Quantitative control of the zero-bias-current electromagnetic bearings for lower power consumption

Abstract

Based on the non-contact characteristics, active magnetic bearings (AMBs) possess great benefits like no lubrication, high speed, high accuracy and long lifespan. Moreover, the rotor dynamic performance is adjustable and working conditions are monitorable. Nonetheless, AMBs suffer from large power loss and rotor heating. One viable approach is omitting the bias current, i.e., zero-bias AMBs, but this also results in high non-linearity and poor controllability. The common control practices of zero-bias AMBs are based on nonlinear models, for there is only one electromagnet being electrified at any moment to produce a net control force. In this study, we propose a linear control strategy for the zero-bias AMB. Assuming that each coil has an average current proportional to the pulse width modulation (PWM) duty cycle, the quantitative relation among the magnetic force, the rotor displacement and the coil current can be acquired. Further, this control algorithm was applied to both the horizontal and the vertical thrust zero-bias AMBs. Experimental results proved the existence of currents in both electromagnetic bearings in the unbalanced state. And the rotor-bearing system restored rapidly to an equilibrium state after sudden disturbances. Overall, this method demonstrates the transition from physics to engineering and shows a good application prospect.