The Fractional Order Sliding Mode Variable Structure Control Of Brushless DC Motor

As a representative of robust control theory in nonlinear systems,sliding mode variable structure control(SMC)has been widely used in various industrial control objects because of its strong robustness.SMC has excellent insensitivity to the model error of the controlled object,the change of object parameters and external disturbance.The switching of the control effect leads to the slow convergence speed and chattering phenomenon.With the increased application of fractional order calculus(FOC)theory,the characteristics of global memory and slow transfer of energy have attracted the attention of researchers in the control field.Brushless DC Motor(BLDCM)has many excellent properties,and they have already been applied in many field of national economy.This paper combines the SMC theory with the FOC theory,and designed the fractional order exponential reaching law(FOERL)and fractional order sliding mode controller.Meanwhile,a fractional order sliding mode observer is designed for the sensorless brushless DC motor,which is used to estimate the rotational speed and commutation signal.Firstly,in view of the fact that traditional Exponent Reaching Law(ERL)still has relative strong chattering.This paper which is based on the exponential term,combines with the fractional calculus of sign function,and designs the Fractional Exponential Reaching Law Ensuring the quickness,it further weakens the system's chattering at the same time.The FOERL is applied to the single closed loop speed system of BLDCM.The simulation results show that the proposed method facilitates the improvement of BLDCM speed chattering problem.Secondly,a fractional order sliding mode controller is designed for the double closed loop speed control system of brushless DC motor.The fractional integral operator is applied to the sliding mode surface,so that the controller output is the fractional integral of the current.The output effect is smoother and the robustness and rapidity of the system are improved.Thirdly,this paper designs a fractional order sliding mode observer for the sensorless brushless DC motor,which avoids the phase lag of the back EMF due to the existence of the filter.With the detection of the line voltage and phase current,we can have the signal of commutation and speed of BLDCM.The simulation results show that the designed observer can reduce the estimation delay of the EMF and improve the control precision of the system.Lastly,the experimental platform of fractional order sliding mode variable structure control system is established,and verification of the controller based on fractional exponential reaching law is also achieved.The experimental results comfirms the effectiveness of the proposed method.