The demand for renewable energy sources, such as solar and fuel cells, are growing due to less pollution compared to fossil fuels. These systems often require storage devices and a bidirectional dc–dc converter (BDC).The BCDs commonly utilize to manage energy and convert voltage level between the dc bus and the storage devices. It is common that the storage device voltage level, low-voltage side VL, ranges from 12 to 48 V, while the dc bus, high-voltage side VH, is in 380–800 V to connect to an inverter. Hence, the voltage-level difference between VH and VL is rather high. By series connection of storage devices, the low-side voltage level can be increased, but this leads to many problems, such as higher cost and shorter life of batteries. The isolated BDCs can achieve a high step-up/step-down voltage gain via the transformer turns ratio. These converters are suitable for high power levels. However, in low-to-medium-power applications where electric isolation between low and high-voltage sides is not essential, such as photovoltaic, electric vehicles, and power factor correction applications, the nonisolated BDCs are more attractive due to fewer switches, lower weight, and cost. Among nonisolated BDCs, the buck/boost converter is the simplest approach in order to have minimum devices, low cost, and complexity. In the high-voltage conversion ratio applications, the duty cycle reaches near unity in the boost operating state and extremely low in the buck operating state, which causes high current stress, reverse recovery problem, and conduction losses. Therefore, a BDC with a high step-up/step-down voltage conversion ratio should be utilized for these applications. Appling coupled inductors to buck/boost bidirectional converter is the most effective way to achieve high voltage conversion ratio and overcome the mentioned problems. These converters have fewer elements and smaller leakage inductance as compared to the isolated bidirectional converters. In this dissertation, the coupled inductors technique is applied to buck/boost converter to extend the voltage conversion ratio and to overcome the associated problems. Key Words High step up/downs bidirectional dc-dc converter, Coupled inductor, soft switching techniques, zero voltage switching (ZVS), zero current switching (ZCS). Pulsating current.
