Digitally controlled switch-mode power driver for active magnetic bearings

This paper presents the concept and the practical implementation of a switch-mode power driver for the use in Active Magnetic Bearings (AMB). The switch-mode driver consists of a full-bridge capable of operating in 2-level, 3-level, or phase-shifted PWM mode. An optimal digital current-programmed mode controller lays out the foundations to a proximate-optimal, robust, large-signal dynamic response of the system under extreme cases of loading and parameters variations. In particular, the developed power driver is capable of following the desired reference for large inductance variations (due to displacement). The power stage combines a newly developed, efficient, passive-based current sensor that is capable of sensing bi-directional and near-zero currents, while being robust to external disturbances and maintaining simple and efficient structure. Performance evaluation of the power driver has been verified experimentally on a closed-loop design for a single-axis AMB platform using a dual channel prototype, controlled using a single 16-bit, low-cost microcontroller.