Differential Power Processing Based Control Framework for Multiple Battery Energy Storage Systems in DC Microgrids

Multiple battery energy storage systems (BESSs) have been widely used in the DC microgrids to balance generation and demand. To achieve this, the BESS converters need to deliver the full required input/output power imposed on BESSs under the conventional BESS-DC bus configuration, which often demands high power ratings for the converters, hence leads to high installation cost as well as high power losses. To reduce the power ratings for BESS converters while delivering the same power from BESSs, this paper proposes a new differential power processing (DPP) based control framework where the DPP techniques and BESSs are firstly combined without losing the following control objectives, namely, the accurate current-sharing and state of charge (SoC) balance of BESSs as well as DC bus voltage regulation. This is achieved first by introducing inverted bidirectional buck converters to function as a front-end converter and DPP converters. Then, a virtual state variable combining BESS output current and its SoC is proposed, based on which a consensus control strategy is proposed. The stability of the proposed DPP-based control framework is also analyzed. Finally, the real-time hardware-in-loop (HIL) tests confirm the effectiveness of the proposed control framework, showing that the proposed DPP-based control framework reduces the power ratings of the converters to less than 20 $\%$ of BESS converters used in conventional BESS-DC bus configuration even in the worst operating scenario, while delivering the same required power from BESSs, paving a way for an innovative BESS DC microgrid design with much down-sized converters for BESSs.