Derivation, analysis and development of coupled-inductor-based non-isolated DC converters with ultra-high voltage-conversion ratio

This study proposes a method of integrating the voltage-lift technique with multiple-winding coupled inductor to form non-isolated DC-DC converters that are able to provide high-voltage gain. Voltage-lift structures containing one diode and one capacitor are inserted in the primary and secondary sides of the coupled inductor, similar to available switched-coupled-inductor boost converters. This idea is further developed in this study, and generalised converters are derived by increasing the number of coupled-inductor windings, with voltage-lift structures applied to all windings. Improved converters with reduced capacitors count are also derived based on the generalised converters. They all feature high-voltage gain and low-voltage stress, which facilitates the selection of low-voltage-rating switch with low on-resistance to increase conversion efficiency. Low-voltage-rating capacitors can also be used to minimise converter cost. Operational principles of the selected converter during four switching stages, and steady-state analysis results of its improved converter are presented. A voltage-clamp passive snubber for dealing with leakage effect is introduced. Prototype converters as well as its improved version are built in laboratory to validate the proposed method. The improved converter achieves maximum efficiency of 94.1% at 200 W nominal output.