Flexible direct-current power grid reclosing method and device based on high-voltage direct-current circuit breaker

Abstract

The invention relates to the technical field of flexible direct-current power transmission, in particular to a flexible direct-current power grid reclosing method and device based on a high-voltage direct-current circuit breaker, and the method comprises the steps: carrying out the opening control of the high-voltage direct-current circuit breaker, starting a deionization time period, carrying out the one-time fault detection in the deionization time period, if the primary fault detection result is judged to be an instantaneous fault, reclosing control over the high-voltage direct-current circuit breaker is ended in the deionization time period, and if the transfer branch is safely conducted and overcurrent protection is not triggered, main branch commissioning control is carried out, secondary fault detection is started, and secondary fault detection is carried out. And if the current directions between the high-voltage direct-current circuit breakers of the direct-current line are the same and the voltage to ground of the line is recovered to a stable state, the secondary fault detection result is that the instantaneous fault disappears, and the direct-current circuit breakers are kept closed. According to the invention, a dual fault discrimination mechanism is carried out in the deionization time period and after the deionization time period, so that the reclosing speed is effectively improved, and the accuracy of fault discrimination is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current power transmission, and in particular to a flexible direct current power grid reclosing method and device based on a high-voltage direct current circuit breaker. Background Art

[0002] In flexible DC transmission technology, modular multilevel converter (MMC) has been widely used due to its advantages such as flexible control, fast dynamic response, and strong weak network connection capability. Especially in long-distance, large-capacity flexible DC transmission projects, MMC has various sub-module types. Among them, the full-bridge sub-module has attracted much attention due to its fault self-clearing capability, but its high IGBT investment and the resulting increased device loss make the economic benefits relatively low, limiting its wide application. On the contrary, the half-bridge sub-module has become the first choice for most current DC transmission projects due to its low cost. However, the half-bridge MMC does not have the fault self-clearing capability, which requires DC circuit breakers to be configured at both ends of the DC transmission line to quickly clear and isolate the fault current when a fault occurs.

[0003] The characteristics of the fault current on the DC side are completely different from those on the AC side. It does not have a zero crossing point. Therefore, the technical difficulty of blocking the DC fault current is much higher than that of cutting off the AC fault. The existing DC circuit breaker reclosing strategy does not distinguish between permanent faults and transient faults when handling faults. When the current reaches the protection set value, the DC circuit breaker trips and then recloses after a fixed time delay. If the current reaches the set value again after reclosing, the DC locking operation is performed. This strategy has a slow response speed and increases the risk of equipment damage. Therefore, it is urgent to provide a high-voltage DC circuit breaker reclosing fast start method that can increase the speed of cutting off the fault current and ensure that the system restarts quickly and safely. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a flexible DC power grid reclosing method and device based on a high-voltage DC circuit breaker.

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

[0006] In response to the received opening command, the high-voltage DC circuit breaker is opened by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch, and the de-ionization time period is started when the opening is completed;

[0007] Performing a fault detection within the de-ionization time period, sampling the DC line voltage, and obtaining a fault detection voltage value at different times;

[0008] If it is detected that the primary fault detection voltage value is not continuously attenuated, the primary fault detection result is judged as a transient fault, and the high-voltage DC circuit breaker is reclosed at the end of the de-ionization time period;

[0009] In response to the DC circuit breaker reclosing command, the transfer branch is controlled to be turned on. If the transfer branch is safely turned on 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;

[0010] During secondary fault detection, if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line voltage to ground returns to a stable state, the secondary fault detection result is judged as the disappearance of the transient fault and the high-voltage DC circuit breaker remains closed.

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

[0012] In response to the received opening command, the auxiliary power electronic switch of the main branch is current locked and the transfer branch is current conducted, 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, in response to the main branch fast mechanical switch opening instruction, the fast mechanical switch of the main branch is opened at the current zero crossing moment;

[0014] When the fast mechanical switch of the main branch is successfully opened or the transfer branch is overcurrent, the transfer branch is subjected to current blocking control so that the current in the transfer branch is transferred to the energy consumption branch;

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

[0016] In a further implementation scheme, if the current in the main branch is not successfully transferred to the transfer branch, the current locking 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 scheme, if it is detected that the primary fault detection voltage value continues to decay, the primary fault detection result is determined to be a permanent fault, and DC blocking is performed.

[0018] In a further embodiment, if the primary fault detection voltage value decays exponentially over time, it is determined that the primary fault detection voltage value continues to decay.

[0019] In a further implementation scheme, if the primary fault detection voltage value decays in a wave-like non-exponential manner over time, it is determined that the primary fault detection voltage value decays non-continuously.

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

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

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

[0023] In a further embodiment, the main branch operation control process includes:

[0024] The fast mechanical switch on the main branch is closed, 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 operating state.

[0025] In a further implementation scheme, during secondary fault detection, if it is detected that the current direction between the high-voltage DC circuit breakers of the DC line is opposite 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 lockout is performed.

[0026] In a second aspect, the present invention provides a flexible DC power grid reclosing device based on a high-voltage DC circuit breaker, wherein the high-voltage DC circuit breaker comprises a main branch, a transfer branch and an energy consumption branch connected in parallel; the flexible DC power grid reclosing device comprises:

[0027] A switch-off control module, for controlling the switch-off of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch in response to the received switch-off instruction, and starting the de-ionization time period when the switch-off is completed;

[0028] A fault discrimination detection module is used to perform a fault detection within the de-ionization time period, sample the DC line voltage, and obtain a fault detection voltage value at different times;

[0029] A primary fault distinguishing module, for distinguishing the primary fault detection result as a transient fault if it is detected that the primary fault detection voltage value is not continuously attenuated, and performing reclosing control on the high-voltage DC circuit breaker at the end of the de-ionization 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 conducted and the overcurrent protection is not triggered, the main branch operation control is performed to put the high-voltage DC circuit breaker back into operation, and the secondary fault detection is started at this time;

[0031] The secondary fault identification module is used to identify the secondary fault detection result as the disappearance of the transient fault, and the high-voltage DC circuit breaker remains closed if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line-to-ground voltage returns to a stable state during secondary fault detection.

[0032] The present invention provides a flexible DC power grid reclosing method and device based on a high-voltage DC circuit breaker. The method responds to a received opening instruction, controls the opening of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch, and starts a de-ionization time period when the opening is completed; performs a fault detection in the de-ionization time period, samples the DC line voltage, and obtains a primary fault detection voltage value at different times; if it is detected that the primary fault detection voltage value is non-continuously attenuated, the primary fault detection result is judged as a transient fault, And at the end of the de-ionized time period, the high-voltage DC circuit breaker is controlled to be reclosed; according to the reclosing instruction of the DC circuit breaker, the transfer branch is controlled to be turned on. If the transfer branch is safely turned on 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, and the secondary fault detection is started at this time; during the secondary fault detection, if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line-to-ground voltage returns to a stable state, the secondary fault detection result is judged as the disappearance of the transient fault, and the DC circuit breaker remains closed. Compared with the prior art, this method adopts a multi-stage fault discrimination mechanism during the de-ionized time period and at the end time, which not only significantly improves the response speed of the reclosing operation, but also improves the accuracy of fault identification, and effectively reduces the potential risk of damage to the equipment due to misclosing. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0034] Figure 2 is a schematic diagram of a flexible direct current transmission system provided by an embodiment of the present invention;

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

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

[0037] Figure 5 It is a schematic diagram of a fault identification process provided by an embodiment of the present invention;

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

[0039] Figure 7 This is an electrical comparison diagram of a high-voltage DC circuit breaker fast reclosing solution provided by an embodiment of the present invention;

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

[0041] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided 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 The embodiment of the present invention provides a flexible DC power grid reclosing method 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 consumption branch connected in parallel, such as Figure 1 As shown, the flexible DC grid reclosing method comprises the following steps:

[0043] S1. In response to the received opening instruction, the high-voltage DC circuit breaker is opened by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch, and the de-ionization time period is started when the opening 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 opening of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch in response to the received opening instruction includes:

[0045] In response to the received opening command, the auxiliary power electronic switch of the main branch is current locked and the transfer branch is current conducted, 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, in response to the main branch fast mechanical switch opening instruction, the fast mechanical switch of the main branch is opened at the current zero crossing moment;

[0047] When the fast mechanical switch of the main branch is successfully opened or the transfer branch is overcurrent, the transfer branch is subjected to current blocking control so that the current in the transfer branch is transferred to the energy consumption branch;

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

[0049] In order to explain in detail the flexible DC grid reclosing method proposed in this embodiment, this embodiment briefly describes the arrangement of the high-voltage DC circuit breaker. Figure 2 As shown, in a flexible DC power transmission system based on a half-bridge submodule, the high-voltage DC circuit breaker of this embodiment is installed on both sides of the positive and negative DC lines of the flexible DC power transmission system, such as Figure 3 As shown, the high-voltage DC circuit breaker is mainly composed of three main current paths of a main branch, a transfer branch and an energy consumption branch connected in parallel, wherein the main branch includes a fast mechanical switch and an auxiliary power electronic switch connected in series, the transfer branch includes a power electronic module, the power electronic module includes a fully controlled power electronic device and a buffer circuit connected in parallel at both ends of the fully controlled power electronic device. In this embodiment, the current of the flexible DC transmission system is monitored in real time by a DC protection device, and when it is detected that the current reaches a preset protection setting I0, it is determined that a fault occurs in the DC line, and a tripping instruction is quickly issued to trigger the DC circuit breaker to operate. The high-voltage DC circuit breaker receives the tripping instruction and starts to perform the tripping operation to achieve safe tripping of the high-voltage DC circuit breaker.

[0050] Specifically, if Figure 4As shown, after receiving the opening command, this embodiment first performs current locking control on the auxiliary power electronic switch of the main branch, and the locking time of the auxiliary power electronic switch of the main branch does not exceed 0.1ms. At the same time, the power electronic module of the transfer branch is controlled to conduct the current to realize the forced transfer of current from the main branch to the transfer branch. This process requires monitoring the current transfer state. If the current is successfully transferred from the main branch to the transfer branch, the high-voltage DC circuit breaker issues a main branch fast mechanical switch opening command and proceeds to the next step; if the current transfer fails, the locking control of the auxiliary power electronic switch of the main branch is released, the auxiliary power electronic switch of the main branch is turned on again, the opening 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 main branch fast mechanical switch opening instruction is sent to the main branch. The time for sending the main branch fast mechanical switch opening instruction does not exceed 0.5ms. This instruction controls the fast mechanical switch of the main branch to perform the opening action after the current passes through zero point, so as to establish insulation tolerance under the conditions of zero voltage and zero current, and control the main branch to maintain an insulating state under the zero voltage and current state, so as to achieve electrical isolation of the main branch under the safe condition of no current flow, thereby establishing sufficient insulation strength under the ideal condition of no voltage and no current. During the opening process, this embodiment needs to continuously monitor the opening state. If the opening operation is not completed, continue to wait and re-judge the opening state; if the fast mechanical switch of the main branch successfully opens or the transfer branch is overloaded, The power electronic module of the transfer branch is subjected to current locking control to realize the forced transfer of current from the transfer branch to the energy consumption branch, ensuring a smooth transition of the current path. The locking 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 consumption branch, the present embodiment controls the activation of the lightning arrester in the energy consumption branch to make it operate to absorb and dissipate the current, thereby completing the current breaking process. The lightning arrester action time of the energy consumption branch does not exceed 0.05ms, and the overall action time of the high-voltage DC circuit breaker from the receipt of the opening command does not exceed 2.85ms. Through the above control method, the present embodiment realizes safe and effective opening control of the DC circuit breaker, ensures a smooth transition of the current path and the insulation tolerance of the equipment, and reduces the losses caused by faults.

[0052] S2. Perform a fault detection within the de-ionization time period, sample the DC line voltage, and obtain a fault detection voltage value at different times.

[0053] S3. If it is detected that the primary fault detection voltage value does not decay continuously, the primary fault detection result is determined to be a transient fault, and the high-voltage DC circuit breaker is reclosed at the end of the de-ionization time period.

[0054] This embodiment realizes the opening control of the DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy-consuming branch, and starts the deionization time period after the opening of the DC circuit breaker is completed. This deionization time period is mainly used to eliminate the residual charge or arc phenomenon in the circuit to ensure the stability of the circuit state. During the deionization time period, the first fault detection is used to evaluate the execution of DC locking or reclosing operation. If the DC circuit breaker is reclosed, a second fault detection is carried out to prevent the equipment from being subjected to excessive impact due to the first misjudgment.

[0055] Specifically, if Figure 5 As shown, after the DC circuit breaker performs the opening operation, the present embodiment immediately starts a preset de-ionizing time period, and the de-ionizing time period is usually set to 150ms to ensure that there is enough time for the circuit state to reach stability. In the de-ionizing time period, the present embodiment starts the first fault detection. Specifically, in the de-ionizing time period t0-t0+100ms, the DC line voltage is sampled to obtain primary fault detection voltage values ​​at different times, and the change trend of the primary fault detection voltage value over time is determined. When it is detected that the primary fault detection voltage value always decays exponentially over time, it is determined that the primary fault detection voltage value is continuously decaying; when it is determined that the primary fault detection voltage value decays in a wave-like non-exponential manner over time, it is determined that the primary fault detection voltage value is non-continuously decaying.

[0056] If it is detected that the primary fault detection voltage value continues to decay, the primary fault detection result is determined as a permanent fault, and a DC locking instruction is immediately issued to execute DC locking, and the overall shutdown of the DC system is achieved through the control circuit; if the voltage value does not decay continuously, it is preliminarily determined to be a transient fault. If the first fault detection result is a transient fault, the second fault detection is started after the DC circuit breaker is reclosed at the end of the de-ionization time period to ensure the accuracy of the reclosing; it should be noted that the permanent fault is capacitor discharge, and the voltage presents an exponential decay cluster curve due to the different locations of the fault points; the transient fault is arc discharge, and the voltage curve presents a wavy non-exponential decay cluster curve because the arc resistance changes with time and presents positive resistance characteristics or negative resistance characteristics.

[0057] S4. In response to the DC circuit breaker reclosing command, the transfer branch is controlled to be turned on. If the transfer branch is safely turned on 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.

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

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

[0060] If the current change of the transfer branch reaches the preset closing overcurrent protection threshold, the transfer branch is locked to keep the high-voltage DC circuit breaker in the open position;

[0061] During the main branch operation control process, 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 enters the operating state.

[0062] In this embodiment, after the first-stage fault identification mechanism determines that the fault is a transient fault, the DC circuit breaker is reclosed through the control circuit according to the DC circuit breaker closing instruction to restore the normal operation of the circuit. Specifically, Figure 6 As shown, in the initial stage of the reclosing operation, this embodiment controls the power electronic module of the transfer branch to turn on the transfer branch, so that the transfer branch is activated and turned on, and the transfer branch submodule is turned on for no more than 0.2ms. During this process, the system monitors the current change of the transfer branch to determine whether its current value reaches the preset closing overcurrent protection threshold. If the current value of the transfer branch does not reach the preset closing overcurrent protection threshold, the next main branch operation control stage is entered; if the current value of the transfer branch exceeds the preset closing overcurrent protection threshold or the current increases abnormally, the power electronic module of the transfer branch is immediately locked and controlled, and the high-voltage DC circuit breaker disconnection operation is performed to exit the high-voltage DC circuit breaker to prevent overcurrent damage.

[0063] After ensuring that the transfer branch is safely turned on and the overcurrent protection is not triggered, the present embodiment enters the main branch operation control stage of the reclosing. The present embodiment first performs a closing operation on the fast mechanical switch of the main branch to quickly establish a current path for the main branch. The time for turning on the auxiliary power electronic switch of the main branch does not exceed 6ms. The fast mechanical switch of the main branch reaches the closed position and stabilizes, and the closing completion time does not exceed 43.8ms. The high-voltage DC circuit breaker takes no more than 50ms from receiving the reclosing instruction to successfully closing. 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 maintains its locked state, waiting for the next possible switching demand. In the entire reclosing control process, the present 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, thereby avoiding the occurrence of overcurrent and ensuring the safe operation of the DC circuit breaker.

[0064] S5. During the secondary fault detection, if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line voltage to ground returns to a stable state, the secondary fault detection result is judged as the disappearance of the transient fault, 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 it is detected that the current directions between the high-voltage DC circuit breakers are 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, that is, the voltage does not return to a stable state), the secondary fault detection result is judged as a permanent fault, and a DC locking instruction is immediately issued, and DC locking is performed according to the DC locking instruction; if it is detected that the current directions between the high-voltage DC circuit breakers are the same and the line-to-ground voltage can be established (when the current directions are detected to be the same, the voltage can reach a stable value or a preset working voltage threshold within the expected time), the secondary fault detection result is judged as the disappearance of the instantaneous fault, and the DC circuit breaker remains closed. The present invention realizes rapid response and judgment of DC line faults through a multi-stage fault judgment mechanism after the high-voltage DC circuit breaker is opened, improves the accuracy of fault judgment and the reliability of reclosing operation, and provides 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 the DC line can form and maintain a stable voltage difference to the ground after the high-voltage DC circuit breaker is reclosed. After the DC circuit breaker is reclosed, if the voltage remains stable for a period of time or recovers to a certain level, it is considered that the voltage has been established; if the voltage cannot be stabilized or is continuously zero, it is considered that the voltage has not been established.

[0066] Figure 7 This is an electrical comparison diagram of the high-voltage DC circuit breaker fast reclosing method proposed in this embodiment and the traditional DC circuit breaker reclosing solution. 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 is tripped, and after the deionization time period, the circuit breakers at both ends are reclosed at time t1. At time t2, the detection current reaches the protection setting value I0 again, and the DC circuit breaker is disconnected; in the high-voltage DC circuit breaker fast reclosing method proposed in this embodiment, the first judgment result is a permanent fault, the DC system is locked, and the judgment result is a transient fault, and the DC circuit breaker is reclosed; the second judgment result is that the transient fault disappears, the DC circuit breaker remains closed, and the judgment result is a permanent fault, the DC is locked, and the detection current value during locking is I1.

[0067] An embodiment of the present invention provides a flexible DC power grid reclosing method based on a high-voltage DC circuit breaker. The method responds to a received opening instruction, controls the opening of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy-consuming branch, and starts a de-ionizing time period when the opening is completed; performs a fault detection in the de-ionizing time period, samples the DC line voltage, and obtains a primary fault detection voltage value at different times; if it is detected that the primary fault detection voltage value is non-continuously attenuated, the primary fault detection result is judged as a transient fault, and the high-voltage DC circuit breaker is reclosed at the end of the de-ionizing time period; according to the DC circuit breaker closing instruction, the transfer branch is turned on, and if the transfer branch is safely turned on and the overcurrent protection is not triggered, the main branch is put into operation, so that the high-voltage DC circuit breaker is put into operation again, and the secondary fault detection is started at this time. During secondary fault detection, if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the voltage returns to a stable state, the secondary fault detection result is judged as the disappearance of the transient fault, and the DC circuit breaker remains closed. Compared with the prior art, this method can more accurately distinguish between permanent faults and transient faults by performing a dual fault judgment mechanism during the de-ionized time period and after the de-ionized time period, which not only significantly improves the response speed of the reclosing operation, but also improves the accuracy of fault identification. If a primary judgment error causes the high-voltage DC circuit breaker to be mistakenly closed, it can also be quickly corrected in the secondary judgment, reducing the risk of damage caused by the long-term tolerance of the equipment to the 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, and can perform isolation operations during the energy dissipation process of the fault line, thereby improving the fault clearing speed.

[0068] It should be noted that the size of the serial numbers of the above-mentioned processes does not mean 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 the present application.

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

[0070] The opening control module 101 is used to control the opening of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch in response to the received opening instruction, and start the de-ionization time period when the opening is completed;

[0071] A fault discrimination detection module 102 is used to perform a fault detection within the de-ionization time period, sample the DC line voltage, and obtain a fault detection voltage value at different times;

[0072] A primary fault determination module 103, configured to determine the primary fault detection result as a transient fault if it is detected that the primary fault detection voltage value is not continuously decaying, and to perform reclosing control on the high-voltage DC circuit breaker at the end of the de-ionization time period;

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

[0074] The secondary fault judging module 105 is used to judge the secondary fault detection result as the disappearance of the transient fault, and keep the high-voltage DC circuit breaker closed, if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line-to-ground voltage returns to a stable state during secondary fault detection.

[0075] For the specific definition of a flexible DC grid reclosing device based on a high-voltage DC circuit breaker, please refer to the above-mentioned definition of a flexible DC grid reclosing method based on a high-voltage DC circuit breaker, which will not be repeated here. A person of ordinary skill in the art will appreciate 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 performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0076] The embodiment of the present invention provides a flexible DC power grid reclosing device based on a high-voltage DC circuit breaker. The opening control module of the device responds to the received opening instruction, controls the opening of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch, and starts the de-ionization time period when the opening is completed; the fault discrimination detection module performs a fault detection within the de-ionization time period, samples the DC line voltage, and obtains the primary fault detection voltage value at different times; if the primary fault discrimination module detects that the primary fault detection voltage value is non-continuously attenuated, the primary fault detection result is The result is judged as a transient fault, and the high-voltage DC circuit breaker is reclosed at the end of the de-ionized time period; the reclosing control module controls the conduction of the transfer branch according to the DC circuit breaker closing instruction, and if the transfer branch is safely conducted 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; when the secondary fault judgment module detects a secondary fault, if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line-to-ground voltage returns to a stable state, the secondary fault detection result is judged as the disappearance of the transient fault, and the DC circuit breaker remains closed. Compared with the prior art, the device can more accurately distinguish permanent faults from transient faults by performing a dual fault discrimination mechanism during and after the de-ionized time period, which not only significantly improves the response speed of the reclosing operation, but also improves the accuracy of fault identification. If a primary discrimination error causes the high-voltage DC circuit breaker to be misclosed, it can also be quickly corrected in the secondary discrimination, reducing the risk of damage caused by long-term tolerance of the equipment to the 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, and can perform isolation operations during the energy dissipation process of the fault line, thereby improving the fault clearing speed.

[0077] The above-mentioned embodiments only express several preferred implementation modes of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in the technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be regarded as the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be based on the protection scope of the claims.

Claims

1. A flexible DC power grid reclosing method based on a high voltage DC circuit breaker, characterized in that: The high-voltage DC circuit breaker comprises a main branch, a transfer branch and an energy consumption branch connected in parallel; the flexible DC power grid reclosing method comprises the following steps: In response to the received opening command, the high-voltage DC circuit breaker is opened by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch, and the de-ionization time period is started when the opening is completed; Performing a fault detection within the de-ionization time period, sampling the DC line voltage, and obtaining a fault detection voltage value at different times; If it is detected that the primary fault detection voltage value is not continuously attenuated, the primary fault detection result is judged as a transient fault, and the high-voltage DC circuit breaker is reclosed at the end of the de-ionization time period; In response to the DC circuit breaker reclosing command, the transfer branch is controlled to be turned on. If the transfer branch is safely turned on 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; During secondary fault detection, if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line voltage to ground returns to a stable state, the secondary fault detection result is judged as the disappearance of the transient fault and the high-voltage DC circuit breaker remains closed.

2. A flexible DC power grid reclosing method based on a high-voltage DC circuit breaker according to claim 1, characterized in that: The main branch includes a fast mechanical switch and an auxiliary power electronic switch connected in series; the step of controlling the opening of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch in response to the received opening instruction includes: In response to the received opening command, the auxiliary power electronic switch of the main branch is current locked and the transfer branch is current conducted, 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 the main branch fast mechanical switch opening instruction, the fast mechanical switch of the main branch is opened at the current zero crossing moment; When the fast mechanical switch of the main branch is successfully opened or the transfer branch is overcurrent, the transfer branch is subjected to current blocking control so that the current in the transfer branch is transferred to the energy consumption branch; After the current is successfully transferred to the energy-consuming branch, the arrester in the energy-consuming branch is controlled to absorb and disconnect the current, thereby completing the DC circuit breaker opening control process.

3. A flexible DC power grid reclosing method based on a high voltage DC circuit breaker according to claim 2, characterized in that: 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.

4. A flexible DC power grid reclosing method based on a high voltage DC circuit breaker according to claim 1, characterized in that: If it is detected that the primary fault detection voltage value continues to decay, the primary fault detection result is determined to be a permanent fault, and DC blocking is performed.

5. A flexible DC power grid reclosing method based on a high voltage DC circuit breaker according to claim 4, characterized in that: If the primary fault detection voltage value decays exponentially over time, it is determined that the primary fault detection voltage value continues to decay.

6. A flexible DC power grid reclosing method based on a high voltage DC circuit breaker according to claim 1, characterized in that: If the primary fault detection voltage value decays in a wave-like non-exponential manner over time, it is determined that the primary fault detection voltage value decays non-continuously.

7. A flexible DC power grid reclosing method based on a high-voltage DC circuit breaker according to claim 2, characterized in that: The step of controlling the conduction of the transfer branch in response to the DC circuit breaker reclosing instruction comprises: In response to the DC circuit breaker reclosing command, the transfer branch is controlled to conduct current and the current of the transfer branch is monitored. If the current of the transfer branch does not reach the preset closing overcurrent protection threshold, the main branch is put into operation; If the current change of the transfer branch reaches the preset closing overcurrent protection threshold, the transfer branch is locked to keep the high-voltage DC circuit breaker in the open position.

8. A flexible DC power grid reclosing method based on a high-voltage DC circuit breaker according to claim 7, characterized in that: The main branch line operation control process includes: The fast mechanical switch on the main branch is closed, 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 operating state.

9. A flexible DC power grid reclosing method based on a high voltage DC circuit breaker according to claim 1, characterized in that: During secondary fault detection, if it is detected that the current direction between the high-voltage DC circuit breakers of the DC line is opposite after closing and the line voltage to ground has not recovered to a stable state, the secondary fault detection result is judged as a permanent fault and DC locking is performed.

10. A flexible DC power grid reclosing device based on a high voltage DC circuit breaker, characterized in that: The high-voltage DC circuit breaker comprises a main branch, a transfer branch and an energy consumption branch connected in parallel; the flexible DC grid reclosing device comprises: A switch-off control module, for controlling the switch-off of the high-voltage DC circuit breaker by controlling the current transfer between the main branch, the transfer branch and the energy consumption branch in response to the received switch-off instruction, and starting the de-ionization time period when the switch-off is completed; A fault discrimination detection module is used to perform a fault detection within the de-ionization time period, sample the DC line voltage, and obtain a fault detection voltage value at different times; A primary fault distinguishing module, for distinguishing the primary fault detection result as a transient fault if it is detected that the primary fault detection voltage value is not continuously attenuated, and performing reclosing control on the high-voltage DC circuit breaker at the end of the de-ionization time period; 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 conducted and the overcurrent protection is not triggered, the main branch operation control is performed to put the high-voltage DC circuit breaker back into operation, and the secondary fault detection is started at this time; The secondary fault identification module is used to identify the secondary fault detection result as the disappearance of the transient fault, and the high-voltage DC circuit breaker remains closed if it is detected that the current directions between the high-voltage DC circuit breakers of the DC line are the same and the line-to-ground voltage returns to a stable state during secondary fault detection.

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