Two-phase short-circuit distance protection method, device and equipment for double-ended weakly fed system and medium

Abstract

The present application relates to the technical field of power system relay protection, and particularly relates to a two-phase short-circuit distance protection method, device and equipment for a double-ended weakly fed system and a medium, comprising: obtaining a power grid system topology, collecting three-phase voltage and current at an MMC converter and d-axis and q-axis current information in a converter controller, calculating the change rate of the d-axis and q-axis current; calculating a measured impedance; calculating positive, negative and zero sequence components of a non-fault phase current at the MMC side, and further calculating a phase angle of an additional impedance; calculating the occurrence distance of a fault according to the corrected measured impedance and the line impedance; and judging whether the fault is inside an AC transmission line, in a lower-level line or outside the system through the calculation results of a plurality of continuous sampling points, so as to trigger corresponding protection actions. In the present application, the protection can correctly act in different operating modes, transition resistances and fault positions, ensuring the safe and stable operation of the double-ended weakly fed system with a high proportion of new energy power sources, and having a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a method, device, equipment and medium for two-phase short-circuit distance protection in a dual-terminal weak-feed system. Background Technology

[0002] With the proposal of the "dual carbon" target, building a new power system with a high proportion of new energy power sources has become an important development direction for the future power system. Compared with the traditional new energy power sources being directly connected to the grid via AC lines, the current new energy power sources present a more flexible grid connection method.

[0003] Existing distance protection methods for weak feeder systems mainly include: traditional three-stage distance protection, adaptive distance protection, and high-frequency distance protection. However, when a two-phase short-circuit fault occurs on the AC transmission line of a double-ended weak feeder system, the positive-sequence network and the negative-sequence network are connected in parallel, and the fault current is entirely provided by the power electronic power supply on both sides. The fault current characteristics depend entirely on the control mode of the two systems, exhibiting the characteristics of limited amplitude and controlled phase on both sides. This is completely different from the fault characteristics of a line connected to the main power grid with a single-ended power electronic power supply. This will cause traditional distance protection for single-ended weak feeder systems to be unable to correctly judge two-phase short-circuit faults on the transmission line of a double-ended weak feeder system.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a method, device, equipment, and medium for protecting two-phase short-circuit distance in a dual-terminal weak-feed system, thereby effectively solving the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a two-phase short-circuit distance protection method for a dual-terminal weak-feed system, comprising the following steps:

[0007] The topology of the power grid system is obtained. The three-phase voltage and the three-phase current flowing through the protection installation point on the MMC converter side are obtained through voltage transformers and current transformers. The d-axis and q-axis current information in the MMC converter controller are collected, and the rate of change of the d-axis and q-axis currents is calculated.

[0008] Calculate the measurement impedance using the fault phase voltage difference and fault phase current difference;

[0009] The positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side are calculated using the symmetrical component method, and the phase angle of the additional impedance is calculated by combining the two faulty phase currents.

[0010] The phase angle of the additional impedance is used to compensate for the phase angle offset of the transmitting line impedance and the measured impedance, and the fault location is calculated based on the corrected line impedance and measured impedance.

[0011] By calculating the results of multiple consecutive sampling points, it can be determined whether the fault is inside the AC transmission line, in the downstream line, or outside the system, thereby triggering the corresponding protection action.

[0012] Furthermore, the d-axis and q-axis current information in the MMC converter controller is collected, and the rate of change of the d-axis and q-axis currents is calculated. When the time difference between the sampling points of a continuously collected set value exceeds the protection start threshold, the protection is activated. The activation criterion is as follows:

[0013]

[0014] In the formula: I d with I q ε1 and ε2 are the per-unit values ​​of the d-axis and q-axis currents in the inner loop of the MMC controller at the sending end, Δt is the protection start threshold, and Δt is the time interval between two sampling points.

[0015] Furthermore, the protection activation thresholds ε1 and ε2 are respectively determined by I within the first 10ms of the sampling point. d and I q Five times the maximum rate of change over time is used as the protection activation threshold, and the rate of change is calculated as follows:

[0016] △I d =I d (t)-I d (t-△t);

[0017] △I q =I q (t)-I q (t-△t);

[0018] In the formula, Δt = 1 / f s f s To protect the sampling frequency.

[0019] Furthermore, the calculation of the positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side using the symmetrical component method, and the calculation of the phase angle of the additional impedance in combination with the two faulty phase currents, includes, for example, taking the faulty phase as phase AB and phase C as the non-faulty phase:

[0020]

[0021] In the formula, Z add For additional impedance, φ add R is the phase angle of the additional impedance. ph For transition resistance, and These represent the positive, negative, and zero-sequence components of the C-phase current on the MMC side. These are the three-phase current phasors of A, B, and C on the MMC side, respectively. When phase A or phase B is a non-faulty phase, the calculation method is the same as above.

[0022] Furthermore, the measuring impedance of the phase-to-phase impedance relay includes:

[0023]

[0024] In the formula, Z MMC-AB The measured impedance is calculated by the phase-to-phase impedance relay on the MMC side, α is the fault location distance, which is the percentage of the distance from the fault point to the beginning of the line on the MMC side to the total line length, and Z is the fault location distance. L The impedance of the outgoing line.

[0025] Furthermore, the calculation of the fault location distance based on the corrected line impedance and measured impedance includes:

[0026] The measured impedance Z is calculated based on the additional impedance phase angle of the AB phase-to-phase impedance relay. MMC-AB and the output line impedance Z L Phase angle offset compensation was performed to obtain the new measured impedance Z′. MMC-AB and line impedance Z L 'for:

[0027]

[0028] Take Z′ MMC-AB and Z L The imaginary part of ′ is used to calculate the fault location distance α, and the calculation formula is as follows:

[0029]

[0030] Furthermore, determining whether the fault is inside the AC transmission line, a downstream line, or outside the system based on the calculation results of multiple consecutive sampling points includes the following steps:

[0031] Perform logical judgment on the calculated fault location distance α:

[0032] When the calculated result of α is x1 consecutive points located in the interval (0, α) set.1 When the fault is detected, the protection determines it to be a fault within the AC transmission line area, which meets the MMC-side distance protection stage I action criteria.

[0033] When the calculated result of α is consecutively x2 points within the interval (α) set.1 ,α set.2When the protection determines that the fault is in the downstream line of the AC transmission line, it meets the time delay action criterion of the distance protection stage II on the MMC side, and the time delay Δt1 is set to 0.2s.

[0034] When either fault discrimination condition a or b is not met within a period of time △t2, the protection should determine that the fault is outside the AC transmission line area or that the system is in normal operation.

[0035] The present invention also includes a two-phase short-circuit distance protection device for a dual-terminal weak feeder system, using the method described above, comprising:

[0036] The data acquisition unit obtains the power grid system topology, acquires the three-phase voltage and three-phase current values ​​flowing through the protection installation point on the MMC converter side through voltage transformers and current transformers, and acquires the d-axis and q-axis current information in the MMC converter controller to calculate the rate of change of the d-axis and q-axis currents.

[0037] The measurement impedance calculation unit is used to calculate the measurement impedance using the fault phase voltage difference and fault phase current difference.

[0038] The additional impedance calculation unit is used to calculate the positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side using the symmetrical component method, and to calculate the phase angle of the additional impedance accordingly.

[0039] The fault location calculation unit is used to compensate for the phase angle offset of the transmitting line impedance and the measured impedance using the additional impedance phase angle, and to calculate the fault location based on the corrected measured impedance and line impedance.

[0040] The protection unit is used to determine whether the fault is inside the AC transmission line, the downstream line, or outside the system by calculating the results of multiple consecutive sampling points, thereby triggering the corresponding protection action.

[0041] The present invention also includes a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as described above.

[0042] The present invention also includes a storage medium having a computer program stored thereon, which, when executed by a processor, implements the method as described above.

[0043] The beneficial effects of this invention are as follows: This invention solves for the additional impedance phase angle by using the MMC converter side current, and compensates for the phase angle offset of the measured impedance and line impedance calculated by the phase-to-phase impedance relay. This weakens the influence of the transition resistance on the accuracy of fault location determination, improves the accuracy of protection fault judgment, and enables the protection to operate correctly under different operating modes, transition resistance, and fault location conditions. This ensures the safe and stable operation of the dual-end weak feeder system with a high proportion of new energy power grid connection, and has good application prospects. Attached Figure Description

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

[0045] Figure 1 This is a flowchart of the method of the present invention;

[0046] Figure 2 This is a schematic diagram of the structure of the device of the present invention;

[0047] Figure 3 A schematic diagram of a dual-terminal weak feeder system, represented by offshore wind power connected to the grid via flexible DC transmission;

[0048] Figure 4 Flowchart of a distance protection method for two-phase short-circuit faults in a double-ended weak feeder system based on additional impedance phase angle offset compensation;

[0049] Figure 5 This is the system topology diagram for a phase-to-phase short-circuit fault.

[0050] Figure 6 This is a topology diagram of the simulation system;

[0051] Figure 7 The calculation results are for a two-phase short-circuit fault occurring at 50% of the AC transmission line through different transition resistors.

[0052] Figure 8 This describes the protection operation when a two-phase short-circuit fault occurs at 50% of the AC transmission line via different transition resistors.

[0053] Figure 9 The calculation results are for a two-phase short-circuit fault occurring at 70% of the AC transmission line through different transition resistors.

[0054] Figure 10 This describes the protection operation when a two-phase short-circuit fault occurs at 70% of the AC transmission line via different transition resistors.

[0055] Figure 11 The calculation results are for a two-phase short-circuit fault occurring at 90% of the AC transmission line through different transition resistors.

[0056] Figure 12 This describes the protection operation when a two-phase short-circuit fault occurs at 90% of the AC transmission line through different transition resistors.

[0057] Figure 13 The calculation results are to protect the installation back side in case of a two-phase short circuit fault through a 20Ω transition resistor;

[0058] Figure 14 To protect against the operation of the protection system when a two-phase short circuit fault occurs on the back side of the installation via a 20Ω transition resistor;

[0059] Figure 15 The calculation results are for a two-phase short-circuit fault occurring in the collector line through a 20Ω transition resistor.

[0060] Figure 16 This describes the protection operation when a two-phase short-circuit fault occurs in the collector line through a 20Ω transition resistor.

[0061] Figure 17 This is a schematic diagram of the structure of a computer device. Detailed Implementation

[0062] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0063] like Figure 1 As shown: A two-phase short-circuit distance protection method for a dual-terminal weak-feed system includes the following steps:

[0064] The topology of the power grid system is obtained. The three-phase voltage and the three-phase current flowing through the protection installation point on the MMC converter side are obtained through voltage transformers and current transformers. The d-axis and q-axis current information in the MMC converter controller are collected, and the rate of change of the d-axis and q-axis currents is calculated.

[0065] Calculate the measurement impedance using the fault phase voltage difference and fault phase current difference;

[0066] The positive, negative, and zero-sequence components of the C-phase current on the MMC side are calculated using the symmetrical component method, and the phase angle of the additional impedance is calculated in combination with the currents of the two fault phases.

[0067] The phase angle of the additional impedance is used to compensate for the phase angle offset of the transmitting line impedance and the measured impedance, and the fault location is calculated based on the corrected measured impedance and line impedance.

[0068] By calculating the results of multiple consecutive sampling points, it can be determined whether the fault is inside the AC transmission line, in the downstream line, or outside the system, thereby triggering the corresponding protection action.

[0069] The phase angle of the additional impedance is solved by the current on the MMC converter side, and the phase angle offset compensation is performed on the measured impedance and line impedance calculated by the phase-to-phase impedance relay. This weakens the influence of the transition resistance on the accuracy of fault location determination, improves the accuracy of protection fault judgment, and enables the protection to operate correctly under different operating modes, transition resistance, and fault location conditions. This ensures the safe and stable operation of the dual-end weak feeder system with a high proportion of new energy power grid connection and has good application prospects.

[0070] In this embodiment, the three-phase voltage and three-phase current flowing through the protection installation point on the MMC converter side are obtained through voltage transformers and current transformers. The d-axis and q-axis current information in the MMC converter controller are collected, and the rate of change of the d-axis and q-axis currents is calculated. When the difference between the sampling points and the time of the continuously collected set value continuously exceeds the protection start threshold, the protection is started. The start criterion is as follows:

[0071]

[0072] In the formula: I d with I q ε1 and ε2 are the per-unit values ​​of the d-axis and q-axis currents in the inner loop of the MMC controller at the sending end, Δt is the protection start threshold, and Δt is the time interval between two sampling points.

[0073] Among them, the protection start thresholds ε1 and ε2 are respectively adopted from the I within the first 10ms of the sampling point. d and I q Five times the maximum rate of change over time is used as the protection activation threshold. The rate of change is calculated as follows:

[0074] △I d =I d (t)-I d (t-△t);

[0075] △I q =I q (t)-I q (t-△t);

[0076] In the formula, Δt = 1 / f s f s To protect the sampling frequency.

[0077] The positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side are calculated using the symmetrical component method, and the phase angle of the additional impedance is calculated in combination with the currents of the two faulty phases, including: taking phase AB as the faulty phase and phase C as the non-faulty phase as an example:

[0078]

[0079] In the formula, Z add For additional impedance, φ add R is the phase angle of the additional impedance. ph For transition resistance, and These represent the positive, negative, and zero-sequence components of the C-phase current on the MMC side. These are the three-phase current phasors of A, B, and C on the MMC side, respectively. When phase A or phase B is a non-faulty phase, the calculation method is the same as above.

[0080] The measured impedance is calculated using the fault phase voltage difference and fault phase current difference. The measured impedance includes:

[0081]

[0082] In the formula, Z MMC-AB The measured impedance is calculated for the phase-to-phase impedance relay on the MMC side.

[0083] In this embodiment, the fault location distance is calculated based on the corrected line impedance and the measured impedance, including:

[0084] The measured impedance Z is calculated based on the phase angle of the additional impedance to the AB phase-to-phase impedance relay. MMC-AB and the output line impedance Z L Phase angle offset compensation was performed to obtain the new measured impedance Z′. MMC-AB and line impedance Z L 'for:

[0085]

[0086] Take Z′ MMC-AB and Z L The imaginary part of ′ is used to calculate the fault location distance α, and the calculation formula is as follows:

[0087]

[0088] Based on the calculation results of multiple consecutive sampling points, the system determines whether the fault is inside the AC transmission line, in a downstream line, or outside the system, including the following steps:

[0089] Perform logical judgment on the calculated fault location distance α:

[0090] When the calculated result of α is x1 consecutive points located in the interval (0, α) set.1 When the fault is detected, the protection determines it to be a fault within the AC transmission line area, which meets the MMC-side distance protection stage I action criteria.

[0091] When the calculated result of α is consecutively x2 points within the interval (α)set.1 ,α set.2 When the protection determines that the fault is in the downstream line of the AC transmission line, it meets the time delay action criterion of the distance protection stage II on the MMC side, and the time delay Δt1 is set to 0.2s.

[0092] When either fault discrimination condition a or b is not met within a period of time △t2, the protection should determine that the fault is outside the AC transmission line area or that the system is in normal operation.

[0093] This embodiment fully utilizes the negative sequence current of the non-faulty phase flowing through the protection point and the phasors of the two faulty phase currents to calculate the additional impedance phase angle. The fault location α is calculated by compensating for the phase angle offset of the measured impedance calculated by the impedance relay and the line impedance. Since the phase angle offset compensation method and the method of taking the imaginary part of the compensated phasor eliminate the influence of transition resistance, this method is minimally affected by transition resistance. Furthermore, this method shows significant differences for faults within and outside the AC transmission line area, as well as under normal operating conditions, ensuring reliable protection operation. Because this protection method fully utilizes the negative sequence component control strategy of the weak feeders on both sides during asymmetrical faults, it overcomes the problem of incorrect protection operation in traditional distance protection scenarios with double-ended weak feeder systems, greatly improving the accuracy of the protection method. It has good application prospects for ensuring the safe and reliable operation of double-ended weak feeder systems, especially for AC transmission lines in double-ended weak feeder systems where one side of the power supply adopts negative sequence voltage control and the other side adopts negative sequence current suppression strategies during asymmetrical faults.

[0094] like Figure 2 As shown, this embodiment also includes a two-phase short-circuit distance protection device for a dual-ended weak feeder system, using the method described above, including:

[0095] The data acquisition unit obtains the power grid system topology, acquires the three-phase voltage and three-phase current values ​​flowing through the protection installation point on the MMC converter side through voltage transformers and current transformers, and acquires the d-axis and q-axis current information in the MMC converter controller to calculate the rate of change of the d-axis and q-axis currents.

[0096] The measurement impedance calculation unit is used to calculate the measurement impedance using the fault phase voltage difference and fault phase current difference.

[0097] The additional impedance calculation unit is used to calculate the positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side using the symmetrical component method, and to calculate the phase angle of the additional impedance accordingly.

[0098] The fault location calculation unit is used to compensate for the phase angle offset of the transmitting line impedance and the measured impedance using the additional impedance phase angle, and to calculate the fault location based on the corrected measured impedance and line impedance.

[0099] The protection unit is used to determine whether the fault is inside the AC transmission line, the downstream line, or outside the system by calculating the results of multiple consecutive sampling points, thereby triggering the corresponding protection action.

[0100] Example 2:

[0101] To overcome the potential failure to operate or maloperation issues of distance protection for AC transmission lines in double-ended weak-feed systems, this embodiment proposes a distance protection method for two-phase short-circuit faults in double-ended weak-feed systems based on additional impedance phase angle offset compensation. The method calculates the additional impedance phase angle using the MMC converter-side current and compensates for the phase angle offset of the measured impedance calculated by the phase-to-phase impedance relay and the line impedance. This reduces the impact of transition resistance on the accuracy of fault location determination, improves the accuracy of fault judgment, and enables the protection to operate correctly under different operating modes, transition resistances, and fault locations. This ensures the safe and stable operation of double-ended weak-feed systems with a high proportion of new energy power grid connection and has promising application prospects.

[0102] This embodiment proposes a distance protection method for two-phase short-circuit faults in a double-ended weak-feed system based on additional impedance phase angle offset compensation, and takes a double-ended weak-feed system of an offshore wind farm connected to a flexible DC converter station via an AC line as an example for analysis. A schematic diagram of offshore wind power grid connection is shown below. Figure 3 As shown, after offshore wind power is collected and boosted, it is connected to the flexible DC-side transformer via an AC transmission line. The positive current at both ends of the line flows from the busbar towards the line. During a fault, the wind turbine adopts a negative sequence current suppression strategy and does not output negative sequence current, while the MMC converter adopts a negative sequence voltage control strategy.

[0103] The flowchart of the distance protection method for two-phase short-circuit faults in a double-ended weakly fed system based on additional impedance phase angle offset compensation is as follows: Figure 4 As shown. The specific steps are as follows:

[0104] 1) Taking an A / B phase-to-phase short-circuit fault on an AC transmission line as an example, the fault system topology is as follows: Figure 5 As shown, R ph Z represents the transition resistance, α is the percentage of the total line length relative to the distance from the fault point to the beginning of the line on the MMC side, and Z represents the transition resistance. L The impedance of the AC transmission line. The distance protection device on the MMC side collects the three-phase voltage and the three-phase current flowing through the protection installation point on that side using voltage transformers and current transformers, respectively, and calculates the three-phase voltage phasors on that side using the Fourier algorithm. and three-phase current phasors

[0105] 2) The protection device collects the d-axis and q-axis values ​​of the current in the inner current loop of the sending-end MMC converter controller and calculates the d-axis and q-axis current change rates. When the time difference of 10 consecutive sampling points exceeds the start threshold value, the protection is started. The start criterion is shown in equation (1):

[0106]

[0107] Among them: I d with I q The per-unit values ​​are the d-axis and q-axis currents of the inner loop current of the sending-end MMC controller. ε1 and ε2 are the start-up threshold values, and their specific selection depends on the actual situation. To avoid the influence of fluctuations on the protection action, the values ​​within 10ms before the sampling point are used. d and I q Five times the maximum rate of change over time is used as the protection activation threshold. (I) d For example, the method for calculating the change is △I d =I d (t)-I d (t-△t), where △t=1 / f s f s To protect the sampling frequency.

[0108] 3) The measured impedance Z calculated by the MMC-side AB phase-to-phase impedance relay MMC-AB for:

[0109]

[0110] 4) Calculate the positive, negative, and zero-sequence components of the C-phase current on the MMC side using the symmetrical component method. and And further calculate the additional impedance Z in the measured impedance. add The phase angle, the additional impedance and its phase angle φ add The expression is:

[0111]

[0112] 5) The measured impedance Z calculated based on the phase angle of the additional impedance to the AB phase-to-phase impedance relay. MMC-AB and the output line impedance Z L Phase angle offset compensation was performed to obtain the new measured impedance Z′. MMC-AB and line impedance Z L 'for:

[0113]

[0114] 6) Take Z′ MMC-AB and Z L The imaginary part of ′ is used to calculate the fault location distance α, and the calculation formula is as follows:

[0115]

[0116] 7) Perform logical judgment on the fault location distance α:

[0117] a. When the calculated result of α is x1 consecutive points located in the interval (0, α) set.1 When the fault is detected, the protection determines it to be a fault within the AC transmission line area, which meets the MMC-side distance protection stage I action criteria.

[0118] b. When the calculated result of α contains x2 consecutive points within the interval (α) set.1 ,α set.2 When the protection determines that the fault is in the downstream line of the AC transmission line, it meets the time delay action criterion of the distance protection stage II on the MMC side. The delay Δt1 is set to 0.2s. The protection criterion is used as the backup protection criterion of this protection method to form a redundant protection configuration.

[0119] c. When either of the above fault discrimination conditions a or b is not met within a period of time △t2, the protection should determine that the fault is outside the AC transmission line area or that the system is in normal operation.

[0120] A simulation model was built based on the PSCAD / EMTDC simulation platform. The system topology is as follows: Figure 6 As shown, the offshore wind turbines are connected to the 220kV wind farm-side transformer via a 35kV collector system. Wind farms 1 and 2 have capacities of 400MW and 300MW, respectively. The unit impedance of the AC transmission line is z. L =0.018+j0.3Ω / km, the line length is 10km. F1, F2, and F3 are located at 50%, 70%, and 90% of the distance from the beginning of the line on the MMC side, respectively. F4 is on the back side of the AC transmission line, and F5 is on the wind farm's second collector line. The signal acquisition frequency is 10kHz. Take x1 = 120, x2 = 140, α set.1 =0.95, α set.2 =1.2, the calculation results of α and the protection action are shown below.

[0121] When a two-phase short-circuit fault occurs at point F1, i.e., 50% of the AC transmission line, through transition resistors of 0.1Ω, 20Ω, and 60Ω, the result calculated according to this method is as follows: Figure 7 As shown, with the change in transition resistance, α stabilizes around 0.5 ms after the fault occurs, allowing for accurate determination of the fault location. Figure 8 It can be seen that the protection can operate correctly within 35ms regardless of the change in transition resistance.

[0122] When a two-phase short-circuit fault occurs at point F2, which is 70% of the AC transmission line, through transition resistors of 0.1Ω, 20Ω, and 60Ω, the result calculated according to this method is as follows: Figure 9 As shown, with the change in transition resistance, α stabilizes around 0.7 ms after the fault occurs, allowing for accurate determination of the fault location. According to... Figure 10 It is evident that this protection method can operate correctly within 35ms under conditions of transition resistance change.

[0123] When a two-phase short-circuit fault occurs at point F3, which is 90% of the AC transmission line through transition resistors of 0.1Ω, 20Ω, and 60Ω, the result calculated according to this method is as follows: Figure 11 As shown, with the change in transition resistance, α stabilizes around 0.9 ms after the fault occurs, allowing for accurate determination of the fault location. According to... Figure 12 It is evident that the proposed protection method can operate correctly within 35ms under conditions of transition resistance change.

[0124] When a two-phase short-circuit fault occurs at point F4, i.e., on the back side of the AC transmission line after passing through the 20Ω transition resistor, the result calculated according to this method is as follows: Figure 13 As shown, when a fault occurs on the back side, the calculation results alternate between positive and negative. At this time, the protection action conditions are not met, and the protection will not malfunction. Figure 14 It was verified that the protection would not malfunction when a fault occurred on the back side of the protection.

[0125] When a two-phase short-circuit fault occurs at point F5, i.e., the collector line of wind farm 2 through the 20Ω transition resistor, the result calculated according to this method is as follows: Figure 15 As shown, when the fault occurs on the downstream line of the AC transmission line, the calculated result stabilizes at a value greater than 1 after 100ms. At this point, the operating conditions for the new type of distance protection stage I on this line section are not met, and the protection will not malfunction. Figure 16 It is evident that when a lower-level line fails, the proposed algorithm can accurately reflect the fault distance and can provide remote backup protection after a delay of Δt1.

[0126] The simulation results show that when a two-phase short-circuit fault occurs within the zones (F1, F2, and F3) through different transition resistors, the method proposed in this patent can operate correctly within 35ms. The calculated α value is greater than 0 and stabilizes at the fault location after 100ms, allowing for fault location identification. When a two-phase short-circuit fault occurs on the back side of the protection installation (F4), the calculated α value fluctuates around 0, failing to meet the protection criteria, and the protection reliably does not operate. When a fault occurs on a downstream line, the calculated α value is greater than 1, failing to meet the protection criteria, protection stage I will not malfunction, and protection stage II will operate correctly after a delay of Δt1, providing backup protection for the downstream line. In summary, this protection can operate correctly within 35ms, is not affected by weak power supply and will not experience malfunctions or failures to operate, and α can accurately reflect the fault distance after 100ms.

[0127] Please see Figure 17 The diagram shows a structural schematic of a computer device provided in an embodiment of this application. An embodiment of this application provides a computer device 400, including a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410. When the computer program is executed by the processor 410, it performs the method described above.

[0128] This application embodiment also provides a storage medium 430, on which a computer program is stored, and the computer program is executed by a processor 410 to perform the above method.

[0129] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0130] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0131] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0132] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0133] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0134] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0135] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0136] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0137] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for protecting two-phase short-circuit distance in a dual-terminal weak-feed system, characterized in that, Includes the following steps: The topology of the power grid system is obtained. The three-phase voltage and the three-phase current flowing through the protection installation point on the MMC converter side are obtained through voltage transformers and current transformers. The d-axis and q-axis current information in the MMC converter controller are collected, and the rate of change of the d-axis and q-axis currents is calculated. Calculate the measurement impedance using the fault phase voltage difference and fault phase current difference; The positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side are calculated using the symmetrical component method, and the phase angle of the additional impedance is calculated by combining the two faulty phase currents. The phase angle of the additional impedance is used to compensate for the phase angle offset of the transmitting line impedance and the measured impedance, and the fault location is calculated based on the corrected line impedance and measured impedance. By calculating the results of multiple consecutive sampling points, it can be determined whether the fault is inside the AC transmission line, the downstream line, or outside the system, thereby triggering the corresponding protection action. The method of using the additional impedance phase angle to compensate for phase angle offset of the transmitting line impedance and the measured impedance includes: based on the additional impedance phase angle The measured impedance calculated by the AB phase-to-phase impedance relay and the impedance of the transmitting line Phase offset compensation was performed to obtain new measured impedances. and line impedance for: 。 2. The two-phase short-circuit distance protection method for a dual-terminal weak-feed system according to claim 1, characterized in that, The system collects the three-phase voltage and three-phase current values ​​flowing through the protection installation point on the MMC converter side, and also collects the d-axis and q-axis current information in the MMC converter controller. The rate of change of the d-axis and q-axis currents is calculated. When the difference between the sampling points and the time of a continuously collected set value exceeds the protection start threshold, the protection is activated. The start criterion is shown in the following formula: ； In the formula: and These are the per-unit values ​​of the d-axis and q-axis currents in the inner loop of the MMC controller at the sending end. and To protect the startup threshold, The time interval between two sampling points. , The time intervals between two sampling points represent the per-unit values ​​of the d-axis and q-axis currents of the inner current loop of the sending-end MMC controller. The amount of change between them.

3. The two-phase short-circuit distance protection method for a dual-terminal weak-feed system according to claim 2, characterized in that, The protection activation threshold and Using the first 10ms of each sampling point and Five times the maximum rate of change over time is used as the protection activation threshold, and the amount of change is calculated as follows: ； ； In the formula , To protect the sampling frequency.

4. The two-phase short-circuit distance protection method for a dual-terminal weak-feed system according to claim 1, characterized in that, The method of calculating the positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side using the symmetrical component method, and calculating the phase angle of the additional impedance in combination with the two faulty phase currents, includes: Taking phases AB as the faulty phases and phase C as the non-faulty phase as an example: ； ； In the formula, For additional impedance, The phase angle of the additional impedance. For transition resistance, , and These represent the positive, negative, and zero-sequence components of the C-phase current on the MMC side. , , These are the three-phase current phasors of A, B, and C on the MMC side, respectively; when phase A or phase B is a non-faulty phase, the calculation method is the same as above.

5. The two-phase short-circuit distance protection method for a dual-terminal weak-feed system according to claim 4, characterized in that, The measured impedance of the phase-to-phase impedance relay includes: ； In the formula, The measured impedance calculated for the phase-to-phase impedance relay on the MMC side AB. The fault location is the distance from the fault point to the beginning of the MMC-side line, representing a percentage of the total line length. The impedance of the outgoing line.

6. The two-phase short-circuit distance protection method for a dual-terminal weak-feed system according to claim 5, characterized in that, The calculation of the fault location distance based on the corrected measured impedance and line impedance includes: Pick and The imaginary part is calculated, and the distance to the fault is determined. The calculation formula is: 。 7. The two-phase short-circuit distance protection method for a dual-terminal weak-feed system according to claim 1, characterized in that, The step of determining whether a fault exists inside the AC transmission line, in a downstream line, or outside the system based on the calculation results of multiple consecutive sampling points includes the following steps: Calculated fault location Perform logical judgments: a.When The calculation results are continuous The points are located in the interval When the protection determines that the fault is within the AC transmission line area, it meets the MMC side distance protection stage I action criteria; b. When The calculation results are continuous The points are located in the interval When the protection determines that there is a fault in the downstream line of the AC transmission line, and the MMC-side distance protection stage II time delay action criterion is met, a time delay is set. It takes 0.2 seconds; c. When the above fault detection conditions a or b are met for a period of time If none of the above conditions are met, the protection should determine that the fault is outside the AC transmission line area or that the system is in normal operation.

8. A two-phase short-circuit distance protection device for a dual-terminal weak-feed system, characterized in that, Using the method as described in any one of claims 1 to 7, comprising: The data acquisition unit obtains the power grid system topology, acquires the three-phase voltage and three-phase current values ​​flowing through the protection installation point on the MMC converter side through voltage transformers and current transformers, and acquires the d-axis and q-axis current information in the MMC converter controller to calculate the rate of change of the d-axis and q-axis currents. The impedance calculation unit is used to calculate the measured impedance using the fault phase voltage difference and fault phase current difference. The additional impedance calculation unit is used to calculate the positive, negative, and zero-sequence components of the non-faulty phase current on the MMC side using the symmetrical component method, and to calculate the phase angle of the additional impedance accordingly. The fault location calculation unit is used to compensate for the phase angle offset of the transmitting line impedance and the measured impedance using the additional impedance phase angle, and to calculate the fault location based on the corrected measured impedance and line impedance. The protection unit is used to determine whether the fault is inside the AC transmission line, the downstream line, or outside the system by calculating the results of multiple consecutive sampling points, thereby triggering the corresponding protection action.

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, it implements the method as described in any one of claims 1-7.

10. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the method as described in any one of claims 1-7.

Images