Fault valve bank retreating circuit and method for hybrid direct-current power transmission system

Abstract

The invention provides a hybrid direct-current power transmission system fault valve bank retreating circuit and method. The hybrid direct-current power transmission system fault valve bank retreating circuit comprises a sending end circuit electrically connected with a first alternating-current power grid; the receiving end circuit is electrically connected with the transmitting end circuit through a direct-current line and is electrically connected with a second alternating-current power grid; wherein the electric energy of the first alternating-current power grid is transmitted to the second alternating-current power grid through the sending end circuit, the direct-current line and the receiving end circuit; when the second alternating-current power grid fails, a fault current converter of the receiving end circuit is controlled to be locked, and the direct-current voltage of a non-fault current converter is reduced; and when the sending end circuit detects that the pole bus voltage of the hybrid direct-current power transmission system is greater than a first threshold value and the current is smaller than a second threshold value, the pole bus voltage of the hybrid direct-current power transmission system is reduced. The fault detection efficiency, the response speed, the safety, the accuracy and the maintainability of the fault valve withdrawing group of the hybrid direct current power transmission system can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-high voltage transmission circuits, and in particular to a hybrid direct current transmission system fault valve group circuit and method. Background Art

[0002] Ultra-high voltage direct current (UHVDC) transmission systems offer the advantages of low losses and high efficiency for long-distance power transmission, but their design faces the dual challenges of cost-effectiveness and reliability. Hybrid DC transmission systems typically use LCCs (line-commutated converters) on the sending end to achieve high-power and efficient conversion, and MMCs (modular multilevel converters) on the receiving end to improve waveform quality and reduce the risk of commutation failure. However, in long-distance transmission, if an MMC converter fails at the receiving end and needs to be removed online, traditional valve group removal strategies that rely on inter-station communication may fail due to communication delays or interruptions, leading to uncontrolled energy management, overvoltage or overcurrent, and threatening system safety. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a hybrid DC transmission system fault valve group return circuit and method, which can improve the fault detection efficiency, response speed, safety, accuracy and maintainability of the hybrid DC transmission system fault valve group return circuit.

[0004] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0005] A hybrid DC transmission system fault valve group circuit, comprising:

[0006] a sending-end circuit electrically connected to the first AC power grid;

[0007] a receiving-end circuit electrically connected to the sending-end circuit via a DC line, wherein the receiving-end circuit is electrically connected to a second AC power grid;

[0008] The electric energy of the first AC grid is transmitted to the second AC grid through the sending-end circuit, the DC line and the receiving-end circuit;

[0009] When the second AC power grid fails, controlling the faulty converter of the receiving circuit to lock out and reducing the DC voltage of the non-faulty converter;

[0010] When the sending-end circuit detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced.

[0011] Optionally, the receiving circuit includes:

[0012] a first voltage transformer and a second voltage transformer;

[0013] A third AC switch is provided at one end of the first voltage transformer, the other end of the first voltage transformer is electrically connected to a first multilevel converter, a third bypass switch is connected in parallel to one side of the first multilevel converter, and the first multilevel converter is a high-voltage converter;

[0014] A fourth AC switch is provided at one end of the second voltage transformer, the other end of the second voltage transformer is electrically connected to a second multilevel converter, a fourth bypass switch is connected in parallel to one side of the second multilevel converter, and the second multilevel converter is a low-voltage converter;

[0015] The second multi-level converter blocks and trips the second AC switch connected thereto; and reduces the DC voltage of the first multi-level converter.

[0016] Optionally, the DC voltage of the first multi-level converter is reduced to zero, and the current reference value before the phase shift is saved.

[0017] Optionally, the sending-end circuit includes:

[0018] a first three-phase transformer and a second three-phase transformer,

[0019] A first AC switch is provided at one end of the first three-phase transformer, and the other end of the first three-phase transformer is electrically connected to a first line-commutated converter. A first bypass switch is connected in parallel to one side of the first line-commutated converter, and the first line-commutated converter is a high-voltage converter.

[0020] A second AC switch is provided at one end of the second three-phase transformer, the other end of the first three-phase transformer is electrically connected to a second line-commutated converter, a second bypass switch is connected in parallel to one side of the second line-commutated converter, and the second line-commutated converter is a low-voltage converter;

[0021] When the first line-commutated converter or the second line-commutated converter detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced.

[0022] Optionally, when the pole bus voltage of the hybrid DC transmission system is reduced to zero, the sending-end circuit is controlled to lock the first-line phase-commutating converter, trip the first AC switch, close the first bypass switch, and save the DC voltage reference value before the fault.

[0023] Optionally, when the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit exits the converter of the same type as the faulty converter in the receiving-end circuit, specifically by locking the second-line phase-commutating converter, tripping the second AC switch, and closing the second bypass switch.

[0024] Optionally, when the receiving-end circuit detects that the pole bus voltage of the hybrid DC transmission system reaches zero, the fourth bypass switch of the second multilevel converter is closed; and the first multilevel converter restores the DC voltage to a DC voltage reference value before the fault at a first preset rate.

[0025] Optionally, in the sending-end circuit, the first line-commutated converter or the second line-commutated converter that has not exited recovers to the current reference value before the phase shift at a second preset rate.

[0026] An embodiment of the present invention further provides a method for returning a valve group to a fault in a hybrid direct current transmission system, which is applied to the circuit described in the above solution. The method includes:

[0027] When a fault in the second AC power grid is detected, the faulty converter of the receiving-end circuit is controlled to be locked and the DC voltage of the non-faulty converter is reduced;

[0028] When the sending-end circuit detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced;

[0029] When the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit exits the converter of the same type as the faulty converter that has failed in the receiving-end circuit.

[0030] Optionally, the sending-end circuit exiting a converter of the same type as the faulty converter that has failed in the receiving-end circuit includes:

[0031] Lock the second line commutation converter, trip the second AC switch, and close the second bypass switch.

[0032] The above technical solution of the present invention has at least the following technical effects:

[0033] The hybrid DC transmission system fault valve removal group circuit of the present invention is configured to transmit power from the first AC grid to the receiving circuit via a sending-end circuit electrically connected to the first AC grid, and from the receiving circuit via a DC line electrically connected to the sending circuit, wherein the receiving circuit is electrically connected to a second AC grid. The circuit transmits power from the first AC grid to the second AC grid via the sending-end circuit, the DC line, and the receiving circuit. When the second AC grid fails, the faulty converter in the receiving circuit is controlled to lock out and the DC voltage of the non-faulty converter is reduced. When the sending-end circuit detects that the hybrid DC transmission system's pole bus voltage is greater than a first threshold and the current is less than a second threshold, the sending circuit reduces the hybrid DC transmission system's pole bus voltage. This improves the fault detection efficiency, response speed, safety, accuracy, and maintainability of the hybrid DC transmission system fault valve removal group. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1This is a schematic diagram of a fault-return valve group circuit for a hybrid DC power transmission system according to the present invention;

[0035] Figure 2 It is a flow chart of the hybrid DC transmission system fault valve group withdrawal method of the present invention. DETAILED DESCRIPTION

[0036] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0037] like Figure 1 As shown, an embodiment of the present invention provides a hybrid DC transmission system fault valve group circuit, comprising:

[0038] a sending-end circuit electrically connected to the first AC power grid D1;

[0039] a receiving-end circuit electrically connected to the sending-end circuit via a DC line XL, wherein the receiving-end circuit is electrically connected to a second AC grid D2;

[0040] The electric energy of the first AC grid D1 is transmitted to the second AC grid D2 through the sending-end circuit, the DC line XL and the receiving-end circuit;

[0041] When the second AC grid D2 fails, the faulty converter of the receiving circuit is controlled to be locked and the DC voltage of the non-faulty converter is reduced;

[0042] When the sending-end circuit detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced.

[0043] In this embodiment, Figure 1 As shown in the figure, the sending end refers to the place where electric energy is output, which is the power output end of the transmission system and is provided to the power grid or other power loads. The voltage level at the sending end is usually higher and needs to be transformed and stepped down before it can be transmitted to the user side. The receiving end is the place where electric energy is input, which is also the power input end of the transmission system. It generally needs to be connected to the load side of the transmission system to receive the electric energy consumed by the load. In contrast to the sending end, the voltage level at the receiving end is usually lower. Figure 1As shown, in the fault-removal valve group circuit of the hybrid DC transmission system, the sending-end circuit and the receiving-end circuit are electrically connected via a DC line XL. The sending-end circuit is electrically connected to the first AC grid D1, and the receiving-end circuit is electrically connected to the second AC grid D2. The electric energy of the first AC grid D1 is transmitted to the second AC grid D2 via the sending-end circuit, the DC line XL, and the receiving-end circuit. When a fault occurs in the second AC grid D2, first, fault information of the receiving end of the hybrid DC transmission system is obtained. The fault information includes changes in the receiving-end voltage, changes in the voltage and current on the pole bus, etc. Then, the sending end of the hybrid DC transmission system triggers fast phase shift control based on the fault information to reduce the pole bus voltage of the hybrid DC transmission system and stop the sending end from supplying electric energy to the receiving end. Third, the sending end determines the sending-end converter that needs to be deactivated based on the fault information sent by the receiving end, and causes the corresponding sending-end converter to deactivate the transmission system. Finally, the receiving-end non-fault converter and the sending-end converter that has not deactivated gradually resume normal operation based on the pole bus voltage, thereby completing the fault isolation of the hybrid DC transmission system.

[0044] like Figure 1 As shown, in an optional embodiment of the present invention, the receiving circuit includes:

[0045] The first voltage transformer H1 and the second voltage transformer H2,

[0046] A third AC switch K13 is provided at one end of the first voltage transformer H1. The other end of the first voltage transformer H1 is electrically connected to the first multilevel converter MMC1. A third bypass switch K23 is connected in parallel to one side of the first multilevel converter MMC1. The first multilevel converter MMC1 is a high-voltage converter.

[0047] A fourth AC switch K14 is provided at one end of the second voltage transformer H2. The other end of the second voltage transformer H2 is electrically connected to the second multilevel converter MMC2. A fourth bypass switch K24 is connected in parallel to one side of the second multilevel converter MMC2. The second multilevel converter MMC2 is a low-voltage converter.

[0048] The second multilevel converter MMC2 blocks and trips the second AC switch K12 connected thereto, and reduces the DC voltage of the first multilevel converter MMC1.

[0049] In this embodiment, Figure 1As shown, the receiving-end circuit includes a first voltage transformer H1 and a second voltage transformer H2; one end of the first voltage transformer H1 is electrically connected to a third AC switch K13, and the other end is electrically connected to the first multilevel converter MMC1. A third bypass switch K23 is connected in parallel to one side of the first multilevel converter MMC1. The first multilevel converter MMC1 is a high-voltage converter, which has a higher voltage level and better performance, such as fast dynamic response and low energy loss. One end of the second voltage transformer H2 is electrically connected to a fourth AC switch K14, and the other end is electrically connected to the second multilevel converter MMC2. A fourth bypass switch K24 is connected in parallel to one side of the second multilevel converter MMC2. The second multilevel converter MMC2 is a low-voltage converter, which has a lower voltage level, lower cost, but relatively weaker performance. When a fault occurs in the receiving-end circuit of the hybrid DC transmission system, the faulty converter at the receiving end immediately locks out and disconnects the corresponding AC switch.

[0050] In an optional embodiment of the present invention, the DC voltage of the first multi-level converter MMC1 is reduced to zero, and the current reference value before the phase shift is saved.

[0051] In this embodiment, after a fault occurs in the receiving end circuit, the non-fault converter at the receiving end reduces the DC voltage to a preset value and saves the reference value, preferably the preset value of the DC voltage is zero; the receiving end reduces the DC voltage to zero through the non-fault converter and sends fault information of the receiving end converter.

[0052] like Figure 1 As shown, in an optional embodiment of the present invention, the sending-end circuit includes:

[0053] The first three-phase transformer B1 and the second three-phase transformer B2,

[0054] A first AC switch K11 is provided at one end of the first three-phase transformer B1, and the other end of the first three-phase transformer B1 is electrically connected to a first line-commutated converter LCC1. A first bypass switch K21 is connected in parallel to one side of the first line-commutated converter LCC1. The first line-commutated converter LCC1 is a high-voltage converter.

[0055] A second AC switch K12 is provided at one end of the second three-phase transformer B2, and the other end of the second three-phase transformer B2 is electrically connected to a second line-commutated converter LCC2. A second bypass switch K22 is connected in parallel to one side of the second line-commutated converter LCC2. The second line-commutated converter LCC2 is a low-voltage converter.

[0056] When the first line-commutated converter LCC1 or the second line-commutated converter LCC2 detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced.

[0057] In this embodiment, Figure 1 As shown, the sending-end circuit includes: a first three-phase transformer B1 and a second three-phase transformer B2, wherein one end of the first three-phase transformer B1 is electrically connected to a first AC switch K11, and the other end is electrically connected to a first line-commutated converter LCC1, and a first bypass switch K21 is connected in parallel to one side of the first line-commutated converter LCC1. The first line-commutated converter LCC1 is a high-voltage converter, which has a higher voltage level and better performance, such as fast dynamic response and low power loss; one end of the second three-phase transformer B2 is electrically connected to a second AC switch K12, and the other end is electrically connected to a second line-commutated converter LCC2, and a second bypass switch K22 is connected in parallel to one side of the second line-commutated converter LCC2. The second line-commutated converter LCC2 is a low-voltage converter, which has a lower voltage level and lower cost but relatively weaker performance;

[0058] The sending-end converter detects the DC voltage and DC current of the pole bus in the transmission system in real time; when the DC voltage and DC current of the pole bus exceed the corresponding thresholds, the sending end performs rapid phase shifting to reduce the DC voltage of the pole bus of the hybrid DC transmission system to a preset value, preferably the preset value of the DC voltage is zero; when judging the fault of the receiving end, the minimum voltage of the pole bus voltage is set as the first threshold, and the maximum current of the pole bus is set as the second threshold; when the first line-commutated converter LCC1 or the second line-commutated converter LCC2 of the sending end detects that the pole bus voltage is greater than the first threshold and the pole bus current is less than the second threshold, it is determined that a fault has occurred at the receiving end, and the sending end performs rapid phase shifting to reduce the pole bus voltage to zero; the sending end stops power output, reduces energy injection, and prevents energy accumulation in the transmission system, thereby preventing dangerous overvoltage and overcurrent.

[0059] In an optional embodiment of the present invention, when the pole bus voltage of the hybrid DC transmission system is reduced to zero, the sending-end circuit is controlled to lock the first line-commutated converter LCC1, trip the first AC switch K11, close the first bypass switch K21, and save the DC voltage reference value before the fault.

[0060] In this embodiment, if there is no communication or a communication failure occurs between the sending-end circuit and the receiving-end circuit, the sending-end circuit defaults to exiting the first-line phase-commutating converter LCC1 with a higher voltage to ensure system safety redundancy; when exiting, the first-line phase-commutating converter LCC1 is first locked, then the first AC switch K11 is tripped, and then the first bypass switch K21 is closed. Before executing the phase shift, the sending end saves the current reference value before the phase shift, so that the normal operation of the sending end can be restored based on the current reference value.

[0061] In an optional embodiment of the present invention, when the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit exits the converter of the same type as the faulty converter in the receiving-end circuit, specifically by locking the second line-commutated converter LCC2, tripping the second AC switch K12, and closing the second bypass switch K22.

[0062] In this embodiment, when the communication between the sending-end circuit and the receiving-end circuit is normal, the sending-end circuit exits the converter of the same type as the receiving-end circuit according to the fault information; if the converter in the receiving-end circuit where the fault occurs is a low-voltage converter, the sending-end circuit also exits the low-voltage converter; if the converter in the receiving-end circuit where the fault occurs is a high-voltage converter, the sending-end circuit also exits the high-voltage converter; the high and low voltage of the converter mainly refer to the voltage level and performance difference of the converter transformer valve group. The high-voltage valve group has a higher voltage level and better performance, such as fast dynamic response and low energy loss, while the low-voltage valve group has a lower voltage level and lower cost but relatively weaker performance; specifically, the sending-end circuit converter exit operation is to lock the second line commutation converter LCC2, trip the second AC switch K12, and close the second bypass switch K22, so that the bypass switch is closed to form a loop.

[0063] In an optional embodiment of the present invention, when the receiving-end circuit detects that the pole bus voltage of the hybrid direct current transmission system reaches zero, the fourth bypass switch K24 of the second multilevel converter MMC2 is closed;

[0064] The first multilevel converter MMC1 restores the DC voltage to a DC voltage reference value before the fault at a first preset rate.

[0065] In this embodiment, when the receiving circuit detects that the pole bus voltage of the hybrid DC transmission system has reached zero, the faulty converter of the receiving circuit exits and the fourth bypass switch K24 of the second multilevel converter MMC2 is first closed. The non-faulty converters of the receiving circuit restore the voltage to the voltage reference value at a preset rate. Specifically, the first multilevel converter MMC1 restores the DC voltage to the DC voltage reference value before the fault at a first preset rate.

[0066] In an optional embodiment of the present invention, in the sending-end circuit, the first line-commutated converter LCC1 or the second line-commutated converter LCC2 that has not exited recovers to the current reference value before the phase shift at a second preset rate.

[0067] In this embodiment, during the process of power supply restoration of the power transmission system, the non-exited converter at the sending end restores the current to the current reference value at a second preset rate. Specifically, the non-exited first line-commutated converter LCC1 or the second line-commutated converter LCC2 restores the current to the current reference value before the phase shift at the second preset rate.

[0068] The implementation process of the present invention is described below with an application example:

[0069] like Figure 2 As shown, in the power transmission system of this example, the AC grid D1 transmits electric energy to the AC grid D2, the first AC grid D1 is the sending end, and the second AC grid D2 is the receiving end; the first AC grid D1 is provided with two three-phase transformers B1 and B2, one end of the first three-phase transformer B1 is provided with a first AC switch K11, and the other end is electrically connected to the first line-commutated converter LCC1, the line-commutated converter is composed of a plurality of diodes connected in series, and can achieve high-power and efficient conversion, a first bypass switch K21 is connected in parallel on one side of the first line-commutated converter LCC1; one end of the second three-phase transformer B2 is provided with a second AC switch K12, and the other end is electrically connected to the second line-commutated converter LCC2, the line-commutated converter can achieve high-power and efficient conversion, and the second line-commutated converter LCC1 is provided with a second bypass switch K21; A second bypass switch K22 is connected in parallel to one side of the converter LCC2; the second AC grid D2 is provided with two voltage transformers H1 and H2. A third AC switch K13 is provided at one end of the first voltage transformer H1, and the other end is electrically connected to the first multilevel converter MMC1. The multilevel converter can improve waveform quality and reduce the risk of commutation failure. The third bypass switch K23 is connected in parallel to one side of the first multilevel converter MMC1; a fourth AC switch K14 is provided at one end of the second voltage transformer H2, and the other end is electrically connected to the second multilevel converter MMC2. The multilevel converter consists of diodes and transistors connected in parallel, which can improve waveform quality and reduce the risk of commutation failure. A fourth bypass switch K24 is connected in parallel to one side of the second multilevel converter MMC2;

[0070] Here, the first on-line commutated converter LCC1 and the second line commutated converter LCC2 have the same circuit structure, both including two diodes connected in series, and the first on-line commutated converter LCC1 and the second line commutated converter LCC2 are connected in series;

[0071] The first multilevel converter MMC1 and the second multilevel converter MMC2 have the same circuit structure, both including a transistor and a diode, with both ends of the diode electrically connected to the source and drain of the transistor respectively; and the transistor of the first multilevel converter MMC1 is electrically connected to the transistor of the second multilevel converter MMC2.

[0072] The following is an example of a fault in the second multilevel converter MMC2 in the receiving circuit:

[0073] Fault valve group return process:

[0074] 1. Receiving-end circuit fault detection and initial response: The faulty second multilevel converter MMC2 is immediately blocked and its connected fourth AC switch K14 is tripped. The non-faulty first multilevel converter MMC1 controls the DC link voltage to zero and preserves the pre-fault DC voltage reference value.

[0075] 2. Sending-end circuit detection and action: The first line-commutated converter (LCC1) and the second line-commutated converter (LCC2) of the sending-end circuit monitor the DC voltage and DC current of the pole bus. If the conditions are met (the pole bus voltage is greater than the first threshold and the current is less than the second threshold), the sending-end circuit performs a rapid phase shift to reduce the pole bus voltage to zero and saves the current reference value before the phase shift.

[0076] 3. Sending-end converter shutdown, communication normal: If the sending-end converter is the same type as the faulty receiving-end converter, and if the second multilevel converter MMC2 has a low-voltage fault, the corresponding low-voltage second line-commutated converter LCC2 is shut down. Operation: Lock the second line-commutated converter LCC2, trip the second AC switch K12, and close the second bypass switch K22.

[0077] Communication failure: The sending end defaults to the high-voltage first-line commutation converter LCC1. Operation: Block the first-line commutation converter LCC1, trip the first AC switch K11, and close the first bypass switch K21.

[0078] 4. Bypass and recovery at the receiving end: After detecting that the pole bus voltage is zero, the receiving end closes the fourth bypass switch K24 of the faulty second multilevel converter MMC2; the non-faulty first multilevel converter MMC1 gradually restores the DC voltage to the pre-fault reference value at a set rate.

[0079] 5. The sending-end current is restored, and the first-line commutated converter LCC1 or the second-line commutated converter LCC2 of the sending-end converter that has not exited closes the loop to control the DC current, gradually restoring it to the reference value before the phase shift.

[0080] 6. Fault exit is completed. When both the sending-end current and the receiving-end voltage return to the reference values, the system completes the exit process of the faulty second multilevel converter MMC2.

[0081] The above-mentioned embodiment of the present invention analyzes the electrical parameters of the sending-end circuit, such as the changes in the pole bus DC voltage and current, and autonomously identifies the need to exit the valve group due to a fault in the receiving-end circuit, thereby achieving rapid fault detection and response without relying on inter-station communication. When a fault occurs in the receiving-end circuit, the non-fault converter immediately reduces the DC side voltage to zero, while the sending-end circuit returns the pole bus voltage to zero through rapid phase shift control and saves the reference value, thereby reducing energy injection from the source. When the communication between the sending-end circuit and the receiving-end circuit is normal, the exit categories of the converters at both ends are kept consistent. In the event of a communication fault, the high-voltage converter is exited by default first, ensuring system safety and redundancy. A phased coordinated recovery mechanism is adopted for the sending-end circuit and the receiving-end circuit, whereby the receiving end gradually restores the voltage at a preset rate, and the sending end accurately adjusts the current through closed-loop control, ensuring a smooth transition of system parameters and avoiding secondary faults.

[0082] like Figure 2 As shown, an embodiment of the present invention further provides a method for returning a valve group to a fault in a hybrid DC transmission system, which is applied to the circuit described in the above solution, and the method includes:

[0083] Step S1, when a fault is detected in the second AC grid D2, the faulty converter of the receiving circuit is controlled to be locked and the DC voltage of the non-faulty converter is reduced;

[0084] Step S2: when the sending-end circuit detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold value and the current is less than a second threshold value, the pole bus voltage of the hybrid DC transmission system is reduced;

[0085] Step S3: When the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit exits the converter of the same type as the faulty converter in the receiving-end circuit.

[0086] In an optional embodiment of the present invention, the sending-end circuit exits a converter of the same type as the faulty converter that has failed in the receiving-end circuit, including:

[0087] The second line-commutated converter LCC2 is locked, the second AC switch K12 is tripped, and the second bypass switch K22 is closed.

[0088] above Figure 1 All implementations in the circuit shown are applicable to the embodiments of the method and can achieve the same technical effects.

[0089] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0090] 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.

[0091] In the embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of 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. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0092] 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.

[0093] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0094] If the functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product, stored in a storage medium, includes instructions for causing a computer device (such as a personal computer, server, or network device) to execute all or part of the steps of the various embodiments of the method of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, mobile hard drives, ROM, RAM, magnetic disks, or optical disks.

[0095] In addition, it should be pointed out that in the apparatus and method of the present invention, it is obvious that each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent solutions of the present invention. Moreover, the steps of performing the above-mentioned series of processing can naturally be performed in chronological order according to the order of description, but they do not necessarily need to be performed in chronological order, and some steps can be performed in parallel or independently of each other. For those of ordinary skill in the art, it can be understood that all or any steps or components of the method and apparatus of the present invention can be implemented in hardware, firmware, software or a combination thereof in any computing device (including a processor, storage medium, etc.) or a network of computing devices. This can be achieved by those of ordinary skill in the art using their basic programming skills after reading the description of the present invention.

[0096] Therefore, the purpose of the present invention can also be achieved by running a program or a group of programs on any computing device. The computing device can be a well-known general-purpose device. Therefore, the purpose of the present invention can also be achieved simply by providing a program product containing program code for implementing the method or device. That is to say, such a program product also constitutes the present invention, and the storage medium storing such a program product also constitutes the present invention. Obviously, the storage medium can be any well-known storage medium or any storage medium developed in the future. It should also be pointed out that in the device and method of the present invention, it is obvious that each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent schemes of the present invention. In addition, the steps of performing the above-mentioned series of processing can naturally be performed in chronological order according to the order of description, but do not necessarily need to be performed in chronological order. Certain steps can be performed in parallel or independently of each other.

[0097] The above is a preferred embodiment of the present invention. 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 invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A hybrid DC transmission system fault valve group circuit, characterized in that: include: a sending-end circuit electrically connected to the first AC power grid (D1); a receiving-end circuit electrically connected to the sending-end circuit via a DC line (XL), the receiving-end circuit being electrically connected to a second AC power grid (D2); The electric energy of the first AC grid (D1) is transmitted to the second AC grid (D2) through a sending-end circuit, a DC line (XL) and a receiving-end circuit; When the second AC power grid (D2) fails, controlling the faulty converter of the receiving circuit to lock out and reducing the DC voltage of the non-faulty converter; When the sending-end circuit detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced.

2. The hybrid DC transmission system fault valve group circuit according to claim 1, characterized in that: The receiving end circuit comprises: a first voltage transformer (H1) and a second voltage transformer (H2); A third AC switch (K13) is provided at one end of the first voltage transformer (H1), the other end of the first voltage transformer (H1) is electrically connected to a first multilevel converter (MMC1), a third bypass switch (K23) is connected in parallel to one side of the first multilevel converter (MMC1), and the first multilevel converter (MMC1) is a high-voltage converter; A fourth AC switch (K14) is provided at one end of the second voltage transformer (H2), the other end of the second voltage transformer (H2) is electrically connected to a second multilevel converter (MMC2), a fourth bypass switch (K24) is connected in parallel to one side of the second multilevel converter (MMC2), and the second multilevel converter (MMC2) is a low-voltage converter; The second multilevel converter (MMC2) blocks and trips the second AC switch (K12) connected thereto, and reduces the DC voltage of the first multilevel converter (MMC1).

3. The hybrid DC transmission system fault valve group circuit according to claim 2, characterized in that: The DC voltage of the first multilevel converter (MMC1) is reduced to zero, and the current reference value before the phase shift is saved.

4. The hybrid DC transmission system fault valve group circuit according to claim 2 or 3, characterized in that: The sending-end circuit includes: The first three-phase transformer (B1) and the second three-phase transformer (B2), A first AC switch (K11) is provided at one end of the first three-phase transformer (B1), the other end of the first three-phase transformer (B1) is electrically connected to a first line-commutated converter (LCC1), a first bypass switch (K21) is connected in parallel to one side of the first line-commutated converter (LCC1), and the first line-commutated converter (LCC1) is a high-voltage converter; A second AC switch (K12) is provided at one end of the second three-phase transformer (B2), the other end of the second three-phase transformer (B2) is electrically connected to a second line-commutated converter (LCC2), a second bypass switch (K22) is connected in parallel to one side of the second line-commutated converter (LCC2), and the second line-commutated converter (LCC2) is a low-voltage converter; When the first line-commutated converter (LCC1) or the second line-commutated converter (LCC2) detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced.

5. The hybrid DC transmission system fault valve group circuit according to claim 4, characterized in that: When the pole bus voltage of the hybrid DC transmission system is reduced to zero, the sending-end circuit is controlled to lock the first line-commutated converter (LCC1), trip the first AC switch (K11), close the first bypass switch (K21), and save the DC voltage reference value before the fault.

6. The hybrid DC transmission system fault valve group circuit according to claim 4, characterized in that: When the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit exits the converter of the same type as the faulty converter in the receiving-end circuit, specifically by locking the second line-commutated converter (LCC2), tripping the second AC switch (K12), and closing the second bypass switch (K22).

7. The hybrid DC transmission system fault valve group circuit according to claim 5, characterized in that: When the receiving-end circuit detects that the pole bus voltage of the hybrid DC transmission system reaches zero, the fourth bypass switch (K24) of the second multilevel converter (MMC2) is closed; and the first multilevel converter (MMC1) restores the DC voltage to a DC voltage reference value before the fault at a first preset rate.

8. The hybrid DC transmission system fault valve group circuit according to claim 7, characterized in that: In the sending-end circuit, the first line-commutated converter (LCC1) or the second line-commutated converter (LCC2) that has not exited recovers to the current reference value before the phase shift at a second preset rate.

9. A method for valve group return in case of fault in hybrid DC transmission system, characterized in that: Applied to the circuit according to any one of claims 1 to 8, the method comprises: When a fault in the second AC grid (D2) is detected, the faulty converter of the receiving circuit is controlled to be locked and the DC voltage of the non-faulty converter is reduced; When the sending-end circuit detects that the pole bus voltage of the hybrid DC transmission system is greater than a first threshold and the current is less than a second threshold, the pole bus voltage of the hybrid DC transmission system is reduced; When the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit exits the converter of the same type as the faulty converter that has failed in the receiving-end circuit.

10. The method for valve group removal in a hybrid DC power transmission system according to claim 9, characterized in that: The sending-end circuit exits a converter of the same type as the faulty converter that has a fault in the receiving-end circuit, including: Block the second line-commutated converter (LCC2), trip the second AC switch (K12), and close the second bypass switch (K22).

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