Abstract
We propose a novel combined five-degrees-of-freedom (5-DOFs) hybrid magnetic bearing (HMB) with only one permanent magnet ring (PMR) used for turboexpanders. It has two radial magnetic bearing (RMB) units; each has four poles and one thrust magnetic bearing (TMB) to control 5-DOFs. Based on one PMR, the bias flux of the two radial magnetic bearing units and the one thrust magnetic bearing unit is constructed. As a result, ultra-high-speed, lower power loss, small size, and low cost can be achieved. Furthermore, the equivalent magnetic circuit method and 3D finite element method (FEM) are used to model and analyze the combined 5-DOFs HMB. The force-current, force-position, torque-coil currents, the torque-angle position, and the stiffness models of the combined 5-DOFs HMB are given. Moreover, its coupling problems between the RMB units and the AMB unit are also proposed in this paper. An example is given to clarify the mathematical models and the coupling problems, and the linearized models are proposed for the follow-up controller design.
Highlights
Magnetic bearing can provide many advantages for turbomachinery such as high-speed, long-life, higher efficiency, lower maintenance, and higher reliability
When the rotor locates at radial and axial center and the coil current in x-axis oryaxis of the radial magnetic bearing (RMB) unit changes from −1 A to 1 A, the relationship between net force of the RMB unit and coil current is shown in Figure 8 using linearized method (see (11)), nonlinear method (see (1)), and finite element method (FEM)
The displacement stiffness and current stiffness affected by the rotor position and the coil current in x-axis of the RMB unit are shown in Figures 10 and 11, respectively
Summary
Magnetic bearing can provide many advantages for turbomachinery such as high-speed, long-life, higher efficiency, lower maintenance, and higher reliability. Most of the 5-axis hybrid magnetic bearing (HMB) systems are usually composed of two radial hybrid magnetic bearings (RMBs) and one pair of axial hybrid magnetic bearings (AMBs) [16–18] These magnetic bearing systems are easy to manufacture, but their disadvantages are high power consumption, bulky, complex process, and high cost. Each of RMBs and AMBs has one permanent magnet ring (PMR) that is used to provide bias flux. The low power consumption, compact structure, and small size can be gained due to the combined 5-DOFs HMB, the permanent magnetic bias HMB, and the reduction in the number of the poles of the RMB units. We focus on the configuration, modeling, and analysis of the combined 5-DOFs HMB; a future paper will compare with experimental results
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