Inverter-less active filters - A new concept in harmonic and VAR compensation

Shunt active filters compensate for variable levels of harmonic currents generated by loads, essentially by producing currents in anti-phase with the offending harmonics. DC/AC inverters, with dc energy storage in electrolytic capacitors and high frequency PWM with IGBT switches, represent the most widely used technique for implementing active filters. A companion paper has introduced the concept of using simple AC choppers invoking dual virtual quadrature sources to realize amplitude, phase angle and/or harmonic control on the available ac voltage. This paper discusses a novel implementation of Inverter-Less Active Filters (ILAF), using gate controlled semiconductor switches with inductors, capacitors or existing resistive loads in a plant to realize dynamic VAR and/or harmonic compensation. Eliminating energy storage elements result in lower cost, increased robustness and longer life. The approach is seen to be applicable for single and three phase systems. ILAF are seen to provide lower cost and increased robustness and reliability when compared with conventional active filters.