The Influence of PID Controller Parameters on Polarity Switching Control for Unbalance Compensation of Active Magnetic Bearings Rotor Systems

Unbalance compensation forces the unbalance rotor to rotate around the geometric axis, then suppresses the unbalance vibration of the rotor to the greatest extent. Aim to the unbalance compensation of active magnetic bearings (AMBs) systems in the full rotation range including rigid body mode frequencies, the polarity switching control (PSC) based on PID control was adopted to effectively suppress the rotor vibration. In the PSC, it was necessary to switch the polarity factor of the notching filter before and after the rigid mode frequencies of the rotor system. However, improper polarity switching frequency could increase the rotor vibration, even destabilize the rotor system. Therefore, in this article, the equivalent stiffness and damping defined by PID control was used to obtain the natural frequency of the AMBs rigid rotor system, and the selection method of polarity switching frequency and PID controller parameters was studied to ensure that the rotor system has a better unbalance compensation effect in the full speed range including the rigid body mode frequency. Besides, in order to further study whether the PSC is dependent on the controller types or not, H
^∞
controller based on the PSC was also designed to compare the conclusion drawn from PID controller based on the PSC. PID controller and H
^∞
controller are the representatives of fixed parameter controllers and unfixed parameter controllers, respectively. Finally, experiment results verified the correctness of the theoretical analysis.