Voltage source converters operating either as back-to-back stations or as parallel static var compensators

• US 6,411,067 B1
• Filed: 02/20/2001
• Issued: 06/25/2002
• Est. Priority Date: 02/20/2001
• Status: Expired due to Term

• Current Assignee: ABB Power Grids Switzerland AG (Hitachi, Ltd.)
• Original Assignee: ABB AB (ABB Limited)
• Inventors: Björklund, Hans
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US09/785,168
• Time in Patent Office: 490 Days
• Field of Search: 323/207, 363/34, 363/35, 363/37
• US Class Current: 323/207
• CPC Class Codes: H02J 3/1814 wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: Y02E 40/10 Flexible AC transmission systems [FACTS]

Abstract

A device and a method for controlling the flow of electric power in a transmission line carrying alternating current, in which a first voltage source converter is connected to the transmission line at a first point and a second voltage source converter is connected to the transmission line at a second point. Further, the first and second voltage source converters have their direct current sides connected to a common capacitor unit. Also included is a by-pass switch connected to the transmission line between the first point and the second point in parallel with the first and second voltage source converters so that the first and second voltage source converters will operate as a back-to-back station when the by-pass switch is open and as two parallel static var compensators when the by-pass switch is closed.

Claims

1. A device for controlling the flow of electric power in a transmission line carrying alternating current, said device comprising:

a first voltage source converter connected to the transmission line at a first point;

a second voltage source converter connected to the transmission line at a second point, said first and second voltage source converters having their direct current sides connected to a common capacitor unit;

a by-pass switch connected to the transmission line between said first point and said second point in parallel with the first and second voltage source converters so that the first and second voltage source converters will operate as a back-to-back station when the by-pass switch is open and as two parallel static var compensators when the by-pass switch is closed.

2. A device according to claim 1, wherein the by-pass switch comprises a breaker.

3. A device according to claim 1, wherein the by-pass switch comprises a disconnector.

4. A device according to claim 1, wherein each voltage source converter has at least one phase leg having at least two current valves connected in series, said valves including at least one semiconductor element of a turn-off type and at least one rectifying member connected in anti-parallel therewith, and

wherein a mid point of the phase leg between said valves forms a phase output and is connected to a phase of the transmission line.

5. A device according to claim 4, wherein said semiconductor elements of the turn-off type comprise bipolar transistors having an insulated gate.

6. A device according to claim 4, wherein said semiconductor elements of the turn-off type comprise thyristors of a turn-off type.

7. A device according to claim 4, wherein each current valve comprises a plurality of semiconductor elements of a turn-off type connected in series and a plurality of rectifying members connected in series.

8. A device according to claim 1, wherein each voltage source converter is a six pulse bridge converter.

9. A device according to claim 1, wherein each voltage source converter is a three-level converter.

10. A device according to claim 1, wherein the voltage source converters are arranged to conduct the current through the device in such a way during a breaking operation of the by-pass switch that essentially no current or only a limited current passes the by-pass switch so as to assist the by-pass switch in said breaking operation.

11. A method for controlling the flow of electric power in a transmission line carrying alternating current, wherein the alternating current alternatively is conducted through a back-to-back station comprising a first voltage source converter, connected to the transmission line at a first point, a second voltage source converter, connected to the transmission line at a second point, and a direct current link capacitor unit connected between said first and second voltage source converters, or through a by-pass switch arranged in the transmission line between said first point and said second point in parallel with the first and second voltage source converters, said first and second voltage source converters operating as two parallel static var compensators when the alternating current is conducted through the by-pass switch.

12. An alternating current network, comprising:

devices for controlling the flow of electric power in the network, each device comprising;

a first voltage source converter connected to a transmission line of the network at a first point; and

a second voltage source converter connected to said transmission line at a second point, the first and second voltage source converters being connected to a common direct current link capacitor unit;

a by-pass switch connected to said transmission line between said first point and said second point in parallel with the first and second voltage source converters so that the first and second voltage source converters will operate as a back-to-back station when the by-pass switch is open and as two parallel static var compensators when the by-pass switch is closed; and

control means connected to the voltage source converters and the by-pass switch for controlling each device.

13. An alternating current network according to claim 12, wherein the control means of several devices are remote-controlled from a common control station.