Research On Sliding Mode Control Methods Of Brushless DC Motor

Nowadays,due to stronger overload capacity,reliable performance,wide range regulation of speed and easy maintenance etc,brushless DC motor(BLDCM)is widely used in various fields.However,since the complex characteristics of BLDCM such as time-varying and multi-variable coupling,the traditional control strategy can hardly meet the requirements of the high performance for the BLDCM system.Sliding mode control(SMC)which has strong robustness is not sensitive to external disturbance,internal parameter variation and other uncertainty factors so that it is widely applied to BLDCM control.At the same time,the discontinuous action of SMC which leads to the chattering problem of system.In order to improve the control accuracy of SMC for BLDCM control system,in this paper,the high order sliding mode and the fractional sliding mode are respectively used to design the direct torque control(DTC)system and the speed control system for achieving better control quality of BLDCM by SMC.Firstly,in view of the difficulty of obtaining the back EMF in BLDCM direct torque control,the chattering phenomenon exists in traditional sliding mode control,and the phase delay problem caused by the addition of low-pass filter.A high-order sliding mode observer is designed,it can be applied to the direct torque control of sensorless BLDCM,which can effectively reduce torque ripple and improve the performance of the systemSecondly,in view of the defects of the traditional integral sliding mode surface,as it is in the large initial error,it easily leads to overshoot,long settling time,bad transient performance,and even make the control system unstable.Thus,a fractional order integral sliding mode controller(FOISMC)is designed.The fractional integral operator is used to design the sliding mode surface,meanwhile,the variable exponent reaching law is also used to design the control law.FOISMC can improve the performance of traditional integral sliding mode control,it can also increase the flexibility of the system control at the same time.It makes the control system have better setting value tracking and disturbance rejection performance.Finally,a modified fractional sliding mode speed controller is designed for the double closed loop speed control system of BLDCM and it makes full use of the characteristics of the fractional calculus operator with two degrees of freedom.The fractional order sliding surface and the fractional order reaching law are used to design the fractional order sliding mode controller.The simulation results show that the proposed method can make the BLDCM speed regulating system have better anti-interference and robustness...