The Analysis Of Senseless Brushless DC Motor In Start-up

With the increasing of the awareness of energy conservation and the rapid development of the electronic technology,due to the loss of electromagnetic torque in the frictional commutation with brushed DC motors,the inability to minimized and the sensor failures with the brushless motors.senseless brushless DC motor has been widely used in all of our life and productions,such as home appliance industry,office industry,production industry and high-tech industry.In this paper,it does the research and analysis in start-up conditions and control which using in electric tools.According to the traditional three-stage start-up method,the improved three-stage start method is proposed.At the same time,fuzzy self-adaptive PI control is proposed to control the speed after the motor is started.This paper starts with the analysis of mathematical model with brushless DC motor,and then established the brushless DC motor simulation model on the platform of Matlab/Simulink by the voltage balance equations and the mechanical motive equations.Based on the detailed describtion of the principle of brushless DC motor,the start-up of brushless DC motor is analyzed,and the limitation of the traditional three-stage startup working principle in the electric tool is explained,including the return in pre-positioning and detection inaccurate in acceleration,etc.So an improved three-stage start-up method is proposed,includes the static initial position of the rotor detection by an inductance method,and the position of the rotor prediction by a BP neural network.In addition,in the closed-loop operation by the back-EMF,a fuzzy self-adaptive PI control algorithm is proposed by combining traditional PID and fuzzy control.Through the simulative comparison with traditional PI control algorithms,the fuzzy self-adaptive PI control has better robustness and more suitable for the speed control for the motor.Finally,according to the above algorithm,the hardware and software of the controller are designed and manufactured Through the experiments,the basic signal is normal,the hardware can be used for the motor control;In the motor star-tup phase,the initial position of the rotor can be accurately obtained and no inversion while start-up by using the inductance method;the predicted output of the network obtained in the acceleration phase is the same as the position sensor signal,which can be used for motor acceleration control;in the back-EMF closed-loop operation phase,using the fuzzy self-adaptive PI control algorithm,the acceleration is faster at the initial stage,and the acceleration is slower in the final stage.It has the characteristics of quick response,small overshoot,and low steady-state time,at the same time it has good transient and steady-state performance.