Modeling,Analysis and Simulation ofThree Phase Hybrid Power Filter forPower Quality Improvement

-A three-phase hybrid series power filter is constituted by a series active filter and a passive filter connected in parallel with the load. The control strategy is based on the “dual formulation of the electric power vectorial theory”. The proposed algorithm eliminates the current harmonics of supply. It also improves the power factor and harmonic compensation features of the associated passive filter even if there is a change in system parameters. A shunt hybrid power filter is constituted by a shunt active filter and a passive filter connected in parallel with the load, is proposed with same control strategy. Simulations have been carried out on the MATLAB-SIMULINK platform with different loads and with variation in the source impedance. I.INTRODUCTION The increase of nonlinear loads due to the proliferation of electronic equipment causes power quality in the powersystem to deteriorate. Harmonic current drawn from a supply by the nonlinear load results in the distortion of the supply voltage waveform at the point of common coupling (PCC) due to the source impedance. Both distorted current and voltage may cause end-user equipment to malfunction, conductors to overheat and may reduce the efficiency and life expectancy of the equipment connected at the PCC. Traditionally, a passive LC power filter is used to eliminate current harmonics when it is connected in parallel with the load. This compensation equipment has some drawbacks, due to which the passive filter cannot provide a complete solution. These disadvantages are mainly the following. —The compensation characteristics heavily depend on the system impedance because the filter impedance has to besmaller than the source impedance in order to eliminate source current harmonics. —Overloads can happen in the passive filter due to the circulation of harmonics coming from nonlinear loads connected near the connection point of the passive filter. —They are not suitable for variable loads, since, on one hand, they are designed for a specific reactive power, and on the other hand, the variation of the load impedance can detune the filter. —Series and/or parallel resonances with the rest of the system can appear. An active power filter, APF, typically consists of a three phase pulse width modulation (PWM) voltage source inverter. When this equipment is connected in series to the ac source impedance it is possible to improve the compensation characteristics of the passive filters in parallel connection. This topology is shown in Fig. 1, where the active filter is represented by a controlled source, where is the voltage that the inverter should generate to achieve the objective of the proposed control algorithm. Fig. 1. Series active filter and parallel passive filter. II. THE DUAL INSTANTANEOUS REACTIVE POWER THEORY The instantaneous reactive power theory is the most widely used as a control strategy for the APF. It is mainly applied to compensation equipment in parallel connection. This theory is based on a Clarke coordinate transformation from the phase coordinates (see Fig 2). In a three-phase system such as that presented in Fig 3, voltage and current vectors can be defined by V = [ VaVbVc ] i = [ ia ib ic] (1) Prashanta Kumar Das,B. Srikanth / International Journal of Engineering Research and Applications (IJERA)ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 3, May-Jun 2012, pp.011-017 12 | P a g e Fig. 2. Transformation from the phase reference system (abc) to the 0αβ system. Fig. 3.Three-phase system. The vector transformations from the phase reference system a-b-c to α-β-0 coordinates can be obtained, thus