No‐load losses based method to detect demagnetisation fault in permanent magnet synchronous motors with parallel branches

For permanent magnet synchronous motors with parallel branches, circulating currents are induced by a partial demagnetisation fault. The induced currents increase the losses of the motor. Therefore, detecting such a fault becomes possible by analysing the motor losses. This study analyses the effects of the partial demagnetisation fault and defines an index, which is the ratio of increased losses and total losses when the motor is under no‐load conditions, to monitor the condition of the rotor magnets. The method is easily implemented and sensitive to the fault. The experimental results validate the effectiveness of the proposed method.