Design and performance comparisons of power converters for battery energy storage systems

The use of grid-connected battery energy storage systems (BESSs) has increased around the world. In the scenario of high penetration level of renewable energy sources in distributed generation, BESS plays an important role to combine a sustainable power supply with a reliable dispatched energy source. Different power converter topologies are employed to connect the batteries to the grid, generally using single-stage converters. However, the battery voltage changes according to its state of charge, which can introduce great variations in the dc-link voltage. Therefore, the dc/ac stage converter must have its power switches designed to support this voltage variation. A controllable dc-link voltage is achieved by inserting a dc/dc converter stage to connect the batteries to the dc/ac stage. Among the dc/dc converters, the interleaved bidirectional converter has been widely used due to the low input current ripple. However, the trade-off of the insertion of the dc/dc stage is barely explored in the literature. Therefore, this work presents a methodology of analysis, considering the battery voltage variation and its influence on BESS power conversion system design and efficiency. Furthermore, it is proposed a power conversion system design oriented toward the voltage class of power switches and efficiency. The analysis in this study are conducted through the use of a case study approach, incorporating both simulated and experimental results.