Adaptive robust output-feedback control of a magnetic levitation system by k-filter approach

This paper proposes an adaptive robust output-feedback controller for the position-tracking problem of a magnetic levitation system with a current-feedback power amplifier. The system is governed by a single-input single-output second-order nonlinear differential equation which is different from the standard output-feedback form, since there is a position- dependent nonlinear uncertainty multiplied by the control input. Only the position measurement is available for control. The controller is designed by a backstepping procedure with a robustifying modification of the conventional k-filter approach. The boundedness and the guaranteed transient performance of the error signals are achieved by the nonlinear damping terms, and the ultimate position-tracking error is reduced by the adaptive laws. Experimental results are included to show the excellent control performance of the designed controller.