Radial Force-Current Characteristics Analysis of Three-Pole Radial-Axial Hybrid Magnetic Bearings and Their Structure Improvement

The radial stator of three-pole radial-axial hybrid magnetic bearings (HMB) has three magnetic poles and the three magnetic poles are driven by a three-phase converter, so the three-pole radial-axial HMB has the advantages of compact structure, low cost, low power consumption and so on. However, as the sum of three-phase current is zero and the three radial magnetic poles are asymmetric, the relationship between the radial suspension force and the control current is nonlinear. In this paper, firstly a mathematical model of three-pole radial-axial HMB is built based on the equivalent magnetic circuit method. The radial force-current characteristics are then analyzed based on the non-linearized model. The calculation, finite element method (FEM) and experimental results show that the suspension force on the x-axis is a quadratic function of the control current, but the suspension force on the y-axis is linear with control current. Besides, the suspension forces on the two radial axes are coupled with each other. Then, in order to decrease the nonlinearity and coupling of radial force-current characteristics, the six-pole radial-axial HMB is proposed based on the above analyses. The radial force-current characteristics of the six-pole radial-axial HMB are also analyzed based on the non-linearitzed model and are validated by 3-D FEM analysis. The calculation and FEM results have shown that the radial force-current relationship of a six-pole radial-axial HMB is linear and there is no coupling between the two radial axes.