Improved Negative Sequence Current Detection and Control Strategy for H-Bridge Three-Level Active Power Filter

A three-phase three-wire shunt active power filter based on a H-bridge three-level converter as its main circuit is presented. The dc-link voltage stable conditions and the effects of the fundamental sequence components on the input active power of the inverter are described in details. Then a dc-link voltage control strategy based on the negative sequence current control method is proposed. The dc-link voltage controller is composed of two parts, the first one is to maintain the dc-link average voltage at its reference value, and the second is to achieve the balance of the dc-link voltage by controlling the output negative sequence current. To eliminate the ill effect of the negative sequence fundamental components in load current, a novel harmonic detection algorithm implemented in dual-dq axis is proposed. Finally, experiments are implemented to verify the proposed control strategy, which demonstrate the excellent performance of the new control algorithm.