Modeling Analysis And Optimization Method Of Flux-Focusing Permanent Magnet Eddy Current Couplers

As the burgeoning transmission and adjustable-speed devices,permanent magnet eddy current couplers have changed the traditional transmission mode and speed governing concept.By adjusting the air-gap length,they can control the speed and torque of the load,and realize the energy transfer in the air between the motor and the load.Having the advantages of simple structure,no mechanical connection,isolation vibration and no harmonic wave,etc.,they will have broad application prospects in the fan,water pump,belt machine and other high energy consumption occasions.Flux-focusing permanent magnet eddy current couplers have changed the structure of the conventional permanent magnet rotor and the magnetization mode of magnets,which can achieve shorter air-gap length and prolong the service life,therefore,this paper has launched research in this novel topology.Considering that the most common element analysis method has long calculation period and requires expensive hardware equipment in solving the coupling problem of dynamic eddy current and magnetic field,this paper focuses on the analytical modeling method of electromagnetic fields and torque for the flux-focusing permanent magnet eddy current coupler and its improved topology,and the analytical results are validated by experiment and finite element simulation;then multi-objective optimization strategies for such devices are explored.These studies will provide theoretical basis for the further development of permanent magnet eddy current couplers.The detailed research works are shown as following:(1)In order to analytically solve the problem of the mutual coupling between the dynamic eddy current,induced magnetic field and rotating permanent magnetic field in the permanent magnet eddy current couplers,starting from the their working mechanism,their flux paths of are analyzed,and the reluctance of each region is calculated.Two general equivalent magnetic circuit models,where the eddy current effect is taken into account,are established:First,the permanent magnetic field is individually solved,and then the induced magnetic field is obtained according to the Ampere's law and Faraday's electromagnetic induction law;The other one is that the eddy current is directly regarded as the magnetic source of the equivalent magnetic circuit,which is solved to get the magnetic flux in the air-gap.According to the energy conservation principle,the torque equation of the permanent magnet eddy current coupler is established.The finite element analysis and the 15kW prototype experiment verify the effectiveness of the analytical model.Several important factors affecting the torque performance are analyzed and discussed by means of the analytical model.(2)For the determination of control equation for magnetic field in the discontinuous boundary condition of the flux-focusing permanent magnet eddy current coupler,an improved two-dimensional layer modeling method based on the virtual magnetic source is proposed.In this method,the equivalent magnetic circuit method is firstly used to calculate the virtual magnetization of iron core region,and then the method of separation of variables are applied to solve the control equations of each layer,finally the analytical models for the air-gap magnetic field,eddy current and torque are established respectively.The finite element analysis and the 900W prototype experiment verify the effectiveness of the analytical model.In order to reduce the leakage magnetic effect of the flux-focusing permanent magnet eddy current coupler,a new topology with double conductor rotors is developed,the proposed modeling method is adopted to calculate its electromagnetic field and torque,the simulation results indicate that the new topology with double conductor rotors can increase torque by 20?50%.(3)Considering that the radial variables have been ignored in the electromagnetic field expressions when using the equivalent magnetic circuit model and the two-dimensional layer analytical model,and that the additional three-dimensional correction factors must be introduced when calculating the torque,to improve the accuracy of the calculation model of the motion conductor eddy current problem,a space analytical modeling method under the three-dimensional rectangular coordinate system is proposed for the flux-focusing permanent magnet eddy current coupler with double conductor rotors.The essence of this method is to solve the three-dimensional Maxwell equations by employing the method of separation of variables.The validity and accuracy of magnetic field,eddy current and torque model are verified by the finite element analysis.This modeling method is extended to the 3D modeling analysis of the traditional permanent magnet eddy current coupler and the Halbach array permanent magnet eddy current coupler with the arbitrary magnetization angle.In particular,the effects of the magnetization angle of the Halbach array on the torque performance are discussed.(4)To facilitate the flow of eddy currents in appropriate routes to reduce the losses,the conductor rotor is processed with slot,and filled with the yoke iron,the improved flux-focusing eddy current coupler with double slotted conductor rotors is proposed.Because the new topology has more complex boundary conditions,the aforementioned analytical modeling methods are not applicable.Therefore,based on the accurate sub-domain method,the control equations for each sub-region are solved by using the method of separation of variables and the Fourier series expansion method.The theoretical analytic models of electromagnetic field and torque are obtained.The results show that the slot topology increases the torque by 10?20%.The influences of slot and permanent magnet parameters on torque are further discussed.(5)Multi-objective optimization problem of the permanent magnet eddy current coupler is expounded.In this dissertation,the optimization objectives are set to maximize torque,and minimize moment of inertia and volume.An improved cuckoo search algorithm combined with satisfaction strategy is put forward for the optimization design of permanent magnet eddy current coupler.For the first time,the cuckoo search algorithm is introduced into the optimization of such devices.The simulation results show that the proposed algorithm is superior to the existing particle swarm algorithm and genetic algorithm,etc.,can obtain the optimal comprehensive performance within the shortest possible time.On the basis,when the analytical expression of the optimizing index is very complex,or simply cannot be established,etc.,this paper proposes an optimization strategy based on the mixed surrogate model and entropy weight for the permanent magnet eddy current coupler.For the first time,the optimization problem of permanent magnet eddy current coupler has been extended into the field of data processing.The effectiveness of this design optimization method is verified by the optimization analysis of the flux-focusing permanent magnet eddy current coupler with double slotted conductor rotors.