Direct current control: a novel control strategy for harmonic and reactive compensation with active filters under unbalanced operation

In this paper we present a control technique for the compensation of selected harmonics in a line using an active filter. We treat the cases where both, voltage source and load current, are under unbalanced operation. Our approach does not belong to the class of high gain controllers (advocated in most conventional approaches to reduce the tracking errors) so we avoid the problems entailed by the excitation of unmodeled dynamics. Moreover, the performance of the system is not limited by the low control bandwidth since we account for the information of the references time derivative (as dictated by classical control theory) and compensate for the unavoidable delay associated with the digital implementation.