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CN-115516729-B - Improvements in or relating to bipolar power transmission schemes

CN115516729BCN 115516729 BCN115516729 BCN 115516729BCN-115516729-B

Abstract

A bipolar power transmission scheme (10) includes a first converter station (12) that is located, in use, remote from a second converter station (14). The first converter station (12) includes a first power converter (30) electrically connected to a first variable power source (38). The first power converter (30) also has a first converter controller (44) programmed to control the transfer of the first power feed (46) from the first power source (38) into the first transmission conduit (20) in the form of a first power feed (76). In addition, the first converter station (12) also includes a second power converter (48) electrically connected to a second variable power source (50). The second power converter (48) also has a second converter controller (54) programmed to control the transfer of the second power feed (56) from the second power source (50) into the second transmission conduit (22) in the form of a second power feed (86). During operation of the bipolar power transmission scheme (10) under normal conditions, the first power converter (30) and the associated first power source (38) operate independently of the second power converter (48) and the associated second power source (50), whereby the first power feed (46) into the first transmission pipe (20) and the second power feed (56) into the second transmission pipe (22) are independent of each other. During operation of the bipolar power transmission scheme (10) under abnormal conditions when the return conduit (24) fails and fails to provide a return current path, each converter controller (44, 54) is programmed to monitor a first power feed (76) in the first transmission conduit (20) and a second power feed (86) in the second transmission conduit (22), and if the first power feed (76) in the first transmission conduit (20) and the second power feed (86) in the second transmission conduit (22) are different from each other, at least one converter controller (44, 54) modifies the power feeds (46, 56) from its corresponding power source (38, 50) to reduce a difference between the first power feed (76) and the second power feed (86).

Inventors

  • M. Papua South
  • O. Jasim

Assignees

  • 通用电器技术有限公司

Dates

Publication Date
20260508
Application Date
20210316
Priority Date
20200318

Claims (11)

  1. 1. A bipolar power transfer apparatus (10) comprising a first converter station (12) which in use is located remotely from a second converter station (14), and first and second transfer and return conduits (20, 22, 24) for interconnecting the first converter station (12) with the second converter station (14) in use and thereby allowing the first converter station (12) to transfer power to the second converter station (14), The first converter station (12) comprises: A first power converter (30) having a first DC terminal (32) connected to the first transmission conduit (20), a second DC terminal (34) connected to the return conduit (24), and at least one AC terminal (36A, 36B, 36C) electrically connected to a first variable power source (38), the first power converter (30) further having a first converter controller (44) programmed to control transfer of a first power feed (46) from the first variable power source (38) into the first transmission conduit (20) in the form of a first power feed (76), and A second power converter (48) having a first DC terminal (32) connected to the second transmission conduit (22), a second DC terminal (34) connected to the return conduit (24), and at least one AC terminal (36A, 36B, 36C) electrically connected to a second variable power source (50), the second power converter (48) further having a second converter controller (54) programmed to control transfer of a second power feed (56) from the second variable power source (50) into the second transmission conduit (22) in the form of a second power feed (86), During operation of the bipolar power transmission device (10) under normal conditions, the first power converter (30) and the associated first variable power source (38) operate independently of the second power converter (48) and the associated second variable power source (50), whereby the first power feed (46) into the first transmission conduit (20) and the second power feed (56) into the second transmission conduit (22) are independent of each other, and During operation of the bipolar power transmission device (10) in an abnormal condition when the return conduit (24) fails and a return current path cannot be provided, each converter controller (44, 54) is programmed to monitor the first power feed (76) in the first transmission conduit (20) and the second power feed (86) in the second transmission conduit (22), and if the first power feed (76) in the first transmission conduit (20) and the second power feed (86) in the second transmission conduit (22) are different from each other, at least one converter controller (44, 54) modifies the power feed from its corresponding power source (38, 50) to reduce the difference between the first power feed (76) and the second power feed (86).
  2. 2. The bipolar power transmission device (10) according to claim 1, wherein the converter controller (44, 54) that modifies the power feed (46, 56) from its corresponding power source (38, 50) to reduce the difference between the first power feed (76) and the second power feed (86) is programmed to modify its power feed (46, 56) such that the power feeds (76, 86) in each transmission pipe (20, 22) match each other.
  3. 3. The bipolar power transmission device (10) according to claim 1 or 2, wherein each power source (38, 50) comprises at least one power controller that adjusts the power feed (46, 56) provided by the power source (38, 50) according to an operating frequency of the power source (38, 50) and its associated power converter (30, 48), and each converter controller (44, 54) is programmed to modify the power feed (46, 56) from its corresponding power source (38, 50) by modifying the operating frequency at which its corresponding power converter (30, 48) operates.
  4. 4. The bipolar power transmission device (10) according to claim 1 or 2, wherein the first converter controller (44) is programmed to reduce the first power feed (46) from the first variable power source (38) if the first power feed (76) in the first transmission pipe (20) is greater than the second power feed (86) in the second transmission pipe (22), and the second converter controller (54) is programmed to reduce the second power feed (56) from the second variable power source (50) if the second power feed (86) in the second transmission pipe (22) is greater than the first power feed (76) in the first transmission pipe (20).
  5. 5. The bipolar power transmission device (10) according to claim 1 or 2, wherein each converter controller (44, 54) is programmed to monitor the first power feed (76) in the first transmission pipe (20) and the second power feed in the second transmission pipe (22) by: directly or Indirectly via a corresponding power feed (46, 56) from an associated first variable power source (38) or second variable power source (50).
  6. 6. The bipolar power transfer apparatus (10) of claim 1 or 2, wherein the first converter station (12) is an offshore converter station (16) and at least one of the first variable power source (38) and the second variable power source (50) is an offshore wind farm (40, 52).
  7. 7. The bipolar power transfer apparatus (10) of claim 6 wherein the or each off-shore wind farm (40, 52) comprises a plurality of wind turbines (42), each wind turbine (42) of the plurality of wind turbines (42) comprising a power controller in the form of a separate turbine power controller that adjusts the power provided by a separate wind turbine (42) in accordance with the operating frequency of the wind turbine (42).
  8. 8. The bipolar power transfer apparatus of claim 7, wherein at least one wind turbine (42) includes a power dissipation element selectively operable by a corresponding turbine power controller to temporarily dissipate the power feed provided by the individual wind turbines (42).
  9. 9. The bipolar power transmission device (10) according to claim 1 or 2, further comprising a first excess power absorber (58) electrically connected between the first transmission conduit (20) and the return conduit (24), and a second excess power absorber (60) electrically connected between the second transmission conduit (22) and the return conduit (24), a corresponding one of the excess power absorbers (58, 60) being used to absorb power from one or the other of the first transmission conduit (20) and the second transmission conduit (22) while a change in power feed (76, 86) in the first transmission conduit (20) or the second transmission conduit (22) is occurring.
  10. 10. The bipolar power transmission device (10) according to claim 1 or 2, further comprising a second converter station (14) interconnected with the first converter station (12) by the first (20) and second (22) transmission pipes and the return pipe (24).
  11. 11. A method of operating a bipolar power transmission device (10), the bipolar power transmission device (10) comprising a first converter station (12) located, in use, away from a second converter station (14), and first (20) and second (22) transmission and return (24) conduits for interconnecting, in use, the first converter station (12) with the second converter station (14) and thereby allowing the first converter station (12) to transmit power to the second converter station (14), The first converter station (12) comprises: A first power converter (30) having a first DC terminal (32) connected to the first transmission conduit (20), a second DC terminal (34) connected to the return conduit (24), and at least one AC terminal (36A, 36B, 36C) electrically connected to a first variable power source (38), the first power converter (30) further having a first controller (44) programmed to control transfer of a first power feed (46) from the first variable power source (38) into the first transmission conduit (20) in the form of a first power feed (76), and A second power converter (48) having a first DC terminal (32) connected to the second transmission conduit (22), a second DC terminal (34) connected to the return conduit (24), and at least one AC terminal (36A, 36B, 36C) electrically connected to a second variable power source (50), the second power converter (48) further having a second controller (54) programmed to control transfer of a second power feed (56) from the second variable power source (50) into the second transmission conduit (22) in the form of a second power feed (86), The method comprises the following steps: Operating the bipolar power transmission device (10) under normal conditions by operating the first power converter (30) and the associated first variable power source (38) independently of the second power converter (48) and the associated second variable power source (50), whereby the first power feed (46) into the first transmission pipe (20) and the second power feed (56) into the second transmission pipe (22) are independent of each other, and The bipolar power transmission device (10) is operated during an abnormal condition when the return conduit (24) fails and a return current path cannot be provided by having each controller (44, 54) monitor the first power feed (76) in the first transmission conduit (20) and the second power feed (86) in the second transmission conduit (22), and if the first power feed (76) in the first transmission conduit (20) and the second power feed (86) into the second transmission conduit (22) are different from each other, having at least one controller (44, 54) modify the power feeds (46, 56) from its corresponding power source (38, 50) to reduce the difference between the first power feed (76) and the second power feed (86).

Description

Improvements in or relating to bipolar power transmission schemes Technical Field The present invention relates to a bipolar power transmission scheme and to a method of operating such a scheme. Background In High Voltage Direct Current (HVDC) power transmission networks, AC power is typically converted to DC power for transmission via overhead lines, subsea cables and/or underground cables. This conversion eliminates the need to compensate for the AC capacitive loading effects imposed by the power transmission medium (i.e., transmission line or cable) and reduces the cost per kilometer of line and/or cable and thus becomes cost effective when power needs to be transmitted over long distances. DC power may also be transmitted directly from the offshore wind farm to the onshore AC power transmission network. Conversion between DC power and AC power is used where it is necessary to interconnect the DC and AC networks. In any such power transmission network, a converter (i.e., a power converter) is required at each interface between AC and DC power to achieve the required conversion from AC to DC or from DC to AC. The selection of the most suitable HVDC power transmission scheme within the HVDC power transmission network varies depending on the application and scheme characteristics. One type of such scheme is a bipolar power transmission scheme. Disclosure of Invention According to a first aspect of the present invention there is provided a bipolar power transfer scheme comprising a first converter station located in use remote from a second converter station, and first and second transfer and return pipes (return pipes) for interconnecting the first and second converter stations in use, and thereby allowing the first converter station to transfer power to the second converter station, The first converter station comprises: A first power converter having a first DC terminal connected to the first transmission conduit, a second DC terminal connected to the return conduit, and at least one AC terminal electrically connected to a first variable power source, the first power converter further having a first converter controller programmed to control transfer of a first power feed (infeed) from the first power source into the first transmission conduit in the form of a first power feed, and A second power converter having a first DC terminal connected to the second transmission conduit, a second DC terminal connected to the return conduit, and at least one AC terminal electrically connected to a second variable power source, the second power converter further having a second converter controller programmed to control the transfer of a second power feed from the second power source into the second transmission conduit in the form of a second power feed, During operation of the bipolar power transmission scheme under normal conditions, the first power converter and the associated first power source operate independently of the second power converter and the associated second power source, whereby the first power feed into the first transmission conduit and the second power feed into the second transmission conduit are independent of each other, and During operation of the bipolar power transmission scheme in an abnormal situation when the return conduit fails and fails to provide a return current path, each converter controller is programmed to monitor the first power feed in the first transmission conduit and the second power feed in the second transmission conduit, and if the first power feed in the first transmission conduit and the second power feed in the second transmission conduit are different from each other, at least one converter controller modifies the power feeds from its corresponding power source to reduce the difference between the first power feed and the second power feed. In use, when the return conduit fails and a return current path cannot be provided, any imbalance (i.e. difference) in the respective power feeds in each of the first and second transfer conduits causes a current imbalance between the first and second transfer conduits that instead must be transferred through ground without an active return conduit. Such transport is undesirable, particularly because of concerns about adverse effects on, for example, marine organisms and corrosion of pipes in the earth. There is at least one converter controller that modifies the power feed from its corresponding power source to reduce the difference in power carried by each transmission conduit (i.e., reduce the difference between the first power feed and the second power feed), thereby advantageously reducing the magnitude of unbalanced currents that would otherwise have to flow through ground. This in turn advantageously reduces the adverse effects of such current flow while allowing each power source to continue to provide power and thereby avoid a very undesirable interruption of the power transfer from the first converter station to the sec