ANALYTICAL DESIGN AND SIMULATION OF A STATCOM FOR COMPENSATING OF REACTIVE POWER CONNECTED TO NON- LINEAR LOADS IN POWER SYSTEMS

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1 Internatonal Journal of Electrcal Engneerng & Technology (IJEET) Volume 9, Issue, March- Aprl 08, pp , Artcle ID: IJEET_09_0_0 Avalable onlne at ISSN Prnt: and ISSN Onlne: Journal Impact Factor (06): 8.89 (Calculated by GISI) IAEME Publcaton ANALYTICAL DESIGN AND SIMULATION OF A STATCOM FOR COMPENSATING OF REACTIVE POWER CONNECTED TO NON- LINEAR LOADS IN POWER SYSTEMS J.K. Moharana Department of Electrcal & Electroncs Engneerng, HIT, BBSR, Odsha ABSTRACT The majorty of reactve power s produced by the Reactve Loads n dstrbuton system and transmsson system. To ncrease the reactve power n dstrbuton system, t generates low Power Factor Currents at the Reactve loads. Therefore, STATCOM helps to control the Reactve Power and elmnates the Total Harmonc Dstorton drawn from lnear loads and Non-Lnear Loads. Ths paper presence the 5-Level CMC-STATCOM wth a modular structure, and t has man applcatons n both transmsson system and dstrbuton system. The Applcaton pont of vew STATCOM has many advantages as compared wth the other knds of FACTS famly. The mathematcal model of man topology, the States Feedback Decoupled Reactve Power Control Strategy s based on the p-q co-ordnate system, together wth the generatng PWM Modulaton Waveform of Carrer Phase Shft PWM and Carrer Level Shfted PWM modulaton method n CMCSTATCOM. To gve the stable operaton of the system Dc bus voltage s a key factor. To acheve a DC bus voltage overall control and ndvdual control of each cascaded module applyng closed loop P-I control method s used. Fnally, the smulaton results of KV, -MVA 5-Level CMC STATCOM verfy the correctness and effectveness of the control strategy and modulaton method n ths paper usng MATLAB/SIMULINK Software. Keywords: FACTS, VSI, STATCOM, lnear model and Cte ths Artcle: J.K.Moharana, Analytcal Desgn and Smulaton of a Statcom for Compensatng of Reactve Power Connected to Non-Lnear Loads n Power Systems: Internatonal Journal of Electrcal Engneerng & Technology, 9(), 08, pp INTRODUCTION Generally speakng, deally, the electrcal power suppler supples balanced snusodal current and voltage to the consumers. The consumers use both lnear and non-lnear loads. Hence, consumer gets dstorted current and voltage as well as low power factor. The current dstorton and low power factor are caused by non-lnear loads only [-5] as gven n Fg.. THD 98 edtor@aeme.com

2 J.K.Moharana Generally, these non-lnear loads draw non-snusodal current. The non-snusodal current generates harmoncs, reactve power and excess neutral current along wth makng unbalance loadng of the suppler. Power system engneer, who must antcpate and mtgate problems that arse due to the harmoncs, they need methods of predctng the harmonc mpart of new power electronc equpment. STATc synchronous Compensator (STATCOM) has been appled to regulate bus voltage as well as to provde reactve power for mprovement of the power factor and to flter the harmoncs n dstrbuton and transmsson systems. So, t s used as actve power flter (APF) [6-]. Varous STATCOM controllers wth nner current regulator loop have been developed to acheve fast control of the STATCOM. In the lterature, two typcal control schemes have been proposed for the STATCOM []. In the phase angle, α control scheme [], only the phase angle α s employed as the control varable. However, modulaton ndex (MI) s held constant to avod negatve mpact on harmoncs []. However, rapd adjustments n the reactve power output of the STATCOM cannot be acheved by the lnear α control []. Snce reactve power s less senstve to phase angle than the voltage magntude of the grd and the STATCOM converter termnal [, ]. Fgure Lnear and non-lnear load connected to grd supply To mprove the response speed of the reactve power output, a non-lnear controller that s able to acheve wde-range of the phase angle control has been proposed []. The non-lnear phase angle controller n [] s employed the DC-lnk capactor voltage and ts reference value, wth reactve current and ts reference value as the controller nputs. It may be noted that reactve current was employed as one of the controller nputs snce t s related to the STATCOM reactve power output. The modulaton ndex cannot be adjusted n the phase angle control schemes, as the STATCOM converter termnal voltage and reactve power cannot be modulated rapdly untl the DC-lnk capactor voltage s charged or dscharged to a new level. Ths lmts the response speed of the phase angle control scheme. To mprove the response speed of the STATCOM converter termnal voltage and reactve power, a control scheme, n whch both the modulaton ndex and phase angle are controlled, has been proposed []. However, ths scheme s not favored snce the varable modulaton ndex mght have a negatve mpact on harmonc contents. In ths work, a modfed (as reported n []) control scheme wth constant DC-lnk capactor voltage reference for the STATCOM s proposed. The contents of ths paper are as follows: Frst, the mathematcal model of the STATCOM and non-lnear load are presented. Then, archtecture of the proposed controllers s descrbed. A systematc procedure for the desgn of the current regulators and the DC-lnk voltage controller s gven. To avod the overshoot and oscllatory response n the current regulator loop, pole-zero cancellaton technque s employed to get a frst order system n the current regulator loop. In addton, root-locus method s employed n the desgn of the DC-lnk 99 edtor@aeme.com

3 Analytcal Desgn and Smulaton of a Statcom for Compensatng of Reactve Power Connected to Non-Lnear Loads n Power Systems voltage controller. Hgh pass flter technque s adopted for extractng hgh order harmoncs from actve component of the load current. Fnally, smulaton and expermental results are presented to demonstrate the steady state and transent performance of the STATCOM wth the proposed STATCOM strategy.. SYSTEM MODEL Fgure Smplfed man crcut dagram of the STATCOM The schematc dagram of the STATCOM s shown n Fg.. The prmary modellng of the STATCOM has been presented by the authors [4-8] usng d q transformaton. The - phase grd voltage,, laggng wth the phase angle dfference α to the STATCOM v s, abc converter termnal phase voltage, v o, abc, can be expressed as v s, abc v sa ( t ) ( t ) = v ( ) = sb t v sc ( t ) sn( ω t α ) π V s sn( ω t α ) π sn( ω t + α ) A swtchng functon S or STATCOM output termnal voltage can be defned as follows sn( ωt) S a π S = S b = m c sn( ωt ) S b π sn( ωt + ) The modulaton ndex, beng constant for a programmed PWM, s gven by, vo, peak MI = m = = mc v where mc s called modulaton converson ndex and the complete mathematcal model of the STATCOM n d q reference frame s obtaned as gven: 00 edtor@aeme.com

4 J.K.Moharana R m s c ω L L s s cosα d cd R cd s V s = ω 0 + snα 4 cq cq dt L L v ( ) s v s 0 t m c 0 0 C The actve and reactve powers njected/drawn by the STATCOM are expressed n () and (4) respectvely. p c = V s cd cosα + V s cd sn α 5 qc = V s cd cosα V s cq snα 6 The parameters of the STATCOM systems are gven as: V s = 45V, f R s =.0Ω, L s = f = 50H z, ω = 4rad / sec, = 5.44mH, C = 680µ F, m = 0.866,.0, m c = 0.979,., R l = Ω, L l = 60mH (.6Ω) The detals of the steady state and transent responses of the STATCOM open-loop system are gven n [4-8]. The open-loop steady state and transent responses of the reactve current and the reactve VAR of the STATCOM due to a step change n α n capactve mode of operaton have moderate ampltudes of the transents. These are however less than the steady state value and settle after two and a half power cycles. The hgh transent magntude of cq of the STATCOM unnecessarly ncreases the ratngs of the STATCOM devces. These calculatons are based on the bass of the mathematcal model of the STATCOM. The practcal STATCOM ratngs wll be lmted by the choce of the swtchng devces (IGBT of SEMIKRON make of part no.skm75gbd) and the rpple current, the average current and the voltage ratngs of the DC-lnk capactor as also the current ratng of the ac sde reactor. The above values are actually out of range for our lab set-up.. MODELLING OF THE NON-LINEAR LOADS A three-phase non-lnear load ( φ dode brdge rectfer wth R-L load (level current)) s connected to the grd voltage at pont of common connecton (PCC). It can be shown through smple dervatons that the fundamental power factor (dsplacement factor) s unty always n such case [9]. Over and above there wll be presence of 6 n ± harmoncs component. Wth respect to a synchronously rotatng frame ( d q), both 6 n ± components wll appear as 6 n. Takng the STATCOM converter termnal phase voltage as reference (statonary frame), the load currents can be expressed as gven n equaton (7). v o, abc la = lb lc I ( ) ( ) l snωt α + I l5 snωt α φ π π I sn + sn l ωt α I l5 ωt α φ π π I sn + + sn l ωt α I 5 ωt α φ l edtor@aeme.com

5 Analytcal Desgn and Smulaton of a Statcom for Compensatng of Reactve Power Connected to Non-Lnear Loads n Power Systems Followng usual abc αβ converson, equaton (7) may be rewrtten n (8) and n d q reference frame t s agan gven n (9) l l α β = 0 la lb lc 8 ld lq = sn( ωt) cos( ωt) 9a lα lβ = cos( ωt) sn( ωt) 9b lα + lβ The actve and reactve components of the load current wth ther harmonc are gven as follows: ld = l cos( 6ωt + β5 + 7) + + cos( ω t + β + ) +.. 0a lq = sn( 6ωt + β5 + 7) + + sn( ω t + β + ) b The actve and reactve VAR of the non-lnear load s gven p ( ) v v l t sd sq ld = q vsq vsdlq l The non-lnear load (dode rectfer) connected to the grd (wth the STATCOM system parameters) s smulated. The grd phase-a voltage and current before operaton of the STATCOM s shown n Fg. (a). It may be noted that here and elsewhere (unless otherwse mentoned) the voltage s plotted to a reduced scale of 5:. The peak magntude of the grd phase-a current s about 4A (load sde DC current of 4A). The harmonc spectrum of the grd phase-a current of about 6.5A of fundamental wth THD =0.07=.07% shown n Fg. (b) (a) (b) Fgure Responses of non-lnear load (-phase dode) before the operaton of the STATCOM: (a) Grd phase-a voltage, v sa and current, sa and (b) harmonc spectrum of the grd phase-a, sa Reducton of the grd current harmoncs s needed n order to comply wth the nternatonal standards [9]. Ths s commonly referred to as the Power Factor Improvement (PFI), whch can be expressed as: PF V s I s cosφ = V s I s = K p cosφ 0 edtor@aeme.com

6 J.K.Moharana where, V s, I s and I s are RMS value of the grd voltage, current and ts fundamental component respectvely. I p = p I s s The factor, K [ 0,] K s a measure of the harmonc content of the current and cos φ s the dsplacement factor. Hence, PF depends on both the harmonc content and the dsplacement factor. K s related to the total harmonc dstorton ( THD ) of the current as gven n equaton (). K p + THD p = The total harmonc dstorton of the current s expressed as THD I sn n= = 4 I s where, I sn s the harmonc components of the grd supply current. In case of dode rectfer wth resstve or hghly nductve load, fundamental RMS current and true RMS current are gven n equatons (5) and (6). 6 I, rms I = I = π 6 I rms I = 0. 86I = 7 It s commonly known that the dsplacement factor, K p and THD are, and 0. respectvely for a -phase dode rectfer feedng a level current load. So, load power remanng constant for the level current case, decreasng of the harmonc content s the key to decrease THD (as per equaton (4)) and ncreasng of the system power factor (as per equaton ()) wthout affectng the power delvered. Hence, to mantan upf at supply termnals wll thus mean that both cos φ and K p are.0. To mprove K p from to.0 one has to make THD = 0. The STATCOM can perform ths functon and same has been expermentally establshed. In absence of harmoncs t has been seen that the current reference, lq alone s requred to mprove lne power factor to unty. In case of non-lnear load, assumng system/utlty voltage to be free from harmoncs ( v s = v s ) actve power can only be obtaned due to ld correspondng fundamental I s (laggng V s byφ ). If harmonc gets ntroduced n the load current no more actve power s obtaned [Θ P = V s I s cosφ and vs sndt = 0]. But presence of s = s sn harmoncs ncreases true RMS I [ I + I ] and hence also ncreases system ( S ) VA =. Clearly, therefore, the VAR s ncreased. The STATCOM current cq reference must get modfed accordngly to compensate the new Q (due to non- unty dsplacement factor and addtonal VAR due to harmoncs). In other words, the & = +, should be the new reference. As already understood, lq lq d q reference frame s synchronously rotatng wth lqn 0 edtor@aeme.com

7 Analytcal Desgn and Smulaton of a Statcom for Compensatng of Reactve Power Connected to Non-Lnear Loads n Power Systems respect to abc reference frame. A Fourer expanson for the lne current waveform of the dode rectfer consdered here s clearly havng 6 n± harmoncs component wth respect to a synchronously rotatng frame ( d q ), ( 6 n µ ) wll appear as 6 n. Ths nterestngly symmetry may be utlzed to set lqref = lq( prevos) ( DC) + lq(6n) for all n. Also for the level current load at the output of the dode brdge rectfer t can be shown that dsplacement power factor s unty.e. ( DC) = 0. For other cases (non-level current), (DC ) wll have a lq DC value dependng on the fundamental power factor. So long we had never dscussed about ld. Ths s because ld s responsble for actve power. The STATCOM does not supply the same, n prncple. However f one decdes to compensate for the system loses due to harmoncs through the STATCOM then ldref = ld ( 6 n ) has to be set. Hence, for ths purpose proper reference s as below. + * 7 cq = lq lqn * cd = cos( 6ωt + β5 + 7) + + cos( ω t + β + ) Once the above prncple s mplemented, the STATCOM can take care of both the power factor mprovement and fltraton of harmoncs at the grd supply current. 4. CONTROL STRATEGY 0 The lnear model s that model, where the phase angle α ( α = 0 ) and the modulaton ndex m (modulaton converson ndex m c ) may be assumed constant at gven values. The grd voltage and the STATCOM converter termnal voltage are assumed to be n-phase wth each other. 4.. Proposed control strategy lq Fgure 4 Closed loop control strategy The proposed closed-loop control strategy block dagram s gven n Fg.4. Two out of the three phase voltages, two out of the three phase currents of the STATCOM and load are sensed. These sensed two phases quanttes are converted to three-phase quanttes as usual way. These statonary frame varables are transformed to two-phase α β axs and to the d q reference rotatng frame wth unt vectors sn( ωt) and cosω t) [9]. These unt vectors are generated n order to algn the d -axs along the space-phasor of the grd voltage, v s (t), at PCC. The reference vector s algned along the d -axs, whch s acheved by mantanng zero phase dfference between the phase voltage, v sa (t) and the unt vector. The sensed DC-lnk * voltage of the STATCOM s summed wth (proper sgn) wth reference voltage of V and fed to a PI-controller (). Its output and the hgh frequency components of the load current yeld 04 edtor@aeme.com

8 J.K.Moharana the reference to the d -axs controller (sub-block s shown n Fg.). The error s passed through PI-controller of the d -axs current (9), whch generates the controlled d -axs voltage at the STATCOM converter termnal. Ths controlled voltage s summed by the d - axs voltage of the grd and the reactve drop of the ac sde couplng nductor to form STATCOM converter termnal reference d -axs voltage. The PI controller of the q -axs current (9) s fed wth the reference of q -axs current of the load. Ths controller n turn generates the reference q -axs voltage at the STATCOM converter termnal by summng the q -axs voltage of the grd and the actve drop of the ac sde couplng nductor. Hence, the d and q -axes components of the STATCOM converter termnal reference voltages are transformed to α β wth unt vectors. The sx pulses for the swtchng devces of the STATCOM are generated from α β statonary varables and usng Space Vector Pulse Wdth Modulaton (SVPWM) prncple. The scheme s mplemented n software as well as hardware as per the block dagram gven n Fg.5. The above mathematcal relatons of the PIcontrollers are mplemented on DSP TMS0F40 DgCon-40(CDAC make) envronment. The desgnng of the separate three controllers are gven n the next secton. 4.. Desgn of current controller The phase voltages of the three-phase grd, Fgure 5 Closed loop entre system v, and the STATCOM converter termnal voltage, v o, abc at PCC are n-phase wth each other and the PI-controllers for d and q axes current have been desgned [8,0,] as per the block dagram gven n Fg.6 (a). The parameters are gven n equaton (9) s abc (a) (b) Fgure 6 Block dagrams of control loop: (a) current control and (b) DC-lnk voltage control K p = 08.Ω, K = 0 0 Ω. rad / s 9 The values of K p and K for d and q axes current controllers of the STATCOM edtor@aeme.com

9 Analytcal Desgn and Smulaton of a Statcom for Compensatng of Reactve Power Connected to Non-Lnear Loads n Power Systems 4.. Desgn of DC-lnk voltage controller A PI controller needs to be ncorporated to mprove the dynamc performance of STATCOM and for makng the steady state error nv zero. We know (Fg.), v = dt C Applyng Laplace transform to the above equaton wth zero ntal condton, the transfer functon G s found as: pv 0 V G pv ( s) = I sc = The block dagram for closed-loop control of the DC-lnk voltage s shown n Fg.6 (b). It conssts of nner current control loop (replaced by an equvalent gan block of unty snce the current controller has much faster dynamcs. It wll reach steady state much faster and wll not affect voltage control loop dynamcs) and the outer voltage control loop s explctly shown n Fg.6 (b). To mnmze the steady state error of the voltage loop, PI-control s adopted here and also t produces the reference d -axs current for the control of the d -axs current of the STATCOM. The voltage controller has been desgned followng root locus method and cted n equaton (). K pv =.84, Kv = IMPLEMENTATION OF HPF A hgh pass flter (HPF) s used to extract the hgh frequency components of ld of the nonlnear load current and provdes the reference nput for the harmonc current components to be fltered. However a drect mplementaton of an HPF s avoded snce t njects unwanted nose. The standard practce [8] adopted durng mplementaton of an HPF s shown below. The HPF s realzed as per Fg.7 (a), where a low pass flter (LPF) s used along wth an all pass flter. Ths ncreases nose mmunty. The transfer functons of a st, rd and 5 th order LPF wth a cut off frequency of 55 Hz, (usng the desgn f Butterworth flter) are gven n []. The 5 th order LPF wth a cut off frequency of 55Hz s gven n equaton () and ts performance s shown n Fg.7 (b). Due to smplcty and lower order of transfer functon, the rd order LPF s used here. Ths wll be convenent for mplementng on a DSP platform f = s s s s s G (a) (b) Fgure 7 Schematc dagram and output of the d -axs current of non-lnear load from desgned flter: (a) Schematc dagram of Hgh pass flter and (b) Due to 5 th order flter 06 edtor@aeme.com

10 6. SIMULATION RESULT J.K.Moharana The control strategy s smulated n MATLAB software. The waveforms of the grd vsa and sa (at swtch off and on condton of the STATCOM) and sa harmonc spectrum are llustrated n Fg.. The smulated grd vsa and sa (when STATCOM s off and on) are shown n Fgs. (a) and (b) respectvely. It shows rectangular shape of the current waveform of the dode rectfer wthout capactor at the DC output voltage n both cases (smulated and expermentally). It s easy to elmnate the harmoncs. It s very nterestng that the smulated responses of the grd vsa and sa (harmoncs elmnated and var compensated whch mproves power factor) are n full agreement wth each other. The harmonc spectrum of the grd sa (rectfer load phase-a current) n smulaton are plotted n Fgs. (c) and (d) respectvely when STATCOM s off and on. It depcts that both the plots compare remarkably well (as smulaton shows that THD.of the grd sa (load current) s.07% compared to 0.0% gven by experment). There s a close agreement of THD of the grd sa n smulaton (where THD =.05% ) (a) (b) (c) (d) Fgure Smulated traces, when the STATCOM s off and on condton: (a) smulated waveforms for vsa and sa (for.506) off condton (b) smulated vsa and sa (for.506a) on, (c) smulated harmoncs spectrum at the STATCOM s off condton, and (d) smulated at the STATCOM s on state 7. CONCLUSIONS A modfed control strategy wth fxed modulaton ndex and phase angle ( α = 0 ) has been proposed for a STATCOM operatng wth non-lnear load. It s used to provde reactve power compensaton and harmoncs elmnaton. A low pass flter has been desgned for realzaton of hgh pass flter to extract the hgh order harmoncs. The proposed STATCOM strategy has been tested wth -phase dode rectfed load. The performance of the edtor@aeme.com

11 Analytcal Desgn and Smulaton of a Statcom for Compensatng of Reactve Power Connected to Non-Lnear Loads n Power Systems STATCOM system has been found to be satsfactory for mprovement of the power factor and reducton of the harmonc contents of the grd sde current. In addton, the proposed STATCOM controller wth parameters desgned usng the proposed approach has good dynamc responses n the reactve current reference step change testng. The expermental Osclloscope records valdated the smulated waveforms. ACKNOWLEDGMENT The authors would lke to acknowledge the support receved from the All Inda Councl of Techncal Educaton as a part of ths work s an outcome of an AICTE-RPS Project. The support receved from NaMPET project of the DIT, Govt. of Inda, and ther Nodal Agency, C-DAC Thruvanthapuram s also gratefully acknowledges. Very specal thanks are due to M/s Veeral Controls Pvt Ltd., Gandhnagar, for the techncal support receved. The authors are also grateful to Prof. Ajt K. Chattopadhyay, Fellow IEEE, and Emertus Prof., Dept. of EE, Vce-Chancellor, BESU, Shbpur and Head, Dept. of Electrcal Engneerng, BESU, Shbpur for all support receved. REFERENCES [] R.C. Dugan and D.T. Rzy, Harmonc consderatons for Techncal dstrbuton feeders Ouk Rdge, ORNL/sub/8-95, TN78, 988 [] K. Sangsun and P.N. Enjet, A new hybrd actve power flter topology, IEEE Trans.Power Electronc,Vol.7,pp.48-54,Jan.00 [] E.B. akram, R.B. Hanes and A.A. Grgs, Effect of Harmonc Dstorton n Reactve Power Measurement, IEEE Transactons on Industry Applcatons, Vol.8,No.4,pp ,July/August 99. [4] F.Z. Peng, H. Akag and A. Nabae, A study of Actve Power Flters Usng Quad-Seres Voltage-Source PWM Converters for Harmonc compensator, IEEE Transactons on Power Electroncs, Vol. 5,No.,pp. 9-5, January 990. [5] Y.J. Wang, R.M.O Connel and G. Brownfeld, Modelng and Predcton of Dstrbuton System Voltage Dstorton Caused by Non-lnear Resdental loads, IEEE Transactons on Power Delvery, Vol.6,No.4,pp ,October 00. [6] B. Sngh, A. Adya, A.P. Mttal and J.R.P. Gupta, Performance of DSTATCOM wth non-lnear loads for power qualty mprovement, IIT Madras 60006, December, 7-0, pp [7] D. Masand,S.Jan and G. Agnhotr, Control Strateges for Dstrbuton Statc Compensator for Power Qualty mprovement, IETE Journal of Research,Vol.54,No.6,pp.4-48, Nov/Dec 008. [8] B. Ln and Y.C. Lee, Three-Phase Power Qualty Compensator Under the unbalance source and non-lnear loads, IEEE Transactons on Industral Electroncs, Vol.5, No.5, pp , October 004. [9] Power System Harmoncs Causes and Effects of Varable frequency Drves Related to the IEEE Standard, Bulletn No.880PD940, pp.-8, Ralegh, NC, USA, Aug.994. [0] G. Joos, L.T. Moran and P.D. Zogas, Performance Analyss of a PWM Inverter VAR Compensator, IEEE Transactons on Power Electroncs, Vol.6, No., pp.80-9, July 99. [] B.S. Chen and Y.Y. Hsu, A Mnmal Harmonc Controller for a STATCOM, IEEE Transactons on Industral Electroncs, Vol.55, No., pp , February 008. [] A.R. Bergen and V. Vttal, Power System Analyss, nd edton.englewood clffs, NJ, Prentce-hall, edtor@aeme.com

12 J.K.Moharana [] C. Schauder and H. Mehta, Vector analyss and Control of Advanced Statc VAR Compensator, IEE Proceedngs-C, Generaton, Transmsson and Dstrbuton, Vol.40, No.4, pp.99-06, July, 99. [4] J.K. Moharana, M. Sengupta, A. Sengupta Study on an Advanced Statc Var Compensator swtched from a Space Vector PWM nverter-analyss, Smulaton and Comparson wth the conventonal Snusodal PWM case, NPEC00, IITB, pp7-78, 00. [5] J.K. Moharana, M. Sengupta, A. Sengupta Desgn and Smulaton of Current Controller and Voltage Controller for A STATCOM Applcaton, NPEC005, IITKGP, pp-6, 005. [6] J.K. Moharana, M. Sengupta, A. Sengupta Modelng, Analyss and Smulaton of Varous Control Strateges for a 6kVA STATCOM for reactve power compensaton, NPEC-007, IISc, Bangalore, 007. [7] J.K. Moharana, M. Sengupta, A. Sengupta Closed-Loop Control of a lab-scale STATCOM prototype for Reactve Power compensaton, communcated to NPEC-0, BESU, Shbpur, Howrah, West Bengal, 0. [8] J.K. Moharana, Desgn, Analyss and DSP-Based Implementaton of Varous Control Technques on a STATCOM prototype, Thess, publshed at dept. of EE, BESU, Howrah, West Bengal, Inda, May, 0. [9] V. Kaura and V. Blasko, Operaton of a Phase Locked Loop System under Dstorted Utlty Condtons,IEEE Transactons on Industry Applcatons, Vol., No., pp58-6, January 997. [0] M.P. Karzmerkowsk and L. Malesan, Current Control Technques for Three-Phase Voltage-Source PWM Converters: A survey, IEEE Transactons on Industral Electroncs, Vol.45,No. 5, pp ,October 998. [] P.S. Sensarma, Analyss and Development of a Dstrbuton STATCOM for Power Qualty Compensaton Ph.D. thess, Dept of E.E, IISc, Bangalore, 000. [] Desgn of a Butterworth low-pass flter usng sallen and key crcut edtor@aeme.com