| Because there is no contact between the stator and the rotor of the magnetic bearing,it has the advantages of no friction,high precision,no lubricant,high rotation speed and so on,so it has broad research prospects.In order to ensure that the rotor in the magnetic bearing can be stably suspended at the equilibrium position,and provide a theoretical basis for the optimization and control of the magnetic bearing,it is necessary to conduct a systematic,comprehensive analysis of the magnetic bearing from a number of influencing factors.And then study the variation law of the electromagnetic force of magnetic bearing.In this paper,based on the eight-pole radial magnetic bearing,the electromagnetic force of the magnetic bearing is quantitatively analyzed by the combination of analytic calculation,numerical analysis and experimental measurement,and the comprehensive effect of the rotor eccentricity,bias current,magnetic pole pair energization,silicon steel B-H curve,external air leakage phenomenon,magnetic pole arrangement and rotor speed on the electromagnetic force are investigated.The main research work of this article is as follow:(1)The mathematical model of the electromagnetic force of the eight-pole radial magnetic bearing is established,and the analytic calculation formula of the electromagnetic force is deduced.Divided into five working conditions,this paper uses MATLAB to calculate the electromagnetic force under different rotor eccentricity and bias current.ANSYS is used to establish a 2-D plane model of eight-pole radial magnetic bearing.The influence of various factors on the electromagnetic force is explored when the rotor is in a state of suspension.The error between the resolution value and the numerical analysis value and the degree of coupling between the x and y channels are analyzed.The results show: 1)the relative error of the resolution value of the electromagnetic force over the numerical analysis value increases with the increase of the eccentricity of the rotor and the bias current.The relative error at the eccentricity of ±0.3mm reaches 21%,and the analytic calculation formula is no longer applicable;2)When the eccentricity is-0.2mm to 0.2mm,the relative error is basically less than 10%,and the resolution value is in good agreement with the numerical analysis value;3)Before the magnetic pole reaches saturation,the magnititude of the current has little effect on the degree of coupling between the channels.After reaching saturation,the degree of coupling between the channels corresponding to different current levels is different;4)The magnetic pole pair has a more significant influence on the degree of coupling between the channels;5)Magnetic bearings use high saturation magnetic flux density silicon steel sheet to help increase the size of the electromagnetic force after saturation;6)The NSNS arrangement has a greater electromagnetic force than the NNSS arrangement,but the requirements for the control system are higher.(2)ANSYS is used to establish a 2-D plane model of eight-pole radial magnetic bearing rotating electromagnetic field.The finite element analysis is performed on the radial magnetic bearing with the rotor in suspension and rotating.The results show that the reduction of the electromagnetic force Fx at different rotational speeds compared with the stationary rotor increases with the increase of rotor speed,bias current and rotor eccentricity.When n=2400rpm,I=3A and e=0.3mm,the degree of reduction of the electromagnetic force reaches 76%.(3)The experimental platform of radial magnetic bearing is set up,and the analytic,numerical analysis and experimental results are compared and analyzed.The results show that the relative error between the resolution value and the experimental value and the relative error between the numerical analysis value and the experimental value are both within 10% when the rotor eccentricity is 0.The correctness and rationality of the analytic calculation formula and the finite element model are verified. |
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