Modular, Scalable Li-ion Energy Storage Microgrid with Phasor-based Control
David Altman | Raytheon Integrated Defense Systems
This project will perform Hardware-in-the-Loop (HIL) testing of a modular, scalable micro-grid technology using low cost Li-ion energy storage and advanced phasor-based control. The HIL testing substantiates key assumptions made in the Phase I techno-economic and reliability analysis, which predicted significant cost, performance, and reliability advantages relative to all diesel generation-based alternatives. The design achieves these benefits through high speed control of storage to optimize grid tied economics and increase islanding reliability, while enabling elimination of diesel generators and Uninterruptible Power Supplies (UPS). The HIL testing supports optimal economic operation by demonstrating use case value stacking, using energy storage to affect precision control of power and energy flows within in the micro-grid. The project team colocates modular energy storage with critical loads, and couple them with semiconductor-based switching to supplant traditional UPS units. Each storage module forms its own low voltage micro-grid, which are combined to create a scalable medium voltage micro-grid. The project team HIL test planned and un-planned transitions to islanding, demonstrating coordinated operation of low voltage micro-grids to form the medium voltage micro-grid. Our steady-state islanding HIL tests use phasor-based control to allow multiple undersized (relative to peak load) energy storage units to share load and provide N+1 redundancy, similar to a set of networked generators. The approach thereby realizes the benefits of inverter grid forming (e.g., seamless un-planned transition, increased renewable utilization), with increased reliability and resiliency to potential failures. The Phase II HIL testing validates key functionality assumptions in the Phase I techno-economic and reliability analysis, and reduces risk associated with potential future Phase III field demonstration.
This project will uniquely combine energy storage system, solid state switching, and micro-grid control technologies to achieve the aforementioned objectives. The energy storage system approach couples low cost Li-ion batteries with modular inverter technology incorporating grid forming, dynamic transfer, and black start capabilities. By integrating the latest energy storage inverter technology with a solid state static transfer switch the project team will achieve >3x faster switching speeds than mechanical switch-based alternatives. This enables UPS-grade power quality and switching functionality. The project team will control multiple instances of these energy storage / switch combinations with other Distributed Energy Resources (DERs) using phasor-based micro-grid controls. Our micro-grid controls use Phasor Measurement Unit data, available in modern multi-function relays, to monitor power and energy flows and affect control of DERs as rapidly as sixty times per second. By uniquely combining multiple types of high speed controls, the project team will extract maximum performance and reliability from modern state-of-the-art Li-ion energy storage at minimum cost.
The Phase I program performed techno-economic and reliability analysis for notional micro-grids at five Department of Defense installations. This analysis concluded short duration (1.3-2.7 hour) Li-ion storage can be used to reduce cost per kilowatt protected critical load by 6 to 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 project team will achieve a scalable design that accommodates high renewable penetration and ramp rates, and provides resiliency to potential energy storage failures. The Phase II program builds off initial Phase I HIL testing results to demonstrate the ability to perform all enabling micro-grid functions. Phase II HIL tests validate the ability to realize technoeconomic analysis determined grid-tied operations, achieve equivalent UPS functionality enabling elimination of UPS units, and reliably perform islanding transitions and steady-state operation.