Abstract
Due to the unpredictable characteristic of renewable energy systems such as photovoltaic and wind energy systems, an energy storage subsystem is essential as a buffer for enhancing the safety and power quality of the whole system. Hence, the main purpose of this thesis is focused on the battery energy storage system (BESS) and to propose a high performance dc converter, as an interface between the high voltage DC bus and the low voltage battery. Basically, the major contributions of this thesis can be summarized as follows. First, a new bidirectional dc converter structure with high voltage side in series and low voltage side in parallel is proposed for the battery energy storage system. This new topology can achieve uniform voltage sharing for the active switches in high voltage side and uniform current sharing for the active switches in low voltage side automatically. It is seen that due to the reduced voltage and current stress of the active switches in the proposed converters as well as the interleaved control strategy, much better efficiency and power quality can be achieved. Second, based on the state space averaging technique, the correspond DC and AC models are derived for convenient design of the proposed converter. Finally, a prototype with 300V DC bus voltage and 25V battery voltage is implemented to verify the validity of the proposed converter. It is seen that maximum efficiency of the converter is 93.4% and 94.3% can be achieved for step-down and step-up operation modes respectively.