04-05-2011, 02:15 PM
Abstract
DSTATCOM (Distribution STATic COMpensator) isused for compensation of reactive power and unbalance caused by II. SYSTEM CONFIGURATIONvarious loads in distribution system. This paper evaluates three Fig. 1 shows the basic circuit diagram of the DSTATCOMdifferent methods of determining the compensating current for a system with lagging power factor loads connected to 3-phase,DSTATCOM. The methods compared, are the instantaneous 3-wire distribution system. The lagging power-factor load isreactive power theory, synchronous reference frame theory and a realized by star connected resistive inductive (R-L) load.new Adaline based algorithm. The Adaline based algorithm is an Unbalanced load is realized by disconnecting load from phaseadaptivemethod for extracting reference current signals. These angedircuit breaker by three-hs ltad source three schemes are simulated under MATLAB environment using a using circuit breaker. The three-phase voltage sourceSIMULINK and PSB toolboxes. Simulation results depict the converter (VSC) working as a DSTATCOM is realized usingperformance of these schemes for control of DSTATCOM. six IGBT switches with anti parallel diodes. At ac side theinterfacing inductors are used to filter out the high frequencyI.
INTRODUCTION
components of the compensating currents.The majority of power consumption has been drawn in III. CONTROL ALGORITHMSreactive loads such as fans, pumps etc. These loads draw For reactive power compensation, DSTATCOM provideslagging power-factor currents and therefore give rise to reactive power as needed by the load and therefore the sourcereactive power burden in the distribution system. Moreover the current remains at unity power factor (UPF). Since only realsituation worsens in presence to unbalanced loads. The power is being supplied by the source, load balancing isexcessive reactive power demand increases feeder losses and achieved by making the source reference current balanced Thereduces the active power flow capability of distribution system reference source current used to decide the switching of thewhere as unbalancing affects the operation of transformers and DSTATCOM has real fundamental frequency component ofgenerators [1,2]. DSTATCOM can be used for the the load current which is being extracted by these techniques. compensation of reactive power and unbalance loading indistribution system [3]. The performance of the DSTATCOM A. Instantaneous Reactive Power Theorydepends on the control algorithm i.e. the extraction of the Instantaneous reactive power theory has been initiallycurrent components. For this purpose there are many control proposed by Akagi in 1983 4. The theory is based on theschemes which are reported in the literature and some of these transformation of three phase quantities to two phase quantitiesare instantaneous reactive power (IRP) theory, instantaneous in a -P frame and calculation of instantaneous active andcompensation, instantaneous symmetrical components, reactive power in this frame. The basic block diagram of thesynchronous reference frame (SRF) theory, computation based theory is shown in Fig. 2 and the mathematical derivation ison per phase basis, and scheme based on neural network [4- explained as follows.11]. Among these control schemes instantaneous reactivepower theory and synchronous rotating reference frame are * Amost widely used. B bIn this paper DSTATCOM is controlled by IRP and SRF C Letheory for compensation of reactive power and unbalance and 3pha ACC Unbalance andthese methods are compared with a new Adaline based Source Lf Reactive Loadalgorithm. Adaline based control algorithm is simple and need ----- ---------less computational efforts [12]. A fast adaptive linear element(Adaline) based reference current estimator extracts the realVI~ IC& I positive sequence current component without any phase shift. DSTATCOMThe estimation of this reference current through Adalineutilizes LMS algorithm for calculation of weights [13-14]. AMIATLAB based simulation study of these three control F Control 4techniques of DSTATCOM is presented. Simulation results ihdemonstrate the effectiveness of these three control algorithmsof DSTATCOM for compensation of reactive power burden V hWS LELXt b 1Iand unbalanced loading.
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