Input-series and output-series connected modular single-switch flyback converter operating in the discontinuous conduction mode

This study proposes a modular isolated dc-dc converter, based on the input-series and output-series connection of flyback converters operating in discontinuous conduction mode, as an alternative to provide higher voltage capability for medium-voltage applications (1-10 kV), from low-voltage semiconductors and passive components. The proposed architecture allows the modular system to operate with a simplified control scheme thanks to an intrinsic voltage-balancing mechanism. The voltage-balancing mechanism is investigated by theoretical analysis, both for steady-state and dynamic operations. A small-signal ac modelling of the architecture is developed to design the total output-voltage controller. To experimentally verify the proposed technique, a laboratory prototype system with three single-switch flyback converters, with 3 kW output power, 600 V dc input and output voltages, and 40 kHz of switching frequency was built.