Direct-current fault clearing method and device for multi-terminal flexible direct-current sending-out system

Abstract

The invention discloses a direct-current fault clearing method and device for a multi-terminal flexible direct-current sending-out system, a direct-current circuit breaker can quickly act to cut off a fault current within several milliseconds, the system can only isolate a fault line, and the system keeps running in a non-fault area; the grid-side converter station, the load-side converter station and the alternating-current energy consumption device are matched to perform direct-current voltage reconstruction and power recovery, and the load-side converter station can be quickly restarted after a fault is cleared, so that the power supply reliability is improved; the technical problems that a direct current fault clearing mode of an existing multi-terminal flexible direct current sending-out system can cause system shutdown and cannot meet the direct current fault rapid isolation requirement are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of DC power transmission systems, and in particular, to a method and device for clearing DC faults in a multi-terminal flexible DC transmission system. Background Art

[0002] Traditional AC power grids are difficult to adapt to scenarios with high penetration of new energy, and flexible DC power transmission systems are required to achieve flexible and efficient multi-point access and power regulation. A multi-terminal flexible DC power transmission system can connect multiple new energy power stations and load centers, realizing multi-source input and multi-drop output, and improving the flexibility and reliability of the power grid.

[0003] When a DC system fails, the capacitor discharges, causing the current to rise sharply within a few milliseconds, far exceeding that of an AC system, and causing serious impacts on equipment. In a multi-terminal flexible DC power transmission system, a single-point fault may quickly spread to the entire network through the DC line, threatening the safety of the power grid system. Traditional DC fault clearing schemes are to block the fault current by blocking the converter or rely on the AC-side circuit breaker to isolate the fault. However, blocking the fault current by blocking the converter will cause the system to shut down and the restart time is long, affecting the power supply continuity of the power grid system; the method of relying on the AC-side circuit breaker to isolate the fault cannot meet the rapid isolation requirements of DC faults. Therefore, how to quickly clear DC faults without shutting down the multi-terminal flexible DC transmission system is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0004] The present invention provides a method and device for clearing DC faults in a multi-terminal flexible DC transmission system, which are used to solve the technical problems that the existing methods for clearing DC faults in a multi-terminal flexible DC transmission system will cause the system to shut down and cannot meet the rapid isolation requirements of DC faults.

[0005] In view of this, in the first aspect of the present invention, a method for clearing DC faults in a multi-terminal flexible DC transmission system is provided. The method for clearing DC faults in the multi-terminal flexible DC transmission system is applied to a symmetric monopolar multi-terminal flexible DC transmission system. An AC energy-consuming device with the same rated power as the grid-side converter station is configured on the AC side of the symmetric monopolar multi-terminal flexible DC transmission system, and DC circuit breakers are configured at both the positive and negative ends of the load-side converter station. The method for clearing DC faults in the multi-terminal flexible DC transmission system includes:

[0006] The control host of the load-side converter station receives the protection action signal reported by the load-side converter station when a DC fault is detected;

[0007] The control host of the load-side converter station permanently blocks the load-side converter station that reports the protection action signal, and issues an order to cut off the fault current by the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal;

[0008] The control host of the load-side converter station sends a signal to temporarily block all converter stations except the load-side converter station that reports the protection action signal, and notifies the grid-side converter station to issue an order to fully activate the AC energy-consuming device;

[0009] When the grid-side converter station detects that the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal have reliably cut off the fault current, and the load-side converter station that reports the protection action signal has been blocked, it notifies the load-side converter stations that adopt the fixed DC voltage strategy among all the load-side converter stations to establish the DC voltage at a preset rate after a preset time delay;

[0010] After the grid-side converter station detects that the DC voltage has been established, it exits the AC energy-consuming device in preset time-delay groups, so that the fixed DC power of all load-side converter stations recovers power in preset time-delay groups.

[0011] Optionally, the preset time delay is 10 ms.

[0012] Optionally, the preset rate is 400 kV / 20 ms.

[0013] Optionally, the preset time-delay group is 0.1 p.u. / 100 ms.

[0014] Optionally, the grid-side converter station and the load-side converter station adopt a half-bridge sub-module topology, and the switching device uses IGBT.

[0015] The second aspect of the present invention provides a DC fault clearing device for a multi-terminal flexible DC transmission system. The DC fault clearing device for the multi-terminal flexible DC transmission system is applied to a symmetric monopolar multi-terminal flexible DC transmission system. The AC side of the symmetric monopolar multi-terminal flexible DC transmission system is configured with an AC energy-consuming device with the same rated power as the grid-side converter station. DC circuit breakers are configured at both the positive and negative ends of the load-side converter station. The DC fault clearing device for the multi-terminal flexible DC transmission system includes a load-side converter station control host and the grid-side converter station;

[0016] The load-side converter station control host is used to receive the protection action signal reported by the load-side converter station when detecting a DC fault;

[0017] The load-side converter station control host is further used to permanently block the load-side converter station that reports the protection action signal, and issue an order to cut off the fault current of the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal;

[0018] The control host of the load-side converter station is also used to send a signal to lock all converter stations except the load-side converter station that reports the protection action signal temporarily, and notify the grid-side converter station to issue an order to fully turn on the AC energy-consuming device;

[0019] The grid-side converter station is used to, when detecting that the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal have reliably cut off the fault current and the load-side converter station that reports the protection action signal has been locked, notify the load-side converter stations that adopt the constant DC voltage strategy among all the load-side converter stations to establish the DC voltage at a preset rate after a preset time delay;

[0020] The grid-side converter station is also used to, after detecting that the DC voltage has been established, withdraw the AC energy-consuming device in preset time-delay groups, so that the constant DC power of all load-side converter stations recovers power in preset time-delay groups.

[0021] Optionally, the preset time delay is 10 ms.

[0022] Optionally, the preset rate is 400 kV / 20 ms.

[0023] Optionally, the preset time-delay group is 0.1 p.u. / 100 ms.

[0024] Optionally, the grid-side converter station and the load-side converter station adopt a half-bridge sub-module topology, and the switching device adopts IGBT.

[0025] It can be seen from the above technical solutions that the DC fault clearing method of the multi-terminal flexible DC transmission system provided by the present invention has the following advantages:

[0026] The DC fault clearing method for the multi-terminal flexible DC transmission system provided by the present invention, when a DC fault is detected at the load-side converter station, reports a protection action signal to the control host of the load-side converter station. The control host of the load-side converter station permanently locks the load-side converter station, and at the same time issues a command to cut off the fault current to the DC circuit breakers at both the positive and negative ends of the load-side converter station. At the same time, the remaining load-side converter stations are temporarily locked, and all grid-side AC energy-consuming devices are put into operation. When the grid-side converter station detects that the DC circuit breakers connected to both ends of the load-side converter station reporting the protection action signal have reliably cut off the fault current, and the load-side converter station reporting the protection action signal has been locked, after a preset time delay, it notifies the load-side converter stations adopting the fixed DC voltage strategy among all load-side converter stations to establish the DC voltage at a preset rate. After the grid-side converter station detects that the DC voltage has been established, it withdraws the AC energy-consuming devices in groups with a preset time delay, so that the fixed DC power of all load-side converter stations recovers in groups with a preset time delay. The DC circuit breaker can quickly operate to interrupt the fault current within milliseconds. The system can only isolate the fault line, and the non-fault area remains in operation. Cooperating with the grid-side converter station, the load-side converter station and the AC energy-consuming device for DC voltage reconstruction and power recovery, the load-side converter station can be quickly restarted after the fault is cleared, improving the power supply reliability, and solving the technical problems that the existing DC fault clearing method of the multi-terminal flexible DC transmission system will cause the system to shut down and cannot meet the requirements of rapid isolation of DC faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a schematic flowchart of a DC fault clearing method for a multi-terminal flexible DC transmission system provided in an embodiment of the present invention;

[0029] Figure 2 It is a schematic topological structure diagram of a symmetric monopolar four-terminal flexible DC system provided in an embodiment of the present invention;

[0030] Figure 3 It is a schematic structural diagram of a DC fault clearing device for a multi-terminal flexible DC transmission system provided in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] For ease of understanding, please refer to Figure 1 and Figure 2 , the present invention provides an embodiment of a method for clearing DC faults in a multi-terminal flexible DC transmission system. The method for clearing DC faults in a multi-terminal flexible DC transmission system is applied to a symmetric monopolar multi-terminal flexible DC transmission system. An AC energy-consuming device with the same rated power as the grid-side converter station is configured on the AC side of the symmetric monopolar multi-terminal flexible DC transmission system. DC circuit breakers are configured at both the positive and negative ends of the load-side converter station. The method for clearing DC faults in a multi-terminal flexible DC transmission system includes:

[0033] Step 101: The control host of the load-side converter station receives the protection action signal reported by the load-side converter station when a DC fault is detected.

[0034] Step 102: The control host of the load-side converter station permanently locks the load-side converter station that reports the protection action signal and issues an order to cut off the fault current for the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal.

[0035] Step 103: The control host of the load-side converter station sends a signal to temporarily lock all converter stations except the load-side converter station that reports the protection action signal, and notifies the grid-side converter station to issue an order to fully turn on the AC energy-consuming device.

[0036] Step 104: When the grid-side converter station detects that the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal have reliably cut off the fault current and the load-side converter station that reports the protection action signal has been locked, after a preset time delay, it notifies the load-side converter stations that adopt the fixed DC voltage strategy among all load-side converter stations to establish the DC voltage at a preset rate.

[0037] Step 105: After the grid-side converter station detects that the DC voltage has been established, it withdraws the AC energy-consuming device in groups with a preset time delay, so that the fixed DC power of all load-side converter stations is restored in groups with a preset time delay.

[0038] It should be noted that the method for clearing DC faults in the multi-terminal flexible DC transmission system provided in the embodiments of the present invention is applied to a symmetric monopolar multi-terminal flexible DC transmission system to Figure 2Taking the topology of the symmetric monopole four-terminal flexible DC system as an example, the AC side of the symmetric monopole multi-terminal flexible DC transmission system is equipped with an AC energy-consuming device with the same rated power as the grid-side converter station. DC circuit breakers are configured at both the positive and negative ends of the load-side converter station. The grid-side converter station and the load-side converter station adopt a half-bridge sub-module topology, and the switching devices use IGBTs (Insulated-Gate Bipolar Transistors). The AC grid of the grid-side converter station (i.e., Figure 2 Converter Station 1 in Figure 2 can be a 100% photovoltaic power station or a wind farm, and its AC side is equipped with an AC energy-consuming device with the same rated power as the grid-side converter station. The grid-side converter station is a rectifier station. The AC grids connected to the load-side converter stations (i.e., Figure 2 Converter Station 2, Converter Station 3, and Converter Station 4 in

[0039] are the load sides. DC circuit breakers (i.e., Figure 2 DC Circuit Breaker 1 and DC Circuit Breaker 2 in

[0039] are configured on the positive and negative connection lines of the load-side converter stations, and all load-side converter stations are inverter stations.

[0039] Taking the topology of Figure 2 as an example, the process of the DC fault clearing method for the multi-terminal flexible DC transmission system is as follows:

[0040] (1) If a DC fault that requires isolating the converter station is detected inside one of the converters of Converter Stations 2, 3, or 4, such as valve short circuit, valve grounding, arm current overcurrent, DC overvoltage, sub-module redundancy overlimit, etc., the DC protection of this converter station reports a protection action signal to the control host of this converter station.

[0041] (2) After receiving the protection action signal, the control host of the converter station where the DC fault occurs permanently locks the converter. At the same time, the control host issues commands to DC Circuit Breaker 1 and DC Circuit Breaker 2 of this station to cut off the fault current. Mechanical or hybrid DC circuit breakers can interrupt the fault current within a few milliseconds to avoid the locking of the converter station. Combining with the fast operation of the DC circuit breaker, the system can only isolate the faulty line, and the non-faulty area remains in operation.

[0042] (3) The control host of the converter station where the DC fault occurs sends a signal to the control systems of the other three stations, requesting the other three stations to temporarily lock the converter stations, and notifies Converter Station 1 to issue a command to fully turn on the AC energy-consuming device to consume the surplus power generated by the new energy power station.

[0043] (4) After Converter Station 1 detects that DC Circuit Breaker 1 and DC Circuit Breaker 2 of the converter station where the DC fault occurs have reliably cut off the fault current, and the converter where the DC fault occurs has been locked, after a 10 ms delay, it notifies the constant DC voltage converter station of the multi-terminal DC (such as Converter Station 3) to establish the DC voltage at a certain rate (such as 400 kV / 20 ms).

[0044] When Converter Station 1 detects that the DC voltage has been established, it exits the AC energy-consuming device in groups with a certain delay. For example, it exits 0.1 p.u. of the AC energy-consuming device every 100 ms, and the constant DC power of the corresponding multi-terminal DC also recovers at a rate of 0.1 p.u. / 100 ms.

[0045] Quickly isolating faults and restarting the system through DC circuit breakers can reduce power outage time and curtailment of new energy, and can support the grid connection of a high proportion of new energy and the networking of multi-terminal DC (such as the interconnection of offshore wind power clusters and desert photovoltaic bases), meeting the requirements of future power grids.

[0046] In the DC fault clearing method for a multi-terminal flexible DC transmission system provided by the present invention, when the load-side converter station detects a DC fault, it reports a protection action signal to the load-side converter station control host. The load-side converter station control host permanently locks the load-side converter station, and at the same time sends a command to cut off the fault current to the DC circuit breakers at both the positive and negative ends of the load-side converter station. At the same time, the other load-side converter stations are temporarily locked, and all the grid-side AC energy-consuming devices are put into operation. When the grid-side converter station detects that the DC circuit breakers connected to both ends of the load-side converter station that reported the protection action signal have reliably cut off the fault current, and the load-side converter station that reported the protection action signal has been locked, after a preset time delay, it notifies the load-side converter stations that adopt the constant DC voltage strategy among all the load-side converter stations to establish the DC voltage at a preset rate. After the grid-side converter station detects that the DC voltage has been established, it exits the AC energy-consuming device in groups with a preset delay, so that the constant DC power of all the load-side converter stations recovers in groups with a preset delay. The DC circuit breaker can quickly operate to cut off the fault current within a few milliseconds. The system can only isolate the faulty line, and the non-faulty area remains in operation. Cooperating with the grid-side converter station, the load-side converter station and the AC energy-consuming device for DC voltage reconstruction and power recovery, the load-side converter station can be quickly restarted after the fault is cleared, improving power supply reliability and solving the technical problems that the existing DC fault clearing method for a multi-terminal flexible DC transmission system will cause the system to shut down and cannot meet the requirement of rapid isolation of DC faults.

[0047] For ease of understanding, please refer to Figure 3 In this invention, an embodiment of a DC fault clearing device for a multi-terminal flexible DC transmission system is provided. This DC fault clearing device for a multi-terminal flexible DC transmission system is applied to a symmetric monopolar multi-terminal flexible DC transmission system. The AC side of the symmetric monopolar multi-terminal flexible DC transmission system is configured with AC energy-consuming devices with the same rated power as the grid-side converter station. DC circuit breakers are configured at both the positive and negative ends of the load-side converter station. The DC fault clearing device for a multi-terminal flexible DC transmission system includes a load-side converter station control host and a grid-side converter station;

[0048] The load-side converter station control host is used to receive the protection action signal reported by the load-side converter station when it detects a DC fault;

[0049] The control host of the load-side converter station is also used to permanently block the load-side converter station that reports the protection action signal, and issue an order to cut off the fault current by the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal;

[0050] The control host of the load-side converter station is also used to send a signal to temporarily block all converter stations except the load-side converter station that reports the protection action signal, and notify the grid-side converter station to issue an order to put all AC energy-consuming devices into operation;

[0051] The grid-side converter station is used to, when it detects that the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal have reliably cut off the fault current, and the load-side converter station that reports the protection action signal has been blocked, notify the load-side converter stations that adopt the fixed DC voltage strategy among all load-side converter stations to establish the DC voltage at a preset rate after a preset time delay;

[0052] The grid-side converter station is also used to, after detecting that the DC voltage has been established, withdraw the AC energy-consuming devices in preset time-delay groups, so that the fixed DC power of all load-side converter stations is restored in preset time-delay groups.

[0053] In one embodiment, the preset time delay is 10 ms.

[0054] In one embodiment, the preset rate is 400 kV / 20 ms.

[0055] In one embodiment, the preset time-delay group is 0.1 p.u. / 100 ms.

[0056] In one embodiment, the grid-side converter station and the load-side converter station adopt a half-bridge sub-module topology, and the switching device uses an IGBT.

[0057] Those skilled in the art can clearly understand that for the convenience and conciseness of description, the specific working processes of the above-described system, device, and unit can refer to the corresponding processes in the foregoing method embodiments, and will not be elaborated herein.

[0058] The above is the case. The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for clearing DC faults in a multi-terminal flexible DC transmission system, characterized in that, The DC fault clearing method of the multi-terminal flexible DC transmission system is applied to a symmetrical monopole multi-terminal flexible DC transmission system, wherein the AC side of the symmetrical monopole multi-terminal flexible DC transmission system is equipped with an AC energy consumption device with the same rated power as that of the grid-side converter station, and the positive and negative ends of the load-side converter station are both equipped with DC circuit breakers. The DC fault clearing method of the multi-terminal flexible DC transmission system comprises: The load-side converter station control host receives a protection action signal reported by the load-side converter station when a DC fault is detected; The load-side converter station control host permanently locks the load-side converter station that reports the protection action signal, and issues a command for the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal to cut off the fault current; The load-side converter station control host sends a signal to temporarily lock the converter station to all converter stations except the load-side converter station that reports the protection action signal, and notifies the grid-side converter station to send a command to put all AC energy-consuming devices into operation; When the grid-side converter station detects that the DC circuit breakers connected to both ends of the load-side converter station reporting the protection action signal have reliably cut off the fault current, and the load-side converter station reporting the protection action signal has been locked, the grid-side converter station notifies all load-side converter stations that adopt a fixed DC voltage strategy among the load-side converter stations to establish a DC voltage at a preset rate after a delay of a preset time; After detecting that the DC voltage has been established, the grid-side converter station exits the AC energy consumption device in a preset delay group, so that the fixed DC power of all load-side converter stations is restored in a preset delay group.

2. The DC fault clearing method for the multi-terminal flexible DC transmission system according to claim 1, characterized in that, The preset time length is 10ms.

3. The DC fault clearing method for the multi-terminal flexible DC transmission system according to claim 1, characterized in that The preset rate is 400 kV / 20 ms.

4. The DC fault clearing method for a multi-terminal flexible DC transmission system according to claim 1, characterized in that, The preset delay grouping is 0.1pu / 100ms.

5. The DC fault clearing method for the multi-terminal flexible DC transmission system according to claim 1, wherein The grid-side converter station and the load-side converter station adopt a half-bridge submodule topology, and the switching device adopts IGBT.

6. A DC fault clearing device for a multi-terminal flexible DC transmission system, characterized in that, The DC fault clearing device of the multi-terminal flexible DC transmission system is applied to a symmetrical monopole multi-terminal flexible DC transmission system. The AC side of the symmetrical monopole multi-terminal flexible DC transmission system is equipped with an AC energy consumption device with the same rated power as the grid-side converter station. Both the positive and negative ends of the load-side converter station are equipped with DC circuit breakers. The DC fault clearing device of the multi-terminal flexible DC transmission system includes a load-side converter station control host and the grid-side converter station. The load-side converter station control host is used to receive the protection action signal reported by the load-side converter station when a DC fault is detected; The load-side converter station control host is also used to permanently lock the load-side converter station that reports the protection action signal, and issue a command for the DC circuit breakers connected to both ends of the load-side converter station that reports the protection action signal to cut off the fault current; The load-side converter station control host is also used to send a signal to temporarily lock the converter station to all converter stations except the load-side converter station that reports the protection action signal, and notify the grid-side converter station to send a command to put all AC energy consumption devices into operation; The grid-side converter station is used to notify the load-side converter stations adopting the constant DC voltage strategy among all the load-side converter stations to establish the DC voltage at a preset rate after a preset time delay when it is detected that the DC circuit breakers connected to both ends of the load-side converter station reporting the protection action signal have reliably cut off the fault current and the load-side converter station reporting the protection action signal has been blocked. The grid-side converter station is further used to withdraw the AC energy-consuming devices in preset time-delay groups after detecting that the DC voltage has been established, so that the constant DC power of all the load-side converter stations is restored in preset time-delay groups.

7. The DC fault clearing device for the multi-terminal flexible DC transmission system according to claim 6, characterized in that, The preset time delay is 10 ms.

8. The DC fault clearing device of the multi-terminal flexible DC transmission system according to claim 6, characterized in that, The preset rate is 400 kV / 20 ms.

9. The DC fault clearing device for a multi-terminal flexible DC transmission system according to claim 6, characterized in that, The preset time-delay group is 0.1 p.u. / 100 ms.

10. The DC fault clearing device for the multi-terminal flexible DC transmission system according to claim 6, characterized in that, The grid-side converter station and the load-side converter station adopt a half-bridge sub-module topology, and the switching device uses an IGBT.

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