Analysis, Optimization And Sensorless Control Of Permanent Magnet AC Motor With Rotor Squirrel Cage

The common kinds of permanent magnet (PM) AC motor include the line-start permanent magnet synchronous motor (LSPMSM) power supplied by the power grid, permanent magnet synchronous motor (PMSM)(variable frequency permanent magnet brushless AC motor) power supplied by the inverter, and the PM brushless DC (BLDC) motor. This paper mainly researched the permanent magnet brushless DC motor with a squirrel cage on rotor and the LSPMSM.PM BLDC with a squirrel cage on rotor combines the merits of both permanent magnet synchronous motor and induction motors, hence, possesses advantages such as high power density, line-start capability. It has a similar structure to the LSPMSM. However, their control strategies are totally different. The influence of the rotor cage on the operation performance of the BLDC motor is also different from that of the LSPMSM. Therefore, the BLDC motor with rotor cage deserves deep investigations.This dissertation will introduce the developments of high-speed PMBLDC motor briefly; review the basic theory of the BLDC motor with rotor cage and the related literatures presented by both domestic and overseas researchers. Moreover, the main research findings by the author are presented as follows:Firstly, a mathematical model of the BLDC motor with rotor cage is derived. Also, the simulink model of this kind of motor is built using the MATLAB software, the results of which elucidate the influence of the rotor cage on the motor performance. Comparing with the FEA analysis model, the running time of the MATLAB-Simulink model is greatly reduced, while the analysis results have a relatively high accuracy.Secondly, a medium-power high-speed permanent magnet BLDC motor with rotor cage is designed after making a synthesis of the manufacture cost and technology, electromagnetic performance and mechanical strength. Also, experimental investigation is done. The optimization design method is valid for this kind of motor.Then, influence of the rotor cage on the demagnetization of the permanent magnets in this kind of motor is analyzed. Diffusion of the demagnetization is studied. What’s more, three different kinds of optimization methods are proposed to prevent the demagnetization of the PM. Using the2-D FEA method, the stalled-rotor operation performance of a LSPMSM is analyzed. From the FEA analysis result, the optimization methods are effective. Also, prototype motors are manufactured and tested. The experimental results validate that the optimization methods can prevent the demagnetization successfully. After that, influence of the rotor cage on the flux observer is investigated. And a mathematical model of the flux observer under the coordination with a synchronous speed is derived. In the permanent magnet synchronous motor, the rotor position is only related to the fundamental component of the flux and currents, which can be transformed to DC components under a coordination system with the synchronous speed. Then, the low pass filter can eliminate the harmonic components which are also AC components under the coordination system with the synchronous speed. According to the mathematical analysis of the FEA results of a BLDC motor with rotor cage, the improved flux observer method works well.