A diagnosis method for open-circuit faults in NPC three-level inverters based on novel sliding mode observer

To improve the robustness and rapidity of neutral point clamped (NPC) three-level inverter fault diagnosis, a novel sliding mode observer-based fault diagnosis method is proposed in this paper. Firstly, the mixed logic dynamic model of the inverter was established by using the current flow direction of the switch under normal and fault conditions, and a new sliding mode observer is designed to estimate the output current of the inverter under normal conditions. The current residual which is obtained by comparing the output current from the actual system and the observer is used to detect fault, and then combined with the actual output current, fault location is carried out. The new sliding mode observer can not only improve the convergence speed of the observer, but also effectively reduce chattering and improve the robustness of the fault diagnosis system. Finally, the effectiveness and feasibility of the proposed method are verified by simulation.