Study On The Control Methods Of Permanent Magnet Brushless Motor

Permanent magnet brushless motors including brushless DC motor (BLDCM) and permanent magnet synchronous motor (PMSM) are widely used in the control system of the refrigerator compressor, with the seeking of high efficiency and low noise for the refrigerator compressor.The studies in this dissertation are mainly about the control methods of BLDCM and PMSM used for variable frequency refrigerator, corporated with Speedy-Tech Electronics (Shen Zhen) Company Limited. The research content can be divided into two parts according to the request of the subject and practical application. The starting circuit of position-sensorless BLDCM in the first part (2nd chapter and 3rd chapter) and the sliding mode observer (SMO) in the second part (4th chapter and 5th chapter) used for position-sensorless are studied.Based on the certain assumption and simplification, the basic operating principle is analyzed and the mathematical model and the equivalent circuit are established for BLDCM in the first part. The simulation model of the body for BLDCM is constructed in Matlab/Simulink and SimPowerSystems, where the back electromotive force (BEMF) is generated using piecewise linear curves. The various starting methods are analyzed for the BLDCM using BEMF to monitor the position of the rotor. A improved starting method is researched, where the current closed loop is adopted to solve the problem of the large current for the existing position-sensorless BLDCM using three-step starting method. The simulation models of starting circuit for the current closed loop and the whole system are established in Matlab. The simulation results for the current closed loop starting and the steady running indicate the proposed measure solves the problem of the bigger current when starting.Based on the analysis of the mathematical models for PMSM in the rotor reference (d ? q) and stationary reference (α?β) frames, the simulation model of the body for PMSM is established in the rotor reference ( d ? q) frame in Matlab/simulink. The simulation model of the sensorless PMSM system based on sliding mode observer (SMO) is modeled using the vector control strategy of id = 0 and space vector PWM. The structure of the conventional SMO and design principle of Kalman filter are analyzed in detail. The improved SMO is proposed to solve the problems of chattering and BEMF phase shift brought by the conventional SMO, which is modeled in Matlab/Simulink. The simulation results prove the improved SMO solves the existing problems of the conventional SMO, through the contrasting research. The simulation results of the improved SMO prove the improvement measures has the stronger robustness, better disturbance rejection ability and the structure is simple, when a step happens in the reference load and speed respectively.