Impact of Energy Storage System Response Speed on Enhanced Frequency Response Services

This paper investigates the impact of energy storage systems (ESSs) response speed on its ability to perform fast frequency support services such as the UK's enhanced frequency response (EFR) services. The response time of a commercial Siemens SieStorage 240kVA/180kWh grid-linked battery energy storage system (BESS) is characterized and the results are used to model an emulated BESS in a representative micro-grid system using a real-time digital simulator (RTDS). The SieStorage system is also linked to the RTDS micro-grid through an Ethernet connection, forming a hardware-in-the-loop (HIL) system. Simulations and then HIL tests of the emulated BESS providing EFR to the micro-grid are conducted to investigate the impact of the communication latency, the physical power delivery time, and also the installed capacity of the BESS. The study shows that the communication latency has a much more significant impact than the physical power delivery time; for better EFR support, reducing the communication latency of a BESS could be even more effective than increasing the power capacity, which is costly.