Two-Step Process-Based Open-Circuit Fault Diagnosis for Three-Level NPC Converters

Fast open-circuit (OC) fault diagnosis is essential to ensure that a multilevel inverter operates under stable conditions. Conventional diagnosis methods either require additional hardware sensors or complex calculations. However, these conditions are difficult to realize in some low-cost application scenarios. For this reason, a two-step process-based OC fault diagnosis method is proposed according to available data that can be acquired using the existing sensors in the application. At the same time, the proposed method does not involve complex and precise calculation. By analyzing the effects of an OC fault on the AC-side three-phase current, the faulty bridge arm can be quickly located via the average current. Furthermore, through establishing the calculation model of the neutral point potential, an accurate diagnosis of faulty switching devices can be achieved quickly and easily based on the residuals. The proposed OC fault diagnosis method is also proved to be correct and effective based on simulation and experience.