A hybrid DC transmission system fault valve group circuit and method

Abstract

This invention provides a fault-clearing valve group circuit and method for a hybrid DC transmission system. The fault-clearing valve group circuit includes: a sending-end circuit electrically connected to a first AC power grid; and 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. The electrical energy from the first AC power grid is transmitted to the second AC power grid through the sending-end circuit, the DC line, and the receiving-end circuit. When the second AC power grid fails, the faulty converter in the receiving-end circuit is locked out, and the DC voltage of the non-faulty converters 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, it reduces the pole bus voltage of the hybrid DC transmission system. This invention can improve the fault detection efficiency, response speed, safety, accuracy, and maintainability of the fault-clearing valve group in a hybrid DC transmission system.

Description

Technical Field

[0001] This invention relates to the field of ultra-high voltage power transmission circuit technology, and in particular to a fault discharge valve group circuit and method for a hybrid DC power transmission system. Background Technology

[0002] Ultra-high voltage direct current (UHVDC) transmission systems offer advantages such as low loss and high efficiency in long-distance power transmission, but their design faces the dual challenges of economy and reliability. Hybrid DC transmission systems typically employ LCCs (Line-Commutated Converters) at the sending end to achieve high-power, high-efficiency conversion, while MMCs (Modular Multilevel Converters) at the receiving end are used to improve waveform quality and reduce the risk of commutation failure. However, in long-distance transmission, if the receiving-end MMC converter fails and needs to be taken offline, the traditional valve group strategy relying on inter-station communication may fail due to communication delays or interruptions, leading to uncontrolled energy management, overvoltage or overcurrent problems, and threatening system safety. Summary of the Invention

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

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0005] A fault-avoidance valve group circuit for a hybrid DC transmission system includes:

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

[0007] A receiving circuit electrically connected to the sending circuit via a DC line, the receiving circuit being electrically connected to a second AC power grid;

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

[0009] When the second AC power grid fails, the faulty converter in the receiving-end circuit is locked out, and the DC voltage of the non-faulty converter is reduced.

[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, it reduces the pole bus voltage of the hybrid DC transmission system.

[0011] Optionally, the receiving-end circuit includes:

[0012] First voltage transformer and second voltage transformer;

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

[0014] One end of the second voltage transformer is equipped with a fourth AC switch, and the other end of the second voltage transformer is electrically connected to the second multilevel converter. A fourth bypass switch is connected in parallel on one side of the second multilevel converter. The second multilevel converter is a low-voltage converter.

[0015] The second multilevel converter is locked out and tripped by the second AC switch connected to it; and the DC voltage of the first multilevel converter is reduced.

[0016] Optionally, the DC voltage of the first multilevel converter is reduced to zero, and the current reference value before phase shift is preserved.

[0017] Optionally, the sending circuit includes:

[0018] First three-phase transformer and second three-phase transformer

[0019] One end of the first three-phase transformer is equipped with a first AC switch, and the other end of the first three-phase transformer is electrically connected to the first line-commutated converter. A first bypass switch is connected in parallel on one side of the first line-commutated converter. 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, and the other end of the first three-phase transformer is electrically connected to the second line-commutator converter. A second bypass switch is connected in parallel on one side of the second line-commutator converter. The second line-commutator converter is a low-voltage converter.

[0021] Specifically, when the first-line commutator or the second-line commutator 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 control circuit blocks the first line phase converter, trips the first AC switch, closes the first bypass switch, and saves 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 disconnects from the converter of the same type as the faulty converter in the receiving-end circuit, specifically by blocking the second line-commutated 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 has dropped to zero, it closes the fourth bypass switch of the second multilevel converter; the first multilevel converter restores the DC voltage to the 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 been deactivated recovers to the current reference value before the phase shift at a second preset rate.

[0026] Embodiments of the present invention also provide a method for fault-free valve grouping in a hybrid DC transmission system, applied to the circuit described in the above scheme, the method comprising:

[0027] When a fault in the second AC power grid is detected, the faulty converter in the receiving-end circuit is locked out, 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 the first threshold and the current is less than the second threshold, it reduces the pole bus voltage of the hybrid DC transmission system.

[0029] When the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit will disconnect from the converter of the same type as the faulty converter in the receiving-end circuit.

[0030] Optionally, the sending-end circuit may disconnect from a converter of the same type as the faulty converter in the receiving-end circuit, including:

[0031] Lock out the second-line phase-changing converter, trip the second AC switch, and close the second bypass switch.

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

[0033] The fault-removal valve group circuit of the hybrid DC transmission system of the present invention comprises a sending-end circuit electrically connected to a first AC power grid; a receiving-end circuit electrically connected to the sending-end circuit via a DC line, and the receiving-end circuit electrically connected to a second AC power grid; wherein, the electrical energy of the first AC power grid is transmitted to the second AC power grid through the sending-end circuit, the DC line, and the receiving-end circuit; when the second AC power grid fails, the faulty converter in the receiving-end circuit is locked out, 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. This improves the fault detection efficiency, response speed, safety, accuracy, and maintainability of the fault-removal valve group of the hybrid DC transmission system. Attached Figure Description

[0034] Figure 1This is a schematic diagram of the fault relief valve group circuit of the hybrid DC transmission system of the present invention;

[0035] Figure 2 This is a schematic flowchart of the fault-removal valve group method for hybrid DC transmission systems according to the present invention. Detailed Implementation

[0036] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

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

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

[0039] The receiving-end circuit is electrically connected to the sending-end circuit via a DC line XL, and the receiving-end circuit is electrically connected to the second AC power grid D2.

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

[0041] When the second AC power grid D2 fails, the faulty converter in the receiving-end circuit is locked out, 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, it reduces the pole bus voltage of the hybrid DC transmission system.

[0043] In this embodiment, as Figure 1 As shown, the sending end is where electrical energy is output; it is the power output terminal of the transmission system, supplying power to the grid or other electrical loads. The voltage level of the sending end is usually higher, requiring voltage reduction by transmission transformers before being transmitted to the user side. The receiving end is where electrical energy is input, also the power input terminal of the transmission system. It generally needs to be connected to the load side of the transmission system to receive the electrical energy consumed by the load. Conversely, the voltage level of the receiving end is usually lower. For example... Figure 1As shown, in the fault-free valve group circuit of the hybrid DC transmission system, the sending-end circuit and the receiving-end circuit are electrically connected via 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 electrical energy of the first AC grid D1 is transmitted to the second AC grid D2 through the sending-end circuit, DC line XL, and receiving-end circuit. When a fault occurs in the second AC grid D2, firstly, the fault information of the receiving end of the hybrid DC transmission system is acquired, including changes in the receiving-end voltage, changes in voltage and current on the pole bus, etc. Then, based on the fault information, the sending end of the hybrid DC transmission system triggers fast phase-shift control to reduce the pole bus voltage of the hybrid DC transmission system and stop the sending end from outputting electrical energy to the receiving end. Next, based on the fault information sent by the receiving end, the sending end determines the sending-end converter that needs to be taken out of operation and causes the corresponding sending-end converter to exit the transmission system. Finally, the non-faulty receiving-end converter and the non-exiting sending-end converter gradually resume normal operation based on the pole bus voltage, 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-end circuit includes:

[0045] First voltage transformer H1 and second voltage transformer H2

[0046] One end of the first voltage transformer H1 is provided with a third AC switch K13, and 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 on one side of the first multilevel converter MMC1. The first multilevel converter MMC1 is a high-voltage converter.

[0047] One end of the second voltage transformer H2 is provided with a fourth AC switch K14, and 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 on one side of the second multilevel converter MMC2. The second multilevel converter MMC2 is a low-voltage converter.

[0048] Specifically, the second multilevel converter MMC2 is locked out and tripped by the second AC switch K12 connected to it; and the DC voltage of the first multilevel converter MMC1 is reduced.

[0049] In this embodiment, as 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 a first multilevel converter MMC1. A third bypass switch K23 is connected in parallel on 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 power 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 a second multilevel converter MMC2. A fourth bypass switch K24 is connected in parallel on one side of the second multilevel converter MMC2. The second multilevel converter MMC2 is a low-voltage converter, which has a lower voltage level and 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 is immediately locked and the corresponding AC switch is disconnected.

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

[0051] In this embodiment, after a fault occurs in the receiving-end circuit, the non-faulty 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-faulty converter and sends out fault information of the receiving-end converter.

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

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

[0054] One end of the first three-phase transformer B1 is equipped with a first AC switch K11, and the other end of the first three-phase transformer B1 is electrically connected to the first line-commutated converter LCC1. A first bypass switch K21 is connected in parallel on 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 the second line-commutated converter LCC2. A second bypass switch K22 is connected in parallel on one side of the second line-commutated converter LCC2. The second line-commutated converter LCC2 is a low-voltage converter.

[0056] Specifically, 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 the first threshold and the current is less than the second threshold, the pole bus voltage of the hybrid DC transmission system is reduced.

[0057] In this embodiment, as Figure 1 As shown, the sending-end circuit includes: a first three-phase transformer B1 and a second three-phase transformer B2. One end of the first three-phase transformer B1 is electrically connected to the first AC switch K11, and the other end is electrically connected to the first line-commutated converter LCC1. A first bypass switch K21 is connected in parallel on 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 faster dynamic response and lower power loss. One end of the second three-phase transformer B2 is electrically connected to the second AC switch K12, and the other end is electrically connected to the second line-commutated converter LCC2. A second bypass switch K22 is connected in parallel on 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, lower cost, but relatively weaker performance.

[0058] The sending-end converter monitors 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 threshold, the sending end performs rapid phase shifting to reduce the DC voltage of the pole bus in the hybrid DC transmission system to a preset value, preferably zero. When judging a fault at the receiving end, the minimum voltage of the pole bus is set as the first threshold, and the maximum current of the pole bus is set as the second threshold. When the first-line commutator LCC1 or the second-line commutator LCC2 at 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. The sending end performs rapid phase shifting to reduce the pole bus voltage to zero. This stops the power output of the sending end, reduces energy injection, and prevents energy accumulation in the transmission system, which could lead to dangerous overvoltages and overcurrents.

[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 control circuit blocks the first line-commutated converter LCC1, trips the first AC switch K11, closes the first bypass switch K21, and saves the DC voltage reference value before the fault.

[0060] In this embodiment, if there is no communication or a communication failure between the sending circuit and the receiving circuit, the sending circuit defaults to shutting down the first line commutator LCC1 with a higher voltage to ensure system safety redundancy. When shutting down, the first line commutator LCC1 is first locked, then the first AC switch K11 is tripped, and then the first bypass switch K21 is closed. The sending end saves the current reference value before performing the phase shift so that it can be used as a reference value when restoring normal operation of the sending end.

[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 disconnects from the converter of the same type as the faulty converter in the receiving-end circuit, specifically by blocking 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, based on the fault information, will shut down a converter of the same type as the receiving-end circuit. If the converter that failed in the receiving-end circuit is a low-voltage converter, the sending-end circuit will also shut down the low-voltage converter. If the converter that failed in the receiving-end circuit is a high-voltage converter, the sending-end circuit will also shut down the high-voltage converter. The high voltage 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 power loss. The low-voltage valve group has a lower voltage level and lower cost, but relatively weaker performance. Specifically, the converter shutdown operation of the sending-end circuit is to lock the second line-commutated converter LCC2, trip the second AC switch K12, and close the second bypass switch K22 to close the bypass switch and 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 DC transmission system has dropped to zero, it closes the fourth bypass switch K24 of the second multilevel converter MMC2.

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

[0065] In this embodiment, when the receiving-end circuit detects that the pole bus voltage of the hybrid DC transmission system has dropped to zero, the faulty converter of the receiving-end circuit is disconnected. First, the fourth bypass switch K24 of the second multilevel converter MMC2 is closed. The non-faulty converter of the receiving-end circuit restores 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 been deactivated recovers to the current reference value before the phase shift at a second preset rate.

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

[0068] The following application example illustrates the implementation process of this invention:

[0069] like Figure 2 As shown, in this example power transmission system, AC grid D1 transmits electrical energy to AC grid D2. AC grid D1 is the sending end, and AC grid D2 is the receiving end. AC grid D1 is equipped with two three-phase transformers, B1 and B2. One end of the first three-phase transformer B1 is equipped with a first AC switch K11, and the other end is electrically connected to a first line-commutated converter LCC1. The line-commutated converter consists of multiple diodes connected in series, enabling high-power, high-efficiency 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 equipped with a second AC switch K12, and the other end is electrically connected to a second line-commutated converter LCC2. The line-commutated converter also enables high-power, high-efficiency conversion. A second bypass switch K22 is connected in parallel on one side of the LCC2 transformer; the second AC grid D2 is equipped with two voltage transformers H1 and H2. One end of the first voltage transformer H1 is equipped with a third AC switch K13, 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. A third bypass switch K23 is connected in parallel on one side of the first multilevel converter MMC1; one end of the second voltage transformer H2 is equipped with a fourth AC switch K14, and the other end is electrically connected to the second multilevel converter MMC2. The multilevel converter is composed 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 on one side of the second multilevel converter MMC2.

[0070] Here, the circuit structures of the first online commutator LCC1 and the second online commutator LCC2 are the same, both including two diodes connected in series, and the first online commutator LCC1 and the second online commutator LCC2 are connected in series.

[0071] The circuit structures of the first multilevel converter MMC1 and the second multilevel converter MMC2 are the same, each including a transistor and a diode, with the two 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 explanation uses a fault in the second multilevel converter MMC2 of the receiving-end circuit as an example:

[0073] Faulty valve retraction assembly procedure:

[0074] 1. Upon receiving-end circuit fault detection and initial response, the faulty second multilevel converter MMC2 is immediately locked out and its connected fourth AC switch K14 is tripped. The non-faulty first multilevel converter MMC1 controls the DC-side voltage to drop to zero and retains the DC voltage reference value before the fault.

[0075] 2. Sending-end circuit detection and operation: The sending-end circuit converter, first-line commutator LCC1 / second-line commutator LCC2, detects the DC voltage and DC current of the pole bus. If the pole bus voltage is greater than the first threshold and the current is less than the second threshold, the sending-end circuit performs rapid phase shifting to reduce the pole bus voltage to zero and saves the current reference value before the phase shift.

[0076] 3. Sending-end converter out of service, communication normal: If the sending-end converter is out of service with the same type as the faulty receiving-end converter, and the second multi-level converter MMC2 has a low-voltage fault, then the corresponding low-voltage second-line commutator converter LCC2 will be out of service. Operation: Block the second-line commutator converter LCC2, trip the second AC switch K12, and close the second bypass switch K22.

[0077] Communication failure: The first-line commutator LCC1 is automatically disconnected from the high-voltage circuit by default. Operation: Block the first-line commutator LCC1, trip the first AC switch K11, and close the first bypass switch K21.

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

[0079] 5. The current at the sending end is restored. The closed-loop control DC current of the first-line commutated converter LCC1 or the second-line commutated converter LCC2 of the converter whose sending end has not been withdrawn is gradually restored to the reference value before the phase shift.

[0080] 6. Fault exit complete. When both the sending-end current and receiving-end voltage return to their reference values, the system completes the exit procedure for the faulty second multilevel converter MMC2.

[0081] The embodiments of the present invention analyze electrical parameters of the sending-end circuit, such as changes in DC voltage and current of the pole bus, to autonomously identify the fault exit valve group requirements of the receiving-end circuit. This enables rapid fault detection and response without relying on inter-station communication. When a fault occurs in the receiving-end circuit, the non-faulty converter immediately reduces the DC side voltage to zero, while the sending-end circuit uses rapid phase-shift control to return the pole bus voltage to zero and saves the reference value, reducing energy injection from the source. When communication between the sending-end and receiving-end circuits is normal, the exit categories of the converters at both ends are kept consistent. In the event of a communication failure, the high-voltage converter is prioritized for exit by default, ensuring system safety redundancy. A phased coordinated recovery mechanism is adopted between the sending-end and receiving-end circuits. The receiving end gradually restores the voltage at a preset rate, while the sending end precisely adjusts the current through closed-loop control, ensuring a smooth transition of system parameters and avoiding secondary faults.

[0082] like Figure 2 As shown, embodiments of the present invention also provide a method for fault-free valve grouping in a hybrid DC transmission system, applied to the circuit described in the above scheme, the method comprising:

[0083] Step S1: When a fault is detected in the second AC power grid D2, the faulty converter in the receiving-end circuit is locked out 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 the first threshold and the current is less than the second threshold, it reduces the pole bus voltage of the hybrid DC transmission system.

[0085] Step S3: 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 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] Block the second-line phase-changing converter LCC2, trip the second AC switch K12, and close the second bypass switch K22.

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

[0089] Those skilled in the art will recognize that the units and algorithm steps of the various examples 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 implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0090] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0091] In the embodiments provided by this invention, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0092] The units described as separate components may or may not be physically separate. 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 the units can be selected to achieve the purpose of this embodiment according to actual needs.

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

[0094] If the aforementioned 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 this invention, or the part 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 is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, ROM, RAM, magnetic disks, or optical disks.

[0095] Furthermore, it should be noted that in the apparatus and method of the present invention, it is obvious that the components or steps can be decomposed and / or recombined. These decompositions and / or recombinations should be considered equivalent solutions of the present invention. Moreover, the steps performing the above series of processes can naturally be executed in the order described, but are not necessarily required to be executed in chronological order; some steps can be executed in parallel or independently of each other. Those skilled in the art will understand that all or any step or component of the method and apparatus of the present invention can be implemented in any computing device (including processors, storage media, etc.) or network of computing devices, in hardware, firmware, software, or a combination thereof. This is something that those skilled in the art can achieve by using their basic programming skills after reading the description of the present invention.

[0096] Therefore, the object of the present invention can also be achieved by running a program or a set of programs on any computing device. The computing device can be a known general-purpose device. Therefore, the object of the present invention can also be achieved simply by providing a program product containing program code for implementing the method or apparatus. That is, 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 known storage medium or any storage medium developed in the future. It should also be noted that in the apparatus and method of the present invention, it is obvious that the components or steps can be decomposed and / or recombined. These decompositions and / or recombinations should be considered equivalent to the present invention. Furthermore, the steps for performing the above series of processes can naturally be performed in the order described, but are not necessarily required to be performed in chronological order. Some steps can be performed in parallel or independently of each other.

[0097] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fault-avoidance valve group circuit for a hybrid DC transmission system, characterized in that, include: The sending-end circuit is electrically connected to the first AC power grid (D1); A receiving circuit electrically connected to the sending circuit via a DC line (XL), the receiving circuit being electrically connected to a second AC power grid (D2); The electrical energy of the first AC power grid (D1) is transmitted to the second AC power grid (D2) through the sending-end circuit, the DC line (XL), and the receiving-end circuit. When the second AC power grid (D2) fails, the faulty converter of the receiving-end circuit is locked out 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, it reduces the pole bus voltage of the hybrid DC transmission system.

2. The fault-avoidance valve group circuit of the hybrid DC transmission system according to claim 1, characterized in that, The receiving-end circuit includes: First voltage transformer (H1) and second voltage transformer (H2); One end of the first voltage transformer (H1) is equipped with a third AC switch (K13), and 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 on one side of the first multilevel converter (MMC1). The first multilevel converter (MMC1) is a high-voltage converter. One end of the second voltage transformer (H2) is equipped with a fourth AC switch (K14), and 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 on one side of the second multilevel converter (MMC2). The second multilevel converter (MMC2) is a low-voltage converter. The second multilevel converter (MMC2) is locked out and tripped by the fourth AC switch (K14) connected to it; and the DC voltage of the first multilevel converter (MMC1) is reduced.

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

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

5. The fault-return valve group circuit of the hybrid DC transmission system according to claim 4, characterized in that, When the pole bus voltage of the hybrid DC transmission system is reduced to zero, the control sending circuit blocks the first line commutator converter (LCC1), trips the first AC switch (K11), closes the first bypass switch (K21), and saves the DC voltage reference value before the fault.

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

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

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

9. A method for fault-free valve group in a hybrid DC transmission system, characterized in that, Applied to the circuit as described in any one of claims 1 to 8, the method comprises: When a fault is detected in the second AC power grid (D2), the faulty converter in the control receiving circuit is locked out 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 the first threshold and the current is less than the second threshold, it reduces the pole bus voltage of the hybrid DC transmission system. When the sending-end circuit and the receiving-end circuit communicate normally, the sending-end circuit will disconnect from the converter of the same type as the faulty converter in the receiving-end circuit.

10. The method for fault-free valve group in a hybrid DC 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 occurred in the receiving-end circuit, including: Block the second line phase-changing converter (LCC2), trip the second AC switch (K12), and close the second bypass switch (K22).

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