Abstract
M.Ing. (Electrical and Electronic Engineering)
The main purpose of the study is to propose an unique unity power factor AC-DC
converter topology, with isolated output. The proposed converter is obtained by merging
the unity power factor boost converter and the full bridge resonant transition converter.
The converter is unique as resonant switching techniques are used to obtain a zero
voltage switching boost stage, resulting in an all soft switching converter. The result is
lower levels of conducted EMI, as well as lower switching losses. Conventional
topologies utilize more than one converter stage to obtain the required results, whereas _
the proposed converter results in a single step solution.
As the purpose of the proposed converter is power factor regulation resulting in lower
levels of conducted EMI, the study is commenced with a review of the definitions and
equations for both power factor and EM!. Thereafter sources and propagation of
conducted EMI are discussed.
To gain a better understanding of the operation of the proposed converter, the operation
of the unity power factor boost converter, as well as the full bridge resonant transition
converter are discussed in depth.
A switching cycle of the proposed converter is divided into different intervals, and
analytical equations for the relevant currents and voltages for each interval are derived
seperately.
Possible control schemes are introduced and where applicable, conditions for zero
voltage switching are given. It is concluded that a constant frequency PWM controller
is the most ideal control scheme to ensure proper operation of the converter. A simple
design procedure is presented by which the size of the most important circuit parameters
can be designed in terms of the desired switching frequency and permissable duty cycle
variation.
Finally, experimental results obtained from the practical converter, are given. Deviations
from the ideal are interpreted and methods of improving the performance are suggested.