Test bed name: Oxford Flexible Battery System (OxFBS) Currently installed power electronics hardware: MMC v2.01
Type of energy stored:
Electrochemical
Nominal capacity (kWh):
3 x 7.2
Nominal power (kVA):
3 x 14.4
Year of installation:
2016
Response time:
10 milliseconds
Self-discharge (%/month):
0.5
Efficiency (%):
85 – 97
Grid Voltage (V):
230 / 400
ESS communication system:
All high-level functions are performed in MATLAB and so virtually any control interface can be layered on top of this. The data bus internal to the converter and battery pack operates using a custom-designed and fully-documented SPI-like protocol (Serial Peripheral Interface). This bus is used for safety-critical high-speed control.
HMI:
A custom MATLAB interface running on a standard PC
Overview of the AC Grid interface:
The system is made up of 432 20Ah Toshiba LTO cells divided into three 19” cabinets. These cabinets can be operated together or separately with a single or three phase connection. Connection to the grid is via a variable autotransfomer and (optional) isolation transformer. The system is highly reconfigurable and is designed to serve as a test bed for power electronic systems. A key feature is that every cell is individually accessible from the front panel using a standardised connector and mounting system, meaning that virtually any arrangement of the cells and pack design could be tested using this equipment. The unique architecture of the currently installed MMC v2.01 power electronic system means that the cells, inverter and cell balancing/bypass circuits are integrated very tightly and distributed throughout the cabinets, i.e. there is no separate converter.
ANCILLARY SERVICES (<30s response time for voltage control, frequency response):
The system is effectively ‘raw resource’ in that the BMS and low-level control system is in placeto ensure the system will follow real and reactive power setpoints. The higher level control functionality (e.g. for ancillary services) has yet to be developed, but could be customised and then integrated with relatively little effort. The system is cable of ramping 0-100% real and reactive power in sub-20ms timescales.
RESERVE (>30s response, at least 30 min duration):
Yes, see above.
INTRA-DAY PEAK SHIFTING (balancing demand/supply of electrical and thermal within day):
Yes, see above.
INTER-DAY LEVELLING (balancing over days, especially considering low wind events):
Yes, see above.
SEASONAL ELECTRICAL PEAK SHIFTING (storing electrical energy in summer, discharging in winter):
Although technically possible, this is unlikely to be an attractive (i.e. cost effective) use case for this system as it is Li-ion.
SEASONAL THERMAL PEAK SHIFTING (storing hot/cold thermal energy between seasons):
No
BLACK START:
Technically yes, although yet to be demonstrated. All internal electronics and support systems can be run from the internal stored energy (assuming system is not fully depleted).
UNINTERRUPTABLE POWER SUPPLY:
Currently, load change-over switches and other systems required for UPS operation have have not yet been implemented, although these could be developed and inteegrated if required.
CUSTOMER BALANCING:
?