Novel Integrated Three-Port Bidirectional DC/DC Converter for Energy Storage System

The study proposes a novel integrated three-port bidirectional dc/dc converter for energy storage systems. The converter includes two batteries, namely 24- and 48-V batteries, used as input source and for backup energy, respectively. Each battery can supply to dc load in the normal case. When the grid power fails, 24-V battery input is stepped up to the dc bus through a high step-up converter. The 48-V battery serves as a buffer power supply when the load increases instantaneously. At night, when the 48-V battery is under low power consumption, the dc bus can charge the battery. In addition, the converter can monitor both battery voltages simultaneously; when one battery is used excessively, the other battery can charge it, thus keeping the system power stable. The integrated three-port bidirectional dc/dc converter is a combination of a boost-flyback, forward converter, and voltage doubler and has the following advantages: 1) it operates in input continuous current and low voltage stress; 2) it provides input current recovery; 3) it improves high reverse voltage caused by the transformer; 4) it operates in zero current switching (ZCS); and 5) its doubler circuit can flexibly adjust the dc bus voltage. A 500-W three-port bidirectional dc/dc device was implemented to verify the feasibility and practicability of the proposed converter. The highest efficiency achieved for operation in 24-V battery high step-up mode was 95.3%; it was 94.9% and 95.2% in 48-V battery step-up and step-down mode, respectively.