Control Strategies for Highly Gyroscopic Outer Rotors with Diametral Enlargement in Active Magnetic Bearings

Abstract

Flywheels are used for peak shaving or load smoothing to generate a higher efficiency and a more stable power supply. Therefore, this paper investigates highly integrated outer rotor flywheels levitated by active magnetic bearings (AMB). Due to the highly gyroscopic behavior and the diametrical enlargement under rotation, the system behavior changes with the speed, leading to a significant decrease in the maximum force and maximum force slew rate of the AMB. Thus, the speed range in which a decentralized feedback control stabilizes the system is reduced. In the literature, there are numerous approaches for coping with gyroscopic behavior. However, there are far fewer investigations for explicit consideration of the change in the air gap in the control structure. Therefore, the goal of this work is to find a control strategy to reduce the effect of the gyroscopic behavior as well as the change of the air gap. The authors propose a control strategy combining a cross feedback control with a decentralized variable feedback control. With this combination, the drawbacks of the previously described effects are compensated, leading to a higher operating range of the system and a reduced utilization of the amplifier without overcompensation at lower rotational speeds.