Research On High Stiffness Control Strategy Of Hybrid Excitation Magnetic Suspension System

With continuous development of modern industry,requirements of high precision industrial production equipment and high-precision instruments for machining accuracy of parts are getting higher and higher,moreover,the friction between the platform and the stationary guideway of the traditional moving NC machine tool has a negative effect on the stiffness of the machine tool.Therefore,hybrid excitation magnetic levitation's technology is applied to moving NC machine tools with the view of improving the rigidity of moving NC machine tools in this thesis.Furthermore,the quality of the control system has a decisive effect on the control precision and suspension effect of the platform.Therefore,the research on the control system of the hybrid excitation magnetic levitation platform also plays a key role in improving the stiffness of the machine tool.Firstly,this thesis introduces the working principle of repulsion type hybrid excitation magnetic levitation system and the suction type hybrid excitation magnetic levitation system in detail,and chooses the latter as the research object,a mathematical model of single hybrid excitation magnetic levitation system is built.Secondly,due to the phenomenon of buffeting,separate use of sliding mode control can not meet the control requirements of the system.Therefore,adaptive sliding mode control of hybrid excitation magnetic levitation system is presented.Adaptive sliding mode control is divided into the following five steps mainly.The first step is to confirm the switching surface of sliding mode control.The second step is to calculate the equivalent part of the sliding mode control.In the third step,the adaptive control is used to design an adaptive law to estimate the parameters of the sliding mode control,these parameters are used to replace the switching part of control law of the sliding mode control,and the complete control law of adaptive sliding mode is obtained.In the fourth step,the Lyapunov function is constructed to prove that the control satisfies the accessibility condition.The fifth step is to verify the feasibility of the control method by MATLAB simulation.Thirdly,in order to reduce the negative impact of the phenomenon of chattering to a great extent and improve the rigidity of the system,based on the previous adaptive sliding mode control,robust control based on HJI is presented and L2 gain J which represents the robustness of the system is introduced.The smaller the J,the better the robustness of the system.To satisfy the HJI inequality by the reasonable design and complete the control theory.To verify the feasibility of the control method by MATLAB simulation.Finally,results of simulation of the adaptive sliding mode control and adaptive sliding mode robust control based on HJI are compared,which tells whether the latter improves the stiffness of the hybrid excitation magnetic levitation system better than the former.