Research On Three Phase Surface-mounted Magnetic-field Modulated Permanent Magnet Machines

Flux modulation permanent magnet machine(FMPMM)works on the magnetic gearing effect,thus it is a kind of high torque density machine.FMPMM is particularly suitable for low-speed high-torque applications.Recently,the research focus of FMPMMs is on the novel topologies,improvement of power factor and torque density,etc.This thesis will research on the power transfer mechanism,electromagnetic performance analysis including permanent magnet loss,radial force and power factor of three-phase FMPMMs with surface-mounted magnets.The main contribution of this thesis is summarized as follows.The analytical formulas of magnetic flux density distribution,back electromotive force(EMF)and electromagnetic torque of FMPMMs at no-load condition are derived.Six analytical power transferring relations of FMPMMs are summarized and verified by finite element method(FEM).Moreover,the influences of the flux-modulator dimensions on the torque are also analyzed in detail.Besides,to suppress the back EMF harmonics and the torque ripple,the combinations of stator winding pole pairs and PM pole-pairs are optimized.The generic design method of surface-mounted FMPMMs with integer pole ratio are proposed.The influences of pole ratio and winding pole pair number on torque capability,torque ripple,overload capability,power factor,and optimal design parameters such as split ratio,stator slot opening ratio and PM thickness are also analyzed.Moreover,the analytical sizing equation and geometric design formulas of stator and rotor are verified by FEA and experiments on a FMPMM prototype.This thesis also analyzes the influences of the pole ratio and winding pole pair number on the eddy-current losses at no-load and rated load conditions.To reduce the eddy-current loss of the magnets,the PM segmenting technique is applied.The radial forces of both rotor-PM FMPMMs and stator-PM FMPMMs at no-load and load conditions are analyzed in detail.The low-order radial forces,which are dominant in machine vibrations,are tried to be deduced and the theoretical analysis has been verified by both FEA and experiments.In order to improve the power factor of surface-mounted FMPMMs,this thesis has proposed two methods i.e.flux-weakening control and double-stator structure.The field-weakening control can effectively reduce the saturation effect at rated load condition,thus increasing the back EMF and power factor.The double-stator structure can improve the modulated field and reduce the non-modulated field.Thus,it will help to increase the effective magnetic loading,reduce the armature reaction inductance,hence improving the power factor of FMPMMs.