Abstract
For clean distributed energy resources such as photovoltaic (PV) and fuel cells, their output voltages are rather low. Thus, a step-up DC/DC converter is normally required for boosting to a higher voltage level for the following cascaded inverter. Hence, for further improving the overall conversion efficiency, a novel single-stage high step-up inverter as an interface for these new energy systems is proposed in this thesis.Basically, the contributions of this thesis can be summarized as follows. First, a novel single-stage inverter topology is proposed for PV or fuel cell systems. The special features include automatic parallel charging and series discharging of two capacitors to provide a rather high step-up ratio, and decrease the electrical stress of the active switches as well with galvanic isolation between input and output. Second, both dc and ac mathematical models are derived for simplifying the design of close loop control. Finally, a 200W, 20V DC input and 110Vrms AC output prototype is implemented. It is seen that the voltage drop across the active switches on low voltage side is 41.7% lower than that of the conventional ?uk type single-stage inverter, which enables one to use lower RDS(on) MOSFETs. It turns out that the overall efficiency is higher than 90% from 50W to 200W loading. In fact, the highest efficiency, 93%, can be achieved when the load is 150W. Furthermore, both simulation and experimental results indeed verify the effectiveness of the proposed converter.