Development of Transformerless Power Electronic Converter Topologies for High Voltage Gain Applications

Abstract

Due to several environmental challenges inherent to fossil fuels and growing interest newlinefor more environmental-friendly energy sources, the uses of renewable energy sources newline(RES) have attracted global attention. The solar photovoltaic (PV) and fuel cell (FC) newlinehave become attractive energy sources with their advantageous features such as declining newlinemanufacturing cost and improving efficiency. In spite of the many advantages of newlineRES, their applications have some challenges. For instance, the typical output voltages newlineof such sources are relatively lower, which require high-voltage-gain converters to meet newlinethe voltage level required for the load systems and the dc-link voltage in grid-tied applications. newlineIdeally, a conventional boost converter can achieve infinite voltage gain as newlinethe duty ratio approaches unity. However, at higher duty ratio, the voltage gain and efficiency newlineof the converter degrade sharply due to the parasitic resistance of the inductor and newlinethe diode reverse-recovery problem. This thesis is mainly focused on the development newlineof high-voltage-gain transformerless converters that could obtain an improved performance newlinecompared with current state-of-the-art topologies. Three high-gain topologies newlineare proposed for RES applications. Firstly, a switched-capacitor (SC) based high-gain newlineDC-DC converter is proposed. Unlike conventional SC converters, the proposed converter newlinecan provide multiple discrete voltage conversion ratios corresponding to the user newlineinputs. The proposed SC circuit offers lower output impedance, which improves efficiency newlineand voltage regulation. Furthermore, the inductor-less design offers several advantages newlinesuch as light-weight, high power density, and an improved dynamic response. newlineNext, a single-switch hybrid DC-DC converter with diode-capacitor voltage multiplier newlinecircuit (VMC) is proposed. This converter is able to provide a variable and fractional newlinevoltage gain with a high boost ratio, which is a key requirement for MPPT in PV application.