Research on the Multilevel STATCOM based on the H-bridge Cascaded

Transcription

1 JOURAL OF ETWORKS, VOL. 9, O. 1, JAUARY Reearh on the Multilevel STATCOM baed on the H-bridge Caaded Guifeng Wang Shool of Eletroni Information and Eletrial Engineering, Shanghai Jiao Tong Univerity Shanghai 23 China Jianguo Jiang and Shutong Qiao Key Laboratory of Control of Power Tranmiion and Converion, Minitry of Eduation Shanghai Jiao Tong Univerity, Shanghai 23 China Lifeng Guo Shool of Information and Eletrial Engineering, China Univerity of Mining and Tehnology, Xuzhou China Abtrat Thi paper mainly tudie the main iruit topology, the woring priniple, modulation tehniue and ontrol trategy of the STATCOM baed on H-bridge. The STATCOM diret power ontrol algorithm baed on the virtual flux i ued to ontrol the AC ide reative power ompenation, and in aordane with the priniple of onervation of power, the DC ide voltage imbalane fator are analyzed, and a ditributed DC voltage ontrol algorithm i alo introdued. The DC ide ontrol algorithm i divided into upper and lower ontrol part, of whih the upper ontrol etion i aimed at the average of DC ide apaitor voltage of the ub-module unit for the STATCOM devie, the lower ontrol part i mainly for eah ub-module DC ide apaitor voltage. Finally, the ontrol trategy i verified in a three level hain STATCOM ytem with VME ontrol box a it ore ontroller, and the experimental reult how that the algorithm i feaible. Index Term Caade Multi-Level; STATCOM; Carrier Shift Phae PWM; Diret Power Control; Ditributed Control Sytem I. ITRODUCTIO Flexible AC Tranmiion Sytem (FACTS) i an important tehnial mean for power grid to redue energy onumption and improve power uality. A FACTS ore euipment, tati ynhronou ompenator (STATCOM) baed on H-bridge aade, whih tae the full-ontrolled power eletroni devie ontitute a voltage oure inverter (IGBT) a the ore, and ue the aade multi-level and PWM tehnology, ha many advantage, uh a: mall output harmoni urrent, le area, hort repone time, a wide range of reative power ompenation, eay to maintain, eay to expand, and low ot et. So it ha beome the fou of reearh of dometi and foreign expert, and gradually applied to the high-voltage tranmiion grid [1, 2, 3, 4]. owaday, STATCOM AC ide ontrol algorithm ha been widely ued in power deoupling PWM ontrol, whih ha ahieved the deoupling of power model by the PI regulator. It i eay to ue and ha mall amount of alulation; however, to guarantee it normal operation, the networ voltage a well a the networ voltage tranformer are reuired [5, 6]. The power ytem i trongly oupled and nonlinear, and the loal linearization ontrol of the ontrol theory of nonlinear ytem i ued [7]. Thi method ahieve the Taylor expanion of STATCOM nonlinear tate euation, and arrie out loal linearization at a ertain point to obtain the loalized linear euation. Then, the modern ontrol theory i adopted to deign the ontroller baed on the obtained euation. Although thi method ha exellent propertie of ontrol, the loal linearization method ha limited the operation range of STATCOM to ome extent. The virtual flux-baed STATCOM diret power ontrol algorithm ha introdued the onept of virtual flux to obtain the information about networ voltage indiretly, thu omitting the networ voltage tranformer, whih ha optimized the ontrol truture of the ytem and improved it reliability [8, 9, 1]. Firtly, the paper tudie the main iruit truture and woring priniple of the STATCOM baed on the H-bridge aade and arrier phae hift PWM (CPS-SPWM) tehnology; Seondly, On the bai of the STATCOM diret power ontrol algorithm baed on virtual flux, the ditributed DC ide voltage ontrol algorithm i introdued through the priniple of power onervation. Finally, the ontrol trategy i verified on three hain STATCOM ytem ontrolled by a VME hai. II. MAI CIRCUIT STRUCTURE AD PRICIPLE OF THE STATCOM BASED O THE H-BRIDGE CASCADE The STATCOM baed on H-bridge aaded, whih i ontituted by the H-bridge module unit in erie, ha both triangle and tar onnetion mode. Star onnetion i 214 ACADEMY PUBLISHER doi:1.434/jnw

2 148 JOURAL OF ETWORKS, VOL. 9, O. 1, JAUARY 214 hown in Figure 1, euipment apaity an be improved by a imple inreae in the number of lin module, and it i low ot, eay to implement and mall footprint. Ideally, an euivalent iruit diagram of the STATCOM i hown in Figure 2. L and R are the total indutane and reitane in the apparatu main loop (inluding the onneting reatane and the inverter impedane), v i the grid voltage, v i output voltage of the STATCOM, i STATCOM euipment. O e a e b e L L L i i b i a i a Phae a v a L i aborption urrent of the i b v b v a v b v v d1 v d2 v dn L Phae b i v L Phae Figure 1. Caaded STATCOM topologial truture V I L R V Figure 2. Euivalent iruit of STATCOM i l i lb i la reative power an be further ontrolled [3, 4], Figure 3 how the voltage and urrent vetor diagram when the reative power ompenation ytem onnet to the grid through an ideal indutor urrent, X i the value of loop indutane, i the angle of the STATCOM output voltage with the grid voltage. Aording to Figure 3, when the STATCOM output voltage amplitude v and phae hange, the ize and nature of ative and reative power of whih aborbed by the STATCOM alo vary aordingly[5, 6, 7]. III. MODULATIO ALGORITHM OF H-BRIDGE CASCADE MULTILEVEL COVERTER Currently, the modulation algorithm H-bridge aade multilevel onverter mainly inlude: the ladder wave modulation [11], pae voltage vetor method [12, 13] and arrier phae hift PWM method [14, 15]. Ladder wave modulation i a baeband modulation method, the withing freueny i low, and onduive to high-power implementation of STATCOM, but the harmoni ontent of the output voltage i great, only in the ae of a large number of level i high-uality output voltage obtained; In ontrat, pae voltage vetor method with a high DC voltage utilization i eay to failitate the digitization method, but with the inreae in the number of output level, epeially after more than 5 level, it i diffiult to ahieve, and the amount of ontroller operation i inreaed; CPS-SPWM i a multi-arrier SPWM modulation algorithm. PWM trigger pule i generated through a multi-hannel arrier moving on the timeline T (2 ) ( T i arrier yle, i the number of module in erie). Figure 4 i a hemati diagram of the 2 module in erie CPS-SPWM, thi method i imple to be deigned, and eay to be implemented, and an mae the ame a the number of withing yle of the euipment unit module, and i alo eay to implement the DC ide of apaitor voltage eualizer ontrol. Figure 4. Multilevel phae-hifted arrier-baed tehniue Figure 3. Voltage and urrent vetor diagram of STATCOM The phae and amplitude of the urrent aborbed by STATCOM from the grid an be ontrolled by hanging the STATCOM output voltage amplitude and phae with repet to v. And the nature and magnitude of the IV. STATCOM COTROL STRATEGY BASED O H-BRIDGE CASCADE A. STATCOM Diret Power Control Baed on Virtual Flux 1) Priniple of Virtual Flux Oberver 214 ACADEMY PUBLISHER

3 JOURAL OF ETWORKS, VOL. 9, O. 1, JAUARY The priniple of virtual flux i that overall grid ide with onverter ae i een a a three-phae AC motor [16], a i hown in the dar part of the box of Figure 1 and Figure 2, STATCOM onverter grid voltage v i euivalent to indued eletromotive fore whih i generated by the AC motor air gap magneti field in the tator winding, the indutor L and the reitor R are euivalent to the euivalent reitane of the tator winding and the tator leaage indutane repetively, o it an be een that three-phae grid voltage i gotten through a virtual air gap flux indution. Thu the appliation flux an be applied intead of the grid voltage in aordane with the relationhip that flux phae lag indued eletromotive fore phae angle of 9. Aording to the relationhip between flux and indued eletromotive fore, the etimated value, of virtual flux in, oordinate ytem are: v dt v dt Among (1), v, v are the grid voltage omponent in the, oordinate ytem, aording to STATCOM voltage euation under the oordinate ytem di v L v R i dt di v L v R i dt α α α α β β β β Among (2), i α, i β are the STATCOM urrent flow in the, oordinate ytem, if the euivalent reitane flux i: (1) (2) R i ignored, the etimated value of virtual n n n 2 1 α [ vd ( Sai ( Sbi Si ))] dt 3 i1 2 i1 i1 Liα (3) n n 1 β [ vd ( Sbi Si )] dt Liβ 2 i1 i1 Among (3), v d i the H-bridge module ub-unit DC bu voltage, S ai, S bi and S i are repetively i-th unit of eah bridge arm withing tate. By the formula (3), virtual flux ignal an be een a the ytem phae-loed loop to partiipate in the ytem ontrol, phae lo iruit and the grid voltage enor are omitted, at the ame time, when the grid voltage ditort, the atified grid angular information an be obtained beaue of the exitene of the integral part. Sine the pure integral part of the formula (3), if the integral initial value in t eleted properly, The DC bia will be introdued to the virtual flux. Uually a low pa filter i ued intead of a pure integrator in order to eliminate the teady tate DC offet. Aording to the literature [12], the improved virtual flux oberver uing aade inertia intead of the pure integral part i hown in Figure 5, the tranfer funtion of the aade inertia ( ) H () o differene in amplitude and phae hift hould be enured when the pure integrator i replaed. Under thee two ondition, the relationhip an be obtained a follow. v α i α i β v β L L (4) 2, (5) +ω +ω +ω +ω Figure 5. Improved virtual flux oberver Ψ α Ψ β Figure 6. The iruit and vetor of the ell 2) Intantaneou Power Detetion Baed on Virtual Flux Improved virtual flux oberver i able to ahieve fat and aurate flux etimate, Aording to the intantaneou power theory, the intantaneou power aborbed by the STATCOM devie an be expreed a: p Re( v i) Im( v i) where, v i the grid voltage vetor, i i the inflow of the STATCOM urrent vetor. In aordane with the priniple of the virtual flux the grid voltage i: (6) d d jt v ( e ) dt dt d d j( j ) dt dt Binding of formula (6) and (7), and when the ytem meet the three-phae balaned inuoidal line voltage, the virtual flux amplitude i ontant. It i poible to obtain the intantaneou power aborbed by the STATCOM: p ( i i ) ( i i ) (7) (8) 214 ACADEMY PUBLISHER

4 15 JOURAL OF ETWORKS, VOL. 9, O. 1, JAUARY 214 v d PI (v d1 + +v dn )/n i a, i b, i S ai, S bi, S i ref p ref p PI PI Current detetion Power etmation Flux oberver Ψ α v d v Ψ β MI v 2 d v d v 2 tan 1 ( v / v ) d in o v a v b v (v d1 + +v dn )/n v da1 (v d1 + +v dn )/n v db1 (v d1 + +v dn )/n v d1 i a i b i P P P v a v b v a1 a2 an b1 b2 bn 1 2 n Upper ontrol Lower ontrol Figure 7. Hierahial ontroller for ytem Aording to the formula (4) and (8), the STATCOM diret power ontrol ytem blo diagram baed on virtual flux i hown in Figure 7 the upper ontrol i the STATCOM diret power ontrol baed on virtual flux, i grid voltage orientation angle. A Figure 7 i hown, the STATCOM ontrol trategy doe not reuire a grid voltage tranformer through introduing virtual flux theory. So it an effetively overome the problem of the detetion error due to a voltage tranformer, the algorithm i imple and eay to digital implementation. B. The Control Strategy in the Ditributed DC Side DC apaitor of eah module of STATCOM baed on H-bridge aade i independent of eah other, and withing loe, iruit loe, the with alloation tatu and pule delay differene, whih led to the DC bu voltage imbalane exit [17,18]. In thi paper, the DC ide ontrol trategy of the hierarhial ditributed whih i divided into the upper ontrol and lower ontrol i adopted. The upper ontrol tabilize overall DC bu voltage, that i the average of the entire devie module DC bu voltage; lower ontrol tabilize eah module DC bu voltage. The upper ontrol tae all module DC voltage a a whole C, aording to the power balane, the mathematial model for the STATCOM DC ide apaitor voltage in the d oordinate ytem i dvd 3 K 3V S ( i do i in ) (9) dt 2 C L where, v d i the average value of DC apaitor voltage, K i SPWM modulation ratio, C i the DC bu voltage, V i the AC grid voltage pea. i angle between STATCOM output voltage vetor and the grid-ide voltage vetor, if i mall, v d and i d an be regarded a a linear relationhip. So that the DC bu voltage upper ontrol i deigned for the outer ring of the ative urrent. Lower ontrol i for ub-module DC bu voltage, aording to the priniple of power balane, a i hown in Figure 6, C i DC apaitor, R i module euivalent lo reitane, i i arm urrent, u i the module output voltage fundamental amount. The ative amount aborbed and emitted by the ub-module unit i deided by i, u and their phae angle. Thu, the DC ide apaitor voltage an be adjuted by adjuting the amplitude and phae of u. The adjutment amount, whih ha relationhip with the bridge arm urrent, i deigned to P regulator, the output i uperimpoed to the output modulated wave of the reative power ompenation in the AC ide, and thi doe not affet the reative power ontrol in the AC ide. Aording to the AC and DC ide ontrol algorithm analyi, the aaded STATCOM ontrol blo diagram i hown in Figure 7. Where, a, b, are the modulation wave of the arrier hift phae PWM modulation. V. EXPERIMETAL VERIFICATIO To verify the above ontrol trategy, a 3 H-bridge aade STATCOM ytem in a tar onnetion i developed. A i hown in Figure 7, the main iruit parameter are hown in Table 1. The hot ontroller for experimental platform i ontrol abinet baed on the VME bu produed by the wing ompany in United State, the laboratory euipment onnet with 38V power grid through the auto-tranformer. Figure 8 how the output of the onverter line voltage v b, v a and the grid line voltage v ab, v b. The line output voltage of the onverter i 13 level, it an be een by omparing STACOM output line voltage v with the grid voltage v b, aording to the priniple of virtual voltage, grid voltage phae diretional meet the ontrol reuirement. Figure 9 i the onverter dynami tet waveform, the reative power i meaured by output of D / A board of the VME hai. Figure 9(a) i tranient waveform when STATCOM ytem aborb the indutive reative power, Figure 9(b) i tranient waveform when it aborb the apaitive reative power, the ytem running the urrent value i 3.5 A. In the ae of a apaitive mode, the output urrent THD of inverter i 2.8%, whih i 3.2% in b 214 ACADEMY PUBLISHER

5 JOURAL OF ETWORKS, VOL. 9, O. 1, JAUARY the ae of indutive mode. The figure how that the ontrol ytem i table, good dynami performane, and the tability of the DC bu voltage i good. TABLE I. MAI PARAMETERS OF THE LABORATORY EQUIPMET Parameter Value Grid voltage (rm) U /V 23 Grid freueny f /Hz 5 Grid indutane L /mh 4mH Module DC apaitor C/uf 34 DC bu voltage v d /V 63 Rated output urrent I /A 1 Figure 1 i reative power ompenation ytem, in the ae of a apaitive load, The STATCOM ytem i not put into operation firtly, and opened at time t. The waveform how that the ytem ompenation effet i good and the urrent amplitude i ignifiantly redued. v b v ab v b v a Figure 8. The line voltage of the 3-ell aade STATCOM and grid v (V) ab v (V) ab v ab i a (a) STATCOM aborb the indutive reative power v ab (b) STATCOM aborb the apaitive reative power i a i (A) a i (A) a Figure 9. The dynami waveform of the 3-ell aade STATCOM v (V) ab vab t i (A) a 15 1 Figure 1. The voltage and urrent waveform of grid voltage VI. ia COCLUSIO The main iruit truture and priniple of STATCOM baed on the H-bridge aade, the arrier phae hift PWM tehnology, diret power ontrol algorithm baed on virtual flux and ditributed DC voltage ontrol algorithm are tudied in thi paper. The ontrol trategy on 3 H-bridge aade STATCOM ytem ontrolled by a ingle VME hai i teted by the experiment, the reult how that the STATCOM diret power ontrol algorithm baed on the virtual flux i imple, the amount of alulation i mall, grid voltage tranformer i not needed, and the dynami performane of the STATCOM ytem i good; The hierarhial, ditributed DC voltage ontrol algorithm an effetively uppre the DC bu voltage flutuation. The above algorithm an alo be extended to the multi-tage high-preure STATCOM ytem baed on H-bridge aaded. ACKOWLEDGMET Thi wor wa upported by the ational High Tehnology Reearh and Development Program of China (863 Program) under Grant o. 211AA543; Dotoral Program of Higher Speialized Reearh Fund (new teaher la) Projet ( ) REFERECES [1] K. Eel-Hwan, K. Jae-Hong, K. Se-Ho, et al. Impat analyi of wind farm in the Juju Iland power ytem. IEEE tran on Sytem Journal, 212(6) pp [2] Qing-ing Zheng, Jing Wu, Xuan Wang. The appliation of arrier phae hift tehnology hain STATCOM. Power eletroni tehnology, 21, 44(12) pp (Chinee) [3] Y. Pal, A. Swarup, B. Singh. A Review of Compenating Type Cutom Power Devie for Power Quality Improvement. IEEE Power India Conferene, 28 pp. 1-8 [4] L. Zhao, L. Bangyin, D. Shanxu, el al. A ovel DC Capaitor Voltage Balane Control Method for Caade Multilevel STATCOM. IEEE Tran on Power Eletroni, (1) pp [5] Zhang Yong Gao, Kang Yong, Liu Liming, et. Double-loop ontrol deign of STATCOM. Eletri Power Automation Euipment, 26, 26 (1) pp [6] Siriupraert S, Huang AQ, and Lai J-S. Modeling analyi and ontrol of aaded-multilevel onverter-baed STATCOM. Pro. Power Eng. So. General Meeting, 23 pp ACADEMY PUBLISHER

6 152 JOURAL OF ETWORKS, VOL. 9, O. 1, JAUARY 214 [7] Chia B H K, Morri S, Dah P K. A feedba linearization baed fuzzy-neuro ontroller for urrent oure inverter-baed STATCOM. Power Engineering Conferene, 23 pp [8] CAO Kai, Jiang Jianguo, Yangxing Wu, et. Diret Power Control with Contant Swithing Freueny for STATCOM with Compenation in Virtual Flux Etimation. Eletrial Automation, 21, 37 (5) pp [9] Shi-hao Liu, Xing-wu Yang, Jian-guo Jiang. Diret Power Control with Contant Swithing Freueny for STATCOM Baed on Virtual Flux. Eletrial Automation, 29, 31(5) pp (Chinee) [1] Hanen S, Malinowi M, Blaabjerg F, et al. Senorle ontrol trategie for PWM retifier. Fifteenth Annual IEEE Applied Power Eletroni Conferene and Expoition, 2 pp [11] Ben-Sheng Chen, Yuan-Yih Hu. A Minimal Harmoni Controller for a STATCOM. IEEE Tran on Indutrial Eletroni, 28, 55(2) pp [12] Aneeh M A S, Gopinath A, Baiju M R. A Simple Spae Vetor PWM Generation Sheme for Any General n-level Inverter. IEEE Tran on Indutrial Eletroni, 29, 56(5) pp [13] Lin Ping, Wang Qiao, Li Jianlin, et al. Baed on Caaded wrong ampled pae vetor modulation multi-level onverter APF tudy. China Proeeding of the CSEE, 25, 25 (8) pp [14] MGrath B P, Holme D G. Multiarrier PWM trategie for multilevel inverter. IEEE Tran on Indutrial Eletroni, 22, 49(4) pp [15] Young-Min Par, Han-Seong Yoo, Hyun-Won Lee, el al. A Simple and Reliable PWM Synhronization & Phae-Shift Method for Caaded H-Bridge Multilevel Inverter baed on a Standard Serial Communiation Protool. IEEE Indutry Appliation Conferene, 26 pp [16] Cihowla M, Malinowi M, Kazmierowi M P, Sobzu D L, Rodriguez P, Pou J. Ative filtering funtion of three-phae PWM boot retifier under different line voltage ondition. IEEE Tran on Indutrial Eletroni, 25, 52(2) pp [17] Woodhoue M L, Donoghe M W. Type teting of the GTO value for a novel STATCOM onvertor. IEEE Tran on AC-DC Power, 21, 48(5) pp [18] WAG Zhibing, YU Kunhan, ZHOU Xiaoxin. Control Strategy for DC Bu Voltage Balane in Caaded H-bridge Multilevel Converter. Proeeding of the CSEE, 212, 32 (6) pp Guifeng Wang wa born in Linyi Shandong provine China in February, He reeived the bahelor and mater degree in Shool of Information and Eletrial Engineering at China Univerity of Mining and Tehnology, China, in 24 and 27, repetively. He i a PH.D Candidate in Shool of Eletroni Information and Eletrial Engineering at Shanghai Jiao Tong Univerity. Hi mainly reent reearh interet in the field of power eletroni onverter for power uality. Jianguo Jiang wa born in Yanheng Jiangu provine China in Deember, He reeived hi B.S., M.S. and the Ph.D. degree in Department of Eletrial Engineering at China Univerity of Mining And Tehnology, China, in 1982, 1985 and 1988, repetively. He i now a Profeor of Shanghai Jiao Tong Univerity and the diretor of the Key Laboratory of Control of Power Tranmiion and Converion, Minitry of Eduation. Hi urrent reearh interet inlude power eletroni onverter for eletrial drive and power uality. Shutong Qiao wa born in Hebei provine China in He reeived the bahelor and mater degree in Shool of Information and Eletrial Engineering at China Univerity of Mining and Tehnology, China, in 21 and 24, repetively. He ia reearh aitant of Shanghai Jiao Tong Univerity. Hi mainly reent reearh interet in the field of power eletroni onverter for power uality. Lifeng Guo wa born in Reniu Heibei provine China in Otober,1986. He reeived the bahelor degree at China Univerity of Mining and Tehnology, China, in 26. He i now a graduate tudent in Shool of Information and Eletrial Engineering at China Univerity of Mining and Tehnology. Hi mainly reent reearh interet in the field of power uality. 214 ACADEMY PUBLISHER