PWM ripple currents based turn fault detection for 3-phase permanent magnet machines

Most permanent magnet (PM) machines are driven by inverter with pulse-width-modulation (PWM) voltages. The resultant phase current contains high frequency (HF) components, based on which, a new technique to detect turn fault is proposed. The machine model at high frequency is established and the HF current components are analyzed. A bandpass filter is used to extract the selected sideband components, and their root-mean-square (RMS) values are measured. The ratio of the RMS values in two adjacent phases are calculated. Both the individual ratio and the variance of 3 ratios are studied and testified to show the feasibility of detecting fault. Simulations have shown that both of them are valid fault indicator in ideal conditions while the variance is better in conditions with phase imbalance.