Three-Phase Shunt Active Power Filter

Transcription

1 Amercan Journal of Appled Scences 5 (8): , 28 ISSN Scence Publcatons Three-Phase Shunt Actve Power Flter 1 Moleykutty George and 2 Kartk Prasad Basu 1 Faculty of Engneerng and Technology, Multmeda Unversty, 7545 Melaka, Malaysa 2 Faculty of Engneerng, Multmeda Unversty, 631 Cyberjaya, Malaysa Abstract: Actve power flters have been wdely used for harmonc elmnaton. The performance of a conventonal three-phase shunt Actve Power Flter (APF) usng Synchronous Detecton Method (SDM) has been compared wth Nonlnear Autoregressve-Movng Average (NARMA)-L2 based APF. The novelty of ths study les n the applcaton of NARMA-L2 control to generate the ampltude of the reference supply current requred by the APF crcut and the successful mplementaton of the APF system for harmonc elmnaton. The entre system has been modeled usng MATLAB 6.1 toolbox. Smulaton results demonstrate the applcablty of NARMA-L2 controller for the control of APF. Key words: APF, NARMA-L2, VSI, harmoncs, THD, SDM, power qualty INTRODUCTION Power Qualty (PQ) s an mportant measure of an electrcal power system. The term PQ means to mantan purely snusodal current wave form n phase wth a purely snusodal voltage wave form. The power generated at the generatng staton s purely snusodal n nature. The deteroratng qualty of electrc power s manly because of current and voltage harmoncs due to wde spread applcaton of statc power electroncs converters, zero and negatve sequence components orgnated by the use of sngle phase and unbalanced loads, reactve power, voltage sag, voltage swell, flcker, voltage nterrupton etc. To mprove the power qualty tradtonal compensaton methods such as passve flters, synchronous capactors, phase advancers, etc. were employed. However tradtonal controllers nclude many dsadvantages such as fxed compensaton, bulkness, electromagnetc nterference, possble resonance etc.. These dsadvantages urged power system and power electronc engneers to develop adjustable and dynamc solutons usng custom power devces. Custom power devces are power condtonng equpments usng statc power electronc converters to mprove the power qualty of dstrbuton system customers. These nclude APF [1-11], dynamc voltage restorer (DVR) [12-16] and Unfed Power Qualty Condtoner (UPQC) [17-21]. APF s a shunt compensator used to elmnate the dsturbances n current, whereas DVR s a seres compensator used to elmnate the dsturbances n voltage. Recently UPQC, whch conssts of both shunt and seres compensators s proposed as a one shot soluton for power qualty problems. Ths study proposes the effectveness of NARMA-L2 controller for the control of APF system. The novelty of ths paper les n the applcaton of NARMA-L2 controller for the determnaton of ampltude of reference supply current requred n an APF system. Ths paper also dscusses the control of APF system usng SDM. The control strateges of APF system are detaled n the second part of ths paper. Smulaton results n the thrd part demonstrate the effectveness of NARMA-L2 controller for the control of APF system. CONTROL TECHNIQUES OF APF SYSTEM In ths secton, control scheme of APF system usng SDM s dscussed and compared wth that usng NARMA-L2 controller. Correspondng Author: Moleykutty George, Faulty of Engneerng and Technology, Melaka Campus, Multmeda Unversty, 7545, Melaka, Malaysa Tel: Fax:

2 Am. J. Appled Sc., 5 (8): , 28 S(t) l(t) s(t) l(t) APF OFF Nonlnear load APF ON Nonlnear Load Fg. 1: Block dagram of a smple power system wth APF OFF Fg. 2: Block dagram of a smple power system wth APF ON R s L s sa La ca Three-Phase Supply R s L s Three-Phase Load sb Lb cb R s L s sc Lc cc L IGBT Inverte r L V dc L Gate sgnals control crcut Fg. 3: Schematc dagram of an APF system Prncple of operaton: A three-phase system has been selected to study the performance of the APF system. Comparson of Fg. 1 [22] and 2 [22] shows the compensaton prncple of a shunt actve power flter. 91 APF njects a current equal n magntude but n phase opposton to harmonc current. Fgure 3 shows the block dagram of a three-phase APF system. The heart of the APF system s the IGBT based Voltage

3 Am. J. Appled Sc., 5 (8): , 28 Fg. 4: Smulnk Model of the control crcut usng SDM Fg. 5: Smulnk model of NARMA-L2 controlled APF Source Inverter (VSI). A dc capactor s used to delver power for the VSI. For the successful operaton of APF, capactor voltage should be at least 15% of maxmum lne-lne supply voltage. used for the determnaton of ampltude of the source currents. In ths algorthm, the three-phase mans currents are assumed to be balanced after compensaton. The real power P(t) consumed by the load could be calculated from the nstantaneous voltages and load currents as: Control of APF system usng SDM: Fgure 4 shows la (t) the control crcut of an APF system usng SDM. The p(t) = [v sa (t) v sb(t) v sc(t)] control crcut conssts of an outer voltage control loop lb(t) and two nner current control loops. The outer control lc(t) (1) loop s used to mantan the capactor voltage constant where v sa (t), v sb (t), v sc (t) are the nstantaneous and to determne the ampltude of the mans currtents values of supply voltages and la (t), lb (t), lc (t) are requred n an APF system. SDM method s bascally the nstantaneous values of load currents. The average 911

4 Am. J. Appled Sc., 5 (8): , 28 Fg. 6: Plant Model Fg.7: Performance graph value P dc s determned by applyng P(t) to a low pass flter. The real power s then splt nto the three phases as follows: ca (t) = sa (t) la (t) Pdc Vsmb Pb = V + V + V sma smb smc Thus for purely snusodal balanced supply voltages, Pdc Vsmc Pc = V + V + V sma smb smc (2a) (2b) (2c) 912 Pdc Pa = Pb = Pc = 3 2 v (t) Pa (t) = sa sa 2 Vsma 2 v (t) Pb (t) = sb sb 2 Vsmb 2 v (t) Pc (t) = sc sc 2 Vsmc (3) (4a) (4b) (4c) where, V sma, V smb, V smc are the ampltudes of the supply voltages. Wth the objectve of achevng Unty Power Factor (UPF), the desred mans currents are

5 Am. J. Appled Sc., 5 (8): , 28 Input Plant output Plant output X1 3 NN Output X1 3 Fg. 8: Tranng data X1 3 X1 3 obtaned by equatons 4a-c. The compensaton currents are calculated usng equatons 5a-5c. Snce the PWM VSI s assumed to be nstantaneous and nfntely fast to track the compensaton currents, t s modeled as a current amplfer wth unty gan [23]. ca (t) = sa (t) la (t) cb(t) = sb(t) lb(t) cc(t) = sc(t) lc (t) (5a) (5b) (5c) Control of APF system sng NARMA-L2 controller: NARMA-L2 controller [24, 25] s successfully used for the control of UPQC [24] and the speed control of separately excted DC motor [25]. The smulnk model of a NARMA-L2 controlled APF system s shown n Fg. 5. The smulnk plant model shown n Fg. 6 s used to tran the NARMA-L2 controller. As shown n Fg. 5, the control nput of the plant s the ampltude of the desred mans current and the capactor voltage s the plant output. NARMA-L2 controller checks the desred capactor voltage and the actual capactor voltage and the control nput s adjusted to acheve the reference value. Table 1 shows the specfcatons used to tran the controller. It has been observed that the complcated equatons n SDM could be elmnated by the use of NARMA-L2 controller. Sample performance graph and tranng data obtaned from a NARMA-L2 controller are llustrated n Fg. 7 and Fg. 8 respectvely. 913 Table 1: Plant model specfcatons Sze of hdden layer 1 Samplng nterval (s) 6.254e -5 No. of delayed plant nputs 2 No. of delayed plant outputs 1 Tranng samples 4 Maxmum plant nput 1.8 Mnmum plant nput 1.5 Maxmum nterval value (s) 8e-3 Mnmum nterval value (s) 6.254e-5 Maxmum plant output 8 Mnmum plant output 7 Tranng Epochs 1 Tranng Functon trancgf Use current weghts selected Use valdaton data selected Use testng data selected Table 2: Performance of APF system SDM NARMA-L2 SDM NARMA-L2 Controller = = 75 Is_THD (%) IL_THD (%) Is1 (A) Is5 (A).9 Is7 (A).1 Is11 (A).18 Is13 (A).12 Il1 (A) Il5 (A) Il7 (A) Il11 (A) Il13 (A) DPF

6 Plots of supply voltages, supply curents load currents Fg. 9: Plots of v,(t) (A), I,(t) (A), (t)(a) Fg. 1: Plot of Compensaton current (A) Fg. 11: THD of source and load currents Am. J. Appled Sc., 5 (8): , Compensaton Current (A) THD of source current and load current Tme(s) Tme (s) sfhd hfhd Ffth Harmonc components of load and source currents (A) Tme(s) Fg. 12: 5th harmonc components of source and load currents (A) Is 5(A) II5 (A) 1 RESULTS AND DISCUSSION MATLAB 6.1 toolbox s used to model the system. The effectveness of the system has been tested for NARMA-L2 controller has been successfully varous frng angles (α) n the range of and modeled and tested for the control of APF system. 9. The performance of the developed system 914

7 Seventh harmonc components of source and load currents (A) Am. J. Appled Sc., 5 (8): , 28 Fg. 13: 7th harmonc components of source and load currents (A) Eleventh harmonc components of source and load currents (A) Fg. 14: 11 th harmonc components of source and load currents Thrteenth harmonc components of source and load currents (A) Tme (s) Fg. 15: 13 th harmonc components of source and load currents IS7 (A) II 7 (A) Tme(s) Is 11 (A) II 11 (A) Tme (s) Is 13 (A) II 13 (A) s llustrated wth the one usng SDM for two dfferent frng angles as tabulated n Table 2. Smulaton results for α = shown n Fg. 9 and Fg. 15 demonstrate the effectveness of the developed system for the control of APF. system has been compared. It has been observed that the complcated calculatons used n SDM could be elmnated by the use of NARMA-L2 controller. ACKNOWLEDGMENT CONCLUSION A NARMA-L2 controlled APF system has been modeled and successfully tested for the control of APF. The novelty of ths paper les n the applcaton of NARMA-L2 controller to determne the ampltude of the reference source current requred n an APF system. Ths paper also dscusses modelng and control of APF system usng SDM. The performance of the dfferent 915 The authors are grateful to Alan Tan Wee Chat, Dr. Abdulazeez S. Boujarwah, Chrsto George, Prof. K Ramar and Dr. Saurabh Kumar Mukerj for valuable dscussons. REFERENCES 1. Hrofum Akag, Trends n Actve Power Lne Condtoners: IEEE Tran. Power Electroncs, 9:

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