Variable Structure Control Of Magnetic Levitation System

Magnetic levitation is a technology that uses electromagnetic force to suspend an object in space and realizes that the object does not have mechanical contact with supporting system.It has very broad application prospects in bearings,trains and heart pumps.More and more attention has been attracted to the magnetic levitation system due to its low noise,friction-free and low loss.The performance of magnetic levitation systems mainly depends on the control technique,so it is of great significance to develop its control technology and methods for the magnetic levitation system.Uncertainties caused by parameter perturbation and external interference are challenges for the traditional control methods.Sliding mode variable structure control,as a nonlinear control method,has a fast response and robustness to system parameter perturbation and external interference.This article uses the magnetic levitation ball system as a platform,and focuses on the variable structure controller design in the magnetic levitation control system.In this paper,for the position control of the magnetic levitation ball,firstly,the mathematical model of the magnetic levitation ball control system is obtained according to the force analysis,and the state equation of the magnetic levitation system is obtained by the linearization of the nonlinear model.Secondly,the uncertainty in the magnetic levitation ball system is analyzed,and the conventional sliding mode variable structure controller is designed for the magnetic levitation ball system.The stability of the system is proved by the Lyapunov theory.The conventional sliding mode variable structure is validated by the simulation and experiment.The conventional sliding mode variable structure controller is superior to the conventional PID controller by simulation and experiment comparison.To deal with the large control chattering of conventional sliding mode variable structure controllers,an improved power reaching law is proposed in this paper based on the conventional power reaching law.The comparison results of the new reaching law combined with the traditional sliding mode surface,complementary sliding mode surface and fractional sliding mode surface shows that the improved power reaching law combined with the traditional sliding mode surface achieves better control performance.The comparison results using the conventional power reaching law,improved power reaching law,super helix reaching law and exponential reaching law combined with the traditional sliding surface show that the new improved reaching law achieves better performance and reduced chattering effect.A variable gain proportional robust term sliding mode control method is proposed by combining the improved power approaching law with the traditional sliding surface to improve the system transient performance.For the constant,sinusoidal and square wave references,the simulation and experiment results show that the proposed variable gain proportional sliding mode control algorithm can effectively improve the response speed of the system without affecting the steady-state performance,and ensure the controlled system to track the given references.