(1. School of Electrical Engineering and Automation, Henan Polytechnic University， Jiaozuo 454003， China; 2. School of Electrical Engineering, Shandong University, Jinan 250061, China)

The active power filter (APF) is usually based on three-phase six-switch topology. In order to improve its reliability, a three-phase four-switch redundancy fault-tolerant APF topology is proposed. For an open-circuit fault in the three-phase six-switch APF, a fault identification method based on power device voltage change is proposed. By studying the relation between harmonic detection APF compensation algorithm and supply current tracking APF compensation algorithm, it is pointed out that the latter is more suitable for fault-tolerant APF application. Based on the mathematical model of three-phase four-switch APF, a direct current (DC) bus midpoint voltage feed-forward compensation algorithm is presented to compensate for the side-effect on output imbalance; if energy storage is configured on the DC side, APF active power regulation is also available. The APF fault tolerant switching control strategy is proposed. Based on a three-phase four-switch APF platform, the effectiveness of the proposed method is verified by experiment.