Switch-Mode Current Amplifier for Active Magnetic Bearings

This paper presents the concept and the practical implementation of a switch-mode current amplifier for the use in Active Magnetic Bearings (AMB). The switch-mode amplifier consists of a full-bridge capable of operating in 2-level, 3- level or phase-shifted PWM mode. An optimal digital currentprogrammed 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 current amplifier developed 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. The presented current amplifier concept has been verified experimentally on a single-axis AMB platform using a dual channel amplifier prototype, controlled by a single 16 bit low-cost microcontroller.