Power supply system and power supply method combining multi-terminal flexible direct current transmission system and alternating current power grid

Abstract

The present invention relates to the field of joint power supply technology, and specifically discloses a power supply system and a power supply method of a multi-terminal flexible direct current transmission system and an alternating current power grid, wherein the power supply system comprises a land main grid system, a first passive grid system, a second passive grid system, a first circuit breaker, a first alternating current channel, a second alternating current channel, a first converter and a second converter station. The power supply system and the power supply method provided by the present invention utilize the automatic switching function of the alternating current power grid to optimize the coordination between the flexible direct current transmission system and the alternating current power grid, and can still maintain reliable power supply of one main and one backup during a power outage of an alternating current channel, thereby reducing the risk of a power outage of the passive grid caused by a component failure and improving the reliability of the power supply of the passive grid.

Description

Technical Field

[0001] The present invention relates to the technical field of combined power supply, and in particular to a power supply system and a power supply method combining a multi-terminal flexible direct current transmission system and an alternating current power grid. Background Art

[0002] Flexible DC transmission technology is a new type of transmission technology based on self-shutdown devices and a new generation of high-voltage DC transmission technology. Compared with traditional high-voltage DC transmission, flexible DC transmission has all the advantages of conventional DC, and also has many advantages such as fast power flow reversal, fast recovery after faults, black start, and no commutation failure problems, and avoids problems such as large harmonics and the need for reactive power support. Although the development and promotion of flexible DC technology is very rapid, the AC power grid will continue to exist. If the two are to coexist for a long time, they will inevitably face the problem of how to cooperate with the current mainstream AC power grid.

[0003] At present, the working process of the flexible DC transmission system is as follows: a status detection device is set in each AC substation to monitor the active power and switch position information of the relevant AC components in real time, and the detection results are reported to the flexible DC converter station; the flexible DC converter station automatically identifies the AC channel status according to the switch position information of the AC components sent by each AC substation; once the AC channel status changes, the flexible DC transmission system will automatically switch the operation mode to cooperate with the operation of the AC power grid.

[0004] For a power system where a multi-terminal flexible DC transmission system and two or more AC channels are jointly responsible for the transmission of electric energy from a passive power grid (such as a wind power station, a photovoltaic power station, a load side, etc.), this coordination mode of automatically switching the operation mode by the flexible DC converter station will reduce the reliability of the entire power system for the following reasons: When one of the AC channels is out of service, the power system will switch to the multi-terminal flexible DC transmission system and the other AC channel to jointly transmit electric energy. Once the only remaining AC channel fails and trips, the operation mode of the flexible DC transmission system will switch from "AC and DC parallel operation" to "pure DC operation". There is a risk of switching failure in this switching process. If the operation mode switching fails, the flexible DC transmission system will also trip, and the passive power grid will lose pressure across the entire network. Summary of the invention

[0005] One object of the present invention is to provide a power supply system and a power supply method combining a multi-terminal flexible direct current transmission system and an alternating current power grid, which can effectively improve the power supply reliability of the power supply system combining a multi-terminal flexible direct current transmission system and an alternating current power grid, and effectively prevent the entire network from losing voltage.

[0006] To achieve the above objectives, on the one hand, the present invention provides a power supply system combining a multi-terminal flexible direct current transmission system and an alternating current grid, comprising:

[0007] A land main grid system, the land main grid system comprising a first main grid AC substation and a second main grid AC substation that are electrically connected;

[0008] a first passive power grid system, the first passive power grid system comprising a first passive AC substation for connecting to a first load;

[0009] a second passive power grid system, the second passive power grid system comprising a second passive AC substation for connection to a second load;

[0010] a first circuit breaker, wherein the first passive AC substation is connected to the second passive AC substation through the first circuit breaker;

[0011] a first AC channel, the first passive AC substation is connected to the first main grid AC substation through the first AC channel, and the first AC channel includes a second circuit breaker;

[0012] a second AC channel, the second passive AC substation is connected to the second main grid AC substation via the second AC channel, and the second AC channel includes a third circuit breaker;

[0013] a first converter station, wherein the first converter station is electrically connected to the second main grid AC substation;

[0014] A second converter station, wherein the second converter station is electrically connected to the first passive AC substation.

[0015] Preferably, it also includes:

[0016] Several third converter stations;

[0017] A busbar, wherein the third converter station is electrically connected to the first converter station via the busbar.

[0018] Preferably, it further comprises: a DC circuit breaker, and the third converter station is electrically connected to the busbar via the DC circuit breaker.

[0019] Preferably, the second converter station is electrically connected to the first converter station through the busbar.

[0020] On the other hand, a power supply method is provided, which is applicable to any of the above-mentioned power supply systems combining a multi-terminal flexible direct current transmission system and an alternating current grid. When the first alternating current channel is out of power for some reason, the power supply method includes a power outage operation and a power restoration operation.

[0021] The power outage operation includes:

[0022] Convert the multi-terminal flexible DC transmission system from a multi-terminal operation mode to a dual-terminal operation mode;

[0023] Confirm that the operation settings of the backup automatic switching device of the second passive AC substation are normal;

[0024] Setting a target value of "fixed active power" for the second converter station;

[0025] operating the first passive power grid system and the second passive power grid system in parallel;

[0026] Switch the second communication channel to standby mode;

[0027] Adjust the target value of the "fixed active power" of the second converter station;

[0028] Switch the first communication channel to maintenance status;

[0029] The power restoration operation includes:

[0030] Restore the first communication channel to operation;

[0031] Put the second AC channel back into operation;

[0032] Put the "power flow automatic control" soft pressure plate into use at the second converter station;

[0033] enabling the first passive power grid system and the second passive power grid system to operate separately;

[0034] Convert the multi-terminal flexible DC transmission system from a two-terminal operation mode to a multi-terminal operation mode.

[0035] Preferably, the making the first passive power grid system and the second passive power grid system operate in parallel comprises:

[0036] Closing the first circuit breaker to enable the first passive power grid system and the second passive power grid to operate in parallel;

[0037] Confirm that the "automatic power flow control" soft pressure plate of the second-side converter station has been exited.

[0038] Preferably, the step of switching the second communication channel to a standby state includes:

[0039] Disconnect the third circuit breaker;

[0040] Confirm that the second passive AC substation backup automatic transfer device connected to the backup second AC channel is charging normally.

[0041] Preferably, the step of switching the first communication channel to a maintenance state includes:

[0042] Disconnect the second circuit breaker;

[0043] Confirm that the second converter station has switched from "AC / DC parallel operation" to "pure DC operation";

[0044] Confirm that the operation settings of the backup automatic switching device of the second passive AC substation are normal;

[0045] Switch the first AC channel to maintenance status.

[0046] Preferably, resuming operation of the first communication channel comprises:

[0047] Switching the first communication channel to an operating state;

[0048] Confirm that the second converter station has switched from "pure DC operation" to "AC / DC parallel operation".

[0049] Preferably, the step of making the first passive power grid system and the second passive power grid system operate separately comprises:

[0050] Disconnect the first circuit breaker;

[0051] Confirm that the backup automatic transfer device of the second passive AC substation is charging normally.

[0052] The beneficial effects of the present invention are: providing a power supply system and a power supply method combining a multi-terminal flexible DC transmission system and an AC power grid, utilizing the automatic backup function of the AC power grid to optimize the coordination between the flexible DC transmission system and the AC power grid, and maintaining reliable power supply of one main and one backup during a power outage of an AC channel, reducing the risk of a passive power grid power outage caused by a component failure, and improving the reliability of the passive power grid power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0054] Figure 1 A structural block diagram of a power supply system combining a multi-terminal flexible direct current transmission system and an alternating current grid provided in an embodiment.

[0055] In the figure:

[0056] 1. Land main grid system; 101. First main grid AC substation; 102. Second main grid AC substation;

[0057] 2. A first passive power grid system; 201. A first passive AC substation;

[0058] 3. Second passive power grid system; 301. Second passive AC substation

[0059] 4. The first converter station;

[0060] 5. The second converter station;

[0061] 6. The third converter station;

[0062] 7. First circuit breaker;

[0063] 8. first AC channel; 801. second circuit breaker;

[0064] 9. Second AC channel; 901. Third circuit breaker;

[0065] 10. Busbar;

[0066] 11. DC circuit breaker. DETAILED DESCRIPTION

[0067] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] In the description of the present invention, it is to be understood that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally disposed component. When a component is considered to be "disposed on" another component, it may be directly disposed on the other component or there may be a centrally disposed component.

[0069] In addition, terms such as "long", "short", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention. They do not indicate or imply that the device or component referred to must have this specific direction or operate with a specific direction structure, and should not be understood as a limitation of the present invention.

[0070] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0071] This embodiment provides a power supply system and power supply method combining a multi-terminal flexible direct current transmission system and an alternating current power grid, which can effectively improve the power supply reliability of the power supply system combining a multi-terminal flexible direct current transmission system and an alternating current power grid, and effectively prevent the entire network from losing voltage.

[0072] See also Figure 1 The power supply system combining a multi-terminal flexible direct current transmission system and an alternating current power grid includes a land main grid system 1, a first passive grid system 2, a second passive grid system 3, a first circuit breaker 7, a first alternating current channel 8, a second alternating current channel 9, a first converter station 5 and a second converter station 5.

[0073] The land main grid system 1 includes an electrically connected first main grid AC substation 101 and a second main grid AC substation 102; the first passive grid system 2 includes a first passive AC substation 201 for connecting to a first load; the second passive grid system 3 includes a second passive AC substation 301 for connecting to a second load; the first passive AC substation 201 is electrically connected to the second passive AC substation 301 through the first circuit breaker 7; the first passive AC substation 201 is electrically connected to the first main grid AC substation 101 through the first AC channel 8, and the first AC channel 8 includes a second circuit breaker 801; the second passive AC substation 301 is electrically connected to the second main grid AC substation 102 through the second AC channel 9, and the second AC channel 9 includes a third circuit breaker 901; the first converter station 4 is electrically connected to the second main grid AC substation 102; the second converter station 5 is electrically connected to the first passive AC substation 201. Preferably, both the first passive AC substation 201 and the second passive AC substation 301 are connected to a wind farm.

[0074] The power supply system further includes a plurality of third converter stations 6 and a busbar 10. The third converter stations 6 are electrically connected to the first converter station 4 through the busbar 10. The second converter station 5 is electrically connected to the first converter station 4 through the busbar 10.

[0075] The power supply system further includes a DC circuit breaker 11 , and the third converter station 6 is electrically connected to the busbar 10 via the DC circuit breaker 11 .

[0076] The power supply system provided in this embodiment uses a power supply method. When the first AC channel 8 is powered off for some reason, the power supply method includes a power off operation and a power restoration operation.

[0077] Specifically, the main ideas of the power supply method are as follows:

[0078] When an AC channel is out of power for some reason, multiple passive power grids of the multi-terminal flexible DC power supply system are connected in parallel (if the passive power grids are already connected in parallel, skip this step), and another available AC channel is disconnected as a backup line. The dual-terminal operation mode of the multi-terminal flexible DC transmission system (that is, only two ends are in operation) transmits power to the merged passive power grid alone.

[0079] When the first AC channel 8 is out of power, if the multi-terminal flexible DC power supply system fails and trips, the backup automatic switch of the second passive AC substation 301 will close the backup line, and the passive power grid will be powered by the backup AC channel. When the second AC channel 9 is out of power, if the flexible DC system fails and trips, the backup automatic switch of the first passive AC substation 201 will close the backup line, and the passive power grid will be powered by the backup AC channel. During the power outage of one AC channel, reliable power supply with one main and one backup can still be maintained. The use of this strategy can improve the reliability of power supply of the passive power grid.

[0080] The following is a detailed description taking the power outage of the first AC channel 8 as an example, and the coordination strategy of the second AC channel 9 is similar.

[0081] S10: The power outage operation includes:

[0082] S101: Convert the multi-terminal flexible DC transmission system from a multi-terminal operation mode to a dual-terminal operation mode;

[0083] Specifically, S101 can be divided into the following two situations:

[0084] ① When there is a DC circuit breaker 11 on the DC side of the third converter station 6, the DC circuit breaker 11 is operated to disconnect the third converter station 6 from the busbar 10, thereby realizing the online exit of the third converter station 6;

[0085] ② There is no DC circuit breaker 11 on the DC side of the third converter station 6. In the actual operation environment, many converter stations are not equipped with DC circuit breakers 11. At this time, the flexible DC transmission system can be shut down and then restarted to the double-end operation mode.

[0086] S102: confirming that the operation setting of the backup automatic switching device of the second passive AC substation 301 is normal;

[0087] Specifically, the inspection includes:

[0088] ①Confirm that the standby automatic start-up device is operating normally;

[0089] ②Confirm that the standby automatic transfer device has not activated the "superior load shedding and blocking standby automatic transfer function". If activated, it must be exited.

[0090] S103: Setting a target value of “fixed active power” for the second converter station 5;

[0091] Specifically, "automatic power flow control" is an active power control strategy to effectively utilize the advantages of the flexible DC transmission system in transmitting intermittent new energy. Its principle is that the flexible DC transmission system transmits as much active power as possible to reduce the active power transmitted by the AC line. In subsequent operations, the first circuit breaker 7 will be closed, and the first passive power grid system 2 and the second passive power grid system 3 will be operated in parallel. The "automatic power flow control" soft pressure plate of the passive grid side converter station will automatically exit, and the active power control strategy will be converted to "fixed active power control". The active power will be transmitted at the set value and will no longer be controlled by the system itself. Reasonable setting of the "fixed active power" target value can reduce the impact of active power in subsequent operations.

[0092] S104: operating the first passive power grid system 2 and the second passive power grid system 3 in parallel;

[0093] Specifically, the S104 includes:

[0094] ① Close the first circuit breaker 7 to make the first passive power grid system 2 and the second passive power grid operate in parallel;

[0095] ② Confirm that the "automatic power flow control" soft pressure plate of the second-side converter station has been exited.

[0096] S105: switching the second communication channel 9 to a standby state;

[0097] Specifically, the S105 includes:

[0098] ① Disconnect the third circuit breaker 901;

[0099] ② Confirm that the backup automatic switching device of the second passive AC substation 301 connected to the backup second AC channel 9 is charging normally.

[0100] S106: adjusting the target value of the “fixed active power” of the second converter station 5;

[0101] Specifically, adjust the "fixed active power" target value of the second converter station 5, and try to control the power of the AC channel to be powered off to "0". Controlling the power of the AC channel to be powered off to "0" can reduce the impact of the flexible DC system switching from "AC / DC parallel operation" to "pure DC operation".

[0102] S107: switching the first AC channel 8 to a maintenance state;

[0103] Specifically, the S107 includes:

[0104] ① Disconnect the second circuit breaker 801;

[0105] ② Confirm that the second converter station 5 has switched from "AC / DC parallel operation" to "pure DC operation";

[0106] ③ Confirm that the operation settings of the backup automatic switching device of the second passive AC substation 301 are normal;

[0107] ④ Switch the first AC channel 8 to the maintenance state.

[0108] S20: The power restoration operation includes:

[0109] S201: resuming operation of the first AC channel 8;

[0110] Specifically, the S201 includes:

[0111] ① Switch the first AC channel 8 to the operating state;

[0112] ② Confirm that the second converter station 5 has switched from "pure DC operation" to "AC / DC parallel operation".

[0113] S202: resuming operation of the second AC channel 9;

[0114] Specifically, the third circuit breaker 901 is closed to restore the second AC channel 9 .

[0115] S203: Putting into operation the "automatic power flow control" soft pressure plate of the second converter station 5;

[0116] S204: operating the first passive power grid system 2 and the second passive power grid system 3 separately;

[0117] Specifically, the S204 includes:

[0118] ① Disconnect the first circuit breaker 7;

[0119] ② Confirm that the backup automatic switching device of the second passive AC substation 301 is charging normally.

[0120] S205: Convert the multi-terminal flexible direct current transmission system from a two-terminal operation mode to a multi-terminal operation mode.

[0121] Specifically, S205 can be divided into the following two situations:

[0122] ① When there is a DC circuit breaker 11 on the DC side of the third converter station 6, the DC circuit breaker 11 is operated to connect the third converter station 6 with the busbar 10, thereby realizing the online parallel connection of the third converter station 6;

[0123] ② There is no DC circuit breaker 11 on the DC side of the third converter station 6. In the actual operation environment, many converter stations are not equipped with DC circuit breakers 11. At this time, the flexible DC transmission system can be shut down and then restarted to the multi-terminal operation mode.

[0124] Specifically, the operation is completed and the multi-terminal flexible direct current power supply system is restored to the following state: Figure 1 The daily operation shown.

[0125] The power supply system provided in this embodiment is suitable for a power system in which a multi-terminal flexible direct current transmission system and two or more AC channels are used to transmit electric energy from a passive power grid (such as a wind power station, a photovoltaic power station, a load side, etc.). When an AC line in such a power grid fails, the operation mode of the AC power grid and the flexible direct current power supply system is adjusted, and the backup automatic switching function of the AC power grid is used to improve the reliability of the power grid.

[0126] The power supply system and power supply method provided in this embodiment utilize the automatic backup function of the AC power grid to optimize the coordination between the flexible DC transmission system and the AC power grid. During a power outage in an AC channel, reliable power supply of one main and one backup can still be maintained, reducing the risk of passive power grid power outage caused by failure of a certain component and improving the reliability of passive power grid power supply.

[0127] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A power supply method, applicable to a power supply system combining a multi-terminal flexible direct current transmission system and an alternating current power grid, characterized in that: The power supply system combining the multi-terminal flexible direct current transmission system and the AC power grid includes: A land main grid system (1), the land main grid system (1) comprising a first main grid AC substation (101) and a second main grid AC substation (102) which are electrically connected; A first passive power grid system (2), the first passive power grid system (2) comprising a first passive AC substation (201) for connecting to a first load; A second passive power grid system (3), the second passive power grid system (3) comprising a second passive AC substation (301) for connecting to a second load; A first circuit breaker (7), wherein the first passive AC substation (201) is connected to the second passive AC substation (301) via the first circuit breaker (7); A first AC channel (8), the first passive AC substation (201) being connected to the first main grid AC substation (101) via the first AC channel (8), the first AC channel (8) comprising a second circuit breaker (801); a second AC channel (9), the second passive AC substation (301) being connected to the second main grid AC substation (102) via the second AC channel (9), the second AC channel (9) comprising a third circuit breaker (901); A first converter station (4), the first converter station (4) being electrically connected to the second main grid AC substation (102); A second converter station (5), the second converter station (5) being electrically connected to the first passive AC substation (201); When the first AC channel (8) is powered off for some reason, the power supply method includes a power off operation and a power restoration operation; The power outage operation includes: Convert the multi-terminal flexible DC transmission system from a multi-terminal operation mode to a dual-terminal operation mode; Confirm that the operation settings of the backup automatic switching device of the second passive AC substation (301) are normal; Setting a target value of "fixed active power" for the second converter station (5); Allowing the first passive power grid system (2) and the second passive power grid system (3) to operate in parallel; Switching the second communication channel (9) to a standby state; Adjusting the target value of the "fixed active power" of the second converter station (5); Switching the first AC channel (8) to a maintenance state; The power restoration operation includes: Resuming operation of the first AC channel (8); Resuming operation of the second AC channel (9); Put the "automatic power flow control" soft pressure plate of the second converter station (5) into operation; The first passive power grid system (2) and the second passive power grid system (3) are operated separately; Convert the multi-terminal flexible DC transmission system from a two-terminal operation mode to a multi-terminal operation mode.

2. The power supply method according to claim 1, characterized in that: Also includes: a plurality of third converter stations (6); A busbar (10), wherein the third converter station (6) is electrically connected to the first converter station (4) via the busbar (10).

3. The power supply method according to claim 2, characterized in that: Also includes: A DC circuit breaker (11), wherein the third converter station (6) is electrically connected to the busbar (10) via the DC circuit breaker (11).

4. The power supply method according to claim 3, characterized in that: The second converter station (5) is electrically connected to the first converter station (4) via the busbar (10).

5. The power supply method according to claim 1, characterized in that: The method of making the first passive power grid system (2) and the second passive power grid system (3) operate in parallel comprises: Closing the first circuit breaker (7) to allow the first passive power grid system (2) and the second passive power grid to operate in parallel; Confirm that the "automatic power flow control" soft pressure plate of the second-side converter station has been exited.

6. The power supply method according to claim 5, characterized in that: The step of switching the second communication channel (9) to a standby state comprises: Disconnect the third circuit breaker (901); Confirm that the backup automatic switching device of the second passive AC substation (301) connected to the backup second AC channel (9) is charging normally.

7. The power supply method according to claim 6, characterized in that: The step of switching the first communication channel (8) to a maintenance state comprises: Disconnect the second circuit breaker (801); Confirm that the second converter station (5) has switched from "AC / DC parallel operation" to "pure DC operation"; Confirm that the operation settings of the backup automatic switching device of the second passive AC substation (301) are normal; Switch the first AC channel (8) to the maintenance state.

8. The power supply method according to claim 7, characterized in that: The step of restoring the first AC channel (8) to operation comprises: Switching the first communication channel (8) to an operating state; Confirm that the second converter station (5) has switched from "pure DC operation" to "AC / DC parallel operation".

9. The power supply method according to claim 8, characterized in that: The step of operating the first passive power grid system (2) and the second passive power grid system (3) separately comprises: Disconnecting the first circuit breaker (7); Confirm that the backup automatic switching device of the second passive AC substation (301) is charging normally.

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