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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:10732 |
| Date | 15 April 2014 |
| Creators | Theron, Philippus Coenraad |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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