A Bidirectional Modular DC-AC Converter with High Frequency Isolation for Marine Application

A new configuration of isolated DC-AC converter unit for marine application is proposed. This bidirectional DC-AC tie has been made with DAB cascaded with inverter and the configuration is modular in structure. A control strategy has been proposed to eliminate double frequency oscillation from the intermediate DC bus caused due to the inverter and experimental results are shown to verify it. As the oscillation is not present in the DC bus, we can use high frequency film capacitor of much smaller value than electrolytic ones. That will reduce overall converter size, weight and increases durability of the converter in many folds. Input DC bus voltage variation within a certain range has been considered and quasi square wave operation of DAB has been proposed. This bidirectional DC-AC converter has high frequency (HF) galvanic isolation. The HF transformer has been designed and tested to achieve high power density as well as high efficiency at 20 kHz frequency. Fundamental reactive power flow analysis of DAB has been done to get minimum transformer RMS current at different input DC bus voltage to minimize the transformer copper loss.