Digital Implementation of Shunt Active Filter Using Hysteresis Controller

Abstract

Power Quality is highly degraded due to presence of nonlinear loads in the circuit, which inject current harmonics at the mains. Adjustable Speed Drives, Switched Mode Power Supplies, etc are examples of nonlinear loads that draw non-sinusoidal currents from the mains and inject harmonics into the system. Earlier passive filters were used to tackle this problem, but these suffer from series and parallel resonances, and have poor flexibility. Now Shunt Active Power Filters are gaining attention for immunity to the drawbacks. Active Power Filters are used to compensate current and voltage harmonics, compensate reactive power, improve power factor, and to improve voltage balance in three phase systems. Due to handling of these many tasks Active Power Filters are sometimes also called as Active Power Line Conditioners. In this project the harmonic currents are eliminated by sensing the harmonics present in the system and injecting compensating currents which are equal and opposite to the harmonic currents. Compensating currents are generated by using Fryze Current Computation Technique. Inverter is driven by Hysteresis Current controller to inject the actual compensating currents to the mains at Point of Common Coupling (PCC) through an injecting inductor to compensate the harmonic currents and thus obtaining sinusoidal source current waveform.