ol p ocesso needs a
compu a ional ime (Tc) since he las sampling ime (T0), hen an addi ional delay o Tmwill be inse ed
be o e he ac ion will be execu ed, because he con ol signal can only be upda ed in he peaks and he
alleys. The p oposed echnique upda es he con ol signal a T1wi h some es ic ions. Then, only Tc
delay happens, and he peak cu en unde aul y condi ions will d op.
As an example, Fig. 5shows all ou possible cases in he up-slope PWM ca ie semi-cycle, bu
simila cases could be exposed in he down-slope semi-cycle. On he one hand, du ing he up-slope,
i p e ious con ol signal (D0) is g ea e han he iangula ca ie alue a T1, no ex a ansi ion is
gua an eed and he new con ol signal (D1) could be upda ed wi hou any addi ional swi ching in he
semi-cycle (cases cand din Fig. 5). On he o he hand, i D0is lowe han he iangula ca ie a T1,
a leas h ee ansi ions may occu i D1is upda ed a T1: he i s one belongs o D0le el; a second
ansi ion happens a T1; and a hi d ansi ion will happen a D1le el. Consequen ly, con ol signal will
be upda ed in he nex alley o peak o a oid ex a-swi ching (case ain Fig. 5). Finally, case bdoes no
p oduce any ex a-swi ching bu nei he modi ies he con ol ou pu .
Ene gies 2015,xx 8
T0T1T2
Con ol
delay Modula ion
delay
PWM ca ie
Du y con ol
signal
Tc
Tm
Figu e 4. Typical delay added in a powe con e e con olle . The measu es a e aken a
T0, bu Tcis needed o calcula e nex con ol signal. Finally, con ol signal is upda ed and
applied a T2.
T1
D0
D1
T0T2
aT1
D0
D1
T0T2
b
T1
D1
D0
T0T2
cT1
D1
D0
T0T2
d
D
Figu e 5. All ou possible du y upda ing cases in he ising PWM semi-cycle. Con ol
signal could be upda ed a T1in cases cand d, bu mus be upda ed a T2in cases aand b.
G aphically, Fig. 6shows an example o PWM signals gene a ed in cases aand c. In case c
he du y signal is upda ed (blue line) wi hou p oducing ex a-swi ching, educing he on s a e o he
semiconduc o . Howe e , in case a, he con ol signal mus be upda ed in T2(solid blue line), o he wise,
wo swi ching e en s will happen (do ed ed line).
Following he same s eps, along he modula ion down-slope cycle, i D0is lowe han he modula ion
alue a T1, con ol signal could be upda ed wi hou any change in he swi ching equency. Fig. 7shows
all ou possible cases on he down-slope semi-cycle.
Fo una ely, no all cases a e ele an wi h espec cu en aul s. So a s udy could be made o
de e mine he e ec i eness o he imp o emen in hese special cases. The e a e wo aul condi ions: A
posi i e and a nega i e o e -cu en peak. F om he e, he up-slope case will be analysed, bu a simila
easoning could be done o he down-slope semi-cycle.
Acco ding o Eq. 2a ins an k=1, he wo s o e -cu en peak (IL0) would happen i he cu en
peak aul was add up o e he maximum cu en alue modula ed. Consequen ly, D0is expec ed o be
Ene gies 2015,xx 9
T1
D0
D1
T0T2
a
0
PWM
1
T1
D1
D0
T0T2
c
0
1
Figu e 6. PWM signals gene a ed wi h cases aand co ising PWM semi-cycle. Red do ed
line poin s ou possible mal unc ioning wi h wo swi chings in same semi-cycle i p oposed
ule is no applied. Blue line poin s ou PWM signals gene a ed wi h DSUI me hod.
T1
D0
T0T2
aT1
D0
D1
T0T2
b
T1
D1
D0
T0T2
cT1
D0
D1
T0T2
d
D1
Figu e 7. All ou possible du y upda ing cases in he alling PWM semi-cycle. Con ol
signal could be upda ed a T1in cases aand b, bu mus be upda ed a T2in cases cand d.
posi i e and big enough. In addi ion, i a dange ous peak cu en happened, he con olle would ha e o
d op IL o a sa e y egion. Acco ding o Eq. 2, o ake down IL1,D1will be e y low. The e o e, i a
posi i e o e -cu en peak happens, case co Fig. 5is expec ed. As p e iously men ioned, his is one o
he allowed cases o e esh he con ol signal, so he o e -cu en peak will be educed.
A simila easoning could be made wi h a nega i e o e -cu en aul . On he one hand, now D0is
expec ed o be nega i e big enough. On he o he hand, om Eq. 2D1expec ed alue will be e y high.
Consequen ly, i a nega i e o e -cu en peak happens, case ao do Fig. 5a e expec ed. I case d
happens, he con ol signal will be upda ed and he o e -cu en peak will be educed. Un o una ely, i
case ahappens, he me hod will no ac in his semi-cycle.
Ene gies 2015,xx 10
Fig. 5poin s ou ha Tcin luences he e ec i eness o he me hod. I Tcis o zed o ze o, all con ol
s eps will be in he cand dcases, so i is impo an o ha e a small delay Tc o sho he measu ed peak
cu en in mos si ua ions.
Finally, one mo e ac ion could be pe o med o educe he o e -cu en peak. A aul happened in
semi-cycle kwill be measu ed a he beginning o he nex semi-cycle k+ 1, and he con ol ac ion will
be placed a T1in bes case, o in he beginning o k+ 2 in he wo s case. So he maximum delay could
be 2Tso Ts+Tc.
I Tcis ela i ely sho , a new con ol s ep could be done a he middle o he semi-cycle. This con ol
signal will be applied wi h he same ules han he o he s, so in a gene al way, i will be placed a he inal
o he semi-cycle. In his case, i a aul happens a he middle o he semi-cycle k′, i will be measu ed a
he beginning o he nex con ol s ep k′+1, and he con ol ac ion will be placed a T1in bes case, o in
he beginning o k′+ 2 in he wo s case. So he maximum delay could be Tso 0.5·Ts+Tc. Assuming
VLcons an in a sho pe iod o ime du ing he aul condi ion,
IL=1
LZVLd −→ ∆IL=VL
L·Tdelay (4)
whe e ∆ILis he expec ed inc emen on he peak cu en induced by he aul , and Tdelay is he ime
necessa y o con ol he aul . So, acco ding o Eq. 4 he peak cu en will be educed in,
PImax =
VL
L·1.5Ts
VL
L·2Ts
= 0.75p.u.
PImin = limTc→0
VL
L·(0.5Ts+Tc)
VL
L·Ts+Tc
= 0.5p.u. (5)
whe e PIis he p opo ion o he peak cu en educed wi h he imp o emen (be ween 50 and 75%).
3. Simula ions
A high powe indus ial PV sola in e e has been modelled o es FPCC. Howe e , simila esul s
could be ob ained wi h o he applica ions. Following de ices ha e been modelled in he simula ion:
a sola panel ield; a de ailed comme cial model o a wo-le el h ee-phase powe in e e ; a medium
ol age ans o me ; he Poin O In e connec ion (POI) wi h he u ili y g id; a RL di ide o gene a es
ol age sags and phase-jumps.
Two ypes o aul s ha e been analysed a ull powe . The wo s cases desc ibed in he in e na ional
legisla ion [5]-[13] ha e been selec ed. The sys em will be es ed agains symme ic and asymme ic
ol ages sags and phase-jump aul s. Fig. 8shows line o line ol ages o he deepes aul s o each ype
used o es he sys em. Case ashows a h ee-phase ol age aul wi h a ze o emaining ol age. Case b
shows an asymme ic ol age aul wi h wo phases o e lapped. Case cshow a h ee-phase 45◦ ol age
phase-jump. And inally, case dshows he same phase-jump o only one phase.
Fig. 9and 10 show he ansien powe con e e esponse agains a 45◦ h ee-phase jump dis u bance
and a 0.0p.u. h ee-phase dip ol age, espec i ely, i ed a 0.00s. Fo bo h igu es, plo (a) shows
ansien beha iou o one phase ol age (Vg). Fig. 9(b) shows he phase (θ) ansien o 45◦, and Fig. 10
(b) he ol age module (m) ansien o 0.0p.u., du ing he aul . Cases c o eshow wo cu es each one,
solid line cu e ep esen s he e olu ion o he sys em wi h a Classical App oach (CA), and dash line
Ene gies 2015,xx 11
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(a)
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(b)
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(c)
−1.0
−0.5
0.0
0.5
1.0
Vg (p.u.)
(d)
Figu e 8. Line o line h ee-phase g id ol age o all ypes o aul s es ed. Th ee-phase
ze o- ol age aul (a), asymme ic ze o- ol age aul (b), h ee-phase 45◦ ol age phase-jump
(c), and mono-phase 45◦ ol age phase-jump (d).
cu e ep esen s he e olu ion o he sys em wi h FPCC. Cases c o eshow he du y signal con ol (D),
he s ack ou pu cu en (IL), and he con e e ou pu cu en (Iou ), espec i ely. No e ha So wa e
P o ec ion (SP) and Ha dwa e P o ec ion (HP) h eshold a e poin ed ou o e case d, and how wi h he
FPCC ac i e he h eshold is no eached. As a esul , he uni emains connec ed. Iou peak is educed
oo, bu addi ional emaining peaks appea in he con e e ou pu due o he line capaci o il e .
Howe e , esul s may di e depending he igge ing ime o he aul . To cope wi h his e ec all
cases ha e been epea ed en imes, i ing he aul a di e en ins an s o look o he wo s case. Table 3
shows a compa a i e o se e al phase-jumps and ol age sags. Se e al alues ha e been es ed o bo h,
he mono-phase and he h ee-phase cases. In e e y cell, alues a le a e o IL, and alues a igh o
Iou . In o de o quan ize he weigh o each imp o emen in he o e all esul h ee cases a e conside ed
in he s udy: CA me hod, only FPPCS algo i hm, and comple e FPCC echnique.
Table 3shows FPCC o e -cu en s abou 0.4p.u. lowe han CA me hod, and helps o emain in he
ange o ope a ion o he con e e (SP a 1.3p.u.). The able also shows esul s abou he in luence o
e e y pa o he me hod.
4. Expe imen al alida ion
Ene gies 2015,xx 12
−1.0
0.0
1.0
Vg (p.u.)
−45
0
θ (º)
0.0
0.5
1.0
D (p.u.)
CA
FPCC
HP
SP
−1.0
−0.8
IL (p.u.)
CA
FPCC
−0.03 0.02 −0.01 0.00 0.01 0.02
−1.5
−1.0
−0.5
Iou (p.u.)
Time (s)
CA
FPCC
Figu e 9. Con e e esponse agains a 45◦phase-jump aul wi h CA and FPCC echniques.
G id ol age (a), phase (b), du y con ol signal (c), s ack cu en (d), and con e e cu en
ou pu (e).
−1.0
0.0
1.0
Vg (p.u.)
0.0
0.5
1.0
m (p.u.)
0.0
0.5
1.0
D (p.u.)
CA
FPCC
HP
SP
−1.0
−0.8
IL (p.u.)
CA
FPCC
−0.03 0.02 −0.01 0.00 0.01 0.02
−1.5
−1.0
−0.5
Iou (p.u.)
Time (s)
CA
FPCC
Figu e 10. Con e e esponse agains a 0.00p.u. h ee-phase dip ol age wi h CA and FPCC
echniques. G id ol age (a), module (b), du y con ol signal (c), s ack cu en (d), and
con e e cu en ou pu (e).
Ene gies 2015,xx 19
Table 5. PV panel model se up
Panel nominal alues Value Tes condi ions Value
Ac i e powe (PMP P ;STC )500kW Tempe a u e (T)25◦C
Vol age (UMP P ;ST C)825VI adiance (G)1000Wm2
Tempe a u e (TSTC)25◦CPanel echnology Value
I adiance (GST C)1000Wm2Coe icien o ol age change F u 0.8p.u.
Tempe a u e model Value Coe ien o cu en change F i 0.9p.u.
Tempe a u e co ec ion T00◦CTechnology coe icien Cg2.514 ·10−3W/m2
I adiance gain k0.03m2/W Technology coe icien C 0.08593p.u.
Time cons an τ300sTechnology coe icien C 1.088 ·10−4m2/W
I adiance change V l2h0.95p.u.
Cu en empe a u e α0.0004p.u.
Vol age empe a u e β−0.004
Table 6. G ied- ied in e e se up
Pa ame e Value Pa ame e Value
Nominal ac i e powe PDG 500kW O e -cu en So wa e P o ec ion SP 1.3p.u./0.1ms
Nominal ou pu cu en In1202AO e -cu en Ha dwa e P o ec ion HP 1.4p.u.
Nominal g id ol age Vn240VAc i e cu en con ol kpD= 0.05
kiD= 5
FPPCS limi IF P P CS 1.05p.u. Reac i e cu en con ol kpQ= 0.05
kiQ= 5
Delay con ol ime Tc0.6p.u. PWM equency PW M 1980Hz
Table 7. Medium ol age ans o me se up
Pa ame e Value Pa ame e Value
P ima y winding ol age 23kV Nominal powe 0.6MWe
Seconda y winding ol age 0.24kV Nominal g id equency 60Hz
Winding ype Y∆Leakage eac ance 0.12p.u.
Coppe losses 0.01p.u.
The ans o me has a Y Y con igu a ion. Wi h a winding ol ages 400V: 400Vand a sho -ci cui
impedance o 0.09p.u.. Finally, all wi ing in he es bench was enough o ul il powe demands, and no
signi ican induc ance was added (3wi es o 240mm diame e pe phase).
Ene gies 2015,xx 20
ELECTRIC GRID
400 V 50Hz
1000 kVA
400V/240V
AUXILIARY SYSTEM
400 V
AC
DC
DC
AC
DUT
AC
DC
Elec onic
gene a o
Rec i ie
100 kVA
400V/230V
Figu e 16. Tes -bench scheme (a) and pano amic iew (b); he DUT is on he igh side o
he pho o, and ec i ie and gene a o a e a he backg ound. The powe ans o me is inside
he me allic jail.
Acknowledgmen s
This wo k was suppo ed by GPTech Spain (www.g eenpowe .es) and he Elec onic Enginee ing
Depa men o he Uni e si y o Se ille.
Au ho Con ibu ions
Jesús Muñoz-C uzado-Alba concei ed and designed he p oposed con ol s a egy, and signi ican ly
con ibu ed o he implemen a ion o he simula ion and es bench. Ja ie Villegas-Núñez
and José Albe o Vi e-F ías help in he labo a o y es s and he w i ing o he pape .
Juan Manuel Ca asco Solís we e esponsible o he guidance and a numbe o key sugges ions.
Con lic s o In e es
The au ho s decla e no con lic o in e es .
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connec ed o he medium ol age le el in Jo dan. ERC, Jo dan, 2014.
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A¸S2592.
15. M. Cas illa, J. Mi e , A. Camacho, L. Ga cia de Vicuna, J. Ma as, (2014, No .). Modeling and
Design o Vol age Suppo Con ol Schemes o Th ee-Phase In e e s Ope a ing Unde Unbalanced
G id Condi ions. IEEE T ans. Powe Elec on., ol. 29, no. 11, pp. 6139â ˘
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sa, J. Ma as, (2012, Oc .). Con ol Scheme
o Pho o ol aic Th ee-Phase In e e s o Minimize Peak Cu en s Du ing Unbalanced G id-Vol age
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Ride-Th ough Enhancemen o Th ee-Le el-Boos and NPC-Con e e -Based PMSG Wind Tu bine.
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equi emen upda ed o LVRT capabili ies unde ecen g id codes legisla ion. PCIM Eu ope 2014,
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Ride-Th ough Con ol S a egy o G id Connec ed Doubly Fed Induc ion Wind Gene a o s. IEEE
T ans. Powe Sys ., ol. 29, no. 3, pp. 1325-1334.
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Semiconduc o De ices & IC’s (ISPSD), pp. 12-18.
21. R. Bu ka , J.W. Kola , G. G iepen og (2012, Oc .). Comp ehensi e compa a i e
e alua ion o single- and mul i-s age h ee-phase powe con e e s o pho o ol aic applica ions.
Telecommunica ions Ene gy Con e ence (INTELEC), pp. 1-8.
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22. A. Yazdani, R. I a ani (2010). Vol age-Sou ced Con e e s in Powe Sys ems; Modeling, Con ol
and Applica ions. J. Wiley & Sons, USA.
23. E. Monmasson (2011). Powe Elec onic Con e e s: PWM S a egies and Cu en Con ol
Techniques. J. Wiley & Sons, Hoboken, USA.
24. O e all e iciency o g id connec ed pho o ol aic in e e s. CENELEC, Belgium, 2010.
c
2015 by he au ho s; licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle
dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion license
(h p://c ea i ecommons.o g/licenses/by/4.0/).
Appendix C
A New Fas Peak Cu en Con olle
o T ansien Vol age Faul s o Powe
Con e e s
83
A New Fas Peak Cu en Con olle o T ansien
Vol age Faul s o Powe Con e e s
Jes´
us Mu˜
noz-C uzado-Alba,
Ja ie Villegas-N´
u˜
nez,
Jos´
e Albe o Vi e-F ´
ıas
R&D Depa men ,
GPTech
Bollullos de la Mi acion, Spain
jmunoz@g eenpowe .es,
j illegas@g eenpowe .es, ja i e@g eenpowe .es
Edua do Gal ´
an-D´
ıez,
J.M. Ca asco
Elec onics Enginee ing Depa men ,
Se ille Uni e si y,
Se ille, Spain
eg[email p o ec ed], [email p o ec ed]
Abs ac —Powe con e e s a e he basic uni o ansien
ol age aul ide h ough capabili y o mos enewable dis-
ibu ed gene a o s. When a ansien aul happens, he g id
ol age will d op suddenly, and p obably, will also su e a phase-
jump e en also. S a e o he a ol age aul con ol echniques
egula e he cu en injec ed du ing he g id aul . Howe e , he
beginning o he aul could be oo as o he inne cu en s
con ol loops o he in e e , and ansien o e -cu en would be
expec ed. In o de o a oid excessi e peak cu en o me hods
p esen ed in he li e a u e, a new as peak cu en con ol
echnique is p oposed. Con olling he peak cu en magni ude
a oids undesi able disconnec ion o he dis ibu ed gene a o in
a aul s a e and imp o es he li e-expec ancy o he con e e .
Expe imen al and simula ion es s wi h high powe con e e s
p o ide de ailed beha iou o he me hod wi h excellen esul s.
Keywo ds—Dis ibu ed Gene a o s (DGs); Vol age Ride
Th ough (VRT); Fas Peak Cu en Con ol (FPCC); Phase-Jump
Ride Th ough (PJRT); Pho o-Vol aic (PV) sys ems; dip ol age.
I. INTRODUCTION
Powe is ypically p oduced a a wide ange o gene a ion
plan s. Some yea s ago, o powe enewable sou ces, i
was desi able o swi ch o he sou ce when a ol age aul
occu ed. Back hen, disconnec ion o ha powe sou ces had
li le, i any, impac on he eco e y capabili y o he elec ic
powe g id a e a aul . Nowadays, a high pene a ion o
enewable DGs [1]-[4] has oughened he g id connec ion
Minimum Technical Requi emen s (MTRs) in egions like
USA, Sou h-A ica, and Eu ope [5]-[10].
VRT capabili y equi emen has been widely desc ibed in
ecen g id codes [5]-[10]. Table I poin s ou some o he mos
popula MTRs o PV plan s abou VRT.
Fi s , a maximum allowed ol age p o ile is de ined o
ol age excu sions. I he aul eaches he e o p o ile, he
in e e is allowed o disconnec . Then some equi emen s
a e imposed o e he powe gene a ion du ing he ol age
excu sions in o de o help he sys em s abili y. An injec ion
This wo k was suppo ed by GPTech Spain (www.g eenpowe .es) and he
Elec onics Enginee ing Depa men o he Se ille Uni e si y.
o eac i e cu en (Iq) is always equi ed, ollowing a d oop
ela ionship o gene a ing he maximum possible capaci i e
cu en . The e a e wo choices o he ac i e cu en (Id)
equi emen : o ollow he p e ious alue o aul s a e; o o
d op he e e ence o ze o, bu consump ion is no allowed.
Finally, a eco e y ime a e he aul equi emen s could be
needed also. Mos ecen g id codes a e also including phase-
jump aul equi emen s [6].
Wo s scena ios co e he necessi y o emain connec ed
agains 40◦phase-jumps, and 0.0p.u. low ol age excu sions,
o h ee-phase and mono-phase aul s. A sudden occu ence
o his ype o aul could cause a peak in he con e e
ou pu cu en . So hese cu en peaks cause uni e o s and
disconnec ions, being a haza d o he uni sa e y.
Toge he wi h he ope a ion mode and he imposed limi s,
esponse ime is c ucial in his kind o e en s whose du a ions
a e in he o de o milliseconds. A he beginning o he aul ,
any delay could be c i ical, because he g id ol age could
change e y as . The e is a lo o esea ch on powe con e e s
con olle s du ing g id aul condi ions [11]-[16], bu un o -
una ely he e is no enough analysis abou he uncon olled
beginning o he aul .
A new FPCC is p oposed o help he con e e con ol
limi ing o e -cu en peak o he con e e a he beginning
o he aul . Consequen ly, ha dwa e and so wa e cu en p o-
ec ion could be a oided, imp o ing he Minimum Technical
Requi emen s (MTRs) compliance. Fu he , lowe peak cu en
educes IGBTs deg ada ion and unexpec ed disconnec ions
om he g id o he powe con e e s, so Mean Time Be ween
Failu es (MTBF) g ows up.
This manusc ip is o ganized as ollows; Sec ion II analyses
in de ail he p oposed me hod heo y. Sec ions III and IV show
es esul s. Finally, conclusions a e gi en in Sec ion V.
II. FPCC METHOD
A. Powe con e e con ol s a egy
Two le el h ee-phase opology has been selec ed o he
s udy. Indus ial high-powe g id- ie con e e s usually use
978-1-4799-7993-6/15/$31.00 c
2015 IEEE
TABLE I. MTRS REVIEW FOR VRT CAPABILITIES PV PLANTS
Coun y Ge many Pue o Rico Sou h A ica Spain
S anda d BDWE PREPA NERSA REE
VRT
p o ile
VPCC (p.u.)
T (s)
1.00
0.90
0.30
0.0 0.15 0.60 1.50 3.00
VPCC (p.u.)
T (s)
1.00
0.90
0.00
0.0 0.6 3.0
1.15
1.25
1.30
1.40
0.15 1.0
VPCC (p.u.)
T (s)
1.00
0.90
0.00
0.0 0.15 2.0 20.0
0.80
1.10
1.20
VPCC (p.u.)
T (s)
1.00
0.80
0.20
0.0 0.5 1.0 15.0
0.95
Iq
VRT
ΔIQ (p.u.)
V (p.u.)
1.00
1.11.2
-1.00
0.50.0 0.9
ΔIQ (p.u.)
V (p.u.)
1.00
-1.00
V1
0.0 0.85
ΔIQ (p.u.)
V (p.u.)
1.00
1.1 1.2
-1.00
0.50.0 0.9
IQ (p.u.)
V (p.u.)
1.00
0.90
0.00 0.5 0.85
-1.00
Id
VRT 00 Maximum a ailable 0
Reco e y
ime 5s5s5sN/A
Phase
Jump o pUA/NA/N 40 N/A
º
P e SP
Q e SP
Pmax
Pmin
P e ’
Q e
P e
Qmin
Qmax
Id e
Iq e
Cu en
con olle
P e sa lim calcula ion
Q e sa lim calcula ion
High le el
L ow le el
Middle le el
Middle le el
F PPC S
I G B T D i e
Sys em
DSUI
RST/
DQ0
Idq
Ha dwa e
le el
I s
Du y Con ol
V s
V dc
Fig. 1. Simpli ied con ol block scheme o a DG powe con e e .
single s age in e e opology, wi h a LC ou pu il e [17]-
[18].
Fig. 1 shows a classical DG con e e con ol block
scheme. The con olle is di ided in o ou laye s. High le el
con olle gene a es he app op ia e e e ences o he middle
con olle . Middle le el con olle eac s modi ying he e-
sponse in unc ion o en i onmen s agen s ha could limi he
in e e capabili y. Typically, special ol age sag con ol will
be placed in his laye . Then, low le el con olle includes he
inne cu en con ol loop ha se he in e e con ol ac ions
ollowing he e e ences. Finally, ha dwa e le el con olle
ansla es he con ol signals o he physical pulses o he
con e e .
The p oposed FPCC will be imp o ed wi h wo indi idual
ac ions. G ay boxes in Fig. 1 show whe e hese ac ions ake
place. On he one hand, in he lowe le el, he du y cycle
con ol signal is sa u a ed wi h a heo e ical cu en limi called
Fas P edic i e Peak Cu en Sa u a ion (FPPCS) me hod. On
he o he hand, in he ha dwa e le el, delay o du y con ol
DRVdc/2
LC
Zsc
ILR
VLR
LC
Zsc
VgRS
ILS
VLS
LC
Zsc
VgST
ILT
VLT
DSVdc/2
DTVdc/2
VnR
VnS
VnT
Fig. 2. Simpli ied in e e ol age sou ce model.
signal upda ing is educed wi hou modi ying PWM swi ching
equency wi h a echnique deno ed as Du y Signal Upda ing
Imp o emen (DSUI).
B. FPPCS me hod
Fig. 2 shows a simpli ied single-line model o he con e e
as an ideal con olled ol age sou ce. This model has been
widely p esen ed in li e a u e [19]. The con e e ou pu line-
o-line ol age (VgRS,VgST ) is de ined by an impedance (Zsc)
and a g id ol age sou ce. The measu ed ol age could be used
o build up an equi alen ol age sou ce model (VnR,VnS,
VnT ) connec ed o he i ual neu al poin o he con e e
model (no ed by he dash-lines in Fig. 2).
Eq. 1 shows he ela ionship o he induc o ol age (VL)
wi h he ol age sou ce model o Fig. 2, and wi h he di e -
en ial equa ion o an induc o :
VL=DVdc
2−Vn
LdIL
d
(1)
whe e Vdc is he DC-Link ol age, Vnis he g id ol age, D
is he DG du y con ol signal in a ange o [−1,1],Lis he
induc i e alue o he il e alue and ILis he cu en ac oss
he induc ance. Since he con olle is execu ed pe iodically a
a ixed equency Fs, Eq. 1 could be disc e ized, and Dwould
T0T1T2
Con ol
delay Modula ion
delay
PWM ca ie
Du y con ol
signal
Tc
Tm
Fig. 3. Typical delay added in a powe con e e con olle . The measu es
a e aken a T0, bu Tcis needed o calcula e nex con ol signal. Finally,
con ol signal is upda ed and applied a T2.
be gi en by Eq. 2:
Dk= 2L(ILk+1 −ILk)Fs+Vnk
Vdck
(2)
Eq. 2 gi es a ela ionship be ween IL ime e olu ion, and
he con ol signal alue. Consequen ly, cu en measu emen
on nex s ep con ol could be p edic ed. Imposing a con ol
law es ic ion wi h a maximum cu en h eshold IF P P CS ,
Eq. 3 se a heo e ical maximum con ol signal:
DmaxRk= 2L(IF P P CS −IRk)Fs+Vgk
Vdck
DmaxSk= 2L(IF P P CS −ISk)Fs+Vgk
Vdck
DmaxTk= 2L(IF P P CS −ITk)Fs+Vgk
Vdck
(3)
whe e DmaxRk,DmaxSkand DmaxTka e he maximum du y
allowed con ol signals o he de ined IF P P CS in each phase,
and IRk,ISkand ITka e he measu ed cu en s o he h ee
phases a he kins an .
C. DSRI me hod
Typically, Pulse Wid h Modula ion (PWM) echniques
upda e only hei con ol signals in he alleys and peaks
o he iangula ca ie , T0and T2 espec i ely (see Fig.
3), gua an eeing non-desi able i ing, emaining cons an he
swi ching equency, and a oiding ex a powe losses [20].
Fig. 3 shows a ypical delay added in a powe con e e
con olle . I he con ol p ocesso needs a compu a ional ime
(Tc) since he las sampling ime (T0), hen an addi ional delay
o Tmwill be inse ed be o e he ac ion will be execu ed,
because he con ol signal can only be upda ed in he peaks and
he alleys. The p oposed echnique upda es he con ol signal
a T1wi h some es ic ions. Then, only Tcdelay happens, and
he peak cu en unde aul y condi ions will d op.
As an example, Fig. 4 shows all ou possible cases in
he up-slope PWM ca ie semi-cycle, bu simila cases could
be exposed in he down-slope semi-cycle. On he one hand,
du ing he up-slope, i p e ious con ol signal (D0) is g ea e
han he iangula ca ie alue a T1, no ex a ansi ion is
gua an eed and he new con ol signal (D1) could be upda ed
wi hou any addi ional swi ching in he semi-cycle (cases c
and din Fig. 4). On he o he hand, i D0is lowe han he
iangula ca ie a T1, a leas h ee ansi ions may occu i
D1is se a T1: he i s one belongs o D0le el; a second
ansi ion happens a T1; and a hi d ansi ion will happen a
D1le el. Consequen ly, con ol signal will be upda ed in he
nex alley o peak o a oid ex a-swi ching (case ain Fig.
T1
D0
D1
T0T2
aT1
D0
D1
T0T2
b
T1
D1
D0
T0T2
cT1
D1
D0
T0T2
d
Fig. 4. All ou possible du y upda ing cases in he uppe PWM semi-cycle.
Con ol signal could be upda ed a T1in cases cand d, bu mus be upda ed
a T2in cases aand b.
4). Finally, case bdoes no p oduce any ex a-swi ching bu
nei he modi ies he con ol ou pu .
Following he same s eps, du ing he down-slope cycle o
he modula ion signal, i D0is lowe han he modula ion alue
a T1, con ol signal could be upda ed wi hou any change in
he swi ching equency.
Fo una ely, no all cases a e ele an wi h espec cu en
aul s. So a s udy could be made o de e mine he e ec i eness
o he imp o emen in hese special cases. The e a e wo aul
condi ions: A posi i e and a nega i e o e -cu en peak. F om
he e, he up-slope case will be analysed, bu a simila easoning
could be done o he down-slope semi-cycle.
Acco ding o Eq. 2 a ins an k=1, he wo s o e -cu en
peak (IL0) would happen i he cu en peak aul was add
up o e he maximum cu en alue modula ed. Consequen ly,
D0is expec ed o be posi i e and big enough. In addi ion, i
a dange ous peak cu en happened, he con olle would ha e
o d op IL o a sa e y egion. Acco ding o Eq. 2, o ake down
IL1,D1will be e y low. The e o e, i a posi i e o e -cu en
peak happens, case co Fig. 4 is expec ed. As p e iously
men ioned, his is one o he allowed cases o e esh he
con ol signal, so he o e -cu en peak will be educed.
A simila easoning could be made wi h a nega i e o e -
cu en aul . On he one hand, now D0is expec ed o be
nega i e big enough. On he o he hand, om Eq. 2 D1
expec ed alue will be e y high. Consequen ly, i a nega i e
o e -cu en peak happens, case ao do Fig. 4 a e expec ed.
I case dhappens, he con ol signal will be upda ed and he
o e -cu en peak will be educed. Un o una ely, i case a
happens, he me hod will no ac in his semi-cycle.
Fig. 4 poin s ou ha Tcin luences he e ec i eness o he
me hod. I we o ced Tc o ze o, all con ol s eps will be in
he cand dcases, so i is impo an o ha e a small delay Tc
o sho he measu ed peak cu en in mos si ua ions.
Finally, one mo e ac ion could be pe o med o educe he
o e -cu en peak. A aul happened in semi-cycle kwill be
measu ed a he beginning o he nex semi-cycle k+ 1, and
he con ol ac ion will be placed a T1in bes case, o in he
beginning o k+ 2 in he wo s case. So he maximum delay
could be 2Tso Ts+Tc.
I Tcis ela i ely sho , a new con ol s ep could be done
a he middle o he semi-cycle. This con ol signal will be
applied wi h he same ules han he o he s, so in a gene al
way, i will be placed a he inal o he semi-cycle. In his
Elec ic g id
23kV 60Hz
DUT
AC
DC
600 kVA
23kV/240V
PV Panel
Resis i e
load
Fo phase
jumps
Induc i e
load
o ol age
sags
POI
Fig. 5. De ailed simula ion scheme o es FPCC.
case, i a aul happens a he middle o he semi-cycle k′,
i will be measu ed a he beginning o he nex con ol s ep
k′+ 1, and he con ol ac ion will be placed a T1in bes
case, o in he beginning o k′+ 2 in he wo s case. So he
maximum delay could be Tso 0.5·Ts+Tc. Assuming VL
cons an in a sho pe iod o ime du ing he aul condi ion,
IL=1
LZVLd −→ ∆IL=VL
L·Tdelay (4)
whe e ∆ILis he expec ed inc emen on he peak cu en
induced by he aul , and Tdelay is he ime necessa y o con ol
he aul . So, acco ding o Eq. 4 he peak cu en will be
educed in,
PImax =
VL
L·1.5Ts
VL
L·2Ts
= 0.75p.u.
PImin = limTc→0
VL
L·(0.5Ts+Tc)
VL
L·Ts+Tc
= 0.5p.u. (5)
whe e PIis he p opo ion o he peak cu en educed wi h
he imp o emen (be ween 50 and 75%).
III. SIMULATIONS
A high powe indus ial PV sola in e e has been mode-
lled o es FPCC. Howe e , simila esul s could be ob ained
wi h o he applica ions. Simula ions had been pe o med wi h
elec ic ansien powe ool EMTDC/PSCAD.
Fig. 5 shows a de ailed desc ip ion o he simula ion. I
includes a sola panel ield and a de ailed wo-le el h ee-
phase powe in e e ha ac s as De ice Unde Tes (DUT), a
medium ol age ans o me , and he Poin O In e connec ion
(POI) wi h he u ili y g id. Mo eo e , he e is a a iable pa allel
impedance load o pe o m ol age sags and phase-jumps.
The pa ame e s used in simula ion a e summa ized as
ollows:
•Sola in e e ac i e powe : PDG = 500kW
•Sola panel ield: Pmpp = 500kW,Umpp = 825V
•POI: VL= 23kV ,Ssc = 500MV A, = 60Hz
•G id ol age: Vn= 240V
•O e -cu en So wa e P o ec ion:
SP = 1.3p.u./0.1ms
•O e -cu en Ha dwa e P o ec ion: HP = 1.4p.u.
•Nominal ou pu cu en : In= 1202A
•FPPCS limi : IF P P CS = 1.05p.u.
•Con e e cu en con ol: kpD= 0.05,kiD= 5,
kpQ= 0.05,kiQ= 5.
−1.0
0.0
1.0
Vg (p.u.)
−45
0
θ (º)
0.0
0.5
1.0
D (p.u.)
CA
FPCC
HP
SP
−1.0
−0.8
IL (p.u.)
CA
FPCC
−0.03 0.02 −0.01 0.00 0.01 0.02
−1.5
−1.0
−0.5
Iou (p.u.)
Time (s)
CA
FPCC
Fig. 6. Con e e esponse agains a 45◦phase-jump aul wi h CA and
FPCC echniques. G id ol age (a), phase (b), du y con ol signal (c), s ack
cu en (d), and con e e cu en ou pu (e).
•Delay con ol ime: Tc= 0.6p.u.
•PWM equency: P W M = 1980Hz
Two ypes o aul s ha e been analysed a ull powe .
The wo s cases desc ibed in he in e na ional legisla ion [5]-
[10] ha e been selec ed. The sys em will be es ed agains
symme ic and asymme ic ol ages sags and phase-jumps
aul s.
Fig. 6 and 7 show he ansien powe con e e esponse
agains a 45◦ h ee-phase jump dis u bance and a 0.0p.u. h ee-
phase dip ol age, espec i ely, i ed a 0.00s. Fo bo h igu es,
plo (a) shows ansien beha iou o one phase ol age (Vg).
Fig. 6 (b) shows he phase (θ) ansien o 45◦, and Fig. 7
(b) he ol age module (m) ansien o 0.0p.u., du ing he
aul . Cases c o eshow wo cu es each one, solid line
cu e ep esen s he e olu ion o he sys em wi h a Classical
App oach (CA), and dash line cu e ep esen s he e olu ion
o he sys em wi h FPCC. Cases c o eshow he du y signal
con ol (D), he s ack ou pu cu en (IL), and he con e e
ou pu cu en (Iou ), espec i ely. No ice ha SP and HP
h eshold a e poin ed ou o e case d, and how wi h he FPCC
ac i e he h eshold is no eached. As a esul , he uni emains
connec ed. Iou peak is educed oo, bu addi ional emaining
peaks appea in he con e e ou pu due o he line capaci o
il e .
Howe e , esul s may di e depending he igge ing ime
o he aul . To cope wi h his e ec all cases ha e been
epea ed en imes, i ing he aul a di e en ins an s o look
o he wo s case. Table II shows a compa a i e o se e al
phase-jumps and ol age sags. Se e al alues ha e been es ed
o bo h, he mono-phase and he h ee-phase cases. In e e y
cell, alues a le a e o IL, and alues a igh o Iou . In
o de o quan ize he weigh o each imp o emen in he o e all
esul h ee cases a e conside ed in he s udy: CA me hod, only
FPPCS algo i hm, and comple e FPCC echnique.
Table II shows FPCC o e -cu en s abou 0.4p.u. lowe
han CA me hod, and helps o emain in he ange o ope a ion
o he con e e (SP a 1.3p.u.). The able also shows esul s
126 Bibliog aphy
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