Digital Implementation Of Active Power Filter For Power Quality Enhancement

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 lters were used to tackle this problem, but these su er from series and parallel resonances, and have poor exibility. 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 Instantaneous Re- active Power Theory and Fryze Current Computation Technique. A current controller code generates three vectors by the help of DSP TMS320LF2407A. A driver card uti- lizes these vector signals to generate PWM gate pulses to trigger an inverter. Actual compensating currents from the inverter are fed 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.