State-and-disturbance-observer-based sliding mode control of magnetic levitation systems

In this paper, a cascaded sliding mode control is designed for magnetic levitation systems usually comprised of an electrical loop and an electromechanical loop. A disturbance-observer-based sliding mode controller is designed for the electrical loop while a state-and-disturbance-observer-based sliding mode controller is designed for the electromechanical loop. The overall stability of the system is proved. The performance of the proposed scheme is compared with a conventional linear quadratic regulator combined with a proportional–integral controller by simulation as well as experimentation on a magnetic levitation setup in laboratory.