Magnetic circuit designing and structural optimisation for a three degree‐of‐freedom hybrid magnetic bearing

Abstract

The three degree-of-freedom (3-DOF) hybrid magnetic bearing (HMB) sets radial, axial at one entirety, which can effectively save the bearing installation space. Here, a 3-DOF HMB is designed, optimised, and tested for a 30 kW 60,000 r/min high-speed motor system. The radial and axial bearing capacity is analysed by equivalent magnetic circuit method and three dimensional finite element model (FEM) of initial model of 3-DOF HMB is established. Then, the radial bearing capacity, axial bearing capacity, current-stiffness, and displacement-stiffness are selected as the optimised design target by using chaos particle swarm optimisation algorithm. Meanwhile, the axial length, eddy-current loss, and air-gap flux density are selected as constraints of optimization. The optimal results showed that the axial length is decreased, the eddy-current loss is reduced, and the harmonics in the air gap is lower while the bearing capacity is improved. Furthermore, a 30 kW 60,000 r/min high-speed motor with proposed 3-DOF HMB is manufactured, and the experiments of the radial/axial static bearing capacity test, dynamic performance of high-speed motor with no load in 60,000 r/min and with load in 55,000 r/min are carried out. Experiment results show that the optimised 3-DOF HMB has good force performance and dynamic performance.