Abstract
M.Sc. (Electrical & Electronic Engineering)
The behaviour of alternating current machines being fed from an electronic
commutator is investigated. The performance of compound power switches for
use in electric vehicle drives are examined. A detailed study on switching
losses and base current characteristics based upon experimental measurements
was carried out. With further reference to power switches the merit,
development and functioning of an electronic commutator is discussed.
Because of the close association between this study and electric vehicle
drives, a comparative study of the performance of different rotor types
within the same machine was executed. Attention is paid to torque and
efficiency characteristics in particular. The influence of voltage and
current harmonics was established by comparative testing of the machine
with sinusoidal and electronic commutator excitation. The study shows that
the highest specific power was attained with the alternating current machine
with a wound rotor (synchronous machine) while there seems to be merit in the
use of permanent magnet rotors for electric drives as well. On the average
the use of electronic commutator excitation resulted in an efficiency decrease
of approximately 15% for the a.c. machine with different rotor types.
Efficiency and torque for an induction machine with solid rotor were
disappointing so that there seems to be little application for solid steel
rotors. A simple model for the synchronous machine with wound rotor was
developed to explain the dependence of torque and efficiency upon speed of
rotation and commutation angle. To conclude, guidelines are given for
future studies on electric vehicle drives and machine types as primary
drive.