Fault clearing device and DC side fault clearing method for ultra-long-distance multi-terminal transmission

Abstract

The present application relates to a fault clearing device and a method, device and equipment for clearing faults on the DC side of ultra-long-distance multi-terminal transmission, which are applied to a multi-terminal flexible DC system. The multi-terminal flexible DC system includes multiple transmission modules, each of which includes two converter stations and a grounding electrode line. The two converter stations are respectively connected to the grounding electrode line and then connected to the grounding electrode. The fault clearing device includes a grounding unit connected to the grounding electrode line. The grounding unit includes a transformer, a lightning arrester and a resistor. The lightning arrester is connected in series with the resistor and then connected to the secondary side of the transformer; the lightning arrester is used to control the input and output of the resistor; and the resistor is used to consume energy. The fault clearing device is connected to the transmission module of the multi-terminal flexible DC system in a high-resistance grounding manner. After a DC fault occurs in the multi-terminal flexible DC system, the fault current is reduced due to the presence of high grounding resistance, and the energy after the fault is quickly consumed by the resistor, thereby achieving the purpose of clearing the fault current.

Description

Technical Field

[0001] The present application relates to the technical field of DC fault clearing, and in particular to a fault clearing device and a method, device and equipment for clearing DC side faults transmitted over ultra-long distances and multiple terminals. Background Art

[0002] Currently, flexible DC has become the preferred topology for large-scale, ultra-long-distance transmission of renewable energy. Ultra-long-distance transmission often utilizes overhead lines, primarily due to their relatively low cost. However, the use of overhead lines makes it difficult to prevent faults such as wildfires and lightning strikes, which can lead to frequent faults on DC lines. To ensure the safe and stable operation of AC and DC systems, DC transmission systems must have robust overhead line clearance capabilities.

[0003] Existing flexible DC systems mostly use a full-half-bridge hybrid structure to solve the DC fault clearing problem. However, when the full-bridge module outputs reverse voltage, the fault current will continuously charge the capacitor of the full-bridge module, thereby causing the capacitor voltage of the full-bridge module to increase. When it increases to a certain level, it will cause the converter to trip. Summary of the Invention

[0004] The embodiments of the present application provide a fault clearing device and a method, device and equipment for clearing DC side faults for ultra-long-distance multi-terminal transmission, which are used to solve the technical problem that the existing flexible DC uses a full half-bridge hybrid structure to clear DC faults, but this method has the problem of converter tripping and causing unstable operation of flexible DC transmission.

[0005] In order to achieve the above objectives, the embodiments of the present application provide the following technical solutions:

[0006] On the one hand, a fault clearing device is provided, which is applied to a multi-terminal flexible DC system. The multi-terminal flexible DC system includes multiple sending modules, each of the sending modules includes two converter stations and a grounding electrode line, the two converter stations are respectively connected to the grounding electrode line and then connected to the grounding electrode, the fault clearing device includes a grounding unit connected to the grounding electrode line, the grounding unit includes a transformer, a lightning arrester and a resistor, the primary side of the transformer is respectively connected to the grounding electrode and the grounding electrode line, the lightning arrester is connected in series with the resistor and then connected to the secondary side of the transformer; the lightning arrester is used to control the input and output of the resistor; the resistor is used to consume energy.

[0007] On the other hand, a method for clearing a DC side fault with ultra-long-distance multi-terminal transmission is provided, which is applied to the above-mentioned fault clearing device. The DC side fault clearing method includes the following steps:

[0008] Obtain the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each transmission module;

[0009] Determining operating parameters of the grounding unit according to the electrical quantity parameters, the operating parameters including the rated voltage of the lightning arrester and the maximum operating power and resistance value of the resistor;

[0010] Controlling, according to the operating state, whether the grounding unit corresponding to the delivery module operates according to the operating parameters;

[0011] If the operating state is a stable operating state, the corresponding grounding unit is controlled not to operate; if the operating state is a transient operating state, the grounding unit is controlled to operate according to the operating parameters to consume energy.

[0012] Preferably, controlling the grounding unit to operate according to the operating parameters to consume energy includes: controlling the lightning arrester of the grounding unit to start according to the rated voltage, and controlling the resistor to operate according to the maximum operating power and the resistance value to consume energy.

[0013] Preferably, determining the operating parameters of the grounding unit according to the electrical quantity parameters includes:

[0014] The rated voltage of the arrester is obtained by calculation based on the safety factor, transformation ratio, self-inductance of the primary winding of the transformer and the fault current rise rate of the electrical quantity parameters;

[0015] Obtaining the resistance value of the resistor by calculation based on the maximum DC current, the rated DC voltage, the total length, the inductance per unit length, and the capacitance per unit length to ground of the DC transmission line of the electrical quantity parameters;

[0016] The maximum operating power of the resistor is obtained by calculation based on the fault current reduction multiple, grounding electrode line length, grounding electrode inductance per unit length, mutual inductance and fault current falling time of the electrical quantity parameters.

[0017] Preferably, the fault current reduction factor is 4-5; and / or the safety factor is 0.8-0.9; and / or the transformation ratio is 0.01-0.05.

[0018] On the other hand, a DC side fault clearing device with ultra-long distance multi-terminal transmission is provided, which is applied to the above-mentioned fault clearing device. The DC side fault clearing device includes a data acquisition module, a parameter determination module, a judgment module and an execution module;

[0019] The data acquisition module is used to obtain the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each sending module;

[0020] The parameter determination module is used to determine the operating parameters of the grounding unit according to the electrical quantity parameters, wherein the operating parameters include the rated voltage of the lightning arrester and the maximum operating power and resistance value of the resistor;

[0021] The judgment module is used to control, according to the operating state, whether the grounding unit corresponding to the sending module operates according to the operating parameters;

[0022] The execution module is used to control the corresponding grounding unit to not work according to the operating state being a stable operating state; or to control the grounding unit to work according to the operating parameters to consume energy according to the operating state being a transient operating state.

[0023] Preferably, the execution module is further configured to control the lightning arrester of the grounding unit to start at the rated voltage and the resistor to operate at the maximum operating power and the resistance value to consume energy according to the operating state being a transient operating state.

[0024] Preferably, the parameter determination module includes a first calculation submodule, a second calculation submodule and a third calculation submodule;

[0025] The first calculation submodule is configured to calculate the rated voltage of the arrester based on the safety factor, transformation ratio, transformer primary winding self-inductance, and fault current rise rate of the electrical quantity parameters;

[0026] The second calculation submodule is configured to calculate the resistance value of the resistor based on the maximum DC current, the rated DC voltage, the total length, the inductance per unit length, and the capacitance per unit length to ground of the DC transmission line.

[0027] The third calculation submodule is used to calculate the maximum operating power of the resistor based on the fault current reduction multiple, grounding electrode line length, grounding electrode inductance per unit length, mutual inductance and fault current fall time of the electrical quantity parameters.

[0028] Preferably, the fault current reduction factor is 4-5; and / or the safety factor is 0.8-0.9; and / or the transformation ratio is 0.01-0.05.

[0029] In another aspect, a terminal device is provided, comprising a processor and a memory;

[0030] The memory is used to store program code and transmit the program code to the processor;

[0031] The processor is configured to execute the above-mentioned method for clearing DC side faults for ultra-long-distance multi-terminal transmission according to the instructions in the program code.

[0032] The fault clearing device and the method, device and equipment for clearing faults on the DC side of ultra-long-distance multi-terminal transmission are applied to a multi-terminal flexible DC system. The multi-terminal flexible DC system includes multiple transmission modules, each of which includes two converter stations and a grounding electrode line. The two converter stations are respectively connected to the grounding electrode line and then to the grounding electrode. The fault clearing device includes a grounding unit connected to the grounding electrode line. The grounding unit includes a transformer, a lightning arrester and a resistor. The primary side of the transformer is respectively connected to the grounding electrode and the grounding electrode line. The lightning arrester is connected in series with the resistor and then connected to the secondary side of the transformer. The lightning arrester is used to control the input and output of the resistor. The resistor is used to consume energy.

[0033] The method includes obtaining electrical quantity parameters of a multi-terminal flexible direct current system and the operating status of each sending module; determining the operating parameters of a grounding unit according to the electrical quantity parameters, the operating parameters including the rated voltage of a lightning arrester and the maximum operating power and resistance value of a resistor; controlling the grounding unit corresponding to the sending module to determine whether it operates according to the operating parameters according to the operating status; if the operating status is a stable operating state, controlling the corresponding grounding unit not to operate; if the operating state is a transient operating state, controlling the grounding unit to operate according to the operating parameters to consume energy.

[0034] It can be seen from the above technical solution that the present application has the following advantages: the fault clearing device is connected to the sending module of the multi-terminal flexible DC system in a high-resistance grounding manner. After a DC fault occurs in the multi-terminal flexible DC system, the fault current is reduced due to the presence of high grounding resistance, and the energy after the fault is quickly consumed by the resistance, thereby achieving the purpose of clearing the fault current. This solves the technical problem that the existing flexible DC uses a full-half-bridge hybrid structure to clear DC faults, but this method has the problem of unstable operation of flexible DC transmission due to converter tripping.

[0035] This ultra-long-distance multi-terminal DC side fault clearing method reduces the fault current and quickly consumes post-fault energy after a DC fault occurs in a multi-terminal flexible DC system due to the presence of a grounding unit, thereby achieving the purpose of clearing the fault current. This solves the technical problem that the existing flexible DC uses a full-half-bridge hybrid structure to clear DC faults, but this method has the problem of converter tripping, resulting in unstable flexible DC transmission operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0037] Figure 1This is a topological diagram of the connection between the multi-terminal flexible DC system and the fault clearing device according to an embodiment of the present application;

[0038] Figure 2 This is a circuit diagram of the fault clearing device according to an embodiment of the present application;

[0039] Figure 3 This is a flowchart of the steps of the method for clearing DC side faults for ultra-long-distance multi-terminal transmission according to an embodiment of the present application;

[0040] Figure 4 This is a schematic diagram of the framework of the DC side fault clearing device for ultra-long-distance multi-terminal transmission according to an embodiment of the present application;

[0041] Figure 5 A schematic diagram of a terminal device according to an embodiment of the present application;

[0042] Figure 6 This is the topology diagram of the existing multi-terminal flexible DC system;

[0043] Figure 7 The topology diagram of the existing converter is mostly a full half-bridge hybrid structure;

[0044] Figure 8 It is a topology diagram of an existing half-bridge modular multi-level converter;

[0045] Figure 9 This is a schematic diagram of the equivalent circuit before the IGBT tube in the existing converter valve is locked;

[0046] Figure 10 This is a schematic diagram of the equivalent circuit after the IGBT tube in the existing converter valve is locked;

[0047] Figure 11 It is the equivalent circuit diagram of the existing full-bridge MMC in the locked state. DETAILED DESCRIPTION

[0048] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described below 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.

[0049] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0050] In the embodiments of the present application, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections, electrical connections; direct connections, or indirect connections through an intermediate medium; and can refer to internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0051] In the embodiments of this application, Figure 6 As shown in Figure 2, the converters in the multi-terminal flexible DC system are mostly full-half-bridge hybrid structures, and the hybrid modular multilevel converter MMC also follows the topology of the MMC, as shown in Figure 2. Figure 7 As shown in the figure, the power modules in each bridge arm are composed of a combination of half-bridge and full-bridge power modules. The DC fault clearing and step-down capabilities of the hybrid modular multilevel converter (MMC) are related to the proportion of full-bridge power modules. A higher proportion of full-bridge power modules results in better DC fault clearing and stronger step-down capabilities.

[0052] like Figure 8 In the topology of the half-bridge modular multilevel converter MMC shown in the figure, when a DC line fault occurs, the transient current development of the half-bridge MMC converter valve is divided into two stages, namely before and after the IGBT tube is locked. Before the IGBT tube is locked, the equivalent circuit of the converter valve is as follows: Figure 9 As shown in Figure 1, during this stage, the power module discharges to the short-circuit fault point through the conducting IGBT tube. The rate of increase of this discharge current is very high, causing the current of the converter valve bridge arm to exceed the maximum repeatable shutdown current of the IGBT tube within a few milliseconds or even hundreds of microseconds. Therefore, it is generally necessary to lock the converter valve as soon as possible to ensure that the IGBT tube can be reliably shut down and avoid damage to the converter valve. The equivalent circuit of the converter valve after the IGBT tube is locked is as follows: Figure 10As shown, at this stage, the AC system, the anti-parallel diodes of the power modules, and the DC short-circuit fault point form a path, as shown by the dotted line in the figure. During this stage, the anti-parallel diodes must not only withstand significant short-circuit current stress, typically reaching peaks of over 10 kiloamperes, but also possess sufficient I²t capability for melting. Therefore, these diodes require special design. Existing projects typically use auxiliary thyristors for current shunting or to increase the diode's current capacity.

[0053] Since the AC system of the flexible DC can still feed short-circuit current to the fault point through the anti-parallel diode after the half-bridge MMC is locked, the AC circuit breaker must be tripped to isolate the electrical connection between the AC power supply and the fault point to clear the DC fault and restore the insulation of the fault point. After the fault is cleared, the DC system of the flexible DC needs to go through the stages of closing and charging the AC circuit breaker, removing the starting resistor, and unlocking the DC system. This takes a long time, usually several minutes or even dozens of minutes. Figure 7 As shown, the biggest advantage of full-bridge MMC power modules over half-bridge power modules lies in their greater operational flexibility and ability to output negative voltage levels. Full-bridge MMCs offer a wider DC voltage regulation range, enabling continuous and smooth DC voltage rise and fall between negative and positive rated values. This feature meets the requirements for long-distance DC transmission with 70%, 80%, or even lower step-down operation, as well as rapid step-down restart after DC faults.

[0054] In the locked state, the equivalent circuit of the full-bridge MMC is as follows: Figure 11 Taking phases A and C as an example, at this time, regardless of the forward bridge arm current or the reverse bridge arm direction, the voltage applied to the anode and cathode of diodes D1 to D4 is: , where U ac_peak is the peak value of the AC line voltage, U c It is the sum of the capacitor voltages of all power modules in each arm of the full-bridge MMC. In the design phase of the main circuit parameters of the converter station, it is generally satisfied that U ac_peak Less than 0.866U c , so diodes D2 and D3 will be cut off due to the reverse voltage. It is precisely because of this characteristic that the full-bridge MMC has the ability to self-clear DC faults.

[0055] The full-bridge MMC utilizes its inherent blocking characteristics to provide a back EMF with the opposite polarity to the AC power supply voltage in the blocked state, promoting rapid decay of the DC fault current. This process does not require tripping the AC circuit breaker or mechanical switching, resulting in rapid fault clearing. During the flexible DC system restart phase, the converter is re-unlocked, gradually building up the DC voltage. This process also requires no mechanical switching, enabling a rapid restart.

[0056] The embodiments of the present application provide a fault clearing device and a method, device and equipment for clearing DC side faults for ultra-long-distance multi-terminal transmission, which solve the technical problem that the existing flexible DC uses a full half-bridge hybrid structure to clear DC faults, but this method has the problem of converter tripping and causing unstable operation of flexible DC transmission.

[0057] Example 1:

[0058] Figure 1 This is a topological diagram of the connection between the multi-terminal flexible DC system and the fault clearing device according to an embodiment of the present application. Figure 2 This is a circuit diagram of the fault clearing device described in an embodiment of the present application.

[0059] like Figure 1 and Figure 2 As shown, an embodiment of the present application provides a fault clearing device, which is applied to a multi-terminal flexible DC system. The multi-terminal flexible DC system includes multiple sending modules 2, each sending module 2 includes two converter stations 21 and a grounding electrode line 22, and the two converter stations 21 are respectively connected to the grounding electrode line 22 and then connected to the grounding electrode 23. The fault clearing device includes a grounding unit 24 connected to the grounding electrode line 22, and the grounding unit 24 includes a transformer 241, a lightning arrester 242 and a resistor 243. The primary side of the transformer 241 is respectively connected to the grounding electrode 23 and the grounding electrode line 22, and the lightning arrester 242 is connected in series with the resistor 243 and then connected to the secondary side of the transformer 241; the lightning arrester 242 is used to control the input and output of the resistor 243; the resistor 243 is used to consume energy.

[0060] It should be noted that grounding unit 24 is installed between grounding electrode line 22 and grounding electrode 23 of the multi-terminal flexible DC system. This grounding unit 24 uses an AC transformer 241. When a stable DC current is connected to the multi-terminal flexible DC system, the secondary side of transformer 241 does not induce voltage and current, thereby not causing the operation of lightning arrester 242. However, during transient operation of the multi-terminal flexible DC system, the transient process can be induced by the magnetic field of transformer 241 on the secondary side, generating a higher voltage on the secondary side of transformer 241, causing the arrester 242 to operate, thereby activating resistor 243 to damp the fault current.

[0061] In the embodiment of the present application, the grounding unit 24 uses the primary side of a transformer 241 connected between the grounding electrode 23 and the grounding electrode line 22, and the secondary side of the transformer 241 is connected in series with a lightning arrester 242 and a resistor 243. Since a large DC current flows into the primary side of the transformer 241, it is very easy to cause saturation of the ferromagnetic material. Therefore, the transformer 241 adopts a hollow structure, that is, only the magnetic field coupling between the air is used. In addition, the turns ratio of the primary side winding and the secondary side winding of the transformer 241 is N:1, N=0.01~0.05, thereby effectively increasing the AC voltage on the secondary side of the transformer 241 and reducing the AC current on the secondary side of the transformer 241.

[0062] In the embodiment of the present application, the lightning arrester 242 is used to control the switching on and off of the resistor 243 to prevent the resistor 242 from affecting the multi-terminal flexible DC system when it is switched on in a stable state.

[0063] In the embodiment of the present application, the resistor 243 is used to consume transient energy.

[0064] The present application provides a fault clearing device, which is applied to a multi-terminal flexible DC system. The multi-terminal flexible DC system includes multiple sending modules, each sending module includes two converter stations and a grounding electrode line. The two converter stations are respectively connected to the grounding electrode line and then to the grounding electrode. The fault clearing device includes a grounding unit connected to the grounding electrode line. The grounding unit includes a transformer, a lightning arrester, and a resistor. The primary side of the transformer is respectively connected to the grounding electrode and the grounding electrode line. The lightning arrester is connected in series with the resistor and then to the secondary side of the transformer. The lightning arrester is used to control the input and output of the resistor. The resistor is used to consume energy. The fault clearing device is connected to the sending module of the multi-terminal flexible DC system in a high-resistance grounding manner. After a DC fault occurs in the multi-terminal flexible DC system, the high grounding resistance reduces the fault current, and the energy after the fault is quickly consumed by the resistor, thereby achieving the purpose of clearing the fault current. This solves the technical problem that the existing flexible DC uses a full half-bridge hybrid structure to clear DC faults, but this method has the problem of converter tripping and causing unstable operation of flexible DC transmission.

[0065] Example 2:

[0066] Figure 3 This is a flowchart of the steps of the method for clearing DC side faults for ultra-long-distance multi-terminal transmission described in an embodiment of the present application.

[0067] like Figure 3 As shown, an embodiment of the present application provides a method for clearing a DC side fault with ultra-long-distance multi-terminal transmission, which is applied to the above-mentioned fault clearing device. The DC side fault clearing method includes the following steps:

[0068] S1. Obtain the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each transmission module.

[0069] It should be noted that the contents of the fault clearing device have been described in Example 1 and will not be further described in this example. In step S1, the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each sending module are obtained to provide data for subsequent steps. In this embodiment, the electrical quantity parameters include the fault current reduction factor, the length of the grounding electrode line, the grounding electrode inductance per unit length, the mutual inductance, the fault current drop time, the safety factor, the transformation ratio, the transformer primary winding self-inductance, the fault current rise rate, the maximum DC current, the rated DC voltage, and the total length of the DC transmission line, the inductance per unit length, and the capacitance per unit length to ground.

[0070] S2. Determine operating parameters of the grounding unit based on electrical quantity parameters. The operating parameters include the rated voltage of the lightning arrester and the maximum operating power and resistance value of the resistor.

[0071] It should be noted that in step S2, the operating parameters of the grounding unit connected to the multi-terminal flexible DC system in a high-resistance grounding manner are first determined according to the electrical quantity parameters obtained in step S1 to provide data for subsequent steps.

[0072] S3. Control the grounding unit corresponding to the sending module according to the operating status to determine whether it operates according to the operating parameters.

[0073] It should be noted that in step S3 , whether the grounding unit connected to the corresponding delivery module is working is determined based on the operating status of the delivery module obtained in step S1 .

[0074] S4. If the operating state is a stable operating state, the corresponding grounding unit is controlled not to operate; if the operating state is a transient operating state, the grounding unit is controlled to operate according to the operating parameters to consume energy.

[0075] It should be noted that in step S4, the operation is performed based on the result of the determination in step S3 to ensure the stability of the multi-terminal flexible DC system. In this embodiment, controlling the grounding unit to operate according to operating parameters to consume energy includes controlling the grounding unit's lightning arrester to activate at a rated voltage and the resistor to operate at a maximum operating power and resistance value to consume energy.

[0076] The present application provides a method for clearing faults on the DC side of ultra-long-distance multi-terminal transmission, which is applied to the above-mentioned fault clearing device. The DC side fault clearing method includes the following steps: obtaining the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each transmission module; determining the operating parameters of the grounding unit based on the electrical quantity parameters, the operating parameters including the rated voltage of the lightning arrester and the maximum operating power and resistance value of the resistor; controlling whether the grounding unit corresponding to the transmission module operates according to the operating status; if the operating status is a stable operating state, controlling the corresponding grounding unit not to operate; if the operating state is a transient operating state, controlling the grounding unit to operate according to the operating parameters to consume energy. After a DC fault occurs in the multi-terminal flexible DC system, the DC side fault clearing method for ultra-long-distance multi-terminal transmission reduces the fault current due to the presence of the grounding unit, quickly consumes the energy after the fault, and thus achieves the purpose of clearing the fault current. This solves the technical problem that the existing flexible DC uses a full half-bridge hybrid structure to clear DC faults, but this method has the problem of converter tripping and causing unstable operation of flexible DC transmission.

[0077] In one embodiment of the present application, determining the operating parameters of the grounding unit according to the electrical quantity parameters includes:

[0078] The rated voltage of the arrester is calculated based on the safety factor of electrical parameters, transformation ratio, transformer primary winding self-inductance and fault current rise rate;

[0079] The resistance value of the resistor is calculated based on the maximum DC current, rated DC voltage, total length, inductance per unit length, and capacitance per unit length to ground of the DC transmission line.

[0080] The maximum operating power of the resistor is calculated based on the fault current reduction multiple of electrical parameters, grounding electrode line length, grounding electrode inductance per unit length, mutual inductance and fault current drop time.

[0081] It should be noted that the fault current reduction factor can be 4 to 5, the safety factor can be 0.8 to 0.9, and the transformation ratio can be 0.01 to 0.05.

[0082] In the embodiment of the present application, the rated voltage of the arrester is calculated using the voltage formula according to the safety factor, transformation ratio, self-inductance of the transformer primary winding, and fault current rise rate of the electrical quantity parameters; the maximum operating power of the resistor is calculated using the power formula according to the maximum DC current, rated DC voltage, and the total length, unit length inductance, and unit length capacitance of the DC transmission line of the electrical quantity parameters; the resistance value of the resistor is calculated using the resistance formula according to the fault current reduction factor, grounding electrode line length, unit length inductance of the grounding electrode, mutual inductance, and fault current fall time of the electrical quantity parameters. The voltage formula is:

[0083]

[0084] The resistance formula is:

[0085]

[0086] The power formula is:

[0087]

[0088] Where N is the transformer ratio, L is m is the self-inductance of the transformer primary winding, di / dt is the maximum fault current rise rate of the multi-terminal flexible DC transmission system during a fault, L is the total length of the DC transmission line, L1 is the inductance per unit length of the DC transmission line, C is the capacitance per unit length of the DC transmission line to ground, I dc is the maximum DC current of the multi-terminal flexible DC transmission system, U dc is the rated DC voltage of the multi-terminal flexible DC transmission system, K is the fault current reduction factor, usually 4 to 5, and can be determined according to the actual system conditions; L g is the length of the grounding electrode line, L gl is the inductance per unit length of the grounding electrode, M is the mutual inductance of the grounding unit; T is the fault current fall time, and the recommended value of T is around 100ms.

[0089] Example 3:

[0090] Figure 4 This is a schematic diagram of the framework of the DC side fault clearing device for ultra-long-distance multi-terminal transmission described in an embodiment of the present application.

[0091] like Figure 4 As shown, the embodiment of the present application provides a DC side fault clearing device with ultra-long distance multi-terminal transmission, which is applied to the above-mentioned fault clearing device. The DC side fault clearing device includes a data acquisition module 10, a parameter determination module 20, a judgment module 30 and an execution module 40;

[0092] The data acquisition module 10 is used to obtain the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each transmission module;

[0093] A parameter determination module 20 is configured to determine operating parameters of the grounding unit according to electrical quantity parameters, the operating parameters including the rated voltage of the arrester and the maximum operating power and resistance value of the resistor;

[0094] The judgment module 30 is used to control the grounding unit corresponding to the sending module to work according to the operating parameters according to the operating status;

[0095] The execution module 40 is configured to control the corresponding grounding unit to not operate according to the stable operating state; or to control the grounding unit to operate according to operating parameters to consume energy according to the transient operating state.

[0096] In an embodiment of the present application, the execution module 40 is also used to control the lightning arrester of the grounding unit to start at the rated voltage and the resistor to work at the maximum operating power and resistance value to consume energy according to the transient operating state.

[0097] In the embodiment of the present application, the parameter determination module 20 includes a first calculation submodule, a second calculation submodule and a third calculation submodule;

[0098] The first calculation submodule is used to calculate the rated voltage of the lightning arrester based on the safety factor of the electrical quantity parameters, the transformation ratio, the self-inductance of the transformer primary winding and the fault current rise rate;

[0099] The second calculation submodule is used to calculate the resistance value of the resistor based on the maximum DC current and rated DC voltage of the electrical quantity parameters and the total length, inductance per unit length and capacitance per unit length to ground of the DC transmission line;

[0100] The third calculation submodule is used to calculate the maximum operating power of the resistor based on the fault current reduction multiple, grounding electrode line length, grounding electrode unit length inductance, mutual inductance and fault current drop time of the electrical quantity parameters.

[0101] In an embodiment of the present application, the fault current reduction factor is 4-5; and / or the safety factor is 0.8-0.9; and / or the transformation ratio is 0.01-0.05.

[0102] It should be noted that the contents of the modules in the apparatus of Example 3 correspond to the steps of the method of Example 2. The contents of the method for clearing DC side faults for ultra-long-distance multi-terminal transmission have been described in Example 2, and the module contents of the apparatus for clearing DC side faults for ultra-long-distance multi-terminal transmission will not be described in detail in this embodiment.

[0103] Example 4:

[0104] Figure 5 This is a schematic diagram of the terminal device described in an embodiment of the present application.

[0105] like Figure 5 As shown, an embodiment of the present application provides a terminal device, including a processor and a memory;

[0106] A memory, configured to store program codes and transmit the program codes to a processor;

[0107] The processor is configured to execute the above-mentioned method for clearing DC side faults with ultra-long-distance multi-terminal transmission according to instructions in the program code.

[0108] It should be noted that the processor is configured to execute the steps of the aforementioned embodiment of a method for clearing a DC fault in ultra-long-distance multi-terminal transmission according to the instructions in the program code. Alternatively, the processor implements the functions of the modules / units in the aforementioned system / device embodiments when executing the computer program.

[0109] For example, a computer program may be divided into one or more modules / units, one or more of which are stored in a memory and executed by a processor to complete the present application. One or more modules / units may be a series of computer program instruction segments capable of performing specific functions, and the instruction segments are used to describe the execution process of the computer program in a terminal device.

[0110] Terminal devices can be computing devices such as desktop computers, laptops, PDAs, and cloud servers. Terminal devices may include, but are not limited to, processors and memory. Those skilled in the art will appreciate that this does not constitute a limitation on terminal devices and may include more or fewer components than shown, or a combination of certain components, or different components. For example, terminal devices may also include input / output devices, network access devices, buses, and the like.

[0111] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (dSICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0112] Memory can be an internal storage unit of a terminal device, such as a hard drive or memory. It can also be an external storage device, such as a plug-in hard drive, a Smart Memory Card (SMC), a Secure Digital (SD) card, or a flash memory card. Furthermore, memory can include both internal and external storage units. Memory is used to store computer programs and other programs and data required by the terminal device. Memory can also be used to temporarily store data that has been output or is about to be output.

[0113] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0114] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0115] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0116] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0117] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a number of instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0118] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for clearing faults on the DC side of ultra-long-distance multi-terminal transmission, applied to a fault clearing device of a multi-terminal flexible DC system, the multi-terminal flexible DC system comprising multiple transmission modules, each of which comprises two converter stations and a grounding electrode line, the two converter stations being respectively connected to the grounding electrode line and then to the grounding electrode, the fault clearing device comprising a grounding unit connected to the grounding electrode line, the grounding unit comprising a transformer, a lightning arrester, and a resistor, the primary side of the transformer being respectively connected to the grounding electrode and the grounding electrode line, the lightning arrester being connected in series with the resistor and then to the secondary side of the transformer, the lightning arrester being used to control the switching on and off of the resistor; The resistor is used to consume energy and is characterized in that: The DC side fault clearing method comprises the following steps: Obtain the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each transmission module; Determining operating parameters of the grounding unit according to the electrical quantity parameters, the operating parameters including the rated voltage of the lightning arrester and the maximum operating power and resistance value of the resistor; Controlling, according to the operating state, whether the grounding unit corresponding to the delivery module operates according to the operating parameters; If the operating state is a stable operating state, the corresponding grounding unit is controlled not to operate; if the operating state is a transient operating state, the grounding unit is controlled to operate according to the operating parameters to consume energy; Determining the operating parameters of the grounding unit according to the electrical quantity parameters includes: The rated voltage of the arrester is calculated using a voltage formula based on the safety factor of the electrical quantity parameters, the transformation ratio, the self-inductance of the transformer primary winding, and the fault current rise rate; The maximum operating power of the resistor is calculated using a power formula based on the maximum DC current, rated DC voltage, total length of the DC transmission line, inductance per unit length, and capacitance per unit length to ground of the electrical quantity parameters; The resistance value of the resistor is calculated using a resistance formula according to the fault current reduction multiple, grounding electrode line length, grounding electrode unit length inductance, mutual inductance and fault current falling time of the electrical quantity parameters; The voltage formula is: ； The resistance formula is: ； The power formula is: ； Where N is the transformer ratio, L is m is the self-inductance of the transformer primary winding, di / dt is the maximum fault current rise rate of the multi-terminal flexible DC transmission system during a fault, L is the total length of the DC transmission line, L1 is the inductance per unit length of the DC transmission line, C is the capacitance per unit length of the DC transmission line to ground, I dc is the maximum DC current of the multi-terminal flexible DC transmission system, U dc is the rated DC voltage of the multi-terminal flexible DC transmission system, K is the fault current reduction factor, L g is the length of the grounding electrode line, L gl is the inductance per unit length of the grounding electrode, M is the mutual inductance of the grounding unit, T is the fault current falling time, R is the resistance value of the resistor, U ref is the rated voltage of the arrester, and W is the maximum operating power of the resistor.

2. The method for clearing DC side faults for ultra-long-distance multi-terminal transmission according to claim 1 is characterized in that: Controlling the grounding unit to operate according to the operating parameters to consume energy includes: controlling the lightning arrester of the grounding unit to start according to the rated voltage, and controlling the resistor to operate according to the maximum operating power and the resistance value to consume energy.

3. The method for clearing DC side faults for ultra-long-distance multi-terminal transmission according to claim 1, characterized in that: The fault current reduction factor is 4-5; and / or the safety factor is 0.8-0.9; and / or the transformation ratio is 0.01-0.

05.

4. A DC side fault clearing device for ultra-long-distance multi-terminal transmission, applied to a fault clearing device of a multi-terminal flexible DC system, wherein the multi-terminal flexible DC system comprises a plurality of transmission modules, each of the transmission modules comprises two converter stations and a grounding electrode line, the two converter stations are respectively connected to the grounding electrode line and then connected to the grounding electrode, the fault clearing device comprises a grounding unit connected to the grounding electrode line, the grounding unit comprises a transformer, a lightning arrester and a resistor, the primary side of the transformer is respectively connected to the grounding electrode and the grounding electrode line, the lightning arrester is connected in series with the resistor and then connected to the secondary side of the transformer; the lightning arrester is used to control the input and output of the resistor; the resistor is used to consume energy, characterized in that The DC side fault clearing device includes a data acquisition module, a parameter determination module, a judgment module and an execution module; The data acquisition module is used to obtain the electrical quantity parameters of the multi-terminal flexible DC system and the operating status of each sending module; The parameter determination module is used to determine the operating parameters of the grounding unit according to the electrical quantity parameters, wherein the operating parameters include the rated voltage of the lightning arrester and the maximum operating power and resistance value of the resistor; The judgment module is used to control, according to the operating state, whether the grounding unit corresponding to the sending module operates according to the operating parameters; The execution module is configured to control the corresponding grounding unit to not operate according to the stable operating state; or to control the grounding unit to operate according to the operating parameters to consume energy according to the transient operating state; The parameter determination module includes a first calculation submodule, a second calculation submodule and a third calculation submodule; The first calculation submodule is configured to calculate the rated voltage of the arrester using a voltage formula based on the safety factor, transformation ratio, self-inductance of the transformer primary winding, and fault current rise rate of the electrical quantity parameters; The second calculation submodule is configured to calculate the maximum operating power of the resistor using a power formula based on the maximum DC current, the rated DC voltage, the total length, the inductance per unit length, and the capacitance per unit length to ground of the electrical quantity parameters; The third calculation submodule is configured to calculate the resistance value of the resistor using a resistance formula according to the fault current reduction multiple, the grounding electrode line length, the grounding electrode inductance per unit length, the mutual inductance, and the fault current falling time of the electrical quantity parameters; The voltage formula is: ； The resistance formula is: ； The power formula is: ； Where N is the transformer ratio, L is m is the self-inductance of the transformer primary winding, di / dt is the maximum fault current rise rate of the multi-terminal flexible DC transmission system during a fault, L is the total length of the DC transmission line, L1 is the inductance per unit length of the DC transmission line, C is the capacitance per unit length of the DC transmission line to ground, I dc is the maximum DC current of the multi-terminal flexible DC transmission system, U dc is the rated DC voltage of the multi-terminal flexible DC transmission system, K is the fault current reduction factor, L g is the length of the grounding electrode line, L gl is the inductance per unit length of the grounding electrode, M is the mutual inductance of the grounding unit, T is the fault current falling time, R is the resistance value of the resistor, U ref is the rated voltage of the arrester, and W is the maximum operating power of the resistor.

5. The ultra-long-distance multi-terminal DC side fault clearing device according to claim 4 is characterized in that: The execution module is further configured to control the lightning arrester of the grounding unit to start at the rated voltage and the resistor to operate at the maximum operating power and the resistance value to consume energy according to the operating state being a transient operating state.

6. The ultra-long-distance multi-terminal DC side fault clearing device according to claim 4 is characterized in that: The fault current reduction factor is 4-5; and / or the safety factor is 0.8-0.9; and / or the transformation ratio is 0.01-0.

05.

7. A terminal device, characterized in that: including a processor and a memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the method for clearing a DC side fault of ultra-long-distance multi-terminal transmission according to any one of claims 1 to 3 according to the instructions in the program code.

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