Today, with the development of aerospace and aviation industry, the electromechanical and hydraulic systems have been replaced by electrical systems. Also, Increment of electrical systems increases the required power. In modern aircrafts (B787), the power of electrical systems is provided via the high voltage (270VDC) bus. The batteries of power system are charged by this high voltage bus to provide the power for emergency conditions. So a bidirectional DC-DC converter is required to charge the batteries in step down mode under normal conditions and increase the voltage of the battery to the bus voltage in step up mode and supply the power of emergency loads. Bidirectional DAB DC-DC converters, because of the isolation and high power density, are the basic structure of this application. The leakage inductance of this converter leads to high voltage stress of the switches and switching losses and reduces the efficiency. In the recent researches, techniques such as active snubber, active clamp and resonant circuit CLLC are applied to provide the soft switching conditions of the DAB converter. Auxiliary elements for soft switching and variable switching frequency are the main drawbacks of these techniques. In this thesis, a bidirectional isolated DAB DC-DC converter for aerospace applications has been proposed. The leakage inductance of the transformer and a small series capacitor are the resonant network. In the proposed converter, the soft switching conditions ZVZCS using phase shift control without the use of auxiliary switch or circuit is achieved. So that, even in the light load conditions, switching in ZVZCS is provided. . The switching frequency and the resonant frequency of the proposed converter are equal which simplifies the control circuit and optimize the size of the filters. In the second proposed converter, the high voltage side is composed of half-bridge structure and voltage doubler circuit and the soft switching conditions for all switches are provided. This method reduces the transformer ratio to half of the first converter and so, decreases the transformer leakageinductance. Usually, the charge current of the battery is reduced to extend battery life. So the converter power in step down mode can be reduced and charging time is increased. Thus, by reducing the power in the charging mode, the use of half bridge instead of full bridge is suitable and the number of switches is reduced. In this thesis, design and implementation of a 300W (30V/300V) prototype of the proposed converter with 75 kHz switching frequency is presented. The experimental results are in agreement with theoretical and simulation analysis and soft switching condition is provided. Keywords : 1-Isolated Bidirectional Converter 2- DAB Conveter 3-Soft Switching 4- Zero Voltage Zero Current Switching(ZVZCS)