Adaptive Control of Electromagnetic Levitation System Considering Input Unidirectionality and Parameter Uncertainty

The ELS (Electromagnetic Levitation System) of Maglev train is strongly nonlinear, open-loop unstable, which controls the air gap by controlling the magnitude of electromagnetic suction force through the current. ELS are suffering from many factors, such as input unidirectional constraints, maximum limited current, and external perturbations, during work. These factors pose significant challenges to the airgap stability control of the ELS system. In this paper, a continuous adaptive robust control method is proposed to address these problems simultaneously. The unidirectional constraint on the control current is handled by a series of transformation operations on the nonlinear dynamical equations, and the perturbation set sum term and unmatched term are introduced. Half of the control law estimates unknown parameters online, while the other half compensates for parameter uncertainty and external disturbances. Based on Lyapunov's theory, The asymptotic stability is proved without any linearized approximation. Three sets of experiments are carried out on an experimental platform, which demonstrates good follow-through and quickness of the proposed method and is robust to parameter uncertainties and external disturbances.