Comparison of Control Strategies for Shunt Active Power Filter under Different Load Conditions

Transcription

1 Comparson of Control Strateges for Shunt Actve Power Flter under Dfferent Load Condtons Sanjay C. Patel 1, Tushar A. Patel 2 Lecturer, Electrcal Department, Government Polytechnc, alsad, Gujarat, Inda 1 Lecturer, Electrcal Department, Government Polytechnc, Dahod, Gujarat, Inda 2 Abstract: Harmonc njecton n supply current s most common problem arsng n supply network because of the ncreased populaton of nonlnear loads. Ths paper present a comparatve study between two dfferent control strateges to determne the compensatng currents for a three phase three wre Shunt Actve Power Flter(SAPF). The frst strategy s based on the nstantaneous real and magnary powers theory known as p-q theory, the second s Generalzed Instanteneous Power Theory(GIPT). The two control strateges are appled to a three-wre shunt actve power flter for elmnatng load current harmoncs, reactve power compensaton and load balancng. The valdty of the proposed control scheme s verfed by the smulaton study. Index Terms: Actve Power, Harmonc Elmnaton, Non-lnear load, Load Balancng. I. INTRODUCTION The ncreased severty of harmonc polluton n power networks wth the development of power semconductors and power-electroncs applcaton technques has attracted the attenton to develop dynamc and adjustable solutons to the power qualty problems. Control of these harmonc perturbatons by passve flters can generate addtonal resonance, whch could result n destructon of these flters. Ths has lead to development of actve flters. Shunt actve flters have been recognzed as a good soluton to current harmonc and reactve power compensaton of non-lnear loads [1]. Fg.1 shows a typcal system confguraton of a three-phase three-wre; shunt APF wth a voltage source nverter. The basc prncple of a shunt actve power flter s that t generates a current equal and opposte n polarty to the harmonc current drawn by the load and njects t to the pont of common couplng, thereby forcng the to be pure snusodal. Instantaneous power compensaton theory s recognzed as one of the best methods. Instantaneous real and magnary powers have frst been defned n the tme doman by p q theory, and ther concept has been successfully appled to harmonc/reactve current control n three-phase three-wre systems [2-3]. In p q theory, voltages and currents n a three-phase three wre system are transformed nto twophase current/voltage components on orthogonal α β coordnates, and then the nstantaneous real and magnary powers can be calculated wthout any tme delay from the two-phase components. A generalzed theory of nstantaneous reactve power has been proposed for three-phase power systems. The generalzed theory s vald for snusodal or non snusodal and balanced or unbalanced three-phase systems, wth or wthout zero-sequence currents and/or voltages [4].In ths paper generalzed defnton of nstantaneous actve, reactve and apparent power n three-phase system s presented. By drectly takng the nstantaneous voltage and current as two vectors, the nstantaneous reactve quantty s consdered as the second order asymmetrcal tensor resultng from the outer-product operaton of voltage and current vectors. Ths defnton s further extended for Actve Power Lne Condtoners (APLCs) applcatons by decomposng current nto separate component representng dfferent parts of the power. Source Copyrght to IJIREEICE DOI /IJIREEICE sa sb sc ca cb la lb lc cc Non lnear load Actve Power Flter Fg. 1 System dagram of a SI-SAPF In ths paper results obtaned for shunt actve power flter usng GIPT are compared wth that obtaned by more wdely used nstantaneous p-q theory for the known three phase condtons. Applcaton to calculate references for actve power flter are also presented for dfferent applcatons lke harmonc elmnaton, reactve power compensaton and load balancng under snusodal supply condton. II. P-Q THEORY The nstantaneous p-q method s one of the frst compensaton schemes developed by Akag [1].Accordng to ths theory actve flter currents are obtaned from the nstantaneous actve and reactve powers of the nonlnear load. Ths s acheved by prevous calculaton of the mans C

2 voltages and the nonlnear load currents n a statonary reference frames,.e., n αβ0 components by (1) and (2) whch s named as the Clarke transformaton. = [ ] (1) For reactve power compensaton, the oscllatng term of p and q have to be removed. So the powers to be compensated chosen as: (10) For harmonc elmnaton and reactve power compensaton from nonlnear load, the oscllatng term of p and total q have to be removed. So the powers to be compensated chosen as: = (2) (11) [ ] The compensaton currents n α-β quanttes then s, No zero-sequence components exst n a three-phase threewre system, so that 0 and v o can be elmnated from the (12) above equaton (1) & (2). = [ ] (3) By performng the nverse transformaton, the three-phase compensaton s obtaned by (12). = [ ] (4) The conventonal nstantaneous real power n three phase crcut s defned by [1] as the summaton of the products of voltages and current on same axs. (5) (13) Where [ ] III. GENERALIZED INSTANTANEOUS POWER THEORY For the nstantaneous reactve power the authors [1] ntroduced the nstantaneous magnary power space vector defned by The nstantaneous real power p and the nstantaneous magnary power q consumed by the nonlnear load are wrtten n matrx form as follows, (6) (7) Fg. 2 llustrates the control block dagram usng p-q theory. In the nonlnear load case both powers are decomposed nto oscllatory (denoted by ~) and average (DC) component (denoted by -). The DC component represents the fundamental power, whereas the oscllatng component s related wth the harmonc power. [ ] [ ] (8) For harmonc elmnaton from nonlnear load, the oscllatng term of p and q have to be removed. So the powers to be compensated chosen as: (9) For a three-phase system, the nstantaneous quanttes of load voltage and currents are expressed as (14) Loads nstantaneous actve power p s defned as the nner product of voltage and current vectors. (15) Where. denotes the dot (nternal) product, or scalar product of vectors. Equaton (15) can also be expressed n the conventonal defnton, Copyrght to IJIREEICE DOI /IJIREEICE (16) Loads nstantaneous reactve power s defned as the outer product of voltage and current vector. (17) Where the cross (exteror) product of vectors or vector product. ector q s desgnated as the nstantaneous reactve (or nonactve) power vector of the three phase crcut. The outer product s defned by means of the tensor product n the followng way. (18)

3 The tensor product of current vector over voltage vector s: (19) The tensor product of voltage vector over current vector s: Usng Equaton (18), (19) and (20) nto (17),and hence (20) (21) Wth each components beng as: s denoted as nstantaneous reactve tensor and ts norm s defned as nstantaneous reactve power (22) In turn, we defne the nstantaneous actve current vector, the nstantaneous reactve current vector, (23) (24) The three-phase compensaton current s the sum of the nstantaneous actve current vector, the nstantaneous reactve current vector (26) Fg. 2 llustrates the control block dagram usng GIPT theory. When unbalanced nonlnear load s consdered, the equaton (8) s modfed as: [ ] [ ] (27) Where s balanced actve power and s an unbalanced actve power. The powers to be compensated chosen as: a-b-c α-β-0 Clarke Transformaton a-b-c Instantaneous Power Instantaneous Power p q p q Determnaton of Compensaton Powers Determnaton of Compensaton Powers pc qc pc qc αβ-currents a-b-c Compensated Current α-β-0 a-b-c Inverse Clarke Transformaton Fg. 2 Control algorthm p-q theory GIPT I. SIMULATION RESULTS Ic* (28) A smulaton model has been developed for three-phase shunt actve power flter usng p-q theory and GIPT n PSIM Software. Table-I shows the parameters of both confguratons. Table I. Common parameters Supply oltage Source Impedance 0.1mH, 0.5Ω Shunt APLC Inductor 400 (Lne to Lne), 50Hz 0.5mH EMI Flter Lf-1mH,Cf-2uF,Rf 0.1Ω Swtchng Frequency Load-1 Load-2 Load-3 20 KHz Three phase Dode brdge rectfer wth 50 Amp constant current source Three phase Lnear RL load(r-1ω, L-10mH) Dode brdge rectfer wth 50 Amp constant current source and Unbalanced RL load(ra-50ω,la- 12mH,Rb-20Ω,Lb-2.5mH,Rc-100Ω,Lc-27mH) Ic* Where, s denoted as nstantaneous actve current tensor and ts norm s defned as nstantaneous actve current, s denoted as nstantaneous reactve current tensor and ts norm s defned as nstantaneous reactve current. (25) Fg. 3 and fg.6 shows smulaton waveforms for mtgatng supply current harmoncs by p-q theory and GIPT respectvely. It s observed that load current harmoncs are almost removed from all three-phase supply current by both methods as shown n Fg. 3 and Fg. 6. Fg. 4 and Fg.7 shows smulaton waveforms for reactve power compensaton by p-q theory and GIPT respectvely. It s observed that both methods are very effectve for reactve power compensaton and hence supply power factor mproves from 0.3(lag) to 0.99(lag) by both methods. Fg. 5 shows the smulaton waveform Copyrght to IJIREEICE DOI /IJIREEICE

4 for load balancng usng p-q theory. It s observed that when three phase unbalanced non-lnear load s appled to balanced snusodal supply, the p-q theory s not effectve for load balancng and hence three phase supply current s unbalanced as shown n Fg. 5. Fg. 8 shows the smulaton waveform for load balancng usng GIPT. It s observed that when three phase unbalanced non-lnear load s appled to balanced snusodal supply, the GIPT s effectve for load balancng. The three phase supply current s balanced and snusodal as shown n Fg. 8. Fg. 6 Smulaton waveform for Load-1 usng GIPT load voltage and load current of phase-a reference current source voltage and of phase-a three phase Fg. 3 Smulaton waveform for Load-1 usng p-q theory load voltage and load current of phase-a reference current source voltage and of phase-a three phase Fg. 7 Smulaton waveform for Load-2 usng GIPT load voltage and load current of phase-a reference current source voltage and of phase-a three phase Fg. 4 Smulaton waveform for Load-2 usng p-q theory load voltage and load current of phase-a reference current source voltage and of phase-a three phase Fg. 8 Smulaton waveform for Load-3 usng GIPT three phase load current three phase three phase source voltage Fg. 5 Smulaton waveform for Load-3 usng p-q theory three phase load current three phase three phase source voltage Fg. 9 Harmonc spectrum for Load-1 usng p-q theory load current of phase-a of phase-a Copyrght to IJIREEICE DOI /IJIREEICE

5 ISSN (Onlne) Fg. 10 Harmonc spectrum for Load-1 usng GIPT load current of phase-a of phase-a Fg. 9 and Fg.10 shows the FFT analyss of the supply current and load current by p-q theory and GIPT. It shows that ampltude of dfferent- order harmonc s reduced. The supply current THD reduces from 29.47% to 7.38% and the supply current THD reduces from 29.47% to 6.4% wth the use of p-q theory and GIPT respectvely for load-1. Table II Comparson of the two theores Comparson tems p-q theory GIPT Harmonc elmnaton Yes Yes Reactve power compensaton Yes Yes Load balancng No Yes steps(multply) 23 9 Reference power control Yes Yes Reference current control No No Freedom of current control 2(+) 2 Table II shows the comparson results for the two power theores. After measurng the system voltages and currents p q theory requres around 23 multplcaton steps to decde the reference currents, whle GIPT requres just around 9 multplcaton steps. Harmonc elmnaton, Reactve power compensaton and load balancng s possble through GIPT.. CONCLUSION The ncreased use of power electronc equpments n the power system has a profound mpact on power qualty. In ths paper mtgaton of supply current harmoncs, reactve power compensaton and load balancng s done by p-q theory and GIPT. Dfferent smulaton results are studed on both these control theores. The followng conclusons are made. 1. Theoretcal study of p-q theory and GIPT s done. 2. Both theores are very effectve n elmnatng supply current harmoncs and reactve power compensaton. 3. Sgnfcant reducton n ndvdual harmonc component s possble wth both control theory. ()The supply current THD reduces from 29.47% to 7.38% wth use of p-q theory, and () The supply current THD reduces from 29.47% to 6.4% wth use of GIPT. 4. Load balancng s not possble through p-q theory, whle GIPT provdes load balancng. REFERENCES [1] adat M Karsh, Mehmet Tumay and Berrn Susluoglu, An Evaluaton of Tme Doman Technques for compensatng current of shunt actve power flters, IEEE Transactons on Power Electroncs, vol. 10, pp.307, [2] H. Akag, Y. Kanazawa, and A. Nabae, Instantaneous Reactve Power Compensators Comprsng Swtchng Devces wthout Energy Storage Components, IEEE Transactons on Industry Applcatons, vol. 1A-20, pp. 625, May-June 1984 [3] M. Aredes and E. H. Watanabe, New control algorthms seres, and shunt three-phase four-wre actve power flters, n IEEE PES Wnter Meetng, [4] F. Z. Peng and J. S. La, Generalzed nstantaneous reactve power theory for three-phase power systems, IEEE Transactons Instrum. Meas.,vol. 45, no. 1, pp , [5] M. Aredes, J. Häfner, and K. Heumann, Three-Phase Four-Wre Shunt Actve Flter Control Strateges, IEEE Transactons on Power Electroncs, vol. 12, pp. 311, March 1997 [6] C. L. Chen, C. E. Ln, and C. L. Huang, An Actve Flter for Unbalanced Three-Phase System Usng Synchronous Detecton Method, n Proc. IEEE PESC 94, 1994, pp [7] W. Chang, T. Shee, A Comparatve Study of Actve Power Flter Compensaton Approaches, IEEE Power Engneerng Socety Summer Meetng, vol. 2, pp. 1017, 2002 [8] F. Peng, H. Akag, and A. Nabae, A Study of Actve Power Flters Usng Quad-Seres oltage-source PWM Converters for Harmonc Compensaton, IEEE Transactons on Power Electroncs, vol. 5, pp. 9-15, Jan [9] H. Akag, Y. Kanazawa, and A. Nabae, Instantaneous reactve power compensators comprsng swtchng devces wthout energy storage components, IEEE Transactons. Ind. Applcat., vol. 20, pp ,May/June [10] A. Nabae and T. Tanaka, A new defnton of nstantaneous actve reactve current and power based on nstantaneous space vectors on polar coordnates n three-phase crcuts, presented at the IEEE/PES Wnter Meetng, Paper 96 WM PWRD, [11] Herrera, R.S., Salmeron, P., azquez, J.R., Ltran, S.P., Perez, A., Generalsed nstantaneous reactve power theory n poly-phase power systems", 13th European Conference on Power Electroncs and Applcatons, EPE '09. pp Copyrght to IJIREEICE DOI /IJIREEICE