Design and Test Results of Active Magnetic Bearing Control System for High-speed Turbo Compressor

Abstract

In designing turbo compressors driven by high-speed motor directly, there is a rotordynamic problem due to lowered bending mode frequencies. In order to support such flexible and high-speed rotating shaft, active magnetic bearing (AMB) will be one of the solutions. In this paper, the design and test results of the AMB system for such a compressor that has two compression stages are discussed. In a digital processing of AMB control, a large phase lag in high frequency domain cannot be avoided. In order to solve this problem, the following control methods are presented. For levitation control, a practical controller design that uses a combination of phase shifting filters and second order low-pass filters is presented. For unbalance control, a synchronous filter that has an arbitrary phase shift at the reference frequency is applied to cross over the first bending critical speed. By adopting these control methods, very stable operation from zero speed to the rated speed of 55 000 min-1 was realized.