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A New Instantaneous Power Theory-Based Three-phase Active Power FilterShin-KuanChenDepartment of ElectricalEnpeeringC h u g Chou Junior College of Technology & CommerceChang-Hua TAIW..LV 510

Abstract: The active power tiltcr has been proved to be aneffechve devlce to mtigate harmomc current and/or voltagedistortions produced by nonlinear loads as well as to compensatereactive power. In the past some actlve power filters were designedbased on the conventional instantaneous reactive power (IRP)theory. However, these types of filters can only compensate reactivepower for the load If the load generates harmoruc current or isunbalanced, the conventional I RP theory-based achve filter can notcompensate the harmomc distorbon and does not function properly.In order to overcome the drawbacksof the conventional IRP theory,a iiew instantaneous power theory-based algonthm is proposed forthe control strategy of the active filter. In t l u s paper theimplementation of B 10-kVA prototype active power filter whch ISdeveloped based on th e proposed control algorithm is present.Simulation and expenmental results wth vaned source and loadcondihons are descnbed to confirm that the new proposed controlstrategy acheves better performance for the active power filter t hanthose ob m ed by using conventional I RP control strategies.

Keyword - Harmonics , univ power factor, achve power filter,mstantaneous reachve power theory, power disturbances, voltagedistortion.L INTRODUCTION

Power system harmonics are not a new problem. Due tothe widespread proliferation of nonlinear distorting loadssuch as power-electronic controlled devices, the problemscaused by harmonics are of increasing importance. Unlikethe conventional load, the power-electronic device controlsthe flow of power by chopping. flattening, or shaping thewaveforms of the voltage and current. Therefore, harmonicsare generated during the process. These waveformdistortions can cause problems for neighboring loads, andthey tend to have an overall opposite effect on the quality ofelectric power.

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Gary W . ChangDepartment ofElectrical EngmeeringNational Chung Cheng UmversityChia-Yi, TAIWAN 62 1

A concept that can improve the power quality is the activepower filter [l-51. This type of filters can meet diverse loadconditions. In addition to improve power factor, it alsoappears to be an attractive and viable method for reducingvoltage and current harmonic distortion or other powerquality problems such as flicker. The active power filterimproves the system power quality by injecting equal-but-opposite currents to compensate harmonic distortion andreactive power. Ideally. this active power filter shouldmonitor and minimize voltage and w e n t distortion of itsconnected load [6-121.In the past some active power filters were designed based

on the conventional I RP theory [6.7]. However, the IRPtheory-based active filter can not compensate the harmonicdistortion and does not function properly. In order toimprove the drawbacks of the conventional IRP theory, anew instan taneous power theory-based algorithm is proposedfor the control strategy of the active filter.Also, or verifyingthe performance of this algorithm, computer simulations andexperiment are made. From the sim ulation and experimentaltest results, it is found that proposed new instantaneouspower theory-based three-phase active power filter is to bean effective device to reduce harmonic current and tocompensate reactive power.II. REVIEW OF TH E INSTANTANEOUSREACTIVEPOWER THEORY AND THE PROPOSEDINSTANTANEOUSPOWER THEORYThe drawbacks of the conventional instantaneous reactivepower (IRP) theory include:1) It can not com pensate the h armonic current componentwhen the mains voltages are ideal (i.e. sinusoidal andsymmetrical).

are distorted.2) The m ains currents are distorted when the line voltages

3) It can no t solve the unbalanced load problem.In o rder to solve the problems of conventional I RP theory,a new instantaneous power algorithm is proposed for activepower filter.

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A. Review of Instantaneous Reactive Power TheoryTh e conventional instan taneo us reactive power is definedin [6] an d [7]. Figure 1 shows the active power filter forreactive power compensation. The instantaneous reactivepower q supplied by the active power filter for each phase ofthe three-phase! fou r-wire sys tem can be represented as

where ek is the line to neutral voltage and id is the injectedcompensating current from the active power filter.

IActive Power FilterFigure 1Three-phase four-Wire activopower filter system

Since the active power filter does not generate theinstantaneous active power, the following constraint isimposed on (1) :z q k = O . (2)k

The compensating currents of the active power filter, Iicb an d i , are determined to minimize the followingselected performance fu nctio nL, where

This performance function. L,means that the source currentsare to be minimized while satisfying the constraint of (2).A-1. Three-phase Three-W ire Active Power Filter

The performance function and the constraint of the three-phase three-wire active power filter system are

Since the system does not have the zero-sequencecomponent, we haveI , +iCb+lCC o . (6)

The optimal compensating currents ica , icb, and i , can beobtained rom (4) - (6) as

icc= * (9)2

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wherep~ s the instantaneous active power, and where

The compensating currents of (15)-(17) are obtained byabstracting the instantaneous active current from the loadcurrent. Therefore, the conventional I RP defined in (1)includes both the instantaneous reactive (imaginary) powerand the instantaneous power of the zero-sequencecomponent.B. The Proposed Instantaneous Power Theoryfo r Active Pow er F ilter

The proposed instantaneous power theory is based on theassumption that the mains currents i i b , and i must beideal, and are in phase with the mains voltages. Thiscorresponds to taking the power from a undistorted and st i f fpower system. In this way only the altern ate components ofthe power ar e interchanged between the load and the activepower filter. It also means that the power supp lied from themains is the com bination of the active power of the load andthe filter loss.

According to the aforementioned principle and (15)-(17),the reference voltage waveforms of active power filte rcan begenerated. If we assume that the three-phase mains voltagesare ideal, the desired mains currentscan be represented as

i,k = We,, (fork = a, b, c) (19)where

if power balance is obtained and the losses of active powerfilter is neglected. In (201,E is the rmvalue of the mainsvoltage and PI,,,is the mean value of the instantaneous loadpower PI rom (19) and (20), the reference current can berepresented as. (fork = a, 6, ) (21)sk = ekpIm3E2

If the mains voltages are distorted, this implementationdoes not produce a correct calaulation of the instantaneousload power. In h i s case, the mains currents in (15)-( 17) alsowill be distorted. In order to overcome the above problems, areference voltage generator is used. The generator generatesa set of three-phase ideal reference voltages e& to keep inphase with the fundam ental component of mains vo ltage bymeans of phase-locked loop (PLL)echnique.

By using the reference voltage e,k to replace ek and themean powerp,,,, to replace pr in (13417), then i-, i&,nd ican be represented as' eraPimi,, = i t a --,3E:

3E:e m P l m

3E:

erb Plmi,b = lb --,i,, = ~ C -,

where E, is the rms value of the reference voltages eh .II L SIMULATION, MPLEMENTATION NDEXPERIMENTAL RESULS

In order to realize the proposed algorithm, simulations aremade and a 10-kVA prototype of active power filter isdeveloped. Different load conditions such as lagging powerfactor and rectifier loads are extensively tested.

k Simulation ResultsA control circuit of the active power filter based on (22) -(24) is designed for simulation. The simulation results of theproposed algorithm are shown in Figures2-4. In Figure 2,we see that the proposed algorithm is able to compensate hereactive power to unity power factor for a load with laggingpower factor. Figure 3 shows that the proposed algorithmcan keep the mains current nondistorted w hen supplying anonlinear rectifier load. Figure 4 also shows that thisalgorithm can maintain the mains current nondistorted evenwhen the mains voltage contains harmonics.

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B. System ImplementationFigure 5 shows the configuration of the proposed activepower filter. It is connected in parallel with the load. Thepower circuit consisted of voltage source PWM converterusing six-pulse converter as the switching devices. Thecompensating power calculator is implemented based on theproposed instantaneouspower theory for active power lineconditioning, which is used to calculate the referencecompensating currents. The current mode controllerdetermines the PWM switching sequence by means ofcomparing current error signals, the different betweenreference compensate current and actual compensate current,with a &xed-frequency triangu lar Carrier signal. Thus theswitching frequency of the power transistors is equal to theEiequency of the triangu lar carrier signal. In order to have acorrect compensation, the current error signal is transferredby the phase leading controller.

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4001 1

0 00 1 002 0.03Time(a

4 202:y/fj40-001 002 003Time

(c)-401 I0 001 002 003Eme(d)

Figun 2 Simulationresults of the proposed activepower filter under theloadwith laggingpowerfactor. (a) "s oltages @) load current^,(c) compensationcurrent$(d) mains currents

4W r I 100

J0 0.01 002 003Time T"(b)

4 m L 1wi0 001 002 003! 100(a100 Ii 1

-15010 00 1 002 003Time

I0 00 1 002 003Time(4 (d11 50

Figure 3 Simulation esults of the proposed active power filterunder herectifier oad with harmonic current a) mains voltages. (b) load currents,(c) compensate currents, (d) m a m currents, (e) the harmonic analysisof loadcumat, (0heharmonic analysisofmains cumnt.

To design the capacity of active power line conditionerdepends on the order, amplitude and phase angle of theharmonics for which to be compensated [8]. A dc voltagesource is realized with th e capacitorCk across the terminalsof voltage source converter, as shown in Figure 5 . The

inductor value is primarily a function of the system volt-ampere ating and he range of harmonic levels of the load.

-0 001 Time002 003 0 001Time0.02 003(C) (d

Figure 4 Simulation results of the proposed active power filter under thedistcntedmams voltage (a) voltages, (b) load currents, (c) compensationcurrents, (d) mainscurrents.

t : ,I

i t ! I

Figure 5 The active power filter systemBecause of the reactive power flow is varied underM er en t load conditions, the load condition must beconsidered to limit the fluctuation ofdc capacitor voltage. Infact, compensation of phase unbalances andor harmo&sinvolve considerable energy transfer between load andstorage element. w hich m ust be sized accordingly. In orderto reduce the voltage rippIe in the dc bus, a larger dc

capacitor is selected to include the require energy of lowfrequency power harmonics and zero-sequence componentunder unbalanced conditions. A simple low-pass filterconsisting of Lf and C, as shown in Figure 5 , may be used atthe output of the voltage source converter to reduce ripplevoltage on the ac mains caused by switching actions of thevoltage source converter. However, the possibility ofoscillations in the presence of such a low-pass filter must be

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considered. If an adequate damping is not provided, asustained oscillation may occur. For a good design, anadditional damping resistorRf s required.C. Expe rimen tal Results

A prototype of active power filter has been implementedand is used to verify the performance of the proposedalgorithm. The active power filter prototype is tested underdifferent load conditions and shows a good accordance withthe simulation results. The filter is not only for the reactivepower compensation but also for the suppression ofharmonics. Figures 6 an d 7 show that various operationwaveforms resulting from diverse functional tests ofcompensation which is without changing the main circuitconfiguration under different load conditions. The actualoperation of the active power filter is tested with a laggingload and a rectifier load. The rectifier load is composed of athree-phase diode bridge rectS er w ith a smoothing inductorand resistor.

Figure 6(a) shows the relation of the mains voltage andthe lagging load current. Figure 6(b)shows that the mainscurrents are closely in phase with the mains voltages aftercompensation. We see that the power factor is near unityafter the reactive power is compensated for lagging load.The performance of the active power filter is demonstratedby comparing with the simulation results shown in Figure 2.Figures 7(a) and 7(b) show the waveforms before and aftercompensating a three-phase rectifier load, where the activepower filter are used for mitigating harmonics and forcompensating reactive power simultaneously. Theperformance of the active power filter is demonstrated bycomparing the simulation results of Figure 3. It is found thatthe test results and the simulation results are in goodagreement.

IV. CONCLUSIONSThe features of the active power filter based on theproposed instantaneous power theory algorithm aresummarized as follows.

1) Improved com pensating performance: The compensatingperformance is improved because the line current iscompensated to sinusoidal and in phase with line vo ltagein any detrimental load case.2) Easy design of large capacity and compact equipment:

Large capacity equipment can be readily designed with asimplemain circuit configuration.3) Wide application range: This device has a wideapplication range not only as an active conditionersuppressing harmonics but also as a flicker compensatoror a high power factor and high performance activeconditioner.

( b )Figure 6 Testwaveforms for the loadwith laggingpower factor(a ) mains voltage (upper) s. load current (lower) - before compensation@) mainsvoltage (upper)vs. mains current (lower) - after compensation

CO)Figure 7 Tcst wavdomnforthed e r oad@)(a) mainsvoltage (upper)vs. loadcurrent lower) - before compensationmains voltage (upper)vs. mains current (lower) - after com+on

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Based on the test and simulation results. it is shown hat theproposed instantaneous power theory based algorithm is tobe a useful method for implementation of the active powerfilter.V.REFERENCES

H. Aka@. A Nabae and S. Atoh, Control Straegy of Active PowerFilters Using Multiple VoltagaSource PWM Converters, IEEE Trans.onU, Vol. IA-22, No. 3, pp. 460465 , MaylJune 1986W M. Grady, M. J Samoty~ nd A H. Noyola, Survey of m v e PowerLine Conditioning Methodologies, IEEE Trans on Power Defrvery,Vol. 5 , NO.3, pp. 1536-1542. July 1990.H. Aka@.Trendsn Active Power Line Conditionem, IEEE Trans. onPowerElectronrcs,Vol. 9. No. 3. pp. 263-268. May 1994.H. Aka$ and H F uj iy A New Power Line Conditioner for HarmonicCompensation in Power Systems. IEE!? Trans. on Power Delivery. Vol.10, NO.3, pp. 1570-1575,July 1995.H. .UCagi, New Trends in .Active Filters for Power Cond itioners. IEEETrans. on Industry Appbcahons, Vol. 32 , No. 6, pp. 1312-1322.NovembenDectmber 1996.I Talcahah, Anaiysis of InstantmzousCurrent and Power Using SpaceSwtching Functtons *Cot$Aec. o f I . P E S C , pp. 4249,1988.T. FuruhashL S.Okuma and Y Uchikawa, A Study on he Theory ofInstantaneousReacZ~vtPower. IEEE Truns. on L4,Vol. IA-37. No 1,February 1990L Mal-, L Rossetto and P.Tenti, .4ctive Filtas for Reactive Powerand H m m c Compensat~on, Proc ofrbe I=-PESC, pp. 321-330.June 1986.

R Fisher and R. H ok Three-phase Power Line Con&tioner forHarmomc Compensation and Power Factor Correction, Con$ Rsc. ofrhe I.!?EE-hiSAnnualhfeehng.pp. 803-807, October 1987.L T. M o m P.D. iogas and G. Joos, Analyis and Design of a Novel3-0 Slid-State Power Factor Compensator and Harmonic SuppicnwrSystem IEEE Pans on U ,Vol. IA-25, No. 4, July/August 1989.J. D. V Wyk, D. A Marshall and S. BoshoK Simulation andExperimental Study of a Reactwely Loaded PWM Converter as a FastSource of Reactwe Power, LEEE Pans. on U, Vol. IA-22, No. 6,N ovember i /D ber 1985.M.Aredes, K Heumann and E. H. Watanable, A Universal ActivePower Line Conditioner, IEEE Trans on Power Delivery, Vol. 13, No.2, pp. 545-551. April 1998.

VI.BIOGRAPHIESS h i n - K u ~ hew received h a Electrical E n p c e n n g Diploma h m atIonalTaipei -Me of Tzchnology. Tapei. Tawan, in 1985. and the BSEE andMSEE degrees fom Natlonal Tawan M e of Tcchnoiogy and NatlonalCheng Kung University. Taiwa n in 1990 and 1992. respectively. His areas ofinterests include power system analysis. harmonics, power qualify, and powerslectrolllcr He is currently with the Department of ElectricalEnweering atChung Chou Jutuor College of Technology& Commerce, Chunghua, T a ~ wGary W. hnng , (x.194). received his Electrical Engheerhg DiplomahNatlonal Taipei Institute of Tzchnology. Taipei, Taiwan, in 1982. and theMSEE and PkD. degrees fi omNational Tsing Hua University, Hsinchu,Tawa n, and the Um vers~ty f Texas at M n n 1988 and 1994, respectively.Dr. Chang is currently wth the Department of Elecrncal Fqpeering atNatIonal Chung Cheng Umvemty, Chayl, Taiwan. HIS reas of urterestd u d e power systems optirmzation, harmonics, and power quahty. Dr.ChangISa member of Tau Beta Pi and a reBstered professional e n p e e r m the state ofM i n n e S O t a

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