Design And Research Of Brushless DC Motor Servo System

Brushless Direct Current Motor(BLDCM)has the advantages of high efficiency and energy saving,fast dynamic response,non-commutation spark and good mechanical properties,as its using electronic commutation instead of the traditional mechanical commutator.So it has been greatly applied on the intelligent electric vehicles,aerospace and other fields.However,BLDCM speed control system is highly vulnerable in the case of parameter variation when there is external influence.The traditional control method,Proportion Integral Derivative(PID)algorithem,is hard to meet the meet the performance of requirements.And the fuzzy control,the neural network control method is too complicated to realize.So this method in this topic for BLDCM speed control system is of great significance.Traditional BLDCM speed control method use current-speed double closed loop control system.As the actual back electromotive force of BLDCM is ideal trapezoidal wave and there is torque pulse when the motor phase current translate.These problems limit BLDC control performance.According to the problem above,I combine the back electromotive force observer with sliding mode controller.The sliding mode variable structure method is one of the most effective control method for nonlinear system.It can make the motor reach steady quickly.The electromagnetic torque of the system can be calculated with Observed back electromotive force by using the sliding mode observer.BLDC is researching object in this paper.Firstly,I introduces some kinds of BLDC control methods.And study the speed-torque double closed loop control system constitute by back electromotive force observer and sliding mode controller against with the weakness of ability to resist load disturbance of BLDCM speed control system.Secondly,I design the method to estimate the electromotive force based on sliding mode observer according to the mathematical model of BLDCM and the sliding mode variable structure control method.Finally,I establish the sliding surface between the measured current and observations of current of BLDCM motor.So we can get the back electromotive force.According to the observed back electromotive force,the electromagnetic torque can be calculated.Then the torque loop of the speed control system is formed with the sliding mode controller.The speed loop use PI controller.The simulation results show that theBack electromotive force of BLDCM can be accurately observed by the sliding mode observer.The speed-torque double closed loop control method has the advantage of fast response and small overshoot and better anti-interference of external disturbances Compared with the classical PI control method.At the end of this paper,I build the simulation model of speed-torque double closed loop control system of BLDCM.And the control system is successfully simulated.