The Study Of Brushless DC Motor Control System

Brushless DC motor(BLDCM) has small size, less weight, simple structure. It performances well in speed governing as ordinary DC motor, and has little electromagnetic noise, high reljabiljty for the absence of mechanical devices. These advantages provide BLDCM broad prospects in the field of Power Tools industry.First of all, this paper introduces the development and status of BLDCM and its control technologies, In the following chapters, the mathematical model of BLDCM is obtained, based on the analysis of the principle of BLDCM.Secondly, according to the working principle and work characteristics of electric scissors, this paper determines the brushless DC motor sensorless control program. Then this paper introduces traditional Back Electromotive Force (BEMF) method, and the principle of BEMF method is dissertated in detail. In addition,the zero-crossing of BEMF sensing is designed. The reason of rotor position error in the zero-crossing of BEMF sensing method is analyzed, and the compensation metheds are also proposed. According to the problems for BLDCM at high-speed, this paper proposes a new method to expand the speed range of BLDCM. We call it phase advance approach. With this method, the BLDCM can operates in the constant power region at high speed. Then we established the two closed loops control system with a lookup table which is obtained from the phase advance angle. The simulation results proved the feasibility of this method.Then, in the part of hardware design, an overall structure is introduced and an overall strategy of hardware circuit design is given, which includes peripheral circuits of DSPIC30F3010, signal processing circuit, power driver circuit and so on, the position signaldetection circuit, bus current detection circuitare and power circuit also designed. In the part of software design, the dissertation makes detailed discussion about.the software development for state switch strategy, designing start programming, zero-testing procedures.Finally, the results of starting, operating and leading phase current are analyzed in this dissertation. The experimental results proves that the system has good performance.