Abstract
Battery energy storage systems (BESSs) are expected to play a key role in enabling high integration levels of intermittent resources in power systems. Like wind turbine generators (WTG) and solar photovoltaic (PV) systems, BESSs are required to meet grid code requirements during grid disturbances. However, BESSs fundamentally differ from WTG and PV systems because they are not only required to operate as a source (discharging) but also as a load (charging). This paper investigates the system-level behavior of BESSs under grid fault conditions. It presents first a generic electromagnetic transient (EMT)-type model of a two-stage Li-ion BESS that can be configured to comply with grid codes. Compared to previous studies, the proposed model introduces a key step in the characterization of BESSs considering decoupled sequence control (DSC) and the non-linear impact of current limiters under stringent unbalanced faults. The model is used to demonstrate that BESSs behave differently in charging mode, a factor that needs to be accounted in protective relaying practices. The conducted simulations show that the charging mode is more stringent on both dc-link voltage regulation and grid voltage support, and that this is aggravated by the use of DSC scheme compliant with VDE-AR-N 4120 grid code.
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