Study On The Optimization Of Magnetic Pole Shape And Its Characteristics Of Line-start Permanent Magnet Synchronous Motor

Since the line-start permanent magnet synchronous motor(PMSM) combines the both advantages of induction motor which can start on-line and PMSM which has merits of high power factor, high efficiency and energy saving, it is gaining more and more attention and application. However, the complexity of the permanent magnet motor’s magnetic strcucture has made the air-gap magnetic field contains a lot of harmonics, which certainly inevitably leads to harmonic EMF, harmonic current, vibration, noise and increased core loss. Therefore, the pole shape optimization of permanent magnet motor to reduce the total harmonic distortion (THD) of the air-gap magnetic field is of great significance for further improvement of the efficiency and performance of line-start PMSM.With the aim of optimizing the no-load air-gap flux density, using the finite element method and two optimization algorithmas, viz. genetic algorithm(GA) and response surface method(RSM), this thesis optimized the magnetic pole of the line-start PMSM.Firstly, this thesis optimized the magnetic pole shape with one-piece pole arc. Then, based on the large salient pole synchronous generator’s three-piece pole structure design, this thesis put forward the three-piece magnetic pole arc in the line-start PMSM. With GA, RSM and the combination of these two optimization algorithms, two kinds of the optimal design value of magnetic pole shape for line-start PMSM were obtained, which make THD of the no-load electromotive forces (EMF) substantially reduced. Afterwards, steady characteristics of three motors which are different with rotor magnet circuit structures before and after optimization are analyzed and compared with time-stepping finite element method (FEM) which is developed independently. The simulation results show that with the optimizition of magnetic pole shape, the harmonic content of current and the torque ripple are decreased significantly in steady state. Finally, the no-load test on an actual line-start PMSM verified the accuracy of optimization method and the credibility of time-stepping FEM program.The simulation and experimental results show that the proposed optimization method of magnetic pole shape of line-start PMSM can obviously reduce the THD of air-gap magnetic field and improve the steady performance of the motor.