Research Of Control Strategy For Sensorless Permanent Magnet Brushless DC Motor

Our society is facing two major challenges: environmental pollution and energy shortage.China’s oil per head is located in the middle and lower reaches of the world level, while fuel cars annually consumes a lot of oil. At the same time, a large number of automobile exhaust produced by fuel vehicles has led to many negative environmental issues. So the development of energy saving electric vehicles will be the trend of the market. One of the core technology of electric vehicles is the motor control system.Permanent magnet brushless DC motor control system is the first choice of electric vehicle drive motor, which has speed performance high power density, structural reliability, high efficiency and characteristics. The traditional BLDCM normally operated under the conditions of a position sensor, which limits their applications. Therefore, the research on control for BLDCM has been a hot spot all along in recent years.Firstly, the paper introduces the basic structure and principle of BLDCM, the mathematical model of BLDCM is established. Considering the control system having no position sensor,the back EMF zero-crossing method is applied to scan the rotor position signals of the motor, by fixing phase delay problem, the current is commuted correctly.Considering the BEMF very little in the process of motor starting, the back EMF zero-crossing method is expired, this paper adopts the method of three part to start. In order to improve the speed range of the motor, this paper analyzes the weak magnetic control technology, and put forward the implementation method. The simulation model is established in MATLAB simulation environment, verifying the rationality of the Back EMF detection method and the three part start strategy.Secondly, the paper designs motor controller based on microprocessor DSP2812, the controller is composed of driver circuit, back EMF zero-crossing detection circuit, switch optocoupler isolation circuit and a sampling circuit and so on.Introduces the design concept of the various parts of the circuit, and give parameters of some important components. The whole control system takes full advantage of the on-chip resources DSP2812 and efficientdata processing capabilities, eliminating the previous addition circuit complex hardware circuitry.Finally, this paper shows the experimental waveforms and results. The experimental results showed that: the BLDCM on position-sensorless starts quickly, switches state steady and has good flux weakening performance.