Research On Sensorless Startup And Control Of Brushless DC Motor

The operation of brushless DC motor needs commutation control. Traditional brushless DC motor control system depends on rotor position sensors to provide the feedback of the rotor position for commutation control. However, position sensors bring in some problems. Position sensors require higher mechanical installation accuracy, increase more signal lines which are susceptible to interference and are not suitable for high temperature and wet engineering situations. Sensorless control technology can extend the application of brushless DC motor in engineering occasions. The paper designed a set of DSP digital control system to study sensorless control technology.The paper studies detection method of back electromotive force zero-crossing method and analyzes the problems of back electromotive force zero-crossing method, which provides theoretical reference for the hardware design and software compensation method. For the digital control system, the paper establishes current reference model according to motor’s Mathematical model and the discrete formula of digital control system. The current reference model is close to the actual digital control system and can carry on the observation to the rotational speed. The current reference model is proposed to provide speed reference in starting process in the paper.In traditional three-step open-loop startup, starting current is large and the startup process is sensitive to the load changes. On the basis of the torque control mode, the paper studies single current closed-loop starting method based on I-f starting according to the features in starting progress with position sensors. After deducing accelerating theory formula in the whole starting process, a detailed analysis has been done for the factors of affecting starting process. The paper uses inductance method to solve the problem of inversion and oscillation in I-f starting process.The I-f starting method and back EMF zero-crossing system simulation models are established in MATLAB/Simulink to make simulation analysis. Simulation analysis is consistent with the theory.In the end, software and hardware realization and debugging methods of system are introduced. The experimental results verify the correctness of the theory and simulation analysis, which is able to start motor, has high robustness, and can adapt to a certain load changes. In starting process current reference model can provide relatively accurate speed reference, and motor can transfer from single current closed loop starting control to back electromotive force zero-crossing running smoothly.