Non-invasive Open-Circuit Fault Diagnosis of Three-Level NPC Inverters Based on Neutral Point Voltage

Fast open-circuit fault diagnosis is essential to ensure multilevel inverter operates under stable conditions. Conventional diagnosis methods either require additional hardware sensors or state prediction under current closed-loop control. However, these conditions are difficult to be met for high power application scenarios at low switching frequency modulation required. For this reason, a two-step open-circuit fault diagnosis method is proposed based on available data that can be acquired by the existing sensors in the application. Therefore, the proposed method is a non-invasive online fault diagnosis method capable of being used under current open-loop control. By analyzing the effects of open-circuit fault on the phase current and neutral point voltage, that faulty bridge arm can be quickly located via the average current. Furthermore, through establishing the observation model of the neutral point voltage, accurate diagnosis of faulty switching devices can be achieved quickly and easily based on neutral point voltage residual. The proposed open-circuit fault diagnosis method is proved to be correct and effective by simulation.