Abstract
This paper proposes robust control schemes for multi-axis magnetic bearing systems under current control and voltage control. The control schemes are based on a model which characterizes not only the electromagnetic interaction but also secondary effects such as flux leakage, fringing fluxes, and finite core permeance in the magnetic bearing. In the current control case, a sliding-mode-based robust controller, whose control parameters have to be deliberately chosen to account for the uni-directionality of magnetic forces, is proposed to provide robust performance against uncertain dynamics. In the voltage control case, a control scheme that combines the sliding methodology and the backstepping technique is used to provide robust performance under the influence of the electrical dynamics. It is demonstrated through simulations and experiments that, because the nonlinearity and the uncertainty inherently residing in the system behaviour are directly tackled, the proposed controllers achieve superior tracking performances compared to controllers based on linearization. Copyright © 2001 John Wiley & Sons, Ltd.