Soft direct feed-in receiving end power grid short-circuit current optimization control method and device

Abstract

The invention discloses a flexible direct feed-in receiving end power grid short-circuit current optimization control method and device. The method comprises the following steps: identifying a fault of a flexible direct-current feed-in receiving end power grid according to a grid-side alternating-current voltage monitored in real time, and entering a fault ride-through mode after the fault is identified; judging the state of the phase-locked loop in the fault ride-through mode, and determining the state of the phase-locked loop; executing a current limiting strategy according to the phase-locked loop state; detecting the AC voltage recovery speed, and performing delayed fault clearing confirmation according to the detection result of the voltage recovery speed; and after the fault is cleared, executing a voltage recovery strategy, and after the voltage of the fault point recovers a preset value, recovering the reactive current instruction value to an initial value.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission control technology for power systems, and more specifically, to a method and apparatus for optimizing the control of short-circuit current in a flexible DC-fed receiving-end power grid. Background Technology

[0002] With the continuous advancement of the construction of new power systems, the characteristics of "high proportion of new energy, high proportion of power electronics, and high proportion of imported power" are becoming increasingly apparent, posing severe challenges to the safety and stability of the power grid. The large-scale replacement of receiving-end thermal power units by multiple DC feeds will, on the one hand, increase short-circuit current levels, and on the other hand, reduce the dynamic reactive power support capacity of the power grid. During fault disturbances, induction motors and other conventional DC systems absorb a large amount of reactive power from the grid, which will further weaken the reactive power regulation capacity of the receiving-end grid. Flexible DC transmission technology (referred to as Flexible DC technology) has advantages such as independent control of active and reactive power, supplying power to passive networks, and rapidly achieving power flow reversal. It has been vigorously developed and applied in the fields of ultra-long-distance, ultra-large-capacity power transmission from large energy bases and asynchronous interconnection of inter-regional power grids.

[0003] With declining equipment costs and maturing operational control, UHVDC flexible DC transmission has gradually become a key technology for DC feed into the receiving-end power grid. However, with the continuous expansion of installed capacity and scale of receiving-end power grids, represented by the East China, North China, and Southern China power grids, coupled with the dense feed of UHVDC, the grid structure of the receiving-end power grid has become more compact, and its short-circuit current level has also increased accordingly, with the problem of excessive short-circuit current becoming more serious year by year. The receiving-end power grid has different needs during transient periods, requiring both the suppression of short-circuit current levels during faults and the guarantee of system voltage stability during fault recovery. Flexible DC transmission systems can limit the short-circuit current fed into the AC system, avoiding further increases in the system's short-circuit current level; at the same time, they can quickly respond to grid demands during system voltage recovery, shortening the voltage recovery time after a fault by injecting reactive power, thus meeting the system's voltage stability requirements. In addition, to ensure the safe acceptance of UHVDC by the receiving-end power grid, the construction of supporting AC grids and the configuration of equipment such as synchronous condensers further increase the level of system short-circuit current. The problem of excessive short-circuit current caused by flexible DC feed into the receiving-end power grid should not be underestimated and has gradually become a focus of attention for power grid development planning and operation dispatch personnel.

[0004] Different current limiting methods are suitable for different control strategy scenarios. The d-axis current priority strategy is suitable for maintaining DC voltage stability while limiting reactive current during voltage control station disturbances, thereby reducing the short-circuit current injected into the AC system by the flexible DC transmission line. Currently, the common method for suppressing flexible DC short-circuit current is a comprehensive current limiting method that simultaneously employs the d-axis current priority strategy and low-voltage current limiting links, which can effectively suppress the short-circuit current injected into the AC system by the flexible DC transmission line during fault disturbances. However, this current limiting method sacrifices the reactive power support capability of the flexible DC transmission line, which may lead to voltage instability risks in the nearby power grid. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and apparatus for optimizing the control of short-circuit current in a flexible DC-fed receiving-end power grid.

[0006] According to one aspect of the present invention, a method for optimizing control of short-circuit current in a flexible DC-fed receiving-end power grid is provided, comprising:

[0007] Based on the real-time monitored grid-side AC voltage, faults in the flexible DC feed-in receiving-end grid are identified, and the fault ride-through mode is entered after the fault is identified.

[0008] In fault-crossing mode, determine the state of the phase-locked loop (PLL) and confirm its status.

[0009] Execute current limiting strategies based on the phase-locked loop (PLL) state;

[0010] The AC voltage recovery speed is tested, and the delay fault clearance is confirmed based on the test results.

[0011] After the fault is cleared, the voltage recovery strategy is executed, and after the voltage at the fault point is restored to the preset value, the reactive current command value is restored to the initial value.

[0012] Optionally, based on the real-time monitored grid-side AC voltage, faults in the flexible DC-fed receiving-end power grid are identified, including:

[0013] A fault is identified when the AC voltage on the grid side drops; otherwise, no fault exists.

[0014] Optionally, in fault-crossing mode, the state of the phase-locked loop (PLL) is determined, including:

[0015] The phase-locked loop (PLL) state discrimination module detects the q-axis voltage of the flexible DC output and compares it with a preset threshold.

[0016] If the output q-axis voltage of the flexible DC circuit is greater than the threshold, the controller is deemed to be faulty; otherwise, the phase-locked loop is deemed to be operating normally, and the current limiting strategy continues to be executed.

[0017] Optionally, the current limiting strategy is to control the reactive current injected into the system by setting the reactive current command value to 0 or a negative value, or to allow the flexible DC to absorb reactive current from the system.

[0018] Optionally, the AC voltage recovery speed is detected, including:

[0019] Detect the AC voltage recovery rate and compare it with a recovery rate threshold;

[0020] When the AC voltage recovery rate is greater than the recovery rate threshold, it is determined that the circuit breaker near the fault point has tripped, and the AC voltage shows a step increase.

[0021] Optionally, a voltage recovery strategy is implemented, including:

[0022] Increase the reactive current command value to accelerate AC system voltage recovery.

[0023] According to another aspect of the present invention, a flexible DC-fed receiving-end grid short-circuit current optimization control device is provided, comprising:

[0024] The identification module is used to identify faults in the receiving-end power grid fed by flexible DC based on the real-time monitored grid-side AC voltage, and enters fault ride-through mode after the fault is identified.

[0025] The judgment module is used to determine the state of the phase-locked loop (PLL) in fault-crossing mode.

[0026] The execution module is used to execute the current limiting strategy based on the phase-locked loop state;

[0027] The detection module is used to detect the AC voltage recovery speed and confirm the delayed fault clearing based on the detection results of the voltage recovery speed.

[0028] The execution module is used to execute the voltage recovery strategy after the fault is cleared, and to restore the reactive current command value to the initial value after the voltage at the fault point is restored to the preset value.

[0029] According to another aspect of the present invention, a computer-readable storage medium is provided, the storage medium storing a computer program for performing the methods described in any of the above aspects of the present invention.

[0030] According to another aspect of the present invention, an electronic device is provided, the electronic device comprising: a processor; a memory for storing executable instructions of the processor; the processor being configured to read the executable instructions from the memory and execute the instructions to implement the method described in any of the preceding aspects of the present invention.

[0031] Therefore, this invention avoids the influx of short-circuit current into the AC system during a fault and provides reactive power support to the AC system during the fault recovery process, achieving coordinated control of short-circuit current suppression and voltage support. It achieves short-circuit current suppression by the flexible DC during the fault duration, without increasing the short-circuit current level of the receiving-end grid. Furthermore, it provides reactive power and voltage support by the flexible DC during fault recovery, accelerating the voltage recovery of the receiving-end grid after the fault. Attached Figure Description

[0032] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0033] Figure 1 This is a flowchart illustrating an exemplary embodiment of the present invention regarding a method for optimizing control of short-circuit current in a flexible DC-fed receiving-end power grid.

[0034] Figure 2 This is an equivalent circuit diagram of a three-phase symmetrical short-circuit fault provided in an exemplary embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the superposition of synchronous generator and flexible DC short-circuit current provided in an exemplary embodiment of the present invention;

[0036] Figure 4 This is a block diagram of an additional control module for flexible straightness provided in an exemplary embodiment of the present invention;

[0037] Figure 5 This is a control block diagram of a PLL state discrimination module provided in an exemplary embodiment of the present invention;

[0038] Figure 6 This is a control block diagram of an AC voltage detection module provided in an exemplary embodiment of the present invention;

[0039] Figure 7 This is a schematic diagram of the input signal of the reactive power reference value switching module provided in an exemplary embodiment of the present invention;

[0040] Figure 8 This is a flowchart of a fault traversal strategy provided by an exemplary embodiment of the present invention;

[0041] Figure 9a and Figure 9b These are schematic diagrams of short-circuit current consistency and reactive voltage support provided by an exemplary embodiment of the present invention.

[0042] Figures 10a-10h These are, respectively, waveform diagrams of the d-axis and q-axis reference voltages, actual d-axis and q-axis voltages, d-axis and q-axis reference currents, d-axis and q-axis actual currents, signal SigFault, signal SigRecover, switching signal Sig0, and the reactive power of the flexible DC transmission system provided in an exemplary embodiment of the present invention.

[0043] Figure 11a and Figure 11b These are waveform diagrams of the short-circuit current and AC voltage at the fault point provided in an exemplary embodiment of the present invention.

[0044] Figure 12a and Figure 12b These are waveform diagrams of conventional DC power and AC voltage provided in an exemplary embodiment of the present invention;

[0045] Figure 13 This is a schematic diagram of the structure of a flexible DC feed-in receiving-end power grid short-circuit current optimization control device provided in an exemplary embodiment of the present invention;

[0046] Figure 14 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. Detailed Implementation

[0047] Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0048] It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0049] Those skilled in the art will understand that the terms "first," "second," etc., in the embodiments of the present invention are only used to distinguish different steps, devices, or modules, and do not represent any specific technical meaning, nor do they indicate a necessary logical order between them.

[0050] It should also be understood that in the embodiments of the present invention, "multiple" can refer to two or more, and "at least one" can refer to one, two or more.

[0051] It should also be understood that any component, data or structure mentioned in the embodiments of the present invention can generally be understood as one or more unless explicitly defined or given contrary instructions in the context.

[0052] Furthermore, the term "and / or" in this invention is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this invention generally indicates that the preceding and following related objects have an "or" relationship.

[0053] It should also be understood that the description of the various embodiments in this invention emphasizes the differences between the various embodiments, and the similarities or similarities can be referred to each other. For the sake of brevity, they will not be described in detail.

[0054] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0055] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0056] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0057] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0058] The embodiments of this invention can be applied to electronic devices such as terminal devices, computer systems, and servers, and can operate together with a wide range of other general-purpose or special-purpose computing system environments or configurations. Well-known examples of terminal devices, computing systems, environments, and / or configurations suitable for use with electronic devices such as terminal devices, computer systems, and servers include, but are not limited to: personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments including any of the above systems, etc.

[0059] Electronic devices such as terminal devices, computer systems, and servers can be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Typically, program modules can include routines, programs, object programs, components, logic, data structures, etc., which perform specific tasks or implement specific abstract data types. Computer systems / servers can be implemented in distributed cloud computing environments, where tasks are executed by remote processing devices linked through communication networks. In distributed cloud computing environments, program modules can reside on local or remote computing system storage media, including storage devices.

[0060] Exemplary methods

[0061] Figure 1 This is a schematic flowchart of a method for optimizing short-circuit current control in a flexible DC-fed receiving-end power grid according to an exemplary embodiment of the present invention. This embodiment can be applied to electronic devices, such as… Figure 1 As shown, the optimized control method 100 for short-circuit current of the receiving-end grid fed by flexible DC transmission includes the following steps:

[0062] Step 101: Based on the real-time monitored grid-side AC voltage, identify the faults in the flexible DC feed into the receiving-end grid, and enter the fault ride-through mode after the fault is identified.

[0063] Step 102: Determine the state of the phase-locked loop (PLL) in fault-crossing mode;

[0064] Step 103: Execute the current limiting strategy based on the phase-locked loop state;

[0065] Step 104: Detect the AC voltage recovery speed and confirm the delay fault clearance based on the detection results of the voltage recovery speed;

[0066] Step 105: After the fault is cleared, execute the voltage recovery strategy, and after the voltage at the fault point is restored to the preset value, restore the reactive current command value to the initial value.

[0067] Specifically, this invention relates to the field of flexible DC transmission control in power systems, and discloses a short-circuit current suppression strategy for flexible DC feed-in receiving-end power grids. It focuses on addressing the problems of excessive short-circuit current levels and insufficient dynamic reactive power support capacity in the receiving-end power grid, proposing a short-circuit current optimization strategy with voltage support characteristics. This strategy can suppress flexible DC short-circuit currents during faults and, during the recovery period after circuit breaker operation and fault line clearance, inject reactive power into the system through flexible DC, thereby improving the voltage stability of the receiving-end system.

[0068] In the case of a flexible DC transmission system fed into an AC system, when a short-circuit fault occurs in the AC system, this invention provides a short-circuit current suppression strategy for the receiving-end grid fed into the flexible DC system. During the fault, the short-circuit current injected into the AC system by the flexible DC system can be effectively limited, thereby reducing the short-circuit current level at the fault point. At the same time, during the fault recovery process, a certain amount of reactive power is injected into the system to shorten the system voltage recovery time, thereby achieving coordinated control of short-circuit current suppression and voltage support.

[0069] After a three-phase short-circuit fault occurs in the vicinity of a flexible DC converter station, the short-circuit current injected by the flexible DC into the AC system is closely related to its own reactive current level. Therefore, reducing the reactive power exchange between the flexible DC and the system during the fault period can help reduce its contribution to the AC system's short-circuit current. After a short-circuit fault occurs, the circuit breaker closest to the fault point operates first. Generally, the circuit breaker at the far end operates to clear the fault after one cycle. To address the issues of short-circuit current suppression and voltage support coupling under fault disturbances, a control module is added to the original control structure of the flexible DC converter, including an AC voltage detection module, a phase-locked loop (PLL) state determination module, and a reactive power reference value switching module.

[0070] Step 1: Enter fault identification and fault traversal mode.

[0071] When a short-circuit fault occurs at the near-field point of the flexible DC converter station, causing a voltage drop at the point of common coupling, the AC voltage detection module monitors the grid-side AC voltage in real time. Once a drop in grid-side AC voltage is detected, the system immediately enters fault ride-through mode, preparing for subsequent fault handling operations.

[0072] Step 2: Phase-Locked Loop (PLL) Status Determination

[0073] (1) Parameter detection and comparison

[0074] The PLL state discrimination module detects the q-axis voltage of the flexible DC output and compares it with the threshold m.

[0075] (2) Status judgment and subsequent operations

[0076] If the q-axis voltage of the flexible DC output is greater than the threshold m, it indicates that the phase-locked loop failed to track the grid-side phase in time, and the fault is so severe that the controller fails. The system will handle the situation according to the severe fault response mechanism. If the q-axis voltage of the flexible DC output is less than the threshold m, it indicates that the phase-locked loop is operating normally, and the system can continue to execute the current limiting strategy.

[0077] Step 3: Implement rate limiting policy

[0078] By using a reactive current reference value switching module, the reactive current command value is set to 0 or a negative value. Before the circuit breaker operates (within 40-60ms after the fault occurs), based on the set reactive current command value, the reactive current injected into the system by the flexible DC transmission line is controlled to be 0, or the flexible DC transmission line is allowed to absorb reactive current from the system, thereby avoiding short-circuit current injected into the system by the flexible DC transmission line or reducing the short-circuit current level of the AC system.

[0079] Step 4: Voltage recovery detection and delay confirmation of fault clearing

[0080] (1) Voltage recovery speed detection

[0081] The voltage recovery discrimination module detects the AC side voltage recovery rate dV / dt and compares it with a threshold n. When dV / dt is greater than the threshold n, it indicates that the circuit breaker near the fault point has tripped, and the AC voltage shows a step increase.

[0082] (2) Delayed confirmation of fault clearing

[0083] Since the circuit breaker at the remote end of the fault point has not yet tripped and the fault point is not completely isolated, injecting reactive power at this time would increase the short-circuit current. Therefore, after a delay of t0 by the delay module, the fault is confirmed to be cleared and the system enters the voltage recovery stage.

[0084] Step 5: Execute the voltage recovery strategy

[0085] (1) Adjustment of reactive current command value

[0086] The controller executes a voltage recovery strategy by increasing the reactive current command value iqref through the reactive current reference value switching module.

[0087] (2) Reactive power output and voltage establishment

[0088] During the fault recovery phase, increasing the reactive power output of flexible DC helps to re-establish the system voltage.

[0089] Step 6: Restore the reactive current command value to its initial value.

[0090] When the AC voltage detection module detects that the fault point voltage has recovered to 0.95 pu, the reactive current command value is switched back to the initial value of the normal operating state through the reactive reference value switching module, so that the system can resume normal operation.

[0091] The following detailed description of a short-circuit current optimization control strategy for a flexible DC-fed receiving-end power grid according to the present invention, in conjunction with embodiments and accompanying drawings, provides a detailed explanation.

[0092] Step 1: After a three-phase ground fault occurs in the vicinity of the converter station, a simplified diagram of the connection between the flexible DC and the synchronous generator is shown below. Figure 2 As shown, branch n is the equivalent branch of the synchronous generator (n = 1, 2, ..., N), and the flexible DC is equivalent to a current source. UGn represents the equivalent voltage source voltage of each synchronous generator, ZGn represents the equivalent impedance from the synchronous generator to the short-circuit point, ZV represents the equivalent impedance from the flexible DC to the short-circuit point, and Zf is the fault impedance. IGn represents the short-circuit current provided by the synchronous generator, IV represents the short-circuit current provided by the flexible DC, and If is the fault branch current. Figure 3 This is a schematic diagram showing the superposition of short-circuit currents of a synchronous generator and a flexible DC transmission line. The short-circuit current supplied by the flexible DC transmission line to the system and the short-circuit current of the AC system are mainly superimposed reactive currents.

[0093] Step 2: Add a flexible straight-line control module, such as Figure 4 It includes an AC voltage detection module, a PLL status determination module, and a reactive power reference value switching module.

[0094] Step 3: Add a PLL status detection module, such as Figure 5 To determine whether the phase-locked loop (PLL) is tracking the grid phase in a timely manner.

[0095] Step 4: Add an AC voltage detection module, such as Figure 6 The grid status is determined based on the AC voltage on the grid side.

[0096] Step 5: The following optimization strategy for the short-circuit current of the flexible DC converter station is implemented through an additional control module: When a short-circuit fault occurs in the vicinity of the flexible DC converter station, the AC voltage detection module judges the voltage drop of the system and identifies that the grid-side AC voltage US has decreased, thus entering the fault ride-through mode. The PLL status judgment module judges whether the phase-locked loop is operating normally, that is, whether the output q-axis voltage of the flexible DC converter is less than the threshold m. If it is greater than the threshold, the phase-locked loop has not yet tracked the grid-side phase, and the active and reactive currents of the flexible DC converter are limited simultaneously to limit the short-circuit current; if it is less than the threshold, it means that the phase-locked loop has completed phase locking, and the current limiting strategy continues to be executed. The reactive current reference value switching module switches the reactive current command value to Iqref1 to prevent the flexible DC converter from injecting short-circuit current into the AC system before the circuit breaker operates, i.e., during the period of 40-60ms after the fault.

[0097] When the AC voltage detection module detects that the system voltage recovery rate dUS / dt is greater than the threshold n, it indicates that the circuit breaker near the fault point has already tripped, and the AC voltage has experienced a step increase. At this time, the circuit breaker at the far end of the fault point has not yet tripped, and the fault point is not completely isolated. If reactive power is injected into the system at this time, it will further increase the short-circuit current at the fault point. Therefore, after a delay of t1 by the delay module, the fault is confirmed to be cleared, the system is judged to have entered the voltage recovery stage, and the voltage recovery strategy is executed.

[0098] The reactive power reference value switching module switches the reactive current command value to Iqref2, increasing the reactive power output with flexible DC during the fault recovery phase to promote rapid voltage recovery of the near-field AC system. Once the AC voltage detection module detects voltage recovery at the fault point, the reactive power reference value switching module switches the reactive current command value back to Iqref0. The input signals of the reactive power reference value switching module are as follows: Figure 7 As shown, the control flowchart of this short-circuit current optimization strategy is as follows: Figure 8 As shown.

[0099] Table 1 Parameter Settings for Flexible DC Converter Station

[0100]

[0101]

[0102] A fully electromagnetic transient simulation system incorporating a flexible DC-DC converter was established. The receiving end of the flexible DC-DC converter employed constant DC voltage and constant reactive power control. The parameter settings for the flexible DC-DC converter are shown in Table 1, and the optimization strategy parameter settings are shown in Table 2. A three-phase short-circuit fault occurred on the 525kV AC line side of the receiving end of the flexible DC-DC converter at 4.0s, and the fault was cleared at 4.1s. The following three strategies were simulated for comparison: Strategy 1: The reactive current command value of the flexible DC-DC converter remained at 0 during the transient period, providing neither short-circuit current nor reactive power support to the AC system. Strategy 2: The reactive current command value of the flexible DC-DC converter was set as follows: Figure 9bThis strategy provides both short-circuit current to the AC system and reactive power support; Strategy 3: Adopting the proposed short-circuit current optimization strategy, the reactive current command value during a fault is set as follows... Figure 9a The reactive current command value during voltage recovery is set as follows: Figure 9b Flexible DC transmissions both absorb short-circuit current from the AC system and provide reactive power support to the AC system.

[0103] Figures 10a-12b The simulation results are based on the optimization strategy proposed in this patent. Figures 10a-10h This indicates that Strategy 2 results in the largest short-circuit current fed into the fault point by the flexible DC transmission line; Strategy 1 maintains a reactive current reference value of 0 during the fault period, while Strategy 3 absorbs reactive current from the AC system during the fault period, effectively reducing the short-circuit current fed into the fault point. Therefore, limiting the reactive current of the flexible DC transmission line can reduce the short-circuit current fed into the AC system by the flexible DC transmission line. Figure 11a and Figure 11b The results show the voltage recovery at the fault point under different strategies: Strategy 1 does not provide reactive power support to the system during the transient period, Strategy 2 continuously injects reactive current during the transient period, while Strategy 3 injects reactive current into the system during the voltage recovery phase, promoting rapid recovery of the system voltage. Compared with Strategy 1, the time for the system voltage to recover to 1.0 pu is shortened by about 0.15 seconds. Figure 12a and Figure 12b This indicates that, compared to Strategy 1, Strategy 3 results in faster power and AC voltage recovery speeds for the flexible DC near-field conventional DC, further improving the stability of the near-field power grid. This short-circuit current optimization strategy with voltage support characteristics enables coordinated control of short-circuit current suppression and voltage support, improving the interaction characteristics between the flexible DC and AC systems.

[0104] Therefore, this invention avoids the influx of short-circuit current into the AC system during a fault and provides reactive power support to the AC system during the fault recovery process, achieving coordinated control of short-circuit current suppression and voltage support. It achieves short-circuit current suppression by the flexible DC during the fault duration, without increasing the short-circuit current level of the receiving-end grid. Furthermore, it provides reactive power and voltage support by the flexible DC during fault recovery, accelerating the voltage recovery of the receiving-end grid after the fault.

[0105] Exemplary device

[0106] Figure 13 This is a schematic diagram of the structure of a flexible DC-fed receiving-end power grid short-circuit current optimization control device provided in an exemplary embodiment of the present invention. Figure 13 As shown, the device 1400 includes:

[0107] The identification module 1310 is used to identify faults in the receiving-end power grid fed by flexible DC based on the real-time monitored grid-side AC voltage, and enter the fault ride-through mode after the fault is identified.

[0108] The judgment module 1320 is used to judge the state of the phase-locked loop in fault-crossing mode and determine the state of the phase-locked loop.

[0109] Execution module 1330 is used to execute current limiting strategies based on the phase-locked loop state;

[0110] The detection module 1340 is used to detect the AC voltage recovery speed and confirm the delayed fault clearing based on the detection result of the voltage recovery speed.

[0111] The execution module 1350 is used to execute a voltage recovery strategy after the fault is cleared, and to restore the reactive current command value to its initial value after the voltage at the fault point is restored to a preset value.

[0112] Exemplary electronic devices

[0113] Figure 14 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. For example... Figure 14 As shown, the electronic device 140 includes one or more processors 141 and memory 142.

[0114] The processor 141 may be a central processing unit (CPU) or other form of processing unit with data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions.

[0115] The memory 142 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 141 may execute the program instructions to implement the methods of the software programs of the various embodiments of the present invention described above, and / or other desired functions. In one example, the electronic device may also include an input device 143 and an output device 144, these components being interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0116] In addition, the input device 143 may also include, for example, a keyboard, a mouse, etc.

[0117] The output device 144 can output various information to the outside. The output device 144 may include, for example, a display, a speaker, a printer, and a communication network and its connected remote output devices, etc.

[0118] Of course, for the sake of simplicity, Figure 14Only some of the components of this electronic device relevant to the present invention are shown, omitting components such as buses, input / output interfaces, etc. In addition, the electronic device may include any other suitable components depending on the specific application.

[0119] Exemplary computer program products and computer-readable storage media

[0120] In addition to the methods and apparatus described above, embodiments of the present invention may also be computer program products, which include computer program instructions that, when executed by a processor, cause the processor to perform the steps in the methods according to various embodiments of the present invention described in the "Exemplary Methods" section above.

[0121] The computer program product can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments of the present invention. The programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0122] Furthermore, embodiments of the present invention may also be computer-readable storage media storing computer program instructions thereon, which, when executed by a processor, cause the processor to perform the steps of the methods according to various embodiments of the present invention described in the "Exemplary Methods" section above.

[0123] The computer-readable storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or any combination thereof. More specific examples (a non-exhaustive list) of readable storage media include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof.

[0124] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0125] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system embodiments, since they largely correspond to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0126] The block diagrams of devices, systems, devices, and systems involved in this invention are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, systems, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0127] The methods and systems of the present invention may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the methods is for illustrative purposes only, and the steps of the methods of the present invention are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, the present invention may also be implemented as a program recorded on a recording medium, the program comprising machine-readable instructions for implementing the methods according to the present invention. Thus, the present invention also covers recording media storing programs for performing the methods according to the present invention.

[0128] It should also be noted that in the systems, apparatus, and methods of the present invention, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered equivalents of the present invention. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the invention. Therefore, the invention is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0129] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A method for optimizing the control of short-circuit current in a flexible DC-fed receiving-end power grid, characterized in that, include: Based on the real-time monitored grid-side AC voltage, faults in the flexible DC feed-in receiving-end grid are identified, and the fault ride-through mode is entered after the fault is identified. In the fault ride-through mode, the state of the phase-locked loop is determined; Execute the current limiting strategy based on the phase-locked loop state; The AC voltage recovery speed is tested, and the delay fault clearance is confirmed based on the test results. After the fault is cleared, a voltage recovery strategy is executed, and after the voltage at the fault point is restored to a preset value, the reactive current command value is restored to its initial value.

2. The method according to claim 1, characterized in that, Based on real-time monitoring of the grid-side AC voltage, faults in the flexible DC-fed receiving-end power grid are identified, including: A fault is identified if the AC voltage on the grid side decreases; otherwise, no fault exists.

3. The method according to claim 1, characterized in that, Determining the state of the phase-locked loop (PLL) under the fault ride-through mode includes: The phase-locked loop (PLL) state discrimination module detects the q-axis voltage of the flexible DC output and compares it with a preset threshold. If the q-axis voltage of the flexible DC output is greater than the threshold, the controller is determined to be faulty; otherwise, the phase-locked loop is determined to be operating normally, and the current limiting strategy continues to be executed.

4. The method according to claim 1, characterized in that, The current limiting strategy is as follows: by setting the reactive current command value to 0 or a negative value, the reactive current injected into the system by the flexible DC is controlled to be 0, or the flexible DC absorbs reactive current from the system.

5. The method according to claim 1, characterized in that, The AC voltage recovery speed is tested, including: Detect the AC voltage recovery rate and compare it with a recovery rate threshold; When the AC voltage recovery rate is greater than the recovery rate threshold, it is determined that the circuit breaker near the fault point has been activated, and the AC voltage shows a step increase.

6. The method according to claim 5, characterized in that, Implement voltage recovery strategies, including: Increase the reactive current command value to accelerate AC system voltage recovery.

7. A flexible DC-fed receiving-end power grid short-circuit current optimization control device, characterized in that, include: The identification module is used to identify faults in the receiving-end power grid fed by flexible DC based on the real-time monitored grid-side AC voltage, and enters fault ride-through mode after the fault is identified. The judgment module is used to judge the state of the phase-locked loop in the fault ride-through mode and determine the state of the phase-locked loop; The execution module is used to execute a current limiting strategy based on the state of the phase-locked loop; The detection module is used to detect the AC voltage recovery speed and confirm the delayed fault clearing based on the detection results of the voltage recovery speed. The execution module is used to execute a voltage recovery strategy after the fault is cleared, and to restore the reactive current command value to its initial value after the voltage at the fault point is restored to a preset value.

8. The apparatus according to claim 7, characterized in that, The identification module identifies faults in the receiving-end power grid fed by flexible DC transmission based on real-time monitored grid-side AC voltage, including: The determination submodule is used to identify a fault when the AC voltage on the grid side drops; otherwise, no fault exists.

9. A computer-readable storage medium, characterized in that, The storage medium stores a computer program for performing the method described in any one of claims 1-6.

10. An electronic device, characterized in that, The electronic device includes: processor; Memory used to store the processor's executable instructions; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method described in any one of claims 1-6.

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