Adaptive Unbalance Compensation for a Three-Pole Active Magnetic Bearing System

Mass imbalance frequently exists in a rotating machine. It may induce unbalance force, causing undesirable vibrations and noise. Active magnetic bearing (AMB) has been found to be a good device to deal with such problem. This paper is concerned with the unbalance compensation for a three-pole AMB system. An adaptive compensation scheme is proposed based on the theory of immersion and invariance (I&I) control. It is to immerse a higher-order system into a lower-order target system. The lower-order target system in this paper is the three-pole AMB system with known mass imbalance and with a stabilizing integral sliding mode controller (ISMC). On the other hand, the higher-order system is the three-pole AMB system with both the ISMC levitation controller and the adaptive compensator. The adaptive compensator is designed to deal with the case that the mass imbalance may be unknown and may be changing during operation in practical applications. It estimates the information of mass imbalance online and is incorporated into the ISMC so that the unbalance force can be eliminated. Both numerical simulations and experimental results verify the effectiveness of the proposed adaptive compensator for mass imbalance.