Adaptive current differential protection method for power distribution network containing inverter distributed power supply

Abstract

The invention relates to the technical field of power system protection, in particular to a self-adaptive current differential protection method for a power distribution network containing an inverter distributed power supply. Comprising the steps that initialization and parameter setting are conducted, a topological structure is analyzed, and parameters are managed through an integrated system; data acquisition: sensors are reasonably arranged to acquire real-time data; performing fault analysis and current differential calculation, and analyzing and calculating related quantity by using a symmetric component method and real-time data; protection decision and action: calculating and judging whether protection is started or not based on adaptive filtering and an algorithm; and self-adaptive adjustment and resetting: adjusting line parameters and resetting the system. The method adapts to complex topology and distributed power supply characteristics, improves protection coordination, enhances the self-healing capability and operation efficiency of the power distribution network, and effectively overcomes the defects in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of power system protection, and in particular to an adaptive current differential protection method for a distribution network containing an inverter-type distributed power source. Background Art

[0002] With the growth of energy demand and the pursuit of clean energy, distributed power sources are increasingly used in distribution networks. As an important component of distributed power sources, inverter-type distributed power sources have brought a series of new challenges to the operation and protection of distribution networks.

[0003] In traditional distribution network protection technology, faults are mainly judged and protection actions are taken based on simple electrical quantity characteristics such as current and voltage and fixed protection setting values. This method can meet basic protection needs in the traditional distribution network structure, that is, it is mainly powered by centralized power supplies and the topology structure is relatively simple and stable.

[0004] However, when the inverter-type distributed power source is connected to the distribution network, the situation changes significantly. The existing technology faces the following major defects:

[0005] The topological structure is becoming more complex. The access of distributed power sources makes the topological structure of the distribution network no longer limited to the traditional radial structure. Complex structures such as ring structures and multi-power supply structures may appear. This complexity increases the difficulty of judging the fault location and fault type. For example, in a ring topological structure, the path of the fault current is no longer single, and the traditional method of judging the fault location based on the direction and magnitude of the current may fail, because the fault current may form multiple circulation paths in the ring network, making it difficult to accurately determine the fault area.

[0006] The electrical characteristics change. The inverter-type distributed power source has intermittent and fluctuating output characteristics. Its output power will change with the changes of natural factors such as light intensity (for photovoltaic power sources) and wind speed (for wind power sources). This intermittent and fluctuating nature will interfere with the judgment of faults by traditional protection methods.

[0007] In traditional current differential protection, the current difference between the two sides of the line should be within a small range under normal circumstances. However, when the output power of the distributed power source changes suddenly, the current difference between the two sides of the line may exceed the normal range, thus causing false operation. In addition, the access of distributed power sources may also change the voltage distribution of the distribution network, affecting the accuracy of voltage protection.

[0008] Protection coordination problem. Traditional distribution network protection devices are usually designed and set according to the centralized power supply mode. When distributed power sources are connected, the coordination between different protection devices is affected. When a fault occurs, the distributed power source may continue to provide current to the fault area, which is inconsistent with the fault current characteristics expected by traditional protection devices. This may lead to uncoordinated action time between protection devices, or even refusal to act, and the fault area cannot be isolated in time, thereby expanding the scope of the fault.

[0009] The adaptive current differential protection method for a distribution network containing an inverter-type distributed power source proposed in the present invention aims to solve the problems existing in the above-mentioned prior art. Summary of the invention

[0010] In view of the above deficiencies in the prior art, the purpose of the present invention is: the purpose of the present invention is to provide an adaptive current differential protection method for a distribution network containing inverter-type distributed power sources, aiming to solve the problem of how to achieve accurate, fast and adaptive current differential protection in a distribution network environment containing inverter-type distributed power sources.

[0011] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0012] The invention discloses a method for adaptive current differential protection of a distribution network including an inverter-type distributed power source, comprising the following steps:

[0013] S1. Initialization and parameter setting: Analyze the topological structure and electrical characteristics of the distribution network, use an integrated parameter management system, initialize line parameters and the installed capacity of distributed power sources, and ensure that all protection devices are powered on normally and complete self-tests:

[0014] S11. Analyze the radial topology structure, determine the power node S, start from the power node, and mark each line along the direction of power transmission; the starting node of the i-th line is , and the ending node is ; record all branch nodes connected to each line, j represents the j-th branch node and its connection; if there is a branch node on the line from to , record the information of other nodes connected to it, as well as the estimated range of relevant electrical parameters of the branch line (such as resistance, inductance, capacitance, etc.);

[0015] For radial topology, in addition to clarifying the line start and end nodes and connection relationships, it is also necessary to analyze the load distribution of each line:

[0016] For a ring topology, starting from a certain reference node, mark each line in a clockwise direction; then the connection nodes of the i-th line are represented as and;

[0017] S12. Combing the topology of the distribution network. Based on the results of S11 analysis, further confirm the accuracy and completeness of the topology: for radial topology, check whether the starting node, ending node, branch node and connection relationship of each line are correctly recorded; for ring topology, check whether the line marking is carried out in the prescribed direction, whether the node connection is accurate, and whether there are any undetected additional branches or connections;

[0018] S13. Calculate the electrical parameters of the line. For line resistance, the formula is used, where is the conductor resistivity, is the line length, and is the conductor cross-sectional area; inductance is calculated by the formula, is the vacuum magnetic permeability, is the distance between the two conductors, and is the conductor radius; capacitance is calculated based on the line geometry and dielectric properties using the corresponding electric field theory formula;

[0019] S14. Parameter management system initialization:

[0020] Input line parameters and distributed power generation installed capacity using the integrated parameter management system; store different line and distributed power generation parameters in corresponding data tables in the system database;

[0021] The protection device performs a power-on self-test. After the protection device is powered on, it checks the internal circuit connection; detects the resistance value between key nodes, and if it is not within the normal range, an alarm is issued; checks the chip working status, reads the chip internal register value, and if it is abnormal, determines that the chip is faulty.

[0022] S2. Data acquisition, based on the initialization parameters in S1, uses sensors and real-time data acquisition technology to capture the initial moment and response of the fault in real time, providing raw data support for fault analysis:

[0023] S21. Sensor layout: According to the topology and the electrical quantities to be monitored, the sensors should be arranged reasonably. Voltage sensors and current sensors should be placed at the starting and ending nodes of each line to measure the voltage and current at both ends of the line. Power sensors should be placed at the output ports of the distributed power sources to measure their output power. Temperature sensors should be placed near the conductors to measure the line temperature, so as to more accurately calculate the line resistance.

[0024] S22. Real-time data acquisition, using real-time data acquisition technology, collect sensor data at a certain sampling frequency, including: sampling frequency, voltage data sequence, current data sequence and power data sequence, etc., and the sampling frequency should be at least twice the highest frequency of the signal.

[0025] S3. Fault analysis and current differential calculation: Fault analysis is performed based on the real-time data collected by S2, and the positive sequence voltage of each PCC and the fault component output current of the distributed power source are calculated to provide a scientific basis for protection decision-making:

[0026] S31. Obtain the three-phase voltages Ua, Ub, and Uc from the data collected by S2, and calculate the positive sequence voltage U according to the symmetrical component method. 1PCC :

[0027]

[0028] Where a is a complex number, and its real part is The imaginary part is

[0029]

[0030] therefore,

[0031] S32. Calculate the fault component output current of the distributed power source:

[0032] The normal output current I of the distributed power supply can be obtained by analyzing the collected real-time data. f (n) and the output current I′ after the fault f (n), n is the sampling point number; analyze the sudden changes of voltage, current and other data in the collected real-time data to determine the time period when the fault occurs. If the voltage suddenly drops and the current fluctuates abnormally, then the time period is judged to be the fault period;

[0033] Extract the current data sequence during the fault period. If the fault current data is relatively stable, directly use its mean as the estimated value of the output current after the fault, that is, in is the mean value of the current data during the fault period;

[0034] If the fault current data fluctuates greatly, weighted moving average filtering is used to smooth the fault current data. The filtered current value I f (k) is expressed as:

[0035]

[0036] Where N is the filter window size; k is the value of the sampling point; ω i is the weighting coefficient. Different weights can be set according to the needs. For example, the weight close to the current sampling point is larger, and the weight far away from the current sampling point is smaller. I(i) represents the current value for the i-th sampling point.

[0037] Then the fault component output current I fd (n) is:

[0038] I fd (n) = I′ f (n)-I f (n).

[0039] S4. Protection decision and action: Based on the result of S3, adaptive filtering technology and current differential algorithm are used to calculate the fault component differential current and braking current. The logic judgment algorithm is used to determine whether to start the protection action and quickly isolate the fault area:

[0040] S41. Calculate the fault component differential current based on adaptive filtering technology, and select the least mean square (LMS) filtering algorithm according to the characteristics of the distribution network and the fault diagnosis requirements;

[0041] Based on the results of S3, the fault component current I is determined from the current data on both sides of the line. fd1 (n) and I fd2 (n), respectively initialize the adaptive filter, I fd1 (n) The corresponding filter coefficient is ω 1 (0), I fd2 (n) The corresponding filter coefficient is ω 2 (0);

[0042] Adaptive filtering, for I fd1 (n), according to the principle of adaptive filtering, the filter output is:

[0043]

[0044] N 1 is the filter order;

[0045] Calculate the error signal e 1 (n): e 1 (n) = d 1 (n)-y 1 (n); where d 1 (n) is the expected output;

[0046] According to the filter coefficient update formula ω 1 (n+1)=ω 1 (n)+μ 1 e 1 (n)I fd1 (n); where μ 1 Update the filter coefficients for the step factor ω 1 (x).

[0047] After multiple iterations, a relatively accurate filtered fault component current I′ is obtained. fd1 (n);

[0048] Similarly, for I fd2 (n), the adaptive filtering technology is applied to obtain the filtered current data sequence fault component current I′ fd2 (n);

[0049] Calculate the fault component differential current ΔI f :ΔI f =I′ fd1 (n)-I′ fd2 (n);

[0050] S42. Calculate the braking current:

[0051] The rated current I is determined by comprehensively considering the line design parameters and the installed capacity of distributed power sources. n ;

[0052] From the perspective of circuit design, according to the circuit resistance formula Where ρ is the conductor resistivity, l is the line length, S is the conductor cross-sectional area, and the line allowable heating power Pa, according to the formula Pa = In 1 R is derived

[0053] Considering the characteristics of distributed power sources, if the installed capacity is P DG , the power factor is Then the rated output current In of the distributed power supply is 2 for:

[0054]

[0055] U DG is the output voltage of the distributed power supply;

[0056] Finally take I n =max{I n1 ,I n2};

[0057] Braking current I br The empirical braking coefficient k is calculated based on the analysis of the historical fault data of the distribution network, the electrical characteristics of the line, and the operating characteristics of the distributed power source. br =kI n , k is preferably 0.5;

[0058] S43. Determine whether to start the protection action and isolate the fault area, and compare the absolute value of the fault component differential current |ΔI f | and braking current I br ; If ΔIf|>Ibr, it means that the current differential caused by the fault exceeds the set braking threshold, and there is a fault that requires protection action intervention. At this time, the protection action is started to quickly isolate the fault area; if ΔI f |≤I br , it is considered that the current differential condition is within the normal range or the fault is relatively minor, and there is no need to start the protection action.

[0059] S5. Adaptive adjustment and reset: Adaptive adjustment and reset are performed based on the protection action results of S4 to adapt to changes in the operating conditions of the distribution network, and ensure that the system can quickly restore normal power supply after fault processing, thereby improving the self-healing ability and operating efficiency of the distribution network:

[0060] S51. Adaptively adjust line parameters, where the line parameters include line resistance, inductance and capacitance, where:

[0061] Line resistance adjustment: if the protection action is activated, check whether the line is obviously damaged, including broken wires, deformation of wires near short-circuit points, etc., so as to determine the change in line length; for the wire cross-sectional area, if no obvious change is found, keep the original value; if part of the wire is damaged, estimate the reduction ratio of the cross-sectional area according to the actual degree of damage;

[0062] Inductance adjustment: Use magnetic field measuring instruments to measure the magnetic field strength around the fault line and its adjacent lines, and obtain the magnetic field distribution through multi-point measurement. Based on the measurement data and theoretical formula, combined with the line parameters involved in the inductance calculation in S1 and the relative position relationship between adjacent lines, recalculate the line's own inductance L0i and the mutual inductance Mi'j between adjacent lines to obtain the total inductance Li = L0i + Mi'j;

[0063] Capacitor adjustment, detailed inspection of the insulation layer of the faulty line to determine the dielectric loss. If the insulation layer is obviously damaged, measure the ratio of the length of the damaged part to the total length of the line to estimate the tangent value of the dielectric loss angle δ, tanδ. At the same time, re-measure the geometric structure parameters of the line, such as the conductor spacing, insulation layer thickness, etc. According to the formula Recalculate the capacitance value, where C is the original capacitance value, and use the corresponding electric field theory formula to calculate the original capacitance value based on the line geometry and dielectric properties;

[0064] S52. System reset operation, including protection device reset and parameter reinitialization;

[0065] Reset the status of the protection device, including the fault occurrence counter, fault duration counter, etc.; at the same time, reset all flags related to fault judgment, such as the fault trigger flag, protection action execution flag, etc.

[0066] Reinitializing related parameters to return the system to normal operation involves resetting some parameters related to protection decisions, such as braking coefficients, etc. At the same time, the line parameters and distributed power parameters in the integrated parameter management system are updated to reflect the actual status of the line and power after the fault is handled. This ensures that the system can quickly restore normal power supply after the fault is handled, and improves the self-healing ability and operating efficiency of the distribution network.

[0067] In summary, due to the adoption of the above technical solution, the beneficial technical effects of the invention are:

[0068] Adaptability to complex topological structures, accurate topological analysis and parameter setting: In the initialization phase, the topological structure of the distribution network is analyzed in detail, and relevant nodes and line parameters can be accurately identified and recorded regardless of whether it is a complex structure such as radial or ring. By adopting an integrated parameter management system, the line parameters and the installed capacity of distributed power sources can be initialized according to the characteristics of the topological structure and distributed power sources, providing accurate basic data for subsequent protection decisions. This enables the technical solution to adapt to distribution networks with different topological structures, solving the problem of difficulty in judging the location and type of faults in the prior art due to the increased complexity of the topological structure.

[0069] Effectively deal with the impact of topology changes on protection. When a fault occurs, based on accurate topology information and adaptive protection decision algorithms, the fault area can be accurately determined. Even in complex structures such as ring topologies, misjudgment caused by complex fault current paths can be avoided. In a ring topology, traditional methods may fail due to the inability to accurately determine the fault current path, but this solution can accurately identify the fault location and initiate protection actions through in-depth understanding of the topology and adaptive algorithms, quickly isolating the fault area.

[0070] Adaptability to the electrical characteristics of distributed power sources, real-time data collection and fault analysis: Using sensors and real-time data collection technology, the operating status of the distribution network can be captured in real time, including voltage, current, power and other data. By analyzing the collected data, especially when a fault occurs, the positive sequence voltage of each PCC and the fault component output current of the distributed power source can be accurately calculated. This helps to better determine the location and nature of the fault, and overcomes the interference with fault judgment caused by changes in the electrical characteristics of the distributed power source (such as intermittent and fluctuating output) in the existing technology.

[0071] Adaptive protection decision-making takes into account the characteristics of distributed power sources. In the protection decision-making stage, adaptive filtering technology and current differential algorithms are used to dynamically adjust protection parameters according to the real-time operating status of the distribution network. When calculating the fault component differential current and braking current, the output characteristics and topological structure of the distributed power source can be taken into account, and the logic judgment algorithm can be used to accurately determine whether to start the protection action. This avoids false operations caused by sudden changes in the output power of the distributed power source and improves the reliability and accuracy of the protection.

[0072] Improved protection coordination, coordinated actions of different protection devices, through comprehensive consideration of the distribution network topology and distributed power characteristics, this technical solution can coordinate the actions of different protection devices when a fault occurs. In traditional technology, the access of distributed power sources may lead to inconsistent action times between protection devices, or even refusal to act. However, this solution can ensure that the protection device starts the protection action at the right time based on real-time data and adaptive algorithms, quickly isolate the fault area, and avoid the problem of expanding the scope of fault impact due to inconsistent protection.

[0073] Adaptive adjustment and reset ensure system recovery. After the protection action, the line parameters can be adaptively adjusted according to the protection action results to adapt to the changes in the distribution network operating conditions. At the same time, the protection device is reset to ensure that the system can quickly restore normal power supply after the fault is handled. This further improves the operating efficiency and stability of the distribution network, ensures the normal operation of the entire distribution network system, and solves the problem of difficult system recovery caused by uncoordinated protection in the prior art.

[0074] Improve the self-healing ability and operating efficiency of the distribution network, and adaptively adjust line parameters: After fault processing, the line parameters can be adapted to changes in the operating conditions of the distribution network through adaptive adjustment of line resistance, inductance, and capacitance. The resistance value is adjusted according to the actual damage of the line, the inductance value is adjusted according to the changes in the magnetic field environment, and the capacitance value is adjusted according to the condition of the insulation layer. This helps to maintain the normal operation of the distribution network and improve the self-healing ability of the distribution network.

[0075] System reset ensures rapid restoration of power supply: reset the protection device, including resetting the counter and flag, reinitializing the relevant parameters and updating the line parameters and distributed power parameters in the system database. This ensures that the system can quickly restore normal power supply after fault handling, reduces power outage time, and improves the operating efficiency of the distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 A method flow chart of an adaptive current differential protection method for a distribution network including an inverter-type distributed power source;

[0077] Figure 2 Flowchart of the method for initialization and parameter setting;

[0078] Figure 3 A flow chart of the method for data collection;

[0079] Figure 4 A flow chart of the method for fault analysis and current differential calculation;

[0080] Figure 5 Flowchart of methods for protecting decisions and actions;

[0081] Figure 6 The figure is a flow chart of a method for adaptive adjustment and resetting. DETAILED DESCRIPTION

[0082] In order to make the purpose, technical solution and advantages of the invention more clear, the invention is further described in detail below in combination with the embodiments. It should be understood that the specific embodiments described here are only used to explain the invention and are not used to limit the invention.

[0083] like Figure 1 As shown, the adaptive current differential protection method for a distribution network including an inverter-type distributed power source comprises the following steps:

[0084] S1. Initialization and parameter setting: Analyze the topological structure and electrical characteristics of the distribution network, use an integrated parameter management system, initialize line parameters and the installed capacity of distributed power sources, and ensure that all protection devices are powered on normally and complete self-test;

[0085] S2. Data acquisition: Based on the initialization parameters in S1, sensors and real-time data acquisition technology are used to capture the initial moment and response of the fault in real time, providing raw data support for fault analysis;

[0086] S3. Fault analysis and current differential calculation: Fault analysis is performed based on the real-time data collected by S2, and the positive sequence voltage of each PCC and the fault component output current of the distributed power source are calculated to provide a scientific basis for protection decision-making;

[0087] S4. Protection decision and action: Based on the result of S3, adaptive filtering technology and current differential algorithm are used to calculate the fault component differential current and braking current, and a logic judgment algorithm is used to determine whether to start the protection action and quickly isolate the fault area;

[0088] S5. Adaptive adjustment and reset: Adaptive adjustment and reset are performed based on the protection action results of S4 to adapt to changes in the operating conditions of the distribution network, and to ensure that the system can quickly restore normal power supply after fault processing, thereby improving the self-healing ability and operating efficiency of the distribution network.

[0089] like Figure 2 As shown, the S1 includes:

[0090] S11. Analyze the radial topology structure, determine the power node S, start from the power node, and mark each line along the direction of power transmission; the starting node of the i-th line is Si, and the ending node is Ei; record all branch nodes Bij (j represents the j-th branch node) connected to each line and their connection points; if there is a branch node Bi1 on the line from Si to Ei, record the information of other nodes connected to Bi1, as well as the estimated range of relevant electrical parameters of the branch line (such as resistance, inductance, capacitance, etc.);

[0091] For radial topology, in addition to clarifying the line start and end nodes and connection relationships, it is also necessary to analyze the load distribution of each line:

[0092] For the ring topology, take a reference node P as the position and mark each line in clockwise direction (counterclockwise direction can also be selected, which needs to be uniformly specified); the i-th line connects nodes Pi and Pi+1 (when i=n, ​​Pn +1 =P 1 , n is the total number of ring topology lines;

[0093] S12. Combing the topology of the distribution network. Based on the results of S11 analysis, further confirm the accuracy and completeness of the topology: for radial topology, check whether the starting node, ending node, branch node and connection relationship of each line are correctly recorded; for ring topology, check whether the line marking is carried out in the prescribed direction, whether the node connection is accurate, and whether there are any undetected additional branches or connections;

[0094] S13. Calculate the line electrical parameters. For the line resistance Rij, use the formula Where ρ is the conductor resistivity, lij is the line length, Sij is the conductor cross-sectional area; the inductance Lij is calculated by the formula Calculate μ 0 is the vacuum magnetic permeability, Dij is the distance between the two wires, and rij is the wire radius; the capacitance is calculated based on the line geometry and dielectric properties using the corresponding electric field theory formula;

[0095] S14. Parameter management system initialization:

[0096] Input line parameters and distributed power generation installed capacity using the integrated parameter management system; store different line and distributed power generation parameters in corresponding data tables in the system database;

[0097] The protection device performs a power-on self-test. After the protection device is powered on, it checks the internal circuit connection; detects the resistance value between key nodes, and if it is not within the normal range, an alarm is issued; checks the chip working status, reads the chip internal register value, and if it is abnormal, determines that the chip is faulty.

[0098] like Figure 3 As shown, the S2 includes:

[0099] S21. Sensor layout: According to the topology and the electrical quantities to be monitored, the sensors should be arranged reasonably. Voltage sensors and current sensors should be placed at the starting and ending nodes of each line to measure the voltage and current at both ends of the line. Power sensors should be placed at the output ports of the distributed power sources to measure their output power. Temperature sensors should be placed near the conductors to measure the line temperature, so as to more accurately calculate the line resistance.

[0100] S22. Real-time data acquisition, using real-time data acquisition technology, collect sensor data at a certain sampling frequency, including: sampling frequency, voltage data sequence, current data sequence, power data sequence, etc., and the sampling frequency should be at least twice the highest frequency of the signal.

[0101] like Figure 4 As shown, the S3 includes:

[0102] S31. Obtain the three-phase voltages Ua, Ub, and Uc from the data collected by S2, and calculate the positive sequence voltage U according to the symmetrical component method. 1PCC :

[0103]

[0104] Where a is a complex number, and its real part is The imaginary part is

[0105]

[0106] therefore,

[0107] S32. Calculate the fault component output current of the distributed power source:

[0108] The normal output current I of the distributed power supply can be obtained by analyzing the collected real-time data. f (n) and the output current I′ after the fault f (n), n is the sampling point number; analyze the sudden changes of voltage, current and other data in the collected real-time data to determine the time period when the fault occurs. If the voltage suddenly drops and the current fluctuates abnormally, then the time period is judged to be the fault period;

[0109] Extract the current data sequence during the fault period. If the fault current data is relatively stable, directly use its mean as the estimated value of the output current after the fault, that is, in is the mean value of the current data during the fault period;

[0110] If the fault current data fluctuates greatly, weighted moving average filtering is used to smooth the fault current data. The filtered current value I f (k) is expressed as:

[0111]

[0112] Wherein, N is the filter window size; k is the value of the sampling point; ωi is the weighting coefficient, and different weights are set according to needs, such as a larger weight close to the current sampling point and a smaller weight far from the current sampling point; I(i) represents the current value for the i-th sampling point;

[0113] Then the fault component output current I fd (n) is:

[0114] I fd (n) = I′ f (n)-I f (n).

[0115] like Figure 5 As shown, the S4 includes:

[0116] S41. Calculate the fault component differential current based on adaptive filtering technology, and select the least mean square (LMS) filtering algorithm according to the characteristics of the distribution network and the fault diagnosis requirements;

[0117] Based on the results of S3, the fault component current I is determined from the current data on both sides of the line. fd1 (n) and I fd2 (n), respectively initialize the adaptive filter, I fd1 (n) The corresponding filter coefficient is ω 1 (0), I fd2 (n) The corresponding filter coefficient is ω 2 (0);

[0118] Adaptive filtering, for I fd1 (n), according to the principle of adaptive filtering, the filter output is:

[0119]

[0120] N 1 is the filter order;

[0121] Calculate the error signal e 1 (n): e 1 (n) = d 1 (n)-y 1 (n); where d 1 (n) is the expected output;

[0122] According to the filter coefficient update formula ω1 (n+1)=ω 1 (n)+μ 1 e 1 (n)I fd1 (n); where μ 1 Update the filter coefficients for the step factor ω 1 (x).

[0123] After multiple iterations, a relatively accurate filtered fault component current I′ is obtained. fd1 (n);

[0124] Similarly, for I fd2 (n), the adaptive filtering technology is applied to obtain the filtered current data sequence fault component current I′ fd2 (n);

[0125] Calculate the fault component differential current ΔI f :ΔI f =I′ fd1 (n)-I′ fd2 (n);

[0126] S42. Calculate the braking current:

[0127] The rated current I is determined by comprehensively considering the line design parameters and the installed capacity of distributed power sources. n ;

[0128] From the perspective of circuit design, according to the circuit resistance formula Where ρ is the conductor resistivity, l is the line length, S is the conductor cross-sectional area, and the line allowable heating power Pa, according to the formula Pa = In 1 R is derived

[0129] Considering the characteristics of distributed power sources, if the installed capacity is P DG , the power factor is Then the rated output current In of the distributed power supply is 2 for:

[0130]

[0131] U DG is the output voltage of the distributed power supply;

[0132] Finally take I n =max{I n1 ,I n2};

[0133] Braking current I brThe empirical braking coefficient k is calculated based on the analysis of the historical fault data of the distribution network, the electrical characteristics of the line, and the operating characteristics of the distributed power source. br =kI n , k is preferably 0.5;

[0134] S43. Determine whether to start the protection action and isolate the fault area, and compare the absolute value of the fault component differential current ΔI f and braking current I br ; If ΔI f |>I br , it means that the current differential caused by the fault exceeds the set braking threshold, and there is a fault that requires protection action intervention. At this time, the protection action is started to quickly isolate the fault area; if ΔIf|≤Ibr, it is considered that the current differential situation is within the normal range or the fault is relatively minor, and there is no need to start the protection action.

[0135] like Figure 6 As shown, the S5 includes:

[0136] S51. Adaptively adjust line parameters, where the line parameters include line resistance, inductance and capacitance, where:

[0137] Line resistance adjustment: if the protection action is activated, check whether the line is obviously damaged, including broken wires, deformation of wires near short-circuit points, etc., so as to determine the change in line length; for the wire cross-sectional area, if no obvious change is found, keep the original value; if part of the wire is damaged, estimate the reduction ratio of the cross-sectional area according to the actual degree of damage;

[0138] Inductance adjustment: Use magnetic field measuring instruments to measure the magnetic field strength around the fault line and its adjacent lines, and obtain the magnetic field distribution through multi-point measurement. Based on the measurement data and theoretical formula, combined with the line parameters involved in the inductance calculation in S1 (such as the distance between the two wires, the wire radius, etc.) and the relative position relationship between adjacent lines, recalculate the line's own inductance L0i and the mutual inductance Mi'j between adjacent lines to obtain the total inductance Li = L0i + Mi'j;

[0139] Capacitor adjustment, detailed inspection of the insulation layer of the faulty line to determine the dielectric loss. If the insulation layer is obviously damaged, measure the ratio of the length of the damaged part to the total length of the line to estimate the tangent value of the dielectric loss angle δ, tanδ. At the same time, re-measure the geometric structure parameters of the line, such as the conductor spacing, insulation layer thickness, etc. According to the formula Recalculate the capacitance value, where C is the original capacitance value, and use the corresponding electric field theory formula to calculate the original capacitance value based on the line geometry and dielectric properties;

[0140] S52. System reset operation, including protection device reset and parameter reinitialization;

[0141] Reset the status of the protection device, including the fault occurrence counter, fault duration counter, etc.; reset all flags related to fault judgment, such as the fault trigger flag, protection action execution flag, etc. For example, if the protection device records the number of faults and the type of fault during the fault handling process, these records will be cleared during the reset so that the new fault situation can be accurately recorded during the next normal operation.

[0142] Use professional testing equipment to conduct a comprehensive inspection of the internal circuit connections of the protection device, focusing on the connection between nodes and components that may be subject to large current shocks during the protection action. For the resistance value between key nodes, if the measured value deviates from the normal range by more than the set threshold, clean, tighten or replace components at the connection point to ensure that the resistance value returns to normal. Read the internal register value of the chip. If an abnormality is found, perform a reset operation according to the chip operation manual, such as clearing specific register bits or writing default values.

[0143] Parameter reinitialization

[0144] Reinitializing related parameters to return the system to normal operation involves resetting some parameters related to protection decisions, such as braking coefficients, etc. At the same time, the line parameters and distributed power parameters in the integrated parameter management system are updated to reflect the actual status of the line and power after the fault is handled. This ensures that the system can quickly restore normal power supply after the fault is handled, and improves the self-healing ability and operating efficiency of the distribution network.

[0145] The original line parameters and distributed power supply parameter records are obtained from the integrated parameter management system, and the recalculated line resistance, inductance, capacitance values ​​and related parameters of the distributed power supply in the current state (such as output current, power factor, etc.) are updated to the corresponding positions in the system database.

[0146] Check the various conditions required for system startup in turn, including whether the power supply voltage is within the normal range, whether the sensor can collect data normally (which can be determined by sending a test signal and checking whether the returned data is correct), etc. If any condition is found to be unsatisfactory, repair or adjust the corresponding equipment until the system can start and run normally, ensuring that the system can quickly restore normal power supply after fault handling, and improving the self-healing ability and operating efficiency of the distribution network.

[0147] The above description is a preferred embodiment of the invention and is not intended to limit the invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the invention should be included in the protection scope of the invention.

Claims

1. A method for adaptive current differential protection of a distribution network containing an inverter-type distributed power supply, comprising the following steps: S1. Initialization and parameter setting: Analyze the topological structure and electrical characteristics of the distribution network, use an integrated parameter management system, initialize line parameters and the installed capacity of distributed power sources, and ensure that all protection devices are powered on normally and complete self-test; S2. Data acquisition: Based on the initialization parameters in S1, sensors and real-time data acquisition technology are used to capture the initial moment and response of the fault in real time, providing raw data support for fault analysis; S3. Fault analysis and current differential calculation: Fault analysis is performed based on the real-time data collected by S2, and the positive sequence voltage of each PCC and the fault component output current of the distributed power source are calculated to provide a scientific basis for protection decision-making; S4. Protection decision and action: Based on the result of S3, adaptive filtering technology and current differential algorithm are used to calculate the fault component differential current and braking current, and a logic judgment algorithm is used to determine whether to start the protection action and quickly isolate the fault area; S5. Adaptive adjustment and reset: Adaptive adjustment and reset are performed based on the protection action results of S4 to adapt to changes in the operating conditions of the distribution network, and to ensure that the system can quickly restore normal power supply after fault processing, thereby improving the self-healing ability and operating efficiency of the distribution network.

2. According to the method for adaptive current differential protection of a distribution network containing an inverter-type distributed power source in claim 1, said S1 comprises: S11. Analyze the radial topology structure, determine the power node S, and mark each line starting from the power node along the direction of power transmission; The starting node of the i-th line is Si, and the ending node is Ei; record all branch nodes Bij connected to each line, where j represents the j-th branch node and its connection; If there is a branch node Bi1 on the line from Si to Ei, then record the information of other nodes connected to Bi1 and the estimated range of relevant electrical parameters of the branch line; For radial topology, in addition to clarifying the line start and end nodes and connection relationships, it is also necessary to analyze the load distribution of each line: For a ring topology, take a certain reference node P1 as the starting point and mark each line in a clockwise direction; S12. Combing the topology of the distribution network. Based on the results of S11 analysis, further confirm the accuracy and completeness of the topology: for radial topology, check whether the starting node, ending node, branch node and connection relationship of each line are correctly recorded; for ring topology, check whether the line marking is carried out in the prescribed direction, whether the node connection is accurate, and whether there are any undetected additional branches or connections; S13. Calculate the line electrical parameters. For the line resistance Rij, use the formula Where ρ is the conductor resistivity, lij is the line length, and Sij is the conductor cross-sectional area; The inductance Lij is calculated by the formula Calculation, μ0 is the vacuum magnetic permeability, Dij is the distance between the two wires, rij is the wire radius; the capacitance is calculated based on the line geometry and dielectric properties using the corresponding electric field theory formula; S14. Initialization of parameter management system, Input line parameters and distributed power generation installed capacity using the integrated parameter management system; store different line and distributed power generation parameters in corresponding data tables in the system database; The protection device performs a power-on self-test. After the protection device is powered on, it checks the internal circuit connection; detects the resistance value between key nodes, and if it is not within the normal range, an alarm is issued; checks the chip working status, reads the chip internal register value, and if it is abnormal, determines that the chip is faulty.

3. According to the method for adaptive current differential protection of a distribution network containing an inverter-type distributed power source in claim 1, S2 comprises: S21. Sensor arrangement: according to the topological structure and the electrical quantity to be monitored, voltage sensors and current sensors are placed at the starting and ending nodes of each line to measure the voltage and current at both ends of the line; power sensors are placed at the output ports of the distributed power source to measure its output power; Place temperature sensors near the conductors to measure line temperature and more accurately calculate line resistance; S22. Real-time data acquisition, using real-time data acquisition technology, collect sensor data at a certain sampling frequency, including: sampling frequency, voltage data sequence, current data sequence and power data sequence, and the sampling frequency should be at least twice the highest frequency of the signal.

4. According to the method for adaptive current differential protection of a distribution network containing an inverter-type distributed power source in claim 1, said S3 comprises: S31. Obtain the three-phase voltages Ua, Ub, and Uc from the data collected by S2, and calculate the positive sequence voltage U according to the symmetrical component method. 1PCC : Where a is a complex number, and its real part is The imaginary part is therefore, S32. Calculate the fault component output current of the distributed power source: The normal output current I of the distributed power supply can be obtained by analyzing the collected real-time data. f (n) and the output current I′ after the fault f (n), n is the sampling point number; analyze the sudden changes of voltage and current data in the collected real-time data to determine the time period when the fault occurs. If the voltage suddenly drops and the current fluctuates abnormally, then the time period is judged to be the fault period; Extract the current data sequence during the fault period. If the fault current data is relatively stable, directly use its mean as the estimated value of the output current after the fault, that is, in is the mean value of the current data during the fault period; If the fault current data fluctuates greatly, weighted moving average filtering is used to smooth the fault current data. The filtered current value I f (k) is expressed as: Wherein, N is the filter window size; k is the value of the sampling point; ωi is the weighting coefficient, and different weights are set according to needs, such as the weight close to the current sampling point is larger, and the weight far away from the current sampling point is smaller; I(i) represents the current value for the i-th sampling point; Then the fault component output current I fd (n) is: I fd (n)=I′ f (n)-I f (n)。 5. According to the method for adaptive current differential protection of a distribution network containing an inverter-type distributed power source in claim 1, said S4 comprises: S41. Calculate the fault component differential current based on adaptive filtering technology, and select the least mean square (LMS) filtering algorithm according to the characteristics of the distribution network and the fault diagnosis requirements; Based on the results of S3, the fault component current I is determined from the current data on both sides of the line. fd1 (n) and I fd2 (n), respectively initialize the adaptive filter, I fd1 (n) The corresponding filter coefficient is ω1(0), I fd2 (n) The corresponding filter coefficient is ω2(0); Adaptive filtering, for I fd1 (n), according to the principle of adaptive filtering, the filter output is: N1 is the filter order; Calculate the error signal e1(n): e1(n)=d1(n)-y1(n); where d1(n) is the desired output; According to the filter coefficient update formula ω1(n+1)=ω1(n)+μ1e1(n)I fd1 (n); where μ1 is the step factor to update the filter coefficient ω1(x); After multiple iterations, a relatively accurate filtered fault component current I′ is obtained. fd1 (n); Similarly, for I fd2 (n), the adaptive filtering technology is applied to obtain the filtered current data sequence fault component current I′ fd2 (n); Calculate the fault component differential current ΔI f :ΔI f =I′ fd1 (n)-I′ fd2 (n); S42. Calculate the braking current and determine the rated current I by comprehensively considering the line design parameters and the installed capacity information of the distributed power generation. n ; From the perspective of circuit design, according to the circuit resistance formula Where ρ is the conductor resistivity, l is the line length, S is the conductor cross-sectional area, and the allowable heating power of the line Pa is derived from the formula Pa = In1R Considering the characteristics of distributed power sources, if the installed capacity is P DG , the power factor is Then the rated output current In2 of the distributed power supply is: U DG is the output voltage of the distributed power supply; Finally, take In=max{In1,In2}; The braking current Ibr is calculated based on the analysis of the historical fault data of the distribution network, the electrical characteristics of the line and the operating characteristics of the distributed power source to obtain the empirical braking coefficient k, Ibr = kIn; S43. Determine whether to start the protection action and isolate the fault area, and compare the absolute value of the fault component differential current ΔI f and braking current Ibr; if ΔIf|>Ibr, it means that the current differential caused by the fault exceeds the set braking threshold, and there is a fault that requires protection action intervention. At this time, the protection action is started to quickly isolate the fault area; if ΔIf|≤Ibr, it is considered that the current differential situation is within the normal range or the fault is relatively minor, and there is no need to start the protection action.

6. According to the method for adaptive current differential protection of a distribution network containing an inverter-type distributed power source in claim 1, said S5 comprises: S51. Adaptively adjust line parameters, where the line parameters include line resistance, inductance and capacitance; Line resistance adjustment: if the protection action is activated, check whether the line is obviously damaged, including wire breakage and deformation of the wire near the short-circuit point, so as to determine the change in line length; for the wire cross-sectional area, if no obvious change is found, keep the original value; if part of the wire is damaged, estimate the reduction ratio of the cross-sectional area according to the actual degree of damage; Inductance adjustment: Use magnetic field measuring instruments to measure the magnetic field strength around the faulty line and its adjacent lines, and obtain the magnetic field distribution through multi-point measurement; Based on the measurement data and theoretical formula, combined with the line parameters involved in the inductance calculation in S1 and the relative position relationship between adjacent lines, recalculate the line's own inductance L0i and the mutual inductance Mi′j between adjacent lines to obtain the total inductance Li=L0i+Mi′j; Capacitor adjustment, detailed inspection of the insulation layer of the faulty line to determine the dielectric loss. If the insulation layer is obviously damaged, measure the ratio of the length of the damaged part to the total length of the line, and estimate the tangent value tanδ of the dielectric loss angle δ. At the same time, re-measure the geometric structure parameters of the line, such as the conductor spacing and the thickness of the insulation layer. According to the formula Recalculate the capacitance value, where C is the original capacitance value, and use the corresponding electric field theory formula to calculate the original capacitance value based on the line geometry and dielectric properties; S52. System reset operation, including protection device reset and parameter reinitialization; Reset the status of the protection device, including the fault occurrence counter and fault duration counter; at the same time, reset all flags related to fault judgment, such as the fault trigger flag and the protection action execution flag; Parameter reinitialization, reinitialize relevant parameters to return the system to normal operation, reset some parameters related to protection decisions, such as braking coefficient; at the same time, update the line parameters and distributed power parameters in the integrated parameter management system to reflect the actual status of the line and power supply after fault processing, ensure that the system can quickly restore normal power supply after fault processing, and improve the self-healing ability and operation efficiency of the distribution network.

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