Flexible dc grid reclosing method and device based on high-voltage dc circuit breaker

Abstract

The present application relates to the technical field of flexible HVDC transmission, and particularly relates to a flexible HVDC grid reclosing method and device based on HVDC circuit breaker, which comprises the following steps: carrying out opening control on the HVDC circuit breaker, starting a de-ionization period, carrying out primary fault detection in the de-ionization period, if the primary fault detection result is determined as transient fault, carrying out reclosing control on the HVDC circuit breaker at the end of the de-ionization period, if the transfer branch is safely conducted and the overcurrent protection is not triggered, carrying out main branch operation control, starting secondary fault detection, if the current directions between the HVDC circuit breakers of the DC line are the same and the line-to-ground voltage recovers to a stable state, the secondary fault detection result is determined as transient fault has disappeared, and the HVDC circuit breaker remains closed. The present application effectively improves the reclosing speed and the accuracy of fault discrimination through the double fault discrimination mechanism in the de-ionization period and after the de-ionization period.

Description

Technical Field

[0001] This invention relates to the field of flexible DC power transmission technology, and in particular to a method and apparatus for reclosing a flexible DC power grid based on a high-voltage DC circuit breaker. Background Technology

[0002] In flexible DC transmission technology, modular multilevel converters (MMCs) have been widely used due to their advantages such as flexible control, fast dynamic response, and strong weak network connection capability. Especially in long-distance, large-capacity flexible DC transmission projects, MMCs have various sub-module types. Among them, the full-bridge sub-module has attracted much attention due to its fault self-clearing capability. However, its high IGBT deployment and the resulting increase in device losses make its economic benefits relatively low, limiting its widespread application. Conversely, the half-bridge sub-module has become the first choice for most DC transmission projects due to its lower cost. However, the half-bridge MMC does not have fault self-clearing capability, which requires DC circuit breakers to be installed at both ends of the DC transmission line to quickly clear and isolate fault currents in the event of a fault.

[0003] The characteristics of DC fault current are completely different from those of AC fault current. It does not have a zero-crossing point. Therefore, the technical difficulty of blocking DC fault current is much higher than that of clearing AC faults. The existing reclosing strategy of DC circuit breaker does not distinguish between permanent and transient faults when handling faults. When the current reaches the protection setting, the DC circuit breaker trips and then recloses after a fixed time delay. If the current reaches the setting again after reclosing, the DC blocking operation is performed. This strategy has a slow response speed and increases the risk of equipment damage. Therefore, there is an urgent need to provide a fast start method for reclosing high-voltage DC circuit breakers that can improve the speed of interrupting fault current while ensuring rapid and safe restart of the system. Summary of the Invention

[0004] To address the above technical problems, this invention provides a method and apparatus for reclosing a flexible DC power grid based on a high-voltage DC circuit breaker.

[0005] In a first aspect, the present invention provides a method for reclosing a flexible DC power grid based on a high-voltage DC circuit breaker, wherein the high-voltage DC circuit breaker includes a main branch, a transfer branch, and an energy-dissipating branch connected in parallel; the method for reclosing a flexible DC power grid includes the following steps:

[0006] In response to the received tripping command, the high-voltage DC circuit breaker is tripped by controlling the current transfer between the main branch, the transfer branch and the energy-consuming branch, and the deionization period is started when the tripping is completed.

[0007] A fault detection is performed once during the deionization time period, and the DC line voltage is sampled to obtain the fault detection voltage value at different times.

[0008] If the fault detection voltage value is detected to be non-continuously decaying, the fault detection result is identified as a transient fault, and the high-voltage DC circuit breaker is reclosed at the end of the deionization period.

[0009] In response to the reclosing command of the DC circuit breaker, conduction control is performed on the transfer branch. If the transfer branch is safely connected and overcurrent protection is not triggered, the main branch is put into operation, so that the high-voltage DC circuit breaker is put back into operation. At this time, secondary fault detection is initiated.

[0010] During secondary fault detection, if the current direction between the high-voltage DC circuit breakers of the DC line is the same and the line-to-ground voltage has returned to a stable state, the secondary fault detection result is judged as the transient fault has disappeared, and the high-voltage DC circuit breaker remains closed.

[0011] In a further embodiment, the main branch includes a series-connected fast mechanical switch and an auxiliary power electronic switch; the step of controlling the tripping of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch, and the energy-consuming branch in response to a received tripping command includes:

[0012] In response to the received tripping command, the auxiliary power electronic switch of the main branch is subject to current blocking control, and the transfer branch is subject to current conduction control, so that the current in the main branch is transferred to the transfer branch.

[0013] If the current in the main branch is successfully transferred to the transfer branch, then in response to the main branch fast mechanical switch opening command, the fast mechanical switch of the main branch is opened at the moment when the current crosses zero.

[0014] When the fast mechanical switch of the main branch is successfully tripped or the transfer branch is overcurrent, the transfer branch is subject to current blocking control so that the current in the transfer branch is transferred to the energy-consuming branch.

[0015] After the current is successfully transferred to the energy-consuming branch, the surge arrester in the energy-consuming branch is controlled to absorb and disconnect the current, thus completing the DC circuit breaker tripping control process.

[0016] In a further implementation, if the current in the main branch is not successfully transferred to the transfer branch, the current blocking control of the auxiliary power electronic switch of the main branch is released, the current conduction state of the main branch is restored, and the high-voltage DC circuit breaker returns to the closed state.

[0017] In a further implementation, if the primary fault detection voltage value is detected to be continuously decaying, the primary fault detection result is determined to be a permanent fault, and DC blocking is executed.

[0018] In a further implementation, if the fault detection voltage value decays exponentially over time, it is determined that the fault detection voltage value is continuously decaying.

[0019] In a further implementation, if the fault detection voltage value decays in a wave-like, non-exponential manner over time, then the fault detection voltage value is determined to be non-continuously decaying.

[0020] In a further embodiment, the step of controlling the conduction of the transfer branch in response to the reclosing command of the DC circuit breaker includes:

[0021] In response to the reclosing command of the DC circuit breaker, the current conduction control of the transfer branch is performed, and the current of the transfer branch is monitored. If the current of the transfer branch does not reach the preset overcurrent protection threshold, the main branch is put into operation.

[0022] If the current change in the transfer branch reaches the preset overcurrent protection threshold, the transfer branch will be locked to keep the high-voltage DC circuit breaker in the open position.

[0023] In a further implementation, the main branch line commissioning control process includes:

[0024] Perform a closing operation on the fast mechanical switch on the main branch, close the auxiliary power electronic switch on the main branch, establish the current path of the main branch, and put the high voltage DC circuit breaker into operation.

[0025] In a further implementation plan, during secondary fault detection, if it is detected that the current direction between the high-voltage DC circuit breakers of the DC line is reversed after closing and the line-to-ground voltage has not recovered to a stable state, the secondary fault detection result is judged as a permanent fault, and DC blocking is executed.

[0026] Secondly, the present invention provides a flexible DC grid reclosing device based on a high-voltage DC circuit breaker, wherein the high-voltage DC circuit breaker includes a main branch, a transfer branch, and an energy-dissipating branch connected in parallel; the flexible DC grid reclosing device includes:

[0027] The tripping control module is used to respond to the received tripping command by controlling the current transfer between the main branch, the transfer branch and the energy-consuming branch to control the tripping of the high-voltage DC circuit breaker, and to start the deionization period when the tripping is completed.

[0028] The fault detection module is used to perform a fault detection once during the deionization time period, sample the DC line voltage, and obtain the fault detection voltage value at different times.

[0029] A primary fault identification module is used to identify the primary fault detection result as a transient fault if the primary fault detection voltage value is detected to be non-continuously decaying, and to perform reclosing control on the high-voltage DC circuit breaker at the end of the deionization time period.

[0030] The reclosing control module is used to respond to the reclosing command of the DC circuit breaker and control the conduction of the transfer branch. If the transfer branch is safely connected and the overcurrent protection is not triggered, the main branch is put into operation, so that the high-voltage DC circuit breaker is put back into operation. At this time, the secondary fault detection is started.

[0031] The secondary fault detection module is used to determine that the transient fault has disappeared and the high-voltage DC circuit breaker remains closed if the current direction between the high-voltage DC circuit breakers on the DC line is the same and the line-to-ground voltage has returned to a stable state during secondary fault detection.

[0032] This invention provides a method and apparatus for reclosing a flexible DC power grid based on a high-voltage DC circuit breaker. The method responds to a received tripping command by controlling the current transfer between the main branch, transfer branch, and energy-consuming branch to trip the high-voltage DC circuit breaker, and initiates a deionization period upon completion of tripping. During this deionization period, a fault detection is performed, and the DC line voltage is sampled to obtain fault detection voltage values ​​at different times. If the fault detection voltage value is detected to be non-continuously decaying, the fault detection result is determined to be a transient fault. At the end of the deionization period, the high-voltage DC circuit breaker is reclosed. Based on the reclosing command, the transfer branch is controlled to conduct. If the transfer branch conducts safely and overcurrent protection is not triggered, the main branch is put into operation, allowing the high-voltage DC circuit breaker to restart. At this time, secondary fault detection is initiated. During secondary fault detection, if the current direction between the high-voltage DC circuit breakers on the DC line is the same and the line-to-ground voltage has returned to a stable state, the secondary fault detection result is determined to indicate that the transient fault has disappeared, and the DC circuit breaker remains closed. Compared with existing technologies, this method employs a multi-stage fault discrimination mechanism during the deionization period and at its end, which not only significantly improves the response speed of the reclosing operation but also enhances the accuracy of fault identification, effectively reducing the potential damage risk to equipment caused by erroneous reclosing. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the reclosing method for a flexible DC power grid based on a high-voltage DC circuit breaker provided in an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of a flexible DC transmission system provided in an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the high-voltage DC circuit breaker structure provided in an embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of the high-voltage DC circuit breaker tripping control process provided in an embodiment of the present invention;

[0037] Figure 5 This is a schematic diagram of the fault diagnosis process provided in an embodiment of the present invention;

[0038] Figure 6 This is a schematic diagram of the reclosing process of a high-voltage DC circuit breaker provided in an embodiment of the present invention;

[0039] Figure 7 This is an electrical comparison diagram of the fast reclosing scheme for high-voltage DC circuit breakers provided in the embodiments of the present invention;

[0040] Figure 8 This is a block diagram of a flexible DC grid reclosing device based on a high-voltage DC circuit breaker provided in an embodiment of the present invention. Detailed Implementation

[0041] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0042] refer to Figure 1 This invention provides a reclosing method for a flexible DC power grid based on a high-voltage DC circuit breaker. The high-voltage DC circuit breaker includes a main branch, a transfer branch, and an energy-dissipating branch connected in parallel, such as... Figure 1 As shown, the flexible DC grid reclosing method includes the following steps:

[0043] S1. In response to the received tripping command, the high-voltage DC circuit breaker is tripped by controlling the current transfer between the main branch, the transfer branch and the energy-consuming branch, and the deionization period is started when the tripping is completed.

[0044] In this embodiment, the main branch includes a fast mechanical switch and an auxiliary power electronic switch connected in series; the step of controlling the tripping of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch, and the energy-consuming branch in response to the received tripping command includes:

[0045] In response to the received tripping command, the auxiliary power electronic switch of the main branch is subject to current blocking control, and the transfer branch is subject to current conduction control, so that the current in the main branch is transferred to the transfer branch.

[0046] If the current in the main branch is successfully transferred to the transfer branch, then in response to the main branch fast mechanical switch opening command, the fast mechanical switch of the main branch is opened at the moment when the current crosses zero.

[0047] When the fast mechanical switch of the main branch is successfully tripped or the transfer branch is overcurrent, the transfer branch is subject to current blocking control so that the current in the transfer branch is transferred to the energy-consuming branch.

[0048] After the current is successfully transferred to the energy-consuming branch, the surge arrester in the energy-consuming branch is controlled to absorb and disconnect the current, thus completing the DC circuit breaker tripping control process.

[0049] To explain in detail the flexible DC grid reclosing method proposed in this embodiment, this embodiment briefly describes the arrangement of high-voltage DC circuit breakers, such as... Figure 2 As shown, in a flexible DC transmission system based on a half-bridge submodule, the high-voltage DC circuit breaker in this embodiment is installed on both sides of the positive and negative DC lines of the flexible DC transmission system, as follows. Figure 3 As shown, the high-voltage DC circuit breaker mainly consists of three main current paths connected in parallel: a main branch, a transfer branch, and an energy-consuming branch. The main branch includes a series-connected fast mechanical switch and an auxiliary power electronic switch. The transfer branch includes a power electronic module, which includes a fully controlled power electronic device and a buffer circuit connected in parallel across the fully controlled power electronic device. In this embodiment, the DC protection device monitors the current of the flexible DC transmission system in real time. When the detected current reaches the preset protection setting value I0, it determines that a fault has occurred in the DC line and quickly issues a tripping command, triggering the DC circuit breaker to operate. The high-voltage DC circuit breaker receives the tripping command and begins to perform the tripping operation to achieve safe tripping of the high-voltage DC circuit breaker.

[0050] Specifically, such as Figure 4As shown, upon receiving a tripping command, this embodiment first performs current blocking control on the auxiliary power electronic switch of the main branch. The blocking time of the auxiliary power electronic switch of the main branch does not exceed 0.1ms. Simultaneously, current conduction control is performed on the power electronic module of the transfer branch to achieve forced current transfer from the main branch to the transfer branch. This process requires monitoring the current transfer status. If the current is successfully transferred from the main branch to the transfer branch, the high-voltage DC circuit breaker issues a tripping command for the main branch's fast mechanical switch and continues to the next step. If the current transfer fails, the blocking control of the auxiliary power electronic switch of the main branch is released, the auxiliary power electronic switch of the main branch is re-connected, the tripping operation is refused, and the high-voltage DC circuit breaker returns to the closed state.

[0051] After confirming that the current has been successfully transferred from the main branch to the transfer branch, a fast mechanical switch tripping command is sent to the main branch. The time for issuing the fast mechanical switch tripping command is no more than 0.5ms. This command controls the fast mechanical switch of the main branch to perform the tripping action after the current crosses zero, so as to establish insulation withstand capability under zero voltage and zero current conditions. It controls the main branch to maintain the insulation state under zero voltage and current conditions, so as to achieve electrical isolation of the main branch under safe conditions without current flow. Thus, sufficient insulation strength is established under ideal conditions of no voltage and no current. During the tripping process, this embodiment needs to continuously monitor the tripping status. If the tripping operation is not completed, it continues to wait and re-evaluate the tripping status. If the fast mechanical switch of the main branch successfully trips or the transfer branch experiences current overload, The power electronic module of the transfer branch is subject to current blocking control to force the current transfer from the transfer branch to the energy-consuming branch, ensuring a smooth transition of the current path. The blocking time of the power electronic module of the transfer branch does not exceed 2.2ms. After the current is successfully transferred from the transfer branch to the energy-consuming branch, this embodiment controls and activates the surge arrester in the energy-consuming branch to absorb and dissipate the current, thereby completing the current breaking process. The operation time of the surge arrester in the energy-consuming branch does not exceed 0.05ms, and the overall operation time of the high-voltage DC circuit breaker from receiving the tripping command does not exceed 2.85ms. Through the above control method, this embodiment achieves safe and effective tripping control of the DC circuit breaker, ensuring a smooth transition of the current path and the insulation withstand capability of the equipment, while reducing losses caused by faults.

[0052] S2. A fault detection is performed once during the deionization time period, and the DC line voltage is sampled to obtain the fault detection voltage value at different times.

[0053] S3. If the fault detection voltage value is detected to be non-continuously decaying, the fault detection result is identified as a transient fault, and the high-voltage DC circuit breaker is reclosed at the end of the deionization period.

[0054] This embodiment controls the opening of the DC circuit breaker by controlling the current transfer between the main branch, the transfer branch, and the energy-consuming branch. After the DC circuit breaker is opened, a deionization period is initiated. This deionization period is mainly used to eliminate residual charge or arcing in the circuit to ensure circuit stability. During the deionization period, the execution of DC blocking or reclosing operation is evaluated through the first fault detection. If the DC circuit breaker is reclosed, a second fault detection is performed to prevent the equipment from being subjected to excessive impact due to the first judgment error.

[0055] Specifically, such as Figure 5 As shown, in this embodiment, after the DC circuit breaker performs the tripping operation, a preset deionization time period is immediately initiated. This deionization time period is typically set to 150ms to ensure sufficient time for the circuit state to stabilize. During the deionization time period, this embodiment initiates the first fault detection. Specifically, within the deionization time period t0 to t0+100ms, the DC line voltage is sampled to obtain the first fault detection voltage value at different times. The trend of the first fault detection voltage value over time is determined. When it is detected that the first fault detection voltage value always decays exponentially over time, it is determined that the first fault detection voltage value is continuously decaying; when it is determined that the first fault detection voltage value decays non-exponentially over time in a wave-like manner, it is determined that the first fault detection voltage value is not continuously decaying.

[0056] If the detected voltage value of the first fault detection continues to decay, the fault detection result is determined to be a permanent fault, and a DC blocking command is immediately issued to execute the DC blocking, thereby achieving a complete shutdown of the DC system through the control circuit. If the voltage value does not continue to decay, it is initially determined to be a transient fault. If the first fault detection result is a transient fault, a second fault detection is initiated after the DC circuit breaker reclosing ends during the deionization period to ensure the accuracy of reclosing. It should be noted that a permanent fault is capacitor discharge, and the voltage exhibits an exponential decay cluster curve depending on the location of the fault point. A transient fault is arc discharge, and because the arc resistance changes with time, exhibiting positive or negative resistance characteristics, the voltage curve is a wave-shaped non-exponential decay cluster curve.

[0057] S4. In response to the reclosing command of the DC circuit breaker, conduction control is performed on the transfer branch. If the transfer branch is safely connected and overcurrent protection is not triggered, the main branch is put into operation control, so that the high-voltage DC circuit breaker is put back into operation. At this time, secondary fault detection is initiated.

[0058] In this embodiment, the step of controlling the conduction of the transfer branch in response to the reclosing command of the DC circuit breaker includes:

[0059] In response to the reclosing command of the DC circuit breaker, the current conduction control of the transfer branch is performed, and the current of the transfer branch is monitored. If the current of the transfer branch does not reach the preset overcurrent protection threshold, the main branch is put into operation.

[0060] If the current change in the transfer branch reaches the preset overcurrent protection threshold, the transfer branch will be locked to keep the high voltage DC circuit breaker in the open position.

[0061] During the commissioning control of the main branch, the fast mechanical switch on the main branch is closed, the auxiliary power electronic switch of the main branch is turned on, the current path of the main branch is established, and the high voltage DC circuit breaker is put into operation.

[0062] In this embodiment, after the first-stage fault discrimination mechanism determines that the fault is transient, it uses the control circuit to re-close the DC circuit breaker according to the DC circuit breaker closing command, restoring the normal operation of the circuit. Specifically, as follows: Figure 6 As shown, in the initial stage of the reclosing operation, this embodiment controls the power electronic module of the transfer branch to activate and conduct the transfer branch. The activation time of the transfer branch submodule does not exceed 0.2ms. During this process, the system monitors the current change of the transfer branch and determines whether its current value reaches the preset overcurrent protection threshold. If the current value of the transfer branch does not reach the preset overcurrent protection threshold, the system enters the next main branch commissioning control stage. If the current value of the transfer branch exceeds the preset overcurrent protection threshold or the current rises abnormally, the power electronic module of the transfer branch is immediately locked, and the high-voltage DC circuit breaker disconnection operation is performed to allow the high-voltage DC circuit breaker to deactivate and prevent overcurrent damage.

[0063] Under the condition that the transfer branch is safely connected and overcurrent protection is not triggered, this embodiment enters the main branch commissioning control stage for reclosing. In this embodiment, the fast mechanical switch of the main branch is closed first to quickly establish the current path of the main branch. The time for the auxiliary power electronic switch of the main branch to be connected does not exceed 6ms. The fast mechanical switch of the main branch reaches the closed position and stabilizes, and the closing end time does not exceed 43.8ms. The high-voltage DC circuit breaker receives the reclosing command and closes successfully in no more than 50ms. After this step is completed, the DC circuit breaker has been successfully put into operation. The system current mainly flows through the main branch, while the transfer branch remains in its locked state, waiting for the next possible switching demand. In the entire reclosing control process, this embodiment can effectively manage the current flow of the DC circuit breaker during the reclosing process by controlling the transfer branch and the main branch, avoiding the occurrence of overcurrent, thereby ensuring the safe operation of the DC circuit breaker.

[0064] S5. During secondary fault detection, if the current direction between the high-voltage DC circuit breakers of the DC line is the same and the line-to-ground voltage has returned to a stable state, the secondary fault detection result is judged as the transient fault has disappeared, and the high-voltage DC circuit breaker remains closed.

[0065] In the second fault detection, this embodiment monitors the current and voltage status between the high-voltage DC circuit breakers of the DC line. If the current direction between the high-voltage DC circuit breakers is opposite and the line-to-ground voltage cannot be established (the voltage does not reach a stable value or a preset working voltage threshold within the expected time, i.e., the voltage does not recover to a stable state), the second fault detection result is judged as a permanent fault, and a DC blocking command is immediately issued and executed according to the DC blocking command. If the current direction between the high-voltage DC circuit breakers is the same and the line-to-ground voltage can be established (when the current direction is the same, the voltage can reach a stable value or a preset working voltage threshold within the expected time), the second fault detection result is judged as the transient fault disappearing, and the DC circuit breaker remains closed. This invention achieves rapid response and judgment of DC line faults through a multi-stage fault discrimination mechanism after the high-voltage DC circuit breaker is opened, improving the accuracy of fault discrimination and the reliability of reclosing operation, and providing strong support for the rapid restart of the system. It should be noted that whether the voltage can be established is actually to judge whether a stable voltage difference can be formed and maintained between the DC line and ground after the high-voltage DC circuit breaker is reclosed. If the voltage remains stable or recovers to a certain level after the DC circuit breaker is reclosed, the voltage is considered to have been established; if the voltage cannot be stabilized or remains zero, the voltage is considered not to have been established.

[0066] Figure 7 This diagram shows an electrical comparison between the fast reclosing method for high-voltage DC circuit breakers proposed in this embodiment and the traditional reclosing scheme for DC circuit breakers. Figure 7 In the conventional DC circuit breaker reclosing scheme shown, at time t0, the fault current reaches the protection setting value I0, the DC circuit breaker trips, and after a deionization period, the two circuit breakers are reclosed at time t1. At time t2, the detected current reaches the protection setting value I0 again, and the DC circuit breaker opens. In the high-voltage DC circuit breaker fast reclosing method proposed in this embodiment, if the first judgment result is a permanent fault, the DC system is blocked; if the judgment result is a transient fault, the DC circuit breaker recloses; if the second judgment result is that the transient fault has disappeared, the DC circuit breaker remains closed; if the judgment result is a permanent fault, the DC system is blocked, and the detected current value at the time of blocking is I1.

[0067] This invention provides a reclosing method for a flexible DC grid based on a high-voltage DC circuit breaker. The method responds to a received tripping command by controlling the current transfer between the main branch, transfer branch, and energy-consuming branch to trip the high-voltage DC circuit breaker, and initiates a deionization period upon completion of tripping. During this period, a fault detection is performed, and the DC line voltage is sampled to obtain fault detection voltage values ​​at different times. If the fault detection voltage value is found to be not continuously decaying, the fault detection result is identified as a transient fault, and reclosing control is initiated on the high-voltage DC circuit breaker at the end of the deionization period. According to the DC circuit breaker closing command, conduction control is applied to the transfer branch. If the transfer branch conducts safely without triggering overcurrent protection, the main branch is put into operation, allowing the high-voltage DC circuit breaker to be put back into operation. At this time, a secondary fault detection is initiated. During secondary fault detection, if the current direction between the high-voltage DC circuit breakers on the DC line is the same and the voltage has returned to a stable state, the secondary fault detection result is judged as the transient fault having disappeared, and the DC circuit breaker remains closed. Compared with the prior art, this method, through a dual fault discrimination mechanism during and after the deionization period, can more accurately distinguish between permanent and transient faults. This not only significantly improves the response speed of reclosing operations but also enhances the accuracy of fault identification. If a primary discrimination error leads to the misclosing of the high-voltage DC circuit breaker, it can be quickly corrected in the secondary discrimination, reducing the risk of damage caused by the equipment's long-term tolerance to fault current and voltage, and improving the stability and reliability of the system. At the same time, this embodiment optimizes the opening and reclosing control strategies of the DC circuit breaker, enabling isolation operations during the energy dissipation process of the faulty line, thus improving the fault clearing speed.

[0068] It should be noted that the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0069] In one embodiment, such as Figure 8 As shown, this embodiment of the invention provides a flexible DC grid reclosing device based on a high-voltage DC circuit breaker, applied to a high-voltage DC circuit breaker. The high-voltage DC circuit breaker includes a main branch, a transfer branch, and an energy-dissipating branch connected in parallel. The flexible DC grid reclosing device includes:

[0070] The tripping control module 101 is used to respond to the received tripping command by controlling the current transfer between the main branch, the transfer branch and the energy-consuming branch to control the tripping of the high-voltage DC circuit breaker, and to start the deionization period when the tripping is completed.

[0071] The fault detection module 102 is used to perform a fault detection during the deionization time period, sample the DC line voltage, and obtain the fault detection voltage value at different times.

[0072] The primary fault identification module 103 is used to identify the primary fault detection result as a transient fault if the primary fault detection voltage value is detected to be non-continuously decaying, and to perform reclosing control on the high voltage DC circuit breaker at the end of the deionization time period.

[0073] The reclosing control module 104 is used to respond to the reclosing command of the DC circuit breaker and control the conduction of the transfer branch. If the transfer branch is safely connected and the overcurrent protection is not triggered, the main branch is put into operation to put the high voltage DC circuit breaker back into operation. At this time, the secondary fault detection is started.

[0074] The secondary fault detection module 105 is used to determine the result of the secondary fault detection as the transient fault has disappeared and the high voltage DC circuit breaker remains closed if the current direction between the high voltage DC circuit breakers of the DC line is the same and the line-to-ground voltage has recovered to a stable state during secondary fault detection.

[0075] For specific limitations regarding a reclosing device for a flexible DC grid based on a high-voltage DC circuit breaker, please refer to the above-described limitations regarding a reclosing method for a flexible DC grid based on a high-voltage DC circuit breaker, which will not be repeated here. Those skilled in the art will recognize that the various modules and steps described in conjunction with the embodiments disclosed in this application can be implemented in hardware, software, or a combination of both. 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 implementation should not be considered beyond the scope of this application.

[0076] This invention provides a flexible DC grid reclosing device based on a high-voltage DC circuit breaker. The device's tripping control module responds to a received tripping command by controlling the current transfer between the main branch, transfer branch, and energy-consuming branch to trip the high-voltage DC circuit breaker, and initiates a deionization period upon completion of tripping. A fault detection module performs a fault detection during this deionization period, sampling the DC line voltage to obtain fault detection voltage values ​​at different times. If the fault detection module detects that the fault detection voltage value is not continuously decaying, it updates the fault detection result. If the fault is determined to be transient, the high-voltage DC circuit breaker will be reclosed at the end of the deionization period. The reclosing control module will control the transfer branch to conduct according to the DC circuit breaker closing command. If the transfer branch is safely connected and overcurrent protection is not triggered, the main branch will be put into operation, so that the high-voltage DC circuit breaker will be put back into operation. When the secondary fault detection module detects that the current direction between the high-voltage DC circuit breakers of the DC line is the same and the line-to-ground voltage has returned to a stable state, the secondary fault detection result will be determined as the transient fault has disappeared, and the DC circuit breaker will remain closed. Compared with existing technologies, this device, through a dual fault discrimination mechanism during and after the deionization period, can more accurately distinguish between permanent and transient faults. This not only significantly improves the response speed of reclosing operations but also enhances the accuracy of fault identification. If a single discrimination error leads to the misclosing of the high-voltage DC circuit breaker, it can be quickly corrected in the second discrimination, reducing the risk of damage caused by the equipment's long-term tolerance to fault current and voltage, and improving the stability and reliability of the system. In addition, this embodiment optimizes the opening and reclosing control strategies of the DC circuit breaker, enabling isolation operations during the energy dissipation process of the faulty line, thereby improving the fault clearing speed.

[0077] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this invention, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A flexible HVDC grid reclosing method based on HVDC breakers, characterized in that, The high-voltage DC circuit breaker comprises a main branch, a transfer branch and an energy dissipation branch in parallel; the flexible DC power grid reclosing method comprises the following steps: In response to the received opening instruction, the high-voltage DC circuit breaker is controlled by controlling the current transfer among the main branch, the transfer branch and the energy dissipation branch, and a deionization time period is started when the opening is completed; During the deionization time period, a primary fault detection is performed, and the DC line voltage is sampled to obtain a primary fault detection voltage value at different times; If the primary fault detection voltage value is detected to be non-sustained decay, the primary fault detection result is determined to be a transient fault, and the high-voltage DC circuit breaker is controlled to reclose at the end of the deionization time period; In response to a DC circuit breaker reclosing instruction, the transfer branch is controlled to be turned on, and if the transfer branch is safely turned on and the overcurrent protection is not triggered, the main branch is controlled to be put into operation, so that the high-voltage DC circuit breaker is re-operated, and at this time, secondary fault detection is started; During the secondary fault detection, if the current direction among the high-voltage DC circuit breakers of the DC line is detected to be the same and the line-to-ground voltage is restored to a stable state, it is determined that the secondary fault detection result is that the transient fault has disappeared, and the high-voltage DC circuit breaker remains closed.

2. The flexible HVDC grid reclosing method based on HVDC circuit breakers according to claim 1, characterized in that, The main branch comprises a fast mechanical switch and an auxiliary power electronic switch in series; the step of controlling the high-voltage DC circuit breaker by controlling the current transfer among the main branch, the transfer branch and the energy dissipation branch in response to the received opening instruction comprises: In response to the received opening instruction, the auxiliary power electronic switch of the main branch is controlled to be current-locked, and the transfer branch is controlled to be current-on, so that the current in the main branch is transferred to the transfer branch; If the current in the main branch is successfully transferred to the transfer branch, in response to a main branch fast mechanical switch opening instruction, the fast mechanical switch of the main branch is operated to open at the current zero-crossing time; When the fast mechanical switch of the main branch is successfully opened or the transfer branch overflows, the transfer branch is controlled to be current-locked, so that the current in the transfer branch is transferred to the energy dissipation branch; After the current is successfully transferred to the energy dissipation branch, the arrester in the energy dissipation branch is controlled to absorb and break the current, and the DC circuit breaker opening control process is completed.

3. The flexible HVDC grid reclosing method based on HVDC circuit breakers according to claim 2, characterized in that: If the current in the main branch is not successfully transferred to the transfer branch, the current-locked control of the auxiliary power electronic switch of the main branch is released, the current-on state of the main branch is restored, and the high-voltage DC circuit breaker returns to the closed state. 4.The flexible HVDC grid reclosing method based on a HVDC circuit breaker of claim 1, wherein: If the primary fault detection voltage value is detected to be sustained decay, the primary fault detection result is determined to be a permanent fault, and the DC is locked.

5. The flexible HVDC grid reclosing method based on HVDC circuit breakers according to claim 4, characterized in that: If the primary fault detection voltage value decays exponentially with time, it is determined that the primary fault detection voltage value is sustained decay. 6.The flexible HVDC grid reclosing method based on a HVDC circuit breaker of claim 1, wherein: If the primary fault detection voltage value decays in a wave-shaped non-exponential manner with time, it is determined that the primary fault detection voltage value is non-sustained decay.

7. The flexible HVDC grid reclosing method based on HVDC circuit breakers according to claim 2, characterized in that, The step of controlling the transfer branch to be turned on in response to the DC circuit breaker reclosing instruction comprises: In response to the reclosing instruction of the DC circuit breaker, the transfer branch is controlled to be current-conducting, and the current of the transfer branch is monitored, and if the current of the transfer branch does not reach the preset reclosing overcurrent protection threshold, the main branch is controlled to be put into operation; If the current change of the transfer branch reaches the preset reclosing overcurrent protection threshold, the transfer branch is controlled to be locked out, so that the high-voltage DC circuit breaker remains in the open position.

8. The flexible HVDC grid reclosing method based on HVDC circuit breakers according to claim 7, characterized in that, The main branch operation control process comprises: The reclosing operation is performed on the fast mechanical switch on the main branch, the auxiliary power electronic switch on the main branch is closed, the current path of the main branch is established, and the high-voltage DC circuit breaker enters the running state. 9.The flexible HVDC grid reclosing method based on a HVDC circuit breaker of claim 1, wherein: In the secondary fault detection, if the current direction between the high-voltage DC circuit breakers of the DC line is opposite after reclosing and the line-to-ground voltage has not recovered to the stable state, the secondary fault detection result is determined to be a permanent fault, and the DC is locked out.

10. A flexible HVDC grid recloser based on a high voltage direct current circuit breaker, characterized in that, The high-voltage DC circuit breaker comprises a main branch, a transfer branch and an energy consumption branch in parallel; and the flexible DC power grid reclosing device comprises: A tripping control module is configured to, in response to a received tripping instruction, control the high-voltage DC circuit breaker to be tripped by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch, and start a de-ionization period when the tripping is completed; A fault discrimination detection module is configured to, in the de-ionization period, perform primary fault detection by sampling the DC line voltage to obtain primary fault detection voltage values at different times; A primary fault discrimination module is configured to, if the primary fault detection voltage values are detected to be non-sustained decay, determine the primary fault detection result to be a transient fault, and control the high-voltage DC circuit breaker to be reclosed at the end of the de-ionization period; A reclosing control module is configured to, in response to a reclosing instruction of the DC circuit breaker, control the transfer branch to be conductive, and if the transfer branch is safely conductive and overcurrent protection is not triggered, control the main branch to be put into operation, so that the high-voltage DC circuit breaker is re-operated, and secondary fault detection is started at this time; A secondary fault discrimination module is configured to, in the secondary fault detection, if the current direction between the high-voltage DC circuit breakers of the DC line is the same and the line-to-ground voltage recovers to the stable state, determine the secondary fault detection result to be that the transient fault has disappeared, and the high-voltage DC circuit breaker remains closed.

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