Comparison of open-phase fault detection for permanent magnet machine drives using different fault signals

Conventional permanent magnet (PM) machine open-phase fault detection relies on the estimation of current harmonics using existing drive current sensors. Because the magnitudes of current harmonic are proportional to the machine load condition, it is still a challenge to detect a phase fault at light load when fault induced current harmonics are too small to estimate. This paper investigates the phase fault detection specifically for the conditions under low fault harmonic magnitudes. Both fault induced harmonics in dq currents and neutral point (NP) voltage are analyzed to find a suited signal for the phase fault detection. By adding a voltage sensor to measure the NP voltage in a PM machine, a better fault detection performance is achieved because the fault harmonic in NP voltage shows the reduced effect on torque loads and sensor measurement errors. A 50-W PM machine is tested to verify the phase fault detection performance under low fault harmonic magnitudes. This paper includes the experimental evaluation to analyze the detection limitation in terms of load capability based on current and voltage fault signals.