Analysis And Design Of High-Performance Wound-Excited Magnetic Field Modulation-based Brushless Machines

In brushless wound-excited magnetic field modulation(WMFM)machines,both the armature windings and the field winding are placed in the stator,achieving the brushless operation of wound field machines.Compared with permanent magnet(PM)machines,the brushless WMFM machine replaces PMs with field coils,and some inheret disadvantages of PM machines can be overcome,such as the poor flux-weakening performance,irreversible demagnetization and high cost of the rare-earth magnets.Therefore,the brushless WMFM machine is considered as one of the important alternatives of PM machines.However,both DC and AC windings being placed in the stator results that the core and windings suffer from a high temperature.Therfore,both electromagnetic field analysis and thermal field analysis are critical in designing brushless WMFM machines.Based on the air gap field modulation principle,in this thesis the magneto-motive force(MMF)-permeance model is built to analyse the contribution of air-gap field harmonics on the DC winding induced voltage in the brushless WMFM machines.Stator tooth-tip axial pairing method is proposed in this thesis to reduce the DC winding induced voltage of the brushless WSMGM machine.This thesis also builds the lumped parameter thermal model(LPTM)of the brushless WMFM machine,in which the actual locations of the DC and AC windings in the slots are accounted.The novelty and main contents of this paper are shown as follows,(1)Based on the air gap field modulation principle,the magnetic field modulation phenomenon of the brushless WMFM machine is analyzed.The MMF of armature windings and the field winding,the modulator model of the stator and rotor are established,and the resulted spatial-temporal characteristics of air gap field is also given.(2)Based on the air gap flux density distribution of the brushless WMFM machine,the harmonic orders of DC winding induced voltage are derived,and the effective air gap flux density that contribute to DC winding induced voltage are deducted.(3)The stator tooth-tips axial pairing is proposed to reduce the torque ripple and the opencircuit DC winding induced voltage,and the finite element analysis is employed to verify its effectiveness.(4)The LPTM of the brushless WMFM machine is established.Compared with the finite element analysis,the maximum temperature prediction error is 3 ℃.(5)A five-phase brushless WMFM machine prototype was built and tested.The experimental results agree well with the finite element results,which proves that the electromagnetic performance of the prototype meets the design requirements.