A Single-Phase Shunt Active Power Filter Based on Cycle Discrete Control for DC Bus Voltage

Transcription

1 A Sigle-Phae Shut Active Power Filter Baed o Cycle Dicrete Cotrol for DC Bu Voltage FEI-FENG JI, MANSOOR, QIAN AI, DA XIE, CHEN CHEN Departmet of Electrical Egieerig Shaghai Jiaotog Uiverity 1954 Huaha Road, Shaghai CHINA Abtract:-A ew cotrol method for igle-phae hut active power filter (APF) i propoed. It itegrate the DC bu voltage cotrol ad active power filter commad curret geeratio, accordig to the periodicity of ource curret ad eergy balace cocept. The itataeou harmoic compeatio ad liear DC bu voltage cotrol are achieved, without complicated ad ivolved cotrol logic, by uig cycle dicrete cotrol techique to DC bu voltage. A mathematical model of the cheme i developed. Detailed aalyi ad imulatio i the PSCAD/EMTDC eviromet are preeted. A laboratory prototype of thi APF i developed to validate the reult. Both of imulatio ad experimetal reult how the good behavior of thi type of APF. Key-Word:-Active power filter, Dicrete cotrol, Harmoic ad Reactive power, PWM. 1 Itroductio Over the year, power electroic device have become widepread i the idutrial a well a i the dometic world uch a cyclocoverter, variable peed drive, peroal computer. Thee o-liear load draw reactive power ad harmoic curret alog with active power from ac mai. The reactive power ad harmoic compoet of load curret caue poor power factor, poor utilizatio of ditributio ytem, overheatig which deteriorate life expectacy of other equipmet ad caue low efficiecy, diturbace to other coumer ad iterferece to commuicatio etwork. Covetioally, paive -C filter ad capacitor are employed to compeate harmoic ad laggig power-factor of the liear ad o-liear load. But they have may demerit like fixed compeatio, large ize, reoace, oie, ad icreaed loe [1,,3]. Havig the feature of good traiet repoe, accurate compeatio, ad elimiatig reoace, APF ha bee ued to replace the paive filter tep by tep,ad geerated tremedou iteret amog the reearcher. Variou type of active power filter are reported i the literature. Referece [4,5] itroduce a APF baed o itataeou reactive power theory. Adaptive method for the harmoic extractio i utilized i the APF itroduced i referece [6,7]. It i a commo obervatio that the calculatio of harmoic decreae the repoe peed of APF. I order to maitai the DC bu voltage, geeral cotiuou PI cotrol method i ued i voltage cotrol loop, which effect the compeatio preciio [1,8]. I paper [8], a PF i ued to get average value of DC capacitor voltage, thi reult i ~3 cycle delay i repoe time. The o-liear PI cotroller for voltage loop make the APF cotrol more complex [9]. The approximatig method [10] ca get liear cotrol for DC bu voltage, but the overall performace i poor. Thi paper propoe a ew APF cotrol techique, ad i the propoed method, cycle dicrete cotrol i applied to DC voltage cotrol loop. The aliet feature of the propoed method i that it keep the ource curret ychroized to the mai voltage, irrepective of the load traiet. Accordig to eergy balace cocept, the output of cycle dicrete cotroller i equal to the magitude of required active curret to compeate the load active power ad APF loe. The cycle dicrete cotrol method eure that the ource active curret maitai perfect iuoid path i each cycle, eve durig traiet. Thi ew method ca miimize the ource active curret ditortio at load fluctuatio,ad i thi cotrol tructure, there are o delay elemet like PF, hece the harmoic compeatio i itataeou. Problem Statemet Fig.1 how the power torage circuit diagram of the igle-phae hut voltage-mode APF. The filter coit of a PWM voltage ource, iverter liked to

2 the poit of coectio through a filterig iductor f ad capacitor C f. It i operated i a cotrolled curret boot-type iverter mode, ad the curret draw from the utility i i made to follow a iuoidal referece curret i rf i a fixed hyterei bad. Fig.. Oe of the claic cheme of geeratig igle-phae APF output referece curret Fig.1 Baic Circuit of the active power filter.1 Claic Operatio Priciple of APF Uder ormal circumtace, the utility ca be aumed to be a ideal iuoidal voltage ource. u = Vmiωt (1) Where ω i the fudametal frequecy of the utility ource voltage. I the cae of a oliear load, the load curret coit of fudametal compoet ad the higher-order harmoic a follow: i = I i( ω t + θ ) () = 1 From Fig.1, it ca be foud that the deired compeatio curret geerated by power iverter ca be repreeted a: ic = i i (3) I the claic cotrol method of active power filter, load curret ad ource curret i eed to calculate the harmoic ad reactive curret. Owig to the loe i the iverter uch a witchig lo, capacitor leakage curret etc., the utility ot oly provide the real power eeded by the load but alo the additioal power required by the iverter to maitai the capacitor voltage at a precribed value, hece the claical PI cotroller ad PF are ofte ued i voltage loop [8]. Fig. how oe of claic cheme of geeratig igle-phae APF output referece curret reported i variou paper e.g. [11]. I the Fig., the DC compoet I P obtaied after PF i equal to the peak value of active curret of load curret. The igal I p i the output of claical PI cotroller for the DC-bu voltage. If I p i free of harmoic,the I p i a fixed value throughout oe cycle. However, a claical PI cotroller i applied, I p i ot free of harmoic. Ad coequetly, igal i p ca ot be pure iuoidal waveform. Typical waveform of compeated ource curret i thi cae i how i Fig.3. Whe the load curret chage uddely, I p varie a the load curret. Sice i p doe t ot chage at the zero cro poit of ource voltage probably, hece ditortio occur i ource curret a how i Fig.4 [10,1]. Fig.3. Compeated ource curret wave: Tr i i load curret; Tr i i ource curret Fig.4. Source curret i traiet tate: Tr i i load curret; Tr i i ource curret 3 The Propoed Active PowerFilter 3.1 Priciple of Operatio Fig.5 The power flow diagram of igle-phae hut APF The power flow of igle-phae hut APF ytem i how i Fig.5. At full compeatio, ource provide active power P which i equal to the um of APF lo power P A ad active power of the load P. The load reactive power q i provided by the APF. From equtio.1 ad, P ad q ca be expreed a: P = I1 coθ1v i ωt (4) m q = I1iθ 1V mi ( ωt) + Vmi( ωt) I i( ωt + θ) (5) = Itegratig the reactive power of load q i oe fudametal cycle, we ca get: T 0 + q dt = U = T 0 ( I U q i( ω t ) I i( ω t ) co( ω t ) i( ω t + θ )) dt = 0 (6) Where T i the fudametal period of the utility. Itegratig P i oe fudametal cycle reult i followig equatio:

3 T T T P dt = ( I1 coθ 1V m i( ωt)) dt = I1 coθ1v m 0 0 (7) I a voltage-ource iverter, the DC bu capacitor i ued a a eergy torage elemet of the ytem. Eq.6 ad 7 how that the reactive power q reult i eergy exchage betwee AC ource ad DC-ide capacitor by iverter. The DC bu voltage fluctuate with the eergy exchage. Wherea, the itegratio of q i oe fudametal period T i zero, o the reactive power doe t effect the T periodically ampled value of DC bu voltage. However itegratio of active power P i ot zero, that i, if the DC bu capacitor provide active power for the load ad iverter, the the periodically ampled value of DC bu voltage ca ot be cotat.the T periodically ampled value of DC-bu voltage ca upply the active power flow iformatio, ad the amplitude of the mai curret ca be obtaied by uig a voltage regulatio circuit of the DC capacitor. maitaied at a fixed value at the ed of each cycle.hece the APF jut provide the harmoic ad reactive compoet of load curret meawhile. The equatio mathematical model of the APF ca be obtaied a how i Fig.8. I thi model, the curret i ( t ) ca be coidered a a diturbace. A the igal I P ( k ) i a cycle dicrete value, a zero-order hold with fudametal amplig period i ued i the model. The trafer fuctio of DC ide capacitor plat G () i 1 G ( ) = (8) CS Where C i the DC ide capacitor. It ca eaily be verified that the dicrete trafer fuctio betwee the I P ( k ) ad DC bu voltage ca be writte a: T 1 G z (9) ( ) = C z 1 Where T=0.0m i the period of ytem. 3. Model of Propoed Active Power Filter Fig.8 Mathematical model of propoed AFP i DC ide of iverter Fig.6 Simplified model of igle-phae hut APF Fig.7 The waveform of igal ( k ) Geerally, the APF output curret coit of three compoet: load curret i (t), ource curret i (t) ad the fudametal active curret i A which repreet the lo of iverter. A implified APF model of full bridge iverter actig a power torage i how i Fig.6(a). The AC compoet of th capacitor curret i (t) doe t chage the periodically ampled value of DC-bu voltage, wherea the DC compoet of curret i (t) chage it. So the model i Fig.6(a)ca be implified toa model i the DC ide of iverter how i Fig.6(b). I thi model the DC ide capacitor curret i give by i( t) = i( t) IP( t). The curret i i equivalet to the um of load curret i (t) ad curret i A, which coit of DC compoet ad harmoic curret. The DC curret I P ( k ) multiply π i the amplitude of ource fudametal active curret i (t) a how i Fig.7. Accordig to model i Fig.6(b), if DC curret I ( k P ) ca completely compeate the DC compoet of i, the periodically ampled value of DC-bu voltage i I P 3.3 Deig of Cycle Dicrete Cotroller The itegratio of the capacitor curret i (t) i oe fudametal cycle ca be writte a followig: ( K+ 1) T = i kt ( k+ 1) T kt dt = ( i I ) dt ( I ( k) I ( k)) dt = T( I ( k) I ( k)) = U C ( k+ 1) T kt P P P (10) That i I ( ) ( ) T K I P K = U C (11) = T ( u ( k ) u ( k 1)) u( k) C = Where I (K) i the average value of curret i ( t ) durig the iterval [(K-1)t,KT]. From eq.11, the referece curret iput to the iverter to maitai DC bu voltage ca be writte a IP ( k) = IP( k 1) + u( k) (1) The tructure of thi cotroller i illutrated i Fig.9. Fig.9. cycle dicrete cotroller for DC-bu voltage uig capacitor curret From Fig.9, the dicrete trafer fuctio D(Z) ca be give a D ( z) = C / T (13)

4 Eq.13 i a P cotroller how i Fig.10,ad for C=10000uF, P i 0.5. I Fig11, the ope-loop frequecy repoe of thi cotrol ytem how that the gai margi i 3 db ad phae margi i 45 0 repectively. Fig.1 how the good tep repoe with oe cycle delay ad o teady error. I cae of the diturbace, the output of thi ytem will have a error how i Fig.13. Fig.15 Ope-loop frequecy repoe of the cotrol ytem uig PI cotroller Fig.10. Trafer fuctio model of the propoed APF Fig.16 Step repoe of the cotrol ytem uig P cotroller Fig.11. Ope-loop frequecy repoe of the cotrol ytem uig P cotroller Fig.17 Output Sytem of uig periodic dicrete PI cotroller with diturbace 3.4. Cotrol Block Diagram Fig.1 Step repoe of cotrol ytem uig P cotroller Fig.13 Output Sytem of uig P cotroller with diturbace To elimiate the diturbace, a cycle dicrete PI cotroller i ued, which i how Fig.14. Whe the PI cotroller parameter K P ad K I i 0.45 ad 0.1, gai margi of 6 db ad phae margi i 50 0 i obtaied repectively how i Fig15. Fig.16 how the tep repoe of thi ytem. I Fig.17 it ca be foud that thi cloe-loop ytem with cycle dicrete PI cotroller ca maitai the DC bu voltage ear the referece value i pite of the diturbace. Fig.14 Sytem model uig periodic dicrete PI cotroller Fig.18 Baic cotrol block diagram of the propoed cheme for igle-phae APF The baic cotrol block diagram of the propoed cheme for igle-phae APF i how i Fig.18.It ca be foud that the DC bu voltage i ampled at the poitive goig zero-croig itat. I thi way, the high frequecy diturbace i the whole ytem ca be reduced[13]. The periodically ampled value of DC bu voltage U (k) i compared with a referece voltage V ref. The compared output i fed to cycle dicrete cotroller to geerate the deired amplitude of ource curret I P (k). A the U (k) i ampled at the poitive goig zero-croig itat of ource voltage, it i eured that the error iformatio which paed to the cycle dicrete cotroller i ampled oly at the poitive goig zero-croig poit of ource voltage. The deired amplitude I P (k) of ource curret i et at the begiig of each cycle, ad i kept cotat throughout the cycle. The deired ource curret ad the

5 detected ource curret are fed to the curret cotrol loop to geerator the deired output curret i ( t c ). The actual output curret i c (t) i made to follow i ( t c ) withi a hyterei bad. Sice the amplitude of I P (k) i maitaied cotat throughout a ampled cycle of the ource voltage, the ource curret remai ditortio free ad i i phae with the ource voltage durig both teady tate ad traiet operatio. Hece, the compeatio proce i itataeou. icreae, the capacitor iject ome active power to AC ource, ad the DC-bu voltage dip for a hort period of time. The ditortio i traiet-tate i avoided by makig ue of the active power torage fuctio of DC-ide capacitor. The imulatio output of ource curret i ad load curret i i how i Fig.0, it ca be oberved that the ource curret maitai iuoidal i depite of the fluctuatio of load curret. 4 Simulatio ad Expererimet Reult 4.1 Simulatio Reult Simulatio tudie are carried out to predict the performace of propoed APF by PSCAD/EMTDC [14]. I the imulatio, the ytem tructure of APF i how a fig.1, the oliear load i repreeted by atiparallel thyritor. The width of the hyterei widow i maitaied at 0.5A, ad the witchig frequecy i 10 KHz. Fig.19 Wave of DC-bu voltage, the deired amplitude of ource curret ad the deired ource curret Fig.0 Simulatio output of ource curret ad load curret; Tr i i the load curret; Tr i i ource curret. Fig.19 diplay the waveform of DC-bu voltage U, the deired amplitude of ource curret I P (K) ad the deired ource curret i ( t ). It i how that by uig cycle dicrete cotroller, the deired amplitude of ource curret I P (K) i a dicrete value ad keep cotat i oe cycle, o the deired ource curret i i alway iuoid. Sice the witchig frequecy of iverter i 10K Hz, the fluctuatio i DC-bu voltage are mall, ad the cycle ampled value of DC-bu voltage U (K) ca be kept o referece value. Whe the load curret decreae uddely, the DC-ide capacitor aborb a part of itataeou active power, the DC-bu voltage rie for a hort period of time. O the cotrary, while the load curret 4. Experimet Reult Fig.1 Experimet ytem tructure O the bai of the propoed cotrol tructure, a igle-phae hut APF prototype(0v/30kw) baed o TMS30F81DSP i developed. The DC ide capacitor C=10000 uf, filterig iductace f =0.1mH ad capacitor C f =30uF. DC-bu referece value U ref =500V. The oliear load i repreeted by full-wave diode rectifier. The ytem tructure i how i Fig.1. Fig. how the teady-tate performace of APF. It ca be foud that although the DC bu voltage ha ripple,it i table ad ear the et value. It fluctuatio frequecy i twice of the fudametal frequecy of the AC ource [1]. Furthermore the ource curret i almot iuoidal. Fig.3ad 4 how the harmoic pectrum of ource curret ad load curret. It i foud that the THD of load curret i approximately 50%, ad the ource curret THD i le tha 5%. Fig.5 i the traiet performace of propoed APF.Whe witch K ope uddely, the load curret decreae ad the DC-bu voltage will rie a little for 3 period early. I the traiet proce, the ource curret doe t how ay ditortio. Fig. Steady-tate performace: Tr1:DC-bu voltage (50v/div); Tr:ource curret (10A/div); Tr3:load curret (10A/div) time cale =5m/div

6 Fig.3 Harmoic pectrum of the oliear load curret Y=10dB/div; X=15Hz/div Fig.4 Harmoic pectrum of the Y=10dB/div;X=15Hz/div oliear load curret Fig.5 traiet tate performace: Tr1:DC-bu voltage (50v/div); Tr:ource curret (10A/div);Tr3:load curret (10A/div) time cale =5m/div 5 Cocluio A ew type of igle-phae hut APF techique i propoed i thi paper. The cycle dicrete cotroller i ued to implify the APF cotrol tructure ad to realize the liear cotrol for the DC-bu voltage. The merit of thi APF are:(a)simplified the calculatio of the active compoet of load curret.(b)the cotrol of DC-bu voltage i liear.(c)the AC ource curret maitai iuoidal, eve durig the variatio of load curret.(d)ytem i table uder large fluctuatio i load curret. The feaibility of the above cheme i verified by PSCAD/EMTDC imulatio ad experimetal reult. Referece: [1] Sigh, B, Al-Haddad, K, Chadra, A, A Uiveral Active Power Filter for Sigle-Phae Reactive Power ad Harmoic Compeatio, Iteratioal coferece of Power Quality,1998,pp: [] Zargari, N.R, Joo, G.,Performace ivetigatio of a curret-cotrolled voltage-regulated PWM rectifier i rotatig ad tatioary frame, IEEE Traactio o Idutrial Electroic, Vol. 4,No.4, pp [3] Blako, V, Kaura, V,A ew mathematical model ad cotrol of a three-phae AC-DC voltage ource coverter, IEEE Traactio o Power Electroic, Vol. 1, No 1, pp [4] Mihra, M.K, Johi, A, Ghoh, A, A ew algorithm for active hut filter uig itataeou reactive power theory, IEEE Traactio o Power Egieerig Review, Vol.0, No. 1, pp [5] Dobrucky, B, Hyoug Kim, Racek, V, Roch, M, Pokory, M, Sigle-phae power active filter ad compeator uig itataeou reactive power method, Iteratioal Coferece Power Coverio, Vol.1, 00.pp [6] Bakhhai, A.R, Karimi, H, Saeedifard, M,A ew adaptive harmoic extractio cheme for igle-phae active power filter, Proceedig of the 003 Iteratioal Sympoium, Vol.3, 003,pp. III-68 - III-71. [7] Wag Qu, Wu Nig, Jiag Zejia, A adaptive detectig approach of harmoic curret for active power filter, Iteratioal Coferece o POWERCON Vol., 1998,pp [8] Wu, J.-C, Jou, H.-, Simplified cotrol method for the igle-phae active power filter, IEE Proceedig Electric Power Applicatio, Vol.143, No.3 pp.19-4 [9] e Magoarou, F, Moteil, F, Ifluece of the load o the deig proce of a active power filter, 0th Iteratioal Coferece o IECON,Vol , pp vol.1 [10] Hu, C.Y, Wu, H.Y, A ew igle-phae active power filter with reduced eergy-torage capacity, IEE Proceedig- Electric Power Applicatio, Vol. 143, No.1, 1996,pp [11] Doval, J, Nogueira, A, Pealver, C.M, ago, A, Active power filter with harmoic curret cotrol trategy, 9th Aual IEEE Power Electroic Specialit Coferece.Vol.,1998,pp.: [1] K.Nihida, M.Rukouzzma,M.Nakaoka, A dvaced cuuret cotrol implemetatio with robut deadbeat algorithm for hut igle-phae voltage-ource type active power filter, IEE Proc.-Electr.Power Vol.151,No.3,004,pp [13] ShutCota-Catello, R, Grio, R, Foa, E, odd-harmoic digital repetitive cotrol of a igle-phae curret active filter, IEEE Traactio o Power Electroic, Vol.19, No.4, 004,pp [14] Power Sytem Simulatio Software Maual, Maitoba HVDC Reearch Ceter.