Investigation of Irreversible Demagnetization in Switched Flux Permanent Magnet Machines under Short-Circuit Conditions

The irreversible magnet demagnetization phenomena are investigated in this paper , under both healthy and short - circuit conditions for a switched flux permanent magnet (SFPM) machine. The temperature effects on permanent magnet material are taken into account and the influence of short - circuit current over demagnetization is evaluated. In order to calculate the short - circuit current (mainly inter - turn short - circuit), the MATLAB/Simulink model has been employed. The aforementioned short - circuit current is then fed to the finite element model, so the demagnetization analysis can be carried out. Variou s fault scenarios are investigated, including high speeds and high fault severity. It is found that the short - circuit current has li mited effect on the magnet demagnetization due to particular features of the SFPM machines. The mechanism of demagnetization has been revealed and found out to be mainly due to temperature rise and poor PM materials utilization . Experiments have been carried out to validate the MATLAB/Simulink model for short - circuit current predictions.