Magnetic Bearing Dynamic Magnetic Field Calculationand Measurement

Magnetic bearing is a typical electro-mechanical device and processes theadvantage of frictionless, high speed and adjustable stiffness. Current in the statorinduces magnetic field in the air gap. The magnetic field in the air gap induces themagnetic force, which acts on the surface of the rotor and controls the movement ofthe rotor, hence the magnetic field is an important media to link the electronicparameter and the mechanical action.The dynamic performance of the magneticbearing is directly decided by the character of distribution and variation law of themagnetic field in the air gap. Researches on the air gap magnetic field provide animportant guide to the design and control of the magnetic bearing.Air gap magnetic field is a typical nonlinear and time-variant field.Thedistribution and variation laws are quite complicated and researches are focused onthe calculation and measurement. Considering the geometry complicity of themagnetic bearing, analytical methods are restricted and the numeric methods (FEMetc) are widely used. In the measurement aspect, factors such as the air gap distance,the magnitude of the magnetic field density and the field variation frequency greatlyrestrict the application of the typical magnetic filed sensor, so new sensors are neededto be designed to measure the air gap magnetic field.Research on the magnetic filed from the calculation and measurement aspectare given in this paper.In the calculation aspect, analytical and numerical method arecombined.The analytical method provides the FEM method with a basic reference.Magnetic field is calculated in Static，rotate，harmonic， rotate plus rotatesituation. In the post processing of FEM, flux density、flux lines、eddy current lossare calculated and the Influence of the current magnitude,current frequency,rotorspeed on the magnetic filed are discussed.In the experiment aspect,magnetic filed sensor design principle and sensingtheory is discussed based on the formers’ work.By modifying the fiber currentsensor, magnetic field sensor is designed,together with the experiment device.Theexperiment device can fill the demand of changing current magnitude,currentfrequency and rotor speed. Sensor position is decided by the analytical results. Before measuring the magnetic field, a couple of U shape iron is designed toCalibrate the static and dynamic performance of the sensor. In the air gap field test,various distribution of magnetic field is measured and the influences of currentmagnitude, current frequency and rotor speed on the air gap filed are discussed.Results match the analytical results in an acceptable tolerance range.