Affiliations: [a] School of Mechanical Engineering, University of Science and Technology Beijing, Beijing, China | [b] School of Instrument Science and Opto-electronics Engineering, Beijing Information Science and Technology University, Beijing, China | [c] Department of Astronautics Science and Technology, Space Engineering University, Beijing, China
Correspondence:
[*]
Corresponding authors: Xiaojun Ren, School of Mechanical Engineering, University of Science and Technology Beijing, Beijing, China. Tel.: +86 15110058615; E-mail: renxiaojun@ustb.edu.cn. Shaohua Chen, School of Instrument Science and Opto-electronics Engineering, Beijing Information Science and Technology University, Beijing, China. E-mail: chenshaohua@bistu.edu.cn
Abstract: Different from separated magnetic bearing units, combined radial-axial magnetic bearing (CRAMB) has cross coupling problem caused by structure itself. This paper focuses on the study of cross coupling problem for a CRAMB caused by structure itself. An equivalent magnetic circuit model (EMCM) considering the leakage and coupling effects was presented to analyze the mechanism of cross coupling. The analysis results show that due to the influence of magnetic flux leakage and common bias magnetic circuit, cross coupling between axial and radial direction caused by the structure itself of a CRAMB cannot be ignored. The coupling degrees of factors that cause cross coupling are analyzed based on the combination of EMCM and finite element method (FEM). The analysis results show that the coupling effect caused by axial magnetic flux leakage was most serious. To solve the coupling problem caused by the structure itself, the coupled transfer function is derived. This coupled transfer function has been added in the original controller. Experimental results show that the cross coupling effect was reduced effectively and CRAMB can levitate the rotor at 48000 r/min stably with the improved controller.
Keywords: Cross coupling, combined radial-axial magnetic bearing, decoupling design, magnetic flux leakage
