Site selection method and device for active governance device for same-level harmonic waves of radial power distribution network

Abstract

The invention provides an active treatment device site selection method and device for same-level harmonic waves of a radial power distribution network, and belongs to the technical field of electric energy quality treatment. The method comprises the following steps: acquiring equipment parameters of each branch of the power distribution network; determining the harmonic impedance of each branch according to the equipment parameters of each branch of the power distribution network, and calculating the influence coefficient of the harmonic of each nonlinear load branch on the harmonic voltage of the power distribution network; according to the influence coefficients of all the non-linear load branches, calculating the voltage distortion contribution rate of harmonic waves of each non-linear load branch to the power distribution network; according to the variable coefficient and a threshold value, the numerical distribution characteristics of the voltage distortion contribution rates corresponding to all the nonlinear load branches are judged; and determining the optimal site selection of the harmonic active treatment device according to the numerical distribution characteristics, the expected minimum target of harmonic treatment and the voltage distortion contribution rate corresponding to each nonlinear load branch. According to the invention, the problem of difficulty in site selection of a harmonic treatment device with a decentralized harmonic source in a radial power distribution network can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power quality management, and in particular to a method for selecting a site for an active management device of the same-level harmonics in a radial distribution network. Background Art

[0002] The flexible and efficient energy conversion characteristics of power electronics technology meet the needs of the development of various industries in the current society and are an important foundation for promoting the construction of new power systems. It promotes the large-scale grid connection of massive distributed new energy and power electronic equipment, which in turn leads to a rapid increase in the proportion of power electronics in modern distribution networks. However, these devices have significant nonlinearity in the process of power conversion, resulting in an increasing degree of harmonic pollution in the distribution network, which seriously threatens the safe, stable and efficient operation of the distribution network, and also makes the harmonic sources in the distribution network present new characteristics of decentralization and full network, which brings huge challenges to the site selection of harmonic control devices.

[0003] In fact, in order to ensure the safe operation of the distribution network, the harmonic voltage level (distortion degree) is mainly controlled, and the distortion degree of the grid voltage is jointly determined by the harmonic current emitted by the harmonic source and its external harmonic impedance. Under the same harmonic current, the larger the harmonic impedance, the higher the contribution rate to the voltage distortion. If the control device is installed here, the more significant the control effect will be, and the higher the control economy will be. This provides a solution for the site selection of active control devices for distribution networks with multi-point harmonic emission. However, with the increase in the cabling rate of distribution lines, the distribution network is provided with a rich and high-level capacitive part, which forms a complex and multi-band resonance with the inductive part, changing the shape of the harmonic impedance at different frequencies, and no longer having an ideal linear characteristic, resulting in a significant increase in the complexity of the external harmonic impedance of each harmonic source, and the impact on the analysis of the voltage distortion contribution rate cannot be ignored. Summary of the invention

[0004] The embodiments of the present invention provide a method and device for site selection of active harmonic control devices for the same-level harmonics in a radial distribution network, so as to solve the problem of site selection of active harmonic control devices caused by multi-point distribution of harmonic sources and complex and changeable harmonic impedance.

[0005] In a first aspect, an embodiment of the present invention provides a method for selecting a site for an active control device for harmonics of the same level in a radial distribution network, comprising:

[0006] Obtaining equipment parameters of each branch of the distribution network; wherein the distribution network includes a power supply branch, a reactive power compensation branch and a nonlinear load branch;

[0007] Determine the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network, and calculate the influence coefficient of the harmonic of each nonlinear load branch on the harmonic voltage of the distribution network respectively; wherein the equipment parameters of the nonlinear load branch include the capacitive reactance of the line;

[0008] According to the influence coefficient of all nonlinear load branches, the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network is calculated respectively;

[0009] Calculating a coefficient of variation according to the voltage distortion contribution rates corresponding to all nonlinear load branches, and determining numerical distribution characteristics of the voltage distortion contribution rates corresponding to all nonlinear load branches according to the coefficient of variation and a threshold value;

[0010] The optimal location of the active harmonic control device is determined based on the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch.

[0011] In a second aspect, an embodiment of the present invention provides a site selection device for an active control device of the same-level harmonics of a radial distribution network, comprising:

[0012] A data acquisition module, used to acquire equipment parameters of each branch of the distribution network; wherein the distribution network includes a power supply branch, a reactive power compensation branch and a nonlinear load branch;

[0013] An influence coefficient calculation module is used to determine the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network, and respectively calculate the influence coefficient of the harmonic of each nonlinear load branch on the harmonic voltage of the distribution network; wherein the equipment parameters of the nonlinear load branch include the capacitive reactance of the line;

[0014] A voltage distortion contribution rate calculation module is used to calculate the voltage distortion contribution rate of the harmonics of each nonlinear load branch to the distribution network according to the influence coefficient of all nonlinear load branches;

[0015] A numerical distribution characteristic judgment module is used to calculate the coefficient of variation according to the voltage distortion contribution rate corresponding to all nonlinear load branches, and judge the numerical distribution characteristics of the voltage distortion contribution rate corresponding to all nonlinear load branches according to the coefficient of variation and a threshold value;

[0016] The optimal site determination module is used to determine the optimal site for the active harmonic control device based on the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch.

[0017] The embodiment of the present invention provides a method and device for site selection of active control devices for harmonics of the same level in a radial distribution network. The harmonic impedance in a nonlinear load branch is calculated by the capacitive reactance of a power supply line, and the voltage distortion contribution rate of a harmonic source to a power grid is more accurately evaluated. The site selection strategy of the active harmonic control device is determined by the distribution characteristics of the voltage distortion contribution rate of the harmonics in the nonlinear load branch, the expected minimum target for harmonic control, and the voltage distortion contribution rate corresponding to each nonlinear load branch. The complexity of site selection is reduced, the control devices are reasonably reduced, and the inefficiency problem of excessive number and capacity of control devices caused by traditional control schemes is overcome. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0019] Figure 1 It is a schematic diagram of the grid structure of the radial distribution network and the harmonic impedance model of each component device provided by an embodiment of the present invention;

[0020] Figure 2 It is a flowchart of the implementation of the method for selecting a site for an active control device for harmonics of the same level in a radial distribution network provided by an embodiment of the present invention;

[0021] Figure 3 It is a schematic diagram of the contribution rate of each nonlinear load branch to the voltage distortion of the distribution network provided by an embodiment of the present invention;

[0022] Figure 4 It is a schematic diagram of the cumulative result of voltage distortion contribution rates arranged from large to small provided by an embodiment of the present invention;

[0023] Figure 5 It is a structural schematic diagram of a site selection device for active control of same-level harmonics in a radial distribution network provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0026] Figure 1 A schematic diagram of the radial distribution network grid structure and the harmonic impedance model of each component equipment provided in an embodiment of the present invention.

[0027] The radial distribution network structure includes branches connected to the busbar. Each branch is divided into power supply branch, reactive power compensation branch and non-linear load branch according to its attribute. New energy grid-connected branches are treated as non-linear load branches.

[0028] Figure 2 The present invention provides a flowchart of the method for selecting a site for active harmonic control devices in a radial distribution network according to an embodiment of the present invention. Figure 2 As shown, the details are as follows:

[0029] Step 101: Obtain equipment parameters of each branch of the distribution network; wherein the distribution network includes a power supply branch, a reactive power compensation branch, and a nonlinear load branch.

[0030] The power supply branch includes a power supply and a transformer, the nonlinear load branch includes a power supply line and a load, and the reactive power compensation branch includes a plurality of reactive power compensation groups with different series reactance rates.

[0031] The specific process is:

[0032] (1) Determine whether there is a reactive power compensation branch and count the number of nonlinear load branches.

[0033] (2) The nonlinear load branches should be numbered one by one in the same fixed direction. It is recommended to number them incrementally from left to right.

[0034] (3) Collect parameters of power supply, transformer, power supply line, load, and reactive power compensation (if any) equipment of the distribution network.

[0035] Power supply parameters include minimum short-circuit capacity S min , X / R is the reactance / resistance ratio, and the rated voltage value of the distribution network busbar is U N The transformer parameters include rated capacity S t , short-circuit voltage U d , short circuit loss P k The power supply line parameters include the line length l, unit length resistance R0, unit length inductance L0, unit length capacitance C0. The load parameters include the minimum operating apparent power S d , average power factor PF. Reactive compensation parameters include the rated capacity Q of reactive compensation capacitor bank co , capacitor bank rated voltage U C , series reactance rate k.

[0036] Step 102: Determine the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network, and calculate the influence coefficient of the harmonic of each nonlinear load branch on the harmonic voltage of the distribution network; wherein the equipment parameters of the nonlinear load branch include the capacitive reactance of the line.

[0037] Considering the increase in line capacitance after the cable distribution network is converted, the impact of resonance on harmonic impedance is brought about. The harmonic impedance of each branch is calculated by capacitive reactance, and the contribution rate of harmonic sources to the voltage distortion of the power grid is evaluated more accurately by harmonic impedance.

[0038] The power supply branch is composed of the power supply harmonic impedance and the transformer harmonic impedance in series. If there is a reactive compensation branch, if it contains multiple reactive compensation groups with different series reactance rates, the impedance of each reactive compensation group can be calculated first, and then the total harmonic impedance of the reactive compensation branch can be calculated. The nonlinear load branch is composed of the power supply line harmonic impedance and the load harmonic impedance in series and parallel.

[0039] In a possible implementation, determining the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network includes: determining the harmonic impedance of the power supply branch, the reactive power compensation branch and the nonlinear load branch respectively;

[0040] The harmonic impedance of the power supply branch is the sum of the power supply harmonic impedance and the transformer harmonic impedance. The formula is as follows:

[0041] Z g (h) = Z s (h)+Z t (h)

[0042]

[0043] In the formula, Z s (h) is the power supply harmonic impedance, S min is the minimum short-circuit capacity, X / R is the reactance / resistance ratio, U N is the rated voltage of the distribution network busbar, h is the harmonic order, j is the imaginary number symbol in the complex number, Z t (h) is the transformer harmonic impedance, S t is the rated capacity, P k is the short-circuit loss, U d is the short-circuit voltage;

[0044] The reactive power compensation branch contains multiple reactive power compensation groups with different series reactance ratios. The harmonic impedance formula of the reactive power compensation branch is as follows:

[0045]

[0046] In the formula, Z co (h) is the reactive compensation impedance, Q co is the rated capacity of the reactive power compensation capacitor bank, UC is the rated voltage of the capacitor bank, k is the series reactance ratio, e is the number of reactive compensation groups with different series reactance ratios, m is the number of reactive compensation groups with different series reactance ratios, m∈N, h is the harmonic order, h=3,5,7,…,25;

[0047] The nonlinear load branch is composed of the power supply line and the load in series and parallel. The harmonic impedance formula of the nonlinear load branch is as follows:

[0048]

[0049] Z L (h) = Z0(h)·sinh[γ(h)·l]

[0050]

[0051] In the formula, Z d (h) is the load harmonic impedance, S d is the minimum operating apparent power, PF is the average power factor, Z L (h) is the impedance of the distributed parameter π model of the line, Z0(h) is the line characteristic impedance, γ(h) is the line propagation coefficient, l is the length, R0 is the resistance per unit length, L0 is the inductance per unit length, C0 is the capacitance per unit length, ω0 is the fundamental angular frequency, ω0=2πf0, f0=50HZ, Z C (h) is the capacitive reactance of the distributed parameter π model of the line, h is the harmonic order, h = 3, 5, 7, …, 25.

[0052] Under normal circumstances, nonlinear loads only produce odd harmonics and most of them are within 25th order, so the harmonic order h = 3, 5, 7, …, 25.

[0053] In other possible ways, the harmonic impedance of the nonlinear load branch can be calculated by capacitive reactance in other ways. The present application mainly uses the calculation of the harmonic impedance of the nonlinear load branch by capacitive reactance as an example for explanation.

[0054] In a possible implementation, if there is a reactive power compensation branch, the total harmonic impedance Z of the branches other than the i-th nonlinear load branch is p,i , can be calculated as follows:

[0055]

[0056] Where r is the number of the nonlinear load branch in the distribution network; n is the number of nonlinear load branches in the distribution network, n∈N.

[0057] In another possible implementation, if there is no reactive compensation branch, the harmonic impedance Z of the branches other than the i-th nonlinear load branch is p,i, can be calculated as follows:

[0058]

[0059] Where r is the number of the nonlinear load branch in the distribution network; n is the number of nonlinear load branches in the distribution network, n∈N.

[0060] In a possible implementation, respectively calculating the influence coefficient of the harmonics of each nonlinear load branch on the harmonic voltage of the distribution network includes:

[0061] Calculate the influence coefficient of the harmonics of each nonlinear load branch on the harmonic voltage of the distribution network. The formula is as follows:

[0062]

[0063] The results of the influence coefficient of the harmonics of all nonlinear load branches on the harmonic voltage of the distribution network are as follows:

[0064]

[0065] In the formula, α i is the influence coefficient of the harmonic generated by the i-th nonlinear load branch on the harmonic voltage of the distribution network, Z P,i (h) is the total harmonic impedance of the branches other than the i-th nonlinear load branch, Z C,i (h) is the capacitive reactance of the distributed parameter π model for the i-th nonlinear load branch, Z L,i (h) is the impedance of the distributed parameter π model for the i-th nonlinear load branch, and n is the number of nonlinear load branches.

[0066] Step 103: Calculate the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network according to the influence coefficients of all nonlinear load branches.

[0067] The calculation of the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network includes:

[0068] Perform square root calculation on the influence coefficient of each harmonic of a nonlinear load branch on the harmonic voltage of the distribution network;

[0069] The result of the square root operation is subjected to a proportion operation to obtain the contribution rate of the harmonic of the nonlinear load branch to the voltage distortion of the distribution network.

[0070] In actual implementation, it is necessary to execute the above process for each nonlinear load branch respectively to calculate the contribution rate of the harmonics of all nonlinear load branches to the voltage distortion of the distribution network.

[0071] In a possible implementation, calculating the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network according to the influence coefficient of all nonlinear load branches includes:

[0072] The influence coefficient of multiple harmonics of each nonlinear load branch on the harmonic voltage of the distribution network is calculated by square root, and the formula is as follows:

[0073]

[0074] The result of the square root operation is used for proportion operation to obtain the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network. The formula is as follows:

[0075]

[0076] In the formula, β i is the square root calculation result of the influence coefficient of the ith nonlinear load branch on the harmonic voltage of the distribution network, λ k is the contribution rate of the harmonics generated by the kth nonlinear load branch to the voltage distortion of the distribution network, β k is the square root calculation result of the influence coefficient of the kth nonlinear load branch on the harmonic voltage of the distribution network, and n is the number of nonlinear load branches.

[0077] Step 104: Calculate the coefficient of variation according to the voltage distortion contribution rates corresponding to all nonlinear load branches, and determine the numerical distribution characteristics of the voltage distortion contribution rates corresponding to all nonlinear load branches according to the coefficient of variation and the threshold.

[0078] The coefficient of variation is calculated by the average value and standard deviation of the voltage distortion contribution rate corresponding to the harmonic source of all nonlinear load branches. The calculated coefficient of variation is a numerical value. The numerical distribution of the voltage distortion contribution rate corresponding to all nonlinear load branches is judged based on the coefficient of variation and the threshold value, whether it is a concentrated distribution or a discrete distribution. Then, the corresponding harmonic active control device site selection strategy is selected according to the data distribution characteristics, which improves the efficiency of the site selection of the harmonic active control device and reduces the complexity of the site selection process in specific scenarios.

[0079] In a possible implementation, calculating the coefficient of variation according to the voltage distortion contribution rates corresponding to all nonlinear load branches includes:

[0080] Calculate the average value of the contribution rate of the harmonics of all nonlinear load branches to the voltage distortion of the distribution network;

[0081] Calculate the standard deviation of the contribution rate of the harmonics of all nonlinear load branches to the voltage distortion of the distribution network based on the average value;

[0082] Divide the standard deviation by the mean to get the coefficient of variation.

[0083] The average value is calculated as follows:

[0084]

[0085] In the formula, λ k is the contribution rate of the harmonics generated by the kth nonlinear load branch to the voltage distortion of the distribution network, and n is the number of nonlinear load branches.

[0086] The formula for calculating the standard deviation is:

[0087]

[0088] In the formula, λ k is the contribution rate of the harmonics generated by the kth nonlinear load branch to the voltage distortion of the distribution network, and n is the number of nonlinear load branches.

[0089] The formula for calculating the coefficient of variation is:

[0090]

[0091] Where c is the coefficient of variation.

[0092] The threshold value is calculated as:

[0093]

[0094] Where n is the number of nonlinear load branches; ε is the maximum relative error allowed by the value (%), which is 5%. Other values ​​can also be selected based on actual conditions, but should not exceed 10%.

[0095] In a possible implementation, the numerical distribution characteristics of the voltage distortion contribution rates corresponding to all nonlinear load branches are determined based on the coefficient of variation and the threshold, including:

[0096] When the coefficient of variation is greater than the threshold, the voltage distortion contribution rate corresponding to all nonlinear load branches is discretely distributed;

[0097] When the coefficient of variation is less than or equal to the threshold, the voltage distortion contribution rates corresponding to all nonlinear load branches are concentratedly distributed.

[0098] Step 105: Determine the optimal location of the active harmonic control device according to the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch.

[0099] The corresponding site selection strategy for active harmonic control devices is determined based on the numerical distribution characteristics of the contribution rate of the harmonic sources of each nonlinear load branch to the voltage distortion, which reduces the complexity of the site selection process in specific scenarios.

[0100] Nonlinear load branches with high voltage distortion contribution rates are selected as the priority locations for installing harmonic control devices, ensuring active harmonic control devices of the same capacity, which can achieve better control effects and economy, and reduce the inefficiency of installing control devices in the entire distribution network to control multi-point harmonic sources, resulting in excessive number and capacity of devices.

[0101] The embodiment of the present invention provides a method and device for site selection of active control devices for harmonics of the same level in a radial distribution network. The harmonic impedance in a nonlinear load branch is calculated by the capacitive reactance of a power supply line, and the voltage distortion contribution rate of a harmonic source to a power grid is more accurately evaluated. The site selection strategy of the active harmonic control device is determined by the distribution characteristics of the voltage distortion contribution rate of the harmonics in the nonlinear load branch, the expected minimum target for harmonic control, and the voltage distortion contribution rate corresponding to each nonlinear load branch. The complexity of site selection is reduced, the control devices are reasonably reduced, and the inefficiency problem of excessive number and capacity of control devices caused by traditional control schemes is overcome.

[0102] In a possible implementation, according to the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch, the optimal location of the active harmonic control device is determined, including:

[0103] When the voltage distortion contribution rate is concentratedly distributed, the value of the lowest target is divided by the average value of the voltage distortion contribution rate corresponding to all nonlinear load branches to obtain the ratio result;

[0104] According to the ratio result, a corresponding number of nonlinear load branches are randomly selected from all nonlinear load branches to determine the installation positions of the active harmonic control devices;

[0105] When the voltage distortion contribution rate is discretely distributed, the voltage distortion contribution rates corresponding to all nonlinear load branches are arranged in order from large to small;

[0106] The arranged voltage distortion contribution rates are accumulated one by one;

[0107] When the accumulated result meets the judgment condition for the first time, the nonlinear load branch corresponding to the accumulated voltage distortion contribution rate is determined as the installation location of the active harmonic control device.

[0108] In a possible implementation, when the voltage distortion contribution rate corresponding to the nonlinear load branch is concentratedly distributed, the site selection of the active harmonic control device is carried out according to the following strategy:

[0109] a) According to the following formula, the number of branches N that need to be installed with active harmonic control devices is determined by the ratio of the expected minimum target value to the average voltage distortion contribution rate. t :

[0110]

[0111] Where G is the minimum target.

[0112] b) Choose N arbitrarily t The nonlinear load branch is used as the installation location for the active harmonic control device, completing the site selection work.

[0113] In another possible implementation, when the voltage distortion contribution rate corresponding to the nonlinear load branch is discretely distributed, the site selection of the harmonic control device is performed according to the following strategy.

[0114] Arrange the voltage distortion contribution rates corresponding to all nonlinear load branches from large to small, and obtain the result shown in the following formula:

[0115] B=[λ (1) ,λ (2) ,λ (3) , ..., λ (n) ]

[0116] Wherein, the superscripts (1), (2), ..., (n) represent the positions of the voltage distortion contribution rates corresponding to the n nonlinear load branches arranged from large to small.

[0117] The voltage distortion contribution rates after arrangement are accumulated one by one according to the following formula:

[0118]

[0119] Where x represents the voltage distortion contribution rate of the xth position after sorting; M y Indicates the y-th accumulation result. At this time, the y voltage distortion contribution rates are accumulated after arrangement. y=1,2,…,n. When y is 1, it means that the accumulation result is the maximum value of the voltage distortion contribution rate, that is, M1=λ (1) .

[0120] Determine the result of each accumulation M y Whether the condition of being greater than or equal to the minimum target G expected for harmonic control is met, the formula is as follows:

[0121] M y ≥G

[0122] Where M y is the result of each accumulation, and G is the minimum goal.

[0123] When the judgment conditions are met for the first time, the nonlinear load branch corresponding to the accumulated voltage distortion contribution rate will be used as the location for installing the active harmonic control device, and the branch with a higher voltage distortion contribution rate will have higher priority for installing the active harmonic control device to complete the site selection work.

[0124] In one possible implementation, the determination of the minimum target expected for harmonic control includes:

[0125] Obtain the distortion improvement rate of distribution network voltage;

[0126] Obtain the compensation rate of the active harmonic control device;

[0127] Divide the distortion improvement rate by the compensation rate of the active harmonic control device, and the resulting ratio is the minimum target expected for harmonic control.

[0128] The voltage distortion improvement rate of the distribution network can be determined as follows:

[0129] For distribution networks whose total harmonic voltage distortion rate (THDu) exceeds the limit value specified in GB / T 14549, the minimum improvement rate can be determined according to the 95% probability maximum value THDu1 and the limit value THDu2 of the total harmonic voltage distortion rate of the actual operation of the distribution network, as follows:

[0130]

[0131] The expected total harmonic voltage distortion rate THDu3 after the harmonic treatment of the distribution network is artificially set, and combined with the 95% probability maximum value THDu1 of the total harmonic voltage distortion rate of the actual operation of the distribution network, the minimum improvement rate is determined by the following formula:

[0132]

[0133] During actual operation, the harmonic control device is affected by detection, control and other links. The compensation rate η of the harmonic control device b It is impossible to achieve the ideal 100%, the actual compensation rate of each harmonic of the device is η b It can be obtained in two ways:

[0134] a) It can be obtained through the manufacturer's third-party test report on the performance of the harmonic control device;

[0135] b) When the test report cannot be obtained, the harmonic compensation rate limit specified in the relevant national standards for harmonic control devices can be consulted and this value can be used as the compensation rate of the harmonic control device in this method.

[0136] Given the voltage distortion improvement rate of the distribution network and the compensation rate of the harmonic control device, the expected minimum target value of the harmonic control of the distribution network can be calculated as the ratio of the two according to the following formula:

[0137]

[0138] Where G is the minimum target.

[0139] Taking into account the situation that the actual compensation rate of the active harmonic control device cannot reach 100%, combined with the improvement rate of distribution network voltage distortion, the expected minimum target of distribution network harmonic control is determined to ensure that active harmonic control achieves the expected control effect.

[0140] In a possible implementation, the judgment condition is:

[0141] The accumulated result is greater than or equal to the expected minimum target for harmonic control.

[0142] In order to better understand the present invention, the above process is described in detail below in conjunction with a specific example. The numerical values ​​used in this example are only examples, and users can make corresponding changes according to actual needs. This example is a radial distribution network with a voltage level of 35kV. The distribution network has a total of 1 power branch and 8 non-linear load branches. There is no reactive compensation branch. The power branch component equipment parameters are shown in Table 1, and the non-linear load branch component equipment parameters are shown in Table 2.

[0143] Table 1 Power branch component equipment parameters

[0144]

[0145] Table 2 Nonlinear load branch component equipment parameters

[0146]

[0147] Combined with the parameters of the equipment constituting the distribution network, the harmonic impedance of each branch of the distribution network is calculated according to step 102. On this basis, the influence coefficients of the eight nonlinear load branches on the odd harmonic voltage within 25th order of the distribution network are calculated. The results are shown in Table 3.

[0148] Table 3 Calculation results of the influence coefficients of each nonlinear load branch on the harmonic voltage of the distribution network

[0149]

[0150]

[0151] Then, according to step 103, the influence coefficients of the 8 nonlinear load branches on the harmonic voltage of the distribution network in Table 3 are processed by square root, and then their proportions are calculated, and finally the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network is obtained. The results are as follows: Figure 3 As shown. According to the requirements of step 104, the mean value μ and standard deviation σ of the voltage distortion contribution rate are calculated respectively, and the coefficient of variation c is solved. Since the number of nonlinear load branches n is 8, the maximum allowable relative error ε is set to 5%, and the threshold value can be calculated. The results are shown in Table 4. Since the coefficient of variation is greater than the threshold value, it can be judged as a discrete distribution.

[0152] Table 4 Calculation results of voltage distortion contribution rate numerical distribution characteristics judgment parameters

[0153] Object Calculated Value Average value μ 12.5 Standard deviation 3.33 Coefficient of variation c 0.267 Threshold T 0.022

[0154] Set the voltage distortion improvement rate η of the distribution network a is 50%, the compensation rate η of the selected harmonic control device b The expected minimum target G of harmonic control is 85%, and the calculated minimum target G is 58.82%. Under the above results, according to step 105, the contribution rate of each nonlinear load branch harmonic to the voltage distortion of the distribution network is arranged from large to small, and the results are shown in Table 5.

[0155] Table 5 Voltage distortion contribution rate arranged from large to small

[0156]

[0157]

[0158] The arranged voltage distortion contribution rates are accumulated one by one, such as Figure 4 When accumulated for the fourth time, the accumulated result M4 = 58.95%, which exceeds the expected minimum target value of harmonic control for the first time, so it is necessary to install active harmonic control devices on the nonlinear load branches numbered 8, 6, 5 and 3 to complete the site selection of active harmonic control devices for this distribution network.

[0159] The present invention provides a method and device for site selection of active control devices for the same-level harmonics of a radial distribution network, which solves the problem of site selection of active harmonic control devices caused by multi-point emission of harmonic sources and complex and changeable harmonic impedance. It not only reduces the number of control devices installed in the entire distribution network, but also ensures the voltage distortion control effect and economy of the distribution network, and ultimately supports the high-quality and high-reliability operation of the distribution network.

[0160] The present invention takes into account the influence of resonance on harmonic impedance caused by the increase in line capacitance level after the cabling of the distribution network, and more accurately evaluates the contribution rate of harmonic sources to the voltage distortion of the power grid through harmonic impedance; determines the site selection strategy of the active harmonic control device through the distribution characteristics of the contribution rate of each harmonic source to the voltage distortion, and reduces the complexity of the site selection process of the method in a specific scenario; considers the situation that the actual compensation rate of the active harmonic control device cannot reach 100%, and determines the expected minimum target of the harmonic control of the distribution network in combination with the improvement rate of the voltage distortion of the distribution network, so as to ensure that the active harmonic control achieves the expected control effect; the present invention takes the nonlinear load branch with a high voltage distortion contribution rate as the priority harmonic control device installation position, ensures that the active harmonic control device of the same capacity can achieve better control effect and economy, and reduces the inefficiency problem of too many devices and capacity caused by installing control devices in the entire distribution network when controlling multi-point scattered harmonic sources.

[0161] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0162] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0163] Figure 5 The structure diagram of the active control device site selection device for the same-level harmonics of the radial distribution network provided by the embodiment of the present invention is shown. For the convenience of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0164] like Figure 5 As shown, the active control device site selection device 5 for the same-level harmonics of the radial distribution network includes

[0165] The data acquisition module 51 is used to acquire the equipment parameters of each branch of the distribution network; wherein the distribution network includes a power supply branch, a reactive power compensation branch and a nonlinear load branch;

[0166] The influence coefficient calculation module 52 is used to determine the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network, and respectively calculate the influence coefficient of the harmonic of each nonlinear load branch on the harmonic voltage of the distribution network; wherein the equipment parameters of the nonlinear load branch include the capacitive reactance of the line;

[0167] The voltage distortion contribution rate calculation module 53 is used to calculate the voltage distortion contribution rate of the harmonics of each nonlinear load branch to the distribution network according to the influence coefficient of all nonlinear load branches;

[0168] A numerical distribution characteristic determination module 54 is used to calculate the coefficient of variation according to the voltage distortion contribution rate corresponding to all nonlinear load branches, and determine the numerical distribution characteristics of the voltage distortion contribution rate corresponding to all nonlinear load branches according to the coefficient of variation and a threshold value;

[0169] The optimal site determination module 55 is used to determine the optimal site for the active harmonic control device according to the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch.

[0170] In a possible implementation, the numerical distribution feature determination module 54 is used to:

[0171] The coefficient of variation is calculated based on the voltage distortion contribution rate corresponding to all nonlinear load branches, including:

[0172] Calculate the average value of the contribution rate of the harmonics of all nonlinear load branches to the voltage distortion of the distribution network;

[0173] Calculate the standard deviation of the contribution rate of the harmonics of all nonlinear load branches to the voltage distortion of the distribution network based on the average value;

[0174] Divide the standard deviation by the mean to get the coefficient of variation.

[0175] In a possible implementation, the numerical distribution feature determination module 54 is used to:

[0176] The numerical distribution characteristics of the voltage distortion contribution rate corresponding to all nonlinear load branches are determined based on the coefficient of variation and threshold, including:

[0177] When the coefficient of variation is greater than the threshold, the voltage distortion contribution rate corresponding to all nonlinear load branches is discretely distributed;

[0178] When the coefficient of variation is less than or equal to the threshold, the voltage distortion contribution rates corresponding to all nonlinear load branches are concentratedly distributed.

[0179] The embodiment of the present invention provides a method and device for site selection of active control devices for harmonics of the same level in a radial distribution network. The harmonic impedance in a nonlinear load branch is calculated by the capacitive reactance of a power supply line, and the voltage distortion contribution rate of a harmonic source to a power grid is more accurately evaluated. The site selection strategy of the active harmonic control device is determined by the distribution characteristics of the voltage distortion contribution rate of the harmonics in the nonlinear load branch, the expected minimum target for harmonic control, and the voltage distortion contribution rate corresponding to each nonlinear load branch. The complexity of site selection is reduced, the control devices are reasonably reduced, and the inefficiency problem of excessive number and capacity of control devices caused by traditional control schemes is overcome.

[0180] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0181] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0182] If the module is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned embodiments of the method for selecting the site for active control devices for harmonics of the same level of the radial distribution network. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file or some intermediate form. Computer-readable media may include: any entity or device capable of carrying computer program code, recording media, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution media.

[0183] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A method for selecting a site for active harmonic control devices in a radial distribution network, characterized in that: include: Obtain equipment parameters of each branch of the distribution network; wherein the distribution network includes a power supply branch, a reactive power compensation branch and a nonlinear load branch; determine the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network, and calculate the influence coefficient of the harmonic of each nonlinear load branch on the harmonic voltage of the distribution network respectively; wherein the equipment parameters of the nonlinear load branch include the capacitive reactance of the line; calculate the contribution rate of the harmonic of each nonlinear load branch to the voltage distortion of the distribution network respectively according to the influence coefficient of all nonlinear load branches; calculate the coefficient of variation according to the voltage distortion contribution rate corresponding to all nonlinear load branches, and judge the numerical distribution characteristics of the voltage distortion contribution rate corresponding to all nonlinear load branches according to the coefficient of variation and the threshold; determine the optimal location of the active harmonic control device according to the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch.

2. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 1, characterized in that: The calculation of the coefficient of variation according to the voltage distortion contribution rate corresponding to all nonlinear load branches includes: Calculate the average value of the contribution rate of the harmonics of all nonlinear load branches to the voltage distortion of the distribution network; Calculate the standard deviation of the contribution rate of the harmonics of all nonlinear load branches to the voltage distortion of the distribution network based on the average value; The standard deviation is divided by the mean, and the resulting ratio is the coefficient of variation.

3. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 2, characterized in that: The numerical distribution characteristics of the voltage distortion contribution rates corresponding to all nonlinear load branches determined according to the coefficient of variation and the threshold value include: When the coefficient of variation is greater than the threshold, the voltage distortion contribution rates corresponding to all nonlinear load branches are discretely distributed; When the coefficient of variation is less than or equal to a threshold value, the voltage distortion contribution rates corresponding to all nonlinear load branches are concentratedly distributed.

4. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 3, characterized in that: Determining the optimal location of the active harmonic control device according to the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch includes: When the voltage distortion contribution rate is concentratedly distributed, the value of the minimum target is divided by the average value of the voltage distortion contribution rates corresponding to all nonlinear load branches to obtain a ratio result; According to the ratio result, a corresponding number of nonlinear load branches are randomly selected from all nonlinear load branches to determine the installation positions of the active harmonic control devices; When the voltage distortion contribution rate is discretely distributed, the voltage distortion contribution rates corresponding to all nonlinear load branches are arranged in order from large to small; The arranged voltage distortion contribution rates are accumulated one by one; When the accumulated result meets the judgment condition for the first time, the nonlinear load branch corresponding to the accumulated voltage distortion contribution rate is determined as the installation location of the active harmonic control device.

5. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 4, characterized in that: The minimum target for harmonic control is as follows: Obtain the distortion improvement rate of distribution network voltage; Obtain the compensation rate of the active harmonic control device; The distortion improvement rate is divided by the compensation rate of the active harmonic control device, and the ratio obtained is the minimum target expected for harmonic control.

6. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 4, characterized in that: The judgment conditions are: The accumulated result is greater than or equal to the expected minimum target for harmonic control.

7. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 1, characterized in that: Determining the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network includes: determining the harmonic impedance of the power supply branch, the reactive power compensation branch and the nonlinear load branch respectively; The harmonic impedance of the power supply branch is the sum of the power supply harmonic impedance and the transformer harmonic impedance, and its formula is as follows: Z g (h)=Z s (h)+Z t (h) In the formula, Z s (h) is the power supply harmonic impedance, S min is the minimum short-circuit capacity, X / R is the reactance / resistance ratio, U N is the rated voltage of the distribution network busbar, h is the harmonic order, j is the imaginary number symbol in the complex number, Z t (h) is the transformer harmonic impedance, S t is the rated capacity, P k is the short-circuit loss, U d is the short-circuit voltage; The reactive power compensation branch includes multiple reactive power compensation groups with different series reactance rates. The harmonic impedance formula of the reactive power compensation branch is as follows: In the formula, Z co (h) is the reactive compensation impedance, Q co is the rated capacity of the reactive power compensation capacitor bank, U C is the rated voltage of the capacitor bank, k is the series reactance ratio, e is the number of reactive compensation groups with different series reactance ratios, m is the number of reactive compensation groups with different series reactance ratios, m∈N; The nonlinear load branch is composed of a power supply line and a load connected in series and parallel. The harmonic impedance formula of the nonlinear load branch is as follows: Z L (h)=Z0(h)·sin h[γ(h)·l] In the formula, Z d (h) is the load harmonic impedance, S d is the minimum apparent power of the load, PF is the average power factor of the load, Z L (h) is the impedance of the distributed parameter π model of the line, Z0(h) is the line characteristic impedance, γ(h) is the line propagation coefficient, l is the length, R0 is the resistance per unit length, L0 is the inductance per unit length, C0 is the capacitance per unit length, ω0 is the fundamental angular frequency, ω0=2πf0, f0=50HZ, Z C (h) is the capacitive reactance of the distributed parameter π model of the line, h is the harmonic order, h = 3, 5, 7, ..., 25, sinh is the hyperbolic sine function, and cosh is the hyperbolic cosine function.

8. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 7, characterized in that: The method of respectively calculating the influence coefficient of the harmonics of each nonlinear load branch on the harmonic voltage of the distribution network includes: Calculate the influence coefficient of the harmonics of each nonlinear load branch on the harmonic voltage of the distribution network. The formula is as follows: The results of the influence coefficient of the harmonics of all nonlinear load branches on the harmonic voltage of the distribution network are as follows: In the formula, α i is the influence coefficient of the harmonic generated by the i-th nonlinear load branch on the harmonic voltage of the distribution network, Z p,i (h) is the total harmonic impedance of the branches other than the i-th nonlinear load branch, Z C,i (h) is the capacitive reactance of the distributed parameter π model for the i-th nonlinear load branch, Z L,i (h) is the impedance of the distributed parameter π model for the i-th nonlinear load branch.

9. The method for selecting a site for active harmonic control devices in a radial distribution network according to claim 8, characterized in that: The step of calculating the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network according to the influence coefficient of all nonlinear load branches includes: The influence coefficient of multiple harmonics of each nonlinear load branch on the harmonic voltage of the distribution network is calculated by square root, and the formula is as follows: The result of the square root operation is used for proportion operation to obtain the contribution rate of the harmonics of each nonlinear load branch to the voltage distortion of the distribution network. The formula is as follows: In the formula, β i is the square root calculation result of the influence coefficient of the ith nonlinear load branch on the harmonic voltage of the distribution network, λ k is the contribution rate of the harmonics generated by the kth nonlinear load branch to the voltage distortion of the distribution network, β k is the square root calculation result of the influence coefficient of the kth nonlinear load branch on the harmonic voltage of the distribution network, and n is the number of nonlinear load branches.

10. A site selection device for active control of harmonics of the same level in a radial distribution network, characterized in that: include: A data acquisition module, used to acquire equipment parameters of each branch of the distribution network; wherein the distribution network includes a power supply branch, a reactive power compensation branch and a nonlinear load branch; An influence coefficient calculation module is used to determine the harmonic impedance of each branch according to the equipment parameters of each branch of the distribution network, and respectively calculate the influence coefficient of the harmonic of each nonlinear load branch on the harmonic voltage of the distribution network; wherein the equipment parameters of the nonlinear load branch include capacitive reactance; A voltage distortion contribution rate calculation module is used to calculate the voltage distortion contribution rate of the harmonics of each nonlinear load branch to the distribution network according to the influence coefficient of all nonlinear load branches; A numerical distribution characteristic judgment module is used to calculate the coefficient of variation according to the voltage distortion contribution rate corresponding to all nonlinear load branches, and judge the numerical distribution characteristics of the voltage distortion contribution rate corresponding to all nonlinear load branches according to the coefficient of variation and a threshold value; The optimal site determination module is used to determine the optimal site for the active harmonic control device based on the numerical distribution characteristics, the expected minimum target of harmonic control and the voltage distortion contribution rate corresponding to each nonlinear load branch.

Images