METHOD AND APPARATUS FOR IMPROVING AC TRANSMISSION SYSTEM DISPATCHABILITY, SYSTEM STABILITY, AND POWER FLOW CONTROLLABILITY USING DC TRANSMISSION SYSTEMS

• US 20080103630A1
• Filed: 11/01/2006
• Published: 05/01/2008
• Est. Priority Date: 11/01/2006
• Status: Active Grant

• Current Assignee: Electric Power Research Institute Incorporated
• Original Assignee: Electric Power Research Institute Incorporated
• Inventors: Eckroad, Steven Wallace
• Granted Patent: US 7,518,266 B2
• Time in Patent Office: Days
• US Class Current: 700/286
• CPC Class Codes: H02J 3/02 using a single network for simultaneous distribution of power at different frequencies; using a single network for simultaneous distribution of ac power and of dc power

Abstract

An electric power transmission system that isolates a local AC transmission network from a surrounding AC system includes a local AC load center having a plurality of local AC loads, and a distribution feeder serving the plurality of local AC loads and at least one distant electric power generating station or other power source for supplying AC power to the local AC load center. A complete or partial DC transmission ring is interposed between the local AC load center and the distant electric power generating station for isolating the AC power received from the distant electric power generating station from the local AC load center by converting the AC power to DC power. The DC power is re-converted into AC power based on load requirements and the distribution feeder supplies the AC power while all local AC loads are isolated from the distant electric power generating station.

Claims

1. An electric power transmission system that isolates a local AC transmission network from a surrounding AC system, comprising:

(a) a local AC load center having a plurality of local AC loads, and at least one distribution feeder serving the plurality of local AC loads;

(b) at least one distant electric power generating station for supplying AC power to the local AC load center by means of an AC transmission line;

(c) a DC transmission ring having a plurality of DC loads thereon at least partially interposed between the local AC load center and the distant electric power generating station, the DC transmission ring isolating the AC power received from the distant electric power generating station from the local AC load center;

(d) a first plurality of AC/DC converters electrically interfaced with the DC transmission ring exterior to the local AC load center for converting the AC power from the distant generating station into DC power and making available the DC power converted at a one of the AC/DC converters to at least some of the other of the plurality of DC loads on the DC transmission ring;

(e) a second plurality of AC/DC converters electrically interfaced with the DC transmission ring interior to the DC transmission ring for converting the DC power from the DC transmission ring into AC power;

(f) the distribution feeder proximate the local AC load center electrically connected to the DC transmission ring through the second plurality of AC/DC converters for supplying the AC power to the local AC load center while all local AC loads are isolated from the distant electric power generating station.

2. An electric power transmission system according to claim 1, and including a plurality of isolating DC-DC converters, interposed at predetermined locations on the DC transmission ring for isolating faults on the DC transmission ring to prevent the faults from disturbing the system.

3. An electric power transmission system according to claim 1, and including at least one local AC power generator electrically connected to the DC transmission ring.

4. An electric power transmission system according to claim 1, wherein the AC power generated by the distant electric power generating station is brought to the local AC load center via an AC transmission line that is selected from the group consisting of high voltage (HV), extra high voltage (EHV), high voltage DC (HVDC) and DC transmission cable.

5. An electric power transmission system according to claim 1, and including controlled AC/DC converters for directing power scheduled to flow from the distant electric power generating station to a market distant to the local AC load center across the DC transmission ring.

6. An electric power transmission system according to claim 1, and including at least one DOC power source located proximate the DC transmission ring in electrical communication with the DC transmission ring.

7. An electric power transmission system according to claim 1, and including a plurality of diverse distributed generation AC or DC power sources located proximate the DC transmission ring and in electrical communication with the DC transmission ring.

8. An electric power transmission system according to claim 1, and including a plurality of diverse distributed generation DC power sources located proximate the DC transmission ring and in electrical communication with the DC transmission ring, and selected from the group consisting of fuel cells, microturbines, solar photovoltaic devices, batteries, flywheels, superconducting magnets, electrochemical capacitors and DC microgrids.

9. An electric power transmission system according to claim 1, and including a second DC transmission ring interconnected with the system and following a similar but not contiguous route for back-up use.

10. An electric power transmission system that isolates a local AC transmission network from a surrounding AC system, comprising:

(a) a local AC load center having a plurality of AC loads, and at least one AC distribution feeder serving the plurality of AC loads;

(b) a local DC load center having a plurality of DC loads, and at least one DC distribution feeder serving the plurality of DC loads;

(c) at least one distant electric power generating station for supplying AC power to the local AC load center by a DC transmission line;

(d) a DC transmission ring having a plurality of DC loads thereon at least partially interposed between the local AC and DC load centers, and the distant electric power generating station, the DC transmission ring isolating the AC power received from the distant electric power generating station from the local AC and DC load centers;

(e) a first plurality of AC/DC converters electrically interfaced with the DC transmission ring exterior to the local AC load center for converting the AC power from the generating station into DC power and making available the DC power converted at a one of the AC/DC converters to at least some of the other of the plurality of DC loads on the DC transmission ring;

(f) a second plurality of AC/DC converters electrically interfaced with the DC transmission ring proximate the DC transmission ring for converting the DC power from the DC transmission ring into AC power for delivery to the AC loads;

(g) A plurality of DC/DC converters electrically interfaced with the DC transmission ring proximate the DC transmission ring for managing the exchange of power between the DC transmission ring and the local DC load center;

(h) the AC distribution feeder within the local AC load center electrically connected to the DC transmission ring through the second plurality of AC/DC converters for supplying the AC power to the local AC load center while all local loads are isolated from the distant electric power generating station; and

(i) the DC distribution feeder within the local DC load center electrically connected to the DC transmission ring through the plurality of DC/DC converters for supplying the DC power to the local DC load centers.

11. An electric power transmission system according to claim 10, wherein the AC power generated by the distant electric power generating station is selected from the group consisting of high voltage (HV) or extra high voltage (EHV).

12. An electric power transmission system according to claim 10, and including controlled AC/DC converters for directing power scheduled to flow from the distant electric power generating station to a market distant to the local AC load center across the DC transmission ring.

13. An electric power transmission system according to claim 10, and including at least one DC power source located proximate the DC transmission ring and in electrical communication with the DC transmission ring.

14. An electric power transmission system according to claim 10, and including a plurality of diverse distributed generation AC or DC power sources located proximate the DC transmission ring in electrical communication with the DC transmission ring.

15. An electric power transmission system according to claim 10, and including a plurality of diverse distributed generation DC power sources located proximate the DC transmission ring and in electrical communication with the DC transmission ring, and selected from the group consisting of fuel cells, microturbines, solar photovoltaic devices, batteries, flywheels, superconducting magnets, electrochemical capacitors and DC microgrids.

16. A method of isolating a local AC transmission network from a surrounding AC system having an AC load center with a plurality of AC loads, a distribution feeder serving the plurality of local AC loads and at least one distant electric power generating station for supplying AC power to the local AC load center via an AC or DC transmission line, comprising the steps of:

(a) at least partially interposing a DC transmission ring having a plurality of DC loads thereon between the local AC load center and the transmission line delivering power from the distant electric power generating station;

(b) isolating the AC power received from the distant electric power generating station by the DC transmission ring from the local AC load center;

(c) converting the AC power from the generating station into DC power and making available the DC power to at least some of the other of the plurality of DC loads on the DC transmission ring;

(d) converting the DC power from the DC transmission ring into AC power; and

(e) distributing the AC power within the local AC load center while all local AC loads are isolated from the distant electric power generating station.

17. A method according to claim 16, and including the step of interposing at predetermined locations on the DC transmission ring a plurality of isolating DC-DC converters for isolating faults on the DC transmission ring to prevent the faults from disturbing the system.

18. A method according to claim 16, and including the step of electrically connecting at least one local AC power generator to the AC load center within the DC transmission ring.

19. A method according to claim 16, and including the step of directing power scheduled to flow from the distant electric power generating station to a market distant to the local AC load center across the DC transmission ring.

20. A method according to claim 16, and including the step of providing at least one DC power source located proximate the DC transmission ring in electrical communication with the DC transmission ring.

21. A method according to claim 16, and including the step of providing a plurality of diverse distributed generation AC or DC power sources located proximate the DC transmission ring in electrical communication with the DC transmission ring.

22. A method according to claim 16, and including the step of providing a plurality of diverse distributed generation DC power sources located proximate the DC transmission ring, and in electrical communication with the DC transmission ring and selected from the group consisting of fuel cells, microturbines, solar photovoltaic devices, batteries, flywheels, superconducting magnets, electrochemical capacitors and DC microgrids.

23. A method according to claim 16, and including the step of providing a second DC transmission ring interconnected with the system and following a similar but not contiguous route for back-up use.