Abstract
High voltage DC converters have now been widely used in various high-voltage applications. In addition, in recent years due to energy crisis and environmental impact a lot of efforts have been made to promote various clean energy such as photovoltaic(PV), wind energy, and fuel cells(FC). For the PV and FC low output voltage energy sources, they reguire a high step-up ratio converter to raise their voltage for proper applications. Hence, the objective of the thesis is forcused on developing a novel high step-up DC/DC converter. The main contributions of this thesis may be summarized as follows. First, a new qusai-resonant high step-up DC/DC converter topology is proposed. The new converter has characteristics like high step-up ratio, fewer components, with leakage inductor energy recycled, current resonance and soft switching. In addition, compared the new converter with a traditional qusi-resonant converter it is seen that the new converter uses the isolation transformer leakage inductance of the primary side and the secondary side equivalent series capacitor as the resonant tank such that all the active switches can achieve zero voltage switching and all diodes can achieve zero current switching. The second contribution includes the derivation of DC and AC models of the proposed converter and analysis of fundamental characteristics of the new converter. The third contribution is the construction of a 150W prototype with an input voltage of 30V and the output voltage of 400V for verifying the feasibility of the new converter. It is found that this converter can indeed achieve soft switching characteristics and the power conversion efficiency from 30W to 150W is more than 91%. Also, the corresponding measured maximum efficiency is 95% when the load is 60W. Both simulation and experimental results agree with each other very closely.