| Synchronous reluctance machine(Syn RM)has received wide attention due to its advantages like high power density,wide speed range and low cost.This dissertation mainly focuses on the improvement of torque density and anti-demagnetization capability,and the reduction of vibration and cost through study with various topologies of permanent magnet assisted synchronous reluctance machine(PMASyn RM).Firstly,a PMASyn RM which has a stack of surface-mounted permanent magnet(SPM)rotor and a stack of synchronous reluctance(Syn R)rotor axially combined on the shaft is studied.Unlike the traditional PMASyn RM,the magnets are not located in the flux barriers of the Syn R rotor,therefore,the magnets and flux barriers have no more geometric confliction between them.The two rotor stacks can be circumferentially shifted to any relative angle.Clearly,the shifting angle and the axial length ratio between the two rotor stacks,together with the phase angle of the armature current vector,influence the motor performance,and their optimal design is detailed in this dissertation.Analysis of the prototypes shows that the studied axial-rotor-stacks PMASyn RM evidently exhibits higher torque density than the conventional PMASyn RM.Subsequently,considering the high cost of the rare-earth magnet and the low energy product and the demagnetization issue of the ferrite magnet,a new hybrid PMASyn RM is proposed,taking into consideration the effect of the significant magnetic property difference between the rare-earth and ferrite magnet materials.The anti-demagnetization capability of the machine can be largely improved by allocating rare-earth magnets in the barriers adjacent to rotor outer periphery,and the ferrite magnets in the inside barriers.Comprehensive analysis results have indicated an optimal ratio of slightly above 5% between the rare earth and ferrite magnet volumes strikes a balance between the anti-demagnetization capability and the cost per Newton-Meter for such hybrid machines.A prototype with5.5% rare-earth magnet volume ratio is designed to compare with its existing conventional counterparts which employ ferrite and rare-earth magnets respectively.Both the finite element analysis and experimental results have revealed that all three machines have almost identical output performance,but the hybrid machine has evidently enhanced the demagnetization withstanding capability over the ferrite PMASyn RM and significantly reduced the magnet cost over the rare-earth one.Finally,potential negative effect on radial vibration of asymmetrical topologies in PMASyn RM,which was proposed to reduce torque ripple,is studied in this paper.An analytical model is established,through which the spatial orders of radial electromagnetic force with various rotor topologies are derived,and the relationship of the peak frequencies and the corresponding spatial orders in the radial electromagnetic force is revealed.It is shown that with integer-slot windings,some asymmetric rotor topologies will reduce the order of the lowest spatial harmonic for the radial electromagnetic force,and consequently increase the vibration.While with fractional-slot windings,the order of the lowest spatial harmonic in different asymmetric rotor topologies is all the same.Finite element analysis and experiments demonstrate the same results.Finally,with integer-slot windings,a specific rotor topology with asymmetry about both d-axis and q-axis is recommended;while with fractional-slot windings,asymmetric rotor topologies that keep the rotational symmetry are recommended,which can reduce the torque ripple,but would not deteriorate the radial electromagnetic force nor the vibration. |
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