Pseudo-Coordinate-Based Diagnosis for Inter-Turn Fault of Permanent Magnet Synchronous Machines Under Varying Speed Condition

The diagnosis of inter-turn short circuit (ITSC) fault in permanent magnet synchronous machine (PMSM) servo drive has been extensively studied. However, its application in low-cost drive systems without a position sensor under varying speed conditions requires further investigation. The 2nd harmonics in dq-axis signals are widely employed for diagnosis in servo drive, but they are inaccessible without a position sensor. Additionally, extracting fault features under variable speed conditions remains challenging without instantaneous frequency information. This paper proposes a frequency mapping method based on maximum harmonic amplitude extraction in a time-frequency plane to obtain the instantaneous phase (IP) from two-phase currents. A pseudo synchronous coordinate is established to integrate both the amplitude and frequency fault information of the phase currents using the extracted IP. Subsequently, the order tracking method is applied to signals in the proposed pseudo coordinate to extract the fault feature. Experimental validation on a PMSM demonstrates the method's effectiveness in ITSC fault detection under variable speed conditions without requiring speed signals.