Analysis And Design Of A Modular Rotor-permanent-Magnet Flux-switching Machine For Electric Vehicles

The rotor-permanent-magnet flux-switching(RPM-FS)machine is a novel topology of FS machines,which evolves from the stator-permanent-magnet flux-switching(SPM-FS)machines.The RPM-FS machine exhibits high torque density,high efficiency and low torque ripple,etc.,which is suitable for the electric vehicles(EVs).This thesis investigates the electromagnetic torque production mechanism of the RPM-FS machine based on the magnetic field modulation theory,and then the keys of the theoretical and technical issues about RPM-FS machine are deeply and systematically studied,including the design procedure,mathematic model and the comparison of performances with the SPM-FS machine.Moreover,a prototype motor is built and tested.The thesis lays a foundation for the further research and development of the RPMFS machines.The fruits of this thesis are as follows:1.The operation principle of the RPM-FS machine,and the consistency and compensation characteristics between two sets of armature winding coils belonging to one phase are analyzed and revealed.Moreover,the electromagnetic characteristics are investigated by finite element method(FEM),including open-circuit airgap flux density,phase PM flux-linkage,open-circuit back electromotive force(back-EMF),self-inductance,mutual-inductance,cogging torque,and electromagnetic torque,etc.2.The topology of RPM-FS machines evolves from SPM-FS machines,where the stator iron and rotor iron are doubly salient.The electromagnetic torque production mechanism of RPM-FS machines is investigated based on the field modulation theory,and it is found that the torque is mainly produced by the dominant harmonics with the same orders and rotating speeds in the rotor PM field and armature reaction field.In addition,a comprehensive comparison of field modulation principles between RPM-FS and SPMFS machines is conducted from three perspectives,namely PM field,armature reaction field,and torque production mechanism.It is found that the modulation principle not only reveals the similarities of operation principle of two PM-FS machines but also provides a guide for combination of stator slots and rotor poles.3.Based on a magnetomotive-force(MMF)-permeance model,the combination rules of stator slots and rotor pole-pairs with higher torque capacity are determined by analyzing PM-MMF and winding factor.Meanwhile,the candidates with lower torque ripple can be obtained by referring to cogging torque,related to the greatest common divisor of stator slots and rotor pole-pairs.In addition,from the field modulation principle,the RPM-FS machines with the same fundamental magnetic loadings and winding factors exhibit identical fundamental toque,but different modulation harmonic components.Finally,four candidates with attractive torque performance are chosen,and the characteristics are verified by FEM and experiments.4.Based on the electromagnetic characteristics of the RPM-FS machine,the mathematical models are built,including PM flux-linkages,back-EMF and inductances equations.Then,the complete mathematical models of 3-phase RPM-FS machine,both in stator and rotor reference frames,are built respectively.5.The torque-sizing equation of RPM-FS machines is derived,which is particularly necessary to promptly provide the relationship between key geometric dimensions and performance specifications.Then,a 2.5kW 24s/10 p RPM-FS machine is designed by the torque-sizing equation.To evaluate the merits and disadvantages of the RPM-FS machines,performance comparison between a pair of RPM-FS and the SPMFS machines is conducted,sharing the same overall dimensions,material properties and current density.The torque characteristics are investigated based on magnetic and electrical parameters.Then,the electromagnetic performances including overload capability,flux-weakening capacity,and efficiency are analyzed and compared further.The predicted results indicate the RPM-FS machine exhibits larger torque capability,lower torque ripple,and improved flux-weakening capacity.6.For practical EVs,the propulsion machines are designed with a higher current density to obtain an attractive torque(power)density.However,high current density causes some issues,e.g.higher winding temperature,larger iron loss and PM loss.Based on the torque-sizing equation,a 50kW-RPM-FS machine is designed.To evaluate the advantages and disadvantages of the RPM-FS machine,a comprehensive comparison between the RPM-FS and SPM-FS machines is conducted.The results reveal that the 50kW-RPM-FS machine exhibits larger torque(power)density,higher efficiency under rated operation,and wider speed regulation range.Therefore,the RPM-FS machine is a promising candidate for EVs.7.Based on the field modulation principle,the harmonic components of both PM and armature reaction fields are deduced,as well as the corresponding frequencies.Then,the PM loss production mechanisms due to eddy current are revealed for RPM-FS and SPM-FS machines,respectively.Consequently,the similarities and differences between the two FS machines are investigated from the perspectives of both electromagnetic torque and PM eddy current loss production mechanisms.The results indicate that the PM eddy current loss in SPM-FS machines influences efficiency dramatically.However,for the RPM-FS machine,the armature reaction field affects the PM loss more sensitively.In addition,a large PM eddy current loss exhibits associated with high-power rating and large-current density FS machines for EVs,and it can be reduced by utilizing PM segmentation method.8.Finally,a 2.5kW-RPM-FS machine and its test platform are designed and built.The experiments verified the performances of the prototyped RPM-FS machine,including cogging torque,rated torque,overload capability,and the speed regulation range.