Analytical study and numerical simulation of combined voltage source series active and shunt passive filters

Harmonics generated by power converters have become a serious problem for the AC mains as they can only be removed by using bulky passive filters. Besides, harmonic compensation by shunt passive or active filters causes undesirable interference such as resonance with the AC mains. To solve this problem, the authors have proposed a combined system of a shunt passive and series active filter. This system is self-adaptable and only a small power active filter is needed to compensate the harmonics generated by large converters. The control algorithm of the active filter is based on instantaneous active and reactive power calculations. A combined system is used to minimise harmonic currents and voltage in the AC systems. Here, the authors demonstrate that the study of a three phase system can be realized by using a single phase equivalent circuit when the line currents are balanced. The series active filter plays the role of an active impedance. This means that it presents a negligible impedance for the fundamental frequency and a pure resistance for the harmonics.