A decentralized non-linear dynamic droop control of a hybrid energy storage system bluefor primary frequency control in integrated AC-MTDC systems

Power-sharing between energy storage systems (ESSs) is one of the significant challenges in a hybrid energy storage system (HESS). For primary frequency control through multi-terminal DC (MTDC) systems interfacing renewable resources, a decentralized control method based on non-linear dynamic droop control (NLDDC) is proposed in this study for a hybrid energy storage system. Battery energy storage systems (BESS) and super capacitor (SC) make up the hybrid energy storage device in this article. The proposed strategy, which employs dynamic droop gain to distribute power between the SC and the battery, outperforms the previous droop regulation. The SC will be in charge of compensating the high-frequency demand, whereas the BESS will be in charge of compensating the low-frequency power demand, thanks to a decentralized hierarchical energy management process. As a result, the proposed approach improves system transient stability following grid faults, while enhancing primary frequency response under net load variability and generation outage. Finally, simulation results utilizing the Cigre MTDC benchmark and the IEEE 39-bus test system are provided to validate the proposed structure. The NLDDC parameters are fine-tuned using krill herd (KH), an intelligence algorithm with biological inspiration.