Flux-switching permanent magnet (PM) brushless machines have both the permanent
magnets and the excitation coils in the stator. Compared with conventional PM
brushless machines, they offer particular advantages, such as a simple and robust rotor
topology, a high torque density, due to the bipolar flux-linkage, and a high magnetic
loading, by utilizing magnet flux focusing, and generally, an essentially sinusoidal phase
back-emf waveform, which make them good candidates for brushless AC drives. The
magnets are in an environment in which there is greater scope to manage their thermal
environment, since more precise and higher heat flux cooling methods can be applied to
the stator than the rotor, and the influence o f heat-soak from other components can be
similarly more readily managed. In this thesis, the electromagnetic performance of
3-phase flux-switching PM brushless AC machines is investigated.
Systematic design optimization has been carried out for maximum torque density by
finite element analysis, with due account for the influence of size (scaling) and 3-D
end-effects. An analytical approach to predicting the performance of flux-switching PM
machines is developed based on a non-linear adaptive lumped parameter magnetic
circuit model, in order to enable the electromagnetic performance, e.g. airgap field
distribution, phase flux-linkage and back-emf waveforms, stator winding inductance
and torque, of flux-switching PM machines to be predicted both accurately and quickly.
The optimal split ratio for both conventional and flux-switching PM machines is
derived analytically and validated by numerical analysis and experimentally. For
conventional PM machines, the influence o f brushless DC and AC operational modes,
overlapping and non-overlapping winding dispositions, the tooth-tip height and the
end-winding is investigated, while for flux-switching PM machines, the influence o f the
end-winding, and the magnetic and electrical loadings is studied.
The losses in flux-switching PM machines, viz. the copper loss, the iron loss, and the
eddy current loss in the frame and the permanent magnets, are also investigated in detail.
In addition, the influence o f flux-weakening operation and methods for reducing the losses are studied. All the predicted results are validated experimentally.