Study On The Analytical Model And Torque Characteristics Of Permanent Magnet Eddy Current Couplings

Permanent magnet eddy current couplings(PMEC)can transmit torque from the motor to the load without mechanical contact.Because of the relative movements between the conductor rotor and the magnetic field generated by the magnet rotor,the consequent eddy currents induced in the conductor interacts with the airgap field which results in the transmitted torque.Compared with other mechanical couplings,PMEC has many remarkable advantages,such as lower sensitivity to axial alignment,isolation for harmful vibration,higher reliability for overload protection,better performance in terms of energy saving,and ability of dynamic seal.It is a novel and potential torque transmission device.For the increasingly development of this device on the industrial applications,the improvements of its torque density and dynamic behavior are required.Meanwhile,the design and optimization of this device are still conducted by the finite element method(FEM)such as some commercial FEM tools,which are very time-consuming and require much computing resources.In contrast,analytical method can offer an effective tool with less computing time and enough accuracy of the solution.This paper studies two kinds of PMECs with both the magnet structure and conductor structure improvement.Two corresponding analytical models are proposed to predict the magnetic field distributions and torque characteristics.All of these works are the basis of improving the performance of the PMEC,and offer an effective tool for its further study and design.The main works of this paper are listed as follows.First,the analytical modeling methods aimed to the slotless and slotted conductor structures are proposed.Based on the Maxwell equations,the magnetoquasistatic field governing equations are derived.The PM region modeling method corresponding to the different conductor rotor structure is also investigated.Second,a pole-separated three-segment Halbach magnet array is proposed to improve the performance of PMEC.The related analytical model is presented and employed to predict the magnetic field distribution and analyze parameters.The interface boundary conditions between different medium are taken into account in the process of determining the harmonic coefficients of magnetic vector potential.The results reveals the influence of eddy currents on the airgap field.The predictions of magnetic field and torque value and the consequent nonlinear FEM validations prove that the novel magnet structure can strengthen the fundamental amplitude of the airgap flux density and reduce the dependent of magnets on the iron core.The reason for discrepancy of the analytical prediction is also discussed,and the effective solution is given.Third,a general analytical frame for the field modulated PMEC with slotted conductor topology is proposed.By treating the PM region as the source of a temporal harmonic field,the moving conductor eddy current problem can be solved analytically.The expressions of harmonic coefficients are determined by considering the interface boundary conditions.So the results of magnetic field distributions take into account the effects of eddy currents on the airgap field,the interaction between slots,and the harmonics(including time harmonics,airgap spatial harmonics,and slots spatial harmonics).The eddy current clustering phenomenon in the axial flux type is discovered.The reason of this phenomenon is the 3D geometry effect and the curvature effect,which are also the main reason for the discrepancies of the analytical predictions.Based on the analysis of the reasons,this paper presents an improved accurate analytical model,which is established in a polar coordinate,to calculate the field distributions for radial flux type PMEC.The improved analytical model eliminates the curvature effects and have better accuracy compared with the former general frame.Last,the torque characteristics of the PMEC are investigated based on the analytical model.Moreover,the speed governing curves of speed-adjustable PMEC are also analyzed.A prototype and a test bench are established,and torque characteristics are obtained by experiments to validate the analytical model.