On-line Detection of Magnet Demagnetization in Asymmetrical Six-Phase Surface-Mounted Permanent Magnet Synchronous Motor Drives

By splitting the total power among several phases, multiphase drives allow reaching high power levels. Also, a suitable control system can take advantage of the higher number of phases and make the electric drive more robust to open-phase faults. However, in permanent magnet machines, a type of fault that has often been a challenging problem for the researchers is the demagnetization of the rotor magnets, which can be indistinguishable from other types of fault or becomes significant only in a specific working range. In this paper, an on-line control scheme for the monitoring of the status of the rotor magnets is illustrated for an asymmetric six phase permanent-magnet machine with two insulated three-phase windings. The developed control scheme ensures that the drive can still operate in case of a partial rotor magnet demagnetization, and identifies the abnormal operating condition by estimating the demagnetization level. Experimental results are shown to demonstrate the performance of the control scheme.