Abstract
With global energy shortage and strong environment movements, many countries are encouraging and promoting the development of distributed alternative energy sources. It is well-known that photovoltaic and fuel cells play an important role in the small-scale distributed generation systems. However, the output voltage of such new energies is rather low. For this reason, the main objective of this dissertation is therefore to develop a high efficiency high step-up converter as an interface for back-end applications. In this dissertation, a new multiphase converter by integrating a voltage-doubler and a forward-type circuit is first proposed for achieving high step-up and high efficiency objectives. Some topological extensions which include a particular three-phase, the generalized n-phase, and another Ćuk-type integrated circuit are also derived preserving the same advantages of the low switch voltage stress, lower duty ratio, and high voltage gain. Second, steady-state analyses are then made to show the merits of the proposed converter topologies. For further understanding the dynamic characteristic of the proposed forward-type integrated high step-up converter, steady-state and small-signal models of this converter are derived using state-space averaging technique. Open-loop transfer functions such as control-to-output voltage, audio susceptibility, output impedance and control-to-input current in the small-signal model are also derived to analyze the system performance in terms of DC gain, bandwidth, and stability. Third, for higher power applications, modules of high step-up converters are paralleled to further reduce the input and output ripples. Analysis and control of the interconnected converter are also made in the context. Finally, a 400W rating parallel converter prototype system is constructed for verifying the validity of the proposed converter. Experimental results show that the total input current ripple of the prototype system can be reduced to below 50mA, the differences among shared currents of the prototype system are within 5% of the averaged current over the load variation, and the highest efficiency of 95.87% can be achieved.