HIGH GAIN DC-DC CONVERTER TOPOLOGIES FOR POWER SYSTEMS

Abstract

The voltage levels produced from renewable energy, particularly wave energy converters are relatively low and must be stepped up considerably to enable DC grid integration. This necessitates the use of high voltage gain DC-DC boost converters for power systems. These converters are designed for unidirectional power transfer and provide a high voltage gain (ten times or higher), supporting the high wave energy peak and low average power levels required for the integration of distribution networks. In theory, conventional boost converters are the common basic DC-DC step-up converters. However, these converters often operate with excessive duty cycles to obtain high voltage gain, causing severe voltage stress across devices. The main challenge of the high gain transformerless DC-DC converters is the requirement for an extreme (>80%) duty cycle to achieve the desired gain, resulting in poor efficiencies. This thesis presents the development, analysis, and design advanced high gain DC-DC converter topologies integrating magnetic and capacitive techniques and voltage multiplier circuits. The proposed converters could provide enhanced performance compared to currently available state-of-the-art converter topologies, the main advantages of which are the capability to achieve high voltage gain without the need for an extreme duty cycle, as well as low voltage stress on the switching device and self-balanced voltage levels at the output. In addition, the proposed converters require only a single switch, reducing the complexity of the control strategy. Four transformerless high gain DC-DC topologies are presented; Multilevel Boost Converter (MBC), Switched Inductor Multilevel Boost Converter (SIMBC), Voltage Lift Switched Inductor Multilevel Boost Converter (VLSIMBC) and Z-source Multilevel Boost Converter (ZSMBC), which could achieve the desired gains with relatively high efficiencies. The operation principles, steady-state relations, and different input circuit strategies to further improve the voltage gain performance of the proposed converters are described. Furthermore, a theoretical analysis of power losses is provided. In addition, laboratory prototypes are developed to experimentally validate the given theories, simulation results and feasibility of the proposed topologies.