Modelling of high power density electrical machines for aerospace.

This thesis is concerned with the electrical, thermal and mechanical modelling of
electrical machines for the 'more-electric' aircraft. Two specific applications are
considered viz. a permanent magnet brush less DC (BLDC) machine for an electrohydraulic
actuator for a primary flight control surface, and a switched reluctance (SR)
starter/generator for the HP spool of a large civil aero-engine. As a consequence of the
highly variable and often hostile ambient environment and constrained available space
envelope, these electrical machines can rarely be designed in isolation, with thermal and
mechanical constraints often having a significant influence on the design.
In view of these considerations, a transient lumped parameter thermal model has been
developed for the BLDC machine, and validated by experimental measurements on a
prototype machine at various stages of manufacture. Since the rotor cavity of the BLDC
machine is flooded with hydraulic fluid leaking from the pump, fluid friction losses
have been modelled, and validated by tests on a prototype machine. Optimisation of the
BLDC machine airgap has also been investigated using analytical electromagneticlfluiddynamic
modelling.
Detailed investigation of the mechanical stresses in the rotor of the HP spool machine
have led to the development of a novel rotor structure for SR machines which is shown
to have comparable electromagnetic performance with a conventional SR machine. A
specific design of SR machine is analysed in detail in terms of dynamic current
waveforms and the subsequent iron losses, and its thermal performance is modelled in a
representative aero-engine environment.