Abstract
In recent years, with global energy shortage and strong environmental movements, many countries are encouraging and promoting the development of distributed energy sources such as fuel cells and renewable energies. As important roles in new energy, however, the output voltage of the solar cells and the fuel cells is rather low. Hence, a high step-up dc/dc converter is normally required as an interface to increase voltage for back-end applications. Therefore, emphasis of this thesis is placed on developing a high efficiency and high step-up dc/dc converter for these two new energy systems. Basically, the main contributions of this thesis can be summarized as follows. First, a new high efficiency and high step-up dc/dc converter is proposed. It can effectively reduce the voltage stress of active switches and the output voltage ripple of the converter. Moreover, it is able to maintain rather high efficiency in wide load range. Second, the mathematical model of the proposed converter is derived. According to the model, a close-loop controller is designed to achieve better stability and transient response of the converter. Finally, a 200V/100W laboratory prototype is constructed and corresponding simulations as well as experimental results are provided to verify the feasibility of the proposed converter. It is seen that the resulting efficiency curve can be maintained rather flat and above 93% for a load varied from 40W to 100W. Furthermore, the voltage stress of active switches and the output voltage ripple are 25% and 16.7%, respectively, lower than that of the voltage doubler proposed in 2007.