Benchmarking Control Techniques Applied to Magnetic Bearings: Performance Assessment Criteria Analysis

Active Magnetic Bearings, due to a plant-intrinsic instability, require a control system for normal operation. Many control strategies have been proposed for the stabilization task, in some instances emphasizing market recognized control approaches, as PID controllers arranged in decentralized structures, and in other instances modern control approaches are envisaged, like LQR or H8 structures. The objective of this paper is to present criteria to assess the performance of such proposed controllers, in order to establish a metric to compare different control schemes. The performance assessment criteria discussed include time domain as well as frequency domain approaches. Such criteria are applied to two control systems used in a laboratory prototype to stabilize a bearingless motor, being one based on PID controllers and the other being a LQR scheme. Discussion of the results is used to select a metric to be applied in the comparison of some controller algorithms, both centralized and decoupled, in order to determine which control law best suits such a bearingless motor.