Open-circuit Fault Diagnosis Method of NPC Inverter Based on Extended Observer

In order to reduce the influence of external interference and uncertain factors on the fault diagnosis of the inverter system, this thesis proposes an open-circuit fault diagnosis method for the NPC inverter based on the extended observer. The Mixed Logic Dynamic is established by analyzing the relationship between current flow and working state of inverter under normal and fault conditions. An extended observer is designed with current as the detection quantity. Fault diagnosis is carried out according to the negative double residual relation obtained from the estimated current value of the extended observer and the true current value of the physical system. The current expansion observer not only effectively reduces the influence of unknown interference and other factors on the fault diagnosis of the inverter, but also improves the accuracy and robustness of the fault diagnosis system when the load changes suddenly. Finally, the correctness and effectiveness of the method are verified by MATLAB/Simulink simulation.