Research On Nonlinear Control Strategy Of Electromagnetic Levitation System

Levitation control is the core technology of maglev trains.In engineering practice,the system model is often approximately linearized near the operating point,and then linear control technology is used,but there are problems with inaccurate models and poor controller performance.Taking into account the changes of its own parameters and the influence of external disturbances,direct non-linear controller design based on the non-linear model of the suspension system can improve the robustness and anti-interference ability of the system.In this paper,research on the nonlinear control method of electromagnetic levitation is carried out.The main work is as follows:First,the electromagnetic levitation system is analyzed.Using Taylor transform and feedback linearization,respectively,a local linearization model and a global linearization model are established.The suspension chopper is analyzed and modeled,and a current loop correction device is designed.Then,a PID controller with a given compensation is designed,and the parameters of the PID controller are calculated using the linear quadratic optimal algorithm.On this closed-loop structure,a linear extended state observer and tracking differentiator are designed to estimate the differential of the air gap.Through digital control simulation,it is pointed out that the quantization error of the analog-to-digital conversion module in digital control will have a bad influence on the extended observer,and an optimization algorithm is given for this.Both simulation and experiment verify the effectiveness of this optimization algorithm in a singleiron suspension system.Secondly,based on the observer,a feedback linearization controller,a second-order sliding mode controller based on the Super-twisting algorithm,and a current loop based sliding mode controller are designed.The simulation results under simulating various working conditions show that the above two sliding mode control algorithms can effectively suppress the inherent tremor of traditional sliding mode control,and the three nonlinear controllers have strong robustness and anti-interference ability.Finally,based on the ARM+FPGA controller architecture,single-point suspension and four-point suspension experiments were carried out.Experiments show that the sliding mode control based on the Super-twisting algorithm can achieve a stable four-point suspension,and can effectively suppress the inherent chattering of the traditional sliding mode.Compared with PID control,ST sliding mode control has better dynamic performance and faster recovery time in the face of interference.