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16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 589 Performance Evaluation of Asynchronous Generator Based Islanded Wind Energy Conversion System Shailendra Sharma and Bhim Singh EED, Indian Institute of Technology, Delhi, New Delhi-110016 (India) [email protected], [email protected] Abstract—This paper deals with the performance evaluation of a voltage and frequency controller (VFC) for an isolated asynchronous generator (IAG) based islanded wind energy conversion system (IWECS) feeding three-phase four-wire loads. The control of VFC is based on IcosΦ control algorithm for extraction of reference source currents. The VFC consists of a three leg voltage source converter (VSC) with a battery at its dc bus and a non-isolated star/delta transformer to feed four loads. The VFC is implemented using a digital signal processor. Test results are presented to study the performance capabilities of the proposed VFC for IAG in the wind power generation. Keywords-Asynchronous generator, Battery, Star-delta transformer, Voltage source converter, Wind power generation. C I. INTRODUCTION APACITOR excited Isolated asynchronous generator (CEIAG) is proved to be prominent generator for the renewable power generation using wind, hydro and biomass etc [1]. There are some bottlenecks in its application as a generator due to its voltage and frequency regulation characteristics which are non-linear functions of consumer loads and the prime-mover speed [2]. A number of attempts have been made to address these problems time to time [3-5]. A satisfactory performance of CEIAG driven by a wind turbine is reported in [6] with some percentage of unbalanced loading. However, this study limits the operation of the system for only partial unbalanced loading. Further, substantial literature is available on the control of CEIAG using static power converters in an islanded wind energy conversion system (IWECS) [7-9]. A stand alone single-phase induction generator is reported in the literature [8] in which the supply voltage and frequency are controlled by single-phase voltage source converter (VSC) and a battery energy storage (BESS). In [9], simulation results are reported on the voltage and frequency controller (VFC) with a three phase CEIAG, feeding three-phase four-wire consumer loads. However, very rare work is reported on its practical implementation. This paper deals with an implementation of VFC based on IcosΦ algorithm for a CEIAG based IWECS using a digital signal processor (DSP). A three leg VSC with a battery at its dc bus is used as a VFC. The star/delta connected transformer is used with VSC in VFC at point of common coupling (PCC) to mitigate the neutral current and to provide the neutral terminal for the distributed single-phase loads. The IcosΦ [10] algorithm based current detection method is used to extract the fundamental active and reactive power component of the load currents. The unit templates sinθ and cosθ are estimated using phase voltages to compute IWECS frequency. The steady-state and dynamic performances of VFC are evaluated under balanced and unbalanced loading of the IWECS. II. STUDIED SYSTEM AND PRINCIPLE OF OPERATION Fig. 1 shows the proposed VFC system for the IWECS. It shows a CEIAG to feed linear and non-linear consumer loads. A three leg VSC is used with a BESS as a VFC and it is connected to the point of common coupling (PCC) through interface inductors. The VSC provides the reactive power to CEIAG to regulate the voltage during application of different kinds of consumer loads. With the BESS at its dc bus, an active power management takes place by exchanging the active power under varying input power and consumer loads. The battery stores the surplus power when the input wind power is more than the load demand and discharges the deficit power to common bus when the input wind power goes below the load demand. The IWECS frequency depends directly on the instantaneous availability of an input wind power and the instantaneous load demand. The VSC consists of IGBTs (Insulated gate bipolar transistors) based three leg VSC module and a capacitor at its dc bus along with BESS. Each leg consists of two IGBTs and a common point of each leg is connected with an individual phase of the generator bus through an interfacing inductor. In practice majority of small loads are single phase loads, therefore to take in to consideration, a three-phase four-wire system is developed in this IWECS. A non-isolated star-delta transformer is connected at the PCC to realize the three-phase four-wire system. The load neutral terminal is provided by the common terminal of the star-delta transformer primary windings. The proposed IcosΦ control algorithm is implemented using a DSP. The VFC implementation requires an appropriate selection of VSC, a BESS, a dc bus capacitor, an interface inductor, a scaling circuits for sensing the input signals and driver circuit for output signals. Three Hall effect current sensors (ABB EL50 BB) are used to sense load currents for phase ‘A’, ‘B’ and ‘C’. To sense the source currents for phase ‘A’ and ‘B’, another set of Hall effect current sensors (ABB EL50 BB) are used. The generator is star connected, therefore its third phase source current is estimated by considering that the algebraic sum of three phase source currents is zero. Two voltage sensors (LEM CV3-1500) are used to sense the phase ‘A’ and ‘B’ voltages. Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA. 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 590 B C vsA vsB isA isB iLA iLB iLC s1 s3 s5 CP1104(ADC) dSPACE DSP Battery Rack CP1104 (DAC) Vbb Driver Circuit s1 s4 s3 s6 s5 s2 Fig. 1 System Configration of CEIAG based IWECS The third phase voltage is estimated considering the algebraic sum of three phase source voltages is zero. A scaling circuit is designed to use in between the sensed signals and ADC of DSP to have a zero offset with the sensed signals. The control algorithm is realized in MATLAB environment in support with real time blocks. After compilation, hex codes are loaded in the dSPACE DSP to generate the switching signals for IGBT’s through DAC of DSP. An opto-coupler (6N136) based driver circuit is designed to drive IGBTs of VSC of VFC. III. DESIGN OF VOLTAGE AND FREQUENCY CONTROLLER The proposed VFC for a 3.7 kW, 230V CEIAG consists of a three-leg in-direct current controlled voltage source converter (CC-VSC) with the BESS at its dc link. The midpoint of three half bridges are connected individually to each phase of the generator bus through an inductor. The nonisolated star-delta transformer provides a path for zero sequence components current present in the loads. It consists of three single phase transformers with turn ratio of 1:1. For positive sequence and negative sequence load currents, it behaves as an open circuit. The current flows in to it only s4 s6 s2 when zero sequence component present in consumer load currents. The neutral terminal of the load is connected with star point of a star-delta transformer. In case of unbalanced loads, the star-delta transformer provides the path for return load currents. A. Excitation Capacitors The CEIAG requires the reactive power support to build the rated terminal voltage. The reactive power demand of the CEIAG is a function of consumer loads connected on the load bus. Therefore choice of an excitation capacitor affects VSC rating. In this case the excitation capacitor is selected in such a way that it delivers the rated terminal voltage at 100% loading of the machine. The delta connected capacitor bank with 4 kVAR is used in this implementation. B. DC Bus Voltage The minimum dc bus voltage of VSC of VFC should be greater than twice the peak of the phase voltage at the AC terminals of VSC [11]. The DC bus voltage is calculated as, ( ) Vdc = 2 2 / 3m VL Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA. (1) 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 where m is the modulation index, considered 1 in this case and VL is the line rms voltage. Thus Vdc is obtained as 376 V for VL (230 V) and it is selected as 432 V. C. Selection of Battery Since the battery is an energy storage unit, its energy is represented in kilowatt-hours (kWh). As required Vdc is more than 376V, therefore the minimum battery rack voltage should be 432V. A battery rack with capacity of 3 kWh is used for energy storage. For the DC bus voltage of 432 V, 36 units of 12 V, 7Ah are connected in series. D. AC Inductor The design of ac inductor depends on permissible current ripple (icr_pp), DC bus voltage (Vdc) and switching frequency (fs) of VSC and is given as [11], 3mVdc Li = (2) 12af s icr _ PP where m is the modulation index and a is the overloading factor. Considering m=1, Vdc=432 V, a=1.2, icr_pp=1.5 % and fs=10 kHz, the value of Li is obtained as 3.46 mH. A value of 4 mH is selected in this investigation. IV. CONTROL SCHEME As shown in Fig. 2, the control strategy of the proposed VFC is realized using IcosΦ algorithm for the derivation of reference source currents. The operation of VFC enforces to maintain the rated terminal voltage under varying load conditions and to maintain IWECS frequency along with balanced and harmonic-free source currents. To achieve this, the reference source currents need to be controlled through proper gating of VSC switches. The reference source currents have two component for each phase, one is active power component i.e. I.cosφ and other is reactive power component i.e. I.sinφ. These two components are estimated for each phase load current. The phase voltages vA and vB are sensed and vC are estimated from sensed phase voltages. A set of in-phase (uAp, uBp, uCp) and quadrature unit templates (uAq, uBq, uCq) are computed using the fundamental phase voltages (filtered using band pass Butterworth filter). Three phase load currents iLA, iLB and iLC are sensed and filtered using a 2nd order low pass Butterworth filter (cutoff frequency 55 Hz) with inherent phase shift of 900 to extract the amplitude of the fundamental component of three-phase load currents. A zero crossing detector (ZCD) is used to detect the negative-going zerocrossing of the corresponding phase voltage. The phaseshifted fundamental current is held as the sample input and ZCD output pulse is as a hold input to the sample and hold circuit (SHC) which output is ‘ILp’ as amplitude. The output of the frequency PI (Proportional-Integral) controller is treated as ‘Ifp’. The average of three-phase active power component of load currents is derived using the summing amplifier with a gain (1/3) for the load balancing. The algebraic difference between the ‘Ifp’ and average of three-phase load currents ‘ILp’ (ILAp, ILBp, ILCp) estimates the amplitude of active power 591 component of the source currents (Ip). Similarly a ZCD is used to detect the negative-going zero-crossing of the quadrature template of the respective phase voltage. The phase-shifted fundamental current is held as the sample input and ZCD output pulse is as a hold input to the SHC which output is ‘ILq’ as amplitude of reactive power component of the respective phase current. The average of three-phase reactive power component of load currents is derived using summing amplifier with a gain (1/3) for load balancing. The algebraic difference between the output of the voltage PI regulator ‘Ivq’ and average of three-phase reactive power component of the load currents ‘ILq’ (ILAq, ILBq, ILCq) computes the amplitude of the reactive power component of the reference source currents (Iq). Basic equations of the control algorithm used in the proposed VFC are as follows. A. Estimation of IWECS Frequency The in-phase unit templates are derived using amplitude of point of common coupling voltage (PCC) Vt and phase voltages as, Vt = 2(v A2 + vB2 + vC2 ) / 3 (3) u Ap = v A / Vt , uBp = vB / Vt , uCp = vC / Vt (4) Moreover the quadrature unit template is computed as, u Aq = (−u Ap + uCp ) / 3, (5) u Bq = (u Ap 3 + u Bp − uCp ) / 3, (6) u Cq = (−u Ap 3 + uBp − uCp ) / (2 3); (7) The in-phase unit templates are in phase with the CEIAG terminal voltages, so it can be considered as a sinusoidal function rotating at an angular frequency of the CEIAG voltage. The quadrature unit template of phase ‘A’ is shifted from in-phase unit template by an angle of 900, so it can be treated as a cosine function rotating with a CEIAG angular frequency. uAp= sinθ , uBq=cosθ (8) The instantaneous value of ‘f’’ is estimated using the in-phase and quadrature templates for phase ‘A’. The supply frequency wms in radian/sec can be given as, wms = cos θ p (sin θ ) − sin θ p(cos θ ) (9) where p is the time derivative operator and CEIAG frequency is as f=wms/(2π). B. Extraction of Amplitude of Fundamental Active Power Component of Load currents The amplitudes (ILpA, ILpB, ILpC) of the active power component of the three-phase consumer load currents are extracted for phase ‘A’, ‘B’ and ‘C’. These are extracted as the amplitude of the consumer load currents, phase shifted by +900, at the negative zero-crossing of the phase voltage. A low pass Butterworth filter with a cut-off frequency of 55 Hz is used to shift the load current with an inherent phase shift of +900. A ZCD is used to detect the negative zero crossing of the corresponding in-phase unit templates. The phase-shifted Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA. 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 amplitude of fundamental active power component of the load current is held as the sample input and ZCD output is considered as the hold input to the SHC. The output of SHC is the ILp. amplitude. The amplitude of three-phase fundamental active power component of the load currents are as follows, (10) I LAp = I LA .cos ϕ A , I LBp = I LB .cos ϕ B , I LCp = I LC .cos ϕC 592 reactive power component of the reference source currents. The ac voltage error at the nth sampling instant is given as, Ve (n) = Vtr (n) − V (n) (16) where φA, φB and φC are the phase angles of the fundamental currents in A, B and C phases. C. Extraction of Amplitude of Fundamental Reactive Power Component of Load currents The amplitudes (ILqA, ILqB, ILqc) of the reactive power component of the three-phase consumer load currents are extracted for phase ‘A’, ‘B’ and ‘C’. These are extracted as the amplitude of the fundamental load current, phase shifted by +900, at the negative zero-crossing of the quadrature phase template. The +900 phase shifted load current is used here. A ZCD is used to detect the negative zero crossing of the corresponding quadrature unit templates. The phase-shifted amplitude of reactive component of the load current is held as the sample input and ZCD output is considered as the hold input to the SHC. The output of SHC is the ILq amplitude. (11) I LAq = I LA .sin ϕ A , I LBq = I LB .sin ϕ B , I LCq = I LC .sin ϕC D. Estimation of Active Power Component of Source Currents The weighted average amplitude of the fundamental active power component of the consumer load currents is subtracted from the output of the frequency PI controller to estimate the amplitude of the active power component of reference source currents. The frequency error is given as, f e ( n) = f rf ( n) − f ( n) (12) where frf the reference frequency ( i.e. 50 Hz in this case) and “f” is the frequency of the terminal voltage of an IWECS. The instantaneous value of “f” is estimated as discussed above in equation (5). At the nth sampling instant, the output of the frequency PI controller is as, i f p (n) = i fd (n − 1) + k pf { f e (n) − f e (n − 1)} + kif f e (n) (13) so the instantaneous value of active power component of reference source currents (I*P) is as, (14) I *p = I fp − I LP ( ) where I LP = I LAp + I LBp + I LCp / 3 Therefore the fundamental reference active power components of the source currents for two phases ‘A’ and ‘B’ and ‘C’ are given as, * * * isAp = I * p u Ap , isBp = I * p u Bp , isCp = I * p uCp (15) E. Reactive Power Component of Reference Source Currents The weighted average amplitude of the reactive power component of the load currents is subtracted from the output of the voltage PI controller to estimate the amplitude of the Fig. 2 Control Shceme of the proposed Controller where Vtr(n) is the amplitude of the reference ac terminal phase voltage and Vt(n) is the amplitude of the sensed three phase ac voltage. The output of the voltage PI controller for maintaining a constant ac terminal voltage at the nth sampling instant is expressed as, I vq (n) = I vq (n − 1) + k pa {Ve (n) − Ve (n − 1)} + k piVe (n) (17) where kpa and kpi are the proportional and integral gain constants of the PI controller. Ve(n) and Ve(n-1) are the voltage errors in the nth and (n-1)th sampling instant and Ivq (n) and Ivq(n-1) is the output of voltage PI controller in the nth and (n-1)th instant needed for the voltage control. Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA. 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 Therefore the amplitude of fundamental reference reactive power components of the source current is given as, (18) I *q = I vq − I Lq ( ) where I Lq = I LAq + I LBq + I LCq / 3 , 593 generated power Pg, load power PL and battery charging power Pb are shown in Fig. 4 (j-l). However small amount of generated power is consumed as iron and cu losses takes place in non-isolated star-delta transformer. Three-phase fundamental reference reactive power component of source currents for phase ‘A’ and ‘B’ and ‘C’ are given as, * * * isAq = I *q u Aq , isBq = I *qu Bq , isCq = I *q uCq (19) F. Estimation of Reference Source Currents Three-phase reference source currents are estimated for each phase as the vector sum of individual phase fundamental reference active power component of the source current and fundamental reference reactive power component of the source current as, * * * isA = i*sAp + i*sAq , isB = i*sBp + i*sBq , isC = i*sCp + i*sCq (20) G. Current Controller These three-phase reference source currents (i*sA, i*sB, i*sC) are compared with sensed source currents (isA, isB, isC). The independent PWM controllers are used for each leg of threeleg VSC. The resulting current error for each phase is amplified using a proportional gain and amplified signals are compared with a fixed frequency (10 kHz) triangular wave to generate gating signals for the VSC of VFC. V. RESULTS AND DISCUSSION The performance of developed voltage and frequency controller is tested with linear and nonlinear loads under both steady-state and dynamic conditions. Load perturbations with linear loads are made and results are recorded in terms of the generator line voltage (vAB), generator currents (igA, igB and igC), source currents (isA, isB and isC), capacitor currents (iCA, iCB and iCC), star-delta transformer primary currents (iTA, iTB and iTC) and VSC currents (ivscA, ivscB and ivscC). A. Performance of VFC With Non-linear Loads The performance of the VFC is demonstrated with nonlinear loads. A diode bridge rectifier with resistive-inductive load is chosen as a non-linear load to study the operation of the controller as a voltage regulator, harmonic eliminator and as a load leveler. The steady state performance of the controller is shown in Fig. 3. Test results are recorded with vAB. The igA, igB and igC are shown with vAB in Figs. 3 (a-c). The iSA, iSB and iSC along with vAB are shown in Figs. 3 (d-f). The iCA, iCB and iCC and load currents iLA, iLB and iLC are recorded with vAB and shown in Figs. 3 (g-l). The VSC currents ivscA, ivscB and ivscC with vAB are shown in Figs. 4 (a-c). The load neutral current iLn flowing through star terminal of non-isolated star-delta transformer is given in Fig. 4 (d). The non-isolated star-delta transformer primary winding currents iTA, iTB and iTC with vAB are observed in Figs. 4 (e-g). The recorded harmonic spectra of generator voltage vA, generator current igA are shown in Figs. 4 (h-i). The THD’s of generator current and voltage are well within IEEE- 519 limits. The (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) Fig. 3 Test results of IWECS (a) vAB and igA (b) vAB and igB (c) vAB and igC (d) vAB and isA (e) vAB and isB (f) vAB and isC (g) vAB and iCA (h) vAB and iCB (i) vAB and iCC (j) vAB and iLA (k) vAB and iLB (l) vAB and iLC (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) Fig. 4 Test results of IWECS (a) vAB and ivscA (b) vAB and ivscB (c) vAB and ivscC (d) vAB and iLn (e) vAB and iTA (f) vAB and iTB (g) vAB and iTC (h) harmonic spectrum of vAB (i) harmonic spectrum of igA (j) vAB and Pg (k) vAB and PL (l) vAB and Pb Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA. 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 B. Performance of VFC during Load Removal Fig. 5 shows the dynamic performance of the controller during the load removal on phase ‘B’. Test results are recorded using Agilent make digital oscilloscope (DSO6014A), voltage differential probe (1/100), current probe (100mA/V). These waveforms of various test signals are recorded with vA. Figs. 5(a) shows the three phase source currents isA, isB and isC during load removal of phase ‘B’. There is no change in source currents observed during these conditions. Fig. 5 (b) shows the load currents iLA, iLB and iLC during the removal of load on phase ‘B’. The dynamic variation in VSC current ivscA, ivscB and ivscC are observed in Fig. 5(c). It is clearly seen that during the load removal on phase ‘B’ leads to necessary change in ivscB magnitude to absorb the active component of source current towards BESS. The non-isolated star-delta transformer primary winding currents iTA, iTB and iTC are recorded in Fig. 5 (d) and are in consent with the recorded results in Fig. 5 (b) for load balancing. The dynamic variation in respective phase currents isB, iLB and ivscB are shown in Fig. 5 (e) during the load removal on phase ‘B’. To check the variations in battery current ib during load removal, the results are recorded in Fig. 5 (f). 594 application of phase ‘B’. There is hardly any change in source current magnitude observed load perturbations. Fig. 6 (b) shows the load currents iLA, iLB and iLC during the application of load on phase ‘B’ The dynamic variation in VSC current ivscA, ivscB and ivscC are observed in Fig. 6(c). It is clearly seen that applying load on phase ‘B’ leads to necessary reduction in ivscB magnitude and after load application ivscA, ivscB and ivscC magnitude are observed identical. The non-isolated star-delta transformer primary winding currents iTA, iTB and iTC are recorded in Fig. 6 (d) and are in consent with the recorded results in Fig. 6 (b). The dynamic variation in respective phase currents isB, iLB and ivscB are shown in Fig. 6 (e) during the load application on phase ‘B’. To check the variations in battery current ib during load removal, the results are recorded in Fig. 6 (f). VI. CONCLUSION The performance of developed VFC for CEIAG based IWECS has been evaluated under both steady-state and dynamic conditions. Test results have verified the control algorithm used for VFC and it performs satisfactory under both steady state and dynamic conditions. The use of conventional star-delta transformer has reduced the stress on (a){ch.1 (75v/div), ch.2-4(5A/div)} (b) {ch.1 (75v/div), ch.2-4(5A/div)} ( c) {ch.1 (75v/div), ch.2-4(2.5A/div)} (d) {ch.1 (75v/div), ch.2-4(1.25A/div)} (e) {ch.1 (75v/div), ch.2-4(2.5A/div)} (f) {ch.1 (75v/div), ch.2-4(2.5A/div)} Fig. 5 Test results of IWECS dynamics during load removal (a) vA, isA, isB and isC (b) vA, iLA, iLB and iLC (c) vA, ivscA, ivscB and ivscC (d) vA, iTA, iTB and iTC (e) vA, isB, iLB and ivscB (f) vA, isB, iLB and ib C. Performance of VFC during Load Application Fig. 6 shows the dynamic performance of the controller during the load application on phase ‘B’. Fig. 6 (a) shows the three phase source currents isA, isB and isC during load the VSC for the load balancing which has also facilitated the IWECS to be used for three-phase four-wire system. The battery supported VFC has served efficiently for the load leveling, neutral current compensation and harmonic elimination. Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA. 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 595 (a){ch.1 (75v/div), ch.2-4(5A/div)} (b) {ch.1 (75v/div), ch.2-4(5A/div)} ( c) {ch.1 (75v/div), ch.2-4(2.5A/div)} (d) {ch.1 (75v/div), ch.2-4(1.25A/div)} (e) {ch.1 (75v/div), ch.2-4(2.5A/div)} (f) {ch.1 (75v/div), ch.2-4(2.5A/div)} Fig. 6 Test results of IWECS dynamics during load application (a) vA, isA, isB and isC (b) vA, iLA, iLB and iLC (c) vA, ivscA, ivscB and ivscC (d) vA, iTA, iTB and iTC (e) vA, isB, iLB and ivscB (f) vA, isB, iLB and ib [6] APPENDIX IAG Data 3.7 kW, 230 V, 14.5 A, 50 Hz, Y- Connected, 4Pole Prime-Mover Data 3.7 kW, 415 V, 7A, ∆-connected, 4-pole, 1430 rpm, induction motor driven by ABB make AC Drive ACS 550-01-015A Ready to shelf semikron make voltage source converter 25kVA, Lf=4 mH, Rf= 0.01 Ω, Cdc=4000 µF, Kpav=2, Kaiv=0.05, Kpaf=2, Kpif=0.8 Vdc=432V, 3kWh, 36 units of 12 V , 7Ah connected in series 1 kVA Three phase transformer with each phase having two windings with 133V ratings VFC Parameters Battery Rack Star /delta Transformer REFERENCES [1] [2] [3] [4] [5] M. Kaltschmitt, W.Streicher and A. Wiese, "Renewable Energy, Technology and Environment, Economics," Springer-Verlag Berlin Heidelberg, 2007. Ion Boldea, Variable Speed Generator, The Electrical Generator Handbook, New York: Taylor & Francis, CRC, 2006. N.H. Malik and A.A. Mazi, “Capacitance requirements for isolated self excited induction generators,” IEEE Trans. on Energy Conversion, vol. EC-2, no. 1, pp. 62-69, March 1987. T.F. Chan, “Capacitance requirements of self-excited induction generators,” IEEE Trans. Energy Conversion, vol. EC-8, no. 2, pp. 304311, June 1993. L. Wang and C.H. Lee, “A novel analysis on the performance of an isolated self-excited induction generator,” IEEE Trans. Energy Conversion, vol. EC-12, no. 2, pp. 109-117, June 1997. I. Kassa, R. Djamila, R. Toufik, and T. Abdelmounim, “Performance of an Isolated Induction Generator Under Unbalanced Loads,” IEEE Trans. Energy Conversion, vol. 25, no.2, pp. 303-311, June 2010. [7] Bhim Singh and G. K. Kasal, “Solid state voltage and frequency controller for a standalone wind power generating system,” IEEE Trans Power Electronics, vol. 23, no.3, pp.1170-1177, May 2008. [8] O. Ojo, O. Omozusi, A. Ginart and B. Gonoh, “The Operation of StandAlone Single-phase Induction Geneerator using a Single-Phase PulseWidth modulated Inverter With a Battery Supply,” IEEE Trans. Energy Conversions, vol. 14, no. 3, pp. 526-531, Sept.1999. [9] Bhim Singh and G. Kasal, “Voltage and Frequency Controller for a Three Phase Four –Wire Autonomous Wind Energy Conversion System,” IEEE Trans. Energy Conversion, vol. 23, no. 2, pp. 509-518, June 2008. [10] G. Bhuvaneswari and M.G. Nair, “Design, Simulation, and Analog Circuit Implementation of a Three-Phase Shunt Active Filter Using the Icosφ Algorithm,” IEEE Trans. Power Delivery, vol. 23, no. 2, pp. 1222 – 1235,April 2008. [11] B. N. Singh, P. Rastgoufard, B. Singh, A. Chandra, and K. Al. Haddad, “Design, simulation and implementation of three pole/four pole topologies for active filters,” in Inst. Electr. Eng. Proc. Electr. Power Appl., vol. 151, no. 4, pp. 467–476, Jul. 2004. Shailendra Sharma was born in Indore, India, in 1972. He received his M.E. in Electrical Engineering with specialization in power electronics in 2004 from the Shri Govindram Seksaria Institute of Technology and Science, Indore, India. He has five years of industrial experience as an erection and commissioning engineer. He joined the Department of Electrical Engineering, Shri GSITS, Indore in 2004 as a Lecturer. Presently, he is pursuing research at Indian Institute of Technology, Delhi, India, under the Quality Improvement Programme. His fields of interest include power electronics, drives, power quality, and renewable energy. He is Associate Member of the Institution of Engineers India. Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA. 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 Bhim Singh was born in Rahamapur, India, in 1956. He received his B.E. from the University of Roorkee, Roorkee, India, in 1977 and his M.Tech and Ph.D. from the Indian Institute of Technology (IIT) Delhi, New Delhi, India, in 1979 and 1983, respectively. In 1983, he joined the Department of Electrical Engineering, University of Roorkee, as a Lecturer, and in 1988 he became a Reader. In December 1990, he joined the Department of Electrical Engineering, IIT Delhi, as an Assistant Professor. He became an Associate Professor in 1994 and a Professor in 1997. His areas of 596 interest include power electronics, electrical machines and drives, active filters, FACTS, HVDC and power quality. He is a Fellow of the Indian National Academy of Engineering (INAE), the National Science Academy (FNSc), the Institution of Engineers (India) (IE(I)), and the Institution of Electronics and Telecommunication Engineers (IETE). He is also a life member of the Indian Society for Technical Education (ISTE), the System Society of India (SSI), and the National Institution of Quality and Reliability (NIQR). In addition he is a Fellow of the Institute of Electrical and Electronics Engineers (IEEE). Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.