A fault clearing method and device for a new energy island system

Abstract

The application discloses a fault clearing method and device for a new energy island system, and the new energy island system comprises a new energy power plant, a sending-end flexible DC converter station, a receiving-end flexible DC converter station, a DC line and an AC energy consumption device. After a DC line fault occurs, the DC fault is rapidly cleared by adopting a temporary blocking control strategy for the sending-end and receiving-end flexible DC converter stations, and a seamless unlocking strategy is adopted according to different system operation modes, and the AC energy consumption is switched over, so that the arc extinguishing time of the converter station is greatly shortened under the premise that the new energy base is not caused to be tripped off and the converter station is not caused to be shut down, the problem of long DC fault clearing time of the super-long distance flexible DC transmission system is solved, the stability of the new energy island power grid sending system is improved, the number of full-bridge modules required by the full-half bridge hybrid flexible DC valve of the sending-end and receiving-end converter stations is minimized, and the overall cost and volume of the flexible DC sending system are reduced.

Description

Technical Field

[0001] This invention relates to the field of power transmission and distribution technology, and in particular to a method and apparatus for clearing faults in a renewable energy islanding system. Background Technology

[0002] Most renewable energy bases are located in remote areas with low load levels and weak grid structures, creating a significant need for stable power transmission from isolated renewable energy sources. Flexible DC transmission, characterized by its flexibility, controllability, and high efficiency, is one of the important means of transmitting renewable energy to other regions. For the sending end, flexible DC converters can provide stable AC voltage to renewable energy fields, operate in isolated environments, and provide sufficiently rapid dynamic compensation to reduce the risk of renewable energy units disconnecting from the grid, thereby improving the utilization rate of renewable energy.

[0003] DC fault ride-through technology is a key technology to be considered when applying flexible DC transmission systems to new scenarios of large-scale onshore renewable energy development and long-distance transmission. Currently, due to the small energy storage capacity of the sub-module capacitors in the converter valve, the overcurrent and overvoltage capabilities are weak. At the moment of DC fault, the new energy power regulation capability is weak and the speed is slow, making it difficult to quickly and significantly resolve the energy imbalance between AC and DC sides. When a fault occurs at the far end of a long-distance line, the energy-consuming device takes longer to receive the fault command and start communication. The surplus power of the renewable energy islands flowing into the flexible DC valve can easily cause module overvoltage. On larger capacity overhead lines, it will reduce the arc extinction speed. The flexible DC converter station uses full-bridge output negative pressure to extinguish the arc, which increases the risk of module overvoltage and prolongs the fault clearing time beyond the maximum allowable time. Summary of the Invention

[0004] This invention provides a fault clearing method and apparatus for a renewable energy islanding system, solving the technical problems of existing systems where the submodule capacitors in the converter valve have small energy storage capacity and weak overcurrent and overvoltage capabilities, resulting in weak and slow renewable energy power regulation capabilities during DC faults, making it difficult to quickly and significantly resolve AC / DC energy imbalances. Furthermore, in cases of faults occurring at the far end of long-distance lines, the energy-consuming devices take longer to receive fault commands and engage in communication. The influx of surplus power from renewable energy islanding into the flexible DC valve can easily cause module overvoltage. On larger capacity overhead lines, this reduces the arc extinguishing speed, and the flexible DC converter station uses full-bridge output negative pressure for arc extinguishing, increasing the risk of module overvoltage and extending the fault clearing time beyond the maximum allowable duration.

[0005] The first aspect of this invention provides a fault clearing method for a renewable energy islanding system, applicable to such a system, which includes multiple AC energy-consuming devices, a sending-end flexible DC converter station, and a receiving-end flexible DC converter station. The method includes:

[0006] In response to a received line fault signal, determine the grid surplus power, real-time DC current data, and target operating condition corresponding to the line fault signal;

[0007] The number of AC energy-consuming devices to be put into the new energy island system is determined based on the surplus power of the power grid.

[0008] Based on the real-time DC current data and the target operating conditions, the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station are controlled, and after the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold.

[0009] Based on the real-time DC current data and the target operating conditions, the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station are controlled, and after the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to the preset current threshold.

[0010] When the preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, the preset current threshold in the sending-end flexible DC converter station is increased to the sending-end current reference value according to a preset gradient, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to a preset gradient.

[0011] Optionally, the step of controlling the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station according to the real-time DC current data and the target operating condition, and adjusting the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to a preset current threshold after the sending-end converter is unlocked, includes:

[0012] Compare the real-time DC current data with the preset rated DC current data;

[0013] When the real-time DC current data is less than the preset rated DC current data, the sending-end converter in the sending-end flexible DC converter station is controlled to perform a blocking operation.

[0014] Based on the target operating conditions, control the sending-end converter to perform an unlocking operation;

[0015] After the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold.

[0016] Optionally, the step of controlling the sending-end converter to perform an unlocking operation according to the target operating condition includes:

[0017] When the target operating condition is a single-pole operating condition of a single-sending-end converter station, a seamless unlocking strategy is adopted to perform the unlocking operation when the real-time DC current data is equal to the preset unlocking DC current data.

[0018] When the target operating condition is not a single-pole operating condition of a single sending-end converter station, the unlocking operation is performed after the preset deionization time.

[0019] Optionally, the step of performing the unlocking operation using a seamless unlocking strategy when the real-time DC current data equals the preset unlocking DC current data, when the target operating condition is a single-pole operation of a single sending-end converter station, includes:

[0020] When the target operating condition is a single-pole operation of a single-sending-end converter station, the AC voltage reference value input to the AC outer loop is adjusted to the preset real-time AC voltage sampling value when the real-time DC current data is equal to the preset unlocking DC current data.

[0021] Optionally, it also includes:

[0022] When the target operating condition is a single-pole operation of a single-sending-end converter station, the current control mode of the new energy island system will be switched to the self-locking phase mode.

[0023] Optionally, it also includes:

[0024] When the target operating condition is a single-pole operating condition of a single-sending-end converter station and the unlocking operation is performed using the seamless unlocking strategy, the current control mode of the sending-end flexible DC converter station is switched to the AC port phase-following mode.

[0025] When the target AC voltage in the sending-end flexible DC converter station reaches the preset standard AC voltage, the current control mode of the sending-end flexible DC converter station is switched to the self-locking phase mode, and the current control mode of the new energy island system is switched to the following phase mode.

[0026] Optionally, the step of controlling the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station based on the real-time DC current data and the target operating condition, and adjusting the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to the preset current threshold value after the sending-end converter is unlocked, includes:

[0027] Compare the real-time DC current data with the preset DC current threshold data;

[0028] When the real-time DC current data is equal to the preset DC current threshold data, the receiving-end converter in the receiving-end flexible DC converter station is controlled to perform a blocking operation.

[0029] Based on the target operating conditions, control the receiving-end converter to perform an unlocking operation;

[0030] After the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to the preset current threshold.

[0031] Optionally, the step of controlling the receiving-end converter to perform an unlocking operation according to the target operating condition includes:

[0032] When the target operating condition is a single-pole operating condition of a single sending-end converter station, the unlocking operation is performed within a first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current.

[0033] When the target operating condition is not a single-pole operating condition of a single sending-end converter station, the unlocking operation is performed after the preset deionization time.

[0034] Optionally, the step of performing the unlocking operation within a first preset time after the target DC current associated with the receiving-end converter reaches a preset standard DC current when the target operating condition is a single-pole operating condition of a single sending-end converter station includes:

[0035] When the target operating condition is a single-pole operation of a single sending-end converter station, the AC outer loop control will be switched from DC voltage control to power module average voltage control within a first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current, and the power module average voltage reference value input by the AC outer loop will be adjusted to the preset real-time sampling value of the power module average voltage.

[0036] The second aspect of this invention provides a fault clearing device for a renewable energy islanding system, applied to a renewable energy islanding system, the renewable energy islanding system including multiple AC energy-consuming devices, a sending-end flexible DC converter station and a receiving-end flexible DC converter station, the device comprising:

[0037] The response module is used to respond to the received line fault signal and determine the grid surplus power, real-time DC current data and target operating conditions corresponding to the line fault signal.

[0038] An AC energy consumption device input module is used to determine the number of AC energy consumption devices to be input into the new energy island system based on the surplus power of the power grid.

[0039] The sending-end flexible DC converter station control module is used to control the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station according to the real-time DC current data and the target operating conditions, and to adjust the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to a preset current threshold after the sending-end converter is unlocked.

[0040] The receiving-end flexible DC converter station control module is used to control the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station according to the real-time DC current data and the target operating conditions, and to adjust the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to the preset current threshold after the sending-end converter is unlocked.

[0041] The adjustment module is used to, when a preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, increase the preset current threshold in the sending-end flexible DC converter station to the sending-end current reference value according to a preset gradient, and increase the preset current threshold in the receiving-end flexible DC converter station to the receiving-end current reference value according to a preset gradient.

[0042] As can be seen from the above technical solutions, the present invention has the following advantages:

[0043] In response to a received line fault signal, the system determines the corresponding grid surplus power, real-time DC current data, and target operating condition. Based on the grid surplus power, it determines the number of AC energy-consuming devices to be put into the renewable energy islanding system. Based on the real-time DC current data and target operating condition, it controls the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station. After the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold. Based on the real-time DC current data and target operating condition, it controls the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station. After the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to a preset current threshold. When a preset deionization time is reached and the sending-end flexible DC converter station and the receiving-end flexible DC converter station are both locked, the system can be activated. When all DC converter stations are unlocked, the preset current threshold in the sending-end flexible DC converter station is increased to the sending-end current reference value according to a preset gradient, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to a preset gradient. This invention is applicable to ultra-long-distance power transmission in large-scale new energy islands. By adopting the control strategy based on temporary blocking and seamless unlocking of converter stations proposed in this invention, and combining it with the switching strategy of AC energy consumption devices, the arc extinction time of converter stations is greatly shortened without causing the new energy base to disconnect from the grid or the converter station to stop operating. This solves the problem of excessively long DC fault clearing time in ultra-long-distance flexible DC transmission systems, improves the stability of the new energy island grid transmission system, and minimizes the number of full-bridge modules required for the full-half-bridge hybrid flexible DC valves in the sending and receiving converter stations, thereby reducing the overall cost and volume of the flexible DC transmission system. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a flowchart illustrating the steps of a fault clearing method for a new energy islanding system provided in Embodiment 1 of the present invention.

[0046] Figure 2 This is a flowchart illustrating the steps of a fault clearing method for a new energy islanding system provided in Embodiment 2 of the present invention.

[0047] Figure 3 A schematic diagram of a flexible DC transmission system for a new energy island system.

[0048] Figure 4 This is a control block diagram of the sending-end flexible DC converter station;

[0049] Figure 5 This is a control block diagram of the receiving-end flexible DC converter station;

[0050] Figure 6 Flowchart for clearing faults in a new energy island system;

[0051] Figure 7 This is a structural block diagram of a fault clearing device for a new energy islanding system provided in Embodiment 3 of the present invention. Detailed Implementation

[0052] This invention provides a fault clearing method and apparatus for a renewable energy islanding system. It addresses the existing technical problems of insufficient energy storage in the submodule capacitors of the converter valve, resulting in weak overcurrent and overvoltage capabilities. These issues lead to slow and ineffective regulation of renewable energy power during DC faults, making it difficult to quickly and significantly resolve AC / DC energy imbalances. Furthermore, in cases of faults occurring at distant ends of long-distance lines, the energy-consuming devices take longer to receive fault commands and engage in communication. Excess power from renewable energy islands flowing into the flexible DC valve can easily cause module overvoltage. On larger capacity overhead lines, this reduces the arc-extinguishing speed. The flexible DC converter station uses full-bridge output negative pressure for arc extinguishing, increasing the risk of module overvoltage and extending the fault clearing time beyond the maximum permissible duration.

[0053] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0054] Please see Figure 1 , Figure 1 The flowchart illustrates the steps of a fault clearing method for a new energy islanding system provided in Embodiment 1 of the present invention.

[0055] This invention provides a fault clearing method for a renewable energy islanding system, applicable to such systems. The renewable energy islanding system includes multiple AC energy-consuming devices, a sending-end flexible DC converter station, and a receiving-end flexible DC converter station. The method includes:

[0056] Step 101: In response to the received line fault signal, determine the grid surplus power, real-time DC current data and target operating conditions corresponding to the line fault signal.

[0057] Line fault signal refers to the fault signal issued in response to a line fault in a new energy island system.

[0058] The surplus power of the power grid refers to the surplus power of the isolated power grid in the renewable energy islanding system.

[0059] Real-time DC current data refers to the DC current of the sending-end flexible DC converter station.

[0060] The target operating condition refers to the operating condition of the flexible DC converter station at the sending end within the new energy island system.

[0061] In this embodiment of the invention, in response to the received fault signal for a line fault in a renewable energy islanding system, the renewable energy islanding system corresponding to the line fault signal is determined, and the grid surplus power, real-time DC current data and target operating conditions corresponding to the renewable energy islanding system are obtained.

[0062] Step 102: Determine the number of AC energy-consuming devices to be put into the new energy islanding system based on the surplus power of the power grid.

[0063] In this embodiment of the invention, based on the surplus power of the power grid, the AC energy-consuming devices are immediately and simultaneously activated to absorb the surplus power of the isolated power grid upon receiving the instruction. Considering that the voltage drop at the port will affect energy absorption due to the instantaneous activation, the number of AC energy-consuming devices activated is no less than the surplus power of the isolated power grid. Based on the surplus power of the power grid, the initial AC energy consumption of each AC energy-consuming device is obtained. Multiple AC energy-consuming devices are used to absorb the surplus power of the isolated power grid. The AC power of the initial AC energy consumption associated with multiple AC energy-consuming devices is determined as long as it is greater than the surplus power of the power grid, thereby determining the AC energy-consuming devices to be activated in the renewable energy islanding system.

[0064] Step 103: Based on the real-time DC current data and the target operating conditions, control the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station, and after the sending-end converter is unlocked, adjust the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to the preset current threshold.

[0065] Lockout refers to the converter performing a lockout operation.

[0066] Unlocking refers to the converter performing an unlocking operation.

[0067] The preset current threshold refers to the threshold used to adjust the new energy islanding system to a balanced state. In this embodiment, the preset current threshold is 0.

[0068] In this embodiment of the invention, based on the acquired real-time DC current data and target operating conditions, the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station are controlled, and after the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold.

[0069] Step 104: Based on real-time DC current data and target operating conditions, control the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station, and after the sending-end converter is unlocked, adjust the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to the preset current threshold.

[0070] In this embodiment of the invention, the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station are controlled according to real-time DC current data and target operating conditions. After the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to a preset current threshold.

[0071] Step 105: When the preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, the preset current threshold in the sending-end flexible DC converter station is increased to the sending-end current reference value according to the preset gradient, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to the preset gradient.

[0072] Deionization time depends mainly on the voltage level of the line and the magnitude of the fault current. The higher the voltage and the greater the fault current, the longer the deionization time. The deionization time is a set value.

[0073] In this embodiment of the invention, when the preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, the preset current threshold in the sending-end flexible DC converter station is increased to the sending-end current reference value according to a preset gradient, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to a preset gradient.

[0074] In this embodiment of the invention, in response to a received line fault signal, the surplus power of the power grid, real-time DC current data, and target operating conditions corresponding to the line fault signal are determined. Based on the surplus power of the power grid, the number of AC energy-consuming devices to be put into the new energy islanding system is determined. Based on the real-time DC current data and target operating conditions, the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station is controlled. After the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold. Based on the real-time DC current data and target operating conditions, the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station is controlled. After the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to a preset current threshold. When a preset deionization time is reached and both the sending-end and receiving-end flexible DC converter stations are unlocked, the power consumption of the sending-end flexible DC converter station is increased according to a preset gradient. The preset current threshold is increased to the sending-end current reference value, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to the preset gradient. This solves the existing problems caused by the small energy storage capacity of the sub-module capacitors in the converter valve, weak overcurrent and overvoltage capabilities, weak and slow new energy power regulation capability during DC faults, difficulty in quickly and significantly solving the energy imbalance between AC and DC sides, longer communication time for energy-consuming devices to receive fault commands when faults occur at the far end of long-distance lines, and the influx of surplus power from the new energy island into the flexible DC valve, which can easily cause module overvoltage. In larger capacity overhead lines, it will reduce the arc extinction speed. The flexible DC converter station uses full-bridge output negative pressure for arc extinction, which increases the risk of module overvoltage and prolongs the fault clearing time beyond the maximum allowable time. This improves the stability of the new energy island grid transmission system, while minimizing the number of full-bridge modules required for the full-half-bridge hybrid flexible DC valve at the sending and receiving end converter stations, thus reducing the overall cost and volume of the flexible DC transmission system.

[0075] Please see Figure 2 , Figure 2 The flowchart illustrates the steps of a fault clearing method for a new energy islanding system provided in Embodiment 2 of the present invention.

[0076] This invention provides a fault clearing method for a renewable energy islanding system, applicable to such systems. The renewable energy islanding system includes multiple AC energy-consuming devices, a sending-end flexible DC converter station, and a receiving-end flexible DC converter station. The method includes:

[0077] Please see Figure 3 , Figure 3 This is a schematic diagram of a new energy islanded system transmitted via a flexible DC transmission system, taking the monopolar polarity connection method as an example.

[0078] The renewable energy islanding system includes a renewable energy islanding grid, a sending-end flexible DC converter station, a receiving-end flexible DC converter station, overhead lines, and AC energy dissipation devices. The renewable energy islanding grid is connected to the sending-end flexible DC converter station via a three-phase AC bus. The AC energy dissipation devices are connected at the AC bus connecting the sending-end flexible DC converter station and the islanding grid. The AC energy dissipation devices are used to dissipate the continuous active power output of the renewable energy field when the active power transmission channel of the DC line is blocked, thus avoiding overvoltage problems caused by energy accumulation on the sending-end AC feeder.

[0079] It is worth mentioning that the sending and receiving ends are configured with AC-DC decoupling control strategies. The AC side of the sending station adopts power-frequency control, while the AC side of the receiving station adopts a constant DC voltage control strategy. The DC voltage bias is controlled by a current controller on both the sending and receiving ends.

[0080] Please see Figure 4 , Figure 4 This is a control block diagram of the sending-end flexible DC converter station.

[0081] Configure the control strategy for the flexible DC converter station of the sending system. The flexible DC converter station adopts a hybrid full-bridge and half-bridge topology, and the negative voltage output capability of the full-bridge module can achieve AC / DC decoupling control. Therefore, the control strategy for the AC side of the sending-end converter station is shown in the control block diagram below. Figure 4 As shown, the AC side employs a dual-closed-loop constant AC voltage-frequency control strategy to provide stable voltage and frequency for the islanded power grid. The DC side uses a DC current control strategy. When the converter station detects an increase in the DC port current in real time, it automatically reduces the DC voltage bias through the current controller. At this time, the full-bridge module outputs a negative level to reduce the current, thus actively clearing DC faults. Here, PWM stands for Pulse Width Modulator, and the full-bridge module refers to the module within the MMC.

[0082] Please see Figure 5 , Figure 5 This is a control block diagram of the receiving-end flexible DC converter station.

[0083] The control strategy for the AC side of the receiving-end converter station is shown in the control block diagram below. Figure 3 As shown, under normal operating conditions, the AC side adopts dual closed-loop DC voltage-reactive power control to provide stable DC voltage and reactive power support for the system. During DC faults, dual closed-loop power module average voltage-reactive power control is adopted to provide stable power module voltage and reactive power support for the system. The DC side adopts a DC current control strategy. When the converter station detects a decrease in the DC port current in real time, the DC voltage bias is automatically reduced through the current controller. At this time, the full-bridge module outputs a negative level to reduce the current to zero, thereby achieving the purpose of actively clearing DC faults.

[0084] Step 201: In response to the received line fault signal, determine the grid surplus power, real-time DC current data and target operating conditions corresponding to the line fault signal.

[0085] In this embodiment of the invention, the specific implementation process of step 201 is similar to that of step 101, and will not be repeated here.

[0086] Step 202: Determine the number of AC energy-consuming devices to be put into the new energy islanding system based on the surplus power of the power grid.

[0087] In this embodiment of the invention, the specific implementation process of step 202 is similar to that of step 102, and will not be repeated here.

[0088] Step 203: Compare the real-time DC current data with the preset DC current data.

[0089] The preset rated DC current data refers to the per-unit value of the current. In this embodiment, the preset rated DC current data is 1.0 per-unit value.

[0090] In this embodiment of the invention, real-time DC current data is compared with preset rated DC current data.

[0091] Step 204: When the real-time DC current data is less than the preset rated DC current data, the sending-end converter in the sending-end flexible DC converter station is controlled to perform a blocking operation.

[0092] In this embodiment of the invention, the converter is locked out when the real-time DC current data is less than 1.0 per unit value.

[0093] Step 205: Based on the target operating conditions, control the sending-end converter to perform an unlocking operation.

[0094] Furthermore, step 205 includes the following sub-steps:

[0095] S11. When the target operating condition is a single-pole operating condition of a single-sending-end converter station, the unlocking operation is performed by using a seamless unlocking strategy when the real-time DC current data is equal to the preset unlocking DC current data.

[0096] It is worth mentioning that, for the single-pole operation of a single-sending converter station, since no other converter provides voltage and frequency for the islanded AC system after the converter is locked, it is necessary to quickly unlock the converter to avoid system instability in the single-pole operation of the single-sending converter station. Therefore, the converter is unlocked again at the moment when the DC current first crosses zero.

[0097] Furthermore, S11 may include the following sub-steps:

[0098] S111. When the target operating condition is a single-pole operation of a single-sending-end converter station, the AC voltage reference value of the AC outer loop input will be adjusted to the preset real-time AC voltage sampling value when the real-time DC current data is equal to the preset unlocking DC current data.

[0099] The preset unlocking DC current data refers to the unlocking current value used to determine whether to adjust the AC voltage reference value input to the AC outer loop to a preset real-time AC voltage sampling value. In this embodiment, the preset unlocking DC current data...

[0100] The seamless unlocking strategy refers to shutting down all AC outer loop and DC current PI controllers during the lockout period, and setting the AC voltage reference value input to the AC outer loop as the real-time sampled value of the AC voltage at the moment of unlocking.

[0101] In this embodiment of the invention, when the target operating condition is a single-pole operating condition of a single-sending-end converter station, the AC voltage reference value input to the AC outer loop is adjusted to the preset real-time AC voltage sampling value when the real-time DC current data is equal to the preset unlocking DC current data.

[0102] S12. When the target operating condition is not a single-pole operating condition of a single-sending-end converter station, the unlocking operation will be performed after the preset deionization time.

[0103] In this embodiment of the invention, when the sending-end system has other healthy poles / stations providing AC system voltage and frequency, the lockout converter can be unlocked after the deionization time.

[0104] Furthermore, step 205 includes the following sub-steps:

[0105] When a single sending-end converter station is operating under unipolar conditions, the control mode switching of the new energy island system (such as photovoltaic) needs to be coordinated with the blocking of the sending-end converter station.

[0106] S13. When the target operating condition is a single-pole operation of a single-sending-end converter station, switch the current control mode of the new energy island system to the self-locking phase mode.

[0107] In this embodiment of the invention, since no other converter provides voltage and frequency for the islanded AC system after the converter is locked out, the new energy islanded system power station will switch the control strategy mode from phase following mode to phase locking mode during the lockout period.

[0108] Furthermore, step 205 includes the following sub-steps:

[0109] When a single sending-end converter station operates under unipolar conditions, the control mode switching of a renewable energy islanded system (such as photovoltaic) needs to be coordinated with the blocking of the sending-end converter station.

[0110] S14. When the target operating condition is a single-pole operating condition of a single-sending-end converter station and the unlocking operation is performed using a seamless unlocking strategy, the current control mode of the sending-end flexible DC converter station will be switched to the AC port phase-following mode.

[0111] S15. When the target AC voltage in the sending-end flexible DC converter station reaches the preset standard AC voltage, the current control mode of the sending-end flexible DC converter station is switched to the self-locking phase mode, and the current control mode of the new energy island system is switched to the following phase mode.

[0112] In this embodiment of the invention, at the moment of re-unlocking, in order to avoid a severe impact on the AC voltage, the control mode of the sending-end flexible DC converter station is switched to the unlocking mode following the phase of the AC port. After the AC voltage stabilizes, it switches back to the self-locking mode, and the new energy islanded system power station simultaneously switches back to the following phase mode.

[0113] Step 206: After the sending-end converter is unlocked, adjust the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to the preset current threshold.

[0114] In this implementation, the preset current threshold specifically refers to 0.

[0115] In this embodiment of the invention, after the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to 0.

[0116] It is worth mentioning that the specific implementation method in steps 203-206 is as follows:

[0117] When the sending-end flexible DC converter station detects a DC line fault in real time, the DC side of the sending-end station automatically reduces the DC voltage bias after sensing that the DC current has increased due to the fault through the current controller. At this time, the full-bridge module outputs a negative level to gradually reduce the DC current. Considering that if the DC current is too large after the sending-end station is locked, the energy on the DC line will flow back to the power module of the sending-end converter through the grounding point, causing module voltage problems, the sending-end converter station temporarily locks the converter when the DC current drops below the rated DC current, and unlocks the converter again when it receives the unlocking command. After that, the current reference value of the DC current controller is set to zero.

[0118] Step 207: Based on real-time DC current data and target operating conditions, control the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station, and after the sending-end converter is unlocked, adjust the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to the preset current threshold.

[0119] S21. Compare the real-time DC current data with the preset DC current threshold data.

[0120] In this embodiment, the preset DC current threshold data is specifically referred to as 0.

[0121] In this embodiment of the invention, real-time DC current data is compared with preset DC current threshold data.

[0122] S22. When the real-time DC current data is equal to the preset DC current threshold data, the receiving-end converter in the receiving-end flexible DC converter station is controlled to perform a blocking operation.

[0123] In this embodiment of the invention, the converter is temporarily locked out when the DC current data drops to zero.

[0124] S23. Based on the target operating conditions, control the receiving-end converter to perform an unlocking operation.

[0125] Furthermore, S23 may include the following sub-steps:

[0126] S231. When the target operating condition is a single-pole operating condition of a single sending-end converter station, the unlocking operation is performed within the first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current.

[0127] In this embodiment of the invention, for the single-pole operation of a single converter station at the sending end, the converter is immediately unlocked again within 5ms after the DC current stabilizes at zero following the converter lockout.

[0128] Furthermore, S231 may include the following sub-steps:

[0129] S2311. When the target operating condition is a single-pole operation of a single sending-end converter station, the AC outer loop control will be switched from DC voltage control to power module average voltage control within the first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current, and the power module average voltage reference value input by the AC outer loop will be adjusted to the preset real-time sampling value of the power module average voltage.

[0130] The preset standard DC current is specifically referred to as 0 in this embodiment.

[0131] The first preset time, in this embodiment, specifically refers to 5ms.

[0132] In this embodiment of the invention, when the target operating condition is a single-pole operating condition of a single sending-end converter station, a seamless unlocking strategy is executed when the receiving-end station is unlocked again. That is, during the lockout period, all AC outer loop and DC current PI controllers are shut down, and at the moment of unlocking, the AC outer loop control is switched from DC voltage control to power module average voltage control mode. The power module average voltage reference value input by the AC outer loop is set as the real-time sampling value of the power module average voltage at the moment of unlocking.

[0133] S232. When the target operating condition is not a single-pole operating condition of a single-sending-end converter station, the unlocking operation shall be performed after the preset deionization time.

[0134] In this embodiment of the invention, if the sending-end system has other healthy poles / stations providing AC system voltage and frequency operating conditions, the lockout converter is unlocked after the deionization time.

[0135] S24, and after the sending-end converter is unlocked, adjust the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to the preset current threshold.

[0136] In this embodiment of the invention, after the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to 0.

[0137] It is worth mentioning that the specific implementation methods in S21-S24 are as follows:

[0138] When the receiving-end flexible DC converter station detects a DC line fault in real time, the DC side of the receiving-end station automatically reduces the DC voltage bias after sensing that the DC current has increased due to the fault through the current controller. At this time, the full-bridge module outputs a negative level to make the DC current gradually decrease. When the DC current drops to zero, the converter is temporarily locked. The converter is unlocked again at the moment the unlock command is received, and the current reference value of the DC current controller is set to zero.

[0139] Step 208: When the preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, the preset current threshold in the sending-end flexible DC converter station is increased to the sending-end current reference value according to the preset gradient, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to the preset gradient.

[0140] In this embodiment of the invention, when the deionization time is reached and both the sending and receiving end converter stations unlock their converters, each sending-end flexible DC converter station and the receiving-end flexible DC converter station restores the slope of the DC reference value input by the DC current controller on the DC side, rebuilds the DC voltage, and gradually disconnects the AC energy-consuming devices and restores the DC power.

[0141] In a specific application example of the present invention, please refer to Figure 6 , Figure 6 A flowchart for clearing faults in a new energy island system.

[0142] Step 1) Build a new energy island system, the architecture diagram is as follows: Figure 3As shown, the system includes a renewable energy islanded power grid, a sending-end flexible DC converter station, a receiving-end flexible DC converter station, overhead lines, and AC energy dissipation devices. The renewable energy islanded power grid is connected to the sending-end flexible DC converter station via a three-phase AC bus. The AC energy dissipation devices are connected at the AC bus connecting the sending-end flexible DC converter station and the islanded power grid. The AC energy dissipation devices are used to dissipate the continuous active power output of the renewable energy field when the active power transmission channel of the DC line is blocked, thus avoiding overvoltage problems caused by energy accumulation on the sending-end AC feeder.

[0143] Step 2) Configure the control strategy for the sending-end flexible DC converter station. The flexible DC converter station adopts a hybrid full-bridge and half-bridge topology, utilizing the negative voltage output capability of the full-bridge module to achieve AC / DC decoupling control. Therefore, the control block diagram of the AC side control strategy for the sending-end converter station is as follows: Figure 4 As shown, the AC side adopts a dual closed-loop constant AC voltage-frequency control strategy to provide stable voltage and frequency for the islanded power grid. The DC side adopts a DC current control strategy. When the converter station detects an increase in the DC port current in real time, it automatically reduces the DC voltage bias through the current controller. At this time, the full-bridge module outputs a negative level to reduce the current, thereby achieving the purpose of actively clearing DC faults.

[0144] The control strategy for the AC side of the receiving-end converter station is shown in the control block diagram below. Figure 5 As shown, under normal operating conditions, the AC side adopts dual closed-loop DC voltage-reactive power control to provide stable DC voltage and reactive power support for the system. During DC faults, dual closed-loop power module average voltage-reactive power control is adopted to provide stable power module voltage and reactive power support for the system. The DC side adopts a DC current control strategy. When the converter station detects a decrease in the DC port current in real time, the DC voltage bias is automatically reduced through the current controller. At this time, the full-bridge module outputs a negative level to reduce the current to zero, thereby achieving the purpose of actively clearing DC faults.

[0145] Step 3) After the fault signal is detected, steps 4), 5), and 6 are executed simultaneously.

[0146] Step 4) Upon receiving the instruction, the AC power consumption device shall be immediately put into operation to absorb the surplus power of the isolated power grid. Considering that the voltage drop at the port will affect the energy absorption, the number of power consumption devices put into operation shall be no less than the number of surplus power of the isolated power grid.

[0147] Step 5): The DC current controller command value at the sending station switches from the preset value to control 0, and the DC current drops rapidly. When the DC current is less than 1.0 per unit value, the converter is locked. If the sending station is operating under single-converter single-pole conditions, proceed to step 7); if the sending system has other healthy poles / stations providing AC system voltage and frequency, proceed to step 9).

[0148] Step 6) On the DC side of the receiving station, the current controller automatically reduces the DC voltage bias after sensing an increase in DC current due to a fault. At this time, the full-bridge module outputs a negative level to gradually reduce the DC current. When the DC current drops to zero, the converter is temporarily and momentarily blocked. If the sending station is a single converter station operating in a single-pole mode, proceed to step 8); if the sending system has other healthy poles / stations providing AC system voltage and frequency, proceed to step 9).

[0149] Step 7) Since no other converter provides voltage and frequency to the islanded AC system after the converter is locked, during the lockout period, the new energy islanded system power station switches the control strategy mode from phase following to self-locking phase mode. Simultaneously, to quickly unlock the single-pole operation of the converter station at the single sending end and avoid system instability in the islanded system, the converter station re-unlocks the converter the instant the DC current first crosses zero. During re-unlocking, a seamless unlocking strategy is executed: during the lockout period, all AC outer loop and DC current PI controllers are shut down, and at the moment of unlocking, the AC voltage reference value input to the AC outer loop is set to the real-time sampled value of the AC voltage at the moment of unlocking. To avoid severe AC voltage surges, the converter station control mode switches to phase following AC port voltage mode, and then switches back to self-locking phase mode after the AC voltage stabilizes. The new energy islanded system power station simultaneously switches back to following mode. After re-unlocking, the current reference value of the DC current controller is set to zero. Then proceed to step 10).

[0150] Step 8) When the deionization time is reached, unlock the converter again and set the current reference value of the DC current controller to zero. Execute step 10).

[0151] Step 9) After the converter is locked out, immediately unlock it again within 5ms after the DC current stabilizes at zero, executing a seamless unlocking strategy. This means that during the lockout period, all AC outer loop and DC current controllers are shut down. Notably, the inner loop controller is not shut down. At the moment of unlocking, the AC outer loop control is switched from DC voltage control to power module average voltage control mode. The power module average voltage reference value input to the AC outer loop is set to the real-time sampled value of the power module average voltage at the moment of unlocking. After unlocking, the current reference value of the DC current controller is set to zero, and step 10) is executed.

[0152] Step 10) When the deionization time is reached and both the sending and receiving end converter stations unlock their converters, each sending-end flexible DC converter station and the receiving-end flexible DC converter station restores the DC reference value slope input by the DC current controller on the DC side, rebuilds the DC voltage, and gradually disconnects AC energy-consuming devices and restores DC power.

[0153] In this embodiment of the invention, in response to a received line fault signal, the surplus power of the power grid, real-time DC current data, and target operating conditions corresponding to the line fault signal are determined. Based on the surplus power of the power grid, the number of AC energy-consuming devices to be put into the new energy islanding system is determined. Based on the real-time DC current data and target operating conditions, the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station is controlled. After the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold. Based on the real-time DC current data and target operating conditions, the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station is controlled. After the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to a preset current threshold. When a preset deionization time is reached and both the sending-end and receiving-end flexible DC converter stations are unlocked, the power consumption of the sending-end flexible DC converter station is increased according to a preset gradient. The preset current threshold is increased to the sending-end current reference value, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to the preset gradient. This solves the existing problems caused by the small energy storage capacity of the sub-module capacitors in the converter valve, weak overcurrent and overvoltage capabilities, weak and slow new energy power regulation capability during DC faults, difficulty in quickly and significantly solving the energy imbalance between AC and DC sides, longer communication time for energy-consuming devices to receive fault commands when faults occur at the far end of long-distance lines, and the influx of surplus power from the new energy island into the flexible DC valve, which can easily cause module overvoltage. In larger capacity overhead lines, it will reduce the arc extinction speed. The flexible DC converter station uses full-bridge output negative pressure for arc extinction, which increases the risk of module overvoltage and prolongs the fault clearing time beyond the maximum allowable time. This improves the stability of the new energy island grid transmission system, while minimizing the number of full-bridge modules required for the full-half-bridge hybrid flexible DC valve at the sending and receiving end converter stations, thus reducing the overall cost and volume of the flexible DC transmission system.

[0154] Please see Figure 7 , Figure 7 This is a structural block diagram of a fault clearing device for a new energy islanding system provided in Embodiment 3 of the present invention.

[0155] This invention provides a fault clearing device for a renewable energy islanding system, applicable to such a system. The renewable energy islanding system includes multiple AC energy-consuming devices, a sending-end flexible DC converter station, and a receiving-end flexible DC converter station. The device includes:

[0156] The response module 301 is used to respond to the received line fault signal and determine the power grid surplus power, real-time DC current data and target operating conditions corresponding to the line fault signal.

[0157] The AC energy consumption device input module 302 is used to determine the number of AC energy consumption devices to be input into the new energy islanding system based on the surplus power of the power grid.

[0158] The sending-end flexible DC converter station control module 303 is used to control the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station according to real-time DC current data and target operating conditions, and to adjust the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to a preset current threshold after the sending-end converter is unlocked.

[0159] The receiving-end flexible DC converter station control module 304 is used to control the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station according to real-time DC current data and target operating conditions, and to adjust the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to a preset current threshold after the sending-end converter is unlocked.

[0160] The adjustment module 305 is used to increase the preset current threshold in the sending-end flexible DC converter station to the sending-end current reference value according to a preset gradient when the preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, and to increase the preset current threshold in the receiving-end flexible DC converter station to the receiving-end current reference value according to a preset gradient.

[0161] Furthermore, the sending-end flexible DC converter station control module 303 includes:

[0162] The first comparison submodule is used to compare real-time DC current data with preset rated DC current data.

[0163] The first interlocking operation submodule is used to control the sending-end converter in the sending-end flexible DC converter station to perform an interlocking operation when the real-time DC current data is less than the preset rated DC current data.

[0164] The first unlocking operation submodule is used to control the sending-end converter to perform unlocking operations according to the target operating conditions.

[0165] The sending-end current reference value adjustment submodule is used to adjust the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to a preset current threshold value after the sending-end converter is unlocked.

[0166] Furthermore, the first unlocking operation submodule includes:

[0167] The first operating condition processing unit is used to perform the unlocking operation by adopting a seamless unlocking strategy when the real-time DC current data is equal to the preset unlocking DC current data when the target operating condition is a single-pole operating condition of a single sending-end converter station.

[0168] The second operating condition processing unit is used to perform an unlocking operation after a preset deionization time when the target operating condition is not a single-pole operating condition of a single sending-end converter station.

[0169] Furthermore, the first operating condition processing unit includes:

[0170] The AC voltage reference value adjustment subunit is used to adjust the AC voltage reference value input from the AC outer loop to the preset real-time AC voltage sampling value when the target operating condition is a single-pole operation of a single-sending-end converter station and the real-time DC current data is equal to the preset unlocking DC current data.

[0171] Furthermore, the first unlocking operation submodule also includes:

[0172] The first mode switching unit is used to switch the current control mode of the new energy island system to the self-locking phase mode when the target operating condition is a single-pole operation of a single-sending-end converter station.

[0173] Furthermore, the first unlocking operation submodule also includes:

[0174] The second mode switching unit is used to switch the current control mode of the sending-end flexible DC converter station to the AC port phase-following mode when the target operating condition is a single-pole operation of a single sending-end converter station and the unlocking operation is performed using a seamless unlocking strategy.

[0175] The third mode switching unit is used to switch the current control mode of the sending-end flexible DC converter station to the self-locking phase mode and the current control mode of the new energy islanding system to the following phase mode when the target AC voltage in the sending-end flexible DC converter station reaches the preset standard AC voltage.

[0176] Furthermore, the receiving-end flexible DC converter station control module 304 includes:

[0177] The second comparison submodule is used to compare real-time DC current data with preset DC current threshold data.

[0178] The second interlocking operation submodule is used to control the receiving-end converter in the receiving-end flexible DC converter station to perform an interlocking operation when the real-time DC current data is equal to the preset DC current threshold data.

[0179] The second unlocking operation submodule is used to control the receiving-end converter to perform the unlocking operation according to the target operating conditions.

[0180] The receiving-end current reference value adjustment submodule is used to adjust the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to a preset current threshold value after the sending-end converter is unlocked.

[0181] Furthermore, the second unlocking operation submodule includes:

[0182] The third operating condition processing unit is used to perform an unlocking operation within a first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current when the target operating condition is a single pole operating condition of a single sending-end converter station.

[0183] The fourth operating condition processing unit is used to perform an unlocking operation after a preset deionization time when the target operating condition is not a single-pole operating condition of a single sending-end converter station.

[0184] Furthermore, the third operating condition processing unit includes:

[0185] The power module adjustment subunit is used to switch the AC outer loop control from DC voltage control to power module average voltage control within a first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current when the target operating condition is a single pole operation condition of a single sending-end converter station. It also adjusts the power module average voltage reference value input by the AC outer loop to the preset real-time sampling value of the power module average voltage.

[0186] In this embodiment of the invention, in response to a received line fault signal, the surplus power of the power grid, real-time DC current data, and target operating conditions corresponding to the line fault signal are determined. Based on the surplus power of the power grid, the number of AC energy-consuming devices to be put into the new energy islanding system is determined. Based on the real-time DC current data and target operating conditions, the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station is controlled. After the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold. Based on the real-time DC current data and target operating conditions, the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station is controlled. After the sending-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to a preset current threshold. When a preset deionization time is reached and both the sending-end and receiving-end flexible DC converter stations are unlocked, the power consumption of the sending-end flexible DC converter station is increased according to a preset gradient. The preset current threshold is increased to the sending-end current reference value, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to the preset gradient. This solves the existing problems caused by the small energy storage capacity of the sub-module capacitors in the converter valve, weak overcurrent and overvoltage capabilities, weak and slow new energy power regulation capability during DC faults, difficulty in quickly and significantly solving the energy imbalance between AC and DC sides, longer communication time for energy-consuming devices to receive fault commands when faults occur at the far end of long-distance lines, and the influx of surplus power from the new energy island into the flexible DC valve, which can easily cause module overvoltage. In larger capacity overhead lines, it will reduce the arc extinction speed. The flexible DC converter station uses full-bridge output negative pressure for arc extinction, which increases the risk of module overvoltage and prolongs the fault clearing time beyond the maximum allowable time. This improves the stability of the new energy island grid transmission system, while minimizing the number of full-bridge modules required for the full-half-bridge hybrid flexible DC valve at the sending and receiving end converter stations, thus reducing the overall cost and volume of the flexible DC transmission system.

[0187] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0188] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0189] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0190] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0191] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0192] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for clearing faults in a new energy islanding system, characterized in that, The method, applied to a renewable energy islanding system, which includes multiple AC energy-consuming devices, a sending-end flexible DC converter station, and a receiving-end flexible DC converter station, comprises: In response to a received line fault signal, determine the grid surplus power, real-time DC current data, and target operating condition corresponding to the line fault signal; The number of AC energy-consuming devices to be put into the new energy island system is determined based on the surplus power of the power grid. Based on the real-time DC current data and the target operating conditions, the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station are controlled, and after the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold. Based on the real-time DC current data and the target operating conditions, the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station are controlled, and after the receiving-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to the preset current threshold. When the preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, the preset current threshold in the sending-end flexible DC converter station is increased to the sending-end current reference value according to a preset gradient, and the preset current threshold in the receiving-end flexible DC converter station is increased to the receiving-end current reference value according to a preset gradient.

2. The fault clearing method for a new energy islanding system according to claim 1, characterized in that, The step of controlling the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station based on the real-time DC current data and the target operating condition, and adjusting the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to a preset current threshold after the sending-end converter is unlocked, includes: Compare the real-time DC current data with the preset rated DC current data; When the real-time DC current data is less than the preset rated DC current data, the sending-end converter in the sending-end flexible DC converter station is controlled to perform a blocking operation. Based on the target operating conditions, control the sending-end converter to perform an unlocking operation; After the sending-end converter is unlocked, the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station is adjusted to a preset current threshold.

3. The fault clearing method for a new energy islanding system according to claim 2, characterized in that, The step of controlling the sending-end converter to perform an unlocking operation according to the target operating condition includes: When the target operating condition is a single-pole operating condition of a single-sending-end converter station, a seamless unlocking strategy is adopted to perform the unlocking operation when the real-time DC current data is equal to the preset unlocking DC current data. When the target operating condition is not a single-pole operating condition of a single sending-end converter station, the unlocking operation is performed after the preset deionization time.

4. The fault clearing method for a new energy islanding system according to claim 3, characterized in that, The step of performing the unlocking operation using a seamless unlocking strategy when the target operating condition is a single-pole operation of a single-sending-end converter station, and the real-time DC current data equals the preset unlocking DC current data, includes: When the target operating condition is a single-pole operation of a single-sending-end converter station, the AC voltage reference value input to the AC outer loop is adjusted to the preset real-time AC voltage sampling value when the real-time DC current data is equal to the preset unlocking DC current data.

5. The fault clearing method for a new energy islanding system according to claim 3, characterized in that, Also includes: When the target operating condition is a single-pole operation of a single-sending-end converter station, the current control mode of the new energy island system will be switched to the self-locking phase mode.

6. The fault clearing method for a new energy islanding system according to claim 3, characterized in that, Also includes: When the target operating condition is a single-pole operating condition of a single-sending-end converter station and the unlocking operation is performed using the seamless unlocking strategy, the current control mode of the sending-end flexible DC converter station is switched to the AC port phase-following mode. When the target AC voltage in the sending-end flexible DC converter station reaches the preset standard AC voltage, the current control mode of the sending-end flexible DC converter station is switched to the self-locking phase mode, and the current control mode of the new energy island system is switched to the following phase mode.

7. The fault clearing method for a new energy islanding system according to claim 1, characterized in that, The step of controlling the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station based on the real-time DC current data and the target operating condition, and adjusting the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to the preset current threshold value after the receiving-end converter is unlocked, includes: Compare the real-time DC current data with the preset DC current threshold data; When the real-time DC current data is equal to the preset DC current threshold data, the receiving-end converter in the receiving-end flexible DC converter station is controlled to perform a blocking operation. Based on the target operating conditions, control the receiving-end converter to perform an unlocking operation; After the receiving-end converter is unlocked, the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station is adjusted to the preset current threshold.

8. The fault clearing method for a new energy islanding system according to claim 7, characterized in that, The step of controlling the receiving-end converter to perform an unlocking operation according to the target operating condition includes: When the target operating condition is a single-pole operating condition of a single sending-end converter station, the unlocking operation is performed within a first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current. When the target operating condition is not a single-pole operating condition of a single sending-end converter station, the unlocking operation is performed after the preset deionization time.

9. The fault clearing method for a new energy islanding system according to claim 8, characterized in that, The step of performing the unlocking operation within a first preset time after the target DC current associated with the receiving-end converter reaches a preset standard DC current when the target operating condition is a single-pole operating condition of a single sending-end converter station includes: When the target operating condition is a single-pole operation of a single sending-end converter station, the AC outer loop control will be switched from DC voltage control to power module average voltage control within a first preset time after the target DC current associated with the receiving-end converter reaches the preset standard DC current, and the power module average voltage reference value input by the AC outer loop will be adjusted to the preset real-time sampling value of the power module average voltage.

10. A fault clearing device for a new energy islanding system, characterized in that, This technology is applied to a renewable energy islanding system, which includes multiple AC energy-consuming devices, a sending-end flexible DC converter station, and a receiving-end flexible DC converter station. The devices include: The response module is used to respond to the received line fault signal and determine the grid surplus power, real-time DC current data and target operating conditions corresponding to the line fault signal. An AC energy consumption device input module is used to determine the number of AC energy consumption devices to be input into the new energy island system based on the surplus power of the power grid. The sending-end flexible DC converter station control module is used to control the locking and unlocking of the sending-end converter in the sending-end flexible DC converter station according to the real-time DC current data and the target operating conditions, and to adjust the sending-end current reference value of the sending-end DC controller in the sending-end flexible DC converter station to a preset current threshold after the sending-end converter is unlocked. The receiving-end flexible DC converter station control module is used to control the locking and unlocking of the receiving-end converter in the receiving-end flexible DC converter station according to the real-time DC current data and the target operating conditions, and to adjust the receiving-end current reference value of the receiving-end DC controller in the receiving-end flexible DC converter station to the preset current threshold after the receiving-end converter is unlocked. The adjustment module is used to, when a preset deionization time is reached and both the sending-end flexible DC converter station and the receiving-end flexible DC converter station are unlocked, increase the preset current threshold in the sending-end flexible DC converter station to the sending-end current reference value according to a preset gradient, and increase the preset current threshold in the receiving-end flexible DC converter station to the receiving-end current reference value according to a preset gradient.

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