Abstract
In recent years, due to the environment impact and shortage of fossil fuels, many countries around the world begin to promote using renewable energy rather actively. Among various renewable energy systems, photovoltaic (PV) systems which do not having any moving mechanic parts are perhaps most attractive. However, the output voltage of a PV module is rather low. For practical application, a high step-up dc converter is normally required for boosting to a higher voltage level for the following cascaded inverter. Hence, a novel high step-up isolated DC/DC converter as an interface for these PV energy systems is proposed in this thesis. The major contributions of this thesis may be summarized as follows. A novel isolated high step-up DC/DC converter is first proposed for achieving much higher voltage gain as an interface. The special feature of this new converter lies in its zero voltage switching (ZVS) characteristic for reducing greatly the electric stress of the switches and the switching loss as well as the interleaved control to reduce the input current ripple. Also, it can be modularized and the duty ratio of the active switch can be operated in full range. Furthermore, a 200W rating prototype with 20V to 35V input and 400V output is constructed for verifying the feasibility of the prototype. The experimental results show that the resulting efficiency can be maintained above 93.8% as the load is varied from 40W to 200W, and the highest efficiency of 95.7% is achieved at 80W.