| With the increase of energy problems and environmental pollution,electric vehicles(EVs),wind power and other new energy fields have gained more and more attention.At the same time,the direct drive system has become a hot research field in the motor field due to its high transmission performance.In the past decade,some scholars have presented a new type of composite motor,namely coaxial magnetic gears,which incorporate a PM motor and a magnetic gear into one volume.The principle of the proposed motor relies on the use of stationary ring pieces to modulate the magnetic fields generated by two sets of PMs.The modulated magnetic field of inner rotor couples with the magnetic field of outer rotor to achieve high torque density.However,in order to obtain high torque density,coaxial magnetic gears adopt a large number of rare–earth PMs,which lead to high PM eddy current loss.In addition,complex structures increase the difficulty in heat dissipation,thus,the losses may cause significant amount of heat generated in the PMs,resulting in partial irreversible demagnetization of the rare-earth PMs.Moreover,the eddy currents in the PMs may also affect the flux density distributions in the air-gap.Therefore,it is very necessary to reduce PM eddy current loss when designing coaxial magnetic gears.Hence,in order to improve the feasibility and service life of the motor and avoid the demagnetization of the PMs at high temperature,the topic of loss analysis and reduce the eddy current loss of the permanent magnet have practical value.In this paper,the torque capability and loss characteristics of the proposed motor are analyzed,and the harmonic components of the constant torque and eddy current loss are investigated.A new type of series-spoke inner rotor structure is proposed.The new structure considers the eddy current losses of PMs and the balance between the pull-out torque of magnetic gear and the electromagnetic torque of the PM brushless motor,which makes the proposed motor have almost the same output torque and lower eddy current loss compared with the conventional surface-mount motor.The fruits of this work are as follows:1.Based on the analytical method,the operation principle of coaxial magnetic gears is analyzed and explained.The operation principle of coaxial magnetic gears a verified by finite element simulation(FEA).2.Based on the modulation principle of coaxial magnetic gears,the space harmonic components which produce eddy current loss and a constant torque are investigated.From the calculation and comparison of the loss of each part,it can be concluded that the eddy current loss of the PMs mainly concentrates on the inner rotor,which provides the theoretical basis for reducing the loss and improving the motor efficiency by changing the inner rotor structure.3.By adopting the magnetic ring change the inner rotor structure,the influence of the magnetic ring on the torque and loss of coaxial magnetic gears is analyzed from the coupled and uncoupled magnetic circuit of the inner rotor.Based on the analysis of coupled and uncoupled motor characteristics,the effect of changing the inner rotor structure on the torque and loss characteristics is further verified.4.Based on the condition that the pull-out torque of the proposed motor is constant compared with the conventional surface-mount motor,a novel series-spoke rotor structure is proposed.By using Ansoft Maxwell2 D,the performances of the proposed motor will be analyzed and compared with the existed surface-mounted structure motor and the new series-spoke structure have the advantages on the eddy current loss. |
PDF Full Text Request