Open-circuit fault diagnosis for a grid-connected NPC inverter with unity Power Factor

This paper presents an open-circuit fault detection method for a grid-connected Neutral-Point Clamped (NPC) inverter. The open-circuit fault mainly occurs due to bonding wire failures like lift-off and crack in the power module where the thermal stress is major factor among the stresses that can lead to bond-wire failures. Under the grid-connected condition, it is impossible to identify the location of faulty switch by the conventional methods, which usually use the output currents as it has the same distortions in several fault cases. The clamping diode is also one of fragile component in the NPC inverter, but usually it is not considered. The proposed method identifies precisely the faulty location of switch and clamping diode without any additional hardware or complex calculations. The feasibility of the proposed fault detection method for the grid-connected NPC inverter is verified by simulations and experimental results.