Novel method of inverter switch open-circuit fault diagnosis based on wavelet transform

In the AC speed control system, the DC bus current can be divided into three parts, which are the total loss equivalent current, the electromagnetic-power equivalent current and the reactive fluctuated current. Firstly, according to the electro-magnetic torque and speed, the currents of first two parts are reconstructed. Then the DC bus fluctuated current, which is the difference between inverter's DC bus current and the above reconstruction current, is decomposed through the wavelet transform to get the coefficients of wavelet transform decomposition, and the root mean square value of the coefficients are regarded as the feature of single-switch or double-switches open-circuit fault. Finally, with the root mean square value of three-phase currents, the faulty switches can be localized. The theoretical analysis and simulation results proved the effectiveness of the proposed method.