Protection device for DC collection systems

Patent metadata

Field	Value
Publication number	US-9419428-B2
Application number	US-201414278832-A
Country	US
Kind code	B2
Filing date	May 15, 2014
Priority date	May 15, 2014
Publication date	Aug 16, 2016
Grant date	Aug 16, 2016

Abstract

A protection device includes a diode having its forward direction in a normal power flow of a region of a DC collection system, a first switch in parallel with the diode, a second switch in series with the diode and a control unit for controlling the switches. The first switch can be opened so that current can flow through the diode in the forward direction without the first switch bypassing the diode, and closed if no current is flowing through the diode in the forward direction and power is needed upstream of the diode. The second switch can be closed so that current can flow through the diode in the forward direction to an AC grid interface of the DC collection system, and opened if no current is flowing through the diode in the forward direction due to a fault in a DC feeder to which the device is coupled.

First claim

What is claimed is:

1. A DC collection system, comprising:
a plurality of DC feeders for transferring power generated from energy sources to an AC grid interface;
a plurality of protection devices for isolating the energy sources from faults on the DC feeders, each protection device comprising a diode having its forward direction in the power flow to the AC grid interface, a first switch in parallel with the diode, a second switch in series with the diode, and a control unit operable to:
open the first switch so that current can flow through the diode in the forward direction without the first switch bypassing the diode, and close the first switch if no current is flowing through the diode in the forward direction and power is needed upstream of the diode; and
close the second switch so that current can flow through the diode in the forward direction to the AC grid interface, and open the second switch if no current is flowing through the diode in the forward direction due to a fault in a DC feeder to which the protection device is coupled; and

a plurality of current sensors each operable to sense the current flowing through one of the diodes in the forward direction,
wherein the control unit of each protection device is operable to open the second switch responsive to the corresponding current sensor indicating no current is flowing through the diode in the forward direction.

2. The DC collection system of claim 1 , wherein at least some of the protection devices connect the DC feeders to a DC bus that connects the DC feeders to the AC grid interface.

3. The DC collection system of claim 2 , wherein the AC grid interface comprises a substation operable to convert DC power collected from the plurality of DC feeders to AC power, and wherein the protection devices that connect the DC feeders to the DC bus are disposed within the substation.

4. The DC collection system of claim 1 , wherein at least some of the energy sources are wind towers that generate power from wind energy, and wherein the protection devices that connect the DC feeders to the wind towers are disposed within the respective wind towers.

5. The DC collection system of claim 1 , wherein the DC feeders are protected by at least two of the protection devices so that each DC feeder has at least two separately isolatable sections.

6. The DC collection system of claim 5 , wherein the DC feeders are arranged in a radial configuration, and wherein the second switch of the protection device located downstream of a fault on one of the DC feeders is opened during the fault so that each section of the DC feeder downstream of the protection device with the opened second switch continues to transfer power to the AC grid interface.

7. The DC collection system of claim 5 , wherein the DC feeders are arranged in a ring configuration, and wherein the second switch of the protection devices located on each side of a fault on one of the DC feeders is opened during the fault so that each section of the feeder upstream of the fault transfers power to another one of the DC feeders during the fault by a cable connecting the DC feeders through a connecting switch.

8. The DC collection system of claim 5 , wherein at least some of the DC feeders are divided in to at least two different DC sub-feeders, and wherein each of the DC sub-feeders is protected by at least two of the protection devices so that each DC sub-feeder has at least two separately isolatable sections.

9. The DC collection system of claim 1 , further comprising an auxiliary bus operable to connect at least some of the DC feeders to the AC grid interface during a startup mode in which power is required to flow upstream in the opposite direction as the normal power flow.

10. The DC collection system of claim 9 , wherein the control unit of each protection device coupled to the auxiliary bus is operable to close the first switch and the second switch responsive to a startup command that indicates the DC collection system is in the startup mode.

11. The DC collection system of claim 1 , wherein the current sensors are collocated with the respective protection devices.

12. A protection device for a DC collection system, the protection device comprising:
a diode having its forward direction in a normal power flow of a region of the DC collection system;
a first switch in parallel with the diode;
a second switch in series with the diode;
a control unit operable to:
open the first switch so that current can flow through the diode in the forward direction without the first switch bypassing the diode, and close the first switch if no current is flowing through the diode in the forward direction and power is needed upstream of the diode; and
close the second switch so that current can flow through the diode in the forward direction to an AC grid interface of the DC collection system, and open the second switch if no current is flowing through the diode in the forward direction due to a fault in a DC feeder to which the protection device is coupled; and

a current sensor operable to sense the current flowing through the diode in the forward direction,
wherein the control unit is operable to open the second switch responsive to the current sensor indicating no current is flowing through the diode in the forward direction.

13. The protection device of claim 12 , wherein the control unit is operable to close the first switch and the second switch responsive to a startup command that indicates a startup mode in which power is needed upstream of the diode in the opposite direction as the normal power flow.

14. The protection device of claim 12 , further comprising at least one additional diode in series with the diode and each diode having its forward direction in the normal power flow, and wherein the first switch is in parallel with the series-connected diodes and the second switch is in series with the series-connected diodes.

15. The protection device of claim 14 , further comprising an RC snubber circuit in parallel with each of the diodes.

16. The protection device of claim 14 , further comprising a surge arrester in parallel with the series-connected diodes.

17. The protection device of claim 12 , wherein the first and the second switches are both mechanical switches.

18. ADC collection system, comprising:
a plurality of DC feeders for transferring power generated from energy sources to an AC grid interface;
a plurality of protection devices for isolating the energy sources from faults on the DC feeders, each protection device comprising a diode having its forward direction in the power flow to the AC grid interface, a first switch in parallel with the diode, a second switch in series with the diode, and a control unit operable to:
open the first switch so that current can flow through the diode in the forward direction without the first switch bypassing the diode, and close the first switch if no current is flowing through the diode in the forward direction and power is needed upstream of the diode; and
close the second switch so that current can flow through the diode in the forward direction to the AC grid interface, and open the second switch if no current is flowing through the diode in the forward direction due to a fault in a DC feeder to which the protection device is coupled; and

an auxiliary bus operable to connect at least some of the DC feeders to the AC grid interface during a startup mode in which power is required to flow upstream in the opposite direction as the normal power flow.

19. The DC collection system of c

Assignees

• Abb Technology Ag

Inventors

• Qi Li
• Liang Jiaqi
• Pan Jiuping

Classifications

• H02H7/268

  for DC systems · CPC title

• H02H3/087 Primary

  for DC applications · CPC title

• H02H3/18

  responsive to reversal of direct current · CPC title