Abstract
D.Ing. (Electrical and Electronic Engineering)
increased dramatically during the past few years. This progress can mainly be
attributed to recent developments in power electronic switching devices. Switching
times are reduced, resulting in lower switching power loss, on-state voltage is reduced
leading to lower conduction power losses, and higher voltage and current capabilities
are possible. These advances are mainly responsible for a reduction in physical size of
the converters, especially of the reactive components; an increase in dynamic
response; and also, to a lesser extent, have an influence on the converter behaviour.
Different applications of DC-DC converters require different characteristic
behaviour, and the trend to obtain these different characteristics is usually
accomplished by adding additional components to existing DC-DC converters. The
disadvantage of such an approach is that it adds to the complexity of the converter
topology and controller, and consequently increases the manufacturing cost, and
reduces reliability.
In this thesis, the objective is to identify a galvanic isolated DC-DC converter
having inherent short circuit protection, sinusoidal transformer current, a low number
of components and a simple controller. Hard switched DC-DC converters are
approached from a fundamental point of view, weighing simplicity against
characteristics, and a systematical classification is addressed. In order to address the
issue of sinusoidal transformer current and inherent short circuit protection, a
systematic classification of simple resonant converters is also addressed.
The partial series resonant converter, which is a new converter topology, is
identified and analysed. It does not follow the trend of increased converter and
controller complexity with different characteristics, and meets all the objectives
mentioned above. In addition to these objectives, it has the following characteristics:
Output current can be controlled without any current measurement, while obtaining
inherent short circuit protection. Switching losses are ultra low due to zero voltage
switching at reduced turn-off current, enabling the use of insulated gate bipolar
transistors at switching frequencies in excess of 50 kHz, which, among others, benefits
dynamic response. The output load line resembles a natural constant output power
load line at constant switchingfrequency.
The combination of these characteristics is shown to provide major advances in
low inductance load applications, such as arc welding and battery charging.
Furthermore, all the magnetic components are integrated into one physical structure,
which benefits, among others, manufacturability and cooling. The analysis and
feasibility of the partial series resonant converter is verified by the construction of
multi kilowatt prototypes for both battery charging and arc welding.