Energy consumption device and fault control method applicable to ultra-high voltage flexible direct current transmission system

Abstract

The present application discloses an energy consumption device and fault control method suitable for an ultra-high voltage flexible direct current transmission system. The device includes: a first direct current energy consumption module, whose two ends are respectively electrically connected to the positive pole line on the receiving end side and between the third end of the first valve group and the first end of the second valve group; a second direct current energy consumption module, whose two ends are respectively electrically connected to the neutral line on the receiving end side and between the third end of the first valve group and the first end of the second valve group; a third direct current energy consumption module, whose two ends are respectively electrically connected to the neutral line on the receiving end side and between the third end of the third valve group and the first end of the fourth valve group; and a fourth direct current energy consumption module, whose two ends are respectively electrically connected to the negative pole line on the receiving end side and between the third end of the third valve group and the first end of the fourth valve group. The device can improve the energy consumption efficiency of the direct current energy consumption device, thereby improving the overall economic efficiency of the ultra-high voltage flexible direct current transmission technology and improving system safety.

Description

Technical Field

[0001] The present application relates to the field of flexible direct current (DC) transmission technology, and in particular to an energy consumption device and a fault control method applicable to an ultra-high voltage flexible DC transmission system. Background Art

[0002] Currently, due to the high environmental requirements of wind and photovoltaic power generation, many large-scale wind and photovoltaic bases are located far from densely populated areas. In these situations, UHVDC Flexible transmission technology is often used as the primary solution for large-scale, long-distance transmission and consumption of renewable energy to densely populated areas. However, as the power capacity of UHVDC Flexible transmission projects increases, multiple high-capacity DC feeds tend to be concentrated in load centers located in densely populated areas. When high-capacity DC feeds into the AC system at the receiving end through a single point of connection, this can lead to localized power surges and DC fault outages, potentially impacting the AC grid at the receiving end. Furthermore, since the distance between the two ends of UHVDC Flexible transmission systems is generally over 2000 km, transient faults in the AC system at the receiving end can easily lead to significant excess power at the receiving end, potentially triggering protective trips or even shutting down the UHVDC Flexible transmission system, resulting in severe economic losses and safety hazards.

[0003] In related technologies, a DC energy dissipation device is typically placed directly between the positive and negative lines on the receiving end to reduce impact on the receiving end and consume excess power. However, placing the DC energy dissipation device directly between the positive and negative lines on the receiving end has low energy dissipation efficiency, resulting in high deployment costs and potential safety risks due to insufficient energy dissipation efficiency. Summary of the Invention

[0004] In order to solve the above technical problems, the embodiments of the present application propose an energy consumption device and a fault control method suitable for an ultra-high voltage flexible direct current transmission system, which can improve the energy consumption efficiency of the direct current energy consumption device to enhance the overall economy of the ultra-high voltage flexible direct current transmission technology and improve the system safety.

[0005] In a first aspect, an embodiment of the present application provides an energy consumption device applicable to an ultra-high voltage flexible direct current transmission system, wherein the ultra-high voltage flexible direct current transmission system has a receiving side, and the receiving side includes:

[0006] a first valve group, a first end of which is electrically connected to the positive electrode line on the receiving end side, and a second end of which is electrically connected to the first AC system;

[0007] a second valve group, a first end of which is electrically connected to the third end of the first valve group, a second end of which is electrically connected to the second AC system, and a third end of which is electrically connected to the neutral line on the receiving end side;

[0008] a third valve group, a first end of which is electrically connected to the neutral line on the receiving end side, and a second end of which is electrically connected to the second AC system; and

[0009] a fourth valve group, a first end electrically connected to the third end of the third valve group, a second end electrically connected to the first AC system, and a third end electrically connected to the negative electrode line on the receiving end side;

[0010] Wherein, the energy consumption device includes:

[0011] A first DC energy consumption module, two ends of which are electrically connected to the positive electrode line on the receiving end side, and between the third end of the first valve group and the first end of the second valve group;

[0012] A second DC energy consumption module, both ends of which are electrically connected to the neutral line on the receiving end side, and between the third end of the first valve group and the first end of the second valve group;

[0013] A third DC energy consumption module, both ends of which are electrically connected to the neutral line on the receiving end side, and between the third end of the third valve group and the first end of the fourth valve group; and

[0014] The fourth DC energy consumption module has two ends electrically connected to the negative electrode line on the receiving end side, and between the third end of the third valve group and the first end of the fourth valve group.

[0015] Optionally, the total capacity of the energy consumption device is equal to the DC transmission rated capacity of the receiving end multiplied by a set ratio, wherein the set ratio is less than 1, and the total capacity of the energy consumption device refers to the sum of the capacities of the first DC energy consumption module, the second DC energy consumption module, the third DC energy consumption module and the fourth DC energy consumption module.

[0016] Optionally, the first DC energy consumption module, the second DC energy consumption module, the third DC energy consumption module and the fourth DC energy consumption module have the same capacity;

[0017] The set ratio is 0.5.

[0018] Optionally, at least one of the first valve group, the second valve group, the third valve group, and the fourth valve group is a full half-bridge hybrid module structure.

[0019] Optionally, the UHV flexible DC power transmission system further has a sending end side, and both ends of the sending end side are electrically connected to the positive pole line and the negative pole line of the receiving end side, respectively, wherein:

[0020] When the AC side of the sending-end converter station in the sending-end side is in the interconnected mode, the sending-end side is configured to adopt a control strategy based on fixed active power and fixed reactive power to control its own power;

[0021] When the AC side of the sending-end converter station in the sending-end side is in island mode, the AC side of the sending-end converter station is connected to an AC energy consumption device, wherein the AC energy consumption device is composed of multiple groups of AC energy consumption sub-devices configured in groups.

[0022] In a second aspect, an embodiment of the present application provides a fault control method applicable to the energy consuming device described in the first aspect above, wherein the energy consuming device does not enter the energy consumption mode by default, the method comprising:

[0023] When a fault is detected in the first AC system, if the positive sequence component of the three-phase voltage of the first AC system is greater than or equal to a first threshold, the first DC energy consumption module and the fourth DC energy consumption module are controlled to enter an energy consumption mode, and after it is detected that the fault is eliminated, the first DC energy consumption module and the fourth DC energy consumption module are controlled to exit the energy consumption mode;

[0024] When a fault is detected in the second AC system, if the positive sequence component of the three-phase voltage of the second AC system is greater than or equal to a second threshold, the second DC energy consumption module and the third DC energy consumption module are controlled to enter an energy consumption mode until it is detected that the fault is eliminated, and then the second DC energy consumption module and the third DC energy consumption module are controlled to exit the energy consumption mode.

[0025] Optionally, the UHV flexible direct current transmission system further has a sending end side, two ends of the sending end side are electrically connected to the positive pole line and the negative pole line of the receiving end side respectively, and the sending end side is provided with a sending end converter station communicatively connected to the energy consuming device. The method further includes:

[0026] When a fault is detected in the first AC system, if the positive sequence component of the three-phase voltage of the first AC system is less than the first threshold, the first DC energy consumption module and the fourth DC energy consumption module are controlled to enter an energy consumption mode, and according to the detected AC side mode of the sending-end converter station, a corresponding first sending-end control instruction is sent to the sending-end converter station. After it is detected that the fault has been eliminated, the first DC energy consumption module and the fourth DC energy consumption module are controlled to exit the energy consumption mode, and a first cancellation instruction is sent to the sending-end converter station, wherein the first cancellation instruction is used to cancel the control of the first sending-end control instruction;

[0027] When a fault is detected in the second AC system, if the positive sequence component of the three-phase voltage of the second AC system is less than the second threshold value, the second DC energy consumption module and the third DC energy consumption module are controlled to enter an energy consumption mode, and according to the detected mode of the AC side of the sending-end converter station, a corresponding second sending-end control instruction is sent to the sending-end converter station. After it is detected that the fault is eliminated, the second DC energy consumption module and the third DC energy consumption module are controlled to exit the energy consumption mode, and a second cancellation instruction is sent to the sending-end converter station, wherein the second cancellation instruction is used to cancel the control of the second sending-end control instruction.

[0028] Optionally, the AC side of the sending-end converter station is connected to an AC energy consumption device, and the AC energy consumption device does not enter an energy consumption mode in a default state. The mode of the AC side of the sending-end converter station includes a network mode or an island mode;

[0029] When the AC side of the sending-end converter station is in the interconnected mode, the first sending-end control instruction is used to instruct the sending-end converter station to reduce the active power to a specified power value that matches the first sending-end control instruction, and the second sending-end control instruction is used to instruct the sending-end converter station to reduce the active power to a specified power value that matches the second sending-end control instruction;

[0030] When the mode of the AC side of the sending-end converter station is the island mode, the first sending-end control instruction is used to instruct the sending-end converter station to control the AC energy consumption device to enter an energy consumption mode that matches the first sending-end control instruction, and the second sending-end control instruction is used to instruct the sending-end converter station to control the AC energy consumption device to enter an energy consumption mode that matches the second sending-end control instruction.

[0031] Optionally, the specified power value P that matches the first sending end control instruction pu,1 It is expressed by the following formula:

[0032]

[0033] The specified power value P that matches the second sending end control instruction pu,2 It is expressed by the following formula:

[0034]

[0035] Among them, U ac,pu,1 is the per-unit value of the positive sequence component of the three-phase voltage of the first AC system after a fault occurs in the first AC system, U ac,pu,2 is the per-unit value by which the positive sequence component of the three-phase voltage of the second AC system drops after a fault occurs in the second AC system.

[0036] Optionally, the AC energy consumption device is composed of multiple groups of AC energy consumption sub-devices configured in groups;

[0037] in,

[0038] an energy consumption mode matched with the first sending-end control instruction, adapted to indicate a first number of AC energy consumption sub-devices that need to enter the energy consumption mode, the first number being determined based on a ratio of a decrease in a positive sequence component of a three-phase voltage of the first AC system after a fault occurs in the first AC system;

[0039] The energy consumption mode that matches the second sending-end control instruction is suitable for indicating a second number of AC energy consumption sub-devices that need to enter the energy consumption mode, and the second number is determined based on the proportion of the decrease in the positive sequence component of the three-phase voltage of the second AC system after a fault occurs in the second AC system.

[0040] In summary, the embodiments of the present application have at least the following beneficial effects:

[0041] By adopting the embodiment of the present application, on the premise that the receiving side is configured to be connected to the AC system through valve group layering (that is, the first valve group and the fourth valve group are connected to one AC system, and the second valve group and the third valve group are connected to another AC system), the energy consumption device is also configured accordingly to adapt to the structure of the valve group layering, so that a small-capacity DC energy consumption module can be used to adapt to the capacity demand changes of different valve groups, so as to improve energy consumption efficiency and reduce the total capacity of the energy consumption device, thereby improving the overall economy of the ultra-high voltage flexible DC transmission technology and improving system safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1A This is a structural diagram of the ultra-high voltage flexible direct current transmission system and its energy consumption device provided in an embodiment of the present application;

[0043] Figure 1B This is a structural diagram of the ultra-high voltage flexible direct current transmission system and its energy consumption device provided in an embodiment of the present application;

[0044] Figure 2 This is a flowchart of a fault control method provided in an embodiment of the present application;

[0045] Figure 3 This is a schematic diagram of parameter information of the ultra-high voltage flexible direct current transmission system when a fault occurs in the interconnected mode provided by an embodiment of the present application;

[0046] Figure 4 Schematic diagram of the voltage of the high-end converter valve submodule of the receiving station when a fault occurs in the networking mode provided by an embodiment of the present application;

[0047] Figure 5This is a schematic diagram of parameter information of a UHVDC flexible power transmission system when a fault occurs in island mode, provided by an embodiment of the present application;

[0048] Figure 6 This is a schematic diagram of the voltage of the high-end converter valve submodule of the receiving station when a fault occurs in the island mode provided by an embodiment of the present application. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0050] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, "multiple" means two or more. In the description of this application, the term "including" and its variations are open inclusions, i.e., "including but not limited to". The term "based on" means "at least partially based on". The term "according to" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments".

[0051] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0052] 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 meanings as those commonly understood by those skilled in the art. The terms used in this specification are only for the purpose of describing specific embodiments and are not intended to limit this application. Those of ordinary skill in the art will understand the specific meanings of the above terms in this application in specific circumstances.

[0053] First, see Figure 1A and Figure 1B ,in, Figure 1A This is the case when the AC side of the sending-end converter station is in interconnected mode. Figure 1B For the case where the AC side of the sending-end converter station on the sending-end side is in island mode, a structural schematic diagram of an energy dissipation device applicable to a UHV flexible DC transmission system provided in an embodiment of the present application is shown. The UHV flexible DC transmission system has a receiving-end side, and the receiving-end side includes:

[0054] A first valve group 121 , a first end of which is electrically connected to the positive electrode line on the receiving end side, and a second end of which is electrically connected to the first AC system 131 ;

[0055] A second valve group 122, a first end of which is electrically connected to the third end of the first valve group 121, a second end of which is electrically connected to the second AC system 132, and a third end of which is electrically connected to the neutral line on the receiving end side;

[0056] A third valve group 123 , a first end of which is electrically connected to the neutral line on the receiving end side, and a second end of which is electrically connected to the second AC system 132 ; and

[0057] The fourth valve group 124 has a first end electrically connected to the third end of the third valve group 123 , a second end electrically connected to the first AC system 131 , and a third end electrically connected to the negative electrode line on the receiving end side.

[0058] In one example, this embodiment can be applied to a typical ±800kV / 8GW receiving-end layered ultra-high voltage flexible direct current transmission system, with the following main circuit parameters: submodule rated operating voltage 2.0kV, submodule capacitance 24mF, bridge arm reactor 25mH, current-limiting reactor 300mH. The DC transmission line is 2400km long, uses 6 split conductors, and the line resistance is approximately 10Ω. The ultra-high voltage flexible direct current transmission system adopts a true bipolar wiring scheme, with two valve groups cascaded per pole, and the DC voltage of each valve group is 400kV. The valve group uses a full half-bridge hybrid module with a full-bridge ratio of 60%. The inter-station communication delay of the flexible direct current system is 30ms. The receiving station included in the receiving side is connected to the AC system through a layered manner of high-end and low-end valve groups, that is, the high-end valves of the positive and negative poles (i.e., the first valve group 121 and the fourth valve group 124) are connected to the first AC system 131, and the low-end valves of the positive and negative poles (i.e., the second valve group 122 and the third valve group 123) are connected to the second AC system 132. The electrical distance between the two AC systems is relatively far, so they can be approximated as two independent AC systems.

[0059] Wherein, the energy consumption device includes:

[0060] The first DC energy consumption module 111 has two ends electrically connected to the positive electrode line on the receiving end side, and between the third end of the first valve group 121 and the first end of the second valve group 122;

[0061] The second DC energy consumption module 112 has two ends electrically connected to the neutral line on the receiving end side, and between the third end of the first valve group 121 and the first end of the second valve group 122;

[0062] The third DC energy consumption module 113 has two ends electrically connected to the neutral line of the receiving end side, and between the third end of the third valve group 123 and the first end of the fourth valve group 124; and

[0063] The fourth DC energy consumption module 114 has two ends electrically connected to the negative electrode line on the receiving end side, and between the third end of the third valve group 123 and the first end of the fourth valve group 124 .

[0064] In one example, the energy consumption device is configured on the DC side of a receiving-end converter station provided on the receiving-end side, with a total capacity of 4GW, where:

[0065] The first DC energy consumption module 111 has a capacity of 1GW and is arranged between the positive pole line and the 400kV connecting busbar of the positive pole (the 400kV connecting busbar of the positive pole is arranged between the third end of the first valve group 121 and the first end of the second valve group 122), so that it can be connected in parallel with the high-end valve group of the positive pole.

[0066] The second DC energy consumption module 112 has a capacity of 1 GW and is arranged between the 400 kV connecting busbar of the positive pole and the neutral line, so as to be connected in parallel with the low-end valve group of the positive pole.

[0067] The third DC energy consumption module 113 has a capacity of 1GW and is configured between the negative pole 400kV connecting bus (the negative pole 400kV connecting bus is provided between the third end of the third valve group 123 and the first end of the fourth valve group 124) and the neutral line, so that it can be connected in parallel with the negative pole low-end valve group.

[0068] The fourth DC energy consumption module 114 has a capacity of 1GW and is arranged between the negative pole line and the negative 400kV connecting busbar, so as to be connected in parallel with the negative high-end valve group.

[0069] Therefore, the total capacity of DC energy consumption devices can be reduced to only 50% of the rated capacity of the DC transmission system.

[0070] In some cases, energy-consuming devices can adopt a variety of technical routes such as centralized, distributed or hybrid.

[0071] In an optional embodiment, the total capacity of the energy consumption device is equal to the DC transmission rated capacity of the receiving end multiplied by a set ratio, wherein the set ratio is less than 1, and the total capacity of the energy consumption device refers to the sum of the respective capacities of the first DC energy consumption module 111, the second DC energy consumption module 112, the third DC energy consumption module 113 and the fourth DC energy consumption module 114.

[0072] In an optional embodiment, the first DC energy consumption module 111, the second DC energy consumption module 112, the third DC energy consumption module 113 and the fourth DC energy consumption module 114 have the same capacity;

[0073] The set ratio is 0.5.

[0074] In an optional embodiment, at least one of the first valve group 121 , the second valve group 122 , the third valve group 123 , and the fourth valve group 124 is a full half-bridge hybrid module structure.

[0075] In an optional embodiment, the UHV flexible DC power transmission system further has a sending end side, and both ends of the sending end side are electrically connected to the positive pole line and the negative pole line of the receiving end side, respectively, wherein:

[0076] When the AC side of the sending-end converter station in the sending-end side is in the interconnected mode, the sending-end side is configured to adopt a control strategy based on fixed active power and fixed reactive power to control its own power;

[0077] When the AC side of the sending-end converter station in the sending-end side is in island mode, the AC side of the sending-end converter station is connected to an AC energy consumption device, wherein the AC energy consumption device is composed of multiple groups of AC energy consumption sub-devices configured in groups.

[0078] In this embodiment, if the AC side of the sending converter station is in interconnected mode, a fixed active power and fixed reactive power control strategy must be implemented. If the AC side of the sending converter station is in islanded mode, a 2GW AC energy consumption device must be deployed on the AC side of the sending converter station. If AC energy consumption devices are deployed at the sending converter station, they should be grouped, with each group holding 250MW, for a total of 8 groups, totaling 2GW. Various technologies, such as thyristor control, can be used for AC energy consumption devices.

[0079] Second, see Figure 2 , shows a flow chart of a fault control method provided by an embodiment of the present application, which is applicable to the energy consuming device described in the first aspect above. The energy consuming device does not enter the energy consumption mode in the default state. The method includes steps S201-S202, which are specifically as follows:

[0080] S201: When a fault is detected in the first AC system 131, if the positive sequence component of the three-phase voltage of the first AC system 131 is greater than or equal to a first threshold, controlling the first DC energy consumption module 111 and the fourth DC energy consumption module 114 to enter an energy consumption mode. After detecting that the fault is eliminated, controlling the first DC energy consumption module 111 and the fourth DC energy consumption module 114 to exit the energy consumption mode.

[0081] S202: When a fault is detected in the second AC system 132, if the positive sequence component of the three-phase voltage of the second AC system 132 is greater than or equal to a second threshold, the second DC energy consumption module 112 and the third DC energy consumption module 113 are controlled to enter an energy consumption mode. After detecting that the fault has been eliminated, the second DC energy consumption module 112 and the third DC energy consumption module 113 are controlled to exit the energy consumption mode. Exemplarily, the first threshold and / or the second threshold is 0.5 pu.

[0082] In this embodiment, when a fault occurs in the AC system connected to the high-end valve group of the receiving-end converter station and the positive-sequence component of the three-phase voltage of the AC system drops to 0.5 pu or above, the receiving-end converter station immediately puts into operation the DC energy consumption devices connected in parallel with the high-end valve group after detecting the fault (one group of DC energy consumption devices connected in parallel with the positive high-end valve group is put into operation at the positive pole, and one group of DC energy consumption devices connected in parallel with the negative high-end valve group is put into operation at the negative pole, for a total of 2GW of DC energy consumption devices). When the receiving-end converter station detects that the AC system fault has been cleared, the DC energy consumption devices are withdrawn. When a fault occurs in the AC system connected to the low-end valve group of the receiving-end converter station and the positive-sequence component of the three-phase voltage of the AC system drops to 0.5pu or above, the receiving-end converter station will immediately start the DC energy consumption device in parallel with the low-end valve group after detecting the fault (one group of DC energy consumption devices in parallel with the positive low-end valve group is put into operation at the positive pole, and one group of DC energy consumption devices in parallel with the negative low-end valve group is put into operation at the negative pole, with a total of 2GW of DC energy consumption devices put into operation); when the receiving-end converter station detects that the AC system fault has been cleared, it will exit the DC energy consumption device.

[0083] In an optional embodiment, the UHV flexible DC power transmission system further has a sending end side, both ends of the sending end side are electrically connected to the positive pole line and the negative pole line of the receiving end side, respectively, and the sending end side is provided with a sending end converter station communicatively connected to the energy consuming device. The method further includes:

[0084] When a fault is detected in the first AC system 131, if the positive sequence component of the three-phase voltage of the first AC system 131 is less than the first threshold, the first DC energy consumption module 111 and the fourth DC energy consumption module 114 are controlled to enter an energy consumption mode, and according to the detected AC side mode of the sending-end converter station, a corresponding first sending-end control instruction is sent to the sending-end converter station. After it is detected that the fault is eliminated, the first DC energy consumption module 111 and the fourth DC energy consumption module 114 are controlled to exit the energy consumption mode, and a first cancellation instruction is sent to the sending-end converter station, wherein the first cancellation instruction is used to cancel the control of the first sending-end control instruction;

[0085] When a fault is detected in the second AC system 132, if the positive sequence component of the three-phase voltage of the second AC system 132 is less than the second threshold value, the second DC energy consumption module 112 and the third DC energy consumption module 113 are controlled to enter the energy consumption mode, and according to the detected mode of the AC side of the sending-end converter station, a corresponding second sending-end control instruction is sent to the sending-end converter station. After it is detected that the fault is eliminated, the second DC energy consumption module 112 and the third DC energy consumption module 113 are controlled to exit the energy consumption mode, and a second cancellation instruction is sent to the sending-end converter station, wherein the second cancellation instruction is used to cancel the control of the second sending-end control instruction.

[0086] In an optional embodiment, the AC side of the sending-end converter station is connected to an AC energy consumption device, and the AC energy consumption device does not enter the energy consumption mode in a default state. The mode of the AC side of the sending-end converter station includes a network mode or an island mode;

[0087] When the AC side of the sending-end converter station is in the networking mode, the first sending-end control instruction is used to instruct the sending-end converter station to reduce the active power to a specified power value that matches the first sending-end control instruction, and the second sending-end control instruction is used to instruct the sending-end converter station to reduce the active power to a specified power value that matches the second sending-end control instruction; at this time, the first cancellation instruction is also used to restore the DC power of the sending-end converter station to the rated power value or to the DC power at the moment before the first sending-end control instruction is received, and the second cancellation instruction is also used to restore the DC power of the sending-end converter station to the rated power value or to the DC power at the moment before the second sending-end control instruction is received;

[0088] When the mode of the AC side of the sending-end converter station is the island mode, the first sending-end control instruction is used to instruct the sending-end converter station to control the AC energy consumption device to enter an energy consumption mode that matches the first sending-end control instruction, and the second sending-end control instruction is used to instruct the sending-end converter station to control the AC energy consumption device to enter an energy consumption mode that matches the second sending-end control instruction.

[0089] In an optional embodiment, the specified power value P that matches the first sending end control instruction pu,1 It is expressed by the following formula:

[0090]

[0091] The specified power value P that matches the second sending end control instruction pu,2 It is expressed by the following formula:

[0092]

[0093] Among them, U ac,pu,1 is the per-unit value of the positive sequence component of the three-phase voltage of the first AC system 131 after a fault occurs in the first AC system 131, U ac,pu,2 is the per-unit value by which the positive sequence component of the three-phase voltage of the second AC system 132 drops after a fault occurs in the second AC system 132 .

[0094] In an optional embodiment, the AC energy consumption device is composed of multiple groups of AC energy consumption sub-devices configured in groups;

[0095] in,

[0096] The energy consumption mode matched with the first sending-end control instruction is adapted to indicate a first number of AC energy consumption sub-devices that need to enter the energy consumption mode, where the first number is determined based on a ratio of a decrease in a positive sequence component of a three-phase voltage of the first AC system 131 after a fault occurs in the first AC system 131;

[0097] The energy consumption mode that matches the second sending-end control instruction is suitable for indicating the second number of AC energy consumption sub-devices that need to enter the energy consumption mode, and the second number is determined based on the proportion of the decrease in the positive sequence component of the three-phase voltage of the second AC system 132 after a fault occurs in the second AC system 132.

[0098] In this embodiment, when the AC system connected to the high-side valve group of the receiving-end converter station fails and the positive sequence component of the three-phase voltage of the AC system drops below 0.5 pu, the AC side of the sending-end converter station is in either interconnected mode or island mode.

[0099] 1) If the AC side of the sending-end converter station is in interconnected mode, when the receiving-end converter station detects a fault, it immediately activates the DC energy consumption device connected in parallel to the high-end valve group and simultaneously notifies the sending-end converter station via inter-station communication to reduce power. The power command value is calculated according to the following formula. When the sending-end converter station receives the power reduction command via inter-station communication, it immediately reduces the active power to the specified value. When the receiving-end converter station detects that the AC system fault has been cleared, it deactivates the DC energy consumption device and simultaneously notifies the sending-end converter station via inter-station communication to restore the DC power to the rated value or the previous value. When the sending-end converter station receives the power command via inter-station communication, it restores the DC power to the rated value or the previous value.

[0100]

[0101] Among them, U ac,pu,1 is the per-unit value of the positive sequence component of the three-phase voltage of the first AC system 131 after a fault occurs in the first AC system 131, and the specified power value P that matches the first sending-end control instruction pu,1 Expressed in per-unit form.

[0102] 2) If the AC side of the sending-end converter station is in island mode, when the receiving-end converter station detects a fault, it immediately activates the DC energy-consuming devices connected in parallel to the high-end valve group and simultaneously notifies the sending-end converter station via inter-station communication to activate the AC energy-consuming devices. The number of activated AC energy-consuming devices is calculated according to the following formula. When the sending-end converter station receives the instruction to activate the AC energy-consuming devices via inter-station communication, it immediately activates the specified number of AC energy-consuming devices. When the receiving-end converter station detects that the AC system fault has been cleared, it deactivates the DC energy-consuming devices and simultaneously notifies the sending-end converter station via inter-station communication to deactivate the AC energy-consuming devices. When the sending-end converter station receives the instruction to deactivate the AC energy-consuming devices via inter-station communication, it deactivates all AC energy-consuming devices.

[0103]

[0104] Among them, ROUNDUP[] is rounded up.

[0105] In this embodiment, when the AC system connected to the low-end valve group of the receiving-end converter station fails and the positive sequence component of the three-phase voltage of the AC system drops below 0.5 pu, the AC side of the sending-end converter station is in either interconnected mode or island mode.

[0106] 1) If the AC side of the sending-end converter station is in interconnected mode, when the receiving-end converter station detects a fault, it immediately activates the DC energy dissipation device connected in parallel to the low-end valve group and simultaneously notifies the sending-end converter station via inter-station communication to reduce power. The power command value is calculated according to the following formula. When the sending-end converter station receives the power reduction command via inter-station communication, it immediately reduces the active power to the specified value. When the receiving-end converter station detects that the AC system fault has been cleared, it deactivates the DC energy dissipation device and simultaneously notifies the sending-end converter station via inter-station communication to restore the DC power to the rated value or the previous value. When the sending-end converter station receives the power command via inter-station communication, it restores the DC power to the rated value or the previous value.

[0107]

[0108] Among them, U ac,pu,2 is the per-unit value of the positive sequence component of the three-phase voltage of the second AC system 132 that decreases after a fault occurs in the second AC system 132, and the specified power value P that matches the second sending-end control instruction pu,2 Expressed in per-unit form.

[0109] 2) If the AC side of the sending-end converter station is in island mode, when the receiving-end converter station detects a fault, it immediately activates the DC energy-consuming devices connected in parallel to the low-end valve group and simultaneously notifies the sending-end converter station via inter-station communication to activate the AC energy-consuming devices. The number of activated AC energy-consuming devices is calculated according to the following formula. When the sending-end converter station receives the instruction to activate the AC energy-consuming devices via inter-station communication, it immediately activates the specified number of AC energy-consuming devices. When the receiving-end converter station detects that the AC system fault has been cleared, it deactivates the DC energy-consuming devices and simultaneously notifies the sending-end converter station via inter-station communication to deactivate the AC energy-consuming devices. When the sending-end converter station receives the instruction to deactivate the AC energy-consuming devices via inter-station communication, it deactivates all AC energy-consuming devices.

[0110]

[0111] Among them, ROUNDUP[] is rounded up.

[0112] Two specific embodiments are given below.

[0113] Example 1

[0114] Based on a typical ±800kV / 8GW receiving-end layered UHVDC flexible transmission system, its main circuit parameters are as follows: submodule rated operating voltage 2.0kV, submodule capacitance 24mF, bridge arm reactor 25mH, and current-limiting reactor 300mH. The DC transmission line is 2400km long, using six split conductors, with a line resistance of approximately 10Ω. The UHVDC flexible transmission system uses a true bipolar connection scheme, with two cascaded valve groups per pole, each with a DC voltage of 400kV. The valve groups use full half-bridge hybrid modules with a full-bridge ratio of 60%. The inter-station communication delay of the flexible DC system is 30ms. The receiving stations are connected to the AC system through a layered high-end and low-end valve group system. The high-end valves for the positive and negative poles are connected to one AC system, while the low-end valves for the positive and negative poles are connected to another. The electrical distance between the two AC systems is relatively large, making them similar to two independent AC systems. The AC side of the sending-end converter station is in interconnected mode, with the sending end adopting a fixed active power and fixed reactive power control strategy, and the receiving end adopting a fixed DC voltage and fixed reactive power control strategy. A 4GW DC energy consumption device is configured on the DC side of the receiving-end converter station, of which 1GW is configured between the positive pole line and the 400kV positive pole connecting busbar (that is, in parallel with the high-end valve group of the positive pole), 1GW is configured between the 400kV positive pole connecting busbar and the neutral line (that is, in parallel with the low-end valve group of the positive pole), 1GW is configured between the negative pole line and the 400kV negative pole connecting busbar (that is, in parallel with the high-end valve group of the negative pole), and 1GW is configured between the 400kV negative pole connecting busbar and the neutral line (that is, in parallel with the low-end valve group of the negative pole). Figure 1A shown.

[0115] Before the fault occurs, the UHVDC flexible transmission system operates at full capacity. Figure 3 (As shown in Figure 5.1s), a two-phase metallic ground fault occurred in the AC system connected to the high-side valve group at the receiving-end converter station, causing the positive sequence component of the three-phase voltage to drop to 0.33 pu. Approximately 10 ms after the fault, the receiving-end converter station detected the fault and immediately activated the DC energy consumption device connected in parallel to the high-side valve group. Simultaneously, it notified the sending-end converter station via inter-station communication to reduce power to a power command of 0.915 pu. Approximately 40 ms after the fault, the sending-end converter station received the power reduction command via inter-station communication and immediately reduced its active power to 0.915 pu. Approximately 100 ms after the fault, the AC system connected to the high-side valve group at the receiving-end converter station cleared the fault, and the positive sequence component of the three-phase voltage increased to 1 pu. Approximately 110 ms after the fault, the receiving-end converter station detected that the AC-side fault had cleared, deactivated the DC energy consumption device, and simultaneously notified the sending-end converter station via inter-station communication to restore the DC power to its previous value. About 140ms after the fault, the sending-end converter station receives the power command through inter-station communication and restores the DC power to 1 pu. Figure 3As shown in Figure 1, about 300ms after the fault, the voltage and power on the DC pole line basically returned to the operating state before the fault. Figure 4 is the maximum voltage of the high-side converter valve submodule at the receiving station during fault ride-through, which does not exceed 2.8 kV and is lower than the submodule's overvoltage protection setting. This indicates that the energy dissipation device configuration scheme and AC-side fault ride-through method for a receiving-end layered UHVDC flexible transmission system, as provided by the present invention, can achieve system fault ride-through after a fault occurs on the AC side of a receiving station.

[0116] Example 2

[0117] Based on a typical ±800kV / 8GW receiving-end layered UHVDC flexible transmission system, its main circuit parameters are as follows: submodule rated operating voltage 2.0kV, submodule capacitance 24mF, bridge arm reactor 25mH, and current-limiting reactor 300mH. The DC transmission line is 2400km long, using six split conductors, with a line resistance of approximately 10Ω. The UHVDC flexible transmission system uses a true bipolar connection scheme, with two cascaded valve groups per pole, each with a DC voltage of 400kV. The valve groups use full half-bridge hybrid modules with a full-bridge ratio of 60%. The inter-station communication delay of the flexible DC system is 30ms. The receiving stations are connected to the AC system through a layered high-end and low-end valve group system. The high-end valves for the positive and negative poles are connected to one AC system, while the low-end valves for the positive and negative poles are connected to another. The electrical distance between the two AC systems is relatively large, making them similar to two independent AC systems. The AC side of the sending-end converter station is in island mode, with the sending end adopting a fixed AC voltage amplitude and fixed AC frequency control strategy, and the receiving end adopting a fixed DC voltage and fixed reactive power control strategy. A 4GW DC energy consumption device is configured on the DC side of the receiving-end converter station, of which 1GW is configured between the positive pole line and the 400kV positive pole connecting busbar (that is, in parallel with the high-end valve group of the positive pole), 1GW is configured between the 400kV positive pole connecting busbar and the neutral line (that is, in parallel with the low-end valve group of the positive pole), 1GW is configured between the negative pole line and the 400kV negative pole connecting busbar (that is, in parallel with the high-end valve group of the negative pole), and 1GW is configured between the 400kV negative pole connecting busbar and the neutral line (that is, in parallel with the low-end valve group of the negative pole). A 2GW AC energy consumption device is configured on the AC side of the sending-end converter station, such as Figure 1B shown.

[0118] Before the fault occurs, the UHVDC flexible transmission system operates at full capacity. Figure 5(As shown in Figure 5.1s), a two-phase metallic ground fault occurred in the AC system connected to the low-end valve group at the receiving-end converter station, causing the positive sequence component of the three-phase voltage to drop to 0.33 pu. Approximately 10 ms after the fault, the receiving-end converter station detected the fault and immediately activated the DC energy consumption devices connected in parallel to the low-end valve group. Simultaneously, it notified the sending-end converter station via inter-station communication to activate three AC energy consumption devices. Approximately 40 ms after the fault, the sending-end converter station received the instruction to activate the AC energy consumption devices via inter-station communication and immediately activated all three AC energy consumption devices. Approximately 100 ms after the fault, the AC system fault connected to the low-end valve group at the receiving-end converter station was cleared, and the positive sequence component of the three-phase voltage increased to 1 pu. Approximately 110 ms after the fault, the receiving-end converter station detected that the AC fault had cleared and deactivated the DC energy consumption devices. Simultaneously, it notified the sending-end converter station via inter-station communication to deactivate the AC energy consumption devices. About 140ms after the fault, the sending-end converter station receives the instruction to shut down the AC energy consumption device through inter-station communication and shuts down all the AC energy consumption devices. Figure 5 As shown in Figure 1, about 300ms after the fault, the voltage and power on the DC pole line basically returned to the operating state before the fault. Figure 6 = is the maximum voltage of the low-end converter valve submodule at the receiving station during fault ride-through, which does not exceed 2.8 kV and is lower than the submodule's overvoltage protection setting. Therefore, the energy dissipation device configuration scheme and AC-side fault ride-through method for the UHVDC flexible transmission system provided by the present invention can achieve system fault ride-through after a fault occurs on the AC side of the receiving-end converter transformer.

[0119] In summary, the embodiments of the present application have at least the following beneficial effects:

[0120] By adopting the embodiment of the present application, on the premise that the receiving side is configured to be connected to the AC system through valve group layering (that is, the first valve group and the fourth valve group are connected to one AC system, and the second valve group and the third valve group are connected to another AC system), the energy consumption device is also configured accordingly to adapt to the structure of the valve group layering, so that a small-capacity DC energy consumption module can be used to adapt to the capacity demand changes of different valve groups, so as to improve energy consumption efficiency and reduce the total capacity of the energy consumption device, thereby improving the overall economy of the ultra-high voltage flexible DC transmission technology and improving system safety.

[0121] Through the description of the above implementation methods, those skilled in the art can clearly understand that the present application can be implemented by means of software plus the necessary hardware platform, and of course it can also be implemented entirely by hardware. Based on this understanding, all or part of the contribution of the technical solution of the present application to the background technology can be embodied in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in various embodiments or certain parts of the embodiments of the present application.

[0122] The above is a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. An energy dissipation device suitable for an ultra-high voltage flexible direct current transmission system, characterized in that: The ultra-high voltage flexible direct current power transmission system has a receiving side, and the receiving side includes: a first valve group, a first end of which is electrically connected to the positive electrode line on the receiving end side, and a second end of which is electrically connected to the first AC system; a second valve group, a first end of which is electrically connected to the third end of the first valve group, a second end of which is electrically connected to the second AC system, and a third end of which is electrically connected to the neutral line on the receiving end side; a third valve group, a first end of which is electrically connected to the neutral line on the receiving end side, and a second end of which is electrically connected to the second AC system; and a fourth valve group, a first end electrically connected to the third end of the third valve group, a second end electrically connected to the first AC system, and a third end electrically connected to the negative electrode line on the receiving end side; Wherein, the energy consumption device includes: A first DC energy consumption module, two ends of which are electrically connected to the positive electrode line on the receiving end side, and between the third end of the first valve group and the first end of the second valve group; A second DC energy consumption module, both ends of which are electrically connected to the neutral line on the receiving end side, and between the third end of the first valve group and the first end of the second valve group; A third DC energy consumption module, both ends of which are electrically connected to the neutral line on the receiving end side, and between the third end of the third valve group and the first end of the fourth valve group; and The fourth DC energy consumption module has two ends electrically connected to the negative electrode line on the receiving end side, and between the third end of the third valve group and the first end of the fourth valve group.

2. The energy consumption device according to claim 1, characterized in that: The total capacity of the energy consumption device is equal to the DC transmission rated capacity of the receiving end multiplied by a set ratio, wherein the set ratio is less than 1, and the total capacity of the energy consumption device refers to the sum of the capacities of the first DC energy consumption module, the second DC energy consumption module, the third DC energy consumption module, and the fourth DC energy consumption module.

3. The energy consumption device according to claim 2, characterized in that: The first DC energy consumption module, the second DC energy consumption module, the third DC energy consumption module and the fourth DC energy consumption module each have an equal capacity; The set ratio is 0.

5.

4. The energy consumption device according to claim 1, characterized in that: At least one of the first valve group, the second valve group, the third valve group, and the fourth valve group is a full half-bridge hybrid module structure.

5. The energy consumption device according to claim 1, characterized in that: The UHV flexible DC power transmission system further comprises a sending end side, both ends of which are electrically connected to the positive pole line and the negative pole line of the receiving end side, respectively, wherein: When the AC side of the sending-end converter station in the sending-end side is in the interconnected mode, the sending-end side is configured to adopt a control strategy based on fixed active power and fixed reactive power to control its own power; When the AC side of the sending-end converter station in the sending-end side is in island mode, the AC side of the sending-end converter station is connected to an AC energy consumption device, wherein the AC energy consumption device is composed of multiple groups of AC energy consumption sub-devices configured in groups.

6. A fault control method, characterized in that: The energy consumption device according to claim 1, wherein the energy consumption device does not enter the energy consumption mode in a default state, and the method includes: When a fault is detected in the first AC system, if the positive sequence component of the three-phase voltage of the first AC system is greater than or equal to a first threshold, the first DC energy consumption module and the fourth DC energy consumption module are controlled to enter an energy consumption mode, and after it is detected that the fault is eliminated, the first DC energy consumption module and the fourth DC energy consumption module are controlled to exit the energy consumption mode; When a fault is detected in the second AC system, if the positive sequence component of the three-phase voltage of the second AC system is greater than or equal to a second threshold, the second DC energy consumption module and the third DC energy consumption module are controlled to enter an energy consumption mode until it is detected that the fault is eliminated, and then the second DC energy consumption module and the third DC energy consumption module are controlled to exit the energy consumption mode.

7. The method according to claim 6, wherein The ultra-high voltage flexible direct current transmission system further comprises a sending end side, wherein two ends of the sending end side are electrically connected to the positive pole line and the negative pole line of the receiving end side respectively, and the sending end side is provided with a sending end converter station communicatively connected to the energy consumption device. The method further comprises: When a fault is detected in the first AC system, if the positive sequence component of the three-phase voltage of the first AC system is less than the first threshold, the first DC energy consumption module and the fourth DC energy consumption module are controlled to enter an energy consumption mode, and according to the detected AC side mode of the sending-end converter station, a corresponding first sending-end control instruction is sent to the sending-end converter station. After it is detected that the fault has been eliminated, the first DC energy consumption module and the fourth DC energy consumption module are controlled to exit the energy consumption mode, and a first cancellation instruction is sent to the sending-end converter station, wherein the first cancellation instruction is used to cancel the control of the first sending-end control instruction; When a fault is detected in the second AC system, if the positive sequence component of the three-phase voltage of the second AC system is less than the second threshold value, the second DC energy consumption module and the third DC energy consumption module are controlled to enter an energy consumption mode, and according to the detected mode of the AC side of the sending-end converter station, a corresponding second sending-end control instruction is sent to the sending-end converter station. After it is detected that the fault is eliminated, the second DC energy consumption module and the third DC energy consumption module are controlled to exit the energy consumption mode, and a second cancellation instruction is sent to the sending-end converter station, wherein the second cancellation instruction is used to cancel the control of the second sending-end control instruction.

8. The method according to claim 7, wherein The AC side of the sending-end converter station is connected to an AC energy consumption device, and the AC energy consumption device does not enter an energy consumption mode in a default state. The mode of the AC side of the sending-end converter station includes a network mode or an island mode; When the AC side of the sending-end converter station is in the interconnected mode, the first sending-end control instruction is used to instruct the sending-end converter station to reduce the active power to a specified power value that matches the first sending-end control instruction, and the second sending-end control instruction is used to instruct the sending-end converter station to reduce the active power to a specified power value that matches the second sending-end control instruction; When the mode of the AC side of the sending-end converter station is the island mode, the first sending-end control instruction is used to instruct the sending-end converter station to control the AC energy consumption device to enter an energy consumption mode that matches the first sending-end control instruction, and the second sending-end control instruction is used to instruct the sending-end converter station to control the AC energy consumption device to enter an energy consumption mode that matches the second sending-end control instruction.

9. The method according to claim 8, wherein The specified power value P that matches the first sending end control instruction pu,1 It is expressed by the following formula: The specified power value P that matches the second sending end control instruction pu,2 It is expressed by the following formula: Among them, U ac,pu,1 is the per-unit value of the positive sequence component of the three-phase voltage of the first AC system after a fault occurs in the first AC system, U ac,pu,2 is the per-unit value by which the positive sequence component of the three-phase voltage of the second AC system drops after a fault occurs in the second AC system.

10. The method according to claim 8, wherein The AC energy consumption device is composed of multiple groups of AC energy consumption sub-devices configured in groups; in, an energy consumption mode matched with the first sending-end control instruction, adapted to indicate a first number of AC energy consumption sub-devices that need to enter the energy consumption mode, the first number being determined based on a ratio of a decrease in a positive sequence component of a three-phase voltage of the first AC system after a fault occurs in the first AC system; The energy consumption mode that matches the second sending-end control instruction is suitable for indicating a second number of AC energy consumption sub-devices that need to enter the energy consumption mode, and the second number is determined based on the proportion of the decrease in the positive sequence component of the three-phase voltage of the second AC system after a fault occurs in the second AC system.

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