Research On Improved Sliding Mode Control Strategy Of Permanent Magnet Linear Motor Drive System

In servo system,the linear motor has better dynamic performance and reliability.And the motor is widely used in all kinds of direct drive occasions,such as CNC machine tools,electromagnetic ejection,and rail transit and so on.With the wide application,it is essential to diminish the control property of the linear motor.Among them,the inhibitory capacity of motor control system to uncertain disturbance and the control accuracy of control system should be considered.In this thesis,in order to overcome the disadvantages of slow convergence and chattering of the exponential reaching law of sliding mode control,the variable integral power term and the saturation function are introduced.And switching gain is designed with self-adjusting by fuzzy control algorithm,and this thesis mainly designs a sliding mode controller with an improved variable exponential reaching law and a fuzzy self-adjusting switching gain.The controller has a simple structure and can significantly enhance the inhibitory capacity to uncertain interference and reduce the control error of the system.In speed loop,this thesis uses the fuzzy PI algorithm to enhance the response performance of the motor’s speed.Firstly,it states the historical background and application of linear motor.The development of sliding mode control is described,and it introduces some usual keys to fix the problem of sliding mode chattering at home and abroad.Secondly,the control theory of SVPWM is analyzed briefly,and the vector control module is built.And the position loop PI controller is designed and simulated.The disadvantages of poor robustness and low precision of PI controller are pointed out.After that,the traditional exponential reaching law sliding mode controller is designed,and the results of simulation tell us that the sliding mode controller has the strong points of good suppression ability for disturbance of system and good control accuracy,but it also has the problem of chattering.Thirdly,the main reason of chattering in sliding mode is analyzed theoretically,and an improved scheme of exponential reaching law is proposed from the design of sliding mode controller.That is,the variable integral power term of state variables,and saturation function are added to the original exponential reaching law to build the improved sliding mode controller.Through simulation analysis,the improved sliding mode controller significantly improves the chattering problem,and further enhances the control accuracy and robustness of the system.Finally,from the aspect of sliding mode chattering caused by sliding mode switching gain,a sliding mode control with a fuzzy self-adjusting switching gain is proposed,which takes the switching surface and its first derivative as the input and the switching gain increment as the output,so that the switching gain in the original improved reaching law can be adjusted adaptively online with the operation of the system,and it represses the initial sliding mode chattering problem.Fuzzy PI controller is proposed in the speed loop to improve the speed control quality of the motor.And the experimental method is used to verify its effectiveness and implement ability under actual working conditions.