Adaptive control of horizontal magnetic levitation system subject to external disturbances

In this paper, an adaptive controller is designed to a magnetic levitation system to cope with internal time-varying uncertainties and external disturbances. Since, in an experimental study, the traditional magnetic levitation design is not easy to realize external disturbances to the system, a horizontal configuration is constructed in this paper. To facilitate the analysis and controller design, the equation of motion is derived in detail. Due to the asymmetric nature of the magnetic loop, there is a big challenge in the controller design process. In addition, since some of the uncertainties enter the system in a mismatched manner, few control strategies are feasible. A multiple-surface sliding control law is proposed with the function approximation technique to stabilize the closed loop system under various uncertainties and disturbances. A rigorous mathematical proof is given to verify the feasibility of the design. Experimental studies are conducted with the comparisons with the conventional PID design to clarify the performance of the proposed controller.