Research On Fractional Sliding Mode Control Method For AC Servo System

AC servo system is widely used in industrial control,military and other fields.With the concept of new industrialization put forward,people not only require AC servo system with a wide range of speed regulation,good dynamic performance,high positioning accuracy,but also require stable operation and energy saving.However,because of uncertain disturbances such as time-varying parameters and external disturbances,the traditional control is difficult to meet the high requirements of the AC servo system.Therefore,it is very necessary to apply the advanced control algorithm in the AC servo system.This paper studies AC servo system from the following aspects.Firstly,in order to improve the control precision and dynamic response performance of AC servo system,a fractional-order integral sliding mode controller based on a new approach law is designed.By introducing fractional calculus operator on the integral sliding surface,the integral saturation effect is reduced and the robustness of the system is improved by using its slow transfer energy.In order to further reduce the system chattering,a new approach law is designed.By changing the switching function gain to the logarithm of the state variable,the state variable approaches the origin at a gradually decreasing speed on the switching surface.Secondly,in order to accurately obtain the rotor speed and position,and improve the accuracy of the traditional sliding mode observer to estimate the rotor speed and angle,a fractional-order non-singular terminal sliding mode observer is designed.The continuous smooth back electromotive force is obtained by the control law containing the integral term and the fractional differential term,which avoids the phase lag problem caused by the introduction of the low pass filter.The fractional-order PID(Fractional Order PID,FOPID)is introduced into the phaselocked loop to form a fractional-order phase-locked loop(Fractional order phaselocked loop,FO-PLL),which makes the rotor position and velocity accurately and quickly.The results show that the problem of low accuracy and phase delay of traditional sliding mode observer can be solved.Finally,with DSP TMS320F28335 as the core,the fractional-order sliding mode control(Fractional Order Sliding Mode Control,FOSMC)algorithm is written and debugged on the CCS3.3 software development platform.It is verified by the motor control experimental platform that the steady-state error can be reduced and the robustness to load disturbance can be improved.