Related Theory And Measurement Research On Magnetic Bearing Electromagnetic Field

Magnetic bearing(MB) is a kind of electromechanical device with mutual conversion between electromagnetic energy and mechanical energy.MB's basic performance is represented essentially by electromagnetic field features.Magnetic material's nonlinear magnetic permeability and saturation,magnetic leakage, magnetic coupling,eddy current effect and etc make MB's electromagnetic field present fundamentally nonlinearities.It is significant to make researches on MB's electromagnetic field with theory calculation and measurement for MB's performance improvement.For MB's two typical working states,electromagnetic field potential equations are derived and boundary conditions are defined for an eight-pole radial MB.Finite element method(FEM) is utilized to solve the electromagnetic field equations.For rotor suspension,static electromagnetic field distribution is calculated through 3D FEM with consideration of nonlinearities mentioned above.Calculation results show that MB's key performance parameters--air gap magnetic flux density and magnetic forces are affected by the nonlinearities apparently.A radial MB static electromagnetic field measurement platform is constructed and a three channel Guassmeter is utilized to measure the magnetic flux density distribution.The 3D FEM model is modified by the measurement results and achieves certain accuracy.For rotor rotation,magnetic flux distribution,air gap magnetic flux density, suspension force,drag force and power loss of MB are calculated through 2D nonlinear FEM under different coil current and rotating speed conditions.Results show that rotor material's magnetic saturation induces saturation in air gap magnetic flux density and drag force,and the saturation points are determined by both coil current and rotating speed.To solve air gap magnetic flux density online measurement problem,it is introduced to apply Fiber Bragg Grating(FBG) in magnetic flux density measurement. A novel FBG electromagnetic field sensing device is designed and fabricated,and its feasibility in air gap magnetic flux density measurement is verified.A FBG-based air gap magnetic flux density online measurement system is established,which realizes air gap,rotor speed and coil current adjustments to simulate MB working states.Air gap magnetic flux density is measured through the FBG electromagnetic field sensing device under different coil current,air gap and rotating speed conditions when the rotor is static or rotating.Comparison results between measurement and FEM calculation show that air gap magnetic flux density measurement through FBG electromagnetic field sensing device achieves certain accuracy. Key words:Magnetic bearing(MB);electromagnetic field;Finite element method(FEM);Fiber Bragg Grating(FBG);magnetic flux density...