Fault control method and system for a direct current transmission system

Abstract

The application discloses a fault control method and system of a direct current power transmission system. The method comprises the following steps: when a receiving end converter station detects that a fault occurs on an alternating current side of the receiving end converter station, sending an opening instruction to an energy consumption device, and sending a closing instruction to the energy consumption device when detecting that the occurred fault is eliminated, the opening instruction being used for opening and maintaining the operation of the energy consumption device, the energy consumption device being used for consuming at least part of direct current when operating, the at least part of direct current being at least part of direct current received by the receiving end converter station, and the closing instruction being used for closing the energy consumption device; when a sending end converter station detects that electrical parameter information of a sending end converter valve arranged in the sending end converter station meets a set fault condition, continuously reducing the power of the direct current transmitted to the receiving end converter station until the electrical parameter information meets a set maintenance condition, and then maintaining the power of the direct current transmitted to the receiving end converter station, so that the safety and economy of an extra-high voltage flexible direct current power transmission system can be improved.

Description

Technical Field

[0001] This application relates to the field of flexible DC transmission technology, and in particular to a fault control method and system for DC transmission systems. Background Technology

[0002] Currently, since the distance between the two ends of ultra-high voltage flexible direct current transmission technology is generally over 2000km, for ultra-long transmission distance ultra-high voltage flexible direct current systems, when a transient fault occurs in the AC system at the receiving end, it can easily lead to a significant surplus power at the receiving end. In particular, when inter-station communication is lost, the sending-end converter station cannot obtain timely information about the operating status of the receiving-end converter station, which may lead to a more serious power surplus problem, and may trigger protection blocking or even shutdown of the ultra-high voltage flexible direct current transmission system, causing serious economic losses and safety hazards. Summary of the Invention

[0003] To address the aforementioned technical problems, this application proposes a fault control method and system for DC transmission systems, which can improve the safety and economy of ultra-high voltage flexible DC transmission systems.

[0004] This application provides a fault control method for a DC transmission system, the DC transmission system including a receiving-end converter station, a sending-end converter station, and energy dissipation devices, the method including:

[0005] When the receiving-end converter station detects a fault on its AC side, it sends an activation command to the energy-consuming device, and when it detects that the fault has been cleared, it sends a deactivation command to the energy-consuming device. The activation command is used to activate the energy-consuming device and maintain its operation. The energy-consuming device is used to consume at least a portion of the DC power during operation. The at least a portion of the DC power is at least a portion of the DC power received by the receiving-end converter station. The deactivation command is used to deactivate the energy-consuming device.

[0006] When the sending-end converter station detects that the electrical parameters of its internal sending-end converter valve meet the set fault conditions, it continuously reduces the power of the DC power supplied to the receiving-end converter station until the electrical parameters meet the set maintenance conditions, and then maintains the power of the DC power supplied to the receiving-end converter station.

[0007] Optionally, the method further includes:

[0008] After the sending-end converter station detects that the electrical parameter information meets the set maintenance conditions, when it detects that the electrical parameter information meets the set fault clearance conditions, it increases the power of the DC power supplied to the receiving-end converter station until it increases to the target power value.

[0009] Optionally, the electrical parameter information includes the inter-terminal voltage of the feed-end converter valve;

[0010] The set fault conditions include: the inter-terminal voltage exceeds a set threshold and the inter-terminal voltage increases with time;

[0011] The set maintenance condition includes: the inter-terminal voltage exceeds the set threshold and the inter-terminal voltage does not increase with time;

[0012] The set fault clearance conditions include: the inter-terminal voltage is lower than the set threshold.

[0013] Optionally, the continuous reduction of the DC power supplied to the receiving-end converter station includes:

[0014] The power of the DC power supplied to the receiving-end converter station is continuously reduced at a first rate, wherein the first rate is constant.

[0015] Optionally, increasing the power of the DC power supplied to the receiving-end converter station includes:

[0016] According to the second rate, the power of the DC power supplied to the receiving-end converter station is increased, wherein the rate of the second rate is constant.

[0017] Optionally, the target power value includes:

[0018] Preset rated power value;

[0019] or,

[0020] The power value of DC power supplied to the receiving-end converter station at the moment before the electrical parameter information is detected to meet the set fault conditions.

[0021] Optionally, the receiving-end converter station includes N valve groups, each of which is connected to the same AC system.

[0022] M valve groups are connected in series between the positive pole line and the neutral line of the receiving-end converter station, where N≥2 and M<N;

[0023] (NM) valve groups are connected in series between the neutral line and the negative pole line of the receiving-end converter station, and the (NM) valve groups are all valve groups other than the M valve groups among the N valve groups;

[0024] The positive and negative poles of the receiving-end converter station are electrically connected to the two ends of the sending-end converter station, respectively.

[0025] Optionally, the energy-consuming device includes:

[0026] The first DC power consumption module is electrically connected at both ends to the positive pole and the neutral pole of the receiving-end converter station, respectively; and,

[0027] The second DC power consumption module is electrically connected at both ends to the neutral line and the negative line of the receiving-end converter station, respectively.

[0028] Optionally, the N valve groups are as follows:

[0029] The first valve group has its first end electrically connected to the positive pole of the receiving-end converter station, and its second end electrically connected to the AC system.

[0030] The second valve group has its first end electrically connected to the third end of the first valve group, its second end electrically connected to the AC system, and its third end electrically connected to the neutral line of the receiving-end converter station.

[0031] The third valve group has its first end electrically connected to the neutral line of the receiving-end converter station and its second end electrically connected to the AC system; and...

[0032] The fourth valve group has its first end electrically connected to the third end of the third valve group, its second end electrically connected to the AC system, and its third end electrically connected to the negative pole of the receiving-end converter station.

[0033] Optionally, each of the N valve groups adopts a full-half-bridge hybrid modular structure.

[0034] This application embodiment also provides a fault control system for a DC transmission system, the DC transmission system including a receiving-end converter station, a sending-end converter station, and an energy consumption device;

[0035] The receiving-end converter station is configured to send an activation command to the energy-consuming device when a fault is detected on its AC side, and to send a shutdown command to the energy-consuming device when the fault is detected to be cleared. The activation command is used to activate the energy-consuming device and maintain its operation. The energy-consuming device is used to consume at least a portion of the DC power during operation. The at least a portion of the DC power is at least a portion of the DC power received by the receiving-end converter station. The shutdown command is used to shut down the energy-consuming device.

[0036] The sending-end converter station is configured to continuously reduce the power of the DC power supplied to the receiving-end converter station when it detects that the electrical parameter information of its internal sending-end converter valve meets the set fault conditions, until it detects that the electrical parameter information meets the set maintenance conditions, and then maintains the power of the DC power supplied to the receiving-end converter station.

[0037] Optionally, the sending-end converter station is further configured to, after detecting that the electrical parameter information meets the set maintenance conditions, increase the power of the DC power supplied to the receiving-end converter station when detecting that the electrical parameter information meets the set fault clearance conditions, until it increases to the target power value.

[0038] Optionally, the electrical parameter information includes the inter-terminal voltage of the feed-end converter valve;

[0039] The set fault conditions include: the inter-terminal voltage exceeds a set threshold and the inter-terminal voltage increases with time;

[0040] The set maintenance condition includes: the inter-terminal voltage exceeds the set threshold and the inter-terminal voltage does not increase with time;

[0041] The set fault clearance conditions include: the inter-terminal voltage is lower than the set threshold.

[0042] Optionally, the continuous reduction of the DC power supplied to the receiving-end converter station includes:

[0043] The power of the DC power supplied to the receiving-end converter station is continuously reduced at a first rate, wherein the first rate is constant.

[0044] Optionally, increasing the power of the DC power supplied to the receiving-end converter station includes:

[0045] According to the second rate, the power of the DC power supplied to the receiving-end converter station is increased, wherein the rate of the second rate is constant.

[0046] Optionally, the target power value includes:

[0047] Preset rated power value;

[0048] or,

[0049] The power value of DC power supplied to the receiving-end converter station at the moment before the electrical parameter information is detected to meet the set fault conditions.

[0050] Optionally, the receiving-end converter station includes N valve groups, each of which is connected to the same AC system.

[0051] M valve groups are connected in series between the positive pole line and the neutral line of the receiving-end converter station, where N≥2 and M<N;

[0052] (NM) valve groups are connected in series between the neutral line and the negative pole line of the receiving-end converter station, and the (NM) valve groups are all valve groups other than the M valve groups among the N valve groups;

[0053] The positive and negative poles of the receiving-end converter station are electrically connected to the two ends of the sending-end converter station, respectively.

[0054] Optionally, the energy-consuming device includes:

[0055] The first DC power consumption module is electrically connected at both ends to the positive pole and the neutral pole of the receiving-end converter station, respectively; and,

[0056] The second DC power consumption module is electrically connected at both ends to the neutral line and the negative line of the receiving-end converter station, respectively.

[0057] Optionally, the N valve groups are as follows:

[0058] The first valve group has its first end electrically connected to the positive pole of the receiving-end converter station, and its second end electrically connected to the AC system.

[0059] The second valve group has its first end electrically connected to the third end of the first valve group, its second end electrically connected to the AC system, and its third end electrically connected to the neutral line of the receiving-end converter station.

[0060] The third valve group has its first end electrically connected to the neutral line of the receiving-end converter station and its second end electrically connected to the AC system; and...

[0061] The fourth valve group has its first end electrically connected to the third end of the third valve group, its second end electrically connected to the AC system, and its third end electrically connected to the negative pole of the receiving-end converter station.

[0062] Optionally, each of the N valve groups adopts a full-half-bridge hybrid modular structure.

[0063] In summary, the embodiments of this application have at least the following beneficial effects:

[0064] According to the embodiments of this application, the DC transmission system includes a receiving-end converter station, a sending-end converter station, and an energy-consuming device. The method includes: when the receiving-end converter station detects a fault on its AC side, it sends an activation command to the energy-consuming device; and when it detects that the fault has been cleared, it sends a deactivation command to the energy-consuming device. The activation command is used to activate the energy-consuming device and maintain its operation. The energy-consuming device consumes at least a portion of the DC power during operation, and the at least a portion of the DC power received by the receiving-end converter station is at least a portion of the DC power received by the receiving-end converter station. The deactivation command is used to deactivate the energy-consuming device. When the sending-end converter station detects that the electrical parameters of its internal sending-end converter valve meet a set fault condition, it continuously reduces the power of the DC power supplied to the receiving-end converter station until the electrical parameters meet a set maintenance condition, and then maintains the power of the DC power supplied to the receiving-end converter station. This improves the safety and economy of the UHV flexible DC transmission system. Attached Figure Description

[0065] Figure 1 This is a flowchart illustrating the fault control method for a DC transmission system provided in an embodiment of this application.

[0066] Figure 2 This is a schematic diagram of the structure of the ultra-high voltage flexible DC transmission system provided in the embodiments of this application;

[0067] Figure 3 This is a schematic diagram of the electrical parameter information on the DC pole line during a fault, provided in an embodiment of this application.

[0068] Figure 4 This is a schematic diagram of the maximum voltage of the receiving-end converter valve submodule during a fault, provided in an embodiment of this application. Detailed Implementation

[0069] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0070] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more. In the description of this application, the term "comprising" and its variations are open-ended, meaning "including but not limited to." The term "based on" means "at least partially based on." The term "according to" means "at least partially according to." The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments."

[0071] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0072] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this application is for the purpose of describing specific embodiments only and is not intended to limit the application. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0073] See Figure 1 This document illustrates a flowchart of a fault control method for a DC transmission system according to an embodiment of this application. The DC transmission system includes a receiving-end converter station, a sending-end converter station, and an energy-consuming device. The sending-end converter station transmits DC power to the receiving-end converter station. The energy-consuming device is electrically connected to the receiving-end converter station and is disabled by default. The method includes steps S101-S102, as detailed below:

[0074] S101, when the receiving-end converter station detects a fault on its AC side, it sends an activation command to the energy-consuming device, and when it detects that the fault has been cleared, it sends a deactivation command to the energy-consuming device, wherein the activation command is used to activate the energy-consuming device and maintain its operation, the energy-consuming device is used to consume at least a portion of the DC power during operation, the at least a portion of the DC power is at least a portion of the DC power received by the receiving-end converter station, and the deactivation command is used to deactivate the energy-consuming device;

[0075] S102, when the sending-end converter station detects that the electrical parameter information of its internal sending-end converter valve meets the set fault conditions, it continuously reduces the power of the DC power supplied to the receiving-end converter station until it detects that the electrical parameter information meets the set maintenance conditions, and then maintains the power of the DC power supplied to the receiving-end converter station.

[0076] It is understood that in this embodiment, the sending-end converter station and the receiving-end converter station need to detect different information to determine whether a fault has occurred, and they detect each other independently. Therefore, it is not necessary to rely on the communication interaction between the sending-end converter station and the receiving-end converter station to inform each other whether a fault has occurred, which is more effective in dealing with the serious power surplus problem caused by the loss of inter-station communication.

[0077] For example, the DC transmission system in this embodiment can be a typical ±800kV / 8GW UHV flexible DC transmission system, with the following main circuit parameters: submodule rated operating voltage 2.0kV, submodule capacitor 24mF, bridge arm reactor 25mH, and current-limiting reactor 300mH. The DC transmission line is 2400km long, using 6-split conductors, with a line resistance of approximately 10Ω. The UHV flexible DC transmission system adopts a true bipolar connection scheme, with each pole consisting of two cascaded valve groups, each valve group having a DC voltage of 400kV. The valve groups use a hybrid full-bridge and half-bridge module, with a full-bridge ratio of 60%. The AC side of the sending-end converter station is in grid-connected mode, with the sending end employing a constant active power and constant reactive power control strategy, and the receiving end employing a constant DC voltage and constant reactive power control strategy.

[0078] In an optional implementation, the method further includes:

[0079] After the sending-end converter station detects that the electrical parameter information meets the set maintenance conditions, when it detects that the electrical parameter information meets the set fault clearance conditions, it increases the power of the DC power supplied to the receiving-end converter station until it increases to the target power value.

[0080] In one optional implementation, the electrical parameter information includes the inter-terminal voltage of the feed-end converter valve;

[0081] The set fault conditions include: the inter-terminal voltage exceeds a set threshold and the inter-terminal voltage increases with time;

[0082] The set maintenance condition includes: the inter-terminal voltage exceeds the set threshold and the inter-terminal voltage does not increase with time;

[0083] The set fault clearance conditions include: the inter-terminal voltage is lower than the set threshold.

[0084] For example, the threshold value set in this embodiment can be 1.05 pu.

[0085] In one optional implementation, the continuous reduction of the DC power supplied to the receiving-end converter station includes:

[0086] The power of the DC power supplied to the receiving-end converter station is continuously reduced at a first rate, wherein the first rate is constant.

[0087] For example, the first rate in this embodiment can be 50 MW / ms.

[0088] In one optional implementation, increasing the power of the DC power supplied to the receiving-end converter station includes:

[0089] According to the second rate, the power of the DC power supplied to the receiving-end converter station is increased, wherein the rate of the second rate is constant.

[0090] For example, the second rate in this embodiment can be 50 MW / ms.

[0091] In summary, according to the above embodiments, when the sending-end converter station detects that the inter-terminal voltage of the sending-end converter valve exceeds 1.05 pu, it immediately reduces the DC power transmitted to the receiving-end converter station at a rate of 50 MW / ms until the inter-terminal voltage of the sending-end converter valve no longer increases (i.e., reaches its maximum value); when the inter-terminal voltage of the sending-end converter valve begins to decrease from its maximum value, the DC power transmitted from the sending-end converter station to the receiving-end converter station remains unchanged; when the inter-terminal voltage of the sending-end converter valve decreases to below 1.05 pu, the sending-end converter station immediately increases the DC power transmitted to the receiving-end converter station at a rate of 50 MW / ms until the DC power reaches its rated value or a previous value, thereby enabling the receiving-end converter station and the sending-end converter station to exchange information without relying on inter-station communication.

[0092] In one optional implementation, the target power value includes:

[0093] Preset rated power value;

[0094] or,

[0095] The power value of DC power supplied to the receiving-end converter station at the moment before the electrical parameter information is detected to meet the set fault conditions.

[0096] In one optional implementation, the receiving-end converter station includes N valve groups, each of which is connected to the same AC system, wherein...

[0097] M valve groups are connected in series between the positive pole line and the neutral line of the receiving-end converter station, where N≥2 and M<N;

[0098] (NM) valve groups are connected in series between the neutral line and the negative pole line of the receiving-end converter station, and the (NM) valve groups are all valve groups other than the M valve groups among the N valve groups;

[0099] The positive and negative poles of the receiving-end converter station are electrically connected to the two ends of the sending-end converter station, respectively.

[0100] In one alternative implementation, see [link to implementation details]. Figure 2 The energy-consuming device includes:

[0101] The first DC power consumption module 111 is electrically connected at both ends to the positive pole and the neutral pole of the receiving-end converter station, respectively; and,

[0102] The second DC power consumption module 112 is electrically connected at both ends to the neutral line and the negative line of the receiving-end converter station, respectively.

[0103] In some cases, a total DC power consumption device with a capacity of 4GW can be configured on the DC side of the receiving-end converter station, wherein:

[0104] The first DC power consumption module has a capacity of 2GW and is configured between the positive pole and the neutral pole.

[0105] The second DC power consumption module has a capacity of 2GW and is configured between the negative pole and the neutral pole.

[0106] In this way, the capacity of the DC energy-consuming device is only 50% of the rated capacity of the DC transmission system. The aforementioned DC energy-consuming device can be constructed using various technical approaches such as centralized, distributed, or hybrid.

[0107] In one optional implementation, the N valve groups are as follows:

[0108] The first valve group 121 has its first end electrically connected to the positive pole of the receiving-end converter station, and its second end electrically connected to the AC system 131;

[0109] The second valve group 122 has its first end electrically connected to the third end of the first valve group, its second end electrically connected to the AC system 131, and its third end electrically connected to the neutral line of the receiving-end converter station.

[0110] The third valve group 123 has its first end electrically connected to the neutral line of the receiving-end converter station, and its second end electrically connected to the AC system 131; and,

[0111] The fourth valve group 124 has its first end electrically connected to the third end of the third valve group, its second end electrically connected to the AC system 131, and its third end electrically connected to the negative pole of the receiving-end converter station.

[0112] In one alternative implementation, each of the N valve groups adopts a full-half-bridge hybrid modular structure.

[0113] This application embodiment also provides a fault control system for a DC transmission system, the DC transmission system including a receiving-end converter station, a sending-end converter station, and an energy consumption device;

[0114] The receiving-end converter station is configured to send an activation command to the energy-consuming device when a fault is detected on its AC side, and to send a shutdown command to the energy-consuming device when the fault is detected to be cleared. The activation command is used to activate the energy-consuming device and maintain its operation. The energy-consuming device is used to consume at least a portion of the DC power during operation. The at least a portion of the DC power is at least a portion of the DC power received by the receiving-end converter station. The shutdown command is used to shut down the energy-consuming device.

[0115] The sending-end converter station is configured to continuously reduce the power of the DC power supplied to the receiving-end converter station when it detects that the electrical parameter information of its internal sending-end converter valve meets the set fault conditions, until it detects that the electrical parameter information meets the set maintenance conditions, and then maintains the power of the DC power supplied to the receiving-end converter station.

[0116] In an optional implementation, the sending-end converter station is further configured to, after detecting that the electrical parameter information meets the set maintenance conditions, increase the power of the DC power supplied to the receiving-end converter station when detecting that the electrical parameter information meets the set fault clearance conditions, until it increases to the target power value.

[0117] In one optional implementation, the electrical parameter information includes the inter-terminal voltage of the feed-end converter valve;

[0118] The set fault conditions include: the inter-terminal voltage exceeds a set threshold and the inter-terminal voltage increases with time;

[0119] The set maintenance condition includes: the inter-terminal voltage exceeds the set threshold and the inter-terminal voltage does not increase with time;

[0120] The set fault clearance conditions include: the inter-terminal voltage is lower than the set threshold.

[0121] In one optional implementation, the continuous reduction of the DC power supplied to the receiving-end converter station includes:

[0122] The power of the DC power supplied to the receiving-end converter station is continuously reduced at a first rate, wherein the first rate is constant.

[0123] In one optional implementation, increasing the power of the DC power supplied to the receiving-end converter station includes:

[0124] According to the second rate, the power of the DC power supplied to the receiving-end converter station is increased, wherein the rate of the second rate is constant.

[0125] In one optional implementation, the target power value includes:

[0126] Preset rated power value;

[0127] or,

[0128] The power value of DC power supplied to the receiving-end converter station at the moment before the electrical parameter information is detected to meet the set fault conditions.

[0129] In one optional implementation, the receiving-end converter station includes N valve groups, each of which is connected to the same AC system, wherein...

[0130] M valve groups are connected in series between the positive pole line and the neutral line of the receiving-end converter station, where N≥2 and M<N;

[0131] (NM) valve groups are connected in series between the neutral line and the negative pole line of the receiving-end converter station, and the (NM) valve groups are all valve groups other than the M valve groups among the N valve groups;

[0132] The positive and negative poles of the receiving-end converter station are electrically connected to the two ends of the sending-end converter station, respectively.

[0133] In one alternative implementation, see [link to implementation details]. Figure 2 The energy-consuming device includes:

[0134] The first DC power consumption module 111 is electrically connected at both ends to the positive pole and the neutral pole of the receiving-end converter station, respectively; and,

[0135] The second DC power consumption module 112 is electrically connected at both ends to the neutral line and the negative line of the receiving-end converter station, respectively.

[0136] In one alternative implementation, see [link to implementation details]. Figure 2 The N valve groups are as follows:

[0137] The first valve group 121 has its first end electrically connected to the positive pole of the receiving-end converter station, and its second end electrically connected to the AC system 131;

[0138] The second valve group 122 has its first end electrically connected to the third end of the first valve group, its second end electrically connected to the AC system 131, and its third end electrically connected to the neutral line of the receiving-end converter station.

[0139] The third valve group 123 has its first end electrically connected to the neutral line of the receiving-end converter station, and its second end electrically connected to the AC system 131; and,

[0140] The fourth valve group 124 has its first end electrically connected to the third end of the third valve group, its second end electrically connected to the AC system 131, and its third end electrically connected to the negative pole of the receiving-end converter station.

[0141] In one alternative implementation, each of the N valve groups adopts a full-half-bridge hybrid modular structure.

[0142] The following is a specific embodiment.

[0143] Based on a typical ±800kV / 8GW UHV flexible DC transmission system, its main circuit parameters are as follows: submodule rated operating voltage 2.0kV, submodule capacitor 24mF, bridge arm reactor 25mH, and current-limiting reactor 300mH. The DC transmission line is 2400km long, using 6-split conductors, with a line resistance of approximately 10Ω. The UHV flexible DC transmission system adopts a true bipolar connection scheme, with each pole consisting of two cascaded valve groups, each valve group having a DC voltage of 400kV. The valve groups use a hybrid full-bridge and half-bridge module, with a full-bridge ratio of 60%. The AC side of the sending-end converter station is in grid-connected mode, with the sending end employing a constant active power and constant reactive power control strategy, and the receiving end employing a constant DC voltage and constant reactive power control strategy. A 4GW DC energy dissipation device is configured on the DC side of the receiving-end converter station, with 2GW configured between the positive pole and the neutral line, and the other 2GW configured between the negative pole and the neutral line. Figure 2 As shown.

[0144] Before the fault occurred, the UHV flexible DC transmission system was operating at full capacity. At a certain moment (e.g.) Figure 3 As shown in the figure, at 5.1s, U_P1, I_P1, and P_P1 represent the voltage, current, and power on the positive transmission line, respectively, and U_P2, I_P2, and P_P2 represent the voltage, current, and power on the negative transmission line, respectively. A three-phase metallic ground fault occurs on the AC side of the receiving-end converter transformer. Approximately 10ms after the fault, the receiving-end converter station detects the fault and immediately activates the DC power dissipation device. Approximately 20ms after the fault, the inter-terminal voltage of the sending-end converter valve (i.e., the voltage difference between U_P1 and U_P2) exceeds 1.05pu. The sending-end converter station immediately reduces the magnitude of the DC current (i.e., I_P1 or I_P2; it should be understood that I_P1 = I_P2 in the same circuit) and the DC power (i.e., the difference between P_P1 and P_P2) transmitted to the receiving-end converter station at a rate of 50MW / ms. Approximately 80ms after the fault, the inter-terminal voltage of the sending-end converter valve reaches its maximum value and gradually decreases from there, while the DC power output from the sending-end converter station to the receiving-end converter station remains constant. Approximately 100ms after the fault, the AC side fault at the receiving-end converter station is cleared. Approximately 110ms after the fault, after detecting the clearing of the AC side fault, the receiving-end converter station disconnects the DC power dissipation device. Approximately 130ms after the fault, the inter-terminal voltage of the sending-end converter valve drops below 1.05 pu, and the sending-end converter station immediately increases the DC power output to the receiving-end converter station at a rate of 50 MW / ms until the DC power reaches 1 pu. Figure 3 As shown, approximately 350ms after the fault, the voltage, current, and power on the DC line basically returned to their pre-fault operating state. Figure 4The maximum voltage of the receiving-end station converter valve submodule during fault ride-through is a three-phase voltage comprising: Va1, Va3, Vb1, Vb3, Vc1, and Vc3, which are, in order, the maximum voltages of the submodules of the upper and lower arms of phase a, phase b, phase c, and phase c respectively. All of these voltages do not exceed 2.8kV, which is lower than the overvoltage protection setting of the submodule. Therefore, the energy consumption device configuration scheme and AC-side fault ride-through method for UHV flexible DC transmission systems with inter-station communication loss provided by this invention can achieve system fault ride-through after a fault occurs on the AC side of the receiving-end converter transformer.

[0145] In summary, the embodiments of this application have at least the following beneficial effects:

[0146] According to an embodiment of this application, the DC transmission system includes a receiving-end converter station, a sending-end converter station, and an energy-consuming device. The sending-end converter station is used to transmit DC power to the receiving-end converter station. The energy-consuming device is electrically connected to the receiving-end converter station and is disabled by default. The method includes: when the receiving-end converter station detects a fault on its AC side, it sends an activation command to the energy-consuming device; and when it detects that the fault has been cleared, it sends a deactivation command to the energy-consuming device. The activation command is used to activate the energy-consuming device and maintain its operation. The energy-consuming device is used to... During operation, at least a portion of the DC power is consumed, which is at least a portion of the DC power received by the receiving-end converter station. The shutdown command is used to shut down the energy-consuming device. When the sending-end converter station detects that the electrical parameter information of its internal sending-end converter valve meets the set fault conditions, it continuously reduces the power of the DC power supplied to the receiving-end converter station until it detects that the electrical parameter information meets the set maintenance conditions, and then maintains the power of the DC power supplied to the receiving-end converter station, thereby improving the safety and economy of the UHV flexible DC transmission system.

[0147] Through the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary hardware platforms, or it can be implemented entirely by hardware. Based on this understanding, all or part of the technical solutions of this application that contribute to the background technology can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of this application.

[0148] The above description is the preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A fault control method for a DC transmission system, characterized in that, The DC transmission system includes a receiving-end converter station, a sending-end converter station, and energy-consuming devices. If inter-station communication between the receiving-end converter station and the sending-end converter station is lost, the method includes: When the receiving-end converter station detects a fault on its AC side, it sends an activation command to the energy-consuming device, and when it detects that the fault has been cleared, it sends a deactivation command to the energy-consuming device. The activation command is used to activate the energy-consuming device and maintain its operation. The energy-consuming device is used to consume at least a portion of the DC power during operation. The at least a portion of the DC power is at least a portion of the DC power received by the receiving-end converter station. The deactivation command is used to deactivate the energy-consuming device. When the sending-end converter station detects that the electrical parameter information of its internal sending-end converter valve meets the set fault conditions, it continuously reduces the power of the DC power supplied to the receiving-end converter station at a constant first rate until the electrical parameter information meets the set maintenance conditions, and then maintains the power of the DC power supplied to the receiving-end converter station. After the sending-end converter station detects that the electrical parameter information meets the set maintenance conditions, when it detects that the electrical parameter information meets the set fault clearance conditions, it increases the power of the DC power supplied to the receiving-end converter station at a constant second rate until it increases to the target power value. The target power value includes: Preset rated power value; or, The power value of DC power supplied to the receiving-end converter station at the moment before the electrical parameter information is detected to meet the set fault conditions.

2. The method as described in claim 1, characterized in that, The electrical parameter information includes the inter-terminal voltage of the feed-end converter valve; The set fault conditions include: the inter-terminal voltage exceeds a set threshold and the inter-terminal voltage increases with time; The set maintenance condition includes: the inter-terminal voltage exceeds the set threshold and the inter-terminal voltage does not increase with time; The set fault clearance conditions include: the inter-terminal voltage is lower than the set threshold.

3. The method according to any one of claims 1-2, characterized in that, The receiving-end converter station includes N valve groups, each of which is connected to the same AC system. M valve groups are connected in series between the positive pole line and the neutral line of the receiving-end converter station, where N≥2 and M<N; (NM) valve groups are connected in series between the neutral line and the negative pole line of the receiving-end converter station, and the (NM) valve groups are all valve groups other than the M valve groups among the N valve groups; The positive and negative poles of the receiving-end converter station are electrically connected to the two ends of the sending-end converter station, respectively.

4. The method as described in claim 3, characterized in that, The energy-consuming device includes: The first DC power consumption module is electrically connected at both ends to the positive pole and the neutral pole of the receiving-end converter station, respectively; and, The second DC power consumption module is electrically connected at both ends to the neutral line and the negative line of the receiving-end converter station, respectively.

5. The method as described in claim 3, characterized in that, The N valve groups are as follows: The first valve group has its first end electrically connected to the positive pole of the receiving-end converter station, and its second end electrically connected to the AC system. The second valve group has its first end electrically connected to the third end of the first valve group, its second end electrically connected to the AC system, and its third end electrically connected to the neutral line of the receiving-end converter station. The third valve group has its first end electrically connected to the neutral line of the receiving-end converter station and its second end electrically connected to the AC system; and... The fourth valve group has its first end electrically connected to the third end of the third valve group, its second end electrically connected to the AC system, and its third end electrically connected to the negative pole of the receiving-end converter station.

6. The method as described in claim 3, characterized in that, Each of the N valve groups adopts a full-semi-bridge hybrid modular structure.

7. A fault control system for a DC transmission system, characterized in that, The DC transmission system includes a receiving-end converter station, a sending-end converter station, and energy-consuming devices; inter-station communication between the receiving-end converter station and the sending-end converter station is lost. The receiving-end converter station is configured to send an activation command to the energy-consuming device when a fault is detected on its AC side, and to send a shutdown command to the energy-consuming device when the fault is detected to be cleared. The activation command is used to activate the energy-consuming device and maintain its operation. The energy-consuming device is used to consume at least a portion of the DC power during operation. The at least a portion of the DC power is at least a portion of the DC power received by the receiving-end converter station. The shutdown command is used to shut down the energy-consuming device. When the sending-end converter station detects that the electrical parameter information of its internal sending-end converter valve meets the set fault conditions, it continuously reduces the power of the DC power supplied to the receiving-end converter station at a constant first rate until the electrical parameter information meets the set maintenance conditions, and then maintains the power of the DC power supplied to the receiving-end converter station. After the sending-end converter station detects that the electrical parameter information meets the set maintenance conditions, when it detects that the electrical parameter information meets the set fault clearance conditions, it increases the power of the DC power supplied to the receiving-end converter station at a constant second rate until it increases to the target power value. The target power value includes: Preset rated power value; or, The power value of DC power supplied to the receiving-end converter station at the moment before the electrical parameter information is detected to meet the set fault conditions.

8. The system as described in claim 7, characterized in that, The electrical parameter information includes the inter-terminal voltage of the feed-end converter valve; The set fault conditions include: the inter-terminal voltage exceeds a set threshold and the inter-terminal voltage increases with time; The set maintenance condition includes: the inter-terminal voltage exceeds the set threshold and the inter-terminal voltage does not increase with time; The set fault clearance conditions include: the inter-terminal voltage is lower than the set threshold.

9. The system according to any one of claims 7-8, characterized in that, The receiving-end converter station includes N valve groups, each of which is connected to the same AC system. M valve groups are connected in series between the positive pole line and the neutral line of the receiving-end converter station, where N≥2 and M<N; (NM) valve groups are connected in series between the neutral line and the negative pole line of the receiving-end converter station, and the (NM) valve groups are all valve groups other than the M valve groups among the N valve groups; The positive and negative poles of the receiving-end converter station are electrically connected to the two ends of the sending-end converter station, respectively.

10. The system as described in claim 9, characterized in that, The energy-consuming device includes: The first DC power consumption module is electrically connected at both ends to the positive pole and the neutral pole of the receiving-end converter station, respectively; and, The second DC power consumption module is electrically connected at both ends to the neutral line and the negative line of the receiving-end converter station, respectively.

11. The system as described in claim 9, characterized in that, The N valve groups are as follows: The first valve group has its first end electrically connected to the positive pole of the receiving-end converter station, and its second end electrically connected to the AC system. The second valve group has its first end electrically connected to the third end of the first valve group, its second end electrically connected to the AC system, and its third end electrically connected to the neutral line of the receiving-end converter station. The third valve group has its first end electrically connected to the neutral line of the receiving-end converter station and its second end electrically connected to the AC system; and... The fourth valve group has its first end electrically connected to the third end of the third valve group, its second end electrically connected to the AC system, and its third end electrically connected to the negative pole of the receiving-end converter station.

12. The system as described in claim 9, characterized in that, Each of the N valve groups adopts a full-semi-bridge hybrid modular structure.

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