Configuration and Control for AC-DC Three Degrees of Freedom Hybrid Magnetic Bearings

In this paper, an innovated AC-DC 3 degrees of 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 by a common radial polarized permanent magnet ring. The principle of 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 degrees of freedom are studied further by calculating the suspension forces at different displacements and control currents to validate the feasibility of the mathematics models. Then based on the mathematics models of the bearing, a digital control method of this novel bearing is designed. The theory analysis and test 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.