Single phase current-source active rectifier for traction: control system design and practical problems

Ad ances in Elec ical and Elec onic Enginee ing 86 SINGLE PHASE CURRENT-SOURCE ACTIVE RECTIFIER FOR TRACTION: CONTROL SYSTEM DESIGN AND PRACTICAL PROBLEMS J. Michalik, J. Molna , Z. Pe ou ka Uni e si y o Wes Bohemia, Facul y o Elec ical Enginee ing, Depa men o Elec omechanics and Powe elec onics, Plzen, Czech Republic e-mail:jmichali@ke .zcu.cz, [email p o ec ed].cz, pe ou [email protected] g Summa y This esea ch has been mo i a ed by indus ial demand o single phase cu en -sou ce ac i e ec i ie dedica ed o econs uc ion o olde ypes o dc machine locomo i es. This pape p esen s con e e s con ol s uc u e design and simula ions. The p oposed con e e con ol is based on he ma hema ical model and due o possible in e ac ion wi h ailway signaling and equi ed low swi ching equency employs synch onous PWM. The simula ion esul s a e e i ied by expe imen al es s pe o med on designed labo a o y p o o ype o powe o 7kVA. 1. INTRODUCTION This esea ch has been mo i a ed by indus ial demand o design o single phase cu en -sou ce ac i e ec i ie (CSAR) dedica ed o econs uc ion o olde ypes o dc machine locomo i es. Con e e mus be able o ope a e on bo h olley ol ages: 25kV/50 Hz and 15kV/16  Hz. The goal o ou esea ch is he ealiza ion o he low powe (7 kVA) labo a o y p o o ype o his con e e . De elopmen was di ided in o h ee s ages: con ol s uc u e simula ion, ec i ie building and i s ac ua ing. Pa i ion o his pape was made in wo ways – con ol s uc u e simula ion and con ol s uc u e ac ua ing. Applied ec i ie ’s con ol s uc u e is based upon he ma hema ical model de i ed om ec o diag am (Fig. 1 ) and is desc ibed in he pa ag aph 2. The main goal o his pape is o show and desc ibe p ac ical p oblems which appea ed du ing con ol s uc u e ac ua ing. Topic o CSAR is no e y common and he published pape s mos ly deal wi h he h ee phase e sion. Publica ions a e a he heo e ical, esea ches go in o he p oblems connec ed wi h con ol in pa icula using hys e esis con ol o PWM modula ion (e.g. [1] - [3]). Un o una ely, we did no ind any complex pape dealing wi h single phase e sion o ac ion applica ions. 2. RECTIFIER’S CONTROL POSSIBILITIES AND SIMULATIONS Func ion o ec i ie ’s con ol is o main ain g id ( olley) cu en cu e (i) in ha monic shape and in phase wi h powe g id ol age (u). We can gene ally use wo con ol me hods: hys e esis cu en con ol me hod ( o he cu en consumed om he powe g id), o he me hod using PWM modula ion wi h cons an swi ching equency. The second me hod (PWM) is used in he design o CSAR model dedica ed o labo a o y measu emen . This me hod has been chosen ega ding possible in e ac ion wi h ailway signaling, because dis u bance p oduced by cons an swi ching equency is much easie o elimina e han in case o hys e esis con ol. Mo eo e , he PWM con ol makes possible o employ shi ed ca ie s, which is eligible o high powe sys ems wi h low swi ching equency. In consequence o conside ed low swi ching equency, he synch onous PWM has been implemen ed. The powe ci cui con igu a ion and ec o diag am o designed CSAR is shown in Fig. 1. The p oposed con e e con ol is displayed in Fig. 2. This s uc u e includes cu en con ol loop which independen ly on phase shi be ween powe g id ol age (U) and g id cu en (I (1) ) ensu es demanded load cu en (I d ). The ou pu o load cu en con olle is demanded g id cu en ampli ude (I m *). Cos ϕ = 1 (ze o phase shi be ween U and I (1) ) is being eached by con ol o bo h angle  and he ampli ude o I V(1). Con ol o angle  is based upon he ma hema ical model de i ed om ec o diag am (see Fig. 1) and is e alua ed om known pa ame e s. I s alue also has o sa is y he alue o equi ed I d . Fig. 1. Powe ci cui con igu a ion (simula ion wi ing) and ec o diag am o ϕ =0 U I I U ε δ θ I (1) .X σ C(1) V(1) I (1) C Single phase cu en -sou ce ac i e ec i ie o ac ion… 87 Fig. 2. Designed CSAR con ol ci cui I he load cu en is su icien ly high, he designed con ol wo ks p ope ly and ensu es bo h he equi ed load cu en and he phase shi ϕ=0. Howe e , i demanded load cu en is lowe han ce ain le el (I dmin ), he con ol is no able o ensu e he ze o phase shi (ϕ=0) be ween powe g id ol age and g id cu en . When ϕ=0, he lowes possible I V(1) cu en alue is I V(1)min =I C(1) . The e o e, he minimum I dmin is de e mined by I (1)min . In his case, he con e e con ol s uc u e con ols only I d cu en alue by means o du y cycle (z), while angle  is pe manen ly se o ze o. This solu ion was de i ed om he p inciple o con ol s uc u e and he ac ha wi h  = 0, he load cu en ipple is minimal. This esul has been con i med by simula ions. In his case angle ϕ is no con olled and depends only on he load pa ame e s. The solu ion o he abo e desc ibed p oblem wi h con ollabili y o  (and o cou se ϕ) is o choose he lowes possible capaci ance o he inpu il e capaci o (C). On he o he hand, he capaci ance mus also sa is y he condi ion o accep able u C ol age ipple and mus espec he equi ed il e esonan equency. F om his is e iden big disad an age o his model-based con ol s uc u e (Fig. 2), which equi es knowledge o R, Lσ, C and ω (powe g id equency). The con ol equi es measu emen o I d , U, U ou . Du y cycle (z) is being de i ed om he load cu en con olle ou pu (I m* ) by means o low-pass il e . Supply ol age (powe g id ol age) measu emen is also impo an due o ime synch oniza ion o con ol algo i hm wi h his ol age and powe componen s swi ching logic. Simula ions we e made in p og amming language PASCAL wi h he main emphases on he con ol p inciple e i ica ion. I was made wi h espec o se ial diodes e e se pa ame e s, swi ching componen s (IGBTs) we e conside ed ideal. Examples o simula ion esul s a e shown on Fig. 3 - Fig. 5. I is clea ha i is necessa y o bewa e o he inpu il e (L σ C) esonan equency. Swi ching (ca ie ) equency chosen nea his esonan equency causes ib a ion o his ci cui . To each he minimal dis o ion o g id cu en he smoo hing induc o (L) should be app oxima ely 3 imes highe hen in common ec i ie . Fig. 3. Simula ion esul : Id* < Idmin (con olled only du y cycle z,  = 0) Fig. 4. Simula ion esul : Id* > Idmin , close o Idmin Fig. 5. Simula ion esul : 4c Id* > Idmin 3. SYNCHRONIZATION PROBLEMS In o de o keep p ope unc ion o CSAR, i is necessa y o synch onize he con ol s uc u e wi h powe g id ol age cu e. Modula ion cu e equency mus be coinciden al wi h powe g id equency wi h espec o ol age pola i y. This in o ma ion can be ob ained by di e en ways depending on how much in o ma ion we ha e o know abou he ol age cu e. When supposing ( ) ( )         ⋅⋅ −−⋅⋅⋅+⋅⋅ −= * V * 2 * V 2 * 2 *2 2 II2 IIICLCU a ccos U IRU II dou * d * ⋅+ ⋅= 2 I zI * d * ⋅= -500 -400 -300 -200 -100 0 100 200 300 400 500 4,00E-01 4,05E-01 4,10E-01 4,15E-01 4,20E-01 4,25E-01 4,30E-01 4,35E-01 4,40E-01 (10x) i u ud (10x) id -500 -400 -300 -200 -100 0 100 200 300 400 500 4,00E-01 4,05E-01 4,10E-01 4,15E-01 4,20E-01 4,25E-01 4,30E-01 4,35E-01 4,40E-01 (10x) id (10x) i u ud -500 -400 -300 -200 -100 0 100 200 300 400 500 4,00E-01 4,05E-01 4,10E-01 4,15E-01 4,20E-01 4,25E-01 4,30E-01 4,35E-01 4,40E-01 (10x) Id ud u (10x) i Ad ances in Elec ical and Elec onic Enginee ing 88 pu ely sinusoidal ol age cu e, we do no need o obse e i s shape. In his case we only need o know he momen s when he ol age cu e c osses he ze o axes (momen s o pola i y change) and he ol age pola i y in e e y hal -pe iod. The easies way o ollow his condi ion (which is also used in ou applica ion), is o con e sinusoidal cu e (powe g id ol age) in o he squa e shape wi h logical le els o 0 and 3V, o he wise log. 0 and log.1 as well. Log. 0 co esponds o nega i e hal -wa e, log. 1 o posi i e. Signal edges indica e he ze o c ossings. Fig. 6. Failu e s a e o pe iod measu ing Fig. 7. G id cu en esonan glimme Fig. 8. Faul y esponse o g id equency s ep change Fig. 9. Ze o ec o inse ion – p ope esponse o g id equency s ep change Fig. 10. P ope esponse o g id equency s ep change: inc eased equency P ocesso e alua es hese ze o c ossings by means o ex e nal in e up ; pola i y is e alua ed om he ze o c ossing di ec ion - ising o alling edge. This easy p inciple app o ed i sel du ing es ing despi e a ew limi a ions. Sinusoidal / squa e con e e is ealized ou side he DSP, whe e ol age ansduce signal dis u bance appea ed due o powe ansis o s swi ching. Con e e e alua ed hese glimme s like a mul iple pola i y change, which also caused he glimme s o squa e synch oniza ion edges. F equency measu ing has been ealized by ime measu ing be ween wo ollowing edges and his ime was consequen ly used o ollowing hal - pe iod. Because o glimme s in synch oniza ion, p ocesso e alua ed he ime be ween wo ollowing glimme s like a hal -pe iod ime ollowed by aul s a e which caused high swi ching equency du ing he ollowing hal -pe iod o abou 20 kHz ( Fig. 6 ) – he swi ching equency inc eased due o employed synch onous PWM. The solu ion o his p oblem was so wa e implemen a ion o glimme s insensibili y. I s p inciple is o accep only he i s coming edge and igno ing he es du ing he p ese ime ha is o cou se sho e han he ime o longe hal -pe iod o be expec ed. Ano he alid edge is he ollowing ze o c ossing. i d i u u c i i d u ou i d synch oniza ion u c i synch oniza ion i i d synch oniza ion i i d Single phase cu en -sou ce ac i e ec i ie o ac ion… 89 Fig. 11. Final CSAR p o o ype: Id, I, U a UC in s eady s a e Fig. 12. De ail o wa e o ms om Fig. 11 Ano he complica ion o his synch oniza ion me hod is he du y cycle accu acy. As al eady men ioned, DSP measu ed he i s ol age hal - pe iod ime which was hen used o se ing o ollowing hal -pe iod modula ion cu e. This way has an ad an age in as e esponse on equency change, bu has also g ea e demand on du y cycle accu acy. I he i s hal -pe iod is sho e han he ollowing one, in he second hal -pe iod he modula ion cu e comes in o ze o ea lie hen ol age cu e and a gap in he g id cu en appea . I he si ua ion is opposi e, which means he i s hal - pe iod is longe hen he ollowing one, he o e lay o modula ing cu e o e he eal one happen. When he pola i y o g id cu en du ing swi ching-o e is no in ze o ye , esonan glimme o g id cu en appea ed and equency o glimme s is gi en by inpu LC il e . This si ua ion is shown in Fig. 7. The solu ion was o al e na e be ween measu ing o he i s hal -pe iod and he ollowing one and se he modula ion cu e pe iod acco ding o hese al e na ing alues. This way elimina ed g id cu en glimme s du ing ze o c ossing. Ano he p oblem appea ed du ing powe g id ol age equency s ep change (Fig. 8). A e aul y eac ion o hal -pe iod leng h change ea ly swi ch- o e o swi ching ansis o s o posi i e and nega i e powe g id ol age hal -pe iod. Consequen ly, he CSAR ca ied on like a diode ec i ie which means ha g id cu en inc eased apidly and was gi en only by load pa ame e s. As a p ecau ion o his aul we gained ze o ec o inse ing ( ealized as a load sho ci cui ). I he modula ion cu e c osses ze o axes ea lie hen powe g id ol age, ze o ec o con inues un il he nex edge indica ing nex ol age ze o c ossing occu (Fig. 9). This p ecau ion has one mo e unc ion, because when ou age o powe g id happen (e.g. olley bounce), load cu en I d dec eases con inuously o ze o. Opposi e si ua ion happen when equency inc eases (Fig. 10). Modula ion cu e can no inish he cycle and swi ch-o e happen wi h nonze o cu en i. In his case he con ol s uc u e is able o a oid he o e cu en shown in Fig. 8. Fig. 11 and Fig. 12 con i m he p ope beha iou o he inal p o o ype employing all abo e desc ibed imp o emen s o bo h con ol sys em and powe ci cui . 4. CONCLUSION The designed labo a o y p o o ype (7kVA) o ac ion CSAR employs model-based con ol sys em wi h synch onous PWM. This me hod has been chosen ega ding possible in e ac ion wi h ailway signaling, because dis u bance p oduced by cons an swi ching equency (especially in case o synch onous modula ion) is much easie o p edic and, he e o e, elimina e han in case o hys e esis con ol. Mo eo e , he PWM con ol makes possible o employ shi ed ca ie s, which is eligible o high powe sys ems wi h low swi ching equency. The simula ion and expe imen al esul s con i m p ope unc ion o designed con ol s uc u e unde bo h s eady s a e and ansien condi ions. The expe imen s also e i ied he co ec con e e beha iou du ing he aul s. The bigges disad an age o p oposed model-based con ol is necessi y o inpu il e pa ame e s knowledge and he educed obus ness agains pa ame e a ia ions. The ac ual esea ch is ocused on he imp o emen o con e e beha iou unde dis o ed powe g id ol age. 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