Opposing contactors for energy storage device isolation

1. A method for controlling a plurality of contactors in an energy storage system having a first unidirectional contactor coupled to a first terminal of an energy storage device and a second unidirectional contactor coupled to a second terminal of the energy storage device, the first unidirectional contactor coupled to the energy storage device with opposite polarity relative to the second unidirectional contactor, the method comprising:

determining a isolating condition for the energy storage device, the isolating condition occurring when the energy storage device needs to be electrically isolated from a power system;

responsive to determining the isolating condition for the energy storage device, determining a direction of current flow associated with the energy storage device; and

controlling operation of the first unidirectional contactor and the second unidirectional contactor based at least in part on the direction of current flow associated with the energy storage device.

2. The method of claim 1 , wherein when the direction of current flow is determined to be flowing in a first direction, controlling the operation of the first unidirectional contactor and the second unidirectional contactor comprises:

opening the first unidirectional contactor;

subsequent to opening the first unidirectional contactor, opening the second unidirectional contactor.

3. The method of claim 1 , wherein when the direction of current flow is determined to be flowing in a second direction, controlling operation of the first unidirectional contactor and the second unidirectional contactor comprises:

opening the second unidirectional contactor; and

subsequent to opening the second unidirectional contactor, opening the first unidirectional contactor.

4. The method of claim 1 , wherein the first unidirectional contactor and the second unidirectional contactor are designed to accommodate opening with current flow in a single direction.

5. The method of claim 1 , wherein the first unidirectional contactor is coupled to the first terminal such that the first unidirectional contactor has a first polarity and the second unidirectional contactor is coupled to the second terminal such that the second unidirectional contactor has a second polarity, the first polarity corresponding to charging the energy storage device and the second polarity corresponding to discharging the energy storage device.

6. An energy storage system, comprising:

at least one energy storage device comprising a first terminal and a second terminal;

a first unidirectional contactor coupled to the first terminal;

a second unidirectional contactor coupled to the second terminal such that a polarity of the second unidirectional contactor is opposite relative to a polarity of the first unidirectional contactor; and

one or more control devices programmed to perform a control routine, the control routine comprising:

determining a isolating condition for the energy storage device, the isolating condition occurring when the energy storage device needs to be isolated from a power system;

responsive to determining the isolating condition for the energy storage device, determining a direction of current flow associated with the energy storage device; and

controlling operation of the first unidirectional contactor and the second unidirectional contactor based at least in part on the direction of current flow associated with the energy storage device.

7. The energy storage system of claim 6 , wherein the first unidirectional contactor and the second unidirectional contactor are designed to accommodate opening with current flow in a single direction.

8. The energy storage system of claim 6 , wherein the first unidirectional contactor is coupled to the first terminal such that the first unidirectional contactor has a first polarity and the second unidirectional contactor is coupled to the second terminal such that the second unidirectional contactor has a second polarity, the first polarity being different from the second polarity.

9. The energy storage system of claim 8 , wherein the first polarity corresponds to current flowing to the energy storage device and the second polarity corresponds to current flowing from the energy storage device.

10. The energy storage system of claim 6 , further comprising:

a contactor drive circuit configured to operate the first unidirectional contactor and the second unidirectional contactor; and

at least one sensor configured to determine the direction of current flow associated with the at least one energy storage device;

wherein controlling operation of the first unidirectional contactor and the second unidirectional contactor comprises providing a contactor command to the contactor drive circuit based at least in part on the direction of current flow associated with the at least one energy storage device, the contactor command controlling the contactor drive circuit to open at least one of the first unidirectional contactor or the second unidirectional contactor.

11. The energy storage system of claim 10 , wherein when the direction of current flow is determined to flow in a first direction, controlling operation of the first unidirectional contactor and the second unidirectional contactor comprises providing a contactor command controlling the contactor drive circuit to first open the first unidirectional contactor and to subsequently open the second unidirectional contactor to isolate the energy storage device.

12. The energy storage system of claim 11 , wherein when the direction of current flow is determined to flow in a second direction, controlling operation of the first unidirectional contactor and the second unidirectional contactor comprises providing a contactor command controlling the contactor drive circuit to first open the second unidirectional contactor and to subsequently open the first unidirectional contactor to isolate the energy storage device.

13. The energy storage system of claim 6 , wherein the energy storage device comprises a battery energy storage device.

14. The energy storage system of claim 13 , wherein the battery energy storage device is selected from the group consisting of: a sodium nickel chloride battery, sodium sulfur battery, lithium ion battery, or nickel metal hydride battery.

15. A control system for controlling a plurality of contactors in an energy storage system having a first unidirectional contactor coupled to a first terminal of an energy storage device and a second unidirectional contactor coupled to a second terminal of the energy storage device, the first unidirectional contactor coupled to the energy storage device with opposite polarity relative to the second unidirectional contactor, the control system comprising:

a contactor drive circuit configured to operate the first unidirectional contactor and the second unidirectional contactor;

at least one sensor configured to determine the direction of current flow associated with the at least one energy storage device; and

one or more control devices configured to perform a control routine, the control routine comprising:

determining a isolating condition for the energy storage device, the isolating condition occurring when the energy storage device needs to be isolated from a power system;

responsive to determining the isolating condition for the energy storage device, determining a direction of current flow associated with the energy storage device; and

providing a contactor command controlling the contactor drive circuit to first open the first unidirectional contactor and to subsequently open the second unidirectional contactor to isolate the energy storage device.

16. The control system of claim 15 , wherein the first unidirectional contactor and the second unidirectional contactor are designed to accommodate opening with current flow in a single direction.

17. The control system of claim 15 , wherein the first unidirectional contactor is coupled to the first terminal such that the first unidirectional contactor has a first polarity and the second unidirectional contactor is coupled to the second terminal such that the second unidirectional contactor has a second polarity, the first polarity corresponding to current flowing to the energy storage device and the second polarity corresponding to current flowing from the energy storage device.

18. The control system of claim 15 , wherein when the direction of current flow is determined to flow in a first direction, the one or more control devices configured to provide a contactor command controlling the contactor drive circuit to first open the first unidirectional contactor and to open the second unidirectional contactor after the opening of the first unidirectional contactor to isolate the energy storage device.

19. The control system of claim 18 , wherein when the direction of current flow is determined to flow in a second direction, the one or more control devices configured to provide a contactor command controlling the contactor drive circuit to first open the second unidirectional contactor and to open the first unidirectional contactor after the opening of the second unidirectional contactor to isolate the energy storage device.