Power Analysis of a Shunt Active Power Filter For Three-Phase Four-Wire System under Unbalanced Main Voltages S. Riyadi 1* , L. H. Pratomo 1 , Y. Haroen 2 1 Soegijapranata Catholic University, Jl. Pawiyatan Luhur IV–1, Semarang 50234, Indonesia 2 Bandung Institute of Technology, Jl. Ganesa 10, Bandung 40132, Indonesia The power analysis of a three-phase four-wire shunt active power filter (APF) under unbalanced main voltages is described in this paper. To operate properly, a current compensator must fulfill the power equilibrium. By decomposing the current and voltage quantities into positive, negative, zero-sequence, ac and dc components then the power components are determined. Under unbalanced voltages, the nonlinear loads absorb all the power components. On the other hand the sinusoidal currents must flow at the source side, such currents are the fundamental positive sequence which create dc and ac power component as the interaction with the positive sequence voltage and the negative sequence voltage. To achieve the equilibrium, a shunt active power filter must generate the power components which are the subtraction between the source and the nonlinear loads power components. To verify the analysis, simulations are done and the source instantaneous power (SIP) based control method for shunt active power filter will be taken as the case study. 1. General Recently, nonlinear loads are dominantly used in consuming electric energy. Such loads result in power quality degradation. Active power filtering is alternative way to compensate for harmonics produced by these nonlinear loads (1),(2) . For current-type harmonic producing loads, an active power filter must be installed in parallel to inject currents with the same magnitude but the opposite polarity as the undesired currents in order to minimize the harmonic contents at the source side (3) . Under function as a current compensator, a shunt active power filter must be able to make sinusoidal source currents regardless the main voltage conditions therefore the power generated at source side will also contain the ac component. Some control methods of active filterings have been developed by researchers with the aims to improve the filtering characteristics and to reduce the number of sensors (4)-(6) . All the control method always needs detection of dc-link capacitor voltage to see how the power flow in energy storage element. This paper describes the power analysis of shunt active filtering for three-phase four-wire system. Some power components are derived based on the interaction between the voltage and current quantities. To verify the analysis, simulations using the SIP based control method for shunt APF are done. 2. Shunt APF for Three-Phase Four-Wire System Fig.1 depicts four controlled current sources that are functioned as a shunt APF that injects compensating currents to the system contained three-phase four-wire nonlinear loads. To make sinusoidal source current regardless the condition of the main voltages, a shunt APF must supply the power components so that the power equilibrium is achieved. Under ideal source voltages, the sinusoidal source currents result in the dc component of real power generated at the source side but under nonideal source voltages the source will also create ac component as shown in Fig.2. A control method must consider such a condition in order to work properly. Fig.1. Three-phase four-wire shunt active power filter Fig.2. Power flow in three-phase four-wire active filtering If three-phase four-wire nonlinear loads are connected to the system with unbalances source voltages that stated as the following *email : s_riyadi672003@yahoo.com , riyadi@unika.ac.id Proceedings of the International Conference on Electrical Engineering and Informatics Institut Teknologi Bandung, Indonesia June 17-19, 2007 F-30 ISBN 978-979-16338-0-2 806