The demand for power converters is on the rise due to their ability to achieve high power conversion efficiency, small size, light weight and reduced cost. DC-DC converters are used in many applications where, the output voltage needs to be regulated for wide variations in the input voltage and the load. They are also used in applications where electrical isolation is required. Power generation from renewable energy sources suffers from highly fluctuating output voltages. Electrical isolation of renewable energy sources from the grid is essential. Therefore, DC-DC converters are used as an integral part of the power electronic interface required for grid integration of renewable energy sources such as wave energy power conversion. In this dissertation as a first step, the power converters used in wave energy applications are classified and compared. Analysis, design, simulation and experimental results of fixed frequency controlled HF transformer isolated DC-DC resonant converters are presented. The first converter topology presented in Chapter 3 is a ‘fixed frequency controlled single-phase high frequency (HF) transformer isolated DC-DC LCL-type series resonant converter (SRC) with capacitive output filter using a modified gating scheme’. Working of this converter has been explained. Modeling and steady-state analysis of the converter using approximate complex ac circuit analysis method has been done. Various design curves have been obtained. A step-by-step design procedure has been illustrated with an example of a 200 W converter. PSIM simulation results for different operating conditions are presented. Experimental model of the designed converter has been built and the test results are given. Power loss breakdown analysis of the converter has been made. Zero-voltage switching (ZVS) is achieved for different input voltages, and load. This converter cell can be used in interleaved operation to realize higher power converters. The second topology presented in Chapter 4 is ‘a fixed-frequency controlled, 3-phase HF transformer isolated, integrated boost dual 3-phase bridge DC-DC LCL-type SRC with capacitive output filter’. Detailed modeling of the boost section and one of the two identical 3-phase inverter modules is presented. Analysis of the inverter module using approximate complex ac circuit analysis method is presented. Various design curves have been obtained. A step-by-step design procedure has been illustrated with an example of a 600 W converter. Detailed PSIM simulation results for different operating conditions are presented. Experimental model of the designed converter has been built and the test results are given. Power loss breakdown analysis has been made. Major advantage of this converter has been its ability to regulate the output voltage for wide variations in the input voltage and load, while maintaining ZVS for all the switches. Also, due to the parallel connection of the inverter modules the component stresses are significantly reduced. This encourages the converter to be used in high power applications such as wave energy. A 10 kW DC-DC converter cell of the second topology mentioned above has been designed to illustrate the design and working of a high power converter. Performance of the designed converter has been verified by PSIM simulations. This converter operates with ZVS for all the switches for a wide variation in the input voltage and the loading conditions. Power loss breakdown analysis has been performed. / Graduate

Microbeam radiotherapy (MRT), an experimental high-dose rate concept with spatial fractionation at the micrometre range, has shown a high therapeutic potential as well as good preservation of normal tissue function in pre-clinical studies. We investigated the suitability of MRT as a simultaneously integrated boost (SIB) in conventional whole-brain irradiation (WBRT). A 174 Gy MRT SIB was administered with an array of quasi-parallel, 50 m wide microbeams spaced at a centre-to-centre distance of 400 m either on the first or last day of a 5 4 Gy radiotherapy schedule in healthy adult C57 BL/6J mice and in F98 glioma cell cultures. The animals were observed for signs of intracranial pressure and focal neurologic signs. Colony counts were conducted in F98 glioma cell cultures. No signs of acute adverse effects were observed in any of the irradiated animals within 3 days after the last irradiation fraction. The tumoricidal effect on F98 cell in vitro was higher when the MRT boost was delivered on the first day of the irradiation course, as opposed to the last day. Therefore, the MRT SIB should be integrated into a clinical radiotherapy schedule as early as possible.