posted on 2010-11-23, 10:00authored byKhalid Salih Mohammad Al-Hadithi
Brushless dc motor drives have become increasingly
popular, following recent developments in rare-earth
permanent-magnet materials and the semiconductor devices used
to control the stator input power and to sense the rotor
position. They are now frequently used in applications such
as flight control systems and robot actuators, and for
drives which require high reliability, long life, little
maintenance and a high torque-to-weight ratio. In many motor
drives the presence of torque and speed ripples, especially
at low speed, is extremely undesirable. The mathematical
model developed in this thesis was used to investigate their
occurrence in a typical brushless dc drive system, with the
objective of establishing factors which effect their
magnitude and ways by which they may be reduced. The model
is based on the numerical solution of the differential
equations for the system, with those for the motor being
formulated in the phase reference frame. Tensor methods are
used to account for both the varying topology and the
discontinuous operation of the motor arising from changes in
the conduction pattern of the inverter supply switches.
The thesis describes the design, construction and testing
of an experimental voltage source PWM inverter, using MOSFET
switching devices, to drive a 1.3 kW 3-phase brushless dc
motor. A practical circuit is described which implements
current profiling to minimize torque ripple, and the optimum
phase current waveforms are established. The effect of
changes in the firing angle of the inverter switches on the torque ripple are also examined.
Throughout the thesis, theoretical predictions are
verified by comparison with experimental results.
History
School
Mechanical, Electrical and Manufacturing Engineering