PWM Ripple Currents Based Turn Fault Detection for Multiphase Permanent Magnet Machines

Most permanent magnet (PM) machines are driven by inverters with pulse-width modulation (PWM) voltages. The currents contain high-frequency (HF) components which are inversely proportional to machine inductance. The HF PWM ripple currents can be used to detect a turn fault that gives rise to changes in inductance. The features of these HF components under turn fault conditions are analyzed. A bandpass filter is designed to extract the selected sideband components, and their root-mean-square (rms) values are measured. The rms values in all phases are compared. It is shown that the rms ripple current ratios between two adjacent phases provide a very good means of detecting turn fault with high signal-to-noise ratio. The detection method can identify the faulted phase and tolerate inherent imbalance of the machine, and is hardly affected by transient states. The method is assessed by simulations and experiments on a five-phase PM machine.