Sliding control of magnetic bearing systems

This paper proposes a sliding control scheme to deal with the nonlinear, uncertain dynamics of magnetic bearing systems. The control scheme is designed based on a model which characterizes not only the electromagnetic interaction but also effects such as flux leakage, fringing fluxes, and finite core permeance in the magnetic bearing. The controller consists of two parts: the nominal control part that linearizes the nonlinear dynamics, and the robust control part that provides robust performance against the uncertain parameters. Since the uni-directionality of magnetic forces may render the control law ill-defined, a lemma is proved and can be used to select proper control parameters to guarantee the performance. The proposed control scheme is applied experimentally to the thrust bearing of a magnetically levitated rotor. The results indicate that the control system is capable of maintaining stability and consistent performance