Investigation of irreversible demagnetisation in switched flux permanent magnet machines under short-circuit conditions

摘要

The irreversible magnet demagnetisation phenomena are investigated, 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 demagnetisation is evaluated. 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 demagnetisation analysis can be carried out. Various fault scenarios are investigated, including a high speed and high fault severity. It is found that the short-circuit current has limited effect on the magnet demagnetisation due to particular features of the SFPM machines. The mechanism of demagnetisation has been revealed and found out to be mainly due to temperature rise and poor PM materials utilisation. Experiments have been carried out to validate the MATLAB/Simulink model for short-circuit current predictions.