The electromagnetic performance of brushless permanent magnet DC motors - with particular reference to noise and vibration.

A comprehensive analytical technique is developed for predicting the instantaneous
magnetic field distribution in radial-field, surface-mounted permanent magnet brushless DC
motors under any load condition and commutation strategy. It is based on a 2-dimensional
analysis in polar coordinates and accounts implicitly for the corresponding stator winding current
waveforms and the effect of stator slot openings. In addition, a 2-dimensional analytical method
for calculating the back-emf waveform is presented, whilst the analytical technique is applied to
the prediction of the cogging torque waveform and the calculation of the self- and
mutual-winding inductances.
Also developed and validated is an analytical model for predicting the steady-state dynamic
performance of a 3-phase brushless DC drive, by exploiting the periodicity in the stator winding
voltage and current waveforms, with due account of the influence of commutation events in the
inverter bridge, the back-emf waveform, current limiting, and commutation timing etc. The
model is developed further to couple with the motion equation of the rotor to enable the transient
and steady-state dynamic performance of brushless DC drives to be predicted.
The effect of end-shields on the vibrational behaviour of stators is investigated by the modem
modal analysis technique, and new formulae for the calculation of the acoustic power radiated
by a cylindrical stator of finite length, using an analytical method, are presented. A technique
which combines the finite element method and Fourier analysis to account for the effects of
end-shields on the acoustic radiation is developed, and the spherical acoustic radiation model of
motors has been improved by the application of finite elements. Finally, a systematic analytical
approach to the estimation and analysis of the acoustic noise from a radial-field, internal rotor,
brushless DC motor is presented.