Abstract
M.Ing. (Electrical and Electronic Engineering)
Recent world events such as the fall of Communism. attempts at the unification of
Europe and the reaching of the most extensive international trade agreement yet
(GATT ::: General Agreement on Trade and Tariffs). have all contributed to the
expansion of world markets as well as a marked intensification in the competition in
those markets. Rivalry in the market for power electronic equipment is as relentless as
in any other.
Strict regulations with regard to Electromagnetic Interference (EMf) and
Electromagnetic Compatibility (EMC) apply in Europe and compliance with these
standards is legally enforced. In South Africa, compliance with such standards is
merely recommended, hence local manufacturers have not yet considered these
phenomena seriously enough to pose a threat to their European opposition.
The two main causes of EMI are switching action, which is such an integral part of
power electronics, and the excitation of parasitic circuit elements.
This thesis describes the investigation carried out to determine the effect of certain
layout and construction parameters on the generation of EMf. Parasitic loop
inductances, self-capacitances of coils and the ground connection of heat sinks were
examined in the process.
A test convener containing a full-bridge converter perfonning DC·DC conversion, was
built. These converters are important building blocks for equipment such as
uninterruptible power supplies. One configuration of this converter was designated as
the reference configuration. For every modification of a layout or construction
parameter its effect on the interference spectrum was determined through a
comparison with the measured interference spectrum of the reference configuration.
The use of snubbers and the minimisation of the self-capacitances of inductors in an
output filter effected a marked decrease in the measured interference spectrum
(approximately 10 dB or a third less).
Certain loop inductances have to be minimised in the design stages through proper
layout of conveners, and heat sinks should preferably be grounded through high
resistances.
Paying due attention to these aspects in the design of power electronic converters can
aid in decreasing the size and cost of bulky, expensive EMf filters required to meet the
standards. It could give local manufacturers a considerable advantage over their
overseas competitors.