A harmonic reference frame based current controller for active filter

This paper presents a new method of current regulation for active filters based on the idea of compensating each harmonic current at its own rotating reference frame. Because the harmonic current to be compensated for is DC in the steady-state within a rotating reference frame that is rotating in the same direction and at the speed of the harmonic, the steady state error of each harmonic compensated for can be eliminated. Eventually, the harmonics in the line current can be cancelled out. In real situations, there are many unbalanced utility voltage conditions, so the active filters can compensate properly under these conditions too. The proposed current controller can work under unbalanced voltage conditions. The experimental results illustrate the effectiveness of the proposed method.