An Improved Synchronous Reference Frame Method for Active Filters

Active filters are used to eliminate current harmonics near nonlinear loads. This paper presents a new method for the evaluation of the current that should be injected by the active filter in order to eliminate harmonics. The method proposed is based on the Synchronous Reference Frame method and explores the fact that the performance of the active filter depends on the speed of the system that determines the rotating reference frame, but doesn´t depend on its position. Compared with other methods, this method presents some advantages, due to its simplicity and its rudeness to perturbations on the ac network. Normally active filters have poor performances under non symmetrical and non-sinusoidal voltage conditions. The method proposed in this paper presents good response in presence of harmonics on the ac mains voltages and in presence of imbalance.