New Configurations for Hybrid Filters to Improve Power Quality

Abstract

Reforms in Power Sector have given an opportunity to the consumer to demand Quality Power. Unbalance, Distortion and poor regulation in the supply voltage have detrimental effect on the life of equipment and leads to poor efficiency in operation. Variable speed drives, Electric Traction and Furnace Loads inject harmonic currents into the supply system creating Bus voltage distortion. Even linear loads connected to this Bus will experience distorted load currents. These high frequency currents do not generate any useful output but produce over heating of motors, increased reactive power demand and ripples in the generated torque causing vibrations, leading to failure and poor performance efficiency. So there is a need for bypassing the load current harmonics generated by nonlinear loads from entering the system Bus Conventionally passive tuned filters connected to the Bus are used for bypassing the harmonics, but these filters have many limitations and become less effective under some operating conditions. Advent of high frequency, high power switching devices has given rise to new tools to mitigate the harmonic distortion in the Bus Voltage by freewheeling the harmonic currents, these are generally called as Active Filters. There are many configurations of these filters. Many of the limitations faced by tuned passive filters are overcome by the use of Active filters, but by combining the tuned and active filter the reliability and affectivity in improving power quality is enhanced, these are called Hybrid Filters. This paper briefly deals with two new configurations of Hybrid filter, one based on Pulse Width Modulation (PWM) operated Voltage Source Converter and the other on Current Controlled Converter. Results of performance of these two filters applied to a simple distribution system with a nonlinear load are given.