Robust control of active magnetic bearing systems with an add-on controller to cancel gyroscopic effects: Is it worth it?

Abstract

One of the performance-limiting factors in the design of robust controllers for active magnetic bearing systems is the fact that the controller needs to be robust to the gyroscopic effects, that is rotational speed-dependent dynamics of the system. Studies in the literature show that better performance and stability can be achieved when gyroscopic effects are explicitly handled by a cross-feedback control for rigid rotor-active magnetic bearing systems. For flexible rotor-active magnetic bearing systems, gyroscopic effects are mainly dealt by defining the rotational speed as an uncertain parameter of the model or with linear parameter-varying controllers. This study explores the novel idea of compensating gyroscopic effects of a flexible rotor-active magnetic bearing system with an add-on controller and investigates its effects on the achieved performance of μ-controllers. The study is carried out on an experimental active magnetic bearing test rig with relatively high gyroscopic effects. An add-on controller is designed to compensate the gyroscopic effects of the first and second flexible modes of the rotor. Two μ-controllers are designed for the system: (1) benchmark controller that is designed using a standard control approach for active magnetic bearing systems and (2) controller designed with a modified model of the system in which the gyroscopic effects for the first and second flexible modes are reduced because of the presence of the add-on controller. Both controllers are implemented, and their performances are compared for initial levitation, run-up test from 0 to 10,000 r/min, orbit sizes at various speeds, and the computational cost of implementing each controller. The results suggest that better performance is potentially possible at the cost of significant increase in the computational complexity of the controller.