The Research Of Pole-Changing Permanent Magnet Synchronous Motor

Pole-changing induction motors are widely used in many applications. The number of poles can be changed by changing the pole number of stator windings. But the power factor of pole-changing induction motor is low. The power factor and efficiency of permanent magnet synchronous motor are high, but the pole number of permanent magnet can not change in common permanent magnet synchronous motor, pole-changing can not achieved. It has great significance to develop pole-changing permanent magnet synchronous motor which can combine the characteristic of pole-changing and high power factor and high efficiency.Vlado Ostovic first proposed pole-changing permanent magnet motor. In his paper, the rotor is built following the sandwich of permanent magnets, soft iron, all of them being mechanically fixed to a non-magnetic shaft, and the stator is the same as that of pole-changing induction motor. Magnetic equivalent circuit is used to get the current to magnetize the PM and the flux per pole. A prototype is designed and tested at last. The test results verify the author's design. The efficiency and power factor of pole-changing permanent magnet motor is higher than that of induction motor. But the configuration of the rotor is complicated, and construction strength is low. When the permanent magnet is magnetized, the position between stator and rotor has effect on the magnetized state of permanent magnet. Based on Vlado Ostovic's research, the main study works of this dissertation are as follows.1. In order to solve the shortcomings of sandwich configuration rotor, the surfaced-mounted permanent magnet rotor is applied. The configuration of surface-mounted permanent magnet rotor is widely used in permanent magnet direct current machine, brushless direct current machine and permanent magnet synchronous motor. The configuration is very simple, and mechanical strength is good. When the permanent magnet is magnetizing, the position between rotor and stator winding has no effect on the magnetization of permanent magnet.2. The initial magnetization model and remagnetization model of permanent magnet are suggested. In Vlado Ostovic's research, magnetic equivalent circuit is used to get the current to magnetize the PM and the flux per pole on the assumption that all the permanent magnets in the rotor are saturation magnetized. But in fact, it is impossible to make all the permanent magnets be saturation magnetized. In this paper, the magnetic field strength in permanent magnet is calculated by analytical method and finite element method. The magnetized state of permanent magnet is got by combining magnetization model and magnetic field strength result.3. The performance calculation of pole-changing permanent magnet synchronous motor is studied. The technical measures to improve the efficiency and power factor, to broaden the economical operation of permanent magnet synchronous motor are studied.4. Cogging torque of permanent magnet motor is studied. The research work is shown as follows.(1) The analytical expressions of cogging torque of surface-mounted permanent magnet motor and self starting permanent magnet synchronous motor are got by energy method. This analytical expression can be used to study the reduction method of cogging torque.(2) The reduction method of cogging torque by pole arc coefficient of permanent magnet is studied. The pole arc coefficient of PM got in reference is approximation value. In this paper, the method to calculate the pole arc coefficient is got.(3) The reduction method of cogging torque by different slot width pairing is studied. The range of application of this method and the calculation of slot opening with are studied.(4) The reduction method of cogging torque by PM shifting is studied. The research works of PM shifting in references are based on eliminating the harmonics of cogging torque with PM symmetry. When PM shifting is adopted, new lower harmonics of cogging torque are inevitably introduced. In this paper, the PM shifting angles calculation is studied to reduce both the lower original harmonics and newly introduced harmonics of cogging torque.(5) The reduction method of cogging torque by pole arc combination is studied, and the calculation method of pole arc coefficient of PM is got.(6) The reduction method of cogging torque by eccentricity PM is studied.(7) The reduction method of cogging torque by notches is studied. It is very important to select the number of notches in one stator tooth. It is not easy to decide the number when the slot number per pole is an integer. In this paper, the method of notch and pole arc coefficient is combined to reduce the cogging torque.(8) The analytical expression of cogging torque of self starting permanent magnet synchronous motor. The influence factor of cogging torque is studied.