Distributed Storage Inverter and Legacy Generator Integration Plus Renewables Solution for Microgrids
Current microgrid designs integrating distributed generation and renewable energy sources require large-scale energy storage, typically in the form of batteries, to enable a high power quality transition to islanding. These energy storage systems, however, are prohibitively expensive and likely to slow the use of microgrids at U.S. installations. This project seeks to replace these oversized and expensive systems with a power storage approach at lower cost and comparable performance.
The objectives are to demonstrate (1) the ability to operate a microgrid with less expensive power storage and (2) the ability to use renewable energy with small-scale power storage to maintain power quality in islanded mode with minimal use of the backup diesel generators during non-optimal (e.g., cloud covered) periods.
Eaton will demonstrate an integrated system employing power delivery optimized energy storage, transiently rated inverters, and a renewable energy photovoltaic (PV) inverter with microgrid integration controls at Fort Sill, Oklahoma. Feature descriptions follow:
- Power Optimized Energy Storage – The demonstrated technology will include power optimized energy storage devices having high rate charge and discharge capability. Their lower limited energy capacity but high cycle life results in a significantly lower lifetime storage cost. These devices can integrate any type of power storage (e.g., Li-ion, ultracapacitors). The demonstration will involve power optimized storage using Li-ion batteries because they are the most cost effective today.
- Transient Rated Inverter – System stability during the islanding process (i.e., opening the upstream static switch) will be achievable through the transient rated inverter. This inverter supports the load and transfers it to the generator(s) when the static switch is open. This smooth transfer eliminates frequency and voltage swings to enable other generators to connect to the microgrid. The inverter also stabilizes the microgrid during load transients and PV transitions.
PV Inverter with Microgrid Controls – The control strategy used in the transient inverter also applies to the PV inverters, enabling the PV energy source to be the prime source in the microgrid. This will improve microgrid stability, minimize generator run time, and offset the required generator installed capacity for islanding, based on the PV electrical load carrying capacity.
The integrated transient inverter and legacy generator solution provides a commercial path for converting existing distribution systems into microgrid capable systems without the high cost of grid-scale energy storage. The solution achieves energy surety and security, high power quality, ride-through, fast-acting transient real and reactive power support and will enable islanding of microgrids. The power optimized energy storage and inverter used is commercial off-the-shelf technology and costs approximately 67% less than typical utility-scale battery energy storage solutions deployed today. The storage inverter controls and hardware will also provide an islanding inverter (microgrid compatibility) for renewable energy sources (PV for this project) to maximize the effective load carrying capacity of the renewable energy source when grid connected or islanded. (Anticipated Project Completion - 2014)
Points of Contact
Mr. Slobodan Krstic
Energy and Water
SERDP and ESTCP
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