Typical military installations support base electrical demand with diesel generators and uninterruptable power supplies (UPS) to cope with planned and unplanned outages. Microgrids based on networked diesel generators have been demonstrated as an alternate approach to dedicated standby generators, providing increased resilience to single-point failures. However, this approach constrains integration of onsite generation, and limits microgrid operational affordability and reliability. This project performed hardware-in-the-loop (HIL) testing to substantiate performance and reliability benefits of modular lithium-ion (Li-ion) energy storage within a Department of War (DoW) installation micro-grid. Phasor-based control provided coordinated real-time and reactive power control of energy storage units and other distributed resources in a micro-grid to enable new capabilities, enhancing reliability and improving economics.

This project uniquely combined an energy storage system, solid state switching, and microgrid control technologies. The approach involved co-locating modular energy storage with critical loads and coupling them with semiconductor-based switching to supplant traditional UPS units. By integrating the latest energy storage inverter technology with a solid-state static transfer switch, the approach set out to achieve >3x faster switching speeds than mechanical switch-based alternatives. This achievement could enable UPS-grade power quality and switching functionality. Within the concept, each storage module forms its own low-voltage microgrid, which are combined to create a scalable medium voltage microgrid. Multiple modular instances of these energy storage/switch (automatic transfer switch) combinations are controlled with microgrid controllers using phasor measurement unit data to monitor power and energy flows.

Four performance objectives encompassing five groups of tests (T1-T5) based on Institute of Electrical and Electronics Engineers 2030.8 guidance were pursued to complete the HIL testing effort. Grid-tied techno-economic performance objectives (T1 tests) were not tested individually due to time constraints and lack of appropriate input data for stimulation; however, the capability to perform real power control which underlies the functionality was demonstrated extensively as part of other performance objective tests. Grid-functionality performance objectives (T2 tests) were mostly completed successfully; however, three of these tests could not be completed due to test facility limitations. Planned islanding and reconnection performance objectives (T3 and T4 tests) were completed successfully per plan. Lastly, unplanned islanding performance objectives (T5 tests) were completed successfully for all conditions except those in which an open circuit fault occurred while the inverter was in a grid-forming mode of operation. This outcome was limited by the ability of the static transfer switch to sense and react to a condition it was not designed for.

Cost assessment performed under this project was focused on Westover Air Reserve Base, as extensive techno-economic analysis was performed under EW19-5163 for five other installations. The analysis concluded that a 900kW/1.3 hour battery energy storage system configuration would be the most beneficial, reducing the annual net cost of protecting each kW of peak critical load from $166 to $105. This result compliments results from the EW19-5163 which concluded that short duration (1.3-2.7hr) Li-ion storage can be used to reduce cost per kW protected critical load by 6 to 169% with equivalent (or improved) islanding reliability relative to an all-diesel generation-based alternative design.

This project is a follow-on program that builds on techno-economic, reliability, and initial HIL testing performed under ESTCP project EW19-5163 to demonstrate the ability to perform all enabling microgrid functions. In doing so, EW19-5369 HIL tests sought to validate the ability to realize cost-effective grid-tied operations, achieve equivalent UPS functionality enabling elimination of UPS units, and reliably perform islanding transitions and steady-state operation. Demonstrating these outcomes substantiates the assumptions made in techno-economic and reliability analysis performed under EW19-5163 and EW19-5369.

EW19-5163 performed techno-economic and reliability analysis for notional microgrids at five DoW installations. This analysis concluded short duration (1.3-2.7 hr) Li-ion storage could be used to reduce cost per kW protected critical load by 6 - 169% with equivalent (or improved) islanding reliability relative to an all-diesel generation-based alternative design. Economic benefits were enabled primarily by market participation and UPS elimination. Reliability benefits were achieved by reducing required diesel generation capacity and run time, while ensuring high energy storage reliability. By operating the microgrid using multiple modular energy storage units in parallel, the approach achieved a scalable design that accommodates high renewable penetration and ramp rates and provides resilience to potential energy storage failures. (Project Completion - 2023)