Small-signal modeling of grid-connected energy storage system considering impedance characteristics of battery

Abstract

Electrochemical energy storage systems (ESSs) are widely investigated for grid stability enhancement. However, the self-stability of ESSs remains unclear and faces critical converter-driven instability risks under weak grid conditions. Prevailing small-signal models inaccurately simplify the DC-link of ESSs as ideal voltage/current sources, neglecting the variations of battery equivalent voltage and impedance induced by state-of-energy (SOE), cycling, etc. This paper proposes an enhanced dq-impedance model incorporating battery Thevenin equivalent circuit dynamics to resolve this gap. The model quantifies DC-AC coupling through small-signal linearization of battery-electronic interactions, validated via hardware experiments on an 800 V/150 kW lithium-ion battery cluster and simulations. Simulation results confirm the accuracy of the proposed model in shaping ESS impedance characteristics, with significant error reduction compared to conventional approaches neglecting battery dynamics. When deployed for instability risk assessment, the proposed model achieves 69.93 % ∼ 82.71 % higher accuracy in identifying oscillation risks by substantially narrowing misjudgment prediction ranges in grid strength regions, and therefore the risks of stable operation of energy storage can be more accurately grasped under weak grids via the proposed ESS impedance modeling approach.