Online Diagnosis of Slight Interturn Short-Circuit Fault for a Low-Speed Permanent Magnet Synchronous Motor

Online diagnosis of slight interturn short-circuit fault (ISCF) has always been difficult in low-speed permanent magnet synchronous motors (PMSMs). It is found that the residual zero-sequence voltage exists in healthy PMSMs due to the inherent unbalance of a low-speed motor. This article proposes a new ISCF diagnosis method based on zero-sequence voltage vector decomposition to solve this problem. The voltage vector whose phase angle is closest to the ISCF phase angle is extracted from the zero-sequence voltage vector, which improves the sensitivity of fault phase identification. Furthermore, the method of extracting phase voltage from PWM duty-cycle control voltage is proposed, which can reduce the error caused by measuring zero-sequence voltage with three-phase balanced resistance. Experiments demonstrate that the online detection limit of ISCF is reduced from 5% to 1% (short-circuit ratio) for a low-speed PMSM.