Parameter determination method, system and device for distribution network branch line

Abstract

The invention discloses a parameter determination method, system and device for a distribution network branch line, and relates to the field of distribution network calculation, and the method comprises the steps: converting the actual head-end zero-sequence voltage and the actual tail-end zero-sequence voltage of a to-be-detected line at the next moment of the moment when the to-be-detected line breaks down into a sine function of which the amplitude is a time function; determining a calculation head end zero-sequence voltage and a calculation head end zero-sequence current; judging whether the difference between the calculated head-end zero-sequence voltage and the actual head-end zero-sequence voltage meets the precision requirement or not; if the precision requirement is not met, the amplitude of the time function is modified; and if the precision requirement is met, outputting and calculating the zero-sequence current of the head end. When the circuit breaks down, the current of the fault line as the head end cannot be measured, so that the sine function which converts the voltage and the current into the sine function of which the amplitude is a time function is used, the calculated voltage is consistent with the known voltage by modifying the amplitude of the sine function, and then the unknown current can be obtained through calculation.

Description

Technical Field

[0001] The present invention relates to the field of distribution network calculation, and particularly to a method, a system and a device for determining parameters of a distribution network branch line. Background Art

[0002] Currently, due to factors such as investment costs, the parameters of distribution network branch lines cannot be fully obtained, and complete current and voltage data are required for distribution network fault handling and analysis, which is also an obstacle to the wide application of distribution network fault handling and analysis. In the actual operation of the distribution network, the measurement of zero-sequence voltage and phase voltage usually relies on voltage transformers. However, due to the high installation cost and complex layout of voltage transformers, it is impossible to install voltage transformers in every section of the distribution network. The existence of such a scenario of missing measurement data severely restricts the practical application of the precise positioning method based on time-domain fault analysis, especially in the T-shaped branch distribution network. Summary of the Invention

[0003] The purpose of the present invention is to provide a method, a system and a device for determining parameters of a distribution network branch line, which can make the calculated voltage consistent with the known voltage by modifying the amplitude of the sine function, and then the unknown current can be obtained through calculation.

[0004] To solve the above technical problems, the present invention provides a method for determining parameters of a distribution network branch line, including:

[0005] Obtaining the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage of the line to be measured at the next moment after the moment when the line to be measured fails;

[0006] Converting the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage into sine functions with amplitudes as functions of time, and the corresponding relationship between the amplitudes and the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage is relevant;

[0007] Determining the calculated initial zero-sequence voltage and the calculated initial zero-sequence current according to the line distribution characteristics, the converted actual terminal zero-sequence voltage and the converted actual terminal zero-sequence current;

[0008] Judging whether the difference between the calculated initial zero-sequence voltage and the actual initial zero-sequence voltage meets the accuracy requirement;

[0009] If the accuracy requirement is not met, modifying the amplitude of the time function and returning to the step of converting the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage into sine functions with amplitudes as functions of time;

[0010] If the accuracy requirement is met, outputting the calculated initial zero-sequence current.

[0011] On the other hand, determining the calculated initial zero-sequence voltage and the calculated initial zero-sequence current based on the line distribution characteristics, the converted actual terminal zero-sequence voltage, and the converted actual terminal zero-sequence current includes:

[0012] Determining the calculated initial zero-sequence voltage and the calculated initial zero-sequence current based on the line distribution characteristics, the converted actual terminal zero-sequence voltage, and the converted actual terminal zero-sequence current. The expression for the calculated initial zero-sequence voltage is:

[0013] ;

[0014] The expression for the calculated initial zero-sequence current is:

[0015] ;

[0016] Where, is the calculated initial zero-sequence voltage at time t, is the actual initial zero-sequence voltage at time t, R is the resistance per unit length of the faulty line, l is the length of the faulty line, is the calculated initial zero-sequence current at time t, L is the inductance per unit length of the faulty line, is the derivative of, is the voltage parameter function, is the current parameter function, and j is the j-th sampling point.

[0017] On the other hand, the expression for the voltage parameter function is:

[0018] ;

[0019] The expression for the current parameter function is:

[0020] ;

[0021] Where, is the 2j-th power of the line length, is the probability of selecting i sampling points from j sampling points, is the i-th power of the resistance per unit length, is the (j - i)-th power of the inductance per unit length, is the j-th power of the capacitance per unit length, is the (2j - i)-th derivative of the terminal zero-sequence voltage at time t, is the j-th power of the conductance per unit length, is the (2j - i - 1)-th derivative of the terminal zero-sequence voltage at time t, is the (2j + 1)-th power of the line length, is the probability of selecting \(i\) sampling points from \(j + 1\) sampling points, is the \((j - i+1)\) - th power of the inductance per unit length, is the \((2j - i + 1)\) - th derivative of the zero - sequence current at the end at time \(t\), is the \((2j - i)\) - th derivative of the zero - sequence current at the end at time \(t\), is the \((2j - 1)\) - th power of the line length, is the probability of selecting \(i\) sampling points from \(j - 1\) sampling points, is the \((j - i - 1)\) - th power of the inductance per unit length, is the \((2j - i - 1)\) - th derivative of the zero - sequence voltage at the end at time \(t\), is the \((2j - i - 2)\) - th derivative of the zero - sequence voltage at the end at time \(t\), is the \((2j - i)\) - th derivative of the zero - sequence current at the end at time \(t\), is the \((2j - i - 1)\) - th derivative of the zero - sequence current at the end at time \(t\).

[0022] On the other hand, judging whether the difference between the calculated zero - sequence voltage at the head end and the actual zero - sequence voltage at the head end meets the accuracy requirement includes:

[0023] Determine the error between the calculated zero - sequence voltage at the head end and the actual zero - sequence voltage at the head end. The expression of the error is:

[0024] ;

[0025] where \(e\) is the error, is the calculated zero - sequence voltage at the head end at time \(t\), is the actual zero - sequence voltage at the head end at time \(t\), \(j\) is the \(j\) - th sampling point, and there are \(m\) sampling points in total;

[0026] When the error is less than the preset error threshold, it is determined that the difference between the calculated zero - sequence voltage at the head end and the actual zero - sequence voltage at the head end meets the accuracy requirement.

[0027] On the other hand, obtaining the actual zero - sequence voltage at the head end and the actual zero - sequence voltage at the end of the line to be measured at the next moment when the line to be measured fails includes:

[0028] Starting from the next moment of the moment when the fault occurs, obtain multiple actual zero - sequence voltages at the head end and multiple actual zero - sequence voltages at the end of the line to be measured;

[0029] Converting the actual zero - sequence voltage at the head end and the actual zero - sequence voltage at the end into a sine function with the amplitude as a function of time includes:

[0030] Fitting multiple actual zero - sequence voltages at the head end and multiple actual zero - sequence voltages at the end into a sine function with the amplitude as a function of time.

[0031] On the other hand, converting the actual head zero-sequence voltage and the actual tail zero-sequence voltage into sine functions with amplitudes as functions of time includes:

[0032] Converting the actual head zero-sequence voltage and the actual tail zero-sequence voltage into sine functions with amplitudes as functions of time, and the expression of the actual head zero-sequence voltage is:

[0033] ;

[0034] The expression of the actual tail zero-sequence voltage is:

[0035] ;

[0036] Wherein, is the actual head zero-sequence voltage at time t, is the constant term of the amplitude of the cosine function of is the undetermined constant of the q-th order term of the fitting function order of is the q-th power of time, is the constant term of the amplitude of the sine function of is the Hilbert transform of , K is the maximum value of the fitting order, is the actual tail zero-sequence voltage at time t, is the constant term of the amplitude of the cosine function of is the undetermined constant of the q-th order term of the fitting function order of is the constant term of the amplitude of the sine function of .

[0037] On the other hand, the process of setting the initial value of the amplitude includes:

[0038] Determining a constant value according to the corresponding relationship between the actual head zero-sequence voltage and the actual tail zero-sequence voltage, and the expression of the corresponding relationship is ;

[0039] Determining the initial value of the amplitude at the 0th iteration according to the constant value, and the initial value of the amplitude is:

[0040] ;

[0041] Wherein, n is a set constant, is the 0th iteration of , is the 0th iteration of , For the 0th iteration of the undetermined constant of the 0th order term of the fitting function of For the undetermined constant of the 0th order term of the fitting function of For the 0th iteration of the undetermined constant of the 1st order term of the fitting function of For the undetermined constant of the 1st order term of the fitting function of For the 0th iteration of the undetermined constant of the Kth order term of the fitting function of For the undetermined constant of the Kth order term of the fitting function of

[0042] On the other hand, if the accuracy requirement is not met, modify the amplitude of the time function, including:

[0043] If the accuracy requirement is not met, iterate the amplitude of the time function using an iteration function, and the expression of the iteration function is:

[0044] ;

[0045] Wherein, is the (x + 1)th iteration of is the xth iteration of is the (x + 1)th iteration of is the xth iteration of is the (x + 1)th iteration of the undetermined constant of the 0th order term of the fitting function of is the xth iteration of the undetermined constant of the 0th order term of the fitting function of is the (x + 1)th iteration of the undetermined constant of the 1st order term of the fitting function of is the xth iteration of the undetermined constant of the 1st order term of the fitting function of is the (x + 1)th iteration of the undetermined constant of the Kth order term of the fitting function of is the xth iteration of the undetermined constant of the Kth order term of the fitting function of is the convergence factor.

[0046] To solve the above technical problems, the present invention also provides a parameter determination system for a distribution network branch line, including:

[0047] An actual data acquisition unit, configured to acquire the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end of a to-be-tested line at the next moment after the moment when the to-be-tested line fails.

[0048] A conversion unit, configured to convert the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end into a sine function with an amplitude being a function of time, where the correspondence between the amplitude and the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end is relevant.

[0049] A calculation data unit, configured to determine a calculated zero-sequence voltage at the head end and a calculated zero-sequence current at the head end according to the line distribution characteristics, the converted actual zero-sequence voltage at the tail end, and the converted actual zero-sequence current at the tail end.

[0050] An accuracy judgment unit, configured to judge whether the difference between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end meets the accuracy requirement; if not, trigger a modification unit; if so, trigger an output unit.

[0051] A modification unit, configured to modify the amplitude of the time function and trigger the conversion unit.

[0052] An output unit, configured to output the calculated zero-sequence current at the head end.

[0053] To solve the above technical problems, the present invention further provides a parameter determination device for a distribution network branch line, including:

[0054] A memory, configured to store a computer program.

[0055] A processor, configured to implement the steps of the above parameter determination method for the distribution network branch line when executing the computer program.

[0056] The present invention discloses a parameter determination method, system and device for a distribution network branch line, relating to the field of distribution network calculation. The actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end of a to-be-tested line at the next moment after the moment when the to-be-tested line fails are converted into a sine function with an amplitude being a function of time; a calculated zero-sequence voltage at the head end and a calculated zero-sequence current at the head end are determined; it is judged whether the difference between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end meets the accuracy requirement; if the accuracy requirement is not met, the amplitude of the time function is modified; if the accuracy requirement is met, the calculated zero-sequence current at the head end is output. When a circuit fails, since the current at the head end of the faulty line cannot be measured, the voltage and current are converted into a sine function with an amplitude being a function of time, and by modifying the amplitude of the sine function, the calculated voltage is made consistent with the known voltage, and then the unknown current can be obtained through calculation. Description of the Drawings

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings required in the prior art and the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0058] Figure 1 Flowchart of a method for determining parameters of a distribution network branch line provided by the present invention;

[0059] Figure 2 Schematic diagram of a line without branches and faults provided by the present invention;

[0060] Figure 3 Schematic diagram of a T-shaped branch line with a fault provided by the present invention;

[0061] Figure 4 Equivalent circuit diagram of a T-shaped branch line with a fault provided by the present invention;

[0062] Figure 5 Flowchart of another method for determining parameters of a distribution network branch line provided by the present invention;

[0063] Figure 6 Schematic diagram of the structure of a system for determining parameters of a distribution network branch line provided by the present invention;

[0064] Figure 7 Schematic diagram of the structure of a device for determining parameters of a distribution network branch line provided by the present invention. Detailed implementation manners

[0065] The core of the present invention is to provide a method, a system and a device for determining parameters of a distribution network branch line. By modifying the amplitude of the sine function, the calculated voltage is made consistent with the known voltage, and then the unknown current can be obtained through calculation.

[0066] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0067] Figure 1 Flowchart of a method for determining parameters of a distribution network branch line provided by the present invention. The method for determining parameters of the distribution network branch line includes:

[0068] S11: Obtain the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end of the line to be measured at the next moment after the moment when the line to be measured fails.

[0069] S12: Convert the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end into sine functions with amplitudes as functions of time, where the correspondence between the amplitudes and the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end is relevant.

[0070] Starting from the next moment after the fault moment, take multiple data points to fit the zero-sequence voltage at the head end and the zero-sequence voltage at the tail end into sine functions with amplitudes and initial phases both as functions of time. By approximating the sine function model parameters to make them meet the condition that the calculated voltage is consistent with the known voltage, the method has calculation certainty, and the calculation results are more intuitive and reliable, and it also creates conditions for calculating the voltage and current along the line through the distributed parameter model later.

[0071] Setting the initial value of the tail-end voltage according to the characteristic that the zero-sequence voltage waveforms of the entire distribution network are the same can more effectively approximate the true value. That is, there is a fixed ratio relationship between the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end, and the amplitude can be obtained through this ratio relationship.

[0072] It should be noted that the amplitude can be adjusted, and by adjusting the amplitude, the sine function can be made closer to the actual data.

[0073] S13: Determine the calculated zero-sequence voltage at the head end and the calculated zero-sequence current at the head end according to the line distribution characteristics, the converted actual zero-sequence voltage at the tail end, and the converted actual zero-sequence current at the tail end.

[0074] The distributed parameter model for infinite micro-element cascading of distribution network lines is derived based on unbranched lines and has been successfully applied to the transmission network. The distributed parameter model of infinite micro-element cascading uses the idea of electrical network and equivalent the power line as a line composed of infinite micro-elements in cascade. On an unbranched and fault-free line, when the head-end voltage and current and the line parameters are known, the voltage and current at each point along the line can be calculated based on the line distribution characteristics.

[0075] S14: Determine whether the difference between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end meets the accuracy requirement; if not, go to step S15; if so, go to step S16.

[0076] S15: Modify the amplitude of the time function and return to step S12.

[0077] S16: Output the calculated zero-sequence current at the head end.

[0078] If the difference between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end meets the accuracy requirements, it indicates that the amplitude setting is appropriate, and the calculated zero-sequence current at the head end can be directly calculated based on the sine function. If it does not meet the accuracy requirements, it indicates that there is a certain problem with the amplitude setting and needs to be adjusted before calculation.

[0079] The present invention discloses a method, system and device for determining parameters of a distribution network branch line, which relates to the field of distribution network calculation. The actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the tail end of the line to be measured at the next moment when a fault occurs in the line to be measured are converted into sine functions with amplitudes as functions of time; the calculated zero-sequence voltage at the head end and the calculated zero-sequence current at the head end are determined; it is judged whether the difference between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end meets the accuracy requirements; if the accuracy requirements are not met, the amplitude of the time function is modified; if the accuracy requirements are met, the calculated zero-sequence current at the head end is output. When a fault occurs in the circuit, since the current of the faulty line as the head end cannot be measured, the voltage and current are converted into sine functions with amplitudes as functions of time, and by modifying the amplitude of the sine function, the calculated voltage is made consistent with the known voltage, and then the unknown current can be calculated through calculation.

[0080] Based on the above embodiments:

[0081] Figure 2 Schematic diagram of a branchless and fault-free line provided by the present invention;

[0082] Figure 3 Schematic diagram of a T-shaped branch and faulty line provided by the present invention;

[0083] In some embodiments, determining the calculated zero-sequence voltage at the head end and the calculated zero-sequence current at the head end according to the line distribution characteristics, the converted actual zero-sequence voltage at the tail end and the converted actual zero-sequence current at the tail end includes:

[0084] Determining the calculated zero-sequence voltage at the head end and the calculated zero-sequence current at the head end according to the line distribution characteristics, the converted actual zero-sequence voltage at the tail end and the converted actual zero-sequence current at the tail end, the expression of the calculated zero-sequence voltage at the head end is:

[0085] ;

[0086] The expression of the calculated zero-sequence current at the head end is:

[0087] ;

[0088] Wherein, is the calculated zero-sequence voltage at the head end at time t, is the actual zero-sequence voltage at the head end at time t, R is the resistance per unit length of the faulty line, l is the length of the faulty line, is the calculated zero-sequence current at the head end at time t, and L is the inductance per unit length of the faulty line. is the derivative of a voltage parameter function, is a current parameter function, and j is the j-th sampling point.

[0089] Currently, the distributed parameter model of infinite micro-element cascading for distribution network lines is derived based on unbranched lines and has been successfully applied to the transmission network. The distributed parameter model of infinite micro-element cascading uses the idea of electrical network and equivalent the power line as a line composed of infinite micro-elements in cascade. On an unbranched and fault-free line, when the head-end voltage and current and the line parameters are known, the voltage and current at each point along the line can be calculated based on this model. Its model is as Figure 2 shown.

[0090] In the T-shaped branch distribution network as Figure 3 shown, analyzing the zero-sequence electrical quantities, when a single-phase grounding fault occurs in section MN, the zero-sequence current at the head end of this section can be directly measured, the head-end voltage can be obtained from the substation, and the end current can be zero. At this time, when the fault distance is known, the current on the left side of the fault point and the fault point voltage can be calculated using the voltage and current at the head end of section MN through the distributed parameter line model of infinite micro-element cascading. However, due to the lack of measurement data of the end voltage, the zero-sequence current on the right side of the fault point cannot be calculated by the original method. At this time, for the section between the fault point f and the end N, there is a situation where only the zero voltage at the head end of the section and the end current are known.

[0091] Therefore, a calculation method for the parameters of the distribution network branch line with known head-end voltage and end current is adopted. This method uses the known head-end voltage and the assumed current (the first calculation is given by the initial current), calculates the end current according to the distributed parameter circuit model of the line, and then expresses the head-end current of the line through the first derivative of the end current and the voltages of each micro-element, and adjusts the head-end current to make the calculated end current approach the known end current.

[0092] The present invention utilizes a line distributed parameter circuit model, which is far more accurate than the existing comparison calculation models; from the known current end, an initial voltage value is given (in accordance with the characteristic that the zero-sequence voltage waveforms of the entire distribution network are the same); according to the line distributed parameter circuit model, the voltage and current at the head end are calculated from the known current end, and the voltage at the known current end is adjusted so that the calculated head-end voltage is consistent with the known voltage. At this time, the calculated current is the head-end current that needs to be completed. For transient current and voltage data, the present invention, based on the sine representation method of instantaneous signals, fits the transient current and voltage data at both ends into sine functions with amplitudes and initial phases as functions of time, and by approximating the sine function model parameters, makes it satisfy the condition that the calculated voltage is consistent with the known voltage, and its method has calculation certainty.

[0093] In some embodiments, the expression of the voltage parameter function is:

[0094] ;

[0095] The expression of the current parameter function is:

[0096] ;

[0097] Wherein, is the 2j-th power of the line length, is the probability of selecting i sampling points from j sampling points, is the i-th power of the resistance per unit length, is the (j - i)-th power of the inductance per unit length, is the j-th power of the capacitance per unit length, is the (2j - i)-th derivative of the zero-sequence voltage at the end at time t, is the j-th power of the conductance per unit length, is the (2j - i - 1)-th derivative of the zero-sequence voltage at the end at time t, is the (2j + 1)-th power of the line length, is the probability of selecting i sampling points from (j + 1) sampling points, is the (j - i + 1)-th power of the inductance per unit length, is the (2j - i + 1)-th derivative of the zero-sequence current at the end at time t, is the (2j - i)-th derivative of the zero-sequence current at the end at time t, is the (2j - 1)-th power of the line length, is the probability of selecting i sampling points from (j - 1) sampling points, is the (j - i - 1)-th power of the inductance per unit length, is the (2j - i - 1)-th derivative of the zero-sequence voltage at the end at time t, is the (2j - i - 2)-th derivative of the zero-sequence voltage at the end at time t, is the (2j - i)-th derivative of the zero-sequence current at the end at time t, is the (2j - i - 1)-th derivative of the zero-sequence current at the end at time t.

[0098] and As a result of mathematical induction, it includes the calculation of the current and voltage of each micro-element, which involves the intermediate terms of the derivatives of inductance and capacitance of each order, and is finally integrated through iteration and combination. R, L, C, and G respectively represent the resistance per unit length ( ), inductance ( ), capacitance ( ), conductance ( ), and l represents the length of the line ( ).

[0099] In some embodiments, determining whether the difference between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end meets the accuracy requirements includes:

[0100] Determining the error between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end. The expression of the error is:

[0101] ;

[0102] where e is the error, is the calculated zero-sequence voltage at the head end at time t, is the actual zero-sequence voltage at the head end at time t, j is the j-th sampling point, and there are m sampling points in total;

[0103] When the error is less than the preset error threshold, it is determined that the difference between the calculated zero-sequence voltage at the head end and the actual zero-sequence voltage at the head end meets the accuracy requirements.

[0104] Compare the calculated head-end voltage with the actual head-end voltage to calculate the error.

[0105] Specifically, the set threshold of the error is designed according to actual requirements, and this application does not make too many limitations here.

[0106] In some embodiments, obtaining the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the end of the line to be measured at the next moment when a fault occurs in the line to be measured includes:

[0107] Starting from the next moment when the fault occurs, obtain multiple actual zero-sequence voltages at the head end and multiple actual zero-sequence voltages at the end of the line to be measured;

[0108] Converting the actual zero-sequence voltage at the head end and the actual zero-sequence voltage at the end into sine functions with amplitudes as functions of time includes:

[0109] Fit multiple actual initial-end zero-sequence voltages and multiple actual terminal-end zero-sequence voltages into a sine function whose amplitude is a function of time.

[0110] Starting from the next moment after the fault moment, take m data and calculate the initial-end zero-sequence voltage and the terminal-end zero-sequence voltage according to the formula:

[0111] ;

[0112] Fit them into a sine function whose amplitude and initial phase are both functions of time, which is used as a fitting general formula to represent the voltage or current at point v.

[0113] Figure 4 This is the equivalent circuit diagram of a T-shaped branch line with a fault provided by the present invention;

[0114] In some embodiments, converting the actual initial-end zero-sequence voltage and the actual terminal-end zero-sequence voltage into a sine function whose amplitude is a function of time includes:

[0115] Convert the actual initial-end zero-sequence voltage and the actual terminal-end zero-sequence voltage into a sine function whose amplitude is a function of time. The expression of the actual initial-end zero-sequence voltage is:

[0116] ;

[0117] The expression of the actual terminal-end zero-sequence voltage is:

[0118] ;

[0119] Wherein, is the actual initial-end zero-sequence voltage at time t, is the constant term of the amplitude of the cosine function of is the undetermined constant of the q-th order term of the fitting function order of is the q-th power of time, is the constant term of the amplitude of the sine function of is the Hilbert transform of is the actual terminal-end zero-sequence voltage at time t, is the constant term of the amplitude of the cosine function of is the undetermined constant of the q-th order term of the fitting function order of is the constant term of the amplitude of the sine function of

[0120] Such as Figure 4As shown, taking the section between the fault point f and the line end N as an example, this line is composed of multiple micro-elements with a length of n in cascade. The zero-sequence electrical quantities missing due to data in this section are marked with a square box in the figure: the zero-sequence voltage at the beginning of the section is known and the zero-sequence current at the end are given. It is required to solve the zero-sequence current at the beginning of the section.

[0121] In this patent, since the waveforms of the current and voltage change suddenly after a fault and no longer follow regular patterns, the least squares LMS algorithm is used for iteration to continuously approximate the true value. The LMS algorithm has strong adaptability and good convergence. Using the steepest descent algorithm, it searches for the minimum value of a multivariable function along the steepest descent direction (negative gradient direction) of the performance surface, and is suitable for non-stationary signals.

[0122] Since the ( )-order derivatives of the zero-sequence voltage and zero-sequence current are required in the calculation process of this model, but the actually measured signals are all discrete transient data. Therefore, it is necessary to process the discrete transient data. This patent uses the sine representation method of transient signals proposed in existing literature to fit the discrete transient data to obtain a function expression, and then higher-order derivatives can be calculated. The function model of this method is: starting from the next moment after the fault moment, m data are taken, and the zero-sequence voltage at the beginning and the zero-sequence voltage at the end are based on the formula:

[0123] ;

[0124] are fitted into sine functions with amplitudes and initial phases both being functions of time, which is used as the fitting general formula to represent the voltage or current at point v.

[0125] In some embodiments, the process of setting the initial value of the amplitude includes:

[0126] Determine the constant value according to the corresponding relationship between the actual zero-sequence voltage at the beginning and the actual zero-sequence voltage at the end. The expression of the corresponding relationship is ;

[0127] Determine the initial value of the amplitude at the zero-th iteration according to the constant value. The initial value of the amplitude is:

[0128] ;

[0129] where n is a set constant, is the at the 0-th iteration, is the at the 0-th iteration, is the at the 0-th iteration of the undetermined constant of the 0-th order term of the fitting function order of is the The undetermined constant of the 0th order term of the fitting function order is The 0th iteration of the undetermined constant of the 1st order term of the fitting function order of is The undetermined constant of the 1st order term of the fitting function order of is The 0th iteration of the undetermined constant of the Kth order term of the fitting function order of is The undetermined constant of the Kth order term of the fitting function order of

[0130] Set the initial value of the terminal voltage according to the characteristic that the zero-sequence voltage waveforms of the entire distribution network are the same . It can more effectively approximate the true value, and n is a set constant. Substitute the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage into the sine function whose amplitude is a function of time, and obtain Each coefficient

[0131] Use the calculation error e of the initial voltage to correct the terminal voltage parameters

[0132] Figure 5 This is the flowchart of another method for determining the parameters of the distribution network branch line provided by the present invention

[0133] In some embodiments, if the accuracy requirement is not met, modify the amplitude of the time function, including

[0134] If the accuracy requirement is not met, iterate the amplitude of the time function using an iterative function, and the expression of the iterative function is

[0135] ;

[0136] Among them is The (x + 1)th iteration of is The xth iteration of is The (x + 1)th iteration of is The xth iteration of is The (x + 1)th iteration of the undetermined constant of the 0th order term of the fitting function order of is The xth iteration of the undetermined constant of the 0th order term of the fitting function order of is The (x + 1)th iteration of the undetermined constant of the 1st order term of the fitting function order of is The xth iteration of the undetermined constant of the 1st order term of the fitting function order of is The (x + 1)-th iteration of the undetermined constant of the K-th order term of the fitting function order is The x-th iteration of the undetermined constant of the K-th order term of the fitting function order is the convergence factor.

[0137] The subscript in the parentheses represents the number of iterations. The more iterations, the larger the number in the parentheses. Each time an iteration is performed, the subscript is incremented by 1. The error and the convergence factor iterate the amplitude of the time function. After the iteration, it returns to the fitting step.

[0138] Figure 6 FIG. 14 is a schematic structural diagram of a parameter determination system for a distribution network branch line provided by the present invention. The parameter determination system for the distribution network branch line includes:

[0139] An actual data acquisition unit 21, configured to acquire the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage of a to-be-tested line at the next moment after the moment when a fault occurs in the to-be-tested line;

[0140] A conversion unit 22, configured to convert the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage into a sine function with an amplitude being a function of time, and the corresponding relationship between the amplitude and the actual initial zero-sequence voltage and the actual terminal zero-sequence voltage is relevant;

[0141] A calculation data unit 23, configured to determine a calculated initial zero-sequence voltage and a calculated initial zero-sequence current according to the line distribution characteristics, the converted actual terminal zero-sequence voltage, and the converted actual terminal zero-sequence current;

[0142] An accuracy judgment unit 24, configured to judge whether the difference between the calculated initial zero-sequence voltage and the actual initial zero-sequence voltage meets the accuracy requirement; if not, trigger a modification unit 25; if so, trigger an output unit 26;

[0143] A modification unit 25, configured to modify the amplitude of the time function and trigger the conversion unit 22;

[0144] An output unit 26, configured to output the calculated initial zero-sequence current.

[0145] Based on the above embodiments:

[0146] The actual data acquisition unit 21 is specifically configured to start from the next moment after the moment when a fault occurs, and acquire a plurality of actual initial zero-sequence voltages and a plurality of actual terminal zero-sequence voltages of the to-be-tested line;

[0147] The conversion unit 22 is specifically configured to fit a plurality of actual initial zero-sequence voltages and a plurality of actual terminal zero-sequence voltages into a sine function with an amplitude being a function of time.

[0148] The calculation data unit 23 is specifically used to determine the calculated zero-sequence voltage and calculated zero-sequence current at the head end based on the line distribution characteristics, the converted actual zero-sequence voltage at the end, and the converted actual zero-sequence current at the end. The expression for the calculated zero-sequence voltage at the head end is:

[0149] ;

[0150] The expression for the calculated zero-sequence current at the head end is:

[0151] ;

[0152] Where, is the calculated zero-sequence voltage at the head end at time t, is the actual zero-sequence voltage at the head end at time t, R is the resistance per unit length of the faulty line, l is the length of the faulty line, is the calculated zero-sequence current at the head end at time t, L is the inductance per unit length of the faulty line, is the derivative of, is the voltage parameter function, is the current parameter function, and j is the jth sampling point.

[0153] The expression for the voltage parameter function is:

[0154] ;

[0155] The expression for the current parameter function is:

[0156] ;

[0157] Where, is the 2jth power of the line length, is the probability of selecting i sampling points from j sampling points, is the ith power of the resistance per unit length, is the (j - i)th power of the inductance per unit length, is the jth power of the capacitance per unit length, is the (2j - i)th derivative of the voltage at point M at time t, is the jth power of the conductance per unit length, is the (2j - i - 1)th derivative of the zero-sequence voltage at point N at time t, is the (2j + 1)th power of the line length, is the probability of selecting i sampling points from (j + 1) sampling points, is the (j - i + 1)th power of the inductance per unit length, is the (2j - i + 1)th derivative of the zero-sequence current at point N at time t, is the (2j - i)th derivative of the zero-sequence current at point N at time t, is the (2j - 1)th power of the line length, is the probability of selecting i sampling points from j - 1 sampling points, is the (j - i - 1)th power of the inductance per unit length, is the (2j - i - 1)th derivative of the zero - sequence voltage at point N at time t, is the (2j - i - 2)th derivative of the zero - sequence voltage at point N at time t, is the (2j - i)th derivative of the zero - sequence current at point N at time t, is the (2j - i - 1)th derivative of the zero - sequence current at point N at time t, where the fault point f is set between point M and point N, and the current flows from point M to point N.

[0158] The accuracy judgment unit 24 is specifically used to determine the error between the calculated zero - sequence voltage at the head end and the actual zero - sequence voltage at the head end. The expression of the error is:

[0159] ;

[0160] where e is the error, is the calculated zero - sequence voltage at the head end at time t, is the actual zero - sequence voltage at the head end at time t, j is the jth sampling point, and there are m sampling points in total;

[0161] The accuracy determination unit is used to determine that the difference between the calculated zero - sequence voltage at the head end and the actual zero - sequence voltage at the head end meets the accuracy requirements when the error is less than the preset error threshold.

[0162] The conversion unit 22 is specifically used to convert the actual zero - sequence voltage at the head end and the actual zero - sequence voltage at the tail end into sine functions whose amplitudes are functions of time. The expression of the actual zero - sequence voltage at the head end is:

[0163] ;

[0164] The expression of the actual zero - sequence voltage at the tail end is:

[0165] ;

[0166] where, is the actual zero - sequence voltage at the head end at time t, is the constant term of the amplitude of the cosine function of is the undetermined constant of the q - th term of the fitting function order of is the q - th power of time, is the constant term of the amplitude of the sine function of is the Hilbert transform of, K is the maximum value of the fitting order is the actual zero-sequence voltage of the terminal at time t, is the constant term of the amplitude of the cosine function of is the undetermined constant of the q-th term of the fitting function order of is the constant term of the amplitude of the sine function of

[0167] The process of setting the initial value of the amplitude includes:

[0168] Determine the constant value according to the corresponding relationship between the actual zero-sequence voltage of the head end and the actual zero-sequence voltage of the terminal. The expression of the corresponding relationship is ;

[0169] Determine the initial value of the amplitude at the 0th iteration according to the constant value. The initial value of the amplitude is:

[0170] ;

[0171] where n is the set constant, is the 0th iteration of is the 0th iteration of is the 0th iteration of the undetermined constant of the 0th term of the fitting function order of is the undetermined constant of the 0th term of the fitting function order of is the 0th iteration of the undetermined constant of the 1st term of the fitting function order of is the undetermined constant of the 1st term of the fitting function order of is the 0th iteration of the undetermined constant of the Kth term of the fitting function order of is the undetermined constant of the Kth term of the fitting function order of

[0172] The modification unit 25 is specifically used to perform iteration on the amplitude of the time function using an iteration function if the accuracy requirement is not met. The expression of the iteration function is:

[0173] ;

[0174] where, is the (x + 1)th iteration of is the xth iteration of is the (x + 1)th iteration of For the x-th iteration of is the (x + 1)-th iteration of the undetermined constant of the 0-th order term of the fitting function order of is the x-th iteration of the undetermined constant of the 0-th order term of the fitting function order of is the (x + 1)-th iteration of the undetermined constant of the 1-st order term of the fitting function order of is the x-th iteration of the undetermined constant of the 1-st order term of the fitting function order of is the (x + 1)-th iteration of the undetermined constant of the K-th order term of the fitting function order of is the x-th iteration of the undetermined constant of the K-th order term of the fitting function order of is the convergence factor.

[0175] Figure 7 FIG. is a schematic structural diagram of a device for determining parameters of a distribution network branch line provided by the present invention. The device for determining parameters of the distribution network branch line includes:

[0176] A memory 31 for storing a computer program;

[0177] A processor 32 for implementing the steps of the method for determining parameters of the above-mentioned distribution network branch line when executing the computer program.

[0178] For the introduction of the device for determining parameters of the distribution network branch line provided in the present application, please refer to the above-mentioned embodiments, and details are not described herein again.

[0179] It should also be noted that in this specification, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0180] Those skilled in the art may further realize that the units and algorithm steps of each example described in connection with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of the present invention.

[0181] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining parameters of a distribution network branch line, characterized in that: include: Obtaining an actual head-end zero-sequence voltage and an actual terminal zero-sequence voltage of the line to be tested at a moment next to the moment when a fault occurs in the line to be tested; Converting the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage into a sinusoidal function whose amplitude is a time function, wherein the amplitude is related to the corresponding relationship between the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage; Determine the calculated first-end zero-sequence voltage and the calculated first-end zero-sequence current according to the line distribution characteristics, the converted actual terminal zero-sequence voltage and the converted actual terminal zero-sequence current; Determining whether the difference between the calculated first-end zero-sequence voltage and the actual first-end zero-sequence voltage meets the accuracy requirement; If the accuracy requirement is not met, the amplitude of the time function is modified, and the process returns to the step of converting the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage into a sinusoidal function whose amplitude is a time function; If the accuracy requirement is met, the calculated first-end zero-sequence current is output.

2. The method for determining parameters of a distribution network branch line according to claim 1, characterized in that: Determining and calculating the first-end zero-sequence voltage and the first-end zero-sequence current according to the line distribution characteristics, the converted actual terminal zero-sequence voltage, and the converted actual terminal zero-sequence current, includes: The calculated first-end zero-sequence voltage and the calculated first-end zero-sequence current are determined according to the line distribution characteristics, the converted actual terminal zero-sequence voltage, and the converted actual terminal zero-sequence current. The expression for calculating the first-end zero-sequence voltage is: ； The expression for calculating the first-end zero-sequence current is: ； in, is the calculated zero-sequence voltage at the first end at time t, is the actual zero-sequence voltage at the first end at time t, R is the resistance per unit length of the fault line, l is the length of the fault line, is the calculated head-end zero-sequence current at time t, L is the inductance per unit length of the fault line, for The derivative of is the voltage parameter function, is the current parameter function, and j is the jth sampling point.

3. The method for determining parameters of a distribution network branch line according to claim 2, characterized in that: The expression of the voltage parameter function is: ； The expression of the current parameter function is: ； in, is the 2jth power of the line length, is the probability of selecting i sampling points from j sampling points, is the i-th power of the resistance per unit length, is the jth power of the inductance per unit length, is the jth power of the capacitance per unit length, is the 2j-i order derivative of the terminal zero-sequence voltage at time t, is the jth power of the conductance per unit length, is the 2j-i-1 order derivative of the terminal zero-sequence voltage at time t, is the 2j+1th power of the line length, is the probability of selecting i sampling points from j+1 sampling points, is the j-i+1th power of the inductance per unit length, is the 2j-i+1 order derivative of the terminal zero-sequence current at time t, is the 2j-i order derivative of the terminal zero-sequence current at time t, is the 2j-1th power of the line length, is the probability of selecting i sampling points from j-1 sampling points, is the ji-1 power of the inductance per unit length, is the 2j-i-1 order derivative of the terminal zero-sequence voltage at time t, is the 2j-i-2nd order derivative of the terminal zero-sequence voltage at time t, is the 2j-i order derivative of the terminal zero-sequence current at time t, It is the 2j-i-1 derivative of the terminal zero-sequence current at time t.

4. The method for determining parameters of a distribution network branch line according to claim 1, characterized in that: Determining whether the difference between the calculated first-end zero-sequence voltage and the actual first-end zero-sequence voltage meets the accuracy requirement includes: Determine the error between the calculated first-end zero-sequence voltage and the actual first-end zero-sequence voltage, the error being expressed as: ； Wherein, e is the error, is the calculated zero-sequence voltage at the first end at time t, is the actual zero-sequence voltage at the first end at time t, j is the jth sampling point, and there are m sampling points in total; When the error is less than a preset error threshold, it is determined that the difference between the calculated first-end zero-sequence voltage and the actual first-end zero-sequence voltage meets the accuracy requirement.

5. The method for determining parameters of a distribution network branch line according to claim 1, characterized in that: Obtaining the actual head-end zero-sequence voltage and the actual terminal zero-sequence voltage of the line to be tested at the next moment after the moment when the line to be tested has a fault, including: Starting from the next moment after the moment when the fault occurs, a plurality of actual head-end zero-sequence voltages and a plurality of actual terminal zero-sequence voltages of the line to be tested are obtained; Converting the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage into a sinusoidal function whose amplitude is a function of time includes: The plurality of actual first-end zero-sequence voltages and the plurality of actual terminal zero-sequence voltages are fitted to a sinusoidal function whose amplitude is a function of time.

6. The method for determining parameters of a distribution network branch line according to any one of claims 1 to 5, characterized in that: Converting the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage into a sinusoidal function whose amplitude is a function of time includes: The actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage are converted into a sinusoidal function whose amplitude is a time function. The expression of the actual first-end zero-sequence voltage is: ； The expression of the actual terminal zero-sequence voltage is: ； in, is the actual zero-sequence voltage at the first end at time t, for The constant term of the amplitude of the cosine function, for The unknown constant of the q-order term of the fitting function order, is the qth power of time, for The constant term of the amplitude of the sine function, for The Hilbert transform of , K is the maximum value of the fitting order, is the actual terminal zero-sequence voltage at time t, for The constant term of the amplitude of the cosine function, for The unknown constant of the q-order term of the fitting function order, for is the constant term of the amplitude of the sine function, and s is the attenuation coefficient.

7. The method for determining parameters of a distribution network branch line according to claim 6, characterized in that: The process of setting the initial value of the amplitude includes: The constant value is determined according to the corresponding relationship between the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage. The expression of the corresponding relationship is: ; The initial value of the amplitude at the zeroth iteration is determined according to the constant value, and the initial value of the amplitude is: ； Where n is a setting constant, for At the 0th iteration of for At the 0th iteration of for The 0th iteration of the unknown constant of the 0th order term of the fitting function, for The unknown constant of the 0th order term of the fitting function order, for The 0th iteration of the unknown constant of the first-order term of the fitting function order, for The unknown constant of the first-order term of the fitting function order, for The 0th iteration of the unknown constant of the K-order term of the fitting function, for The unknown constant of the K-order term of the fitting function.

8. The method for determining parameters of a distribution network branch line according to claim 6, characterized in that: If the accuracy requirement is not met, modifying the amplitude of the time function includes: If the accuracy requirement is not met, the amplitude of the time function is iterated using an iterative function, and the expression of the iterative function is: ； in, for At the x+1th iteration of for At the xth iteration of for At the x+1th iteration of for At the xth iteration of for The x+1th iteration of the unknown constant of the 0th order term of the fitting function, for The xth iteration of the unknown constant of the 0th order term of the fitting function, for The x+1th iteration of the unknown constant of the first-order term of the fitting function, for The xth iteration of the unknown constant of the first-order term of the fitting function, for The x+1th iteration of the unknown constant of the K-order term of the fitting function, for The xth iteration of the unknown constant of the K-order term of the fitting function, is the convergence factor.

9. A distribution network branch line parameter determination system, characterized in that: include: An actual data acquisition unit, used to acquire an actual head-end zero-sequence voltage and an actual terminal zero-sequence voltage of the line to be tested at a moment next to the moment when a fault occurs in the line to be tested; A conversion unit, used for converting the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage into a sinusoidal function whose amplitude is a time function, wherein the amplitude is related to the corresponding relationship between the actual first-end zero-sequence voltage and the actual terminal zero-sequence voltage; A calculation data unit, used for determining the calculated first-end zero-sequence voltage and the calculated first-end zero-sequence current according to the line distribution characteristics, the converted actual terminal zero-sequence voltage and the converted actual terminal zero-sequence current; An accuracy judgment unit, used to judge whether the difference between the calculated first-end zero-sequence voltage and the actual first-end zero-sequence voltage meets the accuracy requirement; if not, trigger the modification unit; if yes, trigger the output unit; A modification unit, used for modifying the amplitude of the time function and triggering the conversion unit; An output unit is used to output the calculated first-end zero-sequence current.

10. A device for determining parameters of a distribution network branch line, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of the method for determining parameters of a distribution network branch line as claimed in any one of claims 1 to 8 when executing the computer program.

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