| Summary: | The University of 'Canterbury Mark II' electric vehicle has been out of service for
several years due to the lack of a suitable inverter to provide a variable frequency AC supply
to its traction motors.
This thesis describes the design and construction of such an inverter, using high
current bipolar junction transistors as the switching elements, so that the car might be
returned to service in the near future. The inverter is based on an existing commercial AC
motor speed controller. Modifications to this AC motor speed controller were made to suit
the low voltage, high current rating of the traction motors. These modifications are
described and it is shown that these modifications permitted the inverter to deliver the
required increase in current.
The inverter differs from most conventional AC motor speed controllers in that it acts
to shape load current rather than potential, and uses an asynchronous switching technique to
do this. The Thesis describes this technique and the control hardware constructed to
implement it.
Test results, showing the performance of the combined inverter/motor system are then
presented graphically and discussed with reference to standard AC motor theory, giving
consideration to the harmonic content of the AC waveforms. Consideration is also given to
a suitable closed-loop control system which could be expected to ensure that the inverter's
output frequency is controlled in such a manner as to give a safe and predictable response
to the brake and accelerator controls.
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