Research On Linear Eddy Current Brake With Serial Magnet Circuit And Hybird Excitation

Eddy current brake(ECB)is an electromagnetic device which can generate braking force or torque based on Faraday law of electromagnetic induction and the equation of Lorentz force.Compared to the traditional mechanical friction brake,the ECB has the advantages of non-mechanical contact,low noise,convenient maintenance,long working life,easy to control,high reliability and nonpolluting.Therefore,ECBs have been put into many industrial applications,such as braking systems,vibration suppression and transmission systems.Taking the testing platform of the linear motor as the application background,a serial magnet circuit hybrid excitation linear ECB is proposed in this paper.The accurate analytical model,several key problems,design method and temperature rise characteristics have beed studied.Firstly,the equivalent magnetic circuit model of the serial magnet circuit hybrid excitation linear ECB is established,and the amplitude of the air gap magnetic flux density is obtained.The equivalent magnetic circuit model can only get the amplitude of the air gap magnetic flux density but not the distribution of the waveform.Therefore,a piecewise function obtained by empirical formula is introduced in this paper,to achieve the complete distribution of the air gap magnetic flux density.The distribution of the air gap magnetic flux density is fitted by using the piecewise function.The amplitude and waveform of the air gap magnetic flux density can be obtained by using the equivalent magnetic circuit model and the piecewise function.And then,the layer model of the hybrid excitation linear ECB is established.The influence of slots is taken into account by introducing Carter's coefficient.After the layer model is built,the expressions of eddy currents in the secondary conductor plate,braking force and eddy loss are deduced,by solving the governing equation of each layer.Namely,the analytical model of the hybrid excitation linear ECB is developed.Meanwhile,the influence of the core saturation is taken into account,for improving the accuracy of the analytical model.The accuracy of the analytical model is verified by using the two-dimension finite element method.Secondly,the longitudinal and transverse end effect are studied from theorectical perspective.The longitudinal dynamic end effect is analyzed by the one-dimensional field theory.The transverse static end effect is analyzed by the Schwarz-Christoffel transform.The transverse dynamic end effect is analyzed by partition of the conductor plate.The methods of compensating the ends effects above are presented,according to the result from theoretical analysis,therfore,the corrected analytical model is obtained.The corrected analytical model is validated by the finite element method and experimental test.The response speed of excitation current and braking force are the key indicators of the dynamic performance of ECBs,have significant effects on the stability and security of the testing platform of the linear motor.The hvariation trend of the response speed of excitation current and braking force with electromagnetic parameters of ECB are studied based on FEM,and the theoretical basis for use in the linear motor test platform is provided.Moreover,to testify the advantage of the hybrid excitation structural concept,the comparation of the braking force characteristic between electrical excitation and hybrid excitation eddy current brake is made.Then,the design method of the serial magnet circuit hybrid excitation linear ECB is studied.The design objective,principles and procedures are presented.The equation of main dimensions of the serial magnet circuit hybrid excitation linear ECB is deduced using the analytical model.After determining the main dimensions,the size of the permanent magnet,parameters of the excitation windings and slot dimensions are confirmed,based on the effects of electromagnetic parameters on the braking characteristics.A prototype of the serial magnet circuit hybrid excitation linear ECB is manufactured and the braking force testing platform is set up.The braking force characteristics of the prototype as a function of excitation current and speed are are tested,respectively.Finally,the temperature rise characteristics of the serial magnet circuit hybrid excitation linear ECB is analyzed.The air flow field distribution of the serial magnet circuit hybrid excitation linear ECB is calculated by using the three-dimensional fluid field model.Then,the convective heat-transfer coefficient and thermal-convection resistance are calculated by the air fow field distribution and the dimensionless analysis,and the thermal network model of the hybrid excitation linear ECB is established.The three-dimensional thermal finite element model is developed,to verify the veracity of the thermal network model.The time-varying temperature of the hybrid excitation linear ECB vary with time is calculated,and the result is compared with that of the thermal network model.The static state and dynamic state temperature characteristic of the prototype are measured,for verifying the veracity and effectiveness of the thermal network model and FEM model.