M.Ing. (Electrical and Electronic Engineering) / In order to improve the industrialisation of modern power converters, its physical size must be reduced, material must be utilised more efficiently and its manufacturability improved. Consequently, many converters are operated in the ultrasonic frequency range, where the size of its constituent components are considerably reduced. Even at high frequencies of operation, however, magnetic components are still the largest and heaviest components in converters, and do not utilise materials to their maximum benefit. The aim of this work is to investigate the possibility of improving the industrialisation of power electronic converters by making use of a novel, multiple core magnetic component structure, called the distributed transformer. Existing magnetic component structures are evaluated from a materials point of view and the concept of distributed magnetic components introduced. A generalised transformer model is developed for the distributed transformer and pertinent design considerations discussed. A 1.5 kw battery charger industrialised by Spoornet is based on the CukDC-DC converter and is used as a case study. A conventional monolithic isolation transformer is used in its construction after a complete mathematical analysis of the converter topology, and compared with the equivalent distributed transformer configuration. The distributed transformer is then compared with the conventional monolithic transformer and evaluated in terms of its physical and electrical performance, design and ease of manufacture.

This thesis presents new configurations for three-phase AC-to-DC single-stage, softswitched, high frequency (HF) transformer isolated converters with power factor correction (PFC) and low harmonic distortion. Four different configurations are presented. Topology of all these four configurations is based on integration of a front-end DCM boost with a soft switching HF transformer isolated DC-to-DC PWM converter with fixed frequency. DCM operation of the front-end boost provides natural PFC with low total harmonic distortion (THD) and the DC-to-DC HF transformer isolated soft switching PWM converter with an appropriate gating scheme provides output voltage regulation. A double switch AC-to-DC converter is presented in Chapter 2. Due to unsymmetrical gating scheme, DC blocking capacitors are required to avoid transformer saturation. To reduce this problem, a new gating scheme is proposed in Chapter 3, which can be used in full bridge converters providing ZVS. This gating scheme is first used in a DC-to-DC bridge converter. In the next three chapters, this new gating scheme is applied to three different types of single-stage AC-to-DC boost integrated fixed-frequency bridge converters. These configurations are: (i) boost integrated single inductor linear current DC-to-DC PWM bridge converter, (ii) boost integrated series resonant DC-to-DC bridge converter and (iii) boost integrated parallel resonant DC-to-DC bridge converter. The steady state operation of each converter and modes of operation are explained with equivalent circuits for each interval of HF cycle. The general solutions for all the intervals are derived and design curves are obtained based on steady state relations. The design procedure is illustrated with a design example. Detailed PSPICE simulation results and experimental results obtained from a laboratory prototype model are given for all the converters to verify the theory and analysis. THD of the line current without any complex control circuit remains in a reasonable range of 8% to 13% for the total range of operation. Input line current waveforms for all suggested converters shows a low harmonic distortion similar to a single 3-Φ DCM boost. The difference would be in increase or decrease of DC bus voltage in each case, which can affect THD of the boost converter. Three switches in the full bridge converter operate with zero-voltage switching (ZVS) while the main switch operates with ZVS at full load, minimum line voltage and with ZVT at lower loads conditions. Soft switching of all the switches helps in lower loss. Chapter 6 presents the contributions of this thesis, summarizes the advantages and disadvantages of each configuration and gives some suggestions for future work. / Graduate

This thesis presents the design and construction details of a physical model of a six-pulse HVDC converter suitable for steady-state studies. The converter rack has been built to facilitate simple testing and breadboarding. A digital equidistant firing angle controller has been constructed for the converter-rectifier current control. An electronic phase-locked loop has been used to generate an accurate control frequency. Modifications have been suggested to make the rectifier, fully operational. The control system has been constructed for future inverter control circuits and possible computer control. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

D.Ing. (Electrical & Electronic Engineering) / Please refer to full text to view abstract

No description available.

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

An overview of DC/DC converters is given. The operation of the buck converter and the series resonant converter is explained. The advantages and disadvantages of series, parallel, and series-parallel resonant circuits are examined. In addition, the advantages and disadvantages of the clamped series resonant converter when compared to the buck converter are discussed. Both circuits are simulated on the general circuit simulation program SPICE. Lab measurements taken for the series resonant converter are compared to the simulated results from SPICE.