Mitigation of Harmonics by Hysteresis Control Technique of VSI Based Statcom

Transcription

1 Mitigation of Harmonic by Hyterei Control Technique of S Baed Statcom Srikanth D Aitant Profeor Department of Electrical and Electronic Engineering ignan ntitute of Technology and Science, ignan Hill Dehmukhi illage, Pochampally Mandal, Nalgonda Ditrict L Bhanu Ganeh Aitant Profeor Department of Electrical and Electronic Engineering ignan ntitute of Technology and Science, ignan Hill Dehmukhi illage, Pochampally Mandal, Nalgonda Ditrict Abtract- Modern indutrial equipment are more enitive to thee power quality problem than before and need higher quality of electrical power. Power electronic baed power proceing offer higher efficiency, compact ize and better controllability. But on the flip ide, due to witching action, thee ytem behave a non-linear load. Thi create power quality problem uch a voltage Sag/Swell, flicker; harmonic, aymmetric of voltage have become increaingly eriou. At the ame time, modern indutrial equipment are more enitive to thee power quality problem than before and need higher quality of electrical power. Thi paper mainly deal with hunt active power filter which ha been widely ued for harmonic elimination. Active power filter which ha been ued here monitor the load current contantly and continuouly adapt to the change in load harmonic. The performance of three phae hunt active power filter uing three phae two phae tranformation with P and Hyterei current controller i explained in thi paper. Keyword Active power filter (APF), compoite load, harmonic compenation, linear and non linear load, reactive power, Power Quality, Harmonic, and oltage Source nverter.. NTRODUCTON The growing ue of non-linear and time-varying load ha led to ditortion of voltage and current waveform and increaed reactive power demand in ac main. Harmonic ditortion i known to be ource of everal problem, uch a increaed power loe, exceive heating in rotating machinery, and harmonic reonance in the utility, ignificant interference with communication circuit, flicker and audible noie, incorrect operation of enitive load. Until now, to filter thee harmonic and to compenate reactive power at factory level, only capacitor and paive filter were ued. More, new PWM baed converter for motor control are able to provide almot unity power factor operation. Thi ituation lead to two obervation: on one hand, there i electronic equipment which generate harmonic and, on the other hand, there i unity power factor motor drive ytem which doen't need power factor correction capacitor. Alo, we cannot depend on thi capacitor to filter out thoe harmonic. Thi i one of the reaon that the reearch i being done in the area of Active Power Filter (APF) and le pollutant drive. Load, uch a, diode bridge rectifier or a thyritor bridge feeding a highly inductive load, preenting themelve a current ource at point of common coupling (PCC), can be effectively compenated by connecting an APF in hunt with the load. The ytem configuration under conideration i dicued in chapter. The propoed control technique baed on Hyterei controller pule generation i explained in chapter. A SMPOWERSYSTEM (SPS) Matlab/Simulink model baed on propoed control trategy i given in the chapter. The imulation reult are dicued in chapter. The concluion of the PAPER i ummarized in chapter. ol. 2 ue 1 January SSN: X

2 . SYSTEM CONFGURATON UNDER CONSDERATON Figure 1 Block diagram of APF n a modern power ytem, the growing ue of non-linear load and time-varying load are increaing. Thee nonlinear load may caue poor power factor, high degree of harmonic and ditortion of current and voltage waveform. Thee problem are olved by uing APF. By implementing thee for power conditioning, it provide function uch a reactive power compenation, harmonic compenation, negative-equence current or voltage compenation and voltage regulation. The main purpoe of the APF intallation by individual conumer i to compenate current harmonic or current imbalance of their own harmonic-producing load. Beide that, the purpoe of the APF intallation by the utilitie i to compenate for voltage imbalance or provide harmonic damping factor to the power ditribution ytem. Figure 3.1 how the baic APF block diagram including non-linear load on three-phae upply condition. APF coniting of S and a dc capacitor have been reearched and developed for improving the power factor and tability of tranmiion ytem. APF have the ability to adjut the amplitude of the yntheized ac voltage or current of the inverter by mean of pule width modulation or by control of dc-link voltage, thu by drawing either leading or lagging reactive power from the upply. APF i an up-to-date olution to power quality problem. Normally, APF can be claified into hunt and erie. Both are deigned to compenate for reactive power or harmonic. APF conit of an inverter with witching control circuit. The inverter of the APF will generate the deired compenating harmonic baed on the witching gate provided by the controller. The APF inject an equalbut-oppoite ditortion harmonic back into the power line and cancel with the original ditorted harmonic on the line. Figure 3.1 how the baic idea for the compenation principle of an APF, and Figure 3.2 how the baic idea of operation of APF for a diode rectifier. The harmonic current compenation by the APF i controlled in a cloed loop manner. The APF will draw and inject the compenating current, i f to the line baed on the change of the load in the power upply ytem. The upply line current, i i decribed by the following equation 1 i i i (1) f l The line current, i i haped to be inuoidal by adding the compenating current, i f into the ditorted load current, i l. The problem of thi APF i the uitable deign for the controller and the filter configuration. Traditionally, it control technique were motly uing Pule Width Modulation (PWM) technique. However, before developing the controller, the configuration of the APF ued in the deign ha to be defined. ol. 2 ue 1 January SSN: X

3 Figure 2 Principle of operation of an APF compenating a diode rectifier Figure 3.3 how the baic compenation principle of hunt active power filter. A voltage ource inverter (S) i ued a the hunt active power filter [1]. Thi i controlled to generate a current wave uch that it compenate by cancelling out the nonlinear current waveform generated by load i.e. thi active power filter (APF) generate the nonlinearitie oppoite to the load nonlinearitie. Figure 3.4 how the different waveform i.e. the load current, deired ource current and the compenating current injected by the hunt active power filter which contain all the harmonic, to make the ource current purely inuoidal. Thi i the baic principle of hunt active power filter to eliminate the current harmonic and to compenate the reactive power. Figure 3 Baic Compenation Technique ol. 2 ue 1 January SSN: X

4 Total intantaneou power drawn by the nonlinear load can be repreented a:- P L (t) = P F (t) + P R (t) + P H (t) (2) Where f, r, h tand for fundamental, reactive, and harmonic content. Real power upplied by the ource P = P f (3) Reactive power upplied by the ource Q = 0 (4) Real power drawn by the load P L = P f + P h (5) Reactive power drawn by the load Q L = Q f + Q h (6) Real power upplied by the APF P C = P h P Lo (7) Reactive power upplied by APF Q C = Q f + Q h (8) Where P Lo i the lo component of the APF From the ingle line diagram S (t) = L (t) + C (t) (9) The utility voltage i given by S (t) = m Sin(t) (10) The load current will have a fundamental component and the harmonic component which can be repreented a L ( t ) n 1 n Sin ( n t n ) (11) L ( t ) 1 Sin ( t 1) nsin ( n t n ) (12) n 2 ntantaneou load power PL (t) can be expreed a P L ( t ) S ( t ) L ( t ) (13) P P L L ( t ) ( t ) P L( t) m m Sin t Sin t ( 1 Sin ( t 1) m Sin t nsin ( n t n ) n 2 1 Sin t co 1 1 co tsin 1) m Sin t nsin ( n t n ) n 2 2 m 1 Sin t co 1 m 1Sin t co tsin 1 msin t nsin ( nt n) n 2 (15) P L (t) = P F (t) + P R (t) + P H (t) (16) P L (t) = P F (t) + P C (t) (17) (14) Figure 4 Waveform for the actual load current, deired ource current and the compenating current Where, the term P F (t) i the real power (fundamental), the term P R (t) repreent the reactive power and the term P H (t) repreent the harmonic power drawn by the load. For ideal compenation only the real power (fundamental) hould by upplied by the ource while all other power component (reactive and the harmonic) hould by the active power filter i.e. P C (t) = P R (t) + P H (t) be upplied P ( t) 1Sin wt co 2 R m 1 (18) ol. 2 ue 1 January SSN: X

5 P ( t ) ( t ) ( t ) R S S (19) i.e. S ( t ) P R ( t ) / S ( t ) (20) Sin ( t ) (21) m m ince, there are ome witching loe in the inverter. Therefore, the utility 1Co Where, 1 mut upply a mall overhead for capacitor leaking and inverter witching loe in addition to the real power of load. Hence, total peak current upplied by the ource max m SL (22) f active power filter provide the total reactive and harmonic power, then S (t) will be in phae with the utility and pure inuoidal. At thi time, the active filter mut provide the following compenation current: S (t) = L (t) + C (t) (23) Hence, the accurate value of the intantaneou current upplied by the ource, ( t ) max Sin ( t ). The peak value of the reference current max can be etimated by controlling the DC link voltage. The ideal compenation require the main current to be inuoidal and in phae with the ource voltage irrepective of load current nature. Hence, the deired ource current after compenation can be given a * t) Sin ( t) (24) a ( max * ( max a t) Sin ( t 2 / 3) (25) * ( max a t ) Sin ( t 4 / 3 ) (26) Where, max m SL i the amplitude of the deired ource current o, thee current are taken a the reference current for the hunt APF.. THE PROPOSED CONTROL TECHNQUE The STATCOM ha received widepread application thee year. Among which, the tranformer le cacaded multilevel converter baed configuration ha excellent performance. For example, the converter do not need high voltage tre witche, and produce few harmonic. Thi type STATCOM need many power cell, which are compoed by two level full bridge and one DC capacitor. The capacitor voltage varie in the duration of charge or dicharge proce, and becaue of the dicrete characteritic of thee device, the capacitor voltage cannot retain ymmetry, which deteriorate the STATCOM performance and ome witche hould endure higher voltage than other, which doe harm to thee witche and generate evere fault. There are two clae of unbalance capacitor voltage. The three phae current that flow into/out the capacitor could not be ideally ymmetry, o the three phae DC voltage are aymmetry. Moreover, when the cacaded converter are working, ome cell produce zero voltage, o their DC voltage keep contant, meanwhile other cell produce ±E voltage, o thee capacitor are in charge/dicharge tate. Obviouly the different working condition hould reult in the unbalance capacitor voltage of one ingle phae. To avoid thee problem, a great number of method for capacitor voltage balance are propoed. Some paper adjut the phae angle of the STATCOM output voltage, but thi method need complex modulation. t preented one imaginary d-q decoupled control method to equilibrate the three phae voltage. Some reearcher propoed voltage balance control trategy for ingle phae, and they ue current loop or PWM adjuting method to regulate each capacitor voltage. However, thee method do not conider thee two type unbalance problem together. Thi project preented one current control trategy to maintain all capacitor voltage equilibrium, and it include three tage. The decoupled control i implemented to adjuting the active and reactive power of the STATCOM, which directly control the current with fat repone. The q-axi current controller regulate the reactive power, o it doe le influence on the DC voltage. On the other ide, the d-axi current controller regulate the active power retored in STATCOM, which lead DC capacitor to charge or dicharge. The DC voltage loop generate the reference active current and the current loop produce the reference voltage for converter. One voltage angle adjuting method i propoed to balance the three phae voltage, which regulate the power retored in each phae capacitor lightly. The theory analyi diplay that the angle between the ource and the converter voltage ha greatly influence on the charge/dicharge proce. So the angle i regulated eparately for different phae to balance S ol. 2 ue 1 January SSN: X

6 the three phae voltage. To balance the capacitor voltage in each ingle phae, one imple PWM baed method i introduced. Thi method doe not modify the reference voltage of each cell but exchange the power cell output, and the converter could generate the ame voltage determined by the decouple control and phae balance control. But when the current i mall, becaue the energy exchange i under low level, the balancing proce i too low. One new current control i deigned to peed up the equilibrium proce, which increae the reactive current to enlarge the current meanwhile to avoid influencing the dc voltage. Thi chapter decribe how STATCOM i operated in hyterei control mode to regulate the load reactive power and eliminate harmonic from the upply current. Mainly deign include capacitor, Hyterei controller baed P controller. [6-7] 3.1 DESGN OF CAPACTOR The reference value of the capacitor voltage dc ref i elected mainly on the bai of reactive power compenation capability. For atifactory operation the magnitude of dc ref hould be higher than the magnitude of the ource voltage S. By uitable operation of witche a voltage S having fundamental component C1 i generated at the ac ide of the inverter. Thi reult in flow of fundamental frequency component 1, a hown in Figure 3.1. The phaor diagram for c1 > S repreenting the reactive power flow i alo hown in thi Figure. n thi 1 repreent fundamental component. c1 c1 c1 1 (27) L f L f c1 Q Q Q L c C 1 L 1 3 S C 1 (28) c1 C1 QL1 3 S 1 f 1 dc = 2 2 c 1 (30) (29) Figure 3.1 Single line and vector diagram for STATCOM 3.2 AXES TRANSFORMATON Conider a ymmetrical three-phae Supply with tationary a-b-c axe at 2/3-angle apart, a hown. Our goal i to tranform the three-phae tationary reference frame (a ~ b ~ c) variable into two-phae tationary reference frame (d ~q ) variable and then tranform thee to ynchronouly rotating reference frame (d e ~q e ), and vice-vera. Figure 3.2 Stationary frame a~b~c to d ~q axe tranformation ol. 2 ue 1 January SSN: X

7 Aume that the d ~q Axe are oriented at angle, a hown in Figure 3.2. The voltage reolved into a ~ b ~ c component and can be repreented in the matrix form a a co in 1 q 0 0 b = co( 120 ) in( 120 ) 1 d 0 0 c co( 120 ) in( 120 ) 1 o The correponding invere relation i 0 0 q co co( 120 ) co( 120 ) a d = 3 in in( 120 ) in( 120 ) b o c d and q can be The correponding Matlab Simulik model i a hown in Figure 3.3 Where S o i added a the zero equence component, which may or may not be preent. We have conidered voltage a the variable. The current and flux linkage can be tranformed by imilar equation. t i convenient to et = 0, o that the q axi i aligned with the a-axi. gnoring the zero equence component, the tranformation relation can be implified a a q (33) (31) (32) b 1 3 q (34) d 2 2 c And inverely q d 1 3 q (35) d a 1 3 b 1 3 c a 1 1 b c (37) 3 3 (36) 3.3 DESGN OF P CONTROLLER The controller ued i the dicrete P controller that take in the reference voltage and the actual voltage and give the maximum value of the reference current depending on the error in the reference and the actual value [8]. The mathematical equation for the dicrete P controller are: The voltage error (n) i given a: (n) = *(n) (n) (38) The output of the P controller at the nth intant i given a: (n) = (n-1) + K p [ (n) (n-1)] + K i (n) (39) When the DC link voltage i ened and compared with the reference capacitor voltage, to etimate the reference current, the compenated ource current will alo have ixth harmonic ditortion for three-phae ytem and econd harmonic ditortion for ingle phae ytem. A low pa filter i generally ued to filter thee ripple which introduce a finite delay and affect the tranient repone. To avoid the ue of thi low pa filter the capacitor voltage i ampled at the zero croing of the ource voltage. ol. 2 ue 1 January SSN: X

8 Figure 3.3 Matlab Simulink Model of three phae two phae axe tranformation Figure 3.4 Matlab Simulink Model of three phae two phae axe tranformation Figure 3.5 Cloed loop Schematic block diagram of STATCOM 3.4 HYSTERESS CONTROLLER With the hyterei control, limit band are et on either ide of a ignal repreenting the deired output waveform [8].The inverter witche are operated a the generated ignal within limit. The control circuit generate the ine reference ignal wave of deired magnitude and frequency, and it i compared with the actual ignal. A the ignal exceed a precribed hyterei band, the upper witch in the half-bridge i turned OFF and the lower witch i turned ON. A the ignal croe the lower limit, the lower witch i turned OFF and the upper witch i turned ON. The actual ignal wave i thu forced to track the ine reference wave within the hyterei band limit. ol. 2 ue 1 January SSN: X

9 A controlled current inverter i required to generate thi compenating current. Hyterei current control i a method of controlling a voltage ource inverter o that an output current i generated which follow a reference current waveform. Thi method control the witche in an inverter aynchronouly to ramp the current through an inductor up and down o that it track a reference current ignal. Hyterei current control i the eaiet control method to implement. 3.5 PULSE GENERATON A hyterei current controller i implemented with a cloed loop control ytem and i hown in diagrammatic form in Figure 3.6 An error ignal, e(t), i ued to control the witche in an inverter. Thi error i the difference between the deired current, ref (t), and the current being injected by the inverter, actual (t). When the error reache an upper limit, the tranitor are witched to force the current down. When the error reache a lower limit the current i forced to increae. The minimum and maximum value of the error ignal are e min and e max repectively. Figure 3.6 Baic principle of hyterei controller Figure 3.7 Pule generation diagram Figure 3.6 block diagram the range of the error ignal, e max e min, directly control the amount of ripple in the output current from the inverter and thi i called the Hyterei Band. The hyterei limit, e min and e max, relate directly to an offet from the reference ignal and are referred to a the Lower Hyterei Limit and the Upper Hyterei Limit. The current i forced to tay within thee limit even while the reference current i changing. So thee witching ol. 2 ue 1 January SSN: X

10 pule S1, S2, S3, S4, S5 and S6 are given to the voltage ource inverter that will produce harmonic current to compenate the harmonic current produced by non linear load. Pule generation i main and important part of thi technique. Here we have ued hyterei technique for witching. The actual current and the reference current are given to the ummer and it i given to the combination of relay to limit the extent of fault current and NOT gate to produce 6 pule for the STATCOM uing AND gate in a uitable manner and a tep ignal i given to the AND gate to differentiate the change in current waveform before and after the control technique Figure 3.7 how the pule generation diagram. SMULATON MODEL The imulation model of propoed technique i hown in Figure 4.1. Firt the capacitor voltage i ened which i compared with the reference voltage and the error ignal i given to the P controller for proceing to obtain the maximum value ( m ) of the reference current [9-10]. Thi ignal i now delayed by for getting the reference current for phae b, which i further delayed by to get the reference current for the phae c. thee reference current are now compared with the actual ource current and the error i proceed in the hyterei controller to generate the firing pule for the witche of the inverter. The active filter doe not need to provide any real power to cancel harmonic current from the load. The harmonic current to be cancelled how up a reactive power. Reduction in the harmonic voltage ditortion occur becaue the harmonic current flowing through the ource impedance are reduced. Therefore, the dc capacitor and the filter component mut be rated baed on the reactive power aociated with the harmonic to be cancelled and on the actual current waveform (rm and peak current magnitude) that mut be generated to achieve the cancellation. The inverter in the Shunt Active Power filter i a bilateral converter and it i controlled in the current Regulated mode i.e. the witching of the inverter i done in uch a way that it deliver a current which i equal to the et value of ol. 2 ue 1 January SSN: X

11 current in the current control loop. Thu the baic principle of Shunt Active Filter i that it generate a current equal and oppoite to the harmonic current drawn by the load and inject it to the point of coupling there by forcing the ource current to be pure inuoidal. Thi type of Shunt Active Power Filter i called the Current njection Type APF. SMULATON RESULTS Figure 5.1 how the upply voltage, upply current and injected current wave form of the line current before the hunt current and after the hunt current injection. The overall imulation run time i 0.2 ec. the control trategy i tarted after 0.1 ec. After 0.1 ec the P controller acted to ettle the reference DC link voltage and current from the hunt converter injected to make the upply current inuoidal. t i oberved that after the control trategy tarted the wave hape of the line current at the input ide i improved in term of the harmonic ditortion. t i alo oberved that the upply voltage doe not get affected. Figure 5.2 how the Load voltage and current remain unaffected throughout the operation. Figure 5.7 how the current on the main line ide before injection and frequency contain in it. Fat Fourier Tranformation (FFT) analyi of the ame current i carried out and the Total Harmonic Ditortion (THD) in thi cae i 28.93%. Figure 5.8 how the current on the main line ide after injection and frequency contain in it. FFT analyi of the ame current i carried out the THD in thi cae i 3.97% for R Load. oltage (olt) Figure 5.1 Supply voltage waveform Time (ec) Simulation reult for R Load: Figure 6.3 how the output voltage waveform and output current for R load. On X-axi time i taken and on Y- axi oltage and Current are taken. Scale: On X-axi 1 unit = 0.02ec On Y-axi 1 unit = 100 On Y-axi 1 unit = 10A ol. 2 ue 1 January SSN: X

12 oltage (olt) Figure 5.2 (a) Load voltage Time (ec) Current (Amp) Figure 5.2 (b) Load current Time (ec) Figure 5.3 how the waveform of the ource current before and after control for each phae with a tep ignal at 0.1 ec. Current (Amp) Figure 5.3 ource current before and after control for each phae Time (ec) Figure 5.4 how the waveform of the ource current before and after control for all the three phae with a tep ignal at 0.1 ec. ol. 2 ue 1 January SSN: X

13 Current (Amp) Time (ec) Figure 5.4 ource current before and after control for all the three phae. Figure 5.5 how the waveform of the injected current before and after control for each phae with a tep ignal at 0.1 ec. Current (Amp) Figure 5.5 njected current before and after control for each phae. Time (ec) Figure 5.6 how the waveform of the injected current before and after control for all the three phae with a tep ignal at 0.1 ec. Current (Amp) Figure 5.6 njected current before and after control for all the three phae. Time (ec) ol. 2 ue 1 January SSN: X

14 Figure 5.7 Show the FFT Analyi of the ource actual load current before control for 2 cycle by taking the following parameter. n FFT window: Start time=0.14ec Number of cycle = 2 Fundamental Frequency = 50Hz n FFT Setting: Diplay tyle= Bar (relative to fundamental. Frequency axi = Harmonic order Maximum Frequency (Hz) = 1000 Hz Figure 5.7 FFT analyi of upply current before control Figure 5.8 Show the FFT Analyi of the ource actual load current after control for 2 cycle by taking the following parameter. n FFT window: Start time=0.14ec Number of cycle = 2 Fundamental Frequency = 50Hz n FFT Setting: Diplay tyle= Bar (relative to fundamental. Frequency axi = Harmonic order Maximum Frequency (Hz) = 1000 Hz ol. 2 ue 1 January SSN: X

15 Figure 5.8 FFT Analyi of upply current after uing STATCOM.CONCLUSON An extenive review of AF ha been preented to provide a clear perpective on variou apect of the AF to the reearcher and engineer working in thi field. The ubtantial increae in the ue of olid-tate power control reult in harmonic pollution above the tolerable limit. The utilitie in the long run will induce the conumer with nonlinear load to ue the AF for maintaining the power quality at acceptable level. A large number of AF configuration are available to compenate harmonic current, reactive power, neutral current, unbalance current, and harmonic. The conumer can elect the AF with the required feature. Static compenation (STATCOM) get more popular a the flexible AC tranmiion (FACTS) device increae. The tranformer-le STATCOM ha low cot and concentrate the reearch interet; however, the capacitor voltage unbalance problem will deteriorate it performance with more harmonic and over current/voltage fault.a very imple hyterei current controller baed control technique with help of intantaneou power theory i propoed for STATCOM. A MATLAB/Simulink baed model ha been imulated. Simulation reult how the input current harmonic produced by nonlinear load i reduced after uing the control trategy. FFT analyi how the reduction in THD i remarkable. REFERENCES [1] Undertanding FACTS: Concept and Technology of Flexible AC Tranmiion Sytem. Narain G. Hingorani, Lazlo Gyugyi. Wiley EEE pre. [2] A Few Apect of Power Quality mprovement Uing Shunt Active Power Filter -C.Nalini Kiran, Subhranu Sekhar Dah, S.Prema Latha. nternational Journal of Scientific & Engineering Reearch olume 2, ue 5, May-2011, SSN [3] Wang Jianze, Peng Fenghua, Wu Quitao, Ji Yanchao, A novel control method for hunt active power filter uing vpwm, EEE Tran. on ndutry application, vol.1, 3-7 Oct, 2004, pp [4] L. Maleani, L. Roetto, and P. Tenti, Active filter for reactive power, harmonic compenation, in Proc. EEE PESC 86, 1986, pp [5] Y. Hayahi, N. Sato, and K. Takahahi, A novel control of a current ource active filter for AC power ytem harmonic compenation, in Conf. Rec. EEE-AS Annu. Meeting, 1988, pp [6] Amit Jain, Ned Mohan, Karan Johi and Aman Behal "oltage Regulation with STATCOMS:Modeling,Control and Reult." EEE Tranaction on Power Delivery, ol 21, NO. 2, April 2006 PP [7] Yaden Li and Bin Wu A Novel DC oltage Detection Technique in the CHB nverter baed STATCOM EEE Tranaction on Power Delivery, ol. 23, NO. 4, July 2008 PP [8] Yahomani Y. Kolhatkar, and Shyama P. Da, Experimental nvetigation of a Single-Phae UPQC With Minimum A Loading EEE Tranaction on Power Delivery, ol. 22, NO. 1, January 2007 PP [9] Y.Kolhatkar, P.A.Agraval, A.O.Barry and T.D.Nguyen,; A imple New Control Technique for Unified Power Quality conditioner (UPQC), The 11 th nternational Conference on Harmonic and Quality of Power [10] Ronny Sternberger and Dragan Jovic Analytical modelling of a quare-wave controlled cacade Multilevel STATCOM EEE Tranaction on Power Delivery, ol. 24, NO. 4, October 2009 PP [11] Singh.B, Al-Haddad.K, Chandra.A, Review of active filter for power quality improvement, EEE Tran. nd. Electron., (46), 5, Oct, 1999, pp [12] [13] P. Enjeti, W. Shireen, P. Packebuh, and. Pitel, Analyi, deign of a new active power filter to cancel neutral current harmonic in threephae four-wire electric ditribution ytem, in Conf. Rec. EEE-AS Annu. Meeting, 1993, pp [14] A Novel Hyterei Control Technique of S Baed STATCOM R.A.Kantaria1, Student Member, EEE, S.K.Johi, K.R.Siddhapura /11/$ EEE ol. 2 ue 1 January SSN: X