Method and apparatus for improving AC transmission system dispatchability, system stability, and power flow controllability using DC transmission systems

• US 7,518,266 B2
• Filed: 11/01/2006
• Issued: 04/14/2009
• Est. Priority Date: 11/01/2006
• Status: Expired due to Fees

• Current Assignee: Electric Power Research Institute Incorporated
• Original Assignee: Electric Power Research Institute Incorporated
• Inventors: Eckroad, Steven Wallace
• Primary Examiner(s): Paladini; Albert W
• Assistant Examiner(s): RUTLAND WALLIS, MICHAEL
• Application Number:
  US11/555,430
• Publication Number:
  US 20080103630A1
• Time in Patent Office: 895 Days
• Field of Search: 307/18, 307/82, 307/19, 700/286
• US Class Current: 307/82
• 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, comprising:

(a) a group of individual utility customers interconnected by a local AC transmission network within a defined geographical area;

(b) a DC transmission ring substantially surrounding the local AC transmission network, the DC transmission ring isolating the local AC transmission network from an AC generating station;

(c) a first AC/DC converter electrically connected between the DC transmission ring and the AC generating station to receive and convert AC power from the AC generating station to DC power for distribution along the DC transmission ring;

(d) a second AC/DC converter electrically connected between the DC transmission ring and the local AC transmission network, the second AC/DC converter adapted to receive and convert DC power from the DC transmission ring to AC power for distribution to the AC transmission network; and

(e) 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.

2. The electric power transmission system according to claim 1, wherein the DC transmission ring is a cable selected from the group consisting of HVDC overhead conductors, underground DC cable, and low voltage DC superconducting cable.

3. The electric power transmission system according to claim 1, wherein the AC generating station is a local AC power generator electrically connected to the DC transmission ring.

4. The electric power transmission system according to claim 1, wherein the AC power generated by the AC generating station is distributed to the DC transmission ring 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. The electric power transmission system according to claim 1, further including controlled AC/DC converters for directing power scheduled to flow from a distant electric power generating station to a market distant to the local AC transmission network across the DC transmission ring.

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

7. The electric power transmission system according to claim 1, further 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. The electric power transmission system according to claim 1, further 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. The electric power transmission system according to claim 1, further 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, comprising:

(a) a group of individual utility customers interconnected by a local AC transmission network within a defined geographical area;

(b) at least one distant electric power generating station for supplying AC power to the local AC transmission network;

(c) a DC transmission ring having a plurality of DC loads thereon, wherein the DC transmission ring surrounds the local AC transmission network and is interposed between the local AC transmission network 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 transmission network;

(d) a first plurality of AC/DC converters electrically interfaced between the DC transmission ring and the distant electric power generating station to receive and convert 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 of the first plurality of 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 between the DC transmission ring and the local AC transmission network to receive and convert the DC power from the DC transmission ring into AC power for delivery to the local AC transmission network;

(f) a plurality of DC/DC converters electrically interfaced with the DC transmission ring to control power flow on the DC transmission ring, the DC/DC converters being adapted to sectionalize the DC transmission ring and isolate faults occurring in the DC transmission ring to prevent the faults from disturbing the system.

11. The 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. The 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. The electric power transmission system according to claim 10, wherein the DC transmission ring is a cable selected from the group consisting of HVDC overhead conductors, underground DC cable, and low voltage DC superconducting cable.

14. The 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.

15. A method of isolating a local AC transmission network having a plurality of AC loads from a surrounding AC system including at least one distant electric power generating station for supplying AC power to the local AC transmission network via an AC or DC transmission line, comprising the steps of:

(a) substantially surrounding the local AC transmission network with a DC transmission ring having a plurality of DC loads thereon and adapted to receive AC 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 transmission network;

(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) interposing at predetermined locations on the DC transmission ring a plurality of isolating DC-DC converters for segmenting and isolating faults on the DC transmission ring to prevent the faults from disturbing the system;

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

(f) distributing the AC power within the local AC transmission network while all local AC loads therein are isolated from the distant electric power generating station.

16. The method according to claim 15, and including the step of electrically connecting at least one local AC power generator to the local AC transmission network within the DC transmission ring.

17. The method according to claim 15, 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 transmission network across the DC transmission ring.

18. The method according to claim 15, 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.

19. The method according to claim 15, 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.

20. The method according to claim 15, 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.

21. The method according to claim 15, 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.