Negative sequence direction element protection method and system based on negative sequence impedance reconstruction

Abstract

The invention discloses a negative sequence impedance reconstruction-based negative sequence direction element protection method and system. The method comprises the following steps of: reconstructing the negative sequence impedance of a current converter through a negative sequence impedance reconstruction control strategy; performing feedback adjustment on the reconstructed negative sequence impedance angle of the converter; the fault direction is determined according to the phase relation between the fault negative-sequence voltage and the negative-sequence current at the protection installation position after the fault; and detecting a deviation value between a negative sequence impedance angle of the converter and a system impedance angle, and adding a correction value to a final setting result of a negative sequence direction element. The negative sequence direction element protection method based on the negative sequence impedance reconstruction control strategy overcomes the problem that negative sequence direction elements are not adaptive due to the fact that the negative sequence impedance of the converter is controlled, and has certain adaptability to fault types, transition resistance and noise.

Description

Technical Field

[0001] The present invention belongs to the field of control and protection of MMC transmission lines connected to new energy sources, and in particular to a negative-sequence directional element protection method and system based on negative-sequence impedance reconstruction. Background Art

[0002] Driven by energy transformation and the increasing maturity of power electronics technology, large-scale access to new energy sources to the power system is an inevitable trend. Its fault characteristics are different from those of conventional power grids, which makes power frequency quantity protection have adaptation problems. Traditional protection is affected by the access of power electronic devices at both ends of the line, and there is a risk of refusal to operate or false operation.

[0003] In AC line protection, traditional sequence component directional protection elements use the phase relationship between the positive, negative, and zero-sequence fault components of voltage and current to determine the direction of the fault. Since the phase angles of the line impedance and the synchronous machine system impedance in conventional systems are mostly between 75° and 90°, when a fault occurs in the positive direction where the protection element is installed, the phases of the positive, negative, and zero-sequence voltage and current fault components satisfy the following relationship:

[0004]

[0005] Where: U and I represent the phase voltage and phase current phasors of the converter AC side respectively; the superscript + / - / 0 represents the positive sequence, negative sequence or zero sequence component; the subscript m represents the electrical quantity at the measuring point; the prefix Δ represents the fault component.

[0006] However, when the traditional sequence component directional protection element is used in the converter AC connection line, the obvious difference between the converter current control characteristics and the conventional synchronous machine has an adverse effect on the effectiveness of the protection element. When the goal is to suppress power fluctuations, the phase of the current fault component is determined by the power command, that is, the converter equivalent negative sequence impedance is affected by the converter control target. Therefore, the directional element measurement result is affected by the power command during the fault. In some cases, it may approach or cross the fault direction determination boundary, resulting in component malfunction or refusal to operate. If factors such as transition resistance and converter current limiting are introduced, the above effects will be more complicated. In addition, when the goal is to suppress negative sequence current, the negative sequence directional element cannot obtain an effective sequence component and the element fails. Summary of the invention

[0007] The object of the present invention is to provide a negative-sequence directional element protection method and system based on negative-sequence impedance reconstruction to solve the above-mentioned problem.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a negative-sequence directional element protection method based on negative-sequence impedance reconstruction, comprising:

[0010] After a fault occurs in the renewable energy transmission line, the negative sequence impedance of the converter is reconstructed through the negative sequence impedance reconstruction control strategy;

[0011] Feedback adjustment is performed on the negative sequence impedance angle of the reconstructed converter;

[0012] Determine the fault direction based on the phase relationship between the fault negative sequence voltage and the negative sequence current at the protection installation location after the fault;

[0013] Detect the deviation between the negative-sequence impedance angle of the converter and the system impedance angle, and add a correction value to the final setting result of the negative-sequence directional element.

[0014] Furthermore, after a fault occurs in the renewable energy transmission line, the negative sequence impedance of the converter is reconstructed through a negative sequence impedance reconstruction control strategy, including:

[0015] When a fault occurs in the renewable energy transmission line, the negative sequence current suppression control strategy is adopted, and the inversion direction is the positive direction of the current. The dynamic equation of the converter in the negative sequence rotating coordinate system is:

[0016]

[0017] Where: Indicates the negative sequence voltage of the converter output; L f and R f are the equivalent reactance and equivalent resistance of the filter circuit respectively; ω is the angular frequency;

[0018] A virtual negative-sequence impedance is introduced to modify the negative-sequence current reference value so that the angle difference between it and the negative-sequence voltage is the system angle;

[0019] Then write the dynamic equation and take the steady state as follows:

[0020]

[0021] Where: L v and R v are virtual inductance and resistance respectively, I - is the negative sequence current, U - is the negative sequence voltage at the grid connection point, E - is the virtual negative sequence internal potential;

[0022] Take the virtual negative sequence internal potential The negative sequence current reference value is calculated from the actual measurement of the system negative sequence:

[0023]

[0024] Where: R = R v +R f ; X = ω(L v +L f);According to the set total negative sequence impedance, the negative sequence current reference value is obtained.

[0025] Furthermore, the selection of virtual negative sequence impedance parameters is:

[0026] The virtual negative sequence impedance parameters are divided into phase angle and amplitude, and the constraints that need to be met are:

[0027]

[0028] Where: Z - is the negative sequence impedance; is the system phase angle; is the maximum allowable negative sequence current of the converter;

[0029] Calculate the impedance magnitude using the current constraint:

[0030]

[0031] During a fault, the negative sequence current output by the converter is always maintained at the negative sequence current demand value of the protection element.

[0032] Furthermore, the feedback adjustment of the reconstructed negative sequence impedance angle of the converter includes:

[0033] In the early stage of a fault, virtual impedance angle adjustment is added. According to the difference between the actual converter negative sequence impedance value and the system negative sequence impedance value, a correction value is fed back to adjust the negative sequence impedance angle reference value, including:

[0034] Set up additional control strategies as shown below:

[0035]

[0036] Where: U - (t) and I - (t) is the negative sequence voltage and current value at PCC point, e(t) is the deviation value between the negative sequence impedance angle and the system angle; K p With K i is the PI regulator coefficient.

[0037] Further, the method of determining the fault direction according to the phase relationship between the negative sequence voltage and the negative sequence current at the protection installation location after the fault comprises:

[0038] When there is a positive fault at the protection installation after the fault, the negative sequence impedance calculated by the protection according to the fault negative sequence voltage and negative sequence current is the same as the system negative sequence impedance, that is, -Δu n / Δi n =Z n, ignoring the resistance, the impedance angle is 90°; in the case of reverse fault, the calculated negative sequence impedance is the inverse of the sum of the system and line negative sequence impedances, i.e. -Δu n / Δi n =-Z m -Z L , the impedance angle is -90°; the judgment criteria for forward and reverse faults are

[0039]

[0040] Where: To protect the negative sequence voltage at the installation location; To protect the negative sequence current at the installation location;.

[0041] Furthermore, the detecting of the deviation between the negative sequence impedance angle of the converter and the system impedance angle and adding a correction value to the final setting result of the negative sequence directional element include:

[0042]

[0043] Where: α is the corrected setting result.

[0044] In a second aspect, the present invention provides a negative-sequence directional element protection system based on negative-sequence impedance reconstruction, comprising:

[0045] The converter negative sequence impedance reconstruction module is used to reconstruct the converter negative sequence impedance through the negative sequence impedance reconstruction control strategy after a fault occurs in the new energy transmission line;

[0046] A feedback regulation module, used for performing feedback regulation on the reconstructed negative sequence impedance angle of the converter;

[0047] A fault direction determination module, used to determine the fault direction according to the phase relationship between the fault negative sequence voltage and the negative sequence current at the protection installation location after the fault;

[0048] The correction output module is used to detect the deviation between the negative sequence impedance angle of the converter and the system impedance angle, and add a correction value to the final setting result of the negative sequence directional element.

[0049] Furthermore, after a fault occurs in the renewable energy transmission line, the negative sequence impedance of the converter is reconstructed through a negative sequence impedance reconstruction control strategy, including:

[0050] When a fault occurs in the renewable energy transmission line, the negative sequence current suppression control strategy is adopted, and the inversion direction is the positive direction of the current. The dynamic equation of the converter in the negative sequence rotating coordinate system is:

[0051]

[0052] Where: Indicates the negative sequence voltage of the converter output; Lf and R f are the equivalent reactance and equivalent resistance of the filter circuit respectively; ω is the angular frequency;

[0053] A virtual negative-sequence impedance is introduced to modify the negative-sequence current reference value so that the angle difference between it and the negative-sequence voltage is the system angle;

[0054] Then write the dynamic equation and take the steady state as follows:

[0055]

[0056] Where: L v and R v are virtual inductance and resistance respectively, I - is the negative sequence current, U - is the negative sequence voltage at the grid connection point, E - is the virtual negative sequence internal potential;

[0057] Take the virtual negative sequence internal potential The negative sequence current reference value is calculated from the actual measurement of the system negative sequence:

[0058]

[0059] Where: R = R v +R f ; X = ω(L v +L f );According to the set total negative sequence impedance, the negative sequence current reference value is obtained.

[0060] In a third aspect, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the negative-sequence directional element protection method based on negative-sequence impedance reconstruction when executing the computer program.

[0061] In a fourth aspect, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of a negative-sequence directional element protection method based on negative-sequence impedance reconstruction.

[0062] Compared with the prior art, the present invention has the following technical effects:

[0063] The negative-sequence directional element protection method based on the negative-sequence impedance reconstruction control strategy proposed in the present invention overcomes the negative-sequence directional element inadaptability problem caused by the controlled negative-sequence impedance of the converter, and has a certain adaptability to fault types, transition resistance and noise.

[0064] The additional control strategy proposed in this paper is aimed at the sequence component directional elements of the AC line. It takes the converter of the flexible DC line that collects and transmits new energy as the object. In view of the problems that the negative-sequence equivalent impedance of the converter is affected by the converter control target and the negative-sequence control scheme, the impedance characteristics of the VSC under the fault component network are reconstructed. The additional control strategy can effectively control the impedance phase angle in the converter fault component network, make the converter negative-sequence impedance approach the characteristics of the synchronous machine, and realize the support of the fault identification ability of the sequence component directional elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a flow chart of the present invention.

[0066] Figure 2 This is a structural topology of a large-scale photovoltaic flexible direct access power system in an embodiment of the present invention.

[0067] Figure 3 (a)-(i) are the negative sequence impedance values ​​at both ends of the double-ended weakly fed outgoing line when different types of faults occur in the present invention. DETAILED DESCRIPTION

[0068] The present invention is further described below in conjunction with the accompanying drawings:

[0069] Embodiment 1, the present invention provides a negative-sequence directional element protection method based on negative-sequence impedance reconstruction, comprising:

[0070] After a fault occurs in the renewable energy transmission line, the negative sequence impedance of the converter is reconstructed through the negative sequence impedance reconstruction control strategy;

[0071] Feedback adjustment is performed on the negative sequence impedance angle of the reconstructed converter;

[0072] Determine the fault direction based on the phase relationship between the fault negative sequence voltage and the negative sequence current at the protection installation location after the fault;

[0073] Detect the deviation between the negative-sequence impedance angle of the converter and the system impedance angle, and add a correction value to the final setting result of the negative-sequence directional element.

[0074] The negative-sequence directional element protection method based on the negative-sequence impedance reconstruction control strategy overcomes the negative-sequence directional element inadaptability problem caused by the controlled negative-sequence impedance of the converter, and has a certain adaptability to fault types, transition resistance and noise.

[0075] Embodiment 2, the present invention provides a negative-sequence directional element protection method based on negative-sequence impedance reconstruction, comprising:

[0076] Step 1. After a fault occurs in the AC line that transmits new energy through the MMC, the negative sequence impedance of the converter is reconstructed using the negative sequence impedance reconstruction control strategy so that its negative sequence impedance angle presents the characteristics of a synchronous machine, and the negative sequence impedance angle is the same as the system impedance angle;

[0077] Step 2: Feedback and adjust the reconstructed negative sequence impedance angle, and feedback a correction value for adjusting the negative sequence impedance angle reference value according to the difference between the actual converter negative sequence impedance value and the system negative sequence impedance value. ;

[0078] Step 3. Determine the fault direction according to the phase relationship between the fault negative sequence voltage and the negative sequence current at the protection installation location after the fault;

[0079] Step 4. Detect the deviation between the negative sequence impedance angle of the converter and the system impedance, and add a correction value to the final setting result of the negative sequence directional element.

[0080] After a fault occurs in the renewable energy transmission line, the negative sequence impedance of the converter is reconstructed through the negative sequence impedance reconstruction control strategy: When a fault occurs in the renewable energy transmission line, the internal topology of the converter is ignored, and the negative sequence current suppression control strategy is adopted. The inversion direction is the positive direction of the current. The dynamic equation of the converter in the negative sequence rotating coordinate system is:

[0081]

[0082] Where: Indicates the negative sequence voltage of the converter output; L f and R f are the equivalent reactance and equivalent resistance of the filter circuit respectively; ω is the angular frequency.

[0083] In order to simulate the negative sequence characteristics of a conventional synchronous machine, the negative sequence network of the converter should be in the form of a voltage source-series impedance. Therefore, by utilizing the controllability of the converter over the negative sequence current, the concept of virtual negative sequence impedance can be introduced to modify the negative sequence current reference value so that the angle difference between it and the negative sequence voltage is the system angle.

[0084] Then write the dynamic equation and take the steady state as follows:

[0085]

[0086] Where: L v and R v are virtual inductance and resistance respectively, I - is the negative sequence current, U - is the negative sequence voltage at the grid connection point, E - is the virtual negative sequence internal potential.

[0087] Take the virtual negative sequence internal potential The negative sequence current reference value can be calculated from the actual measurement of the system negative sequence:

[0088]

[0089] Where: R = R v+R f ; X = ω(L v +L f ). Thus, the negative sequence current reference value can be obtained according to the set total negative sequence impedance.

[0090] Selection of virtual negative sequence impedance parameters.

[0091] The virtual negative sequence impedance parameters are divided into two aspects: phase angle and amplitude. The constraints that need to be met are:

[0092]

[0093] Where: Z - is the negative sequence impedance; is the system phase angle; is the maximum allowable negative sequence current of the converter.

[0094] To simulate the characteristics of conventional synchronous machines, the virtual impedance phase angle should be set to the system phase angle. The virtual impedance amplitude is limited by the maximum negative sequence current of the converter, and the impedance amplitude can be calculated using the current constraint:

[0095]

[0096] During a fault, the negative sequence current output by the converter is always maintained at the negative sequence current demand value of the protection element. The equivalent negative sequence impedance changes dynamically with the fault type and fault severity. This method can ensure that the protection element can always detect sufficient negative sequence current and avoid the influence of sampling accuracy and noise.

[0097] From another perspective, when the voltage is constant during the fault period, this scheme can also be regarded as negative sequence current constant amplitude / constant phase control. By transforming the negative sequence voltage, we have:

[0098]

[0099] Where: To set the negative sequence virtual impedance reference value

[0100] Comparing equation (3) with equation (4) and equation (6), it can be seen that the two methods are computationally equivalent. Virtual negative-sequence impedance can actually be regarded as another expression of negative-sequence voltage matrix transformation.

[0101] In the early stage of a fault, a virtual impedance angle adjustment is added. According to the difference between the actual converter negative sequence impedance value and the system negative sequence impedance value, a correction value is fed back to adjust the negative sequence impedance angle reference value, so that the negative sequence impedance angle is more stable near the system impedance angle in the early stage of a fault, including:

[0102] Set up additional control strategies as shown below:

[0103]

[0104] Where: U - (t) and I - (t) is the negative sequence voltage and current value at PCC point, e(t) is the deviation value between the negative sequence impedance angle and the system angle; K p With K i is the PI regulator coefficient.

[0105] The fault direction is determined based on the phase relationship between the negative sequence voltage and the negative sequence current at the protection installation after the fault, including:

[0106] When there is a positive fault at the protection installation after the fault, the negative sequence impedance calculated by the protection according to the fault negative sequence voltage and negative sequence current is the same as the system negative sequence impedance, that is, -Δu n / Δi n =Z n , ignoring the resistance, the impedance angle is 90°; in the case of reverse fault, the calculated negative sequence impedance is the inverse of the sum of the system and line negative sequence impedances, i.e. -Δu n / Δi n =-Z m -Z L , the impedance angle is -90°. Considering a certain margin, the criteria for forward and reverse faults are

[0107]

[0108] Where: To protect the negative sequence voltage at the installation location; To protect the negative sequence current at the installation location.

[0109] When the directional protection element is used in the converter AC connection line, the obvious difference between the converter current control characteristics and the conventional synchronous machine has an adverse effect on the effectiveness of the protection element, making the converter negative sequence impedance present a controlled characteristic, and introducing factors such as transition resistance and converter current limiting, the above effects will be more complicated. In addition, when the goal is to suppress negative sequence current and negative sequence voltage, the negative sequence directional element cannot obtain an effective sequence component and the element fails.

[0110] In summary, in order to solve the adaptability problem of typical protection elements, without changing the protection principle, it is necessary to design a suitable additional control algorithm based on the basic control of suppressing negative sequence current and negative sequence voltage of the converters on both sides.

[0111] Detect the deviation between the negative sequence impedance angle of the converter and the system impedance angle, and add a correction value to the final setting result of the negative sequence directional element:

[0112]

[0113] Where: α is the corrected setting result.

[0114] Example 1: Create the following Figure 2 The large-scale two-terminal weak-feedback system shown in the figure is used as a simulation model. The system transmission line is set as shown in the attached figure. Figure 2 The topology shows that asymmetric faults occur at each fault point.

[0115] When AG, ABG, and AB faults occur, the negative-sequence impedance reconstruction control strategy is started, the collected PV and MMC side transmission line negative-sequence voltage and negative-sequence current signal data are preprocessed, the negative-sequence impedance angle is calculated, and the negative-sequence impedance feedback adjustment is started. Finally, the measured angle is added to the adjustment value to see whether it satisfies the setting area of ​​formula (7) to determine the fault direction and distinguish the faults inside and outside the area. The above simulation results are shown in the following table.

[0116] Table 1 Judgment results of different types of faults occurring at different locations of the outgoing line of the double-terminal weak-feed system

[0117]

[0118]

[0119] Example 2: Example 1: Create the following Figure 2 The large-scale two-terminal weak-feedback system shown in the figure is used as a simulation model. The system transmission line is set as shown in the attached figure. Figure 2 The topology shows that each fault point has AG grounding fault through different transition resistances.

[0120] When AG grounding fault occurs through different transition resistances, the collected negative sequence voltage and current signal data of the PV and MMC side transmission lines are preprocessed, the negative sequence impedance angle is calculated, and the negative sequence impedance feedback adjustment is started. Finally, the measured angle is added to the adjustment value to see whether it satisfies the setting area of ​​formula (7) to determine the fault direction and distinguish the fault inside and outside the area. The above simulation results are shown in the following table.

[0121] Table 2 Judgment results of AG grounding fault through transition resistance at different positions of the outgoing line of the double-terminal weak-feed system

[0122]

[0123]

[0124] Example 3: Create the following Figure 2 The large-scale photovoltaic power plant shown in the figure is connected to the power system via MMC as a simulation model. The fault type is set to AG fault, and the photovoltaic output is set to 0%, 20%, 50%, and 75% of the original value. The judgment results are shown in the following table.

[0125] Table 3. Judgment results of AG faults at different locations of the transmission line under different photovoltaic outputs in the double-terminal weak-feed system

[0126]

[0127] In yet another embodiment of the present invention, a negative-sequence directional element protection system based on negative-sequence impedance reconstruction is provided, which can be used to implement the above-mentioned negative-sequence directional element protection method based on negative-sequence impedance reconstruction. Specifically, the system includes:

[0128] The converter negative sequence impedance reconstruction module is used to reconstruct the converter negative sequence impedance through the negative sequence impedance reconstruction control strategy after a fault occurs in the new energy transmission line;

[0129] A feedback regulation module, used for performing feedback regulation on the reconstructed negative sequence impedance angle of the converter;

[0130] A fault direction determination module, used to determine the fault direction according to the phase relationship between the fault negative sequence voltage and the negative sequence current at the protection installation location after the fault;

[0131] The correction output module is used to detect the deviation between the negative sequence impedance angle of the converter and the system impedance angle, and add a correction value to the final setting result of the negative sequence directional element.

[0132] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0133] In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions in a computer storage medium to implement a corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a negative-sequence directional element protection method based on negative-sequence impedance reconstruction.

[0134] In another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the negative-sequence direction element protection method based on negative-sequence impedance reconstruction in the above embodiment.

[0135] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0136] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0137] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0138] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A negative-sequence directional element protection method based on negative-sequence impedance reconstruction, characterized in that: include: After a fault occurs in the renewable energy transmission line, the negative sequence impedance of the converter is reconstructed through the negative sequence impedance reconstruction control strategy; Feedback adjustment is performed on the negative sequence impedance angle of the reconstructed converter; Determine the fault direction based on the phase relationship between the fault negative sequence voltage and the negative sequence current at the protection installation location after the fault; Detect the deviation between the negative-sequence impedance angle of the converter and the system impedance angle, and add a correction value to the final setting result of the negative-sequence directional element.

2. The negative-sequence directional element protection method based on negative-sequence impedance reconstruction according to claim 1 is characterized in that: After the new energy transmission line fails, the negative sequence impedance of the converter is reconstructed through a negative sequence impedance reconstruction control strategy, including: When a fault occurs in the renewable energy transmission line, the negative sequence current suppression control strategy is adopted, and the inversion direction is the positive direction of the current. The dynamic equation of the converter in the negative sequence rotating coordinate system is: Where: Indicates the negative sequence voltage of the converter output; L f and R f are the equivalent reactance and equivalent resistance of the filter circuit respectively; ω is the angular frequency; A virtual negative-sequence impedance is introduced to modify the negative-sequence current reference value so that the angle difference between it and the negative-sequence voltage is the system angle; Then write the dynamic equation and take the steady state as follows: Where: L v and R v are virtual inductance and resistance respectively, I - is the negative sequence current, U - is the negative sequence voltage at the grid connection point, E - is the virtual negative sequence internal potential; Take the virtual negative sequence internal potential The negative sequence current reference value is calculated from the actual measurement of the system negative sequence: Where: R = R v +R f ; X = ω(L v +L f );According to the set total negative sequence impedance, the negative sequence current reference value is obtained.

3. The negative-sequence directional element protection method based on negative-sequence impedance reconstruction according to claim 2 is characterized in that: Selection of virtual negative sequence impedance parameters: The virtual negative sequence impedance parameters are divided into phase angle and amplitude, and the constraints that need to be met are: Where: Z - is the negative sequence impedance; is the system phase angle; is the maximum allowable negative sequence current of the converter; Calculate the impedance magnitude using the current constraint: During a fault, the negative sequence current output by the converter is always maintained at the negative sequence current demand value of the protection element.

4. The negative-sequence directional element protection method based on negative-sequence impedance reconstruction according to claim 1 is characterized in that: The feedback adjustment of the reconstructed converter negative sequence impedance angle includes: In the early stage of a fault, virtual impedance angle adjustment is added. According to the difference between the actual converter negative sequence impedance value and the system negative sequence impedance value, a correction value is fed back to adjust the negative sequence impedance angle reference value, including: Set up additional control strategies as shown below: Where: U - (t) and I - (t) is the negative sequence voltage and current value at PCC point, e(t) is the deviation value between the negative sequence impedance angle and the system angle; K p With K i is the PI regulator coefficient.

5. The negative-sequence directional element protection method based on negative-sequence impedance reconstruction according to claim 1, characterized in that: The method of determining the fault direction according to the phase relationship between the negative sequence voltage and the negative sequence current at the protection installation location after the fault comprises: When there is a positive fault at the protection installation after the fault, the negative sequence impedance calculated by the protection according to the fault negative sequence voltage and negative sequence current is the same as the system negative sequence impedance, that is, -Δu n / Δi n =Z n , ignoring the resistance, the impedance angle is 90°; in the case of reverse fault, the calculated negative sequence impedance is the inverse of the sum of the system and line negative sequence impedances, i.e. -Δu n / Δi n =-Z m -Z L , the impedance angle is -90°; the judgment criteria for forward and reverse faults are Where: To protect the negative sequence voltage at the installation location; To protect the negative sequence current at the installation location.

6. The negative-sequence directional element protection method based on negative-sequence impedance reconstruction according to claim 5 is characterized in that: The detecting the deviation between the negative sequence impedance angle of the converter and the system impedance angle, and adding a correction value to the final setting result of the negative sequence directional element, comprises: Where: α is the corrected setting result.

7. A negative-sequence directional element protection system based on negative-sequence impedance reconstruction, characterized in that: include: The converter negative sequence impedance reconstruction module is used to reconstruct the converter negative sequence impedance through the negative sequence impedance reconstruction control strategy after a fault occurs in the new energy transmission line; A feedback regulation module, used for performing feedback regulation on the reconstructed negative sequence impedance angle of the converter; A fault direction determination module, used to determine the fault direction according to the phase relationship between the fault negative sequence voltage and the negative sequence current at the protection installation location after the fault; The correction output module is used to detect the deviation between the negative sequence impedance angle of the converter and the system impedance angle, and add a correction value to the final setting result of the negative sequence directional element.

8. The negative-sequence directional element protection system based on negative-sequence impedance reconstruction according to claim 7, characterized in that: After the new energy transmission line fails, the negative sequence impedance of the converter is reconstructed through a negative sequence impedance reconstruction control strategy, including: When a fault occurs in the renewable energy transmission line, the negative sequence current suppression control strategy is adopted, and the inversion direction is the positive direction of the current. The dynamic equation of the converter in the negative sequence rotating coordinate system is: Where: Indicates the negative sequence voltage of the converter output; L f and R f are the equivalent reactance and equivalent resistance of the filter circuit respectively; ω is the angular frequency; A virtual negative-sequence impedance is introduced to modify the negative-sequence current reference value so that the angle difference between it and the negative-sequence voltage is the system angle; Then write the dynamic equation and take the steady state as follows: Where: L v and R v are virtual inductance and resistance respectively, I - is the negative sequence current, U - is the negative sequence voltage at the grid connection point, E - is the virtual negative sequence internal potential; Take the virtual negative sequence internal potential The negative sequence current reference value is calculated from the actual measurement of the system negative sequence: Where: R = R v +R f ; X = ω(L v +L f );According to the set total negative sequence impedance, the negative sequence current reference value is obtained.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the negative-sequence directional element protection method based on negative-sequence impedance reconstruction are implemented as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the negative-sequence directional element protection method based on negative-sequence impedance reconstruction as claimed in any one of claims 1 to 7 are implemented.

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