On variable structure control of magnetic levitation systems

In this paper, the model for a prototype magnetic levitation system are first studied. Here four hybrid electromagnetic actuators are used to levitate the car body along the normal direction and another two lateral actuators are employed to suspend the car body on the central line of the rail. With the simplified model, we develop a sliding mode controller (SMC) to reduce the air gap errors of the car body, in the presence of system's model errors and disturbances. Various tests are performed to study effectiveness of the PD and SMC controllers, which show that the SMC controller is more robust than the PD controller. The experience gained from the experiments and the characteristics of the system are discussed.