Dead Zone Compensation Method of H-Bridge Inverter Series Structure

Transcription

1 nd Inernaional Conference on Elecrical, Auomaion and Mechanical Engineering (EAME 7) Dead Zone Compensaion Mehod of H-Bridge Inverer Series Srucure Wei Li Insiue of Elecrical Engineering and Informaion Engineering, Lanzhou Universiy of Technology, Lanzhou 735, China Absrac Based on he analysis of dead zone compensaion principle in H-bridge inverer series srucure, an improved average volage feedforward compensaion mehod of H-bridge inverer series srucure is sudied. Because he radiional average volage feedforward compensaion mehod has he phenomenon of false compensaion in he curren zero crossing region, he zero crossing region of he H-bridge inverer series srucure oupu curren is precisely divided in he improved mehod. Ouside he curren zero-crossing region, adoping he average volage feedforward mehod. During he curren zero-crossing region, he dead zone will no affec he oupu volage, so no compensaion is required, which effecively avoid he radiional average volage feedforward compensaion mehod has he phenomenon of false compensaion caused by misjudgmen of curren direcion in zero crossing region. Finally, he improved dead zone compensaion mehod of H-bridge inverer series srucure is simulaed by MATLAB/SIMULINK sofware. The resuls verify he effeciveness of he mehod. Keywords-dead zone; h-bridge ; inverer series; compensaion mehod I. INTRODUCTION A presen, he H-bridge inverer series srucure has been applied in he elecric car [], phoovolaic grid-conneced power generaion sysem [], series micro-grids [3] and wind/solar hybrid generaion sysem [4] exensively. As he power swich has a cerain urn-on and urn-off ime, in order o preven he phenomenon of shor circui appear in he bridge arm, dead ime is needed o add o he power device swiching process. The dead ime, power device urn-on and urn-off ime, he ube volage drop lead o inverer oupu fundamenal volage loss and ampliudes of low harmonics increase, so resuling in he oupu volage waveform and curren waveform of he H-bridge inverer series srucure disorion [5]. Therefore, i is necessary o compensae he oupu volage waveform of he H-bridge inverer series srucure. A presen, domesic and foreign scholars have proposed a variey of dead-zone compensaion mehods for single-phase or hree-phase bridge inverers. Pulse widh direc adjusmen mehod [6], his mehod conrol he upper or lower swich ube ha on he same arm closing early or opening delay in a lile ime by deecing he direcion of he curren o ensure ha he upper and lower swich will no opening a he same ime during he swiching process, meanwhile he inegriy of he oupu volage waveform can also be ensured. Invalid swich eliminaion mehod [7], his mehod only allow one of he power swiches ha on he same bridge arm o ac by judging he direcion of he curren, hus avoiding he phenomenon of " pass hrough" happened in he same arm, so here is no necessary o se he dead ime. The Average volage feedforward compensaion mehod [8], his mehod calculae he average value of he difference beween he acual oupu volage waveform ha considered he dead zone and he ideal oupu volage waveform (he difference is dead zone pulse volage), hen compensae i o he modulaion wave hrough he feedforward way. In his mehod, he compensaion volage is posiive or negaive depends on he direcion of he inverer oupu curren. When he dead zone in H-bridge inverer series srucure is compensaed by he pulse widh direc adjusmen mehod or he invalid swich eliminaion mehod, he pulse widh direc adjusmen mehod need o adjusmen every swich ube s driving signal of each inverer uni by deecing he direcion of he curren and he invalid swich eliminaion mehod also require masking every swich ube s invalid driving signal. While here are a number of swiches in he H-bridge inverer series srucure ha make he enire conrol sysem becomes very complex, so he compensaion mehod will ake up a lo of compuing resources of he conroller. Since all he inverer unis of H-bridge inverer series srucure share a modulaion wave, applying he average volage feedforward compensaion mehod o H-bridge inverer series srucure o complee he dead zone compensaion for all inverer unis only needs o compensae he modulaion wave. So he average volage feedforward compensaion mehod is more suiable for he dead zone compensaion of H-bridge inverer series srucure. However, because in he curren zero-crossing region of he H-bridge inverer series srucure, he curren jumps beween he posiive and negaive very frequenly, o use he radiional average volage feedforward compensaion mehod is prone o resul in false compensaion by misjudgmen of he curren direcion. Based on his problem, his paper sudied an improved average volage feedforward compensaion mehod for he dead zone compensaion problem of H-bridge inverer series srucure ha under carrier phase shif-spwm modulaion sraegy. This improved mehod divides he zero-crossing region of he H-bridge inverer series srucure oupu curren precisely. Ouside he curren zero-crossing region, compensae he average volage o he modulaion wave. In he zero-crossing region of he curren, because he dead zone has no effec on he oupu volage [9], compensaion is no required anymore. The improved average volage feedforward compensaion mehod no only avoids he false compensaion phenomenon caused by he misjudgmen of he curren direcion in he curren zero-crossing region, bu also makes he dead zone compensaion module in H-bridge inverer series srucure more simplified, so he compensaion module occupying he memory of he conroller will be Copyrigh 7, he Auhors. Published by Alanis Press. This is an open access aricle under he CC BY-NC license (hp://creaivecommons.org/licenses/by-nc/4./). 77

2 reduced. Above all, he improved average volage feedforward compensaion mehod has a grea research significance. II. THE CALCULATION OF DEAD ZONE COMPENSATION TIME IN H - BRIDGE INVERTER SERIES STRUCTURE C V V3 C V V4 C V V3 C V V4 Cn V V3 Cn V V4 U dc i h inverer uni lef arm wihou he compensaion. uma _ i ( uma _ i )is he compensaion pulse volage of he i h inverer uni lef arm. is he dead ime. is he compensaion pulse volage widh of he i h inverer uni. Ton, Toff are respecively he power swich urn-on ime and urn-off ime. Ti, Ti are respecively he ideal opening ime and ideal closing ime of he i h inverer uni s swich V ; U dci is he DC side volage of he i h inverer uni. ia is he oupu curren of he H-bridge inverer series srucure. ia U dc Assuming ha he volage drops across every power ube of he inverer unis are he same, he volage drops of he diodes are he same and he midpoin s volages are balanced. According o he analysis mehod as in [], i can be obained ha he acual oupu volage of he i h inverer uni in a swich period is: Uo U dcn FIGURE I. MODEL OF H-BRIDGE INVERTER SERIES STRUCTURE The circui model of H-bridge inverer series srucure shown in figure I. I is assumed ha each inverer uni has he same power devices. Taking he lef arm swiches of he i h inverer uni as an example o analysis, and he analysis mehods of remaining inverer unis are he same. Si Si Si Si S i Si S i.5u dci.5u dci Toff Ton Toff Ti.5U dci.5u dci Ti.5U dci.5u dci U dci uma _ i uma _ i ia Ton Ti Ti.5U dci.5u dci U dci Tai Tbi )U dci ( U dcitmi Vd Vce ) sign(ia ) () ia sign(ia ) ia where uab _ i is he oupu volage of he i h inverer uni. Tai is he ideal conducion ime of he i h inverer uni s power swich V ( Tai Ti Ti ). Tmi is he ime difference beween he acual conducion and ideal conducion of he i h inverer uni s power swich V or V3 ( Tmi Toff Ton ). Tbi is he ideal conducion ime of he i h inverer uni s power swich V3. Vce is he volage drop of he power swich. Vd is he volage drop of he freewheeling diode. Si.5U dci.5u dci.5u dci.5u dci uab _ i ( In equaion (), he firs erm is he ideal oupu volage of he i h inverer uni. In order o make he acual volage equal o he ideal volage, i is easy o know ha he second erm mus be zero. So ha here is: ( ia U dci Tmi Vd Vce ) sign(ia ) () The condiion of equaion () can be esablished is: FIGURE II. PRINCIPLE OF DEAD ZONE COMPENSATION Figure II is he analysis of dead zone compensaion principle. Signals Si, Si are respecively he ideal driving signals of he i h inverer uni s swiches V, V. Signals Si, Si are respecively he acual driving signals of he i h is he acual oupu inverer uni s swiches V, V. volage waveform of he i h inverer uni lef arm. is he equivalen oupu volage waveform of he i h inverer uni is he equivalen oupu volage waveform of he lef arm. U dcitmi Vd Vce (3) Subsiuing Tmi Toff Ton ino equaion (3), hen ransformed i can obain: Ton Toff (Vd Vce ) 4U dci (4) 78

3 III. DEAD ZONE COMPENSATION METHOD OF H-BRIDGE INVERTER SERIES STRUCTURE The dead-zone compensaion pulse volage uma _ i in figure II can be equivalenly replaced by a square wave, as shown in figure III. In which, um is he compensaion volage. When he carrier raio F is big, assuming ha all he swiching periods are equal, hen: ia U dci U mi U mi U dci ia um [ f c ( Ton Toff ) FIGURE III. WAVEFORM OF AVERAGE COMPENSATION VOLTAGE The ampliude of square wave ha has he same funcion wih he dead zone compensaion pulse volage of he i h inverer uni is: U mi U dci (5) When he inverer DC side volages are equal: U dc U dc U dci U dc ( i,,, n ) From equaion (4) can obain: om _ om _ om ( i,,, n ) The average compensaion volage ampliude of each inverer uni is: U m U m U m U mi ( i,,, n ) U m U dc [ U dc ( Ton Toff ) (Vd Vce ) ] 4U dc (Vd Vce ) ]sign(ia ) U dc (9) I can be seen from Equaion (9) ha he compensaion volage is posiive or negaive depends on he judgmen of he load curren direcion, so he accurae judgmen of he curren direcion direcly affecs he accuracy of he compensaion. In he curren zero-crossing region, he dead zone does no affec he oupu volage of he inverer, so no compensaion is required. Only he par of he curren zero-crossing region is needed o compensae o avoid he phenomenon of false compensaion caused by misjudgmen he curren direcion in he zero-crossing region. Therefore, he precise division of curren zero-crossing region of he H-bridge inverer series srucure is paricularly imporan. When he inverer uni swiches V, V4 urn on and swiches V, V3 urn off, he curren of load rises. When swiches V, V4 urn off and swiches V, V3 urn on, he curren of load drops. Therefore, i is necessary o find he swich posiive or negaive maximum conducion ime of he H-bridge inverer series srucure in he curren zero-crossing region. u Uc Ur om U dc Ton Toff (8) In which, f c is he carrier frequency. Subsiuing equaion (8) ino equaion (7) can obain: ia fc uc a b ur Si (6) Si (V Vce ) d Si3 Si4 And hen he compensaion volage ha compensaed on he modulaion wave is: U sign(ia ) u m U dc / m [ ( Ton Toff ) (V Vce ) d ]sign(ia ) U dc (7) FIGURE IV. BIPOLAR SPWM MODULATION In figure IV, Si, Si, Si3, Si4 are respecively he ideal driving signals of he i h inverer uni s swiches V, V, V3, V4. ur is he modulaion wave. uc is he carrier wave. U r is he ampliude of modulaion wave. U c is he ampliude of carrier wave. is he carrier wave period. When he modulaion wave ur is bigger han carrier wave uc, he 79

4 swiches V, V4 urn on. When he modulaion wave ur is less han carrier wave uc, he swiches V, V3 urn on. Because of symmery, he maximum urn on ime of he swiches V, V4 is also he maximum urn on ime of he swiches V, V3. As shown in figure IV, he riangular wave ha is bipolar carrier can be expressed as follows: 4U c T ( k ) U c c uc 4 U c ( kt ) U c c k k T k c k N ( M sin ) N U R NMU dc sin () So ha making he modulaion raio M U r / U c and making he modulaion ampliude U c remain consan. A he U r sin r 4U c T ( k c ) U c And because of U L L (4) (5) ( M sin r ) UL L () Subsiuing equaion (8) and equaion () ino equaion (), he variaion of curren can be obained as follows: So he conducion ime of swiches is: i, here is: i (3) Solved equaion (4) can obain: 3 ( k M sin r ) 4 4 () U dc ( NM sin ) () Similarly, a he sampling poin b here is: (9) U L U dc U R U dc NMU dc sin From he equaion () can obain: M sin r ) 4 4 (8) Therefore, a he curren zero-crossing poin, he volage ampliude of he load equivalen inducance L is: sampling poin a, here is ur uc, hen: (k (7) When he curren crosses zero, he volage ampliude of he load equivalen resisor is: The equaion of sine modulaion wave is: 4U U r sin r c ( k ) U c ( M sin ) In he carrier phase shif-spwm modulaion mode, he maximum ime ha only one inverer uni s swiches ac, he remaining inverer uni s swiches remain saic is: () In which, k,,, 3,. ur U r sin r (6) Because he curren waveform lag volage waveform in phase, is he power facor angle. Therefore, in he curren zero-crossing, swiches conducion ime can be expressed as follows: i U dc ( NM sin ) ( M sin ) NL () In he curren zero-crossing region, he posiive or negaive maximum value of he curren is less han he curren variaion i. When he load curren is ia ( i, i ), here is no dead zone compensaion. When he load curren is ia i or ia i, he compensaion volage ha calculaed from equaion (9) will be compensaed o he ideal modulaion wave. The compensaion volage expression in differen curren region is: (Vd Vce ) ] ia i [ f c ( Ton Toff ) U dc um ia i (Vd Vce ) [ f c ( Ton Toff ) ] ia i U dc (3) 8

5 The diagram of he compensaion mehod is shown in he following figure: FIGURE V. DIAGRAM OF THE COMPENSATION METHOD IV. SIMULATION ANALYSIS In his paper, ake he five-cell H-bridge inverer series srucure as an example o simulae. The DC side volage is U dc 3 V. The frequency of modulaion wave is f c Hz. Load resisance is R. Load inducance is L 3 mh. Dead ime is 5 s. Modulaion raio is M.8. IGBT urn-on and urn-off ime are respecively on s, off. s. Volage drop of he IGBT in conducion is Vce V. Volage drop of he freewheeling diode in conducion is Vd.5 V. Subsiuing all above parameers ino he equaion () and equaion (3) can obain: i 3.35 A.94 ia 3.35 um ia i 3.35 a 3 4 Fundamenal (5Hz) = 3.3, THD= 3.46% (B) AFTER COMPENSATION FIGURE VII. SPECTRUM OF THE OUTPUT CURRENT Figure VII (a) shows he specrum of he five-cell H-bridge inverer series srucure oupu curren before compensaion. Figure VII(b) is he specrum of he oupu curren afer compensaion. I can be seen from figure VII, afer adoping he compensaion mehod, he ampliude of he fundamenal curren increased from 93.49A o 3.3A. A he same ime, he low harmonics ampliudes decrease and he curren waveform disorion rae decreases from 9.67% o 3.46%. 5 Curren(A) Fundamenal (5Hz) = 939., THD= 36.4% Mag (% of Fundamenal) 4 The simulaion resuls are shown as follows: Time(s) (A) BEFORE COMPENSATION (A) BEFORE COMPENSATION Fundamenal (5Hz) = 38, THD= 3.97% Mag (% of Fundamenal) 6 (A) BEFORE COMPENSATION Mag (% of Fundamenal) Mag (% of Fundamenal) Fundamenal (5Hz) = 93.49, THD= 9.67% Curren(A) volage drop of he power swich, volage drop of he freewheeling diode and dead ime. Figure VI(b) is he specrum of he oupu volage afer compensaion. I can be seen from figure VI, afer ake he compensaion mehod, he ampliude of fundamenal volage increased from 939.V o 38V. A he same ime, he low harmonics ampliudes decrease and he waveform disorion rae decreases from 36.4% o 3.97% Time(s) (B) AFTER COMPENSATION (B) AFTER COMPENSATION FIGURE VI. SPECTRUM OF THE OUTPUT VOLTAGE Figure VI(a) is he specrum of he five-cell H-bridge inverer series srucure oupu volage ha considered urn-on ime of he power swich, urn off ime of he power swich, FIGURE VIII. OUTPUT CURRENT WAVEFORM Figure VIII(a) shows he oupu curren waveform of he five-cell H-bridge inverer series srucure before compensaion. Figure VIII(b) is he oupu curren waveform afer compensaion. I can be seen from figure VIII, afer adoping he compensaion mehod, he oupu curren waveform of he five-cell H-bridge inverer series srucure became more beer. 8

6 V. CONCLUSION In his paper, an improved average volage feedforward compensaion mehod of H-bridge inverer series srucure ha using he CPS-SPWM modulaion sraegy was sudied. As he H-bridge inverer series srucure in he CPS-SPWM modulaion mode, here are power swiches of he inverer uni ac every / N. So in he curren zero-crossing region, H-bridge inverer series srucure oupu curren jumps beween he posiive and negaive very frequenly. In his mehod, he oupu curren zero-crossing region of H-bridge inverer series srucure is precisely divided. In he curren zero-crossing region, dead zone compensaion is no needed. Ouside he curren zero-crossing region, The compensaion volage ampliude is calculaed o complee he dead zone compensaion. The improved mehod solved he phenomenon of false compensaion ha caused by he radiional average volage feedforward compensaion mehod due o he misjudgmen of he curren direcion in he curren zero-crossing region. The simulaion resuls show ha he improved mehod can effecively decrease he influence of he dead zone on oupu volage and curren of he H-bridge inverer series srucure. REFERENCES [] S. H. Hosseini, M. Ahmadi, S. G. Zadeh, reducing he oupu harmonic of cascade H-bridge mulilevel inverer for elecric vehicle applicaions, rd ed, Elecrical Power Sysem,, pp [] B. Xiao, L. Hang, J. Mei, C. Riley, L. M. Tolber, B. Ozpineci, Modular Cascaded H-Bridge Mulilevel PV Inverer Wih Disribued MPPT for Grid-Conneced Applicaions, rd ed, vol. 5, IEEE Transacions on Indusry Applicaions, 5, pp [3] X. Wang, W. Yang, Dynamic modeling of inverer sysem in isolaed series micro-grid, 8rd ed, vol. 4, High Volage Engineering, 4, pp [4] X. Wang, Q. Guo, W. Yang, Scenery complemenary power generaion sysem based on inverer series power balance conrol, rd ed, vol. 38, Chinese Journal of Power Sources, 4, PP [5] A. R. Munoz, T. A. Lipo, On-line dead-ime compensaion echnique for open-loop PWM-VSI drives, 4rd ed, vol. 4, IEEE Transacions on Power Elecronics, 999, pp [6] C. Aaianese, V. Nardi, T. Giuseppe, A novel SVM sraegy for VSI dead-ime-effec reducion, rd ed, vol. 5, IEEE Transacions on Indusry Applicaions, 5, pp [7] L. H. Chen, F. Z. Peng, Dead-ime eliminaion for volage source inverers, rd ed, vol. 3, IEEE Transacions on Power Elecronics, 8, pp [8] T. Sukegawa, K. Kamiyama, K. Mizuno, T. Masui, T. Okuyama, Fully digial vecor-conrolled PWM VSI-fed ac drives wih an inverer dead-ime compensaion sraegy, 3rd ed, vol. 7, IEEE Transacions on Indusry Applicaions, 99, pp [9] B. Yang, J. Wu, W. Li, X. He, Online adapive dead-ime eliminaion mehod for PWM volage source inverers, rd ed, vol. 6, Transacions of China Elecroechnical Sociey,, pp [] L. Yang, Z. Chen, W. Chen, Z. Li, Oupu volage model of VSI-inverer and a novel dead-time compensaion mehod, rd ed, vol. 7, Transacions of China Elecroechnical Sociey,, pp