Bidirectional DC-DC converters are widely employed in power electronic equipment dealing with storage and management of energy in applications such as: hybrid electric vehicles, photovoltaic systems, fuel cell systems and uninterruptable power supplies. The non-isolated converters are used in applications which galvanic isolation between low and high voltage sides is not required. Todays, major research is focused on these convertersdue to their simple structure and easy control. Conventional non-isolated bidirectional DC-DC converters are not suitable for high step-up/down applications due to their limited voltage gain. In order to achieve a high conversion ratio, many techniques are applied such as: coupled inductors, switched inductor, series capacitor and switched capacitor. Moreover, since bidirectional converters are usually employed as an interface between energy storage elements such as batteries, and, high-voltage DC bus, low charge/discharge current rippleis one of the main factors affecting longevity and health of batteries. Besides, in order to reduce switching losses and increase power density, various soft switching techniques are used; but it should be noted that establishing soft switching condition with minimal elements that operate properly in both power flow directions is one of the challenges in these converters. In this thesis, different non-isolated high step-up/down bidirectional DC-DC converters, along with techniques to increase voltage gain and establishing soft switching condition are reviewed. Afterwards, a unidirectional soft switched DC-DC converter with high step-up gain and low voltage stress across switches is proposed. A bidirectional DC-DC converter is introduced with soft switching, high voltage gain characteristics and low number of elements. In order to improve the batteries charge/discharge current ripple, the first interleaved bidirectional converter is proposed.In order to extend voltage gain, reduce semiconductors voltage stress, establish soft switching condition and further charge/discharge batteries current ripple enhancement, the idea of the first proposed converter is combined with simplified WCCI technique and the second interleaved bidirectional converter is introduced. The validity of the theoretical ideasare justified by simulation and practical implementation results. Finally, conclusions along with recommendations for further research are presented. Key Words Bidirectional converter, Non-isolated, High step-up/down, Soft-switching
