Coordinated Dispatch Performance of AC Grid-Connected Energy Storage Systems

Commanding multiple energy storage systems (ESSs) to provide grid balancing services is a popular approach to manage the finite state-of-charge (SoC) of each asset. The communication between the individual assets can be a challenge due to their distribution throughout the land-based power network. Two battery-based ESS, a 240 kW 180 kWh lithium ion polymer (nickel manganese cobalt oxide (NMC)) based system located behind-the-meter on a 400 V power network, and a 2 MW 1 MWh lithium-titanate system, which is located at an 11 kV residential substation, are located 100 km apart. Their performance when delivering grid support services using simple time or frequency synchronised coordinated dispatch methods is evaluated in this research. Experimental results from the real and reactive power step profiles show both energy storage systems (ESSs) are correctly time dispatched, and operate according to the power profile. In the real power test, the 2 MW ESS had a larger SoC change at the end of the discharge period when compared to the 240 kW system, due to its higher power to energy ratio. The reactive power test demonstrated that both systems were able to influence their local voltage. The dynamic demand response profile shows the successful use of frequency to determine the dispatch, and both ESSs delivered or absorbed the correct real power for the frequency deviation, while achieving a 100% service performance measure.