Abstract: This paper presents an open circuit fault diagnosis and location method for full bridge sub module IGBT based on nearest level approximation modulation (NLM) strategy and analyze.the fault characteristics of sub modules. According to the NLM modulation strategy, the sampling values of the capacitance voltage of the sub module of the bridge arm are sorted, and the median is calculated as the predicted value of the capacitance voltage of the sub module. By comparing the predicted value with the measured value, the diagnosis criterion is obtained. This method does not need to occupy too much computing resources and completes the fault diagnosis quickly. At the same time, the fault IGBT positioning and fault tolerant control of the fault sub module are realized by changing the working state of the fault sub module. Finally, a detailed simulation model is built in matlab/simulink. The simulation results verify the effectiveness of the sub module IGBT open circuit fault diagnosis and location method and fault-tolerant control strategy.

Key words: nearest level approximation modulation(NLM), IGBT open circuit fault, sub module fault characteristics, sub module fault tolerance