Understanding Power Factor Limitations in Transverse Flux Machines: A Frozen Permeability Analysis of Magnetic Flux Linkage

Rotational Transverse Flux Machines are often connected with a high specific torque density and efficiency at low speeds. However, the typically low power factor is a challenge to be considered during design process. In order to understand the effects occurring in a Transverse Flux Machine with surface-inset mount permanent magnets, the flux linkage and connected parameters are investigated with the modeling by finite element analysis and the method of frozen permeability. The influence of the current operating point on the phase inductance, spatial harmonics of flux linkage, phasors of flux linkage and voltage, and the power factor is investigated for a single-phase segment. Additionally, the phase coupling with mutual and self-inductance is examined for a 3-phase machine in dependence of the phase distance which is important to achieve the magnetic decoupling resulting in a symmetrical design of the machine. The analysis provides insights into the electromagnetic behavior with increasing saturation, emphasizing the strong fluctuation of phase inductance with a ripple of 35.32 % relative to the mean value of unsaturated inductance during rotation in operating points with a high current loading.