Hybrid Active Filter Based on SVPWM for Power Conditioning using Matlab/Simulink Toolbox Environments

Transcription

1 International Journal o Electronic and Electrical Engineering. ISSN olume 5, Number (01), pp International Reearch Publication Houe Hybrid Active Filter Baed on SPWM or Power Conditioning uing Matlab/Simulink Toolbox Environment 1 Nareh Kumar and Prabhat Kumar 1 Faculty Member, M.Tech. Student Arya College o Engg. & I.T., India narehrajk@yahoo.com Abtract In thi paper preent control method or hybrid active ilter uing pace vector pule width modulation (SPWM). In the propoed control method, the Active Power Filter (APF) reerence voltage vector i generated intead o the reerence current, and the deired APF output voltage i generated by SPWM. A MATLAB code i developed to generate the SPWM witching pule ed to the two-level inverter topology. The entire power ytem block et model o the propoed cheme ha been developed in MATLAB environment. The developed control algorithm i imple. The APF baed on the propoed method can eliminate harmonic, compenate reactive power and balance load aymmetry. Simulation reult how the eaibility o the APF with the propoed control method. Index Term: SPWM, Active Filter, Power Conditioning, Paive Filter Introduction The growing ue o non-linear and time-varying load ha led to ditortion o voltage and current waveorm and increaed reactive power demand in ac main. Harmonic ditortion i known to be ource o everal problem, uch a increaed power loe, exceive heating in rotating machinery, igniicant intererence with communication circuit, licker and audible noie, incorrect operation o enitive load [1-]. Paive ilter are traditional method to eliminate harmonic, but with recent development in power emiconductor witche and converter, coupled with development in control technique and analog and digital implementation, active ilter are becoming an eective and commercially viable alternative to paive ilter. They oer the

2 114 Nareh Kumar and Prabhat Kumar ollowing advantage: able to cover a wide range o harmonic requencie; do not contribute reonant requencie to the network; harmonic attenuation i network impedance dependent [-4]. Among the variou topologie the hunt active power ilter baed on voltage ource inverter (SI) i the mot common one becaue o it eiciency. The perormance o active power ilter depend on the adoptive control approache. There are two major part o an active power ilter controller. The irt i that determine the reerence current o APF and maintain a table DC bu voltage. ariou current detection method, uch a intantaneou reactive power theory [5], ynchronou reerence rame method [6], upplying current regulation [7] and etc., are preented. The commonne o thee method i the requet or generating reerence current o APF, either with the load current or the main current. The econd i that control the SI to inject the compenating current into AC main. Similarly, variou current control method uch a hyterei [8], triangular wave control [9], deadbeat control [10] and etc., are preented. The commonne o thee method i to control SI with the dierence between real current and reerence current. An alternative control method or hunt active power ilter i propoed in thi paper. The propoed method dier rom previouly dicued approache in the ollowing way: a) To generate APF reerence voltage vector intead o reerence current; b) to generate deired APF output voltage by pace vector modulation baed on generated reerence voltage at tep a). Thereore, the propoed method i imple and eay to carry out by DSP. In thi literature dicued the baic principle o thi method in detail and proved it validity by imulation and experimental reult. Mathematical Modelling o SPWM Technique with APF Thi literature i briely dicue the theory and operation o Space ector Pule Width Modulation (SPWM) explain the implementation o SPWM or the two level inverter topology. Philoophy o SPWM Technique SPWM technique wa originally developed a a vector approach to pule width modulation or three-phae inverter. The SPWM method i requently ued in vector controlled application. In vector controlled application thi technique i ued or reerence voltage generation when current control i exercied. It i a more ophiticated, advanced, computation intenive technique or generating ine wave that provide a higher voltage with lower total harmonic ditortion and i poibly the bet among all the pule width modulation technique. It conine pace vector to be applied according to the region where the output voltage vector i located. Becaue o it uperior perormance characteritic, it i been inding wide pread application in recent year. The main aim o any modulation technique i to obtain variable output voltage having a maximum undamental component with minimum harmonic. Many PWM technique have been developed or letting the inverter to poe variou deired output characteritic to achieve the wide linear modulation range, le witching loe, lower harmonic ditortion. The SPWM technique i more popular than conventional technique becaue o it excellent eature.

3 Hybrid Active Filter Baed on SPWM or Power Conditioning 115 More eicient ue o DC upply voltage. 15% more output voltage then conventional modulation. Lower Total Harmonic ditortion (THD). Prevent un-neceary witching hence le commutation loe. Principle o SPWM Firtly model o a three-phae inverter i preented on the bai o pace vector repreentation. The three-phae SI i reproduced in Fig..1. S 1, to S6, are the ix power witche that hape the output, which are controlled by the witching variable,,, a, a,b, b c and,,, a, b, or, c When an upper tranitor i witched on, i.e., the correponding, c i0. Thereore, the on and o tate o the upper witche S 1, S, S 5, can be ued to determine the output voltage. Figure.1: Power Circuit o a three-phae SI The relationhip between the witching variable vector [ a b c ] t and line-to-line voltage vector [ ab, ab bc ca = dc bc, ca ] i given by (.1) in the ollowing: 0 a 1 b 1 c (.1) Alo, the relationhip between the witching variable vector [ a b c ] t and the phae voltage vector [ ab, bc, ca ] t can be expreed below.

4 116 Nareh Kumar and Prabhat Kumar an bn cn = dc a 1 b c (.) A illutrated in Fig..1, there are eight poible combination o on and o pattern or the three upper power witche. The on and o tate o the lower power device are oppoite to the upper one and o are eaily determined once the tate o the upper power tranitor are determined. According to equation (.1) and (.), the eight witching vector, output line to neutral voltage (phae voltage), and output line-to-line voltage in term o DC-link dc, are given in Fig.. and Table.1 and how the eight inverter voltage vector ( 0 to 7 ). Figure.: Eight inverter voltage vector ( 0 to 7 )

5 Hybrid Active Filter Baed on SPWM or Power Conditioning 117 Table.1: Switching vector, phae voltage and output line to line voltage oltage vector Switching vector Line to neutral voltage Line to line voltage a b c an bn cn ab bc ca o / -1/ -1/ / 1/ -/ / / -1/ / 1/ 1/ / -1/ / / -/ 1/ SPWM reer to a pecial witching equence o the upper power witche o a three-phae power inverter. It ha been hown to generate le harmonic ditortion in the output voltage and/or current applied to the phae o a power ytem and to provide more eicient ue o upply voltage compared with other modulation technique. To implement SPWM, the voltage equation in the abc reerence rame can be tranormed into the tationary d q reerence rame that conit o the horizontal (d) and vertical (q) axe a depicted in Fig... Figure.: The relationhip o abc reerence rame and tationary d-q reerence rame From thi igure, the relation between thee two reerence rame i given a k (.) dq0 = abc

6 118 Nareh Kumar and Prabhat Kumar Where, K = 0, dq0 = [ d q 0 ] T, abc = [ T a b ], c And denote either a voltage or a current variable. A decribed in Fig.., thi tranormation i equivalent to an orthogonal projection o [a, b, c] t onto the two dimenional perpendicular to the vector [1, 1, 1] t (the equivalent d-q plane) in a three dimenional coordinate ytem. A a reult, ix non-zero (active) vector and two zero vector are poible. Six non-zero vector ( 1-6 ) hape the axe o a hexagonal a depicted in Fig..4, and eed electric power to the ytem. The angle between any adjacent two non-zero vector i 60 degree. Meanwhile, two zero vector ( 0 and 7 ) are at the origin and apply zero voltage to the load. The eight vector are called the baic pace vector and are denoted by 0 ( 000), 1 ( 100), ( 110), ( 010), 4 ( 011), 5 ( 001), 6 ( 101), 7 ( 111) The binary number indicate the witch tate o inverter leg. Here 1 implie upper witch being on and 0 reer to the lower witch o the leg being on. The ame tranormation can be applied to the deired output voltage to get the deired reerence voltage vector re in the d-q plane. The objective o SPWM technique i to approximate the reerence voltage vector re uing the eight witching pattern. One imple method o approximation i to generate the average output o the inverter in a mall period, T to be the ame a that o re in the ame period. Figure.4: Baic Switching vector and Sector

7 Hybrid Active Filter Baed on SPWM or Power Conditioning 119 Thereore, pace vector PWM can be implemented by the ollowing tep Step 1: Determination o d, q, re an angle(α) Step : Determination o time duration T 1, T, T 0 Step : Determination o the witching time o each witch (S 1 to S 6 ) Step 1: Determination o d, co 60, d = an bn cn = an bn cn q re co co0 co0 q = bn cn 1 = 0 1 = an + bn cn d q re = d + q 1 q α = tan 1 = ωt = πt, d where =undamental requency an bn cn and angle (α) Figure.5: oltage Space ector and it component in (d, q)

8 10 Nareh Kumar and Prabhat Kumar Step : Determination o time duration T 1, T, T 0 From Fig..6, the witching time duration can be calculated a ollow: Switching time duration at Sector 1 T z 0 (Where, 0 α 60 ) in( π α ) T1 = Tz a in( π ) in( α ) T = Tz a in π T 0 re = = T z T 1dt + dt + ( T + T ) 1 T + T T T 0 T + T 1 1 Tz re = ( T T. ) T z re coα = T. inα ( ) 1 wheretz = z z T and a = ( π ) co ( ) in 1 dc dc π re dc Figure.6: Reerence vector a a combination o adjacent vector at ector 1 Block Diagram o Control Sytem The main ection o the APF hown in Fig..7 i a orced-commutated SI connected

9 Hybrid Active Filter Baedd on SPWM or Power Conditioning 11 to dc capacitor. Conidering that the ditortion o the voltage in public power network i uually very low, it cann be aumed that the upply voltage i ideal inuoidal and three-phae balanced a hown below: v v v a b c = in = in = in ( ϖt) ( ωt π ) ( ωt + π ) ) Where i the upply voltage amplitude? It i known that thee three-phae voltage [ a, b, c ] in a b c can be expreed a two-phae repreentation in d q rame by Clark tranormation and it i given by d a = = b (.5) q 0 c It i poible to write equation (.5) more compactly a 0 1 = ( vaa + vba + vca ) = d + jq = θ (.4) Figure.7: Coniguration o a Hybrid APF uing SPWM

10 1 Nareh Kumar and Prabhat Kumar j π Where a = e, o balanced three-phae et o voltage i repreented in the tationary reerence rame by a pace vector o contant magnitude, equal to the amplitude o the voltage, and rotating with angular peedω = π. A hown in Fig..7, the hunt APF take a three-phae voltage ource inverter a the main circuit and ue capacitor a the energy torage element on the dc ide to maintain the dc bu voltage dc contant. Fig..7 how the per-phae (Phae A) equivalent circuit o the ytem decribed in Fig..8. Compenation Principle Figure.8: Equivalent circuit o a imple power ytem together with the Hybrid APF In the Fig..8, a1 and ah denote the output undamental and harmonic voltage o the inverter, repectively. Thee voltage ource are connected to a upply ource a, in parallel via a link inductor L and capacitor C.The upply current i, i orced to be ree o harmonic by appropriate voltage rom the APF and the harmonic current emitted rom the load i then automatically compenated. It i known rom Fig..8, that only undamental component i taken into account, the voltage o the ac upply and the APF exit the ollowing relationhip in the teady tate d I 1 1 = L dt C I dt + (.6) Where i the upply voltage, I 1i the undamental current o APF, 1 i the undamental voltage o APF, and above variable are expreed in orm o pace vector. The APF i joined into the network through the inductor L and C the a

11 Hybrid Active Filter Baed on SPWM or Power Conditioning 1 unction o thee i to ilter higher harmonic nearly witching requency in the current and to link two ac voltage ource o the inverter and the network. So the required inductance and capacitance can jut adopt a mall value. Then the total reactance caued by inductor and capacitor or the requency o 50Hz, and the undamental voltage acro the link inductor and capacitor are alo very mall, epecially compared with the main voltage. Thu the eect o the voltage o the link inductor and capacitor i neglected. So the ollowing impliied voltage balanced equation can be obtained rom equation (.6). = 1 (.7) The control object o APF i to make the upply current inuoidal and in phae with the upply voltage. Thu the nonlinear load and the active power ilter equal to a pure reitance load R, and the upply voltage and the upply current atiy the ollowing equation: = R I (.8) 0 1 Where I = ( iaa + iba + ica ) = I d + ji q = I θi. Then the relationhip between I and the upply voltage amplitude i = R I (.9) Subtituting (.8), (.9) into (.7) reult in 1 = I (.10) I Equation (.10) decribe the relationhip between the output undamental voltage o APF, the upply voltage and the upply current, which enure that the APF operate normally. However, or making the APF normally achieving the required eect, the ha to be high enough and table. In the teady tate, the power dc bu voltage dc upplied rom the upply mut be equal to the real power demanded by the load, and no real power pae through the power converter or a lole APF ytem. Hence, the average voltage o dc capacitor can be maintained at a contant value. I a power imbalance, uch a the tranient caued by load change, occur, the dc capacitor mut upply the power dierence between the upply and the load, the average voltage o the dc capacitor i reduced. At thi moment, the magnitude o the upply current mut be enlarged to increae the real power delivered by the upply. On the contrary, the average voltage o the dc capacitor rie, and the upply current mut be decreaed. Thereore, the average voltage o the dc capacitor can relect the real power low inormation. In order to maintain the dc bu voltage a contant, the detected dc bu voltage i compared with a etting voltage. The compared reult are ed to a PI controller, and amplitude control o the upply current i can be obtained by output o PI controller

12 14 Nareh Kumar and Prabhat Kumar Figure.9: Control block diagram o propoed algorithm The ig..9 how the block diagram o active ilter controller implemented or reducing the harmonic with hybrid active ilter ytem. In each witching cycle, the controller ample the upply current ia, ic and the upply current i c i calculated with the equation o - (i a +i c ), a the ummation o three upply current i equal to zero. Thee three-phae upply current are meaured and tranormed into ynchronou reerence rame (d-q axi). The undamental component o the upply current i tranormed into dc quantitie in the (d-q) axi and the upply current amplitude i generated by the PI controller with dc and re, the reerence value o the dc bu voltage. The obtained d-q axi component generate voltage command ignal. By uing Fourier magnitude block, voltage magnitude and angle i calculated rom the obtained ignal. Thee value are ed to the developed code and compared with the repeating equence. Then the time duration T 1, T, and T 0,the on-time o 1,, and 0 are calculated a already explained in literature. The generated witching action are applied to the APF and power balancing o the ilter take place. Simulation and Reult The developed control method or three-phae hybrid APF i imulated in MATLAB/Simulink. Firtly, the three-phae upply current are ened and tranormed into ynchronou reerence rame (d-q) axi. The undamental component o the upply current i tranormed into dc quantitie in the (d-q) axi and the upply current amplitude I generated by the PI controller. The obtained d-q axi component generate voltage command ignal. By uing Fourier magnitude block, voltage magnitude and angle i calculated rom the obtained ignal. Thee value are ed to the developed code and generated witching action are applied to the hybrid APF. Thu, power balancing o the ilter take place. Further, the perormance with dierent type o load i preented.

13 Hybrid Active Filter Baed on SPWM or Power Conditioning 15 The complete imulation model o APF with dierent type o load i hown in Fig..1 and Fig..0 For an input upply voltage o 0 (rm) and witching requency o 5 khz, the imulation reult beore and ater power balancing are hown. Table.1: Parameter value Sytem parameter alue o parameter Supply ytem 0 rm, 50 H z, three phae upply Balanced linear load Z 1 = 50 + j6.8ω, Unbalanced linear load Z a = j15.70, = 75 + j.56, 1 Ω Z1 b Ω Z1 c = j47.10ω, Non-linear load with reitance R = 500Ω APF Cdc = 450μ, re = 900, C = 70μ, L = 5mH Linear load Cae 1: Balance RL load condition without APF Figure.10: Simulation model o three phae balance RL-load condition without APF.

14 16 Nareh Kumar and Prabhat Kumar Figure (a): Phae-A load current harmonic pectrum phae-a Input ource current harmonic pectrum Figure (b): Phae-A ource Current Harmonic Spectrum Figure.11: Harmonic Spectrum o Linear Balance Load without APF Cae: SPWM Technique or Linear balance RL load condition with APF Figure.1: SPWM Technique or linear balance RL-load condition with APF.

15 Hybrid Active Filter Baed on SPWM or Power Conditioning 17 Figure (a): Output Load current harmonic pectrum Figure (b): Input ource current harmonic pectrum Figure.1: Harmonic pectrum o SPWM Technique or linear balance RL-load condition with APF Cae : For linear unbalance RL load condition without APF Figure.14: Simulink model o three phae unbalance RL-load condition without APF.

16 18 Nareh Kumar and Prabhat Kumar Figure (a): Output load current harmonic pectrum Figure (b): Input ource current harmonic pectrum. Figure.15: Harmonic pectrum o three phae unbalance RL-load condition without APF Cae 4: SPWM Technique or Linear unbalance RL load condition with APF Figure.16: Simulink model o SPWM Technique or linear unbalance RL-load condition with APF.

17 Hybrid Active Filter Baed on SPWM or Power Conditioning 19 Figure (a): Output load current harmonic pectrum. Figure (b): Input ource current harmonic pectrum Figure.17: Harmonic pectrum o SPWM Technique or linear unbalance RLload condition with APF. Nonlinear load Cae 1: or Nonlinear R load condition without APF Figure.18: Simulink model or non linear R load condition without APF

18 10 Nareh Kumar and Prabhat Kumar Figure (a): Output load current harmonic pectrum Figure (b): Input ource current harmonic pectrum Figure.19: Harmonic pectrum o non-linear load without APF Cae : SPWM Technique or Nonlinear R load condition with APF Figure.0: Simulink model o SPWM Technique or Nonlinear R load condition with APF

19 Hybrid Active Filter Baed on SPWM or Power Conditioning 11 Figure (a): Output load current harmonic pectrum. Figure (b): Input ource current harmonic pectrum Figure.1: Harmonic pectrum o SPWM Technique or Nonlinear R load condition with APF Reult Analyi Table:. Type o load Without APF SPWM Technique with APF THD Load Side THD Source ide THD Load THD Source ide Side Linear Balance RL load 0.00% 0.00% 0.0% 1.1% Linear Unbalance RL load 0.00% 0.00% 0.01% 1.1% Nonlinear Rectiier with R load 0.8% 0.% 0.8% 5.47% From table. how the imulation o harmonic pectrum o linear three phae balance load.ig..11 (a) i the harmonic pectrum o the current beore compenation on the load ide. The load current total harmonic ditortion (THD) i 0.00% while the upply current THD i 0.00%. It hould be noted that no harmonic generated in linear three phae balance ytem. But when the APF i ued the harmonic generate at the ource ide the value o upply current THD i 1.1% when SPWM Technique ued. And the value o upply current THD i 1.1% when SPWM Technique ued. From table. how the imulation o harmonic pectrum o linear three phae

20 1 Nareh Kumar and Prabhat Kumar unbalance load.ig..1 (a) i the harmonic pectrum o the current beore compenation on the load ide. The load current total harmonic ditortion (THD) i 0.00% while the upply current THD i 0.00%. It hould be noted that no harmonic generated in linear three phae unbalance ytem. But when the APF i ued, the harmonic generate at the ource ide, the value o upply current THD i 1.1% when SPWM Technique ued. From Table. how the imulation o harmonic pectrum o APF with SPWM Technique ued or non linear load ued. When the non-linear i a three-phae diode bridge rectiier with reitance load. Fig..19 (a) i the harmonic pectrum o the current beore compenation on the load ide. The harmonic pectrum o the load current how that magnitude o the 5 th, 7 th, 11 th and 1 th harmonic i very large. The harmonic pectrum o the ource current how that magnitude o the 5 th, 7 th, 11 th and 1 th harmonic are evidently reduced ater compenation. The load current Total Harmonic Ditortion (THD) i 0.8%, while the upply current THD i 5.47%.when SPWM Technique ued thi i hown by ig..1. Concluion The active power ilter controller ha become the mot important technique or reduction o current harmonic in electric power ditribution ytem. In thi thei a model or three-phae active power ilter or balanced non-linear load i made and imulated uing MATLAB/Simulink otware package or the reduction harmonic in ource current. the concluion o the thei uch a: During thi paper work the perormance o the hybrid active power ilter i analyzed uing SPWM technique or minimizing harmonic, and improving the power actor in the power ytem. The perormance o the hybrid active power ilter i veriied with the imulation reult. Form the reult; it clearly indicate that, the current ripple i le by uing SPWM. In cae o non linear load the THD repone o the ource current beore compenation i 0.8% The THD o the ource current ater compenation i 5.47% by uing SPWM technique. Reerence [1] Singh.B, Al-Haddad.K, Chandra.A, Review o active ilter or power quality improvement, IEEE Tran. Ind. Electron., (46), 5, Oct, 1999, pp [] El-Habrouk. M, Darwih. M. K, Mehta. P, Active power ilter A review, Proc. IEE Elect. Power Applicat. vol. 147, no. 5, Sept. 000, pp [] Akagi, H., New trend in active ilter or power conditioning, IEEE Tran. on Indutry Application, (), 6, Nov-Dec, 1996, pp [4] Peng Fangzheng, Application iue o active power ilter, IEEE Indutry Application Magazine, v 4, n 5, Sep-Oct, 1998, pp. 1-0.

21 Hybrid Active Filter Baed on SPWM or Power Conditioning 1 [5] Akagi.H, Kanazawa.Y, and Nabae.A, Intantaneou reactive power compenator compriing witching device without energy torage component, IEEE Tran. on Indutry Application, (0),, 1984, pp [6] S.Bhattacharya, D.M.Divan. Synchronou rame baed controller implementation or a hybrid erie active ilter ytem IEEE- Indutry Application Society Annual Meeting, vol., 1995, pp [7] Wu. J. C, Simpliied control method or the ingle phae active power ilter, Proc. IEE Elect. Power Applicat. vol. 14, no., 1996, pp [8] David, M.E. and Round, S.D, Fully digital hyterei current controller or an active power ilter, International Journal o Electronic, (86), 10, Oct. 1999, pp [9] Moran. L. A, Dixon. J. W, Wallace. R. R., Three-phae active power ilter operating with ixed witching requency or reactive power and current harmonic compenation, IEEE Tran. Ind. Electron. vol. 4, no. 4, Aug, 1995, pp [10] Hamaaki, Shin-Ichi and Kawamura, Atuo, Improvement o current regulation o line-current-detection-type active ilter baed on deadbeat control, IEEE Tranaction on Indutry Application, v 9, n, 00, pp

22