A new control method for obtaining reference currents of shunt active power filters in unbalanced and non-sinusoidal conditions

Shunt active power filters are used to eliminate the current harmonics and to improve the power factor in systems with nonlinear loads. At the present time, different methods exist to control active power filters. Some of them are based on instantaneous reactive power theory and others are based on the synchronous reference frame using Park's transformation. The purpose of this paper is to present a new control method of shunt active power filters in unbalanced systems, both in load currents and in AC supply voltage, with a high contents of harmonics. The method is based on the time-domain analysis carried out by P. Filipski (1980). With this control method, one can make that the set formed by the nonlinear load and the shunt power filter behaves every time like a resistance, UPF (with unity power factor), or that the current absorbed by the set is perfectly sinusoidal, by simply acting on a switch. The system has been simulated for different load and line conditions. Waveforms of the line currents are shown, with their harmonic distortion contents.