Energy Storage System

• US 20130099581A1
• Filed: 06/21/2011
• Published: 04/25/2013
• Est. Priority Date: 06/21/2010
• Status: Active Grant

• Current Assignee: National University of Singapore
• Original Assignee: National University of Singapore
• Inventors: Khambadkone, Ashwin M., Battacharya, Tanmoy, Zhou, Haihua
• Granted Patent: US 9,293,917 B2
• Time in Patent Office: Days
• US Class Current: 307/82
• CPC Class Codes: H02J 1/001 Hot plugging or unplugging of load or power modules to or from power distribution networks
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 1/12 Parallel operation of dc generators with converters, e.g. with mercury-arc rectifier
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: Y02B 10/30 Wind power

Abstract

An energy storage system comprises a plurality of storage mediums having substantially different energy and power density that are each connected to a DC bus via a respective bidirectional isolated DC-DC converter; and a controller configured to independently determine a current demand for each storage medium based on a control mode.

Claims

1. An energy storage system comprising:

a plurality of storage mediums having substantially different energy and power density each connected to a DC bus via a respective bidirectional isolated DC-DC converter; and

a controller configured to independently determine a current demand for each storage medium based on a control mode.

2. The system in claim 1 wherein a high frequency current demand is determined for at least one of the storage medium with a relatively fast response and a low frequency current demand is determined for at least one of the storage medium with a relatively slow response.

3. The system in claim 2 wherein the capacity of the fast response storage medium is configured to support a desired power density.

4. The system in claim 3 wherein the fast response storage medium is an ultracapacitor.

5. The system in claim 2 wherein the capacity of the slow response storage medium is configured to support a desired energy density.

6. The system in claim 5 wherein the slow response storage medium is one or more batteries.

7. The system in claim 1 wherein the storage mediums are selected from the group consisting of batteries, ultracapacitors, fuel cells, electrolytics, fly wheels and any combination.

8. The system in claim 1 wherein the bidirectional isolated DC-DC converters are dual active bridges (DAB) configured to be connected in a plurality of predetermined configurations for different DC bus voltages.

9. The system in claim 8 wherein a plurality of DABs connected to a plurality of batteries are connected in a modified input parallel output series configuration, a plurality of DABs connected to an ultracapacitor are connected in an input parallel output series configuration and the two pluralities of DBAs are intermittently bridged.

10. The system in claim 9 wherein each DBA includes a high frequency transformer.

11. The system in claim 9 wherein the DABs configured to interleave a plurality of switching instants to reduce an output ripple.

12. The system in claim 2 wherein the low frequency current demand is determined using a low pass filter with a cut-off frequency determined based on a relative capacity of the fast response storage medium compared to the slow response storage medium.

13. The system in claim 1 wherein the control modes are selected from the group consisting of dynamic allocation of current demand between the storage mediums, state of charge balancing between the storage mediums, slow response storage medium removal, fast response storage medium charging and any combination.

14. The system in claim 2 wherein the low frequency current demand for the slow response storage medium is controlled using a current feedback loop.

15. The system in claim 2 wherein the high frequency current demand for the fast response storage medium is fed forward to the output of a voltage feedback loop.

16. An energy apparatus comprising;

an energy generation system, and

an energy storage system according to claim 1, adjacent to the energy generation system and configured to absorb any excess power and supply any shortfall power from the energy generation system.

17. The system in claim 16, wherein the energy apparatus is selected from the group consisting of a micro-grid, an isolated or standalone electrical system and an electric vehicle.

18. The system in claim 16, wherein the energy generation system is selected from the group consisting of a PV solar array, a wind turbine, micro hydro turbine, combined cycle turbine, and any combination.

19. A method of distributing current between a plurality of energy storage mediums connected between a generator and a load comprising:

determining an overall current demand based on an instantaneous generation power from the generator and an instantaneous load power from the load;

controlling a current a slow response energy storage medium based on a low frequency component of the overall current demand; and

controlling a current of a fast response energy storage medium based on a high frequency component of the overall current demand.