Optimal dc link voltage control strategy to enhance the performance of shunt active filter

Abstract

The use of power electronic circuits such as adjustable speed drives, rectifiers, arc furnaces, and uninterruptible power supplies in a wide range of applications for energy efficient operation and for better control of the process has produced distorted current waveforms in a power system. This has been followed by non-sinusoidal voltage drops across the transformers and transmission line impedances leading to non-sinusoidal supply voltage at the Point of Common Coupling (PCC).The non-linear loads do the work of drawing harmonic and reactive power components of current from the supply. The presence of harmonics causes equipment overheating, capacitor blowing, motor vibration, excessive neutral current and poor power factor, apart from a harmful disturbance to other sensitive electronic devices and producing interference to nearby communicating signals. Asymmetrical distribution of large single phase loads further makes the issue complex by causing an imbalance in line currents of the three phase system. Various harmonic mitigation techniques have been proposed for reduction of harmonics. These are passive, active, and hybrid filters. The use of, passive filters for eliminating the line current harmonics has roots of tradition. However, the passive filters have problems of fixed compensation, bulkiness and occurrence of resonance with other elements. Active power filter (APF) emerges as a viable alternative in situations where random variation in the amplitude and the order of harmonic current is seen. The good thing is that these active filters can also eliminate the imbalance in the supply current. The most commonly used active filter is the shunt Active Filter (SAF). SAF is used for the elimination of unwanted harmonics and compensate reactive power consumed by non-linear loads by injecting the compensation currents into supply lines. In order to reduce the harmonic effects, the SAF is connected in parallel with the load and the source at a PCC. The objective of the SAF is to limit the Total Harmonic Distor