Harmonic propagation key influence factor analysis method considering line distribution parameters and load characteristics

Abstract

The invention relates to a harmonic propagation key influence factor analysis method considering line distribution parameters and load characteristics, which comprises the following steps of: constructing a harmonic two-port transmission model considering distribution parameter characteristics so as to represent a relation between harmonic voltage and current at the head end and the tail end of a line; determining a propagation constant and characteristic impedance of the line according to the line distribution parameters; carrying out equivalence processing on a line end load based on a CIGRE load harmonic equivalence model to obtain load harmonic impedance; and based on the harmonic two-port transmission model and the load harmonic impedance, calculating each harmonic voltage amplification factor of the tail end of the line relative to the head end of the line, extracting a peak frequency, obtaining a harmonic propagation rule under each harmonic propagation key influence factor, and completing the analysis process of the harmonic propagation key influence factors. Compared with the prior art, the method has the advantages that multiple harmonic propagation influence factors are considered, the harmonic amplification law is predicted, and the tail-end harmonic exceeding risk is pre-judged.

Description

Technical Field

[0001] This invention relates to the field of power system power quality technology, and in particular to a method for analyzing key influencing factors of harmonic propagation considering line distribution parameters and load characteristics. Background Technology

[0002] In DC receiving-end urban power grids, high-voltage levels contain high-power harmonic sources from converter stations, while low-voltage levels contain other complex nonlinear user harmonic sources. Harmonics exhibit bidirectional conduction characteristics in the power grid lines.

[0003] On the one hand, harmonics generated by high-voltage harmonic sources on the system side may cause the harmonic voltage content of the low-voltage bus to exceed the standard after being transmitted through the line, affecting the normal operation of harmonic-sensitive users; on the other hand, harmonic currents generated by nonlinear users are injected into the system through the line, degrading the power quality of the system.

[0004] Furthermore, urban power grids have a higher cable penetration rate compared to transmission networks. Cables have a greater capacitance to ground than overhead lines, exacerbating the risk of harmonic amplification during harmonic propagation. Therefore, it is necessary to conduct an in-depth study of the propagation patterns of harmonics in power lines. Moreover, the conduction patterns of harmonics in power lines vary depending on the type of line (overhead or cable), line length, load factor, and power factor. Therefore, it is necessary to quantitatively analyze the impact of changes in these key influencing factors on the harmonic propagation patterns. Summary of the Invention

[0005] The purpose of this invention is to provide a method for analyzing key influencing factors of harmonic propagation that considers line distribution parameters and load characteristics, and to quantify the impact of harmonic propagation influencing factors on harmonic propagation.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics includes the following steps: A harmonic two-port transmission model considering the characteristics of distributed parameters is constructed to characterize the relationship between harmonic voltage and current at the beginning and end of the line, and the propagation constant and characteristic impedance of the line are determined based on the distributed parameters of the line. Based on the CIGRE load harmonic equivalent model, the load at the end of the line is equivalently processed to obtain the load harmonic impedance. Based on the harmonic two-port transmission model and load harmonic impedance, the voltage amplification factor of each harmonic at the end of the line relative to the beginning of the line is calculated, and the peak frequency is extracted. The harmonic propagation law under each key influencing factor is obtained, and the analysis process of key influencing factors of harmonic propagation is completed.

[0007] Furthermore, the relationship between the harmonic voltage and current at both ends of the line is expressed as follows: , in, , For a hyperbolic function, the form after separating the real and imaginary parts is as follows: , In the formula, , For the first-terminal harmonic voltage and current, , For the terminal harmonic voltage and current, Let be the propagation constant of the line. The characteristic impedance of the line. l For line length, j The imaginary unit, , These are the attenuation constant and phase shift constant of the line.

[0008] Furthermore, the key influencing factors of harmonic propagation include line length. l Line type, load factor k L and power factor, where power factor = cos(arctan(P) n / Q n )), P n Q n These represent the active power and reactive power corresponding to the load, respectively.

[0009] Furthermore, the expression for calculating the propagation constant of the circuit is as follows: , Among them, the line is h Propagation constant under subharmonics Represented as: , in: , In the formula, Let be the propagation constant of the line. , The lines are respectively at h Resistance and reactance per unit length under subharmonics , The lines are respectively at h Conductivity and susceptance per unit length under subharmonics j The imaginary unit, , The attenuation constant and phase shift constant of the line, forh Attenuation constant and phase shift constant of the line under subharmonics For the line in h Resistance per unit length under subharmonics For the line in h Reactance per unit length under subharmonics For the line in h Electric susceptance per unit length under subharmonics.

[0010] Furthermore, the characteristic impedance of the line The calculation expression is: , In the formula, , , The lines are respectively at h Resistance, reactance, and susceptance per unit length under subharmonics.

[0011] Furthermore, the calculation expression for the load harmonic impedance is as follows: , in: , In the formula, For load harmonic impedance, This indicates the calculation of parallel impedance. , These are the two equivalent reactances of the load. The equivalent resistance of the load. j The imaginary unit, Bus voltage , The active and reactive power corresponding to the load. h This represents the harmonic order.

[0012] Furthermore, the calculation process for the voltage amplification factor of each harmonic includes: according to ,make ,in, , For the terminal harmonic voltage and current, The characteristic impedance of the line. For load harmonic impedance, For Z c With Z L The ratio, a、b for n The real and imaginary parts, j The imaginary unit; Based on the aforementioned harmonic propagation model, the voltage amplification factor of each harmonic at the end of the line relative to the beginning of the line is obtained after the harmonics propagate along the path. , is represented as: , in: In the formula, , , For calculation k U intermediate variables, The attenuation constant of the line, l For line length, , It is a hyperbolic function.

[0013] Furthermore, the expression for calculating the peak frequency is: , In the formula, Peak frequency, It is a positive integer. To calculate the harmonic voltage amplification factor k u intermediate variables, Let be the phase shift constant of the line under the fundamental frequency. l This refers to the line length; Among them, when the line length is from l Change to kl ( k When the value is greater than 1, the peak frequency is shifted accordingly, and the shifted peak frequency is expressed as: , In the formula, The peak frequency after migration. The unit length.

[0014] Furthermore, the harmonic propagation law includes: 1) As the line length increases, the peak amplitude of harmonic amplification decreases, and the peak frequency shifts to lower frequencies as the line length increases; 2) As the load factor increases, the peak amplitude of harmonic amplification decreases, and the peak frequency shifts to higher frequencies, satisfying the following relationship: , In the formula, The amplification factor of each harmonic voltage. n for The characteristic impedance Z of the line c With load harmonic impedance Z L The ratio, b forn The imaginary part, The attenuation constant of the line, , It is a hyperbolic function. l This refers to the line length; 3) As the power factor increases, the peak amplitude of harmonic amplification decreases slightly, and the peak frequency shifts slightly to lower frequencies, satisfying the following relationship: , In the formula, For load harmonic impedance, , The active and reactive power corresponding to the load. h For harmonic order, j The imaginary unit, This refers to the bus voltage. 4) When line cables replace overhead lines, the frequency of harmonic voltage amplification peaks increases and is concentrated in the low-frequency band.

[0015] Furthermore, it also includes the following steps: Based on the harmonic propagation law, the threshold length of the line that does not amplify harmonics is obtained for different voltage levels.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention quantifies the harmonic propagation law under a unified mathematical framework. By simultaneously considering the line distributed parameters and the harmonic propagation influencing factors, it quantifies and analyzes the impact of the harmonic propagation influencing factors on harmonic propagation, revealing the mechanism of harmonic amplification as line and load parameters change. Compared with the traditional lumped parameter model, this invention is consistent with actual simulation and can effectively predict the harmonic amplification trend, achieving early warning of harmonic exceedance risk.

[0017] (2) By establishing a two-port harmonic transmission model that considers distributed parameters, introducing the CIGRE load harmonic equivalent model, deriving the amplification factor law and determining the non-amplification safety zone, this invention can accurately predict the harmonic propagation characteristics under different line operating conditions, and provide a reliable technical basis for harmonic control of high-cable distribution networks and DC receiving-end power grids.

[0018] (3) This invention can accurately predict the harmonic amplification trend in transmission lines of different voltage levels, providing a quantitative basis for the formulation of harmonic limits for converter stations, cable length planning and power quality management, and has good engineering applicability and promotion value. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the harmonic two-port transmission model structure of the present invention; Figure 3 This is a schematic diagram of the CIGRE load harmonic equivalent model of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0021] Example 1 This embodiment provides a method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics, such as... Figure 1 As shown, the method includes the following steps: Step 1: Establish a harmonic two-port transmission model that considers distributed parameters.

[0022] In this embodiment, the distributed parameters include parameters such as resistance and conductance, and the established harmonic two-port transmission model is as follows: Figure 2 As shown, this is used to characterize the relationship between harmonic voltage and current at the beginning and end of a line. Among them, and These represent the equivalent impedance and admittance of the line, respectively, considering the distributed parameter characteristics of the line. This refers to the load harmonic impedance at the end of the line. When the harmonic voltage and current at the system side (head end) of the line are... and At that time, the harmonic voltage and current at the user side (end) of the line and Satisfy the following formula: , In the formula: l Indicates the length of the line. and These represent the propagation constant and characteristic impedance of the line, respectively. Hyperbolic function. and The form after separating the real and imaginary parts is as follows: .

[0023] Step 2: Based on the CIGRE load harmonic equivalent model, perform load harmonic equivalent on the load at the end of the line to obtain the load harmonic impedance.

[0024] CIGRE load harmonic equivalent model, such as Figure 2 As shown, the equivalent load harmonics are calculated as follows: , , In the formula: symbol " "Indicates finding the parallel impedance, This refers to the bus voltage. h Indicates the harmonic order; and These represent the active power and reactive power corresponding to the load, respectively.

[0025] Step 3: Determine the propagation constant and characteristic impedance of the line based on the line distribution parameters.

[0026] The propagation constant and characteristic impedance of the line are respectively used as... and The expressions are as follows: , , in: , , The lines are respectively at h Resistance, reactance, and susceptance per unit length under subharmonics.

[0027] The line is h Propagation constant under subharmonics Represented as: , , In the formula: and These respectively indicate the lines at h Resistance and reactance per unit length under subharmonics; and These respectively indicate the lines at h Conductivity and susceptance per unit length under subharmonics; and These represent the attenuation constant and phase shift constant of the line, respectively.

[0028] Step 4: Calculate the voltage amplification factor k for each harmonic. U Extract the curve of harmonic voltage amplification factor as a function of frequency and extract the peak frequency based on the curve.

[0029] for Figure 2 In this regard, let the load harmonic impedance be... ,but .make Therefore, by combining the above-mentioned relationship between harmonic voltage and current at both ends of the line, we can obtain the amplification factor of the harmonic voltage at the end of the line relative to that at the beginning of the line after the harmonics propagate through the line. for: , in: , Step 5: Analyze the impact of changes in key influencing factors on the peak amplitude, frequency shift, and occurrence frequency of harmonic amplification, and formulate the harmonic propagation law.

[0030] This embodiment will specify the line length. l Line type (including cable and overhead line), load factor k L Power factor is a key influencing factor for harmonic propagation. Power factor = cos(arctan(P)) n / Q n )), P n Q n These represent the active and reactive power corresponding to the load. This step analyzes the impact of these key influencing factors on the harmonic propagation law.

[0031] Based on the magnification in step 4 above The calculation formula shows that when the frequency and line length change, the peak value of the harmonic voltage amplification at the end of the line is typically... When the value is extremely small, it appears; at this time, there is When the line length is constant but the frequency gradually changes, due to... The voltage exhibits periodic fluctuations, therefore the peak value of the harmonic voltage amplification at the end also appears approximately periodically. Similarly, when the frequency is constant but the line length varies, It also exhibits periodic fluctuations, resulting in periodic occurrences of the peak value of the terminal harmonic voltage amplification.

[0032] When the line length is l Change to kl ( k When >1), the frequency corresponding to the peak value of harmonic voltage amplification is changed from... , Migration to: , in: Let be the phase shift constant of the line under the fundamental frequency. l Let be the line length. Therefore, the peak frequency follows the rule that it shifts to lower frequencies as the line length increases.

[0033] when A value greater than 1 indicates harmonic amplification. < 1 indicates harmonic attenuation. The following harmonic propagation laws are obtained for different parameter variations: 1) Line length l Increase: The peak frequency shifts to lower frequencies, and the amplification value decreases.

[0034] 2) Load factor k L Increase: The amplification value decreases, and the peak frequency shifts to higher frequencies.

[0035] When the load factor k L When the load impedance increases, the peak amplitude of the harmonic amplification decreases, and the peak frequency shifts to higher frequencies. This is because of the load impedance. Z L The amplitude varies k L Increasing and decreasing leads to the amplification factor of harmonic voltage at the end of the line. k U Decrease, and satisfy the following relationship: , in: l For line length, This is the attenuation constant of the line.

[0036] 3) Increased power factor: Amplification value decreases slightly, peak frequency shifts slightly to lower frequency.

[0037] When the power factor increases, the peak amplitude of harmonic amplification decreases slightly, and the peak frequency shifts slightly towards lower frequencies. At this time, the reactive power of the load... Q Decreasing the load impedance increases the real part and decreases the imaginary part, resulting in a decrease in the amplification factor and thus suppressing high-frequency harmonic amplification. This also satisfies the following relationship: .

[0038] 4) Cables replace overhead lines: This increases the amplified peak frequency, mainly concentrated in the low-frequency band.

[0039] Example 2 This embodiment provides a method for analyzing key influencing factors of harmonic propagation considering line distribution parameters and load characteristics. Based on the analysis in Embodiment 1, this method further analyzes and obtains a table of harmonic non-amplification length thresholds at different voltage levels, which is used to determine the system-side harmonic voltage limitation level.

[0040] Taking three typical transmission lines—220kV, 110kV, and 35kV—as examples, the frequency response characteristics are calculated through simulation. The steps include: 1) Simulation analysis of lines at different voltage levels; 2) When the line parameters meet the non-amplification condition in the table, determine the corresponding harmonic safety length range; 3) Output harmonic non-amplification interval table for 220kV, 110kV, and 35kV lines.

[0041] 4) The simulation calculation is based on the model and formula, and uses different operating condition parameters to scan the frequency, and identifies whether the peak value of the harmonic voltage amplification exceeds 1 as a criterion.

[0042] The obtained line length ranges from 10 to 100 km, the load factor varies between 25% and 100%, and the power factor is 0.9. Simulation results show that: 1) 220kV lines: When the line length is greater than 40 km, the 23rd and above harmonics are significantly amplified, and the safe length without amplification is determined to be 0~40 km; 2) 110kV lines: When the length exceeds 26 km, the 23rd harmonic amplification factor exceeds 1.5, and the safe length is 0~25 km; 3) 35kV lines: No obvious harmonic amplification phenomenon within the normal length range (10~30 km).

[0043] Based on this, a table of safe length thresholds for harmonic non-amplification of lines at various voltage levels is formed (as shown in Table 1 and Table 2), which can be used as the basis for setting output harmonic limits for converter stations and for cable planning and design.

[0044] Table 1. Corresponding line lengths for which each major harmonic order is not amplified after propagation through overhead lines. Table 2. Corresponding line lengths for which each major harmonic order is not amplified after propagation through the cable. As demonstrated by the above embodiments, the model of this invention can quantify the harmonic propagation law within a unified mathematical framework and reveal the mechanism of harmonic amplification as line and load parameters change. Compared with traditional lumped parameter models, the calculation results of this invention are consistent with actual simulations, effectively predicting harmonic amplification trends and providing early warning of harmonic exceedance risks.

[0045] In summary, this invention, by establishing a two-port harmonic transmission model considering distributed parameters, introducing a CIGRE load harmonic equivalent model, deriving the amplification factor law, and determining the non-amplification safety zone, can accurately predict the harmonic propagation characteristics under different line operating conditions, providing a reliable technical basis for harmonic control in high-cable distribution networks and DC receiving-end power grids.

[0046] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0047] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0048] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0049] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0050] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0051] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0052] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics, characterized in that, Includes the following steps: A harmonic two-port transmission model considering the characteristics of distributed parameters is constructed to characterize the relationship between harmonic voltage and current at the beginning and end of the line, and the propagation constant and characteristic impedance of the line are determined based on the distributed parameters of the line. The load harmonic impedance at the end of the line is obtained by performing equivalent processing on the CIGRE load harmonic equivalent model. Based on the harmonic two-port transmission model and load harmonic impedance, the voltage amplification factor of each harmonic at the end of the line relative to the beginning of the line is calculated, and the peak frequency is extracted. The harmonic propagation law under each key influencing factor is obtained, and the analysis process of key influencing factors of harmonic propagation is completed.

2. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, The relationship between the harmonic voltage and current at both ends of the line is expressed as follows: ， in, , For a hyperbolic function, the form after separating the real and imaginary parts is as follows: ， In the formula, , For the first-terminal harmonic voltage and current, , For the terminal harmonic voltage and current, Let be the propagation constant of the line. The characteristic impedance of the line. l For line length, j The imaginary unit, , These represent the attenuation constant and phase shift constant of the line.

3. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, The key influencing factors of harmonic propagation include line length. l Line type, load factor k L and power factor, where power factor = cos(arctan(P) n / Q n )), P n Q n These represent the active power and reactive power corresponding to the load, respectively.

4. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, The expression for calculating the propagation constant of the line is: ， Among them, the line is h Propagation constant under subharmonics Represented as: ， in: ， In the formula, Let be the propagation constant of the line. , The lines are respectively at h Resistance and reactance per unit length under subharmonics , The lines are respectively at h Conductivity and susceptance per unit length under subharmonics j The imaginary unit, , The attenuation constant and phase shift constant of the line, for h Attenuation constant and phase shift constant of the line under subharmonics For the line in h Resistance per unit length under subharmonics For the line in h Reactance per unit length under subharmonics For the line in h Electric susceptance per unit length under subharmonics.

5. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, Characteristic impedance of the line The calculation expression is: ， In the formula, , , The lines are respectively at h Resistance, reactance, and susceptance per unit length under subharmonics.

6. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, The calculation expression for the load harmonic impedance is as follows: ， in: ， In the formula, For load harmonic impedance, This indicates the calculation of parallel impedance. , These are the two equivalent reactances of the load. The equivalent resistance of the load. j The imaginary unit, Bus voltage , These represent the active and reactive power corresponding to the load. h This represents the harmonic order.

7. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, The calculation process for the voltage amplification factor of each harmonic includes: according to ,make ,in, , For the terminal harmonic voltage and current, The characteristic impedance of the line. For load harmonic impedance, For Z c With Z L The ratio, a、b for n The real and imaginary parts, j The imaginary unit; Based on the aforementioned harmonic propagation model, the voltage amplification factor of each harmonic at the end of the line relative to the beginning of the line is obtained after the harmonics propagate along the path. , represented as: ， in: In the formula, , , To calculate the harmonic voltage amplification factor k U intermediate variables, The attenuation constant of the line, l For line length, , It is a hyperbolic function.

8. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, The expression for calculating the peak frequency is: ， In the formula, Peak frequency, It is a positive integer. For calculation k u intermediate variables, Let be the phase shift constant of the line under the fundamental frequency. l This refers to the line length; Among them, when the line length is from l Change to kl ( k When the value is greater than 1, the peak frequency is shifted accordingly, and the shifted peak frequency is expressed as: ， In the formula, The peak frequency after migration. The unit length.

9. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, The harmonic propagation laws include: 1) As the line length increases, the peak amplitude of harmonic amplification decreases, and the peak frequency shifts to lower frequencies as the line length increases; 2) As the load factor increases, the peak amplitude of harmonic amplification decreases, and the peak frequency shifts to higher frequencies, satisfying the following relationship: ， In the formula, The amplification factor of each harmonic voltage. n for The characteristic impedance Z of the line c With load harmonic impedance Z L The ratio, b for n The imaginary part, The attenuation constant of the line, , It is a hyperbolic function. l This refers to the line length; 3) As the power factor increases, the peak amplitude of harmonic amplification decreases slightly, and the peak frequency shifts slightly to lower frequencies, satisfying the following relationship: ， In the formula, For load harmonic impedance, , These represent the active and reactive power corresponding to the load. h For harmonic order, j The imaginary unit, This refers to the bus voltage. 4) When line cables replace overhead lines, the frequency of harmonic voltage amplification peaks increases and is concentrated in the low-frequency band.

10. The method for analyzing key influencing factors of harmonic propagation considering line distributed parameters and load characteristics according to claim 1, characterized in that, It also includes the following steps: Based on the harmonic propagation law, the threshold length of the line that does not amplify harmonics is obtained for different voltage levels.

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