Control Design for Rotor Suspension

Abstract

This chapter presents the design and implementation of the AMB rotor levitation controllers for the compressor test rig. First of all, we discuss the different standards that have been developed for compressors and other rotating machines with AMBs. The requirements and recommendations defined in these standards are followed in our design of the AMB levitation controllers. Next, we present the derivation of the mathematical model describing the lateral and axial dynamics of the rotor/AMB system. A combination of the finite-element approach with the modal reduction method is employed to obtain an accurate model of the rotor radial dynamics. In the axial direction, linearized approximations of AMB inefficiencies, such as the eddy current losses and the back-EMF effects, are included. Finally, the rotor levitation controllers are designed and implemented for the radial and thrust AMBs. In the lateral direction an LQG controller is designed to minimize the rotor vibrations, while an H ∞ controller is synthesized for the thrust AMB to maximize the impeller position tracking performance. In both cases, the controllers are implemented in the test rig, and experimental measurements are presented.