Iron losses in brushless permanent magnet DC machines.

A closed-loop computer-controlled single-sheet test system has been developed to
characterise lamination materials and to measure, the iron loss density under any
specified flux density waveform. The system has been 'used to validate predictions
from a recently developed theoretical model, for the calculation of the excess loss
component associated with domaiQ wall movement, under flux density waveforms
typical of those encountered in the stator core of brushless permanent magnet dc
motors. In addition, an improved expression for the calculation of the iron loss density
component, from measured 71 and 7!vectors, due to rotatio~ in non-purely rotating
flux conditions, has been derived.
A simple analytical model from which the airgap flux density and spread of magnet
working points can be determined and which accounts for the effects of curvature for
radial-field permanent magnet machines has been developed and validated. The model
has been coupled to an analytical technique for the prediction of the open-circuit flux
density waveforms in different regions of the stator core, and has subsequently been
employed for the prediction of the open-circuit iron loss.
In order to predict the iron loss under any specified load condition, a technique which
couples a brushless dc drive system simulation to a series of magnetostatic finite
element analyses corresponding to discrete instants in a commutation cycle has been
developed. It enables the prediction of the local flux density waveforms throughout
the stator core under any operating condition, and has been employed to predict the
local iron loss density distribution 'and the total iron loss and their variation with both
the load and the commutation strategy, Finally, the theoretical findings have been
validated against measurements on a representative low power brushless drive system.