Pefomance Investigation of Sunt Active Powe Filte Using Hysteesis Cuent Contol Metod VIKASH ANAND M.Tec. (Powe Electonics & Dives) Electical Engineeing Depatment Madan Moan Malviya Engineeing College Goakpu-273010(U.P), India ABSTRACT Te simulation study of PI Contolled, tee pase sunt active powe filte to impove powe quality by compensating amonics and eactive powe equied by a non-linea load is pesented. Te sunt active filte employs a simple metod fo te efeence compensation cuent based on Fast Fouie Tansfom. Classic filtes may not ave satisfactoy pefomance in fast vaying conditions. But auto tuned active powe filtes give bette esults fo amonics minimization, eactive powe compensation and powe facto impovement. Tis pape as poposed an auto tuned sunt active filte, wic maintains te THD well witin te IEEE-519 standads. Te esults ae found to be quite satisfactoy to mitigate amonic distotion, eactive powe compensation and powe facto impovement. KEYWORDS Powe System, Sunt Active Filte, PI Contolle, Hysteesis Cuent Pulse Widt Modulation. 1. INTRODUCTION Hamonics contamination is a seious and a amful poblem in Electic Powe System. Active Powe filteing constitutes one of te most effective poposed solutions. A sunt active powe filte tat acieves low cuent total amonic distotion (THD), eactive powe compensation and powe facto coection is pesented. Hence, it is necessay to educe te dominant amonics below 5% as specified in IEEE-519-1992 amonic standad [1]. Hamonic Amplification is one te most seious poblem. It is caused by amonic esonance between line inductance and powe facto coection (PFC) capacitos installed by consumes. Active filtes fo damping out amonic esonance in industial and D. S. K. SRIVASTAVA Associate Pofesso Electical Engineeing Depatment Madan Moan Malviya Engineeing College Goakpu-273010 (U.P),India utility powe distibution systems ave been eseaced [1]-[5]. Taditionally based, passive L-C filtes wee used to eliminate line amonics in [2]-[4]. Howeve, te passive filtes ave te demeits of fixed compensation, bulkiness and occuence of esonance wit ote elements. Te ecent advances in powe semiconducto devices ave esulted in te development of Active Powe Filtes (APF) fo amonic suppession. Vaious topologies of active filtes ave been poposed fo amonic mitigation. Te sunt APF based on Voltage Souce Invete (VSI) stuctue is an attactive solution to amonic cuent poblems. Te SAF is a pulse widt modulated (PWM) VSI tat is connected in paallel wit te load. It as te capability to inject amonic cuent into te AC system wit te same amplitude but opposite pase tan tat of te load [1]-[2]. Te pincipal components of te APF ae te VSI, a DC enegy stoage device tat in tis case is capacito, a coupling tansfome and te associated contol cicuits. Te pefomance of an active filte depends mainly on te tecnique used to compute te efeence cuent and te contol metod used to inject te desied compensation cuent into te line. Tee ae two majo appoaces tat ave emeged fo te amonic detection [2], namely, time domain and te fequency domain metods. Te fequency domain metods include, Discete Fouie Tansfom (DFT), Fast Fouie Tansfom (FFT), and Recusive Discete Fouie Tansfom (RDFT) based metods. Te fequency domain metods equie lage memoy, computation powe and te esults povided duing te tansient condition may be impecise [4]. On te ote and, te time domain metods equie less calculation and ae widely followed fo computing te efeence cuent. 1
Tee ae seveal cuent contol stategies poposed in te liteatue [5]-[7], [8]-[9], namely, PI contol, Aveage Cuent Mode Contol (ACMC), Sliding Mode Contol (SMC) and ysteesis contol. Among te vaious cuent contol tecniques, ysteesis contol is te most popula one fo active powe filte applications. Hysteesis cuent contol [6] is a metod of contolling a voltage souce invete so tat te output cuent is geneated wic follows a efeence cuent wavefom in tis pape. Geneally, PI contolle [7] is used to contol te DC bus voltage of SAF. Te PI contolle based appoac equies pecise linea matematical model. Tis capte basically deals wit te modeling and design of sunt active powe filte fo compensation of amonics and eactive powe. Designs of diffeent paametes like powe cicuit, contol cicuit, contol stategies, EMI/ Ripple facto ae discussed. 2. Basic Compensation Pinciple Fig.1 sows te basic compensation pinciple of sunt active powe filte. A voltage souce invete (VSI) is used as te sunt active powe filte. Tis is contolled so as to daw o supply a compensating cuent I c fom o to te utility, suc tat it cancels cuent amonics on te AC side i.e. tis active powe filte (APF) geneates te nonlineaities opposite to te load nonlineaities [3]. Fig.1 Basic compensation pinciple Fig.3 Single line diagam of te sunt active powe filte sowing powe flow Total instantaneous powe dawn by te nonlinea load can be epesented as:- p L (t) = p f ( t ) + p ( t ) + p ( t ) Wee, p f (t) - instantaneous fundamental (eal) powe absobed by te load, p (t) instantaneous eactive powe dawn by te load, and p (t) instantaneous amonic powe dawn by te load. In ode to acieve unity powe facto opeation and dawing sinusoidal cuents fom te utility, active powe filte must supply all te eactive and amonics powe demand of te load. At te same time, active filte will daw eal component of powe (P Loss ) fom te utility, to supply switcing losses and to maintain te DC link voltage uncanged. Powe components (eactive and te amonic) sould be supplied by te active powe filtes i.e. p ( t ) = p ( t ) + p ( t ) c 2.1 Estimation of Refeence Souce Cuent Fom te single line diagam sown in fig.3 i s (t) = i L (t) - i c (t) (1) Wee, i s (t), i L (t), i c (t) ae te instantaneous value of souce cuent, load cuent and te filte cuent. And te utility voltage is given by v s (t) = m V sinωt (2) Fig.2 Wavefom fo actual load cuent (A), desied souce cuent (B) and te compensating filte cuent (C). Wee, v s (t) is te instantaneous value of te souce voltage, V m - is te peak value of te souce voltage. 2
If non-linea load is connected ten te load cuent will ave a fundamental component and te amonic components wic can be epesented as i L (t) = In sin(nωt + n) n=1 I1 sin(ωt + 1) + In sin(nωt + n) (3) n=2 Wee, I 1 and 1 ae te amplitude of te fundamental cuent and its angle wit espect to te fundamental voltage, and I n and n ae te amplitude of te nt amonic cuent and its angle. Instantaneous load powe p L(t) = v s(t) i L(t) V sinωt I1 sin(ωt + 1) = m p L(t) can be expessed as + Vm sinωt n n n=2 I sin(nωt + ) = p f ( t ) + p ( t ) + p ( t ) (4) p ( t ) + p ( t ) (5) = f c In te equation (4) and (5) p ( t ) is te eal powe (fundamental), f p ( t) epesents te eactive powe and p ( t) epesents te amonic powe dawn by te load. Fo ideal compensation only te eal powe (fundamental) sould by supplied by te souce wile all ote powe components (eactive and te amonic) sould be supplied by te active powe filtes i.e. p ( t ) = p ( t ) + p ( t ) c. Te total peak cuent supplied by te souce I max = I sm + I sl (6) Wee, I sm = I 1 cos 1 and I sl is te loss component of cuent dawn fom te souce. If active powe filte povide te total eactive and amonic powe, ten i s (t) will be in pase wit te utility and pue sinusoidal. At tis time, te active filte must povide te following compensation cuent: I c (t) = I L (t) i s (t) (7) Hence, fo te accuate and instantaneous compensation of eactive and amonic powe it is vey necessay to calculate te accuate value of te instantaneous cuent supplied by te souce. I s (t) = I max sinωt (8) Wee, I max (= I 1 cos 1 + I sl ) is te amplitude of te desied souce cuents. Te pase angles can be obtained fom te souce voltages. Hence, te wavefom and pases of te souce cuents ae known and only te magnitude of te souce cuents needs to be detemined. Te peak value o te efeence cuent I max is estimated by egulating te DC link voltage of te invete. Tis DC link voltage is compaed by a efeence value and te eo is pocessed in a PI contolle. Te output of te PI contolle is consideed as te amplitude of te desied souce cuents and te efeence cuents ae estimated by multiplying tis peak value wit te unit sine vectos in pase wit te souce voltages. 2.2 Design of Sunt Active Powe Filte Te sunt active powe filte mainly consists of DC link capacito, filte inducto, PI contolle and te ysteesis contolle. 2.2.1 DC Link Capacito Te DC link capacito mainly seves two puposes- (a) It maintains almost a constant DC voltage. (b) It seves as an enegy stoage element to supply eal powe diffeence between load and souce duing tansients. In tis sceme te ole of te DC link capacito is to absob/supply eal powe demand of te load duing tansient. Hence te design of te DC link capacito is based on te pinciple of instantaneous powe flow. Equalizing te instantaneous powe flow on te DC and AC side of te invete consideing only fundamental component [3]. V dc I dc = v ca (t) i ca (t)+ v cb (t) i cb (t)+v cc (t) i cc (t) (9) Assuming tat tee pase quantities ae displaced by 120 0 wit espect to eac ote, is te pase angle by wic te pase cuent lags te invete pase voltage, and 2 V c and 2 I c ae te amplitudes of te pase voltage and cuent, espectively of te input side of te invete. V dc I dc = 2V ca I ca sin ω 1 t sin (ω 1 t- a ) + 2V cb I cb sin (ω 1 t-120 0 ) sin (ω 1 t -120 0 - b ) + 2V cc I cc sin (ω 1 t +120 0 ) sin (ω 1 t +120 0 - c ) (10) 3
Case I: If te tee pase system is balanced- Ten, V ca = V cb = V cc = V c I ca = I cb = I cc = I c, and a = b = c = Hence, V dc I dc = 3 V c I c cos (11) i.e. te DC side capacito voltage is a DC quantity and ipple fee. Case II: If te tee pase system is unbalanced- V dc I dc =(V ca I ca cos a + V cb I cb cos b + V cc I cc cos c ) - [V ca I ca cos (2ω 1 t- a) + V cb I cb cos (2ω 1 t - 240 0 - b) + V cc I cc cos (2ω 1 t + 240 0 - c )] (12) Te above equation sows tat te fist tem is a dc component, wic is esponsible fo te powe tansfe fom dc side to te AC side. Hee it is esponsible fo te loss component of te invete and to maintain te DC side capacito voltage constant. (a) Te AC souce voltage is sinusoidal. (b) Fo Lc, te AC side line cuent distotion is assumed to be 5%. (c) Reactive powe compensation capability of te active filte. (d) Te PWM convete is assumed to opeate in te linea modulation mode (i.e 0 m a 1). Fo satisfactoy opeation te magnitude of V dc,ef sould be ige tan te magnitude of te souce voltage V s. By suitable opeation of switces a voltage V c aving fundamental component V c1 is geneated at te ac side of te invete. Tis esults in flow of fundamental fequency component I s1, as sown in fig.4.te paso diagam fo V c1 >V s epesenting te eactive powe flow is also sown in tis figue. In tis I s1 epesent fundamental component [3]-[11]. Te peak to peak ipple voltage is given by V pp = π * I pp * X c = (π * I pp ) / (ω * C f ) (13) Wee, I pp is te peak to peak second amonic ipple of te DC side cuent. Assuming tat V pp is muc less tan V dc ten using equations (14) and (15) te maximum value of te V pp can be obtained as- V pp = (π * I c1, ated ) / ( 3 ω * C f ) (14) Case III: Since te total load powe is sum of te souce powe and compensato powe (i.e. P L = P c + P s ), so tat wen load cange takes place, te canged load powe must be absobed by te active powe filte and te utility i.e. P L = P c + P s (15) Hence, selection of capacito value C f can be govened by educing te voltage ipple. As pe te specification of V pp, max and I c1, ated te value of te capacito can be found fom te following equation C f = (π * I c1, ated ) / ( 3 ω * V pp, max ) (16) It is obseved tat te value of C f depends on te maximum possible vaiation in load and not on te steady state value of te load cuent. Hence, pope foecasting in te load vaiation educes te value of C f. 2.2.2 Selection of Lc and Refeence Capacito Voltage (V dc,ef ) Te design of tese components is based on te following assumptions: Fig.4 Single line and vecto diagams fo sunt APF As pe te compensation pinciple active powe filte adjusts te cuent I c1 to compensate te eactive powe of te load. In ode to maintain I s1 in pase wit V s, active filte sould compensate all te fundamental eactive powe of te load. Te vecto diagam epesents te eactive powe flow in wic I s1 is in pase wit V s and I c1 is otogonal to it. Fom te vecto diagam, V c1 = V s + jω L f I c1 (17) i.e. to know V c1 it is necessay to know I c1 Vc1- Vs Vc1 Vs I c1 = = 1- ωlf ωlf Vc1 (18) Now te tee pase eactive powe deliveed fom te active powe filte can be calculated fom te vecto diagam as Vc1 Vs Q c1 = Q L1 = 3 V s I c1 = 3 Vs 1- (19) ωlf Vc1 Fom tese equations If V c1 > V s, Q c1 is positive. If V c1 < V s, Q c1 is negative. 4
i.e. active powe filte can compensate te lagging eactive powe fom utility only wenv c1 >V s. Fom[11], If te invete is assumed to opeate in te linea modulation mode i.e. modulation index vaies between 0 and 1, ten te amplitude modulation index is given by- m a = 2 2V Vdc c1 (wee, Vm= 2 V c ) (20) And te value of V dc is taken as V dc = 2 2 V c1 (fo m a =1) (21) Te filte inducto L f is also used to filte te ipples of te invete cuent,and ence te design of L f is based on te pinciple of amonic cuent eduction.te ipple cuent of te invete can be given in tems of te maximum amonic voltage, wic occus at te fequency m f ω. I c (m f ω) = (22) Wee,m f is te fequency modulation atio of PWM convete. On solving (19) and (22) simultaneously, te value of L f and V c1 (i.e V dc ) can be calculated. V c1 and V dc ef, must be set accoding to te capacity equiement of te system (i.e V s < V c1 2V s ).As te switcing fequency is not fixed wit te ysteesis contolle, a pactically feasible value of 10kHz as been assumed. 2.3 PI Contolle Te contolle used is te discete PI contolle tat takes in te efeence voltage and te actual voltage and gives te maximum value of te efeence cuent depending on te eo in te efeence and te actual values. Te matematical equations fo te discete PI contolle ae: Te voltage eo V (n) is given as: V (n) =V*(n) - V (n) Te output of te PI contolle at te nt instant is given as: I(n)=I(n-1) + Kp[V(n)-V(n-1)] + Ki V(n) 2.4 Hysteesis Cuent Contolle Wit te ysteesis contol, limit bands ae set on eite side of a signal epesenting te desied output wavefom. Te invete switces ae opeated as te geneated signals witin limits. Hysteesis-band PWM is basically an instantaneous feedback contol metod of PWM wee te actual signal continually tacks te command signal witin a ysteesis band [10]. Fig.5 Basic pinciple of ysteesis band contol Te ate of cange of inducto cuent is ten given by (23) Making assumption tat te ac supply does not cange duing a cycle of switc opeations, te time taken t m taken to coss a dead band is (24) Te switcing fequency f sw is, teefoe vaiable. Combining above two equations (23) and (24) to obtain te switcing peiod, and inveting, gives 3. Simulation And Pefomance Investigation Of Sunt APF In tis section te simulation analysis of sunt APF is descibed, fist fo R-L load and ten fo DC macine load and te FFT analysis as been caied out simultaneously. 3.1 Opeation of Simulation Model Te opeation of te simulation model sown below is descibed as fist te capacito voltage is sensed wic is compaed wit te efeence voltage and te eo signal is given to te PI contolle fo pocessing to obtain te maximum value (I m ) of te efeence cuent wic is multiplied wit te unit vecto template i.e. sinωt to get te efeence cuent I m sinωt fo pase a. Tis signal is now delayed by 120 0 fo getting te efeence cuent fo pase b, wic is fute delayed by 120 0 to get te efeence cuent fo te pase c. tese efeence cuents ae now 5
compaed wit te actual souce cuents and te eo is pocessed in te ysteesis contolle to geneate te fiing pulses fo te switces of te invete. And te switces ae tuned on and off in suc a way tat if te efeence cuent is moe tan te actual souce cuent ten te lowe switc is tuned on and te uppe switc is tuned off and if te efeence cuent is less tan te actual souce cuent ten te uppe switc of te same leg is tuned on and te lowe switc is tuned off. Te output of te sunt active powe filte is suc tat te souce cuent is puely sinusoidal and te amonic cuent is dawn o supplied by te filte. Te wavefom sown in fig.7 demonstates tat supply voltage is almost sinusoidal of V peak =100 volt in pase 0,- 120 and +120 degee of a, b and c pase espectively. Fig.8 Load cuent Te wavefom sown in fig.8 demonstates tat load cuent is in sinusoidal natue wit containing small amount amonic. Fig.6 MATLAB model fo Sunt active powe filte 3.2 Simulation Result And Discussion Fig.9 Souce cuent befoe and afte compensation Fig.7 Tee pase supply voltages Te wavefom sown in fig.9 demonstates tat souce cuent befoe compensation (i.e fom 0 to 0.1 sec.) and afte compensation (i.e fom 0.1 sec.), it is almost sinusoidal wit educed amonic content. 6
Fig.10 Souce voltage, souce cuent and filte cuent fo pase A Fig.12 FFT Analysis fo load cuent Te wavefom sown in fig.10 demonstates tat souce voltage, souce cuent befoe and afte compensation and filte cuent fo pase A. Fig.13 FFT Analysis fo souce cuent Te wavefom sown in fig.12 and fig.13 demonstates tat souce cuent is educed THD fom 21.83% to 0.89%. Fig.11 Capacito voltage and capacito cuent Te wavefom sown in fig.11 demonstates tat capacito voltage settles at nealy constant value of V dc ef. and capacito cuent settles at almost equal to te value of filte cuent. THD analysis of sunt active powe filte fo RL-Load is sown in table 1. Load type THD(%) Load Cuent R-L Load THD(%) Souce Cuent 21.83 % 0.89 % Table 1 7
4. Conclusion Te pefomance of te system impoves and te THD is educed up to vey lage extent. Also, it is seen fom te simulation esults tat te souce cuent and te souce voltages ae in same pase i.e. te input powe facto is unity and tee is no eactive powe fom te souce. Refeences [1] Roge C.Dugan, Mak F. McGanagan, Suya Santoso and H.Wayne Beaty, Electical Powe System Quality, McGaw Hill. [2] Bim Sing, Kamal Al Haddad and Ambis Canda, A Review of Active Filtes fo Powe QualityImpovement, IEEE Tans on Industial Electonics, Vol.46, No.5, Octobe 1999, pp. 960-970. [3] S.K.Jain, P.Agawal and H.O.Gupta, Fuzzy Logic contolled sunt active powe filte fo powe quality impovement, IEE poceedings in Electical Powe Applications, Vol 149, No.5, Septembe 2002. [4] Y.Sato, T.Kawase, M.Akiyama, and T.Kataoka, A contol stategy fo geneal pupose active filtes based on voltage detection, IEEE Tans. Ind. Appl., vol. 36, no.5, pp.1405 1412, Sep / Oct.2000. [5] M. Kazmiekowsi, L.Malesani,Cuent Contol Tecniques fo Tee Pase Voltage Souce PWM convetes: A suvey, IEEE Tans on Industial Electonics, vol.45, no.5, pp.691-703, Octobe 1998. [6] S. Buso, L. Malesani, P. Mattavelli, Compaison of cuent contol Tecniques fo Active powe Filte Applications, IEEE Tansactions on Industial Electonics, Vol.45, no.5, pp.722-729, Oct 1998. [7] E.E.EL-Koy, A. EL-Sabbe, A.El-Hefnawy, and Hamdy M.Maous, Tee pase active powe filte based on cuent contolled voltage souce invete, Electical Powe and Enegy Systems, 28 (2006), 537-547. [8] V. Agelidis, M. Calais, Application specific amonic pefomance evaluation of multicaie PWM tecniques, IEEEPESC 98 Confeence Recod, pp. 172-178, 1998. [9] G. Caaa, S. Gadelta, M. Macesoni, A new multilevel PWM metod: teoetical analysis, IEEE Tans. On powe electonics Vol. 7. No. 3, July, pp.497-505,1992. [10] PENG, F.Z., AKAGI, H., and NABAE, A,: A study of active powe filtes using quad seies voltage soucc PWM convctcs fo amonic compensation, IEEE Tans.Powe Electon, 1990. 5, (I). pp. 915. [11] LEE, C.C.: Fuzzy logic in contol system: fuzzy logic contolle-pat 1. IEEE Tans. Syst. Man Cyben, 1990, 20, (2). pp. 404-415. Appendix Te values of te diffeent paametes used fo sunt active powe filte. Souce voltage:3-pase, 100V, 50Hz Popotional gain K p : 0.5 Integal gain K i : 10 Capacito efeence voltage: 300V RL load paametes: 10 Ω, 100mH line paametes : 0.2 Ω, 1.5mH Filte inducto : 5mH Hysteesis band gap : -0.01 to 0.01 8