Novel modulator for the hybrid two-cell flying-capacitor based ANPC converter

No el Modula o o he Hyb id Two-cell Flying-Capaci o Based ANPC Con e e Jose I. Leon*, Leopoldo G. F anquelo*, Sami Kou o+, Bin Wu+and Se gio Vazquez* * Elec onic Enginee ing Depa men Uni e si y o Se ille Se ille, Spain 41092 Email: [email p o ec ed] + Depa men o Elec ical and Compu e Enginee ing Rye son Uni e si y To on o, Canada Email: [email p o ec ed] Abs ac —Among he mul ile el con e e s p esen in he indus y, he hyb id lying-capaci o based ac i e-neu al-poin - clamped con e e is e y ecen . I p esen s good ea u es such as high quali y ou pu ol age, high modula i y and easy ex ension o achie e a high numbe o le els wi h educed numbe o powe de ices. This pape in oduces a simple modula o o he single-phase wo-cell hyb id lying-capaci o based ac i e- neu al-poin -clamped con e e . The modula ion echnique is based on he de e mina ion o a swi ching sequence o med by wo swi ching s a es which gene a e he wo nea es ol age le els o he e e ence phase ol age. Some ex a calcula ions a e added o he modula ion me hod o con ol he dc-link capaci o s and he loa ing capaci o ol ages. The compu a ional cos o he modula ion echnique is low only including simple compa isons and ma hema ical exp essions. Simula ion esul s show he high quali y ou pu ol ages and cu en s including he dc ol age con ol. I. INTRODUCTION In he las yea s, mul ile el con e e s ha e had a g ea indus ial impac in he high-powe medium- ol age applica- ions such as pumps, ans, la ge con eyo s, HVDC sys ems, di ec -d i e con e e s o wind ene gy sys ems and ship p opulsion among o he s. Among he ad an ages in oduced by he mul ile el con e e s, high quali y ou pu wa e o ms, high modula i y and low d /d ’s ha e been highligh ed. I can be a i med ha he mul ile el con e e echnology has achie ed a medium le el o ma u i y and, in he las decade, a la ge numbe o comme cial p oduc s can be ound in he ma ke wi h neu al-poin -clamped (NPC), lying capaci o (FC) and cascaded H-b idge (CHB) opologies [1]–[3]. P oblems and conce ns abou he minimiza ion o he powe losses, he balancing o he dc-link capaci o s, he modula ion me hods complexi y and he accu acy o he con ol s a egies ha e been deeply s udied in he las decades. Specially, he h ee-le el NPC con e e is nowadays he mos deeply s udied and comme cialized opology all o e he wo ld achie ing a nominal powe up o 44 MVA [1]. One o he p oblems o his opology is he unequal loss dis ibu ion among he powe semiconduc o s. This issue has been deeply s udied in he las yea s and i has been sol ed in oducing he h ee-le el ac i e-NPC (ANPC) con e e whe e ac i e swi ches a e used ins ead he clamping diodes [4]. The ANPC opology has been implemen ed by ABB as a powe elec onic building block o o m IGCT based high ol age con e e s [5]. Howe e , he ex ension o he ANPC con e e is no easy and a new amily o hyb id ANPC con e e s has ecen ly been bo n. This pape is ocused in one o hese hyb id solu ions: he se el-le el lying-capaci o based ANPC con e e . II. THE HYBRID FLYING-CAPACITOR BASED ANPC CONVERTER In las yea s, a hyb id lying-capaci o based ANPC opol- ogy has been in oduced [6]. This con e e opology is o med by he se ies connec ion o a h ee-le el ANPC and loa ing capaci o powe cells. As an example, he single-phase hyb id ANPC con e e wi h one loa ing capaci o cell is shown in Fig. 1A. The possible swi ching s a es o his opology a e in oduced in Table I. Usually, his con e e is named i e-le el hyb id ANPC (5L-ANPC) because i achie es i e symme ical ou pu ol age le els in he phase ol age ( a) i he loa ing capaci o ol age V a is equal o Vdc/2. Recen ly, he 5L-ANPC opology has been p oposed o be applied o wind powe applica ions wo king as a 6 MVA in e e connec ed o a h ee-le el ANPC ac i e- on -end [7]. ABB has comme cialized he 5L-ANPC opology as a IGBT based back- o-back con e e in he ACS2000 medium ol age d i e. ABB in oduced he con e e o applica ions such as pumps, ans, con eyo s, ex ude s, mixe s, comp esso s and mills [5]. The 5L-ANPC opology can be ex ended o gene a e a highe numbe o le els by adding ex a loa ing capaci o cells. The single-phase hyb id ANPC con e e wi h wo loa ing capaci o cells is shown in Fig. 1B. The swi ching s a es o his opology a e summa ized in Table II. This con e e can be named se en-le el hyb id ANPC (7L-ANPC) because i achie es se en symme ical ou pu ol age le els i he loa ing capaci o ol ages V a1and V a2a e equal o 2Vdc/3and Vdc/3 espec i ely. This pape is ocused on he in oduc ion o a no el and simple modula ion echnique o a 7L-ANPC con e e . a ia 0V a1C a1 VC1C1 C2 VC2 V a2C a2 S2 S1S1 S1S1 S1S1 S1S1 S2 S3 S3 S4 S4 0 S2 V a a C a S3 S1S1 S1S1 S1S1 VC1C1 C2 Flying-capaci o cell Th ee-le el ANPC ia VC2 S1S1 S2S3 A) B) Fig. 1. Hyb id ANPC opology o med by he se ies connec ion o a h ee-le el ANPC and loa ing capaci o powe cells. A) Fi e-le el opology i V a=Vdc/2. B) Se en-le el opology i V a1=2V a2=2Vdc/3. TABLE I ONE-CELL HYBRID FLYING-CAPACITOR BASED ACTIVE-NPC SWITCHING STATES. S1S2S3Phase ol age aPhase ol age aIn luence on In luence on In luence on i VC1=VC2=2V a=Vdc V a i ia>0VC1i ia>0VC2i ia>0 000 −VC2−Vdc − − − 001 V a −VC2−Vdc/2↓ − − 010 −V a −Vdc/2↑ ↑ ↓ 011 0 0 − ↑ ↓ 100 0 0 − ↑ ↓ 101 V a Vdc/2↓ ↑ ↓ 110 VC1−V a Vdc/2↑ − − 111 VC1Vdc − − − TABLE II TWO-CELL HYBRID FLYING-CAPACITOR BASED ACTIVE-NPC SWITCHING STATES. S1S2S3S4Ou pu ol age aOu pu ol age aIn luence on In luence on In luence on In luence on i V 1=2V 2=Vdc/3V a1i ia>0V a2i ia>0VC1i ia>0VC2i ia>0 0 0 0 0 −VC2−Vdc − − − − 0001 V a2−VC2−2Vdc/3− ↓ − − 0010−V a2+V a1−VC2−2Vdc/3↓ ↑ − − 0100 −V a1−2Vdc/3↑ − ↑ ↓ 0 0 1 1 V a1−VC2−Vdc/3↓ − − − 0 1 0 1 V a2−V a1−Vdc/3↑ ↓ ↑ ↓ 0 1 1 0 −V a2−Vdc/3− ↑ ↑ ↓ 0111 0 0 − − ↑ ↓ 1000 0 0 − − ↑ ↓ 1 0 0 1 V a2Vdc/3− ↓ ↑ ↓ 1 0 1 0 −V a2+V a1Vdc/3↓ ↑ ↑ ↓ 1 1 0 0 −V a1+VC1Vdc/3↑ − − − 1011 V a12Vdc/3↓ − ↑ ↓ 1101V a2−V a1+VC12Vdc/3↑ ↓ − − 1110 −V a2+VC12Vdc/3− ↑ − − 1 1 1 1 VC1Vdc − − − − In gene al, o a N-le el hyb id ANPC con e e , k loa ing capaci o cells (N=2k+3) a e needed and hei desi ed ol age alues V∗ ai (i=1, . . . , k) a e equal o (k+ 1 −i)Vdc/(k+ 1). This in o ma ion is summa ized in Table III. III. PROPOSED MODULATOR FOR THE SINGLE-PHASE 7L-ANPC CONVERTER As can be obse ed in Table I and Table II, he e a e se e al swi ching s a es which ob ain he same ou pu ol age and a ec o he lying capaci o ol ages in opposi e way. P e ious publica ions ha e shown he good pe o mance o TABLE III DESIRED VOLTAGES OF THE FLYING CAPACITORS OF THE HYBRID ANPC TOPOLOGY DEPENDING ON THE NUMBER OF FLOATING CAPACITOR CELLS. Numbe o le els Numbe o loa ing capaci o cells V∗ a1V∗ a2V∗ a3. . . V∗ ak N k 5 1 Vdc/2− − . . . − 7 2 2Vdc/3Vdc/3−. . . − 9 3 3Vdc/4 2Vdc/4Vdc/4. . . − ... ... ... ... ... ... N (N-1)/2 kVdc/(k+ 1) (k−1)Vdc/(k+ 1) (k−2)Vdc/(k+ 1) . . . Vdc/(k+ 1) he dc ol age con ol o he lying capaci o o he 5L- ANPC by choosing p ope ly he edundan swi ching s a es o he swi ching sequence. Recen ly a space- ec o modula ion echnique has been applied o a h ee-phase 5L-ANPC o he ec i ie side o a back- o-back con igu a ion [8]. The con ol egion o he con e e is he well-known hexagon plo ed in he alpha-be a ame whe e he swi ching s a es a e loca ed. The swi ching sequence and he du y cycles a e de e mined using he h ee nea es swi ching s a es o he e e ence ec o . Howe e , i has o be no iced ha , he le el o lexibili y and complexi y is eally signi ican because o he high numbe o di e en ou pu ol age ec o s. This ac becomes c i ical when a highe numbe o le els is conside ed in he hyb id lying-capaci o based ANPC con e e . P e-p og ammed modula ion echniques such as he selec- i e ha monic elimina ion (SHE) ha e been also add essed o his con e e opology. In hese me hods, he swi ching o he con e e is de e mined o line o elimina e he ha - monic dis o ion o some low o de ha monics. A simila p e- p og ammed modula ion echnique has been also in oduced o minimize online he o e all o al ha monic dis o ion. The ol age le el o be gene a ed by he con e e is ob ained online aking in o accoun he bes possible swi ching o achie e he loa ing ol age con ol [9]–[12]. Finally, se e al mul i-ca ie based pulse wid h-modula ion (PWM) echnique ha e been in oduced o be applied o he hyb id lying-capaci o based ANPC con e e . The mul i- ca ie PWM echniques a e le el-shi ed [7] o phase-shi ed echniques [13]. The phase-shi ed solu ion ep esen s a good solu ion because i achie es a na u al balance o he lying capaci o s o he con e e . Howe e , i s dynamic pe o mance is poo when a la ge load s ep is applied o he con e e . In his pape , a simple modula ion echnique o he 7L- ANPC is p oposed. This me hod is based on he gene a ion o he e e ence phase ol age as an a e age o he nea es ol age le els. In his way, he modula ion p oblem is educed o e y simple calcula ions de e mining easily he swi ching sequence ( o med by wo swi ching s a es o each phase o he con e e ) and he co esponding swi ching imes. The p oposed modula o includes as an addi ional con ol a ge he balance he lying-capaci o s o he hyb id ANPC con- e e . The balancing con ol algo i hm is based on choosing he p ope edundan swi ching s a e aking in o accoun he ins an aneous alues o he di ec ion o he phase cu en and he lying capaci o imbalances. In he p oposed modula o , he ollowing ma hema ical de ini ions a e necessa y: a= 3V e +Vdc Vdc (1) ai= loo (a)(2) e o a=·V a1−V∗ a1 V a2−V∗ a2¸(3) In each ow o ma ices C1and C2some possible ga e signal alues o a iables S2,S3and S4a e de ined. Fi s column is ocused on a iable S2. Ma ix C1includes he possible swi ching s a es whe e only one o he ga e signals is equal o 1. On he o he hand, C2includes he possible swi ching s a es whe e wo ga e signals a e equal o 1. C1=  0 0 1 0 1 0 1 0 0  (4) C2=  0 1 1 1 0 1 1 1 0  (5) On he o he hand, ma ices M1and M2de ine he in lu- ence o he swi ching s a es de ined by ma ices C1and C2 espec i ely on he loa ing capaci o ol ages V a1and V a2. Fi s and second columns a e ocused on a iables V a1and V a2 espec i ely. When he phase cu en iais nega i e and an speci ic swi ching s a e is applied o he 7L-ANPC, i he loa ing capaci o ol age inc eases, he associa ed elemen in ma ix M1o M2is equal o 1. I loa ing capaci o ol age emains cons an is equal o 0 and inally he elemen is equal o -1 i he loa ing capaci o ol age dec eases. M1=  0 1 1−1 −1 0  (6) M2=  1 0 −1 1 0−1  (7) The low diag am o he single-phase modula o o he 7L-ANPC con e e is shown in Fig. 2. In he low diag am ep esen ed in Fig. 2, he swi ching a iable Si(i= 1,2,3,4) |V e |>2Vdc/3 NOYES S11 = S12 = 1 1 = 1-a+ai s = 1 V e >0 NOYES S11 = S12 = 0 1 = a-ai s = 0 M = sM2+(1-s)M1 G = iaM e o a ind = max(G) S22 = S32 = S42 = s S21 = s C2(ind,1)+(1-s)C1(ind,1) S31 = s C2(ind,2)+(1-s)C1(ind,2) S41 = s C2(ind,3)+(1-s)C1(ind,3) YES M = sM1+(1-s)M2 G = iaM e o a ind = max(G) S21 = S31 = S41 = 1-s S22 = s C1(ind,1)+(1-s)C2(ind,1) S32 = s C1(ind,2)+(1-s)C2(ind,2) S42 = s C1(ind,3)+(1-s)C2(ind,3) |V e |<Vdc/3 M = sM1+(1-s)M2 G = iaM e o a ind = max(G) S21 = s C1(ind,1)+(1-s)C2(ind,1) S31 = s C1(ind,2)+(1-s)C2(ind,2) S41 = s C1(ind,3)+(1-s)C2(ind,3) M = sM2+(1-s)M1 G = iaM e o a ind = max(G) S22 = s C2(ind,1)+(1-s)C1(ind,1) S32 = s C2(ind,2)+(1-s)C1(ind,2) S42 = s C2(ind,3)+(1-s)C1(ind,3) NO Fig. 2. Flow diag am o he single-phase modula o o he 7L-ANPC con e e wi h lying capaci o ol ages con ol. akes he alue Si1du ing 1/2,Si2du ing 1− 1and inally again Si1du ing 1/2. Using he p oposed modula o , a maximum o only one swi ching is p esen du ing he sampling ime Tsin each powe semiconduc o couple commanded by a iables S1,S2,S3and S4. The swi ching signal S1is simply gene a ed by compa ing he e e ence ol age V e wi h ze o. The e o e, he modula o o ces a undamen al swi ching equency in he powe semiconduc o s commanded by S1leading o a educ ion o he swi ching losses o he sys em. This educ ion is due o he ac ha S1commands he swi ching s a e o eigh powe semiconduc o s while S2, S3and S4command he s a e o a couple hem espec i ely. Ope a o loo (x) ounds he elemen s o x o he nea es in ege s owa ds minus in ini y. Ope a o max(x) e u ns he index o he maximum alues in ec o x. I his alue is epea ed in he ec o , he index o he i s one is e u ned. All he possible edundan swi ching s a es a e conside ed in he low diag am o he single-phase modula o o he 7L- ANPC con e e shown in Fig. 2. The compu a ional cos o he modula ion echnique is low only including simple compa - isons and ma hema ical exp essions. When se e al edundan swi ching s a es can be applied, he ac ual ope a ion poin o he 7L-ANPC is conside ed in o de o de e mine he inal swi ching s a e o be pa o he swi ching sequence. In he low diag am, ec o gde e mines he posi i e o nega i e in luence o each possible swi ching s a e aking in o accoun he ma ix M1o M2, he ac ual alue o he phase cu en ia and he dc ol age imbalances in he lying capaci o s. In his way, he elemen o ec o Gwi h maximum alue, called ind in he low diag am, de e mine he inal swi ching s a e om he co esponding ow o ma ix C1o C2. In ac , his me hod implies a minimiza ion o he elec ical ene gy s o ed in he dc-link capaci o s [14], [15]. The minimiza ion o his pa ame e di ec ly means he minimiza ion o he a e aged imbalance in he dc-link ol age. IV. RESULTS OF THE MODULATOR FOR THE SINGLE-PHASE 7L-ANPC CONVERTER The p oposed modula o has been applied o he 7L-ANPC opology whe e he dc-link capaci o s C1and C2a e equal o 3mF, he loa ing capaci o s C a1and C a2a e equal o 2mF and he o al ol age o he dc-link 2Vdc is equal o 3000 ol s. The o al dc-link ol age is kep cons an by an ac i e on end. The desi ed loa ing capaci o ol ages V a1and V a2a e equal o 1000 ol s and 500 ol s espec i ely. The 7L-ANPC is connec ed o a esis i e-induc i e load o med by he se ies connec ion o R=10Ωand L=3mH. The e e ence ol age V e is a pu e sinusoidal ol age wi h an ampli ude equal o 1500 ol s. The loa ing capaci o is ini ially discha ged s a ing om ze o ol s. The sampling equency so he modula o is equal o 800 Hz. The low diag am in oduced in Fig. 2 is applied o he single-phase 7L-ANPC con e e and he ob ained esul s a e ep esen ed in Fig. 3 whe e he phase ol age a, he phase cu en ia, he lying capaci o ol ages V a1and V a2and a hal o he dc-link ol age VC1a e ep esen ed. A de ail o he phase ol age and cu en , he loa ing capaci o ol ages and a hal o he dc-link ol age in s eady s a e condi ions is shown in Fig. 4. I can be obse ed ha he loa ing capaci o ol ages achie e hei desi ed alues while he phase ol age and cu en ha e high quali y. The swi ching equency o powe semiconduc o s commanded by S1is 50Hz while he a e age swi ching equency o S2,S3and S4is a ound 500Hz. As can be obse ed in Fig. 3 and Fig. 4, he dc-link capaci o s ol ages a e na u ally balanced because he ol age o capaci o C1(VC1) emains a ound 1500 ol s ( he hal o he o al dc-link ol age). This phenomenon can be explained conside ing he expe imen shown in Fig. 5 and Fig. 6. In his new es , he powe con e e s a s he ope a ion wi h an unbalanced si ua ion in he dc-link (VC1and VC2a e equal o 1000 and 2000 ol s espec i ely). The loa ing ol ages V a1 and V a2a e 1000 ol s and 500 ol s espec i ely which a e hei desi ed ol ages. F om Fig. 5, i can be obse ed ha he dc-link imbalance dec eases achie ing he desi ed ope a ion poin whe e bo h dc-link capaci o ol ages a e equal o 1500 ol s. A de ail o he wa e o ms o his expe imen is shown in Fig. 6. The dc-link capaci o s ol ages a e na u ally balanced because he ac ual dc-link ol age imbalance c ea es an o se in he phase ol age. This ac leads o an o se in he phase cu en which di ec ly a ec s o he dc-link capaci o ol ages as was in oduced in Table II. In his way, i he dc-link ol age VC1is less han 1500 ol s, a posi i e o se appea s in he phase ol age and he phase cu en . This ends o inc ease he ol age o capaci o C1 educing he dc-link ol age imbalance. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 −2000 0 2000 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 −200 0 200 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 500 1000 1500 2000 Time (s) Vol age [V] Cu en [A] Vol age [V] V C1 V a1 V a2 a i a Fig. 3. Resul s o he p oposed modula ion echnique applied o he single- phase 7L-ANPC. F om op o bo om: Phase ol age, phase cu en , loa ing capaci o ol ages and hal o he dc-link ol age. 0.3 0.31 0.32 0.33 0.34 0.35 0.36 −2000 0 2000 0.3 0.31 0.32 0.33 0.34 0.35 0.36 −200 0 200 0.3 0.31 0.32 0.33 0.34 0.35 0.36 500 1000 1500 Time (s) Vol age [V] Cu en [A] Vol age [V] V C1 V a1 V a2 a i a Fig. 4. De ailed esul s o he p oposed modula ion echnique applied o he single-phase 7L-ANPC. F om op o bo om: Phase ol age, phase cu en , loa ing capaci o ol ages and hal o he dc-link ol age. V. CONCLUSIONS In his pape , a se en-le el hyb id lying-capaci o based ANPC opology o med by he se ies connec ion o a h ee- le el ANPC wi h wo loa ing capaci o cells, called 7L- ANPC, has been s udied. This pape in oduces a simple modula ion echnique o ob ain high pe o mance ou pu wa e- o ms wi h ol age balance con ol o he lying capaci o s and he dc-link capaci o s. The p oposed modula ion me hod is based on he gene a ion o he e e ence phase ol age using he wo nea es ol age le els o he con e e opology. As se e al swi ching s a es a e edundan , a ma hema ical compa ison using ma ices is ca ied ou o de e mine he p ope swi ching s a e o achie e he dc ol age con ol. The 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 −2000 0 2000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 −200 0 200 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 500 1000 1500 2000 Time (s) Vol age [V] Cu en [A] Vol age [V] V C1 V a1 V a2 a i a Fig. 5. Resul s o he p oposed modula ion echnique applied o he single- phase 7L-ANPC s a ing om an unbalanced si ua ion in he dc-link. F om op o bo om: Phase ol age, phase cu en , hal o he dc-link ol age VC1 and loa ing capaci o ol ages. 0 0.02 0.04 0.06 0.08 0.1 −2000 0 2000 0 0.02 0.04 0.06 0.08 0.1 −200 0 200 0 0.02 0.04 0.06 0.08 0.1 1000 1125 1250 Time (s) Vol age [V] Cu en [A] Vol age [V] a i a V C1 Fig. 6. De ailed Resul s o he p oposed modula ion echnique applied o he single-phase 7L-ANPC s a ing om an unbalanced si ua ion in he dc- link. F om op o bo om: Phase ol age, phase cu en and hal o he dc-link ol age VC1. p oposed modula ion echnique akes in o accoun he ac ual alues o he loa ing capaci o ol ages and he phase cu en . The esul ing modula ion echnique has low compu a ional cos only including simple equa ions and compa isons. Applying he p oposed modula ion s a egy o he single- phase 7L-ANPC, he phase capaci o ol ages a e con olled o hei desi ed alues. In addi ion, he dc-link capaci o s ol ages a e na u ally balanced due o he dc o se e ec c ea ed by he modula o . The p oposed modula ion me hod can be applied wi h e y low swi ching equency. In he p esen ed expe imen s, he sampling equency o he modula o is 800Hz leading o a swi ching equency o he powe de- ices (excep S1which has undamen al swi ching equency) a ound 500Hz. The esul s show he good pe o mance o he p oposed modula ion me hod. ACKNOWLEDGMENT The au ho s g a e ully acknowledge he inancial suppo p o ided by he Minis y o Educa ion unde g an PR2010- 0162 and he CCTVal (N◦FB0821). REFERENCES [1] S. Kou o, M. Malinowski, K. Gopakuma , J. Pou, L.G. F anquelo, B. Wu, J. Rod iguez, M. A. Pe ez and J. I. Leon, “Recen Ad ances and Indus ial Applica ions o Mul ile el Con e e s,” IEEE T ans. Ind. Elec on., ol. 57, no. 8, pp. 2553–2580, Aug. 2010. [2] J. Rod iguez, L. G. F anquelo, S. Kou o, J. I. Leon, R. Po illo, M. M. P a s and M. A. 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