Fast Detection and Localization of Open-Circuit Switch Faults in Nested Neutral Point Clamped (NNPC) Inverter

In this study, a method is presented for the detection of open-circuit fault (OCF) in the power switches of nested neutral point clamped (NNPC) inverter for the first time. Using this method, the occurrence and location of OCF are determined in less than one fundamental period. In the proposed method, not only the output voltage and current but also the voltages of capacitors are used for the identification of the OCFs in NNPC. Besides, the effect of each switch OCF on the output voltage and current and also capacitors voltage is analyzed and based on this analysis, an OCF diagnosis scheme is presented. The expected values of capacitors voltages and output voltage and current are compared in each switching state with the measured ones, and the deviation of the measured and the expected values are used for OCF localization. Moreover, for verifying the performance and feasibility of the introduced method, the level-shifted pulse width modulation (LS-PWM) is applied to NNPC, and the OCF detection results are presented in the MATLAB/SIMULINK environment.