Bidirectional DC-DC converters have recently received a lot of critical attention due to the increasing needs for systems capable of transferring power between two dc buses or between dc bus and battery storage. Apart from the traditional uninterruptible power supply (UPS) applications, bidirectional DC-DC converters are also used in many new applications such as renewable energy system, fuel cell energy system, and even hybrid electric vehicle. In this thesis, a bidirectional buck-boost converter with both duty ratio and phase shift control algorithm is proposed.