Solid-state Marx generator design with an energy recovery reset circuit for output transformer association

Transcription

1 Solid-sae Marx generaor design wih an energy recovery rese circui for oupu ransformer associaion L M Redondo J Fernando Silva P Tavares E Margao Insiuo Superior de Engenharia Lisboa, CEEI, CFNUL Insiuo Superior Técnico, CAUTL Cenro de Física Nuclear Universidade Lisboa Insiuo Superior de Engenharia Lisboa, CEEI, CAUTL lmredondo@deeaiseliplp fernandos@alfaisulp pedro@necabop pcc@saiseliplp Keywords: Marx ype Generaor; High-Volage pulses; Solid-sae swiches; Pulse Transformer; Energy recovery circui I INTRODUCTION Today, high volage pulsed power supplies have a wide range of applicaions [1-4], which increase he need of efficien, flexible and suiable power supplies, based on solid sae swiches [4] A number of echniques have been used in order o generae HV pulses from generaors wih opimised performance and characerisics Nowadays, he mos widely used echnique, combines a high volage power supply wih semiconducor swiches, eihen series or resonan circui associaions o overcome he semiconducors high volage limiaions [5] The Marx generaor concep [6], as shown in Fig 1, charging capaciors ( ) in parallel (hrough resisive or inducive charging elemens, Z n ) and discharging hem in series ino he load (hrough swiches, S n ), provides anoher widely used mehod for generaing high-volage pulses, because i requires only a relaively low-volage power supply,, for charging and does no require pulse ransformers o achieve he desired high-volage This approach has been inensively used hrough he years, wih significan echnological improvemens o increase he performance of he original circui [7-12] Pulse ransformers can be applied, in almos all pulsed opologies, o furhencrease he oupu volage However, he ransformer parasiic elemens (leakage inducance and disribued capaciance) deeriorae he pulse shape, which worsens wih increase he number of urns [13] Z 1 Z 2 Z (n-1) S 1 S 2 S (n-1) S n C 2 C (n-1) Z n v Z 1 Z 2 Z (n-1) Z n Fig 1 Basic n sages Marx Generaor opology, for negaive pulses Even so, when he volage is in he order of several ens of kv, due o he sill low semiconducor volage blocking capabiliy, several ens of series solid sae swiches mus be packed in order o hold he high volage [14] Hence, when using series semiconducors, complex mehods mus be used o drive all he semiconducors a he same ime, wih isolaed power supplies As a resul, his high volage generaion echnique can be raher challenging o implemen In his work, we have considered ha a compromise approach can be he bes way This poins o he use of an hybrid opology, wih a Marx generaor conneced o a sep-up pulsed ransformer, in order o: i) decrease he number of needed solid sae swiches; ii) reduce he urns raio of he ransformer; iii) adap he load impedance o he power supply; iv) provide galvanic isolaion o he load One aspec o consider when using ransformers is ha he average volage applied o he windings mus be zero In he case of unipolar pulsed applicaions, auxiliary circuis mus be added o demagneize he core during he ime no pulse is applied, adding complexiy o he pulsed circui [13] Since he auxiliary circui is ofen dissipaive [13], he power losses are increased, which conribue o reduce he yield of he pulsed circui To eliminae his drawback, we devised a hybrid fully inegraed solid-sae Marx generaor circui (Fig 2), which has been developed for khz and kv applicaions needing recangular pulses The proposed circui akes advanage of he power semiconducor swiches inensive use, replacing he convenional circuassive elemens, o increase he performance, srongly reducing losses and increasing he pulse repeiion frequency [12] In addiion, o furher increase he oupu pulse ampliude, he proposed opology is designed wih a magneizing energy rese circui ha enables he use of an oupu pulse ransformer, and recovers he ransformer magneizing energy, during he off sae, back o he energy sorage capaciors This decreases he charging ime, and enables higher frequency operaion, increasing he pulse generaor yield A laboraory prooype wih five sages, of his all silicon Marx generaor circui, was buil using 12 V IGBTs and diodes, operaing wih 1 khz repeiion frequency Firs experimenal resuls show almos recangular pulses wih -5 kv, 4 o 1 µs widh, ino a 5 kω resisive load

2 II CIRCUIT TOPOLOGY A Basic Elecronic Marx Generaor (EMG) opology The use, in he Marx generaor circui of Fig 1, of jus solid-sae swiches o charge and discharge he energy sorage capaciors, wihou he passive elemens Z i, was already an innovaive concep presened and discussed elsewhere [12], called EMG (Elecronic Marx generaor) Fig 2 shows he basic EMG opology, wih n sages, capable of delivering negaive high-volage oupu pulses o a load (Poruguese Paen, PT-1315) Each sage of he EMG consiss of a energy soring capacior C i, a diode D ci and wo IGBTs (T ci and T di ), where he subscrip i {1, 2,, n-1, n} The EMG operaion of Fig 2 can be basically undersood, considering only wo differen operaing modes In he firs mode, Fig 3, swiches T ci and T di are, respecively, on and off T d1 T dn v Fig 2 Basic opology of he Elecronic Marx Generaor circui, wih n sages, for negaive oupu volage pulses in he load During his mode, he capaciors C i are charged wih 2 oal energy, E cap = n5civdc, from he dc power supply,, hrough T ci and D ci, wih curren peak limied by he inernal resisance of swiches, resuling in a small ime consan ha enables khz operaion Td1 i 1 i c1 i n i cn v Fig 3 Operaion of circui in Fig 2: Capacior charging mode; Pulse mode Tdn v capaciors C i are conneced in series and he volage applied o he load is, approximaely, v = nvdc Considering ha, he capaciors charge ime, c, is made much longer han he discharge ime, d, swiches T ci and T di operae, respecively, wih a long (δ c = c /T) and shor (δ d = d /T) swiching duy cycle I is imporan ha, during he pulse, he volage drop, due o he discharge of he energy sorage capaciors, is only a few percen of each capacior volage To guaranee his, he energy sored in he capaciors, E cap, mus be approximaely 1 imes greaer han he energy delivered by each volage pulse, o he load [15], E pulse = nvdcid, where d is he on sae period of T di and is he pulse curren, in a resisive load, wih all capaciors charged wih,, = n Z load Due o he circui opology, Fig 2, i is necessary o avoid cross conducion beween T di and T ci swiches Hence, an auxiliary circurovides a ime delay (ie dwell ime), beween swiching inpu conrol signals, so ha he urn-on conrol inpu o T di IGBTs is delayed wih respec o he urn-off conrol inpu of T ci IGBTs, and vice-versa B Elecronic Marx Generaor wih oupu pulse ransformer The opology of he EMG presened in Fig 2 can be adaped, wih few changes, o accommodae an auxiliary circui o rese he core of a pulse ransformer conneced in he oupu, as shown in Fig 4 The polariy of he oupu pulse depends on he polariy of he diode placed on he secondary of he ransformer In he case shown in Fig 4 he pulses are negaive Considering circui in Fig 2, he circui in Fig 4 presens an addiional semiconducor swich, T da, and wo more diodes, D A e D B, o rese he ransformer Diode D C placed a he secondary, imposes a single volage polariy ono he load, in his case negaive pulses are obained on he load The operaion of Fig 4 circui can be undersood, considering only hree differen operaing modes, wih he simplified heoreical waveforms shown in Fig 6 In he firs mode, Fig 5, swiches T ci and T di (and T da ) are, respecively, on and off During his period, capaciors C i are charged wih oal energy, approximaely, equal o (1) During his mode, diode D A is on and guaranees ha he volage applied o he primary of he ransformes approximaely zero, as seen in Fig 6 c) Diode D C on he secondary of he ransformer assures ha he volage applied o he load is also near zero In he second operaing mode, Fig 3, swiches T ci and T di are, respecively, off and on During his period,

3 T d1 T dn D B D A T da Fig 4 Topology of he Elecronic Marx Generaor circui, wih n sages, associaed wih an oupu pulse ransformer In he second operaing mode, Fig 5, swiches T ci and T di (and T da ) are, respecively, off and on During his period, capaciors C i are conneced in series and he volage applied o he primary of he ransformer, v 1, is, approximaely, equal o, v = nvdc Diode D C is on, so he volage applied o he load is, v = nv N dc 2 N1 D C v In he hird operaing mode, Fig 5 c), swiches T ci and T di (and T da ) are off In he firs par of his period, a, he volage applied o he primary of he ransformer is, approximaely, (Fig 6 c)) and he magneizing curren i m has a pah hrough D B Since he volage applied o he primary of he ransformer has opposie polariy, i m decrease linearly, i m = Vdca Lm Tha, in erms, guaranees he rese of he ransformer, sending his energy back o he energy sorage capaciors The capacior wih he lowes volage receives his curren, which increases he capacior energy During his period, diode D C on he secondary blocks a volage, Fig 6 e), vka = Vdc N 2 N1 v gs (T di ) v gs (T ci ) V i δ d = d /T i 1 i n V i δ c = c /T i c1 i cn c d ab v T a b D A c) -n A B area A= area B D C Td1 v C n Tdn D B v c) Fig 5 Capaciors charging operaion mode; Pulse operaion mode and c) ransformer rese operaion mode for he circui in Fig 4 During his period, curren, Fig 6 f), is equal o, ' im + =, where i m is he magneizing curren of he ransformer, and i is he secondary curren reduced o ' he primary, = i N 2 N1 Considering a linear magneic circui, hen i m increases linearly as, i m = nvdcd Lm, where L m is he primary magneizing inducance and d is he pulse widh, Fig 6 The load curren is given by, i = v Zload v d) (D C ) e) f) g) -n N 2 / i' i m N 2 / Fig 6 Theoreical waveforms for he EMG operaion wih pulse ransformer of Fig 4, considering a resisive load: T di drive signal; T ci drive signal; c) primary volage, ; d) load volage, v ; e) diode reverse volage, ; f) primary curren, ; g) primary curren componens Considering he power supply volage consan,, he volage blocked by D C is always he same (volage in each capacior), independen on he number of sages in he Marx generaor However, increasing he number of sages, he primary volage is bigger and so he rese ime a is longer, o guaranee ha he vol-second produc is equal, Fig, 7 c), during he pulse and during he rese period Taking ino accoun Fig 6 c), afer he rese ime, a, i m goes o zero and diodes are off The volage applied

4 o he primary of he ransformes zero during b, afer which he firs operaion mode begins again, Fig 5 Regarding he drive signals, v gs(tdi) and v gs(tci), respecively, of semiconducors T di and T ci, he EMG of Fig 4 is more complex han he EMG of Fig 2 Due o he rese period, he drive signals o swiches T ci mus be delayed by ab, as can be seen in Fig 6 This difference creaes exra complexiy for he semiconducors drives In boh circuis, he semiconducors mus be driven synchronously, and as all he swiches are a differen poenials, i is required gae circuis wih galvanic isolaion (opical fibres are used o ransmi he gae signals) o ensure he rese of he ransformer This rese volage has an ampliude, abou, he volage of he power supply, 1 V (ie he volage on he capaciors, neglecing he losses), and is applied o he primary during he necessary period of ime o ensure equal vol-second balance The wave form of he rese volage is no squared as i was prediced heoreical, Fig 6 c), because of resonances beween he impedance of he ransformer and he capaciors (his waveform is mosly dependen on he magneizing inducance of he ransformer, for lower values of he magneizing inducance he shape is closer o a recangle) III EXPERIMENTAL RESULTS The purpose of he experimenal procedure was o compare he performance of boh EMG circuis in Fig 2 and Fig 4 o obain - 5 kv pulses In order o do ha, a laboraory prooype of he EMG circui, wih five sages, 45 µf capaciors, was buil using 12 V IGBTs and diodes For he EMG circui of Fig 2, a power supply =1 V was used, and he circui was operaed wih 1 % duy cycle and 1 khz repeiion rae Fig 7 shows he pulse volage, v, ino a 5 kω resisive load Fig 8 Experimenal resuls for he EMG of Fig 4, horizonal scale 2 (µs/div), primary: volage,, 2 (V/div); curren,, 2 (A/div) Fig 7 Experimenal resuls for he EMG of Fig 2, horizonal scale 2 (µs/div), oupu volage, v, 1 (V/div) The volage pulse, in Fig 7, exhibi an almos recangular shape wih -5 kv ampliude, wih approximaely 5 ns rise ime, and 1 µs widh, supplying 1 A, o a 5 kω resisive load For he EMG circui of Fig 4, a power supply =1 V was used, and he circui was operaed wih 4 % duy cycle and 1 khz repeiion rae A 1:1 (sepup ransformer was associaed on he oupu) Fig 8 shows he primary pulse volage,, and primary winding pulse curren, ino a 5 kω resisive load I can be seen from Fig 8 ha afer he 5 V oupu pulse, wih 4 µs widh, applied o he primary of he ransformer, and opposie polariy volage is applied Afer he 4 µs pulse, i can be seen, from Fig 8, he slop of magneizing curren, ha deceases from is maximum value ( 3 A) o zero during he rese of he ransformer As i was described above, his curren is redireced o he capaciors, recovering he magneizing energy Fig 9 shows he pulse volage, v, applied o a 5 kω resisive load The volage pulse, in Fig 9, exhibi an almos recangular shape wih -5 kv ampliude, wih approximaely 5 ns rise ime, and 4 µs widh, giving 1 A, ino a 5 kω resisive load The oupu volage pulse obained wih he EMG of Fig 4 has an, almos, 1 imes longer rise ime, and exhibis more oscillaions, as compared wih he one obained wih he EMG of Fig 2, as i was expeced due o he use of he oupu ransformer However, he

5 volage blocked by he semiconducor swiches is 1 imes lower The EMG of Fig 4 has a diode in he secondary ha mus susain he demagneizing volage of he ransformer refleced on he secondary In addiion, due wo he non-ideal behaviour of he ransformen he circui of Fig 4, he circui in Fig 2 is more efficien and has less EMI generaion Therefore, depending on he oupu pulse volage needed in a paricular applicaion, he number of semiconducors available and heir blocking capabiliies, he urns raio of an equivalen ransformer o achieve he desirable volage, he exising power supply volage and if galvanic isolaion is needed, one can choose beween he wo EMG opologies, here proposed o achieve he bes resuls, wih conrolled coss Fig 9 Experimenal resuls for he EMG of Fig 4, horizonal scale 1 (µs/div), oupu volage, v, 1 (V/div) IV CONCLUSIONS This paper presens a hybrid fully inegraed solidsae Marx generaor circui, which has been developed for high-frequency (khz), high-volage (kv) applicaions needing recangular pulses The proposed circui akes advanage of he inensive use of power semiconducor swiches o increase he performance of he classical Marx circui, srongly reducing losses and increasing he pulse repeiion frequency In addiion, o furhencrease he oupu pulse, he proposed opology is enhanced wih an energy recovery rese circui ha enables he use of an oupu pulse ransformer, and recovers he ransformer magneizing energy, during he pulse off sae, back o he energy sorage capaciors A laboraory prooype wih five sages of his all silicon Marx generaor circui, was consruced using 12 V IGBTs and diodes, operaing wih 1 khz frequency, giving - 5 kv pulses, wih 4 o 1 µs widh, giving 1 A ino a 5 kω resisive load The obained oupu volage pulse waveform from he Marx generaor wih he oupu pulse ransformer has longer rise and fall imes Neverheless, needed blocking volages of he swiching semiconducors are considerable lower Given ha pulse shape is no he only imporan parameer, one can choose beween using or no he oupu ransformer o achieve he bes resuls, depending on: 1) needed galvanic isolaion; 2) he oupu volage pulse needed; 3) he cos of he oal number of semiconducors available blocking volages; 4) he ransformer urns raio needed o achieve he desired pulse volage; 5) he available power supply volage; 6) he efficiency; 7) he EMI generaion V REFERENCES [1] Tian e al, Special modulaor for high frequency, low-volage plasma immersion ion implanaion, Review of Scienific Insrumens, vol 7, no 3, Mar 1999, pp [2] MPJ Gaudreau, T Hawkey, J Pery and M Kempkes, A solid sae pulsed power sysem for food processing, in Proceed Pulsed Power Plasma Science, 21, vol 2, pp [3] EL Neau, Environmenal and Indusrial Applicaions of Pulsed Power Sysems, IEEE Transacions on Plasma Science, vol 22, no 1, February 1994, pp 2-1 [4] EG Cook, Review of Solid-Sae Modulaors, Presened a he XX Inernaional Linac Conference, Monerey, Aug 2 [5] DM Goebel, Pulse Technology, Chaper 8 de Handbook of Plasma Immersion Ion Implanaion & Deposiion, Edior Anders, André, 1 s ediion, John Wiley & Sons, New York, 2, p 76, ISBN [6] Willis, W L: Pulse-Volage Circuis, Chaper 3 de High Power elecronics, Edior Dollinger, R E; Sarjean, W James, Tab Books Inc, 1 s Ediion, 1989, ISBN [7] J O Loughlin,; J Lehr and D Loree, High repeiion rae charging a Marx ype generaor, in Proceed Pulse Power Plasma Science, vol 1, pp , June 21 [8] K Okamura, S Kuroda and M Maeyama, Developmen of he high repeiive impulse volage generaor using semiconducor swiches, 12 h Pulsed Power Conference, Diges of echnical Papers, vol 2, pp 27-3, 1999 [9] VN Rai, M Shukla and RK Khardekar, A ransisorized Marx Bank circuroviding sub-nanosecond high-volage pulses, Meas Sci Technology, vol 5, pp , 1994 [1] RL Cassel, A Solid Sae High Volage Pulse Modulaor which is Compac and wihou oil or pulse ransformer, 24 Power Modulaor Conf, May 23-26, San Francisco CA [11] Jong-Hyun Kim e al, High Volage-Pulse Power Supply Using Marx Generaor & Solid-Sae Swiches, in Proceedings of he Indusrial Elecronics Sociey, 25, IECON, nd Annual Conference of IEEE Annual Conference of he IEEE, 6-1 Nov, 25, pp [12] LM Redondo, J Fernando Silva, P Tavares and E Margao, All Silicon Marx-bank opology for high-volage, highfrequency recangular pulses, in Proceedings of he 25 IEEE 36 h Annual Power Elecronics Specialiss Conference, June, Recife, Brasil, pp [13] L M Redondo, E Margao, J F Silva, Rise ime reducion in high-volage pulse ransformers using auxiliary windings, in IEEE Transacions on Power Elecronics, vol 17, Issue 2, March 22, pp [14] Jong-Hyun Kim e al, High Volage-Pulse Power Supply Using IGBT Sacks, in Proceedings of he 3 h Annual Conference of he IEEE Indusrial Elecronics Sociey, November 2-6, 24, Busan, Korea, pp [15] EG Cook, Review of Solid-Sae Modulaors, Presened a he XX Inernaional Linac Conference, Monerey, Aug 2