Large-scale charging pile harmonic feature extraction and analysis method and system

Abstract

The invention discloses a large-scale charging pile harmonic feature extraction and analysis method and system, and the method comprises the steps: carrying out the sampling of currents of different sampling points of a charging station, and carrying out the harmonic feature extraction, so as to calculate a comprehensive current distortion index; important sampling points of the charging pile are analyzed; according to the charging power of the charging pile in each time period, the electricity price in each time period, the important sampling points and the current amplitude of the charging station, the set number of time periods are divided into four section types; main harmonic waves of the four section types are judged and counted; according to a random forest algorithm, the charging power of the charging pile in each time period is predicted, the section type to which the charging pile belongs is judged, and the main harmonic wave of the section type is the harmonic wave which has the largest influence on the corresponding charging pile in each time period. According to the invention, by analyzing the harmonic wave with the maximum influence, the operation and maintenance personnel of the power distribution network can quickly and accurately carry out targeted harmonic wave compensation, the harmonic wave is prevented from being sent to the superior power grid, and the high-quality power supply capability is improved.

Description

Technical Field

[0001] The present invention relates to the field of power quality of distribution networks, and more specifically, to a method and system for extracting and analyzing harmonic characteristics of large-scale charging piles. Background Technique

[0002] Electric vehicles are leading the automotive industry towards a more green and sustainable direction with their significant advantages such as environmental protection, energy conservation, low noise, and low maintenance costs. As an important infrastructure in the electric vehicle industry, the access of electric vehicle charging piles to the power grid will inevitably affect the power quality of the grid, and the most significant one is the impact on grid harmonics. During the operation of electric vehicle charging piles, they mainly obtain electric energy from the grid and convert it into direct current suitable for use in electric vehicle batteries for charging. This conversion process involves power transmission and power conversion technologies, and may introduce non-linear electrical loads, which are the main reasons for generating harmonics. The non-linear loads mainly come from power electronic devices in the power conversion process, such as rectifiers, inverters, etc. These devices will generate harmonic voltages and harmonic currents during operation, and these harmonic components will be injected into the power grid, thus affecting the power quality of the grid.

[0003] Therefore, in the case of large-scale charging piles accessing the distribution network in the future, technical measures need to be taken to reduce their harmonic impact and ensure the safe and stable operation of the power grid. As a forward-looking basic research, there is an urgent need for a method for extracting and analyzing harmonic characteristics of large-scale charging piles to provide a theoretical basis for subsequent technical measures. Summary of the Invention

[0004] To solve the deficiencies in the prior art, the present invention provides a method and system for extracting and analyzing harmonic characteristics of large-scale charging piles. Its purpose is to efficiently and qualitatively analyze the harmonic impact of charging piles through multi-port charging pile current sampling, a method for extracting harmonic characteristics of charging pile current based on real discrete Fourier transform (RDFT), and a method for analyzing harmonic current characteristics of charging piles based on electricity consumption behavior, so as to provide a theoretical basis for the high-quality operation of the distribution network with large-scale charging piles connected in the future.

[0005] The present invention adopts the following technical solutions.

[0006] A method for extracting and analyzing harmonic characteristics of large-scale charging piles according to the first aspect of the present invention includes the following contents:

[0007] Divide each day into a set number of time periods on average, perform real-time sampling on the currents at different sampling points in the charging station, and extract harmonic characteristics of the sampled currents through real discrete Fourier transform to calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period, and calculate the comprehensive current distortion index according to the current harmonic distortion rates of the previous time period and the current time period and the current change rate in the current time period;

[0008] According to the comprehensive current distortion index of each sampling point, analyze the sampling points that have a greater impact on the charging pile from different sampling points, and set them as important sampling points;

[0009] According to the charging power of the charging pile in each time period, the electricity price in each time period, and the sum of the current amplitudes of the important sampling points and the charging station, divide the set number of time periods into four types of section types; judge and count the main harmonics of the four types of section types;

[0010] Train the random forest algorithm according to the historical charging power data of each charging pile, predict the charging power of the charging pile in each time period, and combine the electricity price in each time period and the current amplitude of the charging station collected in each time period to judge the section type to which it belongs. The main harmonics of this section type are the harmonics that have the greatest impact on the corresponding charging pile in each time period.

[0011] Preferably, the different sampling points include the high-voltage side and the low-voltage side of the charging pile.

[0012] Preferably, the harmonic feature extraction of the sampled current is performed by the discrete Fourier transform, specifically:

[0013] Perform a discrete Fourier transform on the sampled current and convert it into a complex frequency domain form. The formula is as follows:

[0014]

[0015] where i L (nτ) is the sampled current, k represents the harmonic order, ω 1 is the fundamental angular frequency, τ is the sampling period, N m is the highest harmonic order of the frequency, n is the number of samples in the fundamental period, is the real part of the kth current harmonic in the complex frequency domain, is the imaginary part of the kth current harmonic in the complex frequency domain;

[0016] The formulas for calculating the real part and the imaginary part of the kth current harmonic in the complex frequency domain form are as follows:

[0017]

[0018] According to the real part and the imaginary part of the kth current harmonic, calculate the time domain form u k (nτ) of the kth current harmonic. The formula is as follows:

[0019]

[0020] Preferably, calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period, and calculate the comprehensive current distortion index based on the current harmonic distortion rates of the previous time period and the current time period and the current change rate of the current time period, specifically as follows:

[0021] Calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period. The formula is as follows:

[0022]

[0023] Among them, where \(t - 1\) and \(t\) correspond to the previous time period and the current time period respectively, is the current sampling point corresponding to the current harmonic distortion rate of the time period, \(I\) i is the current sampling point corresponding to the effective value of the \(i\)-th harmonic component of the time period, \(I\) 1 is the current sampling point corresponding to the effective value of the fundamental wave of the time period, and \(N\) is the set maximum number of odd harmonics;

[0024] According to the current harmonic distortion rates of each sampling point in the previous time period and the current time period, calculate the comprehensive current distortion index THD of each sampling point in the current time period. The calculation formula is:

[0025]

[0026] Among them, THD t-1 is the current harmonic distortion rate of the previous time period of the current sampling point, and THD t is the current harmonic distortion rate of the current time period of the current sampling point, and \(\Delta I\) is the current change rate of the current sampling point in the current time period.

[0027] Preferably, analyze the sampling points that have a greater impact on the charging pile from different sampling points and set them as important sampling points, specifically as follows:

[0028] Compare the comprehensive current distortion indices THD of two sampling points, and use the larger one as the important sampling point.

[0029] Preferably, divide the set number of time periods into four types of section types according to the charging power of the charging pile in each time period, the electricity price in each time period, and the sum of the important sampling points and the current amplitude of the charging station; judge and count the main harmonics of the four types of section types, specifically as follows:

[0030] Divide the set number of time periods into sections with a higher electricity price and sections with a lower electricity price according to the electricity price in each time period;

[0031] If this time period is between the sections with higher electricity prices, determine whether its average charging power is greater than or equal to 80% of the maximum charging power or whether the current amplitude of its charging station is greater than or equal to 10 A. If either condition is met, it is the main power consumption period; otherwise, it is the secondary power consumption period.

[0032] If this time period is in the section with lower electricity prices, determine whether its average charging power is greater than or equal to 80% of the maximum charging power or whether the current amplitude of its charging station is greater than or equal to 10 A. If either condition is met, the power consumption period is the normal power consumption period; otherwise, it is the non-power consumption period.

[0033] Preferably, the main harmonics of the four section types are judged and counted, specifically: judge whether the harmonic distortion rate of each harmonic of all time periods of each section type exceeds 5%. If so, it is considered that this harmonic is the main harmonic of this section type.

[0034] The second aspect of the present invention proposes a system using the method for extracting and analyzing the harmonic characteristics of a large-scale charging pile described in the first aspect of the present invention, including a harmonic characteristic extraction module, a comprehensive current distortion index calculation module, a section type division module, and a main harmonic judgment module, characterized in that:

[0035] Harmonic characteristic extraction module: used to divide each day into a set number of time periods on average, perform real-time sampling on the currents at different sampling points in the charging station, and extract the harmonic characteristics of the sampled currents through the real discrete Fourier transform to calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period, and calculate the comprehensive current distortion index according to the current harmonic distortion rates of the previous time period, the current time period, and the current change rate of the current time period;

[0036] Important sampling point analysis module: used to analyze the sampling points that have a greater impact on the charging pile from different sampling points according to the comprehensive current distortion index of each sampling point, and set them as important sampling points;

[0037] Section type division module: used to divide a set number of time periods into four types of section types according to the charging power of the charging pile in each time period, the electricity price in each time period, and the sum of the important sampling points and the current amplitude of the charging station; judge and count the main harmonics of the four section types;

[0038] Main harmonic judgment module: used to train the random forest algorithm according to the historical charging power data of each charging pile, predict the charging power of the charging pile in each time period, and combine the electricity price in each time period and the current amplitude of the charging station collected in each time period to judge the section type it belongs to. The main harmonic of this section type is the harmonic that has the greatest impact on the corresponding charging pile in each corresponding time period.

[0039] A third aspect of the present invention is an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the computer program is loaded into the processor, it implements the method for extracting and analyzing harmonic characteristics of large-scale charging piles according to the first aspect of the present invention.

[0040] A fourth aspect of the present invention proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the method for extracting and analyzing harmonic characteristics of large-scale charging piles according to the first aspect of the present invention.

[0041] The beneficial effects of the present invention are as follows. Compared with the prior art, the method for extracting and analyzing harmonic characteristics of large-scale charging piles provided by the present invention respectively samples the currents of multi-port charging piles at different sampling points, and calculates the comprehensive current harmonic rate considering the current harmonic rate and current change rate in the previous time period, and uses the sampling point with the larger value as the subsequent analysis sample. The harmonic coverage range is wide, the analysis object is comprehensive, and the accuracy is high; and based on the real discrete Fourier transform, the harmonic characteristics of the charging pile current are extracted, reducing the amount of calculation and improving the calculation speed; and the number of harmonics is limited, improving the calculation efficiency; according to the average charging power of the charging station in each time period, the electricity price in this time period, and the current amplitude of the charging station at the important sampling point, the 24 time periods are divided into four types of section types; judge and count the main harmonics of the four types of time periods, which can efficiently and qualitatively analyze the harmonic influence of the charging pile; according to the historical charging load data of each charging pile in the previous cycle, use the random forest algorithm to predict the charging power of the charging pile in the next time period, combined with the current amplitude of the charging station in the next time period, judge its section type, and perform corresponding harmonic compensation on the main harmonics of this section type, which can predict the massive harmonic sources brought by the future large-scale access of charging piles. Through simplified calculation, the distribution network operation and maintenance personnel can quickly and accurately perform targeted harmonic compensation, prevent harmonics from being sent to the superior power grid, and improve the high-quality power supply ability. Description of the Drawings

[0042] Figure 1 It is a schematic structural diagram of a method for extracting and analyzing harmonic characteristics of large-scale charging piles in the present invention;

[0043] Figure 2 It is a schematic diagram of the current sampling positions of multi-port charging piles in the present invention;

[0044] Figure 3 It is a schematic diagram of the extraction of the original current signal in the present invention. Detailed Embodiments

[0045] To make the objectives, technical solutions and advantages of the present invention more clear, the following will, in conjunction with the accompanying drawings in the embodiments of the present invention, clearly and completely describe the technical solutions of the present invention. The embodiments described in this application are only a part of the embodiments of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0046] As Figure 1 shown, Embodiment 1 of the present invention proposes a method for extracting and analyzing harmonic characteristics of large-scale charging piles, including the following content:

[0047] The day is evenly divided into a set number of time periods, the current at different sampling points in the charging station is sampled in real time, and the harmonic characteristics of the sampled current are extracted through real discrete Fourier transform to calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period, and the comprehensive current distortion index is calculated according to the current harmonic distortion rates of the previous time period and the current time period and the current change rate of the current time period;

[0048] Specifically, the set number is 24;

[0049] According to the comprehensive current distortion index of each sampling point, analyze the sampling points that have a greater impact on the charging pile from different sampling points and set them as important sampling points;

[0050] According to the charging power of each charging pile in each time period, the electricity price in each time period, and the sum of the current amplitudes of the important sampling points and the charging station, the set number of time periods are divided into four types of section types; judge and count the main harmonics of the four section types;

[0051] Train the random forest algorithm according to the historical data of the charging power of each charging pile to predict the charging power of the charging pile in each time period, and combine the electricity price in each time period and the current amplitude of the charging station collected in each time period to judge the section type to which it belongs. The main harmonic of this section type is the harmonic that has the greatest impact on the corresponding charging pile in each time period.

[0052] It should be noted that analyzing the harmonic that has the greatest impact on the corresponding charging pile in each time period facilitates the personnel in the substation to perform corresponding harmonic compensation on the harmonic that has the greatest impact.

[0053] Preferably, as Figure 2 shown, the different sampling points include the high-voltage side of the charging pile and the low-voltage side of the charging pile. Specifically, the two sampling points are on the 10 kV side of the charging station and the 0.4 kV access point side of the charging pile.

[0054] Preferably, the harmonic characteristics of the sampled current are extracted through real discrete Fourier transform, specifically:

[0055] The sampled current is subjected to discrete Fourier transform and converted into the complex frequency domain form, and the formula is as follows:

[0056]

[0057] where, i L (nτ) is the sampled current, k represents the harmonic order, ω 1 is the fundamental angular frequency, τ is the sampling period, N m is the harmonic order of the highest frequency, n is the number of samples in the fundamental period, is the real part of the k-th current harmonic in the complex frequency domain, is the imaginary part of the k-th current harmonic in the complex frequency domain;

[0058] The formulas for calculating the real part and the imaginary part of the k-th current harmonic in the current in the complex frequency domain are as follows:

[0059]

[0060] According to the real part and the imaginary part of the k-th current harmonic, calculate the time domain form u k (nτ) of the k-th current harmonic, and the formula is as follows:

[0061]

[0062] Preferably, calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period, and calculate the comprehensive current distortion index according to the current harmonic distortion rates of the previous time period and the current time period and the current change rate in the current time period, specifically:

[0063] Calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period, and the formula is as follows:

[0064]

[0065] where, they are t - 1 and t corresponding to the previous time period and the current time period respectively, is the current sampling point corresponding to the current harmonic distortion rate of the time period, I i is the effective value of the i-th harmonic component of the current corresponding to the current sampling point in the time period, U 1 is the effective value of the fundamental wave corresponding to the current sampling point in the time period, N is the set maximum odd harmonic order;

[0066] Specifically, N is set to 13;

[0067] According to the current harmonic distortion rates of each sampling point in the previous time period and the current time period, calculate the comprehensive current distortion index THD of each sampling point in the current time period. The calculation formula is as follows:

[0068]

[0069] Among them, THD t-1 is the current harmonic distortion rate of the previous time period at the current sampling point, THD t is the current harmonic distortion rate of the current time period at the current sampling point, and ΔI is the current change rate of the current sampling point in the current time period.

[0070] Preferably, analyze the sampling points that have a greater impact on the charging pile from different sampling points and set them as important sampling points. Specifically:

[0071] Compare the comprehensive current distortion indexes THD of two sampling points, and take the larger one as the important sampling point.

[0072] Preferably, divide the set number of time periods into four types of section types according to the charging power of the charging pile in each time period, the electricity price in each time period, and the sum of the current amplitudes of the important sampling points and the charging station; judge and count the main harmonics of the four section types. Specifically:

[0073] Divide the set number of time periods into a section with a higher electricity price and a section with a lower electricity price according to the electricity price in each time period;

[0074] If the time period is between the sections with a higher electricity price, judge whether its average charging power is greater than or equal to 80% of the maximum charging power or whether the current amplitude of its charging station is greater than or equal to 10A. If either condition is met, it is the main power consumption period; otherwise, it is the secondary power consumption period;

[0075] If the time period is in the section with a lower electricity price, judge whether its average charging power is greater than or equal to 80% of the maximum charging power or whether the current amplitude of its charging station is greater than or equal to 10A. If either condition is met, the power consumption period is the normal power consumption period; otherwise, it is the non-power consumption period.

[0076] It should be noted that the electricity price obtained in this embodiment is such that the electricity price in the time period between the 12th and 20th time periods is greater than 1.4 yuan / kWh, and the electricity price in the 1st to 11th time periods or the 21st to 24th time periods is less than 1.4 yuan / kWh. Therefore, the time period between the 12th and 20th time periods is the section with a higher electricity price, and the 1st to 11th time periods or the 21st to 24th time periods are the sections with a lower electricity price;

[0077] Preferably, the main harmonics of the four section types are judged and counted as follows: judge whether the harmonic distortion rate of each harmonic in all time periods of each section type exceeds 5%. If so, the harmonic is considered as the main harmonic of the section type.

[0078] Specifically, there are 4 charging piles in a certain charging station analyzed in this embodiment, and the maximum power of a single pile is 60 kW. The current amplitude of the charging station is as Figure 3 shown. Analyze the 4 charging piles. Finally, it is judged that all charging piles are in the main power consumption periods from the 12th time period to the 19th time period, the 20th time period is the secondary time period, the 1st time period, the 6th time period to the 9th time period, and the 21st time period to the 24th time period are ordinary power consumption periods, and the 2nd time period to the 5th time period and the 10th time period to the 11th time period are non-power consumption periods.

[0079] As Figure 3 shown, the main harmonics in the main power consumption periods are the 5th and 7th harmonics, the main harmonic in the secondary time period is the 5th harmonic, the main harmonics in the ordinary power consumption periods are the 9th and 11th harmonics, and the main harmonics in the non-power consumption periods are the 11th and 13th harmonics.

[0080] Embodiment 2 of the present invention proposes a system using the method for extracting and analyzing harmonic characteristics of a large-scale charging pile described in Embodiment 1 of the present invention, including a harmonic characteristic extraction module, a comprehensive current distortion index calculation module, a section type division module, and a main harmonic judgment module, which are characterized in that:

[0081] Harmonic characteristic extraction module: used to divide each day into a set number of time periods on average, perform real-time sampling on the currents at different sampling points in the charging station, and extract the harmonic characteristics of the sampled currents through real discrete Fourier transform to calculate the current harmonic distortion rates of each sampling point in the previous time period and the current time period, and calculate the comprehensive current distortion index according to the current harmonic distortion rates of the previous time period, the current time period, and the current change rate of the current time period;

[0082] Important sampling point analysis module: used to analyze the sampling points that have a greater impact on the charging pile from different sampling points according to the comprehensive current distortion index of each sampling point, and set them as important sampling points;

[0083] Section type division module: used to divide a set number of time periods into four types of section types according to the charging power of the charging pile in each time period, the electricity price in each time period, the sum of the important sampling points, and the current amplitude of the charging station; judge and count the main harmonics of the four section types;

[0084] Main harmonic judgment module: It is used to train a random forest algorithm based on the historical charging power data of each charging pile, predict the charging power of the charging pile in each time period, and combine the electricity price in each time period and the current amplitude of the charging station collected in each time period to judge the type of the section it belongs to. The main harmonic of this section type is the harmonic that has the greatest impact on the corresponding charging pile in each time period.

[0085] Embodiment 3 of the present invention provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the computer program is loaded into the processor, it implements the method for extracting and analyzing the harmonic characteristics of large-scale charging piles according to Embodiment 1 of the present invention.

[0086] Embodiment 4 of the present invention proposes a computer-readable storage medium. The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the method for extracting and analyzing the harmonic characteristics of large-scale charging piles according to Embodiment 1 of the present invention.

[0087] The present disclosure may be a system, a method, and / or a computer program product. The computer program product may include a computer-readable storage medium having computer-readable program instructions thereon for causing a processor to implement various aspects of the present disclosure.

[0088] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (non-exhaustive list) of the computer-readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), a memory stick, a floppy disk, a mechanically encoded device, such as a punched card or raised structures in grooves storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage medium used herein is not construed as an instantaneous signal itself, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission medium (e.g., optical pulses through an optical fiber cable), or electrical signals transmitted through wires.

[0089] The computer-readable program instructions described herein can be downloaded to various computing / processing devices from a computer-readable storage medium or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical fiber transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in a computer-readable storage medium in each computing / processing device.

[0090] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state-setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages such as Smalltalk, C++, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider). In some embodiments, by using the state information of the computer-readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field-programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer-readable program instructions to implement various aspects of the present disclosure.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A method for extracting and analyzing harmonic features of large-scale charging piles, characterized in that: It includes the following: Each day is evenly divided into a set number of time periods, and the current at different sampling points in the charging station is sampled in real time. The sampled current is subjected to harmonic feature extraction through real discrete Fourier transform to calculate the current harmonic distortion rate of each sampling point in the previous time period and the current time period, and the comprehensive current distortion index is calculated based on the current harmonic distortion rate of the previous time period, the current time period and the current change rate of the current time period; According to the comprehensive current distortion index of each sampling point, the sampling points with greater impact on the charging pile are analyzed from different sampling points and set as important sampling points; According to the charging power of the charging pile in each time period, the electricity price in each time period, and the current amplitude of the important sampling points and the charging station, the set number of time periods are divided into four types of sections; the main harmonics of the four types of sections are determined and counted; The random forest algorithm is trained based on the historical charging power data of each charging pile to predict the charging power of the charging pile in each time period. The section type to which it belongs is determined by combining the electricity price in each time period and the current amplitude of the charging station collected in each time period. The main harmonic of this section type is the harmonic with the greatest impact on the corresponding charging pile in each time period.

2. A large-scale charging pile harmonic feature extraction and analysis method as claimed in claim 1, characterized in that: The different sampling points include the high voltage side of the charging pile and the low voltage side of the charging pile.

3. A large-scale charging pile harmonic feature extraction and analysis method as claimed in claim 1, characterized in that: The extraction of harmonic features from the sampled current by real discrete Fourier transform is specifically as follows: The sampled current is discrete Fourier transformed and converted into complex frequency domain form. The formula is as follows: Among them, i L (nτ) is the sampling current, k is the harmonic order, ω1 is the fundamental angular frequency, τ is the sampling period, N m is the harmonic number of the highest frequency, n is the number of samples of the fundamental wave period, is the real part of the kth current harmonic in the complex frequency domain, is the imaginary part of the kth current harmonic in the complex frequency domain; The formula for calculating the real and imaginary parts of the kth current harmonic in the complex frequency domain is as follows: According to the real and imaginary parts of the kth current harmonic, calculate the time domain form u of the kth current harmonic k (nτ), the formula is as follows:

4. A method for extracting and analyzing harmonic features of large-scale charging piles as claimed in claim 3, characterized in that: The current harmonic distortion rate of each sampling point in the previous time period and the current time period is calculated, and the comprehensive current distortion index is calculated according to the current harmonic distortion rate in the previous time period and the current time period and the current change rate in the current time period, specifically: Calculate the current harmonic distortion rate of each sampling point in the previous time period and the current time period. The formula is as follows: in, When t-1 and t correspond to the previous time period and the current time period respectively, is the current sampling point The current harmonic distortion rate of the corresponding time period, I i is the current sampling point The effective value of the i-th harmonic component in the corresponding time period, I1 is the current sampling point The effective value of the fundamental wave in the corresponding time period, N is the maximum number of odd harmonics set; According to the current harmonic distortion rate of each sampling point in the previous time period and the current time period, the comprehensive current distortion index THD of each sampling point in the current time period is calculated. The calculation formula is: Among them, THD t-1 is the current harmonic distortion rate of the previous time period at the current sampling point, THD t is the current harmonic distortion rate of the current sampling point in this time period, and ΔI is the current change rate of the current sampling point in this time period.

5. A method for extracting and analyzing harmonic features of large-scale charging piles as claimed in claim 2, characterized in that: The sampling points that have a greater impact on the charging pile are analyzed from different sampling points and set as important sampling points, specifically: Compare the comprehensive current distortion index THD of the two sampling points, and take the larger one as the important sampling point.

6. A method for extracting and analyzing harmonic features of large-scale charging piles as claimed in claim 5, characterized in that: According to the charging power of the charging pile in each time period, the electricity price in each time period, and the current amplitude of the important sampling points and the charging station, the set number of time periods are divided into four types of sections; the main harmonics of the four types of sections are judged and counted, specifically: According to the electricity price of each time period, the set number of time periods are divided into sections with higher electricity prices and sections with lower electricity prices; If the time period is between the sections with higher electricity prices, determine whether its average charging power is greater than or equal to 80% of the maximum charging power or whether its charging station current amplitude is greater than or equal to 10A. If any of these conditions are met, it is the main electricity consumption period; otherwise, it is the secondary electricity consumption period; If the time period is in a section with lower electricity prices, determine whether its average charging power is greater than or equal to 80% of the maximum charging power or whether its charging station current amplitude is greater than or equal to 10A. If any of these conditions are met, the electricity consumption period is a normal electricity consumption period; The opposite is the non-power consumption period.

7. A method for extracting and analyzing harmonic features of large-scale charging piles as claimed in claim 6, characterized in that: The determining and counting of the main harmonics of the four segment types specifically includes: determining whether the distortion rate of each harmonic in all time periods of each segment type exceeds 5%, and if so, the harmonic is considered to be the main harmonic of the segment type.

8. A system using the large-scale charging pile harmonic feature extraction and analysis method according to any one of claims 1 to 7, comprising a harmonic feature extraction module, an important sampling point analysis module, a section type division module, and a main harmonic judgment module, characterized in that: Harmonic feature extraction module: used to divide each day into a set number of time periods, sample the current at different sampling points in the charging station in real time, and extract the harmonic features of the sampled current through real discrete Fourier transform to calculate the current harmonic distortion rate of each sampling point in the previous time period and the current time period, and calculate the comprehensive current distortion index based on the current harmonic distortion rate of the previous time period, the current time period and the current change rate of the current time period; Important sampling point analysis module: used to analyze the sampling points with greater impact on the charging pile from different sampling points according to the comprehensive current distortion index of each sampling point, and set them as important sampling points; Section type division module: used to divide the set number of time periods into four types of section types according to the charging power of the charging pile in each time period, the electricity price in each time period, and the current amplitude of the important sampling points and charging stations; determine and count the main harmonics of the four types of sections; Main harmonic judgment module: used to train the random forest algorithm according to the historical charging power data of each charging pile, predict the charging power of the charging pile in each time period, and judge the section type to which it belongs based on the electricity price in each time period and the current amplitude of the charging station collected in each time period. The main harmonic of this section type is the harmonic with the greatest impact on the corresponding charging pile in each time period.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the computer program is loaded into the processor, the large-scale charging pile harmonic feature extraction and analysis method according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for extracting and analyzing harmonic features of large-scale charging piles according to any one of claims 1 to 7 is implemented.

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