Discrete Time Sliding Mode Control with Simple VSS Observer of Zero-Power Magnetic Bearing Systems

This paper deals with the discrete time sliding mode control of a rotor-magnetic bearing system with zero power scheme using a permanent magnet. We propose a new actuator in which the flux circuit of the zero power scheme using a permanent magnet can be varied. A mathematical model of zero power sceme using permanent magnet and a flexible rotor is derived. The reduced-order model is described for the controller by eliminating higher-order modes of the mathematical and electrical magnet interation system beyond the fourth flexible mode. The sliding mode control system for reduced-order model is designed using the discrete time VSS observer. The simulations are done for the two cases of lift off and rotations. The two unstable rigid modes can be easily controlled with good stability, and the spillover phenomena of the higher-order modes are not generated. It is also clear that the proposed discrete time sliding mode controller has robustness against model parameter variations and external disturbances, compared with the conventional control methods like PID control and disturbance cancellation control.