Design, Analysis, and Control of a Hybrid Field-Controlled Axial-Flux Permanent-Magnet Motor

This paper presents the design, analysis, control, and experimental evaluation of an innovative field-controlled axial-flux surface-mounted permanent-magnet machine. Topology and design equations, as well as an optimized design study, are attained. The machine is investigated in detail using finite-element analysis, and a prototype machine is built. In order to evaluate the new axial flux machine topology, an experimental system setup is devised and discussed. The experimental results of the prototype machine and a comparison between the analysis and test results are also presented.

Nomenclature

Vector potential.

Flux density in the rotor core.

Flux density in the stator core.

Amplitude of the airgap flux density.

Peak value of airgap flux density created by a permanent-magnet (PM) pole.

Peak value of component created by a dc field current.

Peak value of created by a PM in front of the PM pole.

Peak value of created by a PM in front of an iron pole.

Peak value of created by a dc field in front of the PM pole.

Peak value of created by a dc field in front of the iron pole.

Diameter of the machine inner surface.

Diameter of the machine outer surface.

Total outer diameter of the machine.

Back electromotive force (EMF).

Converter frequency.

Airgap length.

Effective airgap length.

Radial height of the stator slot for the dc winding.

DC field winding current.

Current density of dc winding.

Carter factor for the slot effect of the ac winding.

Slot fill factor of the dc field winding.

Leakage flux factor.

Leakage flux factor between the PM and iron pieces.

Correction factor for computation purposes.

Peak value corrected factor of airgap flux density.

Field-controlled characteristic.

EMF factor.

Peak airgap flux density correction factor in radial direction.

Current waveform factor.

Aspect ratio coefficient.

Correction factor of the axial length of the stator core due to the existence of the stator tooth of dc winding.

Electrical power waveform factor.

DC field slot factor.

Ratio of electrical loading on rotor and stator.

Axial length of the rotor core.

Axial length of the stator core.

Effective stack length of the machine.

Axial length of the rotor.

PM length.

Axial length of the stator.

Axial length of the stator slot for ac winding.

Axial length of the stator slot for dc winding.

Number of phases of the machine.

Number of phases of each stator.

Number of turns for the dc field winding.

Fundamental pole pair for the excitation MMF.

Rated output power of the machine.

Cross-sectional area of the turn.

Protrusion of the end winding.

Recoil relative permeability of the magnet.

Permeability of free space.

Pole arc ratio for PM rotor.

Ratio of the average airgap flux density to peak airgap flux density.

Ratio of average to peak created by PM over one pole.

Ratio of average to peak created by field over one pole.

Ratio of average to peak created by PM over the PM pole.

Ratio of average to peak created by PM over the iron pole.

Ratio of average to peak created by field over the PM pole.

Ratio of average to peak created by field over the iron pole.

Airgap flux.

Diameter ratio for axial flux motor.

Airgap flux.

Airgap flux component created by PM over one pole.

Airgap flux component created by a dc field over one pole.

Airgap flux component created by PM in front of the PM pole.

Airgap flux component created by PM in front of the iron pole.

Airgap flux component created by a dc field in front of the PM.

Airgap flux component created by a dc field in front of the iron.

Motor efficiency.