Power allocation strategy for hybrid energy storage systems in DC microgrids with differential power processing technique

Renewable energy resources (RESs) are gaining popularity as a means to reduce carbon emissions and meet the growing global power demand. Hybrid energy storage systems (HESSs), which integrate both battery energy storage systems (BESSs) and supercapacitors (SCs), are essential for maintaining a balance between RESs power generation and load consumption. BESSs typically address low-frequency power fluctuations, while SCs compensate for high-frequency variations. To effectively manage this, the converters of both BESSs and SCs must be capable of delivering the required full power, necessitating high power-ratings, as well as leading to high installation cost and power loss. To address this issue, this paper proposes a power allocation strategy for HESSs based on differential power processing (DPP) technique without compromising power allocation performance while significantly reducing the power-ratings of converters. Firstly, the inverted bidirectional buck converters are introduced to function as a front-end converter and subsequent DPP converters. Secondly, a modified droop control is implemented based on a triple-loop control algorithm to ensure the fast tracking of the reference current of battery/SC. Thirdly, the stability of the proposed DPP-based framework is analyzed. Finally, the performance of the proposed control framework is validated through hardware-in-loop (HIL) testing. The stability shows that the parameters of equivalent electric circuit models of both the battery and SC have no impact the system dynamics, thereby simplifying the controller design. The test results show that the proposed DPP-based framework achieves the power-sharing among HESSs and DC bus voltage regulation with power-ratings of the converters reducing to less than 15%, thereby reducing the installation costs and power loss of converters.