An active filter for AC harmonics from HVDC converters. Basic concepts and design principles

HVDC converter stations have relied on passive filters to reduce the harmful effects of the harmonic currents. Active filters have found application in association with industrial nonlinear loads. The ratings of the power semiconductor switches commercially available and some HVDC operation characteristics pose obstacles to the straightforward implementation of active filters. The goal of this work is to contribute to the active AC-filtering solution for HVDC systems. The main aspects of an active AC-filter design are considered and have their applicability to HVDC converter stations analyzed. This work proposes an active-filter topology that decouples the reactive-power supplying and filtering tasks that have been characterizing the traditional HVDC passive AC filters. Exclusive devotion to the filtering function offers several advantages that might compensate for the potentially higher initial costs.