A design method and system of an online monitoring system for power system harmonics

Abstract

The application belongs to the field of intelligent power distribution systems, and provides a design method and system for an online harmonic monitoring system of a power system, which comprises the following steps: collecting voltage signals of transformers in a substation in real time through a voltage transformer; performing frequency domain analysis on the collected voltage signals by applying Fourier transform, and extracting each frequency component in the signals; setting a time window and a time interval, obtaining a frequency corresponding to a frequency component with the largest amplitude in each time interval, and recording the frequency as a highest frequency; obtaining a harmonic super-harmonic frequency difference through the highest frequency, and obtaining a harmonic severe wave band time window through the harmonic super-harmonic frequency difference; obtaining a harmonic severe wave band ratio through the harmonic severe wave band time window, and monitoring the operation of the power system through the harmonic severe wave band ratio. According to the design method of the embodiment of the application, problems can be quickly detected in the early stage of harmonic pollution, and a harmonic filter can be started or load distribution can be adjusted in time, so that the stability of the power system is ensured.

Description

Technical Field

[0001] This invention belongs to the field of intelligent power distribution systems, and specifically relates to a design method and system for an online harmonic monitoring system for power systems. Background Technology

[0002] Harmonic pollution can severely impact power system equipment and power quality, easily leading to overheating of transformers and motors. The mechanical vibrations caused by harmonic pollution can create asymmetrical magnetic fields in rotating equipment such as motors, resulting in bearing wear and increasing the risk of equipment failure. At the same time, harmonic pollution is usually accompanied by voltage waveform distortion. Since nonlinear loads cannot consume current according to the sine wave law, the current waveform becomes distorted, which affects the voltage waveform and causes harmonic currents, leading to voltage waveform distortion, resulting in operational failure or equipment damage. Ultimately, it leads to a decrease in the power factor of power system equipment, overload, and consumption of more reactive power, resulting in decreased operating efficiency. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the first objective of this invention is to propose a design method for an online harmonic monitoring system for power systems, which can rapidly detect problems in the early stages of harmonic pollution using electrical sensors and promptly activate harmonic filters or adjust load distribution to ensure the stability of the power system.

[0004] The second objective of this invention is to propose a design system for an online harmonic monitoring system for power systems.

[0005] To achieve the above objectives, the first aspect of this invention proposes a design method for an online harmonic monitoring system for power systems, the method comprising the following steps:

[0006] S100 collects the voltage signal of the transformer in the substation in real time through the voltage transformer;

[0007] S200 applies Fourier transform to perform frequency domain analysis on the acquired voltage signal and extracts each frequency component from the signal.

[0008] S300: Set the time window and time interval, obtain the frequency corresponding to the frequency component with the largest amplitude in each time interval, and record it as the highest frequency;

[0009] S400 obtains the harmonic superharmonic frequency difference through the highest frequency, and obtains the time window of the severe harmonic band through the harmonic superharmonic frequency difference.

[0010] The S500 obtains the harmonic intensity band ratio through the harmonic intensity band time window and monitors the power system operation status through the harmonic intensity band ratio.

[0011] According to the design method of the present invention, problems can be detected quickly in the early stage of harmonic pollution, and harmonic filters can be activated or load distribution can be adjusted in a timely manner to ensure the stability of the power system.

[0012] Furthermore, in step S100, the real-time acquisition of voltage signals from transformers in the substation via voltage transformers includes:

[0013] The voltage transformer is installed on the high-voltage side of the transformer and obtains the voltage signal through the principle of electromagnetic induction. The voltage transformer is a JLSZV voltage and current combined transformer.

[0014] Furthermore, in step S200, Fourier transform is applied to perform frequency domain analysis on the acquired voltage signal, and the various frequency components in the signal are extracted, including:

[0015] Specifically, the fast Fourier transform algorithm is used to convert the time-domain data of the signal into frequency-domain data, and the Fourier transform is used to decompose the voltage signal into various frequency components, including the fundamental frequency and various higher harmonic frequencies. The fundamental frequency is the fundamental frequency of the power system when the voltage and current are normal, and the higher harmonic frequencies are integer multiples of the fundamental frequency.

[0016] Harmonic pollution can severely impact power system equipment and power quality, easily leading to overheating of transformers and motors. The mechanical vibrations caused by harmonic pollution can create asymmetrical magnetic fields in rotating equipment such as motors, resulting in bearing wear and increasing the risk of equipment failure. Furthermore, harmonic pollution is often accompanied by voltage waveform distortion. Since nonlinear loads cannot consume current according to a sinusoidal pattern, the current waveform becomes distorted, affecting the voltage waveform and causing harmonic currents, which in turn leads to voltage waveform distortion, resulting in operational failure or equipment damage (see reference: Gao Jie; Research on Harmonic Source Combination Optimization [D]; North China Electric Power University; 2013). Ultimately, this leads to a decrease in the power factor of power system equipment, overload, and increased reactive power consumption, resulting in decreased operating efficiency. To address these problems, this invention proposes step S300.

[0017] Furthermore, in step S300, a time window and time interval are set, and the frequency corresponding to the frequency component with the largest amplitude within each time interval is obtained and recorded as the highest frequency, including:

[0018] Set a time window TIME and a time interval p, obtain all frequencies within the time interval p within TIME, where the time window TIME is set to 30 minutes and p is set to 1 ms, and record the maximum value among all frequencies of the i-th interval within TIME as the highest frequency K(i), where i is the index, and the value range of i is i=1,2,…,t, where t is the total number of time intervals; obtain the base frequency of the time window TIME and record it as KT.

[0019] Furthermore, in step S400, obtaining the harmonic-superharmonic frequency difference through the highest frequency and obtaining the time window for the most severe harmonic band through the harmonic-superharmonic frequency difference includes the following steps:

[0020] S401 obtains the highest frequency neighbor spacing and frequency balance difference through frequency, and obtains the harmonic superharmonic frequency difference through the highest frequency neighbor spacing and frequency balance difference.

[0021] The methods for obtaining the highest frequency neighbor spacing and frequency balance difference through frequency include: when i < t, KWD(i) = |K(i+1) - K(i)|, and when i = t, KWD(i) = 0; obtaining the frequency balance difference KEV(i), KEV(i) = |K(i) - KT|; obtaining the harmonic and superharmonic frequency difference KAYT(i) = KWD(i) + KEV(i); creating an empty sequence KG, and importing the harmonic and superharmonic frequency difference KAYT(i) into the sequence KG in chronological order;

[0022] Among them, the harmonic superharmonic frequency difference KAYT(i) integrates the highest frequency adjacent spacing and the frequency balance difference, reflecting the amplitude and frequency distribution of harmonic variations in the substation, aiming to comprehensively measure the amplitude and frequency distribution of harmonic variations in the substation. Specifically, the highest frequency adjacent spacing is used to reflect the variation amplitude between the highest frequencies in adjacent time periods. If the highest frequency adjacent spacing is large, it indicates that the harmonic frequency has changed drastically within the time interval corresponding to the highest frequency adjacent spacing in the time window, and there has been load fluctuation or sudden change in the harmonic source.

[0023] Furthermore, the frequency balance difference measures the deviation between the highest frequency of the i-th time interval and the substation's fundamental frequency KT. A larger frequency balance difference indicates that the harmonic components in the substation deviate from the fundamental frequency, usually implying the presence of higher-order harmonics or nonlinear loads. The fundamental frequency KT is the benchmark for judging the substation's operational quality; the greater the deviation of the highest frequency in the harmonic signal, the more significant the harmonic pollution or nonlinear characteristics of the load.

[0024] Furthermore, the harmonic superharmonic frequency difference integrates the amplitude variation of harmonics and the degree of deviation from the fundamental frequency, thus reflecting the overall change of harmonic components more accurately. If the value of KAYT(i) is large, it indicates that the harmonic components in the substation change drastically within the time interval i, and the influence of high-order harmonics or nonlinear loads has appeared, suggesting that there may be a risk of harmonic pollution or abnormal load in the substation.

[0025] S402, obtain the frequency super-harmonic endpoint b and the frequency sub-harmonic endpoint a by the harmonic super-harmonic frequency difference;

[0026] Get the maximum value of all KAYT(i), and denote it as the peak frequency difference Kmax within the time window TIME. When there is only one element in KG with the value of peak frequency difference Kmax, denote the time index corresponding to the maximum value of all KAYT(i) as the frequency superharmonic endpoint b. When there are multiple elements with the value equal to peak frequency difference Kmax, denote the index corresponding to the KAYT(i) with the largest time index among all KAYT(i) with the value equal to peak frequency difference Kmax as the frequency superharmonic endpoint b.

[0027] Obtain the frequency subharmonic endpoint a, wherein the frequency subharmonic endpoint a is obtained by: obtaining the third quartile FourK of the sequence KG, and recording the index of the harmonic superharmonic frequency in the sequence KG that is equal to the third quartile FourK and has the smallest index as the frequency subharmonic endpoint a.

[0028] Among them, the frequency superharmonic endpoint b and the frequency subharmonic endpoint a are indicators for monitoring harmonic pollution and the impact of nonlinear loads in the power system. The frequency superharmonic endpoint b is used to calibrate the moment when harmonic pollution is most severe in the substation. It reflects the moment when the harmonic frequency changes the most in the substation. This moment often occurs when equipment fails, load changes suddenly, or harmonic sources suddenly increase.

[0029] In contrast, the subharmonic endpoint a represents the moment when the harmonic changes in the substation are close to anomalies. This endpoint marks the state before the harmonic components of the substation become unstable and fluctuate significantly. It usually reflects the period when the load is relatively unstable and the power quality is about to decline.

[0030] S403, determine the time window for the severe harmonic band based on the frequency superharmonic endpoint b and the frequency subharmonic endpoint a;

[0031] Obtain the time window for the severe harmonic band, where the subharmonic frequency endpoint a is taken as the starting point of the time window for the severe harmonic band, and the superharmonic frequency endpoint b is taken as the ending point of the time window for the severe harmonic band.

[0032] The beneficial effects of this step are as follows: By using the frequency superharmonic endpoint b and the frequency subharmonic endpoint a, the range of harmonic pollution and the stable operating period in the substation can be clearly defined, the changing trend of harmonic pollution in the substation can be accurately monitored, and the impact of nonlinear loads on the power system can be detected in a timely manner; in addition, the frequency superharmonic endpoint b and the frequency subharmonic endpoint a also have high real-time performance and sensitivity, and can dynamically monitor the fluctuation of harmonics in the power system and their potential impact on equipment. By calculating and comparing these endpoints in real time, the power system can take preventive and remedial measures before or in the early stage of harmonic pollution, thereby avoiding equipment damage, reduced operating efficiency of the power system, or system failure.

[0033] Furthermore, in step S500, the ratio of the most severe harmonic bands is obtained through a time window of the most severe harmonic bands. Monitoring the operation of the power system through the ratio of the most severe harmonic bands includes the following steps:

[0034] S501, denote the highest frequency of the j-th frequency in the severe harmonic band time window as A(j), compare all A(j) in the severe harmonic band time window with the fundamental frequency, and remove A(j) that are proportional to the fundamental frequency. The value range of j is i=1,2,…,q, where q is the number of highest frequencies in the severe harmonic band time window.

[0035] S502, obtain the number of highest frequencies Nenw in the remaining severe harmonic band time window;

[0036] S503, compare the number of the highest frequencies Nenw in the remaining harmonic severe band time window with t to obtain the harmonic severe band ratio BV;

[0037] Specifically, the Harmonic Severity Band Ratio (BV) is calculated within a specified time window by comparing the number of highest frequencies (Nenw) in the remaining harmonic severity bands within that window with the time interval (t). This ratio reflects the widespread distribution and drastic changes of harmonics in the substation during that period. A larger BV indicates a wider distribution of harmonic components in the substation, especially prominent high-frequency harmonic components, usually due to the presence of numerous nonlinear loads in the power system load or an increase in harmonic pollution sources in the substation. Therefore, an increase in BV typically indicates more severe harmonic pollution or a greater impact of nonlinear loads on the substation.

[0038] S504, obtain the harmonic intensity band ratio of the previous r time windows of the current time window and take the average value to obtain the average harmonic intensity band ratio BR, where r=5;

[0039] Specifically, the average harmonic severity ratio (BR) is a smoothed reference index obtained by calculating the average of the harmonic severity ratios (BV) of the r time windows preceding the current time window. BR serves as a benchmark for substation operation, helping to balance short-term harmonic fluctuations and long-term stability. In comparison with BV, BR provides a reference for judging whether there is harmonic pollution or nonlinear load influence in the substation. If the current BV is greater than BR, it indicates that the harmonic pollution of the substation is relatively serious or the influence of nonlinear load is relatively large during this period. Conversely, if BV is less than or equal to BR, it indicates that the substation is operating relatively smoothly with less harmonic pollution and less influence from nonlinear load.

[0040] S505, compare the ratio of severe harmonic bands BV with the ratio of severe harmonic bands BR to determine whether there is harmonic pollution or nonlinear load influence during time period t.

[0041] If BV>BR, it indicates that there is harmonic pollution or nonlinear load in the substation within the time window TIME; it indicates that the harmonic components in the current time period t are widely distributed in frequency and the amplitude of the high-frequency components is large, there are many excessive nonlinear loads in the power system load, or there is a harmonic pollution source in the power system. Real-time adjustment is carried out through automatic control and a warning message is issued.

[0042] If BV≤BR, it indicates that the substation is operating normally within the time window TIME, with less harmonic pollution or less impact from nonlinear loads. At this time, the harmonic components in the substation are concentrated in frequency, and the amplitude of the high-frequency components is small, indicating that the power system is operating normally.

[0043] The beneficial effects of this step are as follows: the ratio of severe harmonic bands can reflect the changing trend of harmonic pollution in substations in the power system in real time, and by comparing the ratio of severe harmonic bands with the average ratio of severe harmonic bands, the operating status of substations in the power system at the current time can be further judged. This dynamic response capability enables the system to quickly detect problems in the early stage of harmonic pollution and promptly activate harmonic filters or adjust load distribution to ensure the stability of the power system.

[0044] The beneficial effects of this invention are: it can quickly detect problems in the early stages of harmonic pollution and promptly activate harmonic filters or adjust load distribution to ensure the stability of the power system.

[0045] To achieve the above objectives, a second aspect of the present invention also proposes a design system for an online monitoring system for power system harmonics. The design system for the online monitoring system for power system harmonics includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps in a design method for an online monitoring system for power system harmonics. The design system for the online monitoring system for power system harmonics runs on computing devices such as satellites, desktop computers, laptops, handheld computers, and cloud data centers.

[0046] By implementing the design methodology of an online harmonic monitoring system for power systems, problems can be quickly detected in the early stages of harmonic pollution, and harmonic filters can be activated or load distribution adjusted in a timely manner to ensure the stability of the power system. Attached Figure Description

[0047] Figure 1 The diagram shows a flowchart of a design method for an online harmonic monitoring system for power systems.

[0048] Figure 2 The diagram shown is a design system structure diagram of an online harmonic monitoring system for power systems. Detailed Implementation

[0049] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0050] Figure 1 The diagram shows a flowchart of a design method for an online harmonic monitoring system for power systems.

[0051] Reference Figure 1 This invention proposes a design method for an online harmonic monitoring system for power systems, the method comprising the following steps:

[0052] S100 collects the voltage signal of the transformer in the substation in real time through the voltage transformer;

[0053] S200 applies Fourier transform to perform frequency domain analysis on the acquired voltage signal and extracts each frequency component from the signal.

[0054] S300: Set the time window and time interval, obtain the frequency corresponding to the frequency component with the largest amplitude in each time interval, and record it as the highest frequency;

[0055] S400 obtains the harmonic superharmonic frequency difference through the highest frequency, and obtains the time window of the severe harmonic band through the harmonic superharmonic frequency difference.

[0056] The S500 obtains the harmonic intensity band ratio through the harmonic intensity band time window and monitors the power system operation status through the harmonic intensity band ratio.

[0057] According to the design method of the present invention, problems can be detected quickly in the early stage of harmonic pollution, and harmonic filters can be activated or load distribution can be adjusted in a timely manner to ensure the stability of the power system.

[0058] S100 collects the voltage signal of the transformer in the substation in real time through the voltage transformer;

[0059] The voltage transformer is installed on the high-voltage side of the transformer and obtains the voltage signal through the principle of electromagnetic induction. The voltage transformer is a JLSZV voltage and current combined transformer.

[0060] S200 applies Fourier transform to perform frequency domain analysis on the acquired voltage signal and extracts each frequency component from the signal.

[0061] Specifically, the fast Fourier transform algorithm is used to convert the time-domain data of the signal into frequency-domain data, and the Fourier transform is used to decompose the voltage signal into various frequency components, including the fundamental frequency of 50Hz and various higher harmonic frequencies.

[0062] S300: Set the time window and time interval, obtain the frequency corresponding to the frequency component with the largest amplitude in each time interval, and record it as the highest frequency.

[0063] Set a time window TIME and a time interval p, obtain all frequencies within the time interval p within TIME, where the time window TIME is set to 30 minutes and p is set to 1ms, and record the maximum value among all frequencies of the i-th interval within TIME as the highest frequency K(i), where i is the index, and the value range of i is i=1,2,…,t. Obtain the base frequency of the time window TIME and record it as KT.

[0064] S400 obtains the harmonic superharmonic frequency difference through the highest frequency, and obtains the time window of the severe harmonic band through the harmonic superharmonic frequency difference.

[0065] S401 obtains the highest frequency neighbor spacing and frequency balance difference through frequency, and obtains the harmonic superharmonic frequency difference through the highest frequency neighbor spacing and frequency balance difference.

[0066] The methods for obtaining the highest frequency neighbor spacing and frequency balance difference through frequency include: when i < t, KWD(i) = |K(i+1) - K(i)|, and when i = t, KWD(i) = 0; obtaining the frequency balance difference KEV(i), KEV(i) = |K(i) - KT|; obtaining the harmonic and superharmonic frequency difference KAYT(i) = KWD(i) + KEV(i); creating an empty sequence KG, and importing the harmonic and superharmonic frequency difference KAYT(i) into the sequence KG in chronological order;

[0067] S402, obtain the frequency super-harmonic endpoint b and the frequency sub-harmonic endpoint a by the harmonic super-harmonic frequency difference;

[0068] Get the maximum value of all KAYT(i), and denote it as the peak frequency difference Kmax within the time window TIME. When there is only one element in KG with the value of peak frequency difference Kmax, denote the time index corresponding to the maximum value of all KAYT(i) as the frequency superharmonic endpoint b. When there are multiple elements with the value equal to peak frequency difference Kmax, denote the index corresponding to the KAYT(i) with the largest time index among all KAYT(i) with the value equal to peak frequency difference Kmax as the frequency superharmonic endpoint b.

[0069] Obtain the frequency subharmonic endpoint a, wherein the frequency subharmonic endpoint a is obtained by: obtaining the third quartile FourK of the sequence KG, and recording the index of the harmonic superharmonic frequency in the sequence KG that is equal to the third quartile FourK and has the smallest index as the frequency subharmonic endpoint a.

[0070] S403, determine the time window for the severe harmonic band based on the frequency superharmonic endpoint b and the frequency subharmonic endpoint a;

[0071] Obtain the time window for the severe harmonic band, where the subharmonic frequency endpoint a is taken as the starting point of the time window for the severe harmonic band, and the superharmonic frequency endpoint b is taken as the ending point of the time window for the severe harmonic band.

[0072] The S500 obtains the harmonic intensity band ratio through the harmonic intensity band time window and monitors the power system operation status through the harmonic intensity band ratio.

[0073] S501, denote the highest frequency of the j-th frequency in the severe harmonic band time window as A(j), compare all A(j) in the severe harmonic band time window with the fundamental frequency, and remove A(j) that are proportional to the fundamental frequency. The value range of j is i=1,2,…,q, where q is the number of highest frequencies in the severe harmonic band time window.

[0074] S502, obtain the number of highest frequencies Nenw in the remaining severe harmonic band time window;

[0075] S503, compare the number of the highest frequencies Nenw in the remaining harmonic severe band time window with t to obtain the harmonic severe band ratio BV;

[0076] S504, obtain the harmonic intensity band ratio of the previous r time windows of the current time window and take the average value to obtain the average harmonic intensity band ratio BR, where r=5;

[0077] S505, compare the ratio of severe harmonic bands BV with the ratio of severe harmonic bands BR to determine whether there is harmonic pollution or nonlinear load influence during time period t.

[0078] If BV>BR, it indicates that there is harmonic pollution or nonlinear load in the substation within the time window TIME; it indicates that the harmonic components in the current time period t are widely distributed in frequency and the amplitude of the high-frequency components is large, there are many excessive nonlinear loads in the power system load, or there is a harmonic pollution source in the power system. Real-time adjustment is carried out through automatic control and a warning message is issued.

[0079] If BV≤BR, it indicates that the substation is operating normally within the time window TIME, with less harmonic pollution or less impact from nonlinear loads. At this time, the harmonic components in the substation are concentrated in frequency, and the amplitude of the high-frequency components is small, indicating that the power system is operating normally.

[0080] Figure 2 The diagram shown is a design system structure diagram of an online harmonic monitoring system for power systems.

[0081] Reference Figure 2 The present invention also proposes a design system 20 for an online monitoring system of power system harmonics. The design system 20 includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps in a design method for an online monitoring system of power system harmonics. The design system 20 runs on computing devices such as satellites, desktop computers, laptops, handheld computers, and cloud data centers.

[0082] The design system includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program within the following design system units:

[0083] The acquisition unit 21 is used to acquire the voltage signal of the transformer in the substation in real time through the voltage transformer;

[0084] The conversion unit 22 is used to perform frequency domain analysis on the acquired voltage signal using Fourier transform and extract each frequency component in the signal.

[0085] Loading unit 23 is used to set the time window and time interval, obtain the frequency corresponding to the frequency component with the largest amplitude in each time interval, and record it as the highest frequency;

[0086] The filtering unit 24 is used to obtain the harmonic superharmonic frequency difference through the highest frequency, and to obtain the time window of the severe harmonic band through the harmonic superharmonic frequency difference;

[0087] Display unit 25 is used to obtain the harmonic intensity band ratio through the harmonic intensity band time window, and to monitor the operation of the power system through the harmonic intensity band ratio.

[0088] The design system for an online monitoring system of power system harmonics described above can run on computing devices such as desktop computers, laptops, handheld computers, and cloud servers. The design system for an online monitoring system of power system harmonics, which can run, may include, but is not limited to, processors and memory. Those skilled in the art will understand that the example described is merely an illustration of a design system 20 for an online monitoring system of power system harmonics and does not constitute a limitation on the design system 20. It may include more or fewer components, or combinations of certain components, or different components. For example, the design system for an online monitoring system of power system harmonics may also include input / output devices, network access devices, buses, etc.

[0089] By implementing the design method of the power system harmonic online monitoring system through system 20, problems can be quickly detected in the early stage of harmonic pollution, and harmonic filters can be activated or load distribution can be adjusted in a timely manner to ensure the stability of the power system.

[0090] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0091] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0092] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0093] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0094] Furthermore, the terms "first," "second," etc., used in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance, or implicitly specifying the number of technical features indicated in this embodiment. Therefore, features defined with terms such as "first" and "second" in the embodiments of this invention can explicitly or implicitly indicate that the embodiment includes at least one of those features. In the description of this invention, the word "multiple" means at least two or more, such as two, three, four, etc., unless otherwise explicitly specified in the embodiments.

[0095] In this invention, unless otherwise explicitly specified or limited in the embodiments, the terms "installation," "connection," "joining," and "fixing" appearing in the embodiments should be interpreted broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral part; it can also be a mechanical connection, an electrical connection, etc. Of course, it can also be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components, or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific implementation.

[0096] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0097] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A design method for an online harmonic monitoring system for power systems, characterized in that, The method includes the following steps: S100 collects the voltage signal of the transformer in the substation in real time through the voltage transformer; S200 applies Fourier transform to perform frequency domain analysis on the acquired voltage signal and extracts each frequency component from the signal. S300 sets a time window and time interval, obtains the frequency corresponding to the frequency component with the largest amplitude in each time interval, and records it as the highest frequency; wherein, S300 includes: setting a time window TIME and time interval p, obtaining all frequency magnitudes within TIME with time interval p, and recording the maximum value among all frequencies in the i-th interval within TIME as the highest frequency K(i), where i is the index, and the value range of i is i=1,2,…,t, and obtaining the base frequency of the time window TIME and recording it as KT; S400, obtaining the harmonic-superharmonic frequency difference through the highest frequency, and obtaining the time window of the severe harmonic band through the harmonic-superharmonic frequency difference; wherein step S400 includes: S401 obtains the highest frequency neighbor spacing and frequency balance difference through frequency, and obtains the harmonic superharmonic frequency difference through the highest frequency neighbor spacing and frequency balance difference. Step S401 includes: where when i < t, KWD(i) = |K(i+1) - K(i)|, and when i = t, KWD(i) = 0, where KWD(i) is the highest frequency neighbor spacing; obtain the frequency balance difference KEV(i), KEV(i) = |K(i) - KT|; obtain the harmonic and superharmonic frequency difference KAYT(i) = KWD(i) + KEV(i); create an empty sequence KG, and import the harmonic and superharmonic frequency difference KAYT(i) into the sequence KG in chronological order; S402, obtain the frequency superharmonic endpoint b and the frequency subharmonic endpoint a by the difference between the most harmonic superharmonic frequencies; S403, determine the time window for the severe harmonic band based on the frequency superharmonic endpoint b and the frequency subharmonic endpoint a; The S500 obtains the harmonic intensity band ratio through the harmonic intensity band time window and monitors the power system operation status through the harmonic intensity band ratio.

2. The design method of a power system harmonic online monitoring system according to claim 1, characterized in that, Step S100 includes: a voltage transformer is installed on the high-voltage side of the transformer to obtain a voltage signal through the principle of electromagnetic induction.

3. The design method of a power system harmonic online monitoring system according to claim 1, characterized in that, Step S200 includes: using a fast Fourier transform algorithm to convert the time-domain data of the signal into frequency-domain data, and using Fourier transform to decompose the voltage signal into various frequency components, including the fundamental frequency and various higher harmonic frequencies.

4. The design method of a power system harmonic online monitoring system according to claim 1, characterized in that, Step S402 includes: Get the maximum value of all KAYT(i) and record it as the peak frequency difference Kmax within the time window TIME. When there is only one element in KG with the value of peak frequency difference Kmax, record the time index corresponding to the maximum value of all KAYT(i) as the frequency superharmonic endpoint b. When there are multiple elements with the value equal to peak frequency difference Kmax, record the index corresponding to the KAYT(i) with the largest time index among all KAYT(i) with the value equal to peak frequency difference Kmax as the frequency superharmonic endpoint b. Obtain the subharmonic endpoint a, wherein the subharmonic endpoint a is obtained by: obtaining the third quartile FourK of the sequence KG, and recording the index of the subharmonic superharmonic frequency in the sequence KG that is equal to the third quartile FourK and has the smallest index as the subharmonic endpoint a.

5. The design method of a power system harmonic online monitoring system according to claim 1, characterized in that, Step S500 includes: S501 compares all the highest frequencies in the time window of the severe harmonic band with the fundamental frequency and removes the highest frequencies that are proportional to the fundamental frequency. S502, obtain the number of highest frequencies Nenw in the remaining severe harmonic band time window; S503, compare the number of the highest frequencies Nenw in the remaining harmonic severe band time window with t to obtain the harmonic severe band ratio BV; S504, obtain the harmonic intensity band ratio of the previous r time windows of the current time window and take the average value to obtain the average harmonic intensity band ratio BR; S505, compare the ratio of severe harmonic bands BV with the average ratio of severe harmonic bands BR to determine whether there is harmonic pollution or nonlinear load influence during time period t; If BV>BR, it indicates that there is harmonic pollution or nonlinear load in the substation within the time window TIME; it indicates that the harmonic components in the current time period t are widely distributed in frequency and the amplitude of the high-frequency components is large, there are many excessive nonlinear loads in the power system load, or there is a harmonic pollution source in the power system. Real-time adjustment is carried out through automatic control and a warning message is issued. If BV≤BR, it indicates that the substation is operating normally within the time window TIME, with less harmonic pollution or less impact from nonlinear loads. At this time, the harmonic components in the substation are concentrated in frequency, and the amplitude of the high-frequency components is small, indicating that the power system is operating normally.

6. A design system for an online harmonic monitoring system for a power system, characterized in that, The design system of the power system harmonic online monitoring system includes: a processor, a memory, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps in the design method of the power system harmonic online monitoring system according to any one of claims 1 to 5. The design system of the power system harmonic online monitoring system runs on a desktop computer, a laptop computer, a handheld computer, or a cloud data center.

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