Fault-Tolerant Operation Approach for Nested Neutral Point Clamp (NNPC) Converter

The nested neutral point clamp (NNPC) converter is one of the most promising solutions for medium voltage motor drive applications. However, reliability due to the presence of semiconductor switches in the structure of this converter is one of the most critical concerns. The semiconductor switches are always one of the main components prone to failure. Switch failure can result in adverse effects, including system shutdown, poor system performance, and a reduction in overall system stability. Therefore, fault-tolerant converters are required to raise system availability in industrial applications. This research investigates and proposes the configuration of a fault-tolerant NNPC converter that uses a redundant phase to create a fault-tolerant converter. The redundant phase is in the bypass mode under normal operating conditions. After detecting the fault, the redundant phase will replace the faulty phase by utilizing a simple control scheme. Also, the proposed fault tolerance method is based on the cold reservation method, which will not increase the switching losses in the converter. The proposed fault-tolerant method’s feasibility and effectiveness are confirmed by simulating the NNPC converter under various scenarios in the MATLAB/Simulink environment.