Abstract: ObjectivesNeutral Point Clampe (NPC) three-level inverters are increasingly used in the field of marine power systems, and the reliable operation of this type of inverters is crucial to the ship electric power system. This type of inverter has a large number of switching tubes, and is prone to open-circuit faults under high-frequency switching conditions. The existing NPC three-level inverter switching tube open-circuit fault diagnosis methods have problems such as difficulty in fault feature extraction and large amount of computation. To this end, an open-circuit fault diagnosis method is proposed based on the DC component and the frequency-double component of the faulty phase current. MethodsThe current sensor is used to accurately and quickly obtain the fault phase current signal, and based on the Fourier transform (FFT), without complex signal processing algorithms, the stator current under open-circuit faults is analyzed by comparing the stator current components in the frequency domain, and fault diagnosis is carried out based on the DC component and the doubled-frequency component of the fault characteristic components. ResultsSimulation is carried out using MATLAB/Simulink to verify the validity of the proposed method; the experimental platform of NPC three-level inverter for 3kW three-phase motor is built for experimental verification, and the experimental results show the fit of mechanism analysis, simulation and experimental results, which verifies the validity and feasibility of the proposed method. ConclusionsThe fault diagnosis method based on the faulty phase current DC component and two times frequency component can accurately identify the open-circuit faults of two tubes and below, and the method is simple in fault feature extraction, small in computation and strong in real-time. The method utilizes the existing current collection signals of the inverter and does not need to set additional sensors, which reduces the hardware requirements and reduces the size of the equipment, which is conducive to the use in the narrow space of the ship.