Finite Element Simulation on Irreversible Demagnetization of Permanent Magnet Synchronous Generator

Irreversible demagnetization of permanent magnet wind turbines is one of the main causes of motor failures. Due to the difficulty in representing irreversible demagnetization faults of wind turbines, online monitoring and fault diagnosis techniques for permanent magnet wind turbines are severely limited. In this paper, Maxwell software is used to build a Permanent magnet generator(PMG) model to simulate the fault characteristics of PMG. 25% and 50% uniform irreversible demagnetization and 50% non-uniform irreversible demagnetization faults of generator are simulated. The characteristics of current harmonics and flux linkage distribution were obtained in this paper, and the correlation between the output current harmonics, motor flux linkage distribution and fault types was established. Compared with the normal motor, the effective value of flux linkage under uniform demagnetization decreases gradually with the increase of the demagnetization degree. When 50% uniform irreversible demagnetization occurs in permanent magnet motor, the effective value of motor flux linkage is only 91.6442Wb, which is only 74.9% of that in the normal motor. The effective value of motor flux linkage gradually decreases with increasing demagnetization under non-uniform demagnetization. The output current produce harmonic current under non-uniform demagnetization, and the contents of 1/2, 2, 5/2, and 7/2 harmonics current changing with the demagnetization area. Our simulation results indicate that the peak value of flux linkage and different frequency harmonics current correspond to different types of irreversible demagnetization faults, which provides a theoretical basis for online monitoring and fault diagnosis of irreversible demagnetization faults in permanent magnet wind generator based on the harmonic of the current and the flux linkage.