A model-based controller for a hybrid power filter to compensate harmonic distortion in unbalanced operation

This paper presents a model-based controller for a hybrid power filter to reduce the current harmonic distortion in a three-phase power system in the general case of unbalanced and distorted source voltages and load currents. The hybrid power filter topology considered is composed of an active filter connected to the grid by means of an LC passive filter. The aim of this topology is to reduce the current rating handled by the active filter voltage source inverter (VSI). The controller design is split in two stages, a regulation stage considering the fundamental component of the system dynamics, and a harmonics compensation stage considering the harmonic component of the system dynamics. In the regulation stage a current control is established to force the active filter current to extract only active power from the source, which is used to maintain the dc-link capacitor charged to a certain level. The load reactive current compensation is left to the passive filter mainly. The harmonic compensation stage forces the injection of current to the mains to compensate the harmonic distortion appearing in the line due to the distorting load. Numerical results are provided to illustrate the benefits of the proposed solution.