Enhanced grid-following BESS control strategy for unbalanced voltage sag conditions

Battery energy storage systems (BESS) play a pivotal role in modern power systems, with most implementations found in distribution networks that operate using a grid-following (GFL) approach. However, these networks often experience voltage unbalances that can negatively impact BESS operation. Under such conditions, conventional dq control may lead to high grid current unbalance, high harmonic distortion, and DC voltage fluctuations. To overcome these challenges, this paper proposes a control scheme for a grid-following BESS using a dual active bridge (DAB) and a three-phase voltage source converter (VSC) to ensure stable operation under grid unbalances. The DAB manages battery charging, while the VSC regulates the DC voltage. By generating independent modulating signals, the BESS maintains balanced, distortion-free grid currents. Real-time simulations and power hardware-in-the-loop (P-HIL) experiments validate the proposed scheme’s performance under unbalanced conditions. The results demonstrate effective operation under various unbalanced conditions in both charging and discharging modes, ensuring power flow continuity and extending the storage component’s operational life.