Freedom Hybrid Magnetic Bearing Research Articles

A Novel Homopolar Four Degrees of Freedom Hybrid Magnetic Bearing

In this article, a novel four degrees of freedom (4-DOF) homopolar hybrid magnetic bearing (HMB) is put forward to reduce the magnetic field coupling of radial 4-DOF. It consists of two pairs of symmetrical radial stators and one rotor, and the radial stators on each side have two pieces, namely, X and Y stator core. Due to the special design of X and Y magnetic poles in the different radial stator cores, the magnetic circuits of X and Y channels are independent of each other. The configuration and operating principle of the homopolar HMB are first discussed, and then, the mathematical model of radial suspension force is deduced by the equivalent magnetic circuit method (EMCM). Besides, some main parameters are given in accordance with the given maximum radial suspension force. Finally, 3-D finite-element (FE) model of the homopolar 4-DOF HMB is established with MagNet software. Meanwhile, the magnetic flux distributions, the magnetic flux density, the force-current relationship of X channel with displacement and current of Y channel are simulated and analyzed. The simulation results indicate that the presented 4-DOF HMB has good performance, and the magnetic fields of X and Y channels decouple well from each other.

Investigation of cross-coupling effect and its restraining methods of a 3-DOF hybrid magnetic bearing

PurposeThe purpose of this paper is to investigate and restrain the cross-coupling effect among X, Y and Z-axes of a three degrees of freedom hybrid magnetic bearing (3-DOF HMB). The influence of the cross-coupling effect on the force characteristics and stiffnesses are analysed. Two additional methods are proposed to eliminate the cross-coupling effect.Design/methodology/approachAnalysis with finite element method (FEM) is time-consuming because of the requirement of a 3D model for the studied 3-DOF HMB. Hence, an improved magnetic circuit model considering the leakage, cross-coupling and saturation effects is used to investigate the cross-coupling effect in this paper. In addition, two restraining methods are proposed. One is adding an auxiliary coil between radial and axial stators. The other is adding an iron ring between the PM and radial or axial stator.FindingsThe X-axis (or Y-axis) force characteristics and stiffnesses are significantly influenced by the Z-axis current, while other axes force characteristics and stiffnesses do not show the cross-coupling effect. Moreover, this cross-coupling effect is inversely related to the distance between axial thrust disk and radial MB part. Besides, adding an auxiliary coil can effectively eliminate the cross-coupling effect in whole work range and adding an iron ring can reduce the cross-coupling effect.Originality/valueThe cross-coupling effect and its restraining methods of a 3-DOF HMB are investigated, which is beneficial to the design and control of such 3-DOF HMB.

Decoupling Control of Three Degrees of Freedom Hybrid Magnetic Bearing Based on LS-SVM

In the paper, the decoupling control method based on least square support vector machine (LS-SVM) inverse system is proposed, and adopting the method realizes decoupling control of an AC-DC three degrees of freedom hybrid magnetic bearing (AC-DC-3DOF-HMB). Aimed at the complicated multivariate nonlinear, strong coupling system of the AC-DC-3DOF-HMB, the reversibility of original system was analyzed, by the ability of least square support vector machines (LS-SVM) in universal approximation and identification fitting to get inverse model of AC-DC three degrees of freedom hybrid magnetic bearing. Then according to the basic principle of inverse system method, the inverse system was connected with the original system. So the complex nonlinear multivariable system is decoupled into three independent pseudo-linear system. The simulation results show that the system was decoupled; the hybrid control method has good dynamic and static performance, verify the feasibility of the proposed control method.

Principles and parameter design for AC-DC three-degree freedom hybrid magnetic bearings

To simplify the mechanical structure, decrease the overall system size of the 3-degree freedom axial-radial magnetic bearings and reduce the manufacturing costs as well as operating costs, an innovated AC-DC 3-degree freedom hybrid magnetic bearing is proposed, which is driven by a DC amplifier in axial direction and a 3-phase power converter in radial directions respectively, and the axial and radial bias magnetic fluxes are provided with a common radial polarized permanent magnet ring. The principle producing magnetic suspension forces is introduced. By using equivalent magnetic circuit method, the calculation formulas of magnetic suspension forces and the mathematics models of the system are deduced. Nonlinearities of suspension forces and cross coupling between different degree freedoms are studied further by calculating the suspension forces at different displacements and control currents to validate the feasibility of the mathematics model. Then based on the mathematics models of the bearing, a control method of this novel bearing is designed. Lastly, the methods on parameter design and calculations of the bearing are presented, and an applicable prototype is simulated to analyze the magnetic path by using finite element analysis. The theory analysis and simulation results have shown that this magnetic bearing incorporates the merits of 3-phase AC drive, permanent magnet flux biased and axial-radial combined control, and reduces overall system size and has higher efficiency and lower cost. This innovated magnetic bearing has a wide application in super-speed and super-precision numerical control machine tools, bearingless motors, high-speed flywheels, satellites, etc.