Detection and Discrimination of Mixed Demagnetization and High-Resistance Connection Faults in Six-Phase Surface-Mounted PMSM Drive

Multiphase permanent magnet synchronous machines are receiving more and more concern in several safety critical industry applications, owing to their higher fault tolerability, when compared to the conventional three-phase permanent magnet synchronous machines. However, PM machines can be subjected to rotor magnets demagnetization, which can be caused by overload conditions and/or stator winding fault, leading to serious performance degradation. In this context, monitoring both rotor magnets status and stator winding asymmetry is necessary to guarantee the required machine performance. This paper investigates the diagnosis of a controlled asymmetrical six-phase ac permanent magnet synchronous machine under mixed rotor and stator fault conditions. Specifically, a non-invasive detection and identification technique for mixed demagnetization of the rotor magnet trailing edges, with unbalance of the stator phases due to High-resistance (HR) connection and based on an improved field-oriented control (IFOC) strategy, is developed. The proposed approach is based on voltage space vector signature analysis evaluated in the accessible α-β planes, necessary to model and control multiphase machines. The reliability of the derived fault signatures, able to discriminate between the two types of faults even under mixed faults configuration, is analytically developed, then validated by numerical simulations and experimental tests.