Local Demagnetization Detection in Six-Phase Permanent Magnet Synchronous Machines

The partial demagnetization process in surface-mounted permanent-magnet synchronous motors (SMPMSMs) negatively affects the performance of an electric drive, reducing the rated torque and the efficiency of the machine. This article presents a comprehensive analysis of the rotor demagnetization caused by an overcurrent event for a six-phase SMPMSM. Multiphase drives may become a key solution for safety-critical applications because they allow one to increase the intrinsic reliability of electric systems and monitor the health state of electric motors and power converters. This article proposes a diagnostic algorithm for the online detection of rotor demagnetization faults that also considers the magnetization direction of the magnets. The effects of the parallel or radial magnetization of the rotor magnets are analyzed for multiphase machines. The technique quantifies the demagnetization degree to estimate the fault severity and corrects the angular position of the encoder to ensure maximum motor performance under postfault conditions. Experimental tests have been carried out on two identical six-phase PMSMs differing only in the size of the rotor magnets to emulate the effect of trailing-edge demagnetization. The experimental results confirm the effectiveness and robustness of the proposed solution.