Robust nonlinear control of a voltage-controlled magnetic levitation system using disturbance observer

This paper considers the control problem of a popular magnetic levitation system, which is open-loop unstable and strongly nonlinear associated with the electromechanical dynamics. The system dynamics is governed by a third-order nonlinear differential equation. The overall controller is designed through a backstepping manner by combining both the robust control and disturbance observer techniques. With the help of nonlinear damping terms, the input-to-state stability property of the overall nonlinear control system is proved, which leads to a major academic contribution of construction of a theoretically guaranteed robust nonlinear controller with disturbance observer for the first time in the literature. Experimental results are included to show the excellent position tracking performance of the designed control system.