Influence Of Thermal Deformation Of Radial Magnetic Bearing On Vibration Of Flywheel Rotor

The flywheel energy storage system is an energy storage device that uses the interaction between the motor and the flywheel rotor to achieve the input and output of electrical energy by converting electrical and mechanical energy.To avoid dissipating friction energy,electromagnetic bearings are usually used to support.However,electromagnetic bearings in operation still generate losses that are converted into heat and act on bearings and rotors,causing them to expand and deform under thermal action.This changes the electromagnetic force of electromagnetic bearings,affects the dynamic performance of the rotor and even creates a risk of collision.This article takes the radial part of the electromagnetic bearing in the flywheel energy storage system as the object of study,analyzes the temperature and thermal deformation of the magnetic bearing during operation,and studies the effect of thermal deformation on rotor vibration.First,a supporting force model and a rotor dynamic model for the electromagnetic bearing under thermal deformation were established.Based on the traditional electromagnetic force model,a model for the supporting force of electromagnetic bearings under thermal deformation was established.The relationship between control parameters and support properties was analyzed and the influence of the air gap change rate on the equivalent stiffness and damping was investigated.On this basis,a dynamic model of the rotor with four degrees of freedom was established taking into account the thermal deformation of the electromagnetic bearing.Secondly,the temperature field of electromagnetic bearings was analyzed by analysis and numerical methods.A differential equation for heat transfer in electromagnetic bearings was established based on the Fourier law and the first law of thermodynamics.The method of separation of variables is used to solve the partial differential equation for heat transfer in the electromagnetic layer.The influence of structural parameters,input current and convection heat transfer coefficients on the temperature of magnetic bearing is discussed;The finite element method analyzes the temperature of various losses and enthusiasm of the electromagnetic bearing in actual operation and gives the temperature distribution of the electromagnetic bearing in operation.Then,based on the results of the temperature field analysis,the thermal deformation of the electromagnetic bearing is analyzed using the sequential coupling method to obtain the relationship between stator and rotor deformation and current and speed.Subsequently,the influence of thermal deformation of electromagnetic bearings on rotor vibrations was analyzed.Using a rotor dynamic model to solve the free oscillation behavior of the rotor,a Campbell diagram of the rigid rotor was created.When considering the thermal deformation of electromagnetic bearings,you get the first two critical speeds and vibration reactions at different speeds.The results were compared with those without consideration of thermal deformation.The influence of thermal deformation of electromagnetic bearings on rotor vibrations was analyzed.If the thermal deformation of the electromagnetic bearing causes a decrease in the air gap,the safety of maintaining the air gap is determined.Finally,a prototype of a 600Wh flywheel energy storage system was tested and rotor vibration data filtered.Obtained the time,frequency and axial maps of the upper and lower rotors during the thermal deformation of the radial magnetic spring bearing and compared them with the theoretical analysis results to verify the rationality of the analysis.