A harmonic impedance estimation method for a distribution network

Abstract

The present invention discloses a method for estimating harmonic impedance of a distribution network. The method includes taking the current feeder in the distribution network system as the user side, taking the non-current feeder as the system side, and calculating an initial value of the system-side harmonic impedance corresponding to the current feeder based on the acquired harmonic data; solving the background harmonic voltage based on the initial value of the system-side harmonic impedance corresponding to the current feeder, sorting and classifying the background harmonic voltage, performing a fluctuation analysis on the classified background harmonic voltage to obtain the system-side harmonic impedance corresponding to the current feeder; calculating the estimated values of the user-side harmonic impedance corresponding to all the feeders based on the system-side harmonic impedances corresponding to all the feeders in the distribution network system. This embodiment realizes the effective estimation of the harmonic impedance of the low-bandwidth communication of the distribution network, reduces the estimation error, and improves the accuracy of the harmonic impedance estimation.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical measurement, and particularly to a method for estimating harmonic impedance of a distribution network. Background Art

[0002] In order to measure the impact of harmonics emitted by each user on the harmonic voltage at the point of common coupling (PCC) of the power grid, it is necessary to calculate the harmonic responsibility of each user. The impedance parameter method is a popular direction in the research of harmonic levels at home and abroad, and its key point is how to effectively estimate the harmonic impedance. In addition, harmonic impedance is a key parameter in the evaluation of harmonic emission levels and the division of harmonic responsibilities. The accurate estimation of harmonic impedance has also become an important prerequisite for the effective implementation of the "reward and punishment scheme" and precise harmonic control.

[0003] The distribution network involves multiple voltage levels and has a wide coverage. Constrained by economy, there is a lack of effective circuit monitoring and power equipment monitoring for medium and low voltage distribution networks below 10 kV. In addition, in engineering practice, due to the limited number of current measurement device installation points, communication limitations of transmission channels and storage capacities, and the industry standard does not stipulate that existing power quality monitoring systems must store harmonic phase information, the information obtained cannot be directly used for the effective estimation of harmonic impedance in current theoretical research.

[0004] Currently, in actual engineering, if one wants to estimate the harmonic impedance, it is necessary to use a power quality monitor to actively measure the phasor information of harmonic current and harmonic voltage at the PCC. However, limited by factors such as insufficient long-term monitoring storage space and delays in the synchronization of harmonic voltage and current, current general power quality monitors can only provide the amplitudes of harmonic voltage and current at the measurement point and the phase difference between them rather than the phasor values of harmonic voltage and current, and the phase difference data may also have inaccurate measurement problems. At this time, to solve the problem of the lack of harmonic voltage and current phases, one can only artificially construct the phase angle information of the two, but the results calculated by artificially constructing the phase angle information lack persuasiveness and usually have large errors, making it impossible to guarantee the accuracy of the estimated harmonic impedance. Summary of the Invention

[0005] The present invention provides a method for estimating harmonic impedance of a distribution network, which can effectively estimate the harmonic impedance of low-bandwidth communication in the distribution network, reduce the estimation error, and improve the accuracy of harmonic impedance estimation.

[0006] To solve the above technical problems, an embodiment of the present invention provides a method for estimating harmonic impedance of a distribution network, including:

[0007] Taking the current feeder in the distribution network system as the user side, taking the non-current feeder as the system side, and calculating the initial value of the system-side harmonic impedance corresponding to the current feeder based on the obtained harmonic data;

[0008] Based on the initial value of the system-side harmonic impedance corresponding to the current feeder, solve the background harmonic voltage, sort and classify the background harmonic voltage, perform a fluctuation analysis on the classified background harmonic voltage, and obtain the system-side harmonic impedance corresponding to the current feeder.

[0009] Based on the system-side harmonic impedances corresponding to all the feeders in the distribution network system, calculate the estimated values of the user-side harmonic impedances corresponding to all the feeders.

[0010] Implementing the embodiments of the present invention, taking the current feeder in the distribution network system as the user side and the non-current feeders as the system side, and based on the obtained harmonic data, calculate the initial value of the system-side harmonic impedance corresponding to the current feeder; based on the initial value of the system-side harmonic impedance corresponding to the current feeder, solve the background harmonic voltage, sort and classify the background harmonic voltage, perform a fluctuation analysis on the classified background harmonic voltage, and obtain the system-side harmonic impedance corresponding to the current feeder; based on the system-side harmonic impedances corresponding to all the feeders in the distribution network system, calculate the estimated values of the user-side harmonic impedances corresponding to all the feeders. By considering the harmonic impedance estimation for low-bandwidth communication in the distribution network and only using the harmonic data such as the amplitude of the harmonic voltage and current and the phase difference between the two that can be accurately provided currently, it is possible to effectively estimate the system-side and user-side harmonic impedances under low-bandwidth communication, effectively reduce the estimation error, and improve the accuracy of the harmonic impedance estimation.

[0011] As a preferred solution, based on the obtained harmonic data, calculating the initial value of the system-side harmonic impedance corresponding to the current feeder specifically includes:

[0012] Establish a Norton equivalent circuit based on the user side and the system side.

[0013] Based on the Norton equivalent circuit, obtain several groups of harmonic data within a preset time period; among them, the harmonic data includes the harmonic voltage amplitude, the harmonic current amplitude, and the phase difference.

[0014] Perform a zero-phase maximum and minimum value processing on the several groups of harmonic data to obtain the initial value of the system-side harmonic impedance corresponding to the current feeder.

[0015] As a preferred solution, performing a zero-phase maximum and minimum value processing on the several groups of harmonic data to obtain the initial value of the system-side harmonic impedance corresponding to the current feeder specifically includes:

[0016] According to each group of harmonic data, use the zero-phase method to calculate the harmonic impedance data of each group.

[0017] Taking the maximum value in the harmonic impedance data of each group as the initial value of the system-side harmonic impedance of each group, and statistically analyzing the initial values of the system-side harmonic impedances of each group to obtain the initial value of the system-side harmonic impedance corresponding to the current feeder. The specific formula is:

[0018]

[0019] Among them, Z sr0 is the real part of the initial value of the harmonic impedance on the system side, and Z si0 is the imaginary part of the initial value of the harmonic impedance on the system side. U pcc_i is the harmonic voltage amplitude, and I pcc_i is the harmonic current amplitude, and θ i is the phase difference.

[0020] As a preferred solution, based on the initial value of the harmonic impedance on the system side corresponding to the current feeder, the background harmonic voltage is solved, specifically:

[0021] According to the initial value of the harmonic impedance on the system side of each group, the background harmonic voltage on the system side of each group is solved inversely, and the formula is:

[0022]

[0023] Among them, |I pcc | is the harmonic current amplitude at the common connection point, and U pccr and U sr are the projections of the harmonic voltage amplitude at the common connection point and the background harmonic voltage amplitude on the system side on the real axis respectively. U pcci and U si are the projections of the harmonic voltage amplitude at the common connection point and the background harmonic voltage amplitude on the system side on the imaginary axis respectively. Z sr and Z si are the real part and the imaginary part of the initial value of the harmonic impedance on the system side respectively;

[0024] The background harmonic voltage of each group is statistically analyzed to obtain the background harmonic voltage.

[0025] As a preferred solution, the background harmonic voltage is sorted and classified, and the classified background harmonic voltage is subjected to fluctuation analysis to obtain the harmonic impedance on the system side corresponding to the current feeder, specifically:

[0026] Sort the background harmonic voltage by magnitude, and based on the preset number of classifications, classify the sorted background harmonic voltage to obtain the classified background harmonic voltage;

[0027] According to the initial value of the harmonic impedance on the system side of each group, the impedance initial value range is obtained, and the current initial value of the harmonic impedance on the system side is selected within the impedance initial value range;

[0028] Calculate the impedance value by using the classified background harmonic voltage and the current initial value of the harmonic impedance on the system side to obtain each type of impedance value;

[0029] Based on each type of impedance value and the current initial value of the system-side harmonic impedance, calculate the current impedance threshold, and the formula is:

[0030]

[0031] where, delta is the current impedance threshold, and Z s0 is the current initial value of the system-side harmonic impedance; Z s (k) is the impedance value of the kth type, and the impedance value includes the real part and the imaginary part of the impedance value;

[0032] Based on the current impedance threshold, perform cyclic approximation adjustment on the current initial value of the system-side harmonic impedance, and calculate the adjusted fluctuation change value according to each type of impedance value and the adjusted system-side harmonic impedance initial value until the adjusted fluctuation change value meets the impedance initial value condition to obtain the adjusted system-side harmonic impedance initial value;

[0033] Perform impedance value calculation on the classified background harmonic voltage and the adjusted system-side harmonic impedance initial value to obtain the adjusted impedance value of each type;

[0034] Based on the adjusted impedance value of each type, calculate the system-side harmonic impedance corresponding to the current feeder.

[0035] As a preferred solution, perform impedance value calculation on the classified background harmonic voltage and the current initial value of the system-side harmonic impedance to obtain the impedance value of each type, specifically:

[0036] Obtain the mean value of the background harmonic voltage of each type after classification and the current initial value of the system-side harmonic impedance to obtain the expected value of each type, and the formula is:

[0037]

[0038] where, E(·) represents the expected value;

[0039] According to the expected value of each type, calculate the impedance value of each type, and the formula is:

[0040]

[0041] where, Z s (k) is the impedance value of the kth type, k is the preset number of classifications, i is the current feeder value, is the harmonic current vector at the current common connection point, is the amplitude of the harmonic current vector at the current common connection point.

[0042] As a preferred solution, based on the current impedance threshold, perform cyclic approximation adjustment on the current initial value of the system-side harmonic impedance, specifically:

[0043] Determine whether the current impedance threshold is less than the preset threshold. If so, add the preset change step to the initial value of the system-side harmonic impedance to obtain the adjusted initial value of the system-side harmonic impedance. If not, subtract the preset change step from the initial value of the system-side harmonic impedance to obtain the adjusted initial value of the system-side harmonic impedance.

[0044] As a preferred solution, calculate the adjusted fluctuation change value according to each type of impedance value and the adjusted initial value of the system-side harmonic impedance. Specifically:

[0045] Calculate the impedance difference between each type of impedance value and the adjusted initial value of the system-side harmonic impedance, and obtain the absolute value of the impedance difference for each type. Sum up the absolute values of the impedance differences for each type to obtain the adjusted fluctuation change value.

[0046] As a preferred solution, calculate the system-side harmonic impedance corresponding to the current feeder based on each type of adjusted impedance value. Specifically:

[0047] Obtain the impedance values of the middle two items within each type of adjusted impedance value, and calculate the average value of the impedance values of the middle two items to obtain the system-side harmonic impedance corresponding to the current feeder.

[0048] As a preferred solution, calculate the estimated values of the user-side harmonic impedance corresponding to all the feeders in the distribution network system. Specifically:

[0049] Calculate the transition harmonic impedance according to the system-side harmonic impedances corresponding to all the feeders in the distribution network system. The formula is:

[0050]

[0051] where, Z G is the transition harmonic impedance, Z s (i) is the system-side harmonic impedance corresponding to the i-th feeder, and n is the number of feeders;

[0052] Calculate the estimated values of the user-side harmonic impedance corresponding to all the feeders according to the transition harmonic impedance. The formula is:

[0053]

[0054] where, Z c (i) is the user-side harmonic impedance corresponding to the i-th feeder.

[0055] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0056] 1. Under low - bandwidth communication, only the harmonic data that can be easily obtained in actual engineering, namely the amplitudes of harmonic voltage and current and the phase - difference data between the two, are required. Compared with the existing methods for obtaining the specific vector information of the two, it has stronger feasibility, smaller data volume requirements, better meets the actual engineering needs, and the harmonic impedance results obtained by the present invention have theoretical support, higher reliability, and stronger persuasiveness.

[0057] 2. Compared with the existing technologies that require one or more assumptions, the present invention adopts a method of cyclic gradual approximation. Without making assumptions such as the harmonic impedance on the user side being much greater than that on the system side, it can effectively solve the problem of the lack of the phase of harmonic voltage and current, and is applicable to any harmonic order, making the present invention more applicable in actual engineering.

[0058] 3. Under the background of limited existing monitoring point numbers and communication data transmission capabilities, the harmonic impedances of the system side and the user side can be accurately estimated. Its principle is simple, the calculation is convenient, and the estimation result is accurate, having great engineering application prospects. Accurate harmonic impedances of the system side and the user side are also the primary premise for the division of harmonic pollution liability, providing a prerequisite and a new theoretical basis for the division of harmonic pollution liability.

[0059] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation part. Brief Description of the Drawings

[0060] Figure 1 : It is a schematic flowchart of an embodiment of a harmonic impedance estimation method for a distribution network provided by the present invention;

[0061] Figure 2 : It is a flowchart of a system in which a PCC bus connects multiple harmonic - source load feeders in an embodiment of a harmonic impedance estimation method for a distribution network provided by the present invention;

[0062] Figure 3 : It is a flowchart of obtaining the system - side harmonic impedance of a feeder in an embodiment of a harmonic impedance estimation method for a distribution network provided by the present invention;

[0063] Figure 4 : It is a Norton equivalent circuit diagram in an embodiment of a harmonic impedance estimation method for a distribution network provided by the present invention;

[0064] Figure 5 : It is a flowchart of fluctuation quantity analysis in an embodiment of a harmonic impedance estimation method for a distribution network provided by the present invention;

[0065] Figure 6 : It is an equivalent topology diagram in an embodiment of a harmonic impedance estimation method for a distribution network provided by the present invention. Detailed Description of the Invention

[0066] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0067] Embodiment 1

[0068] Please refer to Figure 1 , which is a schematic flowchart of a harmonic impedance estimation method for a distribution network provided by an embodiment of the present invention. The harmonic impedance estimation method includes steps 101 to 103, and the specific steps are as follows:

[0069] Step 101: Regard the current feeder in the distribution network system as the user side, regard the non-current feeder as the system side, and calculate the initial value of the system-side harmonic impedance corresponding to the current feeder based on the obtained harmonic data.

[0070] In this embodiment, in a system where the PCC bus connects multiple harmonic source load feeders, as Figure 2 shown, PCC is the point of common coupling. The PCC bus is connected to n harmonic source load feeders. When feeder i (i = 1, 2,..., n) is the feeder of a certain harmonic source of concern, take feeder i as the user side, and regard the remaining feeders as the system side as a whole. Based on each feeder as the user side, calculate the system-side harmonic impedance of this feeder. The process of obtaining the system-side harmonic impedance of the feeder is as Figure 3 shown, that is, it includes steps 101 - step 102.

[0071] Optionally, calculating the initial value of the system-side harmonic impedance corresponding to the current feeder based on the obtained harmonic data specifically includes steps 1011 to 1012, and the specific steps are as follows:

[0072] Step 1011: Establish a Norton equivalent circuit based on the user side and the system side;

[0073] In this embodiment, when taking the current feeder as the user side and the remaining feeders as the system side, the Norton equivalent circuit established based on the harmonic data of any arbitrary order is shown in Figure 4 . Assume that Z s and Z c are the system-side and user-side harmonic impedances respectively, while U pcc , I pcc represent the harmonic voltage and harmonic current at the point of common coupling PCC respectively, and I s , I c represent the harmonic emission currents on the system side and the user side respectively.

[0074] It should be noted that according to Figure 4 the Norton equivalent circuit in pcc , the PCC bus voltage U

[0075] U pcc = I s Z s + I pcc Z s (1)

[0076] where I s Z s is the background harmonic voltage U s .

[0077] Due to the lack of the actual phase information of both U pcc and I pcc , it is necessary to construct the phase difference θ between U pcc and I pcc as the phase angle information and substitute it into Equation (1) for processing. Divide both sides of Equation (1) by the phase angle of I pcc to obtain the relationship between the voltage amplitude and phase angle, as shown in the following equation:

[0078] |U pcc |∠θ = |I pcc |Z s + |U s |∠α (2)

[0079] where |U pcc | and |I pcc | are the amplitudes of U pcc and I pcc respectively, α is the phase difference between U s and I pcc . Furthermore, the relationship formula of the harmonic impedance can be obtained, as shown in the following equation:

[0080]

[0081] where U pccr , U sr are the projections of |U pcc | and |U s | on the real axis respectively, U pcci , U si are the projections of |U pcc | and |U i | on the imaginary axis respectively, Z sr , Z si are the real part and imaginary part of Z s respectively.

[0082] Step 1012: Obtain several groups of harmonic data within a preset time period based on the Norton equivalent circuit; where the harmonic data includes harmonic voltage amplitude, harmonic current amplitude, and phase difference.

[0083] In this embodiment, obtain multiple groups of harmonic data (the harmonic data includes voltage amplitude, current amplitude, and the phase difference data between the two) within a period of time from a power quality monitoring device or an online monitoring platform, etc.

[0084] Step 1013: Perform phase-position zero-maximum value processing on the several groups of harmonic data to obtain the initial value of the system-side harmonic impedance corresponding to the current feeder.

[0085] In this embodiment, after data processing, use the phase-position zero method to calculate the harmonic impedance of each group of data, and select the maximum value of the harmonic impedance as the initial value of the system-side harmonic impedance.

[0086] Optionally, step 1013 is specifically:

[0087] According to each group of harmonic data, use the phase-position zero method to calculate the harmonic impedance data of each group.

[0088] Take the maximum value in the harmonic impedance data of each group as the initial value of the system-side harmonic impedance of each group, and statistically calculate the initial values of the system-side harmonic impedance of each group to obtain the initial value of the system-side harmonic impedance corresponding to the current feeder. The specific formula is:

[0089]

[0090] Where, Z sr0 is the real part of the initial value of the system-side harmonic impedance, Z si0 is the imaginary part of the initial value of the system-side harmonic impedance, U pcc_i is the harmonic voltage amplitude, I pcc_i is the harmonic current amplitude, θ i is the phase difference.

[0091] In this embodiment, the amplitudes of the harmonic voltage and current and the phase difference data between the two are U pcc_i , I pcc_i and θ i . Use the phase-position zero method to calculate the system-side harmonic impedance of each group of data. The phase-position zero method assumes that the phase of the harmonic current is 0 and the phase of the harmonic voltage is the phase difference θ i with it. The real part Z sr_i and the imaginary part Z si_i of the harmonic impedance can be obtained respectively, and the maximum value is selected as the initial value of the system-side harmonic impedance Z sr0 +j*Z si0 . The specific calculation formula is formula (4).

[0092] Step 102: Based on the initial value of the system-side harmonic impedance corresponding to the current feeder, solve the background harmonic voltage, sort and classify the background harmonic voltage, and perform a fluctuation analysis on the classified background harmonic voltage to obtain the system-side harmonic impedance corresponding to the current feeder.

[0093] In this embodiment, the initial value of the system-side harmonic impedance obtained through Step 102 can be used to inversely solve multiple groups of background harmonics U sr 、U si . Then, substituting them into the corresponding expressions can obtain the system-side harmonic impedance. Finally, a cyclic step-by-step approximation method is adopted to obtain the final system-side harmonic impedance corresponding to the feeder.

[0094] Optionally, based on the initial value of the system-side harmonic impedance corresponding to the current feeder, solving the background harmonic voltage is specifically as follows:

[0095] According to the initial value of the system-side harmonic impedance of each group, inversely solve the system-side background harmonic voltage of each group. The inverse solution formula is Equation (3), as follows:

[0096]

[0097] where, |I pcc | is the amplitude of the harmonic current at the point of common coupling, U pccr and U sr are the projections of the harmonic voltage amplitude at the point of common coupling and the system-side background harmonic voltage amplitude on the real axis respectively, U pcci and U si are the projections of the harmonic voltage amplitude at the point of common coupling and the system-side background harmonic voltage amplitude on the imaginary axis respectively, Z sr 、Z si are the real part and the imaginary part of the initial value of the system-side harmonic impedance respectively;

[0098] Statistically analyze the system-side background harmonic voltage of each group to obtain the background harmonic voltage.

[0099] In this embodiment, according to the initial value of the system-side harmonic impedance of each group, inversely solve the system-side background harmonic voltage, that is, substitute Equation (4) into Equation (3). When there are N groups of data, then N groups of U sr 、U si can be obtained. That is, the system-side background harmonic voltage includes the projection U sr of the background harmonic voltage amplitude on the real axis and the projection U si of the background harmonic voltage amplitude on the imaginary axis.

[0100] Optionally, sort and classify the background harmonic voltage, and perform a fluctuation analysis on the classified background harmonic voltage to obtain the system-side harmonic impedance corresponding to the current feeder. The process of the fluctuation analysis is as Figure 5As shown, it includes steps 1021 to 1027, and the specific steps are as follows:

[0101] Step 1021: Sort the magnitudes of the background harmonic voltages, and classify the sorted background harmonic voltages based on a preset number of classifications to obtain the classified background harmonic voltages;

[0102] In this embodiment, when the preset number of classifications is 4, sort U sr , U si by magnitude and divide them into 4 categories. Then each category of data contains N / 4 data. U sr , U si are calculated and sorted separately, and the two can be carried out synchronously. Sort U sr , U si separately and directly recombine them after separate sorting.

[0103] Step 1022: Obtain an impedance initial value range according to the initial value of the system-side harmonic impedance for each group, and select the current initial value of the system-side harmonic impedance within the impedance initial value range;

[0104] Step 1023: Calculate the impedance values for each category by calculating the impedance values of the classified background harmonic voltages and the current initial value of the system-side harmonic impedance;

[0105] Optionally, step 1023 is specifically:

[0106] Obtain the mean value of each category of background harmonic voltages after classification and the current initial value of the system-side harmonic impedance to obtain the expected value for each category. The formula is:

[0107]

[0108] where E(·) represents the expected value;

[0109] Calculate the impedance value for each category according to the expected value for each category. The formula is:

[0110]

[0111] where Z s (k) is the impedance value of the kth category, k is the preset number of classifications, i is the current feeder value, is the harmonic current vector at the current point of common coupling, is the magnitude of the harmonic current vector at the current point of common coupling.

[0112] In this embodiment, taking the mean value of Equation (3) can obtain Equation (5). Then, by combining Equation (3) and Equation (5), Equation (6) can be obtained. Through Equation (6), the impedance value of the system-side harmonic impedance can be calculated according to the data of the kth (k = 1, 2, 3, 4) category.

[0113] Step 1024: Based on each type of impedance value and the current initial value of the system-side harmonic impedance, calculate the current impedance threshold. The formula is:

[0114]

[0115] where delta is the current impedance threshold, and Z s0 is the current initial value of the system-side harmonic impedance; Z s (k) is the impedance value of the k-th type, and the impedance value includes the real part and the imaginary part of the impedance value.

[0116] In this embodiment, taking the calculation of the real part Z sr of the system-side harmonic impedance as an example, the corresponding impedance threshold is:

[0117]

[0118] Taking the calculation of the imaginary part Z si of the system-side harmonic impedance as an example, the corresponding impedance threshold is:

[0119]

[0120] Step 1025: Based on the current impedance threshold, perform cyclic approximation adjustment on the current initial value of the system-side harmonic impedance, and calculate the adjusted fluctuation change value according to each type of impedance value and the adjusted system-side harmonic impedance initial value until the adjusted fluctuation change value meets the impedance initial value condition, and obtain the adjusted system-side harmonic impedance initial value.

[0121] Optionally, in step 1025, based on the current impedance threshold, performing cyclic approximation adjustment on the current initial value of the system-side harmonic impedance is specifically:

[0122] Judge whether the current impedance threshold is less than the preset threshold. If so, add the preset change step to the current initial value of the system-side harmonic impedance to obtain the adjusted initial value of the system-side harmonic impedance. If not, subtract the preset change step from the current initial value of the system-side harmonic impedance to obtain the adjusted initial value of the system-side harmonic impedance.

[0123] In this embodiment, a cyclic step-by-step approximation method is adopted, and the change step λ is set to 0.01. The preset threshold is 0. When delta < 0, Z sr0 = Z sr0 + λ; when delta > 0, Z sr0 = Z sr0 - λ until ΔB no longer decreases, that is, exit the loop. Then check whether the current ΔB meets the impedance initial value condition. The impedance initial value condition: ΔB is the minimum value within 5 times the impedance initial value. If so, the latest Zsr0 Substitute into Equation (5) and Equation (6) to obtain the final harmonic impedance on the system side.

[0124] Optionally, in step 1025, according to each type of impedance value and the initial value of the adjusted harmonic impedance on the system side, calculate the adjusted fluctuation change value, specifically:

[0125] Calculate the impedance difference between each type of impedance value and the initial value of the adjusted harmonic impedance on the system side, take the absolute value of the impedance difference of each type, and sum up the absolute values of the impedance differences of each type to obtain the adjusted fluctuation change value.

[0126] In this embodiment, taking the calculation of the real part \(Z\) of the harmonic impedance on the system side as an example, sr for the 4 types of calculated impedance values \(Z(k)\) and the initial impedance value \(Z\), sr the sum of the absolute values of the differences is defined as the fluctuation change value \(\Delta B\), and the expression is: sr0

[0127]

[0128] Taking the calculation of the imaginary part \(Z\) of the harmonic impedance on the system side as an example, si for the 4 types of calculated impedances \(Z(k)\) and the initial impedance value \(Z\), si the sum of the absolute values of the differences is defined as the fluctuation change value \(\Delta B\), and the expression is: si0

[0129]

[0130] Step 1026: Perform impedance value calculation on the classified background harmonic voltage and the initial value of the adjusted harmonic impedance on the system side to obtain the adjusted impedance value for each type;

[0131] In this embodiment, the method of impedance value calculation is the same as that in step 1023.

[0132] Step 1027: Based on the adjusted impedance value for each type, calculate the harmonic impedance on the system side corresponding to the current feeder.

[0133] Optionally, step 1027 is specifically: Obtain the impedance values of the middle two items within the adjusted impedance value for each type, and calculate the average value of the impedance values of the middle two items to obtain the harmonic impedance on the system side corresponding to the current feeder.

[0134] In this embodiment, taking the calculation of the real part \(Z\) of the harmonic impedance on the system side as an example, sr the real part of the harmonic impedance on the system side corresponding to the feeder is specifically:

[0135]

[0136] Taking the imaginary part \(Z\) of the harmonic impedance on the system side of the computing system as an example, the imaginary part of the harmonic impedance on the system side corresponding to the feeder is specifically: si For example, the imaginary part of the harmonic impedance on the system side corresponding to the feeder is specifically:

[0137]

[0138] Step 103: Based on the harmonic impedances on the system side corresponding to all the feeders in the distribution network system, calculate the estimated values of the harmonic impedances on the user side corresponding to all the feeders.

[0139] In this embodiment, by using the methods in Steps 101 - 102, the harmonic impedances on the system side when the bus and each feeder are regarded as users can be calculated. Based on each harmonic impedance on the system side, the estimated values of the corresponding harmonic impedances on the user side can be estimated.

[0140] It should be noted that the methods in Steps 101 - 102 are also applicable when the PCC bus is regarded as a user, because the PCC bus can also be regarded as a feeder during the calculation of the harmonic impedance on the system side. At this time, all user feeders are regarded as the system side, and the PCC bus is the user side.

[0141] Optionally, Step 103 specifically includes Steps 1031 to 1032, and the specific steps are as follows:

[0142] Step 1031: Calculate the transition harmonic impedance according to the harmonic impedances on the system side corresponding to all the feeders in the distribution network system. The formula is:

[0143]

[0144] where \(Z\) G is the transition harmonic impedance, \(Z\) s (i) is the harmonic impedance on the system side corresponding to the \(i\)-th feeder, and \(n\) is the number of feeders;

[0145] In this embodiment, when the number of feeders in a certain system is \(n\), the harmonic impedances on the system side and the harmonic impedance on the system side when a certain feeder is regarded as a user are calculated respectively. After taking the reciprocals of these \(n + 1\) harmonic impedances on the system side and adding them up and then dividing by \(n\), the transition harmonic impedance of the entire system can be obtained. The calculation formula of the transition harmonic impedance \(Z\) G is Formula (14).

[0146] Step 1032: Calculate the estimated values of the harmonic impedances on the user side corresponding to all the feeders according to the transition harmonic impedance. The formula is:

[0147]

[0148] where \(Z\) c (i) is the harmonic impedance on the user side corresponding to the \(i\)-th feeder.

[0149] In this embodiment, based on the transition harmonic impedance, the harmonic impedance Z c (i) of the bus and each feeder can be calculated, that is, the estimated value of the harmonic impedance on the user side, and its calculation formula is Equation (15). Finally, the calculated estimated value of the harmonic impedance on the user side can provide a prerequisite for the evaluation of the harmonic emission level and the quantification of responsibility.

[0150] Implementing the embodiment of the present invention, the current feeder in the distribution network system is regarded as the user side, and the non-current feeder is regarded as the system side. Based on the obtained harmonic data, the initial value of the harmonic impedance on the system side corresponding to the current feeder is calculated; based on the initial value of the harmonic impedance on the system side corresponding to the current feeder, the background harmonic voltage is solved, and the background harmonic voltage is sorted and classified. The classified background harmonic voltage is analyzed for fluctuation amount to obtain the harmonic impedance on the system side corresponding to the current feeder; based on the harmonic impedances on the system side corresponding to all the feeders in the distribution network system, the estimated values of the harmonic impedances on the user side corresponding to all the feeders are calculated. By considering the harmonic impedance estimation of the low-bandwidth communication in the distribution network, only using the harmonic data such as the amplitude of the harmonic voltage and current that can be accurately provided currently and the phase difference information between the two, the effective estimation of the harmonic impedances on the system side and the user side under low-bandwidth communication can be realized, the estimation error can be effectively reduced, and the accuracy of the harmonic impedance estimation can be improved.

[0151] To further confirm the effectiveness of the present invention, the harmonic impedance estimation method of the present invention is verified by simulation. Taking the partial topology of a substation of a certain power supply bureau as an example, considering the feeders 1, 2, 3 and the bus in it, the equivalent topology is as Figure 6 shown.

[0152] Build the Norton equivalent circuit as shown in Figure 4 in Matlab / Simulink. When the bus is regarded as the user side, the remaining feeders are the system side. At this time, it is assumed that the calculated system harmonic impedance is Z s1 ; when feeder 1 is regarded as the user side, the bus and the remaining feeders are the system side. At this time, it is assumed that the calculated system harmonic impedance is Z s2 ; when feeder 2 is regarded as the user side, the bus and the remaining feeders are the system side. At this time, it is assumed that the calculated system harmonic impedance is Z s3 ; when feeder 3 is regarded as the user side, the bus and the remaining feeders are the system side. At this time, it is assumed that the calculated system harmonic impedance is Z s4 .

[0153] During the simulation, Z s1 is set to 2 + j5Ω, Z s2 is set to 5 + j12Ω, Z s3 is set to 8 + j15Ω, Z s4 is set to 3 + j10Ω, and a random fluctuation of ±10% is added to both the real part and the imaginary part of the harmonic impedance. The harmonic current I on the user sidec The amplitude of is set to 100 A, and ±15% random fluctuations and ±10% sinusoidal fluctuations are superimposed. The phase angle is set to 60°, and ±30% random fluctuations are superimposed. The harmonic current I on the system side s The amplitude of is set to 10 A, and ±10% random fluctuations are superimposed. The phase angle is set to -60°, and ±30% random fluctuations are superimposed. A total of N = 10000 groups of samples are generated.

[0154] The harmonic impedance is solved using the method of the present invention, and the solution results of the harmonic impedance on the system side are shown in Table 1.

[0155] Table 1 Solution Results of Harmonic Impedance on the System Side

[0156]

[0157] As can be seen from Table 1, the accuracy rates of the real part and the imaginary part of the harmonic impedance on the system side are both above 90%.

[0158] At this time, the transition harmonic impedance Z G can be expressed as:

[0159]

[0160] Furthermore, the harmonic impedances Z of the bus and each feeder are obtained c (i). The harmonic impedance on the user side can be obtained through calculation as shown in Table 2.

[0161] Table 2 Harmonic Impedance on the User Side

[0162]

[0163] Similarly, as can be seen from Table 2, the accuracy rates of the real part and the imaginary part of the harmonic impedance on the user side are relatively high.

[0164] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0165] 1. Under low-bandwidth communication, only the harmonic data that can be easily obtained in actual engineering, namely the amplitudes of harmonic voltage and current and the phase difference data between the two, are required. Compared with the prior art for obtaining the specific vector information of the two, the present invention is more feasible, requires less data volume, better meets the actual engineering needs, and the harmonic impedance results obtained by the present invention have theoretical support, higher reliability, and stronger persuasion.

[0166] 2. Compared with the prior art that needs to make one or more assumptions, the present invention adopts a method of cyclic gradual approximation, without making assumptions such as the harmonic impedance on the user side being much larger than that on the system side, can effectively solve the problem of the lack of phase of harmonic voltage and current, and is applicable to any order of harmonics, making the present invention more applicable in actual engineering.

[0167] 3. Under the background of limited existing monitoring point quantity and communication data transmission capacity, it is possible to accurately estimate the harmonic impedance on the system side and the user side. Its principle is simple, the calculation is convenient, and the estimation result is accurate, having great engineering application prospects. Accurate harmonic impedance on the system side and the user side is also the primary prerequisite for the division of harmonic pollution liability, providing a prerequisite condition and a new theoretical basis for the division of harmonic pollution liability.

[0168] In addition, the embodiment of the present application further provides a computer device, which includes a processor and a memory. The memory is used to store a computer program, and when the computer program is executed by the processor, the steps in any of the above method embodiments are implemented.

[0169] The embodiment of the present application further provides a computer-readable storage medium, which stores a computer program, and when the computer program is executed by the processor, the steps in any of the above method embodiments are implemented.

[0170] The above specific embodiments have further elaborated on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. It is particularly pointed out that for those skilled in the art, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for estimating harmonic impedance of a distribution network, characterized in that: include: Taking a current feeder in the distribution network system as a user side and a non-current feeder as a system side, and calculating an initial value of a system-side harmonic impedance corresponding to the current feeder based on the acquired harmonic data; Based on the initial value of the system-side harmonic impedance corresponding to the current feeder, solving the background harmonic voltage, sorting and classifying the background harmonic voltage, and performing fluctuation analysis on the classified background harmonic voltage to obtain the system-side harmonic impedance corresponding to the current feeder; Calculating estimated user-side harmonic impedances corresponding to all feeders in the distribution network system based on the system-side harmonic impedances corresponding to all feeders in the distribution network system; Among them, the background harmonic voltage is sorted and classified, and the fluctuation analysis is performed on the classified background harmonic voltage to obtain the system side harmonic impedance corresponding to the current feeder, specifically: the background harmonic voltage is sorted by size, and based on a preset classification number, the sorted background harmonic voltage is classified to obtain the classified background harmonic voltage; according to the initial value of the system side harmonic impedance of each group, an impedance initial value range is obtained, and the current system side harmonic impedance initial value is selected from the impedance initial value range; the classified background harmonic voltage and the current system side harmonic impedance initial value are calculated to obtain each type of impedance value; based on each type of impedance value and the current system side The initial value of harmonic impedance is used to calculate the current impedance threshold, where the impedance value includes the real part of the impedance value and the imaginary part of the impedance value; based on the current impedance threshold, the current initial value of the harmonic impedance on the system side is adjusted by cyclic approximation, and the adjusted fluctuation change value is calculated according to each type of impedance value and the adjusted initial value of the harmonic impedance on the system side, until the adjusted fluctuation change value meets the initial value condition of impedance, thereby obtaining the adjusted initial value of the harmonic impedance on the system side; the classified background harmonic voltage and the adjusted initial value of the harmonic impedance on the system side are used to perform impedance value calculation to obtain each type of adjusted impedance value; based on each type of adjusted impedance value, the system side harmonic impedance corresponding to the current feeder is calculated; The impedance value of each type of impedance is calculated by calculating the classified background harmonic voltage and the current system-side harmonic impedance initial value, specifically: The mean value of each type of background harmonic voltage after classification and the initial value of the current system-side harmonic impedance are calculated to obtain the expected value of each type. The formula is: Where E(·) represents the expected value; According to each type of expected value, calculate each type of impedance value, the formula is: in, For the The impedance value of the class, is the preset number of categories, is the current feeder value, is the harmonic current vector at the current common connection point, is the magnitude of the harmonic current vector at the current common connection point, |I pcc | is the harmonic current amplitude at the common connection point, U pccr and U sr are the projections of the harmonic voltage amplitude at the common connection point and the background harmonic voltage amplitude on the system side on the real axis, U pcci and U si are the projections of the harmonic voltage amplitude at the common connection point and the background harmonic voltage amplitude on the system side on the imaginary axis, Z sr , Z si are respectively the real and imaginary parts of the initial value of the system side harmonic impedance.

2. The method for estimating harmonic impedance of a distribution network according to claim 1, wherein: The initial value of the system-side harmonic impedance corresponding to the current feeder is calculated based on the acquired harmonic data, specifically: Establishing a Norton equivalent circuit based on the user side and the system side; Based on the Norton equivalent circuit, several groups of harmonic data within a preset time period are obtained; wherein the harmonic data include harmonic voltage amplitude, harmonic current amplitude and phase difference; The harmonic data of the plurality of groups are subjected to phase zero maximum value processing to obtain the initial value of the system side harmonic impedance corresponding to the current feeder.

3. The method for estimating harmonic impedance of a distribution network according to claim 2, wherein: The phase zeroing maximum value processing is performed on the harmonic data of the plurality of groups to obtain the initial value of the system-side harmonic impedance corresponding to the current feeder, specifically: According to the harmonic data of each group, the harmonic impedance data of each group is calculated using the phase position zero method; The maximum value of the harmonic impedance data of each group is used as the initial value of the system-side harmonic impedance of each group, and the initial value of the system-side harmonic impedance of each group is counted to obtain the initial value of the system-side harmonic impedance corresponding to the current feeder. The specific formula is: Among them, Z sr0 is the real part of the initial value of the system side harmonic impedance, Z si0 is the imaginary part of the initial value of the system side harmonic impedance, U pcc_i is the harmonic voltage amplitude, I pcc_i is the harmonic current amplitude, θ i is the phase difference.

4. The method for estimating harmonic impedance of a distribution network according to claim 3, wherein: The background harmonic voltage is solved based on the initial value of the system-side harmonic impedance corresponding to the current feeder, specifically: Based on the initial value of the system-side harmonic impedance of each group, the system-side background harmonic voltage of each group is inversely solved, and the formula is: Among them, |I pcc | is the harmonic current amplitude at the common connection point, U pccr and U sr are the projections of the harmonic voltage amplitude at the common connection point and the background harmonic voltage amplitude on the system side on the real axis, U pcci and U si are the projections of the harmonic voltage amplitude at the common connection point and the background harmonic voltage amplitude on the system side on the imaginary axis, Z sr , Z si are the real and imaginary parts of the initial value of the system side harmonic impedance respectively; The system-side background harmonic voltage of each group is counted to obtain the background harmonic voltage.

5. The method for estimating harmonic impedance of a distribution network according to claim 4, wherein: The formula for calculating the current impedance threshold based on each type of impedance value and the current system-side harmonic impedance initial value is specifically: Wherein, delta is the current impedance threshold, is the current initial value of the system-side harmonic impedance; For the The impedance value of the class.

6. The method for estimating harmonic impedance of a distribution network according to claim 1, wherein: The cyclic approximation adjustment of the current system-side harmonic impedance initial value based on the current impedance threshold is specifically as follows: Determine whether the current impedance threshold is less than a preset threshold; if so, add a preset change step size to the current system side harmonic impedance initial value to obtain the adjusted system side harmonic impedance initial value; if not, subtract the preset change step size from the current system side harmonic impedance initial value to obtain the adjusted system side harmonic impedance initial value.

7. The method for estimating harmonic impedance of a distribution network according to claim 1, wherein: The adjusted fluctuation change value is calculated based on each type of impedance value and the adjusted system-side harmonic impedance initial value, specifically: The impedance difference between each type of impedance value and the adjusted initial value of the system-side harmonic impedance is calculated, and the absolute value of the impedance difference of each type is obtained. The absolute value of the impedance difference of each type is summed to obtain the adjusted fluctuation change value.

8. The method for estimating harmonic impedance of a distribution network according to claim 1, wherein: The system-side harmonic impedance corresponding to the current feeder is calculated based on each type of adjusted impedance value, specifically: The impedance values of the two middle items in each type of adjusted impedance value are obtained, and the average of the two middle impedance values is calculated to obtain the system-side harmonic impedance corresponding to the current feeder.

9. The method for estimating harmonic impedance of a distribution network according to claim 1, wherein: The system-side harmonic impedances corresponding to all feeders in the distribution network system are calculated based on the user-side harmonic impedance estimates corresponding to all feeders, specifically: According to the system-side harmonic impedance corresponding to all feeders in the distribution network system, the transition harmonic impedance is calculated using the formula: in, is the transition harmonic impedance, For the The system side harmonic impedance corresponding to the feeder, n is the number of feeders; According to the transition harmonic impedance, the estimated values of the user-side harmonic impedance corresponding to all the feeders are calculated using the following formula: in, For the The user-side harmonic impedance corresponding to the feeder.

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