A method, system, device and medium for adaptive current differential protection of a network-constructed flexible direct current system in coordination with virtual impedance

Abstract

The application discloses a kind of network type flexible direct system virtual impedance coordination's adaptive current differential protection method, system, equipment and medium, it is related to flexible direct current transmission relay protection technical field.At present, in network type flexible direct system, the problem that sensitivity is insufficient due to the limited output current of converter station.This application includes synchronously collecting the current phasor of the protected line both ends and the effective value of converter station output current;According to the effective value of output current, the virtual resistance parameter of converter station control inner loop is adaptively adjusted;Based on virtual resistance parameter, the adaptive braking coefficient is calculated, so that the braking coefficient is inversely proportional to virtual resistance;Differential current and braking current are calculated, whether differential current is greater than the product of braking coefficient and braking current and action threshold value at the same time is judged, if meet, then determine intra-zone fault and trip.This technical scheme realizes the adaptive improvement of sensitivity at fault, reliable and no misoperation at normal time, without additional judgment link, fast response and easy to realize.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology, and in particular to an adaptive current differential protection method, system, device and medium for virtual impedance coordination in grid-type flexible DC systems. Background Technology

[0002] Traditional grid-connected flexible DC transmission systems rely on grid voltage synchronization, making them prone to instability under weak grid conditions and unable to provide voltage and frequency support to the grid. Grid-connected flexible DC transmission technology, by simulating the external characteristics of synchronous generators, enables converter stations to autonomously establish and maintain AC voltage amplitude and frequency. This significantly enhances system inertia and damping, effectively solving the operational stability problem under weak grid conditions, and has become the mainstream direction for the development of flexible DC technology.

[0003] However, the fault characteristics of grid-type flexible DC systems differ fundamentally from those of traditional synchronous machine-dominated AC power grids. Grid-type converter stations are constrained by the rated current limitations of power electronic devices and control strategies, resulting in short-circuit currents exhibiting characteristics such as limited amplitude, controlled phase angle, and waveform distortion during faults. This poses a serious challenge to the adaptability of traditional relay protection principles designed based on synchronous machine power supply characteristics.

[0004] Differential current protection is widely used in AC line protection of flexible DC systems due to its advantages such as simple principle, reliable operation, and insensitivity to system oscillations. However, in network-type flexible DC systems, traditional differential current protection has the following problems: The protection sensitivity is severely insufficient: Traditional current differential protection uses a fixed braking coefficient, and its setting is based on the characteristics of the large short-circuit current during synchronous machine faults. During faults in grid-type converter stations, the output current amplitude is usually limited to 1.2-1.5 times the rated current, resulting in a small differential current and a relatively large braking current. Under the fixed braking coefficient, the protection criteria are difficult to meet, and failure to operate is very likely to occur.

[0005] There is an inherent conflict between control and protection objectives: to protect power electronic devices, grid-type converter stations generally adopt a virtual impedance control strategy, which limits the peak short-circuit current by increasing the virtual resistance during a fault. However, increasing the virtual resistance further reduces the fault current amplitude, exacerbating the sensitivity problem of traditional current differential protection and creating a vicious cycle of "control current limiting → protection failure to operate".

[0006] To address the above problems, existing technologies have proposed several improvement schemes, but all of them have obvious drawbacks: The negative sequence current retention method increases the fault current amplitude by reducing the negative sequence current suppression intensity, thereby improving protection sensitivity. However, this method can lead to second-harmonic power fluctuations on the AC side, increasing the current stress on power devices and severely affecting power quality, which is detrimental to stable system operation.

[0007] Adding sequence component criteria: Based on the traditional differential protection criteria, additional positive sequence, negative sequence, or zero sequence component criteria are added for auxiliary judgment. However, this method significantly increases the complexity of the protection logic, raises the difficulty of setting calculations, and the sequence component characteristics vary greatly under different operating conditions, resulting in poor engineering practicality.

[0008] Independent adaptive braking method: This method dynamically adjusts the braking coefficient by identifying fault characteristics independently on the protection side. However, this method requires additional fault detection and judgment steps, suffers from response lag, and the fault characteristic identification is easily affected by factors such as system operating mode and transition resistance, resulting in insufficient robustness.

[0009] More importantly, all existing improvement schemes are optimized independently on the protection side without considering coordination with the grid-type converter station control system, thus failing to fundamentally resolve the conflict between control and protection objectives.

[0010] Therefore, there is an urgent need to study a collaborative protection method that can fully utilize the adaptive adjustment characteristics of virtual impedance in the control system of grid-type converter stations, and dynamically improve the sensitivity of current differential protection without weakening the overcurrent suppression capability. Summary of the Invention

[0011] The technical problem to be solved and the technical task proposed by this invention is to improve and refine existing technical solutions, and to provide an adaptive current differential protection method, system, device, and medium for virtual impedance coordination in a network-type flexible DC system. The aim is to effectively improve the sensitivity of current differential protection by dynamically correlating the virtual resistance parameters of the control system with the braking coefficient of the protection criterion. To this end, this invention adopts the following technical solution.

[0012] In a first aspect, the present invention provides an adaptive current differential protection method for a network-type flexible DC system with virtual impedance coordination, comprising the following steps: S1: Synchronously acquire the current phasor at the protection installation points at both ends of the protected line. and and the effective value of the output current of the grid-type flexible DC converter station ; S2: Based on the effective value of the converter station output current Adaptive adjustment of virtual resistance parameters in the virtual impedance control loop of the grid-type flexible DC converter station control system. ; S3: Based on the virtual resistance parameters Calculate the adaptive braking coefficient of current differential protection The adaptive braking coefficient With the virtual resistance parameter Inversely proportional; S4: Based on the collected current phasors , The magnitude of the sum of the phasors of the two is calculated as the differential current. The magnitude of the phasor difference between the two is calculated as the braking current. Combined with the aforementioned adaptive braking coefficient Determine whether the following protection criteria are met simultaneously: Criterion 1: Differential current Greater than the adaptive braking coefficient With braking current The product; Criterion 2: Differential Current The current differential protection operating threshold value is greater than the preset value. ; S5: If both criteria are met, the protected line is determined to have an internal fault, and a trip command is sent to the circuit breakers at both ends of the protected line to disconnect the faulty line; if either criterion is not met, the protected line is determined to be in normal operation, and no trip command is sent.

[0013] This technical solution uses step S3 to adjust the adaptive braking coefficient. With virtual resistance parameters Establish an inverse relationship; when a fault occurs, the virtual resistance parameter... Adaptively increases due to overcurrent. This decreases accordingly, dynamically reducing the braking amount and making it easier for the differential current to meet criterion one, significantly improving the protection sensitivity during faults within the zone. It directly utilizes the existing virtual resistance parameters in the control inner loop of the grid-type converter station. Its adaptive adjustment behavior eliminates the need for additional fault detection or feature extraction steps on the protection side. Follow The changes are synchronized and real-time, and the response speed completely follows the physical response of the control system. It automatically increases sensitivity without needing to determine "whether a fault has occurred," avoiding the response lag problem caused by fault detection in existing adaptive solutions. Because... and Inversely proportional, and Follow The more severe the fault, the greater the overcurrent. The larger (, therefore) The braking term of the protection criterion will further decrease as the severity of the fault increases. The differential current becomes smaller during severe faults, making it easier to exceed the braking phase, thus achieving automatic matching between protection sensitivity and fault severity—the protection operates faster and more reliably during severe faults, while still maintaining selectivity during minor faults. Under normal system operation or without fault disturbances, the converter station output current... Smaller, virtual resistance parameter Maintaining a small baseline value, therefore the adaptive braking coefficient Relatively large (still maintaining an inverse relationship); larger This means the braking term of the protective criterion. It is more robust and has stricter criteria, effectively resisting differential unbalance currents caused by non-fault factors such as current transformer transmission errors, line distributed capacitance current, external fault through current, and system oscillations, significantly reducing the probability of protection maloperation. This solution only requires reading the existing virtual resistance parameters in the control system on the protection side. (This parameter itself is set by the grid-type converter station to suppress overcurrent), and a simple inverse proportional calculation step is added to the protection algorithm. No additional hardware equipment is required, and no complex auxiliary criteria (such as sequence component, power factor angle, etc.) are introduced, making it highly feasible to implement. Compared with the problems of the existing technology of "retaining negative sequence current method" leading to double frequency power fluctuation, increased current stress on power devices, and impact on power quality, and the problems of "adding sequence component criterion method" leading to complex protection logic and difficult setting, this solution improves sensitivity by optimizing the protection criterion itself. It does not rely on negative sequence current or sequence component characteristics at all, thus avoiding the above-mentioned negative effects, while maintaining the inherent advantages of simple current differential protection principle and high reliability.

[0014] As a preferred technical means: in step S2, the virtual resistance parameter The adaptive adjustment rule is: virtual resistance parameter Equal to virtual resistance adjustment coefficient Multiply by the effective value of the converter station output current With current threshold The difference, plus the virtual resistance reference value during normal system operation. .

[0015] When the converter station output current does not exceed the threshold At this time, the virtual resistance parameter remains at a small reference value. It does not affect the voltage quality and power transmission during normal system operation; when the output current exceeds the threshold Subsequently, the virtual resistance parameter increases linearly with the degree of overcurrent, achieving precise suppression of short-circuit current peaks and protecting power devices. Threshold The setting (usually adjusted to be slightly higher than the rated current) avoids false triggering of virtual resistance parameters due to normal load fluctuations; adjustment coefficient It offers flexible design freedom to adapt to the current limiting requirements of systems with different capacities; the linear and continuous variation avoids transient impacts caused by impedance changes, and the setting is simple and highly practical for engineering applications.

[0016] As a preferred technical means: in step S3, the adaptive braking coefficient Equal to the preset fixed braking coefficient Divide by the virtual resistance parameter .

[0017] This technical solution presents a mathematical mapping relationship, i.e., a reciprocal relationship, between the adaptive braking coefficient and the virtual resistance parameter. The mapping relationship is concise, requires minimal computation, and eliminates the need for complex function fitting or table lookup operations. When the virtual resistance parameter increases due to overcurrent, the braking coefficient automatically decreases, and the magnitude of the decrease is inversely proportional to the increase in the virtual resistance parameter, achieving continuous and precise adaptive sensitivity of protection to fault severity.

[0018] As a preferred technical means, the virtual impedance control link of the control inner loop of the grid-type flexible DC converter station also includes virtual inductance parameters. The virtual inductance parameters With the virtual resistance parameter They are inversely proportional, and their product is the preset virtual inductance adjustment coefficient. The virtual inductance adjustment coefficient Pre-tuning based on system stability requirements.

[0019] This technical solution introduces a virtual inductance parameter on top of the virtual resistance parameter. The virtual inductance parameter is inversely proportional to the virtual resistance parameter, so that during fault overcurrent, the virtual resistance parameter increases while the virtual inductance parameter decreases accordingly. This helps maintain the stability of the virtual impedance angle and prevents system oscillation. The addition of the virtual inductance parameter can adjust the equivalent output impedance characteristics of the converter station, improving the system's transient stability and fault ride-through performance. This can be achieved by presetting the virtual inductance adjustment coefficient. It can be flexibly tuned according to the system's requirements for stability indicators such as damping and oscillation suppression, which enhances the adaptability of the control strategy to different operating conditions without adding extra computational burden.

[0020] As a preferred technical means, the control rule of the virtual impedance control loop is as follows: Voltage loop voltage command Axial components Equal to the control of the outer loop Shaft internal potential command Subtract virtual resistance parameters Multiplied by the converter station output current Axial components In addition to the synchronous reference angular frequency Multiply by virtual inductance parameter Multiply by the converter station output current Axial components ; Voltage loop voltage command Axial components Equal to the control of the outer loop Shaft internal potential command Subtract virtual resistance parameters Multiplied by the converter station output current Axial components Subtract the synchronous reference angular frequency. Multiply by virtual inductance parameter Multiply by the converter station output current Axial components .

[0021] This technical solution incorporates virtual resistance and virtual inductance parameters into the calculation of voltage commands, enabling grid-type converter stations to simulate output impedance with physical resistance and inductance characteristics. Among these, the virtual resistance term ( · , · ) provides damping and current limiting, virtual inductance term ( , The system provides voltage compensation related to the rate of change of current, and the combined effect of these two factors makes the fault-out characteristics of the converter station closer to those of a traditional synchronous generator. The control rule adopts a dq-axis decoupling form, which is easy to implement in a digital control system. At the same time, since the virtual resistance and virtual inductance parameters can be adaptively adjusted according to the aforementioned scheme, the control rule can dynamically change the equivalent impedance of the converter station, achieving smooth current limiting and stability support during faults.

[0022] Secondly, the present invention provides an adaptive current differential protection system for a network-type flexible DC system with virtual impedance coordination, comprising: The current acquisition module is used to synchronously acquire the current phasors at both ends of the protected line where the protection is installed. and and the effective value of the output current of the grid-type flexible DC converter station ; The virtual resistance adjustment module is used to adjust the output current of the converter station according to the effective value. Adaptive adjustment of virtual resistance parameters in the virtual impedance control loop of the grid-type flexible DC converter station control system. ; An adaptive braking coefficient calculation module is used to calculate the braking coefficient based on the virtual resistance parameters. Calculate the adaptive braking coefficient of current differential protection The adaptive braking coefficient With the virtual resistance parameter Inversely proportional; The protection criterion judgment module is used to determine the protection criteria based on the acquired current phasor. , Calculate the phasors and amplitudes of the two as the differential current. The magnitude of the phasor difference between the two is calculated as the braking current. And in combination with the adaptive braking coefficient Determine whether the following protection criteria are met simultaneously: Criterion 1: Differential current Greater than the adaptive braking coefficient With braking current The product; Criterion 2: Differential Current The current differential protection operating threshold value is greater than the preset value. ; The action execution module is used to determine that an internal fault has occurred in the protected line when the protection criterion judgment module determines that two criteria are met simultaneously, and to issue a trip command to the circuit breakers at both ends of the protected line to disconnect the faulty line; when either criterion is not met, the protected line is determined to be in normal operation and no trip command is issued.

[0023] The current acquisition module in this technical solution achieves high-precision synchronous sampling, providing a reliable data foundation for protection; the virtual resistance adjustment module directly interacts with the converter station's control inner loop, acquiring or setting virtual resistance parameters in real time, enabling information sharing between control and protection systems; the adaptive braking coefficient calculation module requires only simple reciprocal calculations, with negligible calculation delay; the protection criterion judgment module employs dual-criterion logic to ensure selectivity; and the action execution module quickly outputs trip commands. The entire system features a modular design with clear functional divisions, facilitating software upgrades on existing control and protection platforms without increasing hardware costs.

[0024] As a preferred technical means: in the virtual resistance adjustment module, the virtual resistance parameter The adaptive adjustment rule is: virtual resistance parameter Equal to virtual resistance adjustment coefficient Multiply by the effective value of the converter station output current With current threshold The difference, plus the virtual resistance reference value during normal system operation. .

[0025] As a preferred technical means: in the adaptive braking coefficient calculation module, the adaptive braking coefficient Equal to the preset fixed braking coefficient Divide by the virtual resistance parameter .

[0026] Thirdly, the present invention provides a computer device comprising one or more processors and one or more memories, wherein at least one piece of program code is stored in the one or more memories, and when the program code is executed by the one or more processors, it implements the aforementioned adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system.

[0027] Fourthly, a computer-readable storage medium is provided, wherein at least one piece of program code is stored in the storage medium, and when the program code is executed by a processor, it implements the aforementioned adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system.

[0028] Beneficial effects: 1. This invention achieves coordinated optimization of control and protection in grid-type flexible DC converter stations. This invention creatively incorporates virtual resistance parameters in grid-type control. Adaptive braking coefficient of current differential protection Dynamic correlation. By utilizing the characteristic that virtual impedance automatically increases during a fault to suppress overcurrent, the protection braking coefficient is reduced synchronously and adaptively. This effectively improves the sensitivity of differential protection without significantly affecting the overcurrent suppression effect of the control system, thus resolving the contradiction between control objectives and protection requirements.

[0029] 2. This invention features adaptive protection sensitivity that matches the severity of the fault. The current differential protection sensitivity is not fixed, but rather determined by virtual resistance parameters. With fault current This correlation enables adaptive response to fault severity. The more severe the fault, the greater the overcurrent. The larger the value, the greater the braking coefficient. The smaller the value, the more sensitive the protection mechanism, ensuring rapid and reliable removal of serious faults.

[0030] 3. This invention enhances the reliability of current differential protection during normal operation. During normal system operation, due to... Not exceeding the threshold Maintaining it at a small value makes the adaptive braking coefficient Greater than the traditional fixed braking coefficient This is equivalent to automatically increasing the braking force under non-fault conditions, enhancing the protection's ability to resist interference from factors such as current transmission errors and system oscillations, and effectively reducing the risk of malfunction.

[0031] 4. This invention eliminates the need for a judgment step, resulting in a fast response. When a fault occurs, the sensitivity of the current differential protection is improved based on the natural response of the increased output current, without needing to determine whether a fault has occurred and thus change the braking coefficient, resulting in a faster response speed.

[0032] 5. This invention requires no additional hardware, has clear logic, and is easy to implement in engineering. This invention does not add any hardware devices; it only requires adding an interface for reading virtual resistance parameters in the control system software and modifying the braking coefficient calculation logic in the protection algorithm. The logic is clear and simple, does not add additional sequence component criteria, avoids complex tuning and coordination issues, has low engineering modification costs, and high feasibility of implementation.

[0033] 6. This invention avoids the negative impacts of retaining negative sequence current. By optimizing the protection criterion itself, this invention improves sensitivity, eliminating the need to intentionally retain negative sequence fault current as in existing methods. This avoids problems such as double-frequency power fluctuations, increased current stress on power devices, and decreased power quality caused by negative sequence current. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the current differential protection configuration of the grid-type flexible DC system of the present invention.

[0035] Figure 2 This is the overall control block diagram of the mesh-type flexible straight line system of the present invention.

[0036] Figure 3 This is a block diagram of the virtual impedance control circuit of the present invention.

[0037] Figure 4 This is a flowchart of the virtual impedance cooperative adaptive current differential protection system of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings.

[0039] Example 1: See Figure 1 This embodiment mainly consists of a large power grid, a receiving-end converter station, a sending-end converter station, the protected line, and a renewable energy power station. The object of the current differential protection is the AC line connecting the sending-end converter station and the renewable energy power station. This invention optimizes the current differential protection of the protected line during fault occurrence and normal operation. The specific method is as follows: S1: Synchronously acquire the current phasors at both ends of the line and the effective value of the converter station output current. like Figure 1 As shown, the protection device uses a high-precision current transformer to collect the current phasors at both ends of the protected line in real time and synchronously, which are denoted as follows: (Sending-end converter station side) and (On the side of new energy power plants), and the effective value of the output current of grid-type flexible DC converter stations. .

[0040] S2: Adaptively adjust virtual resistance parameters based on converter station output current. like Figure 2 and Figure 3 As shown, the protection device is based on the effective value of the converter station output current. Adaptive adjustment of virtual resistance parameters in the virtual impedance control loop of the grid-type flexible DC converter station control system. R v The rules have been adjusted as follows:

[0041] in, This is the effective value of the output current measured in real time at the converter station; This is a preset current threshold. This is the virtual resistance adjustment coefficient; This is the virtual resistance reference value when the system is running normally.

[0042] In a preferred embodiment, the above-mentioned virtual impedance control stage is... The specific implementation rules under the synchronous rotating coordinate system are as follows:

[0043] in, , For voltage loop voltage command Axial components; , Commands to control the dq-axis internal potential generated by the outer ring; For virtual resistance; For virtual inductance; , For the output current of the converter station Axial components; The synchronization reference angular frequency is 100π rad / s (corresponding to a 50Hz system). This rule allows the converter station to simulate the physical resistance and inductance characteristics, achieving fault current limiting and stability support.

[0044] S3: Calculation of Adaptive Braking Coefficient Based on Virtual Resistance Parameters The protection device uses the real-time virtual resistance parameters obtained in step S2. and preset fixed braking coefficient k c According to the formula Calculate the current adaptive braking coefficient Based on the adjustment rules in step S2, This can be further expressed as:

[0045] S4. Calculate the differential current and braking current and make judgments based on the criteria. The protection device is based on the current phasor acquired in step S1. and Calculate the differential current With braking current | Combined with adaptive braking coefficient Determine whether the following protection criteria are met simultaneously:

[0046] in, This is the threshold value for differential protection operation. The protection device determines whether the above two inequalities are satisfied simultaneously.

[0047] S5: Perform protective action 1. Fault within the zone is determined: If the result of step S4 is "yes", the protection device determines that a fault has occurred inside the protected line, immediately issues a trip command, drives the circuit breakers at both ends of the line to operate, and quickly disconnects the faulty line.

[0048] 2. Determined to be in normal condition: If the determination result of step S4 is "no", the protection device determines that the system is operating normally, does not issue a trip command, and the protection is reliable and does not operate.

[0049] The adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system of this invention can be analyzed from the following two aspects: 1. Fault scenario adaptation When a fault occurs inside the protected line, the converter station outputs current. I s Rapidly increases and exceeds the threshold The control system automatically increases the current to suppress overcurrent. According to the formula , The increase will lead to Decrease. Braking coefficient The reduction means braking item The decrease causes the differential current to... It is easier for the value to exceed the braking term, thus significantly improving protection sensitivity. The more severe the fault, the more likely it is to exceed the braking term. The larger, The larger, The smaller the value, the more significant the improvement in sensitivity, achieving automatic matching between protection sensitivity and fault severity.

[0050] 2. High reliability in normal operating scenarios When the system is operating normally, the current flowing through the protected line Usually not exceeding ,at this time , is a relatively small value. Therefore, It will be greater than the traditional fixed braking coefficient. This means that the braking factor is amplified and the protection criteria are more stringent, thereby effectively reducing the probability of maloperation caused by non-fault factors such as current transformer transmission error, line distributed capacitance current or external fault through current, and system oscillation, and improving reliability.

[0051] In summary, this invention, through parameter linkage between the control and protection systems, transforms the overcurrent suppression behavior of the control system into the sensitivity enhancement behavior of the protection system, achieving positive synergy between control and protection under fault conditions. Simultaneously, under non-fault conditions, it automatically switches to a safety mode that increases braking force and prevents malfunctions. The entire method has a clear physical concept, requires no complex criteria or additional hardware, and is easily integrated into existing network-type flexible DC control and protection systems.

[0052] Example 2 This embodiment provides the protection system corresponding to the virtual impedance cooperative adaptive current differential protection method, such as... Figure 4 As shown. The system adopts the method of Embodiment 1, specifically including: Current acquisition module: Used for high-precision synchronous acquisition of current phasors at both ends of the protected line. and and the effective value of the output current of the grid-type flexible DC converter station To provide real-time data for protecting computing; Virtual resistance adjustment module: used to adjust the resistance based on the effective value of the converter station output current. Adaptive adjustment of virtual resistance parameters in the virtual impedance control loop of the grid-type flexible DC converter station control system. ; Adaptive braking coefficient calculation module: used to calculate the braking coefficient based on virtual resistance parameters. With preset fixed braking coefficient According to the formula Calculate the real-time adaptive braking coefficient. ; Protection criterion judgment module: used for judging based on the acquired current , and the calculated coefficients k a Perform differential current and braking current calculations and apply criteria. and Perform logical judgments; Action execution module: When the protection criterion judgment module determines that two criteria are met simultaneously, it determines that an internal fault has occurred in the protected line and issues a trip command to the circuit breakers at both ends of the protected line to disconnect the faulty line; otherwise, it determines that the line is in normal operation and does not issue a trip command.

[0053] The system achieves intelligent adaptive protection for grid-type flexible DC AC lines through the coordinated operation of its various modules. This is achieved by adjusting the virtual resistance parameters, which reflect the system's overcurrent status, in real time. And dynamically adjust the braking coefficient of the protection criterion. The system significantly improves protection sensitivity during faults within the affected area, ensuring rapid and reliable operation. During normal operation, it automatically enhances braking characteristics, effectively preventing false tripping. This system requires no additional hardware; it achieves adaptive coordination between control and protection solely through software logic upgrades. Without altering the original control strategy or affecting the system's normal operating performance, it fundamentally solves the problem of insufficient current differential protection sensitivity caused by grid-type power supplies, significantly improving the reliability of AC line protection in flexible DC systems under complex operating conditions.

[0054] Example 3 This embodiment provides an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the virtual impedance cooperative adaptive current differential protection method for a network-type flexible DC system as described in any embodiment of the present invention.

[0055] This electronic device can be an industrial control computer, an embedded protection device, a server, or other device with computing capabilities. By loading and executing the corresponding program code in the device, it can automatically complete the synchronous data acquisition of the protected line, the adaptive adjustment of virtual resistance parameters, the calculation of the braking coefficient, the judgment of criteria, and the output of trip commands, giving full play to the flexibility of software definition while ensuring protection performance.

[0056] Example 4 This embodiment provides a computer-readable storage medium storing a computer program thereon. When the computer program is executed by a processor, it implements the adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system as described in any embodiment of the present invention.

[0057] Those skilled in the art will recognize that the units and algorithm steps described in the embodiments disclosed in this invention can be implemented using electronic hardware, computer software, or a combination of electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0058] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0059] In the several embodiments provided in this application, any function, if implemented as a software functional unit and sold or used as an independent product, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory, random access memory, magnetic disks, or optical disks.

[0060] The above are specific embodiments of the present invention, which demonstrate the substantial features and progress of the present invention. Equivalent modifications can be made to them according to actual usage needs, under the guidance of the present invention, and all such modifications are within the scope of protection of this solution.

Claims

1. An adaptive current differential protection method for a network-type flexible DC system with virtual impedance coordination, characterized in that, Includes the following steps: S1: Synchronously acquire the current phasor at both ends of the protected line at the protection installation points. and and the effective value of the output current of the grid-type flexible DC converter station ; S2: Based on the effective value of the converter station output current Adaptive adjustment of virtual resistance parameters in the virtual impedance control loop of the grid-type flexible DC converter station control system. The virtual resistance parameters The adaptive adjustment rule is: virtual resistance parameter Equal to virtual resistance adjustment coefficient Multiply by the effective value of the converter station output current With current threshold The difference, plus the virtual resistance reference value during normal system operation. ; S3: Based on the virtual resistance parameters Calculate the adaptive braking coefficient of current differential protection The adaptive braking coefficient With the virtual resistance parameter Inversely proportional; S4: Based on the collected current phasors , The magnitude of the sum of the phasors of the two is calculated as the differential current. The magnitude of the phasor difference between the two is calculated as the braking current. Combined with the aforementioned adaptive braking coefficient Determine whether the following protection criteria are met simultaneously: Criterion 1: Differential current Greater than the adaptive braking coefficient With braking current The product; Criterion 2: Differential Current The current differential protection operating threshold value is greater than the preset value. ; S5: If both criteria are met, the protected line is determined to have an internal fault, and a trip command is sent to the circuit breakers at both ends of the protected line to disconnect the faulty line; if either criterion is not met, the protected line is determined to be in normal operation, and no trip command is sent.

2. The adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system according to claim 1, characterized in that: In step S3, the adaptive braking coefficient Equal to the preset fixed braking coefficient Divide by the virtual resistance parameter .

3. The adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system according to claim 1, characterized in that: The virtual impedance control loop of the inner control loop of the grid-type flexible DC converter station also includes virtual inductance parameters. The virtual inductance parameters With the virtual resistance parameter They are inversely proportional, and their product is the preset virtual inductance adjustment coefficient. The virtual inductance adjustment coefficient Pre-tuning based on system stability requirements.

4. The adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system according to claim 3, characterized in that: The control rules for the virtual impedance control circuit are as follows: Voltage loop voltage command Axial components Equals the command for the d-axis internal potential generated by the control outer loop. Subtract virtual resistance parameters Multiplied by the converter station output current Axial components In addition to the synchronous reference angular frequency Multiply by virtual inductance parameter Multiply by the converter station output current Axial components ; Voltage loop voltage command Axial components Equal to the control of the outer loop Shaft internal potential command Subtract virtual resistance parameters Multiplied by the converter station output current Axial components Subtract the synchronous reference angular frequency. Multiply by virtual inductance parameter Multiply by the converter station output current Axial components .

5. An adaptive current differential protection system for a network-type flexible DC system with virtual impedance coordination, characterized in that, include: The current acquisition module is used to synchronously acquire the current phasors at both ends of the protected AC line. and and the effective value of the output current of the grid-type flexible DC converter station ; The virtual resistance adjustment module is used to adjust the output current of the converter station according to the effective value. Adaptive adjustment of virtual resistance parameters in the virtual impedance control loop of the grid-type flexible DC converter station control system. The virtual resistance parameters The adaptive adjustment rule is: virtual resistance parameter Equal to virtual resistance adjustment coefficient Multiply by the effective value of the converter station output current With current threshold The difference, plus the virtual resistance reference value during normal system operation. ; An adaptive braking coefficient calculation module is used to calculate the braking coefficient based on the virtual resistance parameters. Calculate the adaptive braking coefficient of current differential protection The adaptive braking coefficient With the virtual resistance parameter Inversely proportional; The protection criterion judgment module is used to determine the protection criteria based on the acquired current phasor. , Calculate the phasors and amplitudes of the two as the differential current. The magnitude of the phasor difference between the two is calculated as the braking current. And in combination with the adaptive braking coefficient Determine whether the following protection criteria are met simultaneously: Criterion 1: Differential current Greater than the adaptive braking coefficient With braking current The product; Criterion 2: Differential Current The current differential protection operating threshold value is greater than the preset value. ; The action execution module is used to determine that an internal fault has occurred in the protected line when the protection criterion judgment module determines that two criteria are met simultaneously, and to issue a trip command to the circuit breakers at both ends of the protected line to disconnect the faulty line; when either criterion is not met, the protected line is determined to be in normal operation and no trip command is issued.

6. The adaptive current differential protection system for a network-type flexible DC system with virtual impedance coordination according to claim 5, characterized in that: In the adaptive braking coefficient calculation module, the adaptive braking coefficient Equal to the preset fixed braking coefficient Divide by the virtual resistance parameter .

7. A computer device, characterized in that, It includes one or more processors and one or more memories, wherein the one or more memories store at least one piece of program code, and when the program code is executed by the one or more processors, it implements the adaptive current differential protection method for virtual impedance coordination of a network-type flexible DC system as described in any one of claims 1-4.

8. A computer-readable storage medium, characterized in that, The storage medium stores at least one line of program code, which, when executed by a processor, implements the adaptive current differential protection method for virtual impedance coordination in a network-type flexible DC system as described in any one of claims 1-4.

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