Open-Circuit Fault Diagnosis in Shunt Active Power Filters with No Additional Sensors

A real-time fault diagnosis method for neutralpoint-clamped (NPC) active power filters (APF) is proposed. According to the different relationships between the APF's harmonic current and reference voltage under normal condition and fault condition, the fault diagnosis algorithm can detect and locate the open-circuit faults (OCF) with no additional hardware or sensors. The selection basis of the two thresholds required by the fault diagnosis algorithm is also analyzed in the article. Fault detection can be achieved in just a few sample periods (in favorable conditions). All the signals used in this algorithm have already been employed in the APF's controller and only addition and comparison are required in the algorithm, which is very simple. The efficiency of the proposed algorithm is verified by the simulation results.