A harmonic amplification detection method and system for power system

Abstract

The harmonic amplification detection method and system of the power system disclosed in the present invention obtain the topological structure and load distribution of the power system, analyze the frequency response of the power system impedance containing the interharmonic frequency component, and use the harmonic injection method to scan the impedance frequency characteristics of the power system at different frequencies to obtain the impedance frequency response curve; according to the frequency range of harmonic amplification, the harmonic hazard coefficient is evaluated by the voltage distortion rate and current distortion rate caused by the harmonics, and the type of harmonic source equipment that causes harmonic amplification is determined according to the hazard coefficient. This solution can realize the detection of harmonic source equipment, facilitate timely maintenance of the power system, and improve the stability of the power system.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a harmonic amplification detection method and system for power systems. Background Art

[0002] The impact of interharmonic frequency components in power systems on the coupling path between fundamental and harmonics is a complex and unique technical issue. When frequency offset occurs in the power system, non-integer frequency components produce a cumulative effect at the inflection point of the impedance frequency response curve, causing the impedance frequency response curve to be distorted, which in turn causes harmonic amplification. This amplification effect has an important impact on the stability of the power system, and its internal mechanism needs to be further studied. Specifically, there is a complex relationship between interharmonic frequency components and fundamental and harmonics, and they exchange and transfer energy through the inflection point on the impedance frequency response curve. When the power system frequency offsets, non-integer frequency components accumulate at the inflection point, changing the original impedance balance, causing the impedance frequency response curve to be distorted, and causing the harmonic components of specific frequencies to be amplified. This harmonic amplification phenomenon will have an adverse effect on the voltage quality, equipment insulation and protection devices of the power system, and even cause the instability of the power system.

[0003] The existing solutions lack a solution for detecting equipment that causes harmonic amplification effects, making it impossible to perform power system maintenance in a timely manner, and the stability of the power system is poor. Summary of the invention

[0004] In view of the above-mentioned defects, the harmonic amplification detection method and system for the power system provided by the present invention can realize the detection of harmonic source equipment, facilitate timely maintenance of the power system, and improve the stability of the power system.

[0005] An embodiment of the present invention provides a harmonic amplification detection method for an electric power system, the method comprising:

[0006] Obtain the topological structure and load distribution data of the power system, analyze the frequency response of the power system impedance including the interharmonic frequency components, and obtain the impedance frequency response curve;

[0007] Calculating the difference between the impedance value at the inflection point in the impedance frequency response curve and the impedance value at the adjacent frequency point, and performing frequency component analysis of the harmonic amplification phenomenon based on the obtained difference;

[0008] When a non-integer frequency component causing harmonic amplification is detected, it is determined that a frequency offset phenomenon occurs, and the amplitude and duration of the frequency offset are calculated according to the voltage signal of the power system and a preset fundamental wave period multiple;

[0009] Analyzing the frequency response of the power system impedance according to the amplitude and the duration, simulating the change of the impedance frequency characteristic of the power system under the condition of frequency offset, and determining the impedance frequency response curve distortion caused by the frequency offset according to the impedance frequency characteristic change, and determining the frequency range of harmonic amplification by comparing the impedance frequency response curves before and after the frequency offset;

[0010] Determining a voltage distortion rate and a current distortion rate caused by harmonics according to the frequency range, and calculating a harmonic hazard coefficient according to the voltage distortion rate and the current distortion rate;

[0011] The type of harmonic source equipment causing harmonic amplification is determined according to the hazard coefficient.

[0012] Preferably, the topological structure and load distribution data of the power system are obtained, and the frequency response of the power system impedance including the interharmonic frequency components is analyzed to obtain an impedance frequency response curve, including:

[0013] Determine the topological node coordinates and the connection relationship matrix between nodes according to the topological structure and load distribution data of the power system collected by the power distribution terminal;

[0014] Reading node voltage values ​​and node current values ​​of different nodes in the node connection relationship matrix to construct a load distribution matrix;

[0015] Decomposing node voltage values ​​and node current values ​​in the load distribution matrix by Fourier transform to obtain signal amplitudes of multiples of fundamental frequency, and calculating impedance frequency response vectors according to the signal amplitudes;

[0016] Injecting a harmonic current with a non-integer frequency component into the circuit breaker position marked by the impedance frequency response vector to obtain the harmonic voltage amplitude and harmonic phase of the adjacent nodes of the circuit breaker position;

[0017] The harmonic voltage amplitude and the harmonic phase are sequentially connected in time series by linear interpolation, and the slope of the connection point of the fitting curve is calculated according to the numerical deviation before and after the connection point;

[0018] When the calculated connection point slope is not within the preset threshold interval, the number of linear interpolation sampling times is increased, the connection point is re-determined, and the connection point slope of the fitting curve is calculated until the connection point slope is within the threshold interval;

[0019] When the calculated connection point slope is within the threshold interval, the impedance frequency response curve is drawn according to the sampling points.

[0020] Preferably, calculating the difference between the impedance value at the inflection point in the impedance frequency response curve and the impedance value at the adjacent frequency point, and performing frequency component analysis of the harmonic amplification phenomenon according to the obtained difference, including:

[0021] Discretizing the impedance frequency response curve at intervals of multiples of the fundamental frequency;

[0022] The difference between the maximum and minimum impedance values ​​of the discrete point sequence in the window is calculated using a fixed-length data window, and the position where the calculated difference is greater than the preset index is used as the inflection point coordinate of the impedance curve;

[0023] Establishing an impedance difference matrix according to the impedance complex values ​​of the inflection point coordinates;

[0024] Calculating the impedance change at adjacent frequency points using the ratio of the Fourier components of the voltage signal and the current signal according to the impedance difference matrix, calculating the ratio of the impedance value of the preset reference frequency point to the current frequency point, and marking the frequency points whose ratios exceed the preset ratio threshold value;

[0025] Extracting the harmonic amplification frequency interval according to the marked frequency points, and calculating the cumulative product of the impedance values ​​in the window using a sliding window composed of a number of frequency points according to the frequency components contained in the harmonic amplification frequency interval;

[0026] When the ratio of the maximum value to the minimum value of the cumulative product of the sliding window exceeds a preset multiple, the coordinates of the corresponding frequency point are recorded;

[0027] Wavelet transform is used to perform time-frequency analysis on the impedance sequence of the recorded frequency points;

[0028] When the time interval between adjacent peak values ​​of the amplitude spectrum is less than the product of a preset sampling period and a preset multiple, the adjacent frequency point is determined to be a non-integer frequency component of the harmonic amplification phenomenon.

[0029] Preferably, calculating the amplitude and duration of the frequency offset according to the voltage signal of the power system and a preset fundamental wave period multiple includes:

[0030] According to the harmonic current value of the non-integer frequency component, a first preset multiple of the fundamental wave period is used as a sampling window to perform Fourier transform on the voltage signal of the power system, and a difference in phase angle between the fundamental wave signal and the harmonic signal is calculated to obtain a frequency offset sequence;

[0031] A time domain distribution curve is constructed based on the offset sequence in each sampling period;

[0032] The amplitude and duration of the offset in the time domain distribution curve within a preset base frequency range are recorded as the amplitude and duration of the frequency offset.

[0033] Furthermore, the method further comprises:

[0034] The load operating state of the power system is used as a criterion to determine the load capacity of the frequency converter; the occurrence time of the frequency offset is determined according to the corresponding relationship between the load capacity and the offset in the time domain distribution curve;

[0035] A normal distribution function is established for the product term of the occurrence time of the frequency offset and the duration, and the occurrence probability of the frequency offset is calculated using the mean and variance of the normal distribution function.

[0036] Preferably, the frequency response of the power system impedance is analyzed according to the amplitude and the duration, the impedance frequency characteristic change of the power system under the frequency offset is simulated, and the impedance frequency response curve distortion caused by the frequency offset is determined according to the impedance frequency characteristic change, and the frequency range of harmonic amplification is determined by comparing the impedance frequency response curves before and after the frequency offset, including:

[0037] Sampling the impedance frequency response curve according to the fundamental frequency period to construct an impedance frequency response matrix;

[0038] Using Fourier transform to perform spectrum analysis on the impedance frequency response matrix containing frequency offset, and obtaining impedance frequency characteristic parameters by superimposing and calculating the amplitude of the fundamental frequency and the frequency component of the preset multiple;

[0039] Constructing a modified impedance-frequency revision curve according to the impedance-frequency characteristic parameters, and determining the amplitude change after adding the frequency offset;

[0040] Calculating the deformation amount of the impedance frequency characteristic parameter by using the least square method according to the amplitude variation, and obtaining the distortion degree by the difference between the impedance frequency response curve and the impedance frequency revision curve;

[0041] Support vector regression is used to perform numerical fitting on the obtained distortion degree, and the amplitude change curve is determined according to the distribution of the obtained distortion degree sequence on the frequency axis;

[0042] The frequency interval in the amplitude variation curve where the amplitude exceeds a preset reference value is determined as the frequency interval of harmonic amplification.

[0043] Preferably, determining the voltage distortion rate and the current distortion rate caused by the harmonics according to the frequency interval, and calculating the harmonic hazard coefficient according to the voltage distortion rate and the current distortion rate, specifically includes:

[0044] According to the voltage and current sampling data in the frequency interval, a second preset multiple of the fundamental wave period is used as the window length of the sampling window to perform Fourier decomposition on the voltage waveform and the current waveform;

[0045] The voltage distortion rate and the current distortion rate are calculated based on the root mean square value of the harmonic component amplitude obtained by decomposition;

[0046] Constructing a voltage hazard assessment matrix according to the ratio of the voltage distortion rate to a preset voltage reference value;

[0047] Constructing a current hazard assessment matrix according to the ratio of the current distortion rate to a preset current reference value;

[0048] Support vector regression mapping is performed according to the voltage hazard assessment matrix and the current hazard assessment matrix, and the hazard coefficient is calculated according to the proportion of time that the voltage distortion rate exceeds a preset voltage threshold value and the proportion of time that the current distortion rate exceeds a preset current threshold value.

[0049] Preferably, determining the type of harmonic source equipment causing harmonic amplification according to the hazard coefficient includes:

[0050] Obtain the hazard coefficient corresponding to each frequency interval;

[0051] Calculate the overlap between the hazard coefficients corresponding to different frequency intervals and the hazard coefficients of different types of equipment in the preset power equipment database;

[0052] The type of equipment whose overlap degree is not less than a preset threshold is determined as the harmonic source equipment type.

[0053] Preferably, the method further comprises:

[0054] According to the ratio relationship between the preset fundamental frequency and the non-integer frequency component, a node admittance matrix is ​​constructed, coupling characteristics between frequencies are determined according to the node admittance matrix, and a coupling transfer function is obtained by calculating the impedance complex value according to the coupling characteristics;

[0055] constructing a power loss matrix according to the magnitude and phase angle of the coupling transfer function;

[0056] Calculate the input point power and output point power of the power system according to the power loss matrix, and then calculate the transmission efficiency;

[0057] Marking a line section whose transmission efficiency is lower than a preset reference value as a transmission capacity-limited point;

[0058] Acquire three-phase voltage data of the transmission capacity limited point, and perform symmetrical component transformation on the three-phase voltage data using a fundamental wave period data window;

[0059] The calculated ratio of zero-sequence component to positive-sequence component is taken as the three-phase voltage unbalance degree;

[0060] The calculated ratio of the negative sequence component to the positive sequence component is used as the voltage distortion rate of each harmonic;

[0061] The voltage disturbance index is calculated using the short-term flicker value within a preset first time length and the long-term flicker value within a preset second time length.

[0062] An embodiment of the present invention further provides a harmonic amplification detection system for an electric power system, the system comprising a controller, the controller being configured to execute the harmonic amplification detection method for an electric power system as described in any one of the above embodiments.

[0063] The harmonic amplification detection method and system of the power system provided by the present invention obtain the topological structure and load distribution data of the power system, analyze the frequency response of the power system impedance containing the interharmonic frequency component, and obtain the impedance frequency response curve; calculate the difference between the impedance value at the inflection point and the impedance value at the adjacent frequency point in the impedance frequency response curve, and perform frequency component analysis of the harmonic amplification phenomenon according to the obtained difference; when the non-integer frequency component causing the harmonic amplification phenomenon is detected, it is determined that the frequency offset phenomenon occurs, and the amplitude and duration of the frequency offset are calculated according to the voltage signal of the power system and the preset fundamental wave period multiple; the frequency response of the power system impedance is analyzed according to the amplitude and the duration, the impedance frequency characteristic change of the power system under the frequency offset is simulated, and the impedance frequency response curve distortion caused by the frequency offset is determined according to the impedance frequency characteristic change, and the frequency range of the harmonic amplification is determined by comparing the impedance frequency response curves before and after the frequency offset; the voltage distortion rate and the current distortion rate caused by the harmonic are determined according to the frequency range, and the harmonic hazard coefficient is calculated according to the voltage distortion rate and the current distortion rate; the type of harmonic source equipment causing the harmonic amplification is determined according to the hazard coefficient. This solution can detect harmonic source equipment, facilitate timely maintenance of the power system, and improve the stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 The present invention provides a flow chart of a harmonic amplification detection method for an electric power system. DETAILED DESCRIPTION

[0065] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0066] See also Figure 1 , is a flow chart of a harmonic amplification detection method for a power system provided by an embodiment of the present invention, the method comprising steps S1 to S3:

[0067] Step S1, obtaining the topological structure and load distribution data of the power system, analyzing the frequency response of the power system impedance including the interharmonic frequency components, and obtaining an impedance frequency response curve;

[0068] Step S2, calculating the difference between the impedance value at the inflection point in the impedance frequency response curve and the impedance value at the adjacent frequency point, and performing frequency component analysis of the harmonic amplification phenomenon according to the obtained difference;

[0069] Step S3, when a non-integer frequency component causing harmonic amplification is detected, it is determined that a frequency offset phenomenon occurs, and the amplitude and duration of the frequency offset are calculated according to the voltage signal of the power system and a preset fundamental wave period multiple;

[0070] Step S4, analyzing the frequency response of the power system impedance according to the amplitude and the duration, simulating the change of the impedance frequency characteristic of the power system under the condition of frequency offset, and determining the impedance frequency response curve distortion caused by the frequency offset according to the impedance frequency characteristic change, and determining the frequency range of harmonic amplification by comparing the impedance frequency response curves before and after the frequency offset;

[0071] Step S5, determining the voltage distortion rate and the current distortion rate caused by the harmonics according to the frequency interval, and calculating the harmonic hazard coefficient according to the voltage distortion rate and the current distortion rate;

[0072] Step S6: determining the type of harmonic source equipment causing harmonic amplification according to the hazard coefficient.

[0073] In the specific implementation of this embodiment, by acquiring the topological structure and load distribution of the power system, analyzing the frequency response of the power system impedance containing the interharmonic frequency components, and using the harmonic injection method, scanning the impedance frequency characteristics of the power system at different frequencies to obtain an impedance frequency response curve;

[0074] The impedance frequency response curve is analyzed, and the cumulative effect of non-integer frequency components is obtained by calculating the difference between the impedance value at the inflection point and the impedance value at the adjacent frequency point. A threshold is set, and the frequency point where the difference is greater than the threshold is judged as having harmonic amplification phenomenon. If the harmonic amplification phenomenon exists, the non-integer frequency component causing the amplification is determined;

[0075] If a non-integer frequency component causing amplification is determined, it is confirmed that a frequency offset phenomenon has occurred. Combined with the nonlinear load type and operating conditions in the power system, the amplitude and duration of the frequency offset are evaluated to determine the degree of influence of the amplitude and duration of the frequency offset on the stability of the power system.

[0076] In the analysis of impedance frequency response, the frequency offset is introduced to simulate the change of impedance frequency characteristics of the power system under the condition of frequency offset. The degree of distortion of the impedance frequency response curve caused by the frequency offset is obtained according to the change of impedance frequency characteristics. By comparing the impedance frequency response curves before and after the frequency offset, the harmonic amplification range is determined.

[0077] According to the frequency range of harmonic amplification, the harmonic hazard factor is evaluated through the voltage distortion rate and current distortion rate caused by the harmonics;

[0078] The type of harmonic source equipment causing harmonic amplification is determined according to the hazard coefficient.

[0079] The present application scheme first establishes an impedance frequency response model of the power system including interharmonic frequency components, and obtains the impedance frequency response curve through the harmonic injection method. Then analyze the inflection point of the curve to determine whether there is a harmonic amplification phenomenon and the non-integer frequency components that cause the amplification. If so, evaluate the impact of frequency offset on system stability, introduce the frequency offset into the model, and analyze the change in impedance frequency characteristics. According to the frequency range and amplitude change trend of harmonic amplification, evaluate the harmonic hazard coefficient, and determine the type of harmonic source equipment that causes harmonic amplification based on the hazard coefficient. This case can evaluate the type of harmonic source equipment that causes harmonic amplification in the power system, provide a basis for stable system operation and harmonic suppression, and help improve power quality and system reliability.

[0080] In another embodiment provided by the present invention, when the above step S1 is specifically performed, the following steps are specifically performed:

[0081] Determine the topological node coordinates and the node connection relationship matrix based on the topological structure and load distribution data of the power system collected by the power distribution terminal, and construct a load distribution matrix by reading the node voltage value and the current value through the node connection relationship matrix;

[0082] Decomposing the node voltage and current values ​​in the load distribution matrix by Fourier transform, obtaining the fundamental frequency multiple signal amplitude according to the decomposition result, and calculating the impedance frequency response vector according to the signal amplitude;

[0083] Injecting non-integer harmonic current into the circuit breaker position marked by the impedance frequency response vector, and acquiring harmonic voltage amplitude and phase from nodes around the injection point;

[0084] The harmonic voltage amplitude and phase are connected by linear interpolation. If the slope of the connection point exceeds a preset interval, the number of sampling times is increased until the slope is within the interval, and an impedance frequency response curve is drawn according to the sampling points.

[0085] In specific applications, the power network topology connection data is obtained based on the real-time collected distribution terminal data, and the topology node coordinates and the node connection relationship matrix are recorded using a three-column storage method. By reading the voltage and current values ​​of each connected node, a 5-row and 5-column load distribution matrix containing the bus, transformer and circuit breaker positions is constructed, including: according to the real-time collected distribution terminal data, the data is parsed to obtain the power network topology connection relationship.

[0086] The three-column storage method is used to record the topological node coordinates and the node connection relationship matrix, in which the first column stores the node ID, and the second and third columns store the horizontal and vertical coordinates of the node respectively. According to the node connection relationship matrix, the voltage and current values ​​of each connected node are obtained. If a node is connected to multiple child nodes, the total current value of the node is calculated as its current value. The power network is divided into 5x5 grids by constructing a 5-row 5-column load distribution matrix. According to the topological node coordinates, the grid to which each node belongs is determined. According to the topological node coordinates of the bus, transformer and circuit breaker, their positions in the 5x5 grid are determined. According to the voltage and current values ​​of the connected nodes in each grid, the total load power of each grid is calculated. The total load power P is calculated as P=UI, where U is the voltage value and I is the current value. If a grid contains a bus, the sum of the total load power of all child nodes connected to the bus is taken as the load value of the grid. If a grid contains a transformer, the total load power connected to the transformer is taken as the load value of the grid. If a grid contains a circuit breaker, determine whether it is turned on based on the state of the circuit breaker. If the circuit breaker is turned on, the total power of the load connected to the circuit breaker is used as the load value of the grid; if the circuit breaker is not turned on, the load value of the grid is 0. A 5-row 5-column load distribution matrix is ​​constructed based on the calculated load value of each grid, and each element of the matrix represents the load power of the corresponding grid.

[0087] Fourier transform is used to decompose the voltage and current sampling data of each node in the load distribution matrix, and the segment length is divided according to 10% of the sampling frequency.

[0088] The signal amplitude containing 0.5 times the fundamental frequency to 2.5 times the fundamental frequency is obtained from the decomposition result, the impedance frequency response vector is calculated according to the amplitude ratio, and the impedance value corresponding to each frequency is stored in a 4-row 4-column matrix. Harmonic current containing non-integer frequency components is injected at the circuit breaker position marked by the impedance frequency response vector. The harmonic current frequency range is between 0.5 times and 2.5 times the fundamental frequency, and the frequency interval increases by 0.1 times the fundamental frequency. The sampling interval of each frequency point is one tenth of the sampling frequency, and the harmonic voltage amplitude and phase of the nodes around the injection point are obtained.

[0089] Linear interpolation is used to connect the amplitude and phase of the harmonic voltage obtained by sampling in time series. The slope of the fitting curve is determined according to the numerical deviation before and after the connection point. When the slope exceeds the range of 0.5 to 1.5, the number of sampling times of the point is increased until the slope is within the range. The impedance frequency response curve is drawn for the sampling points that meet the slope conditions. The three-column storage method in the power network topology records the node position and connection relationship. The distribution network architecture contains three main types of equipment: transformers, circuit breakers, and busbars. A 5-row and 5-column matrix associated with the nodes is constructed to describe the feeder path between the nodes and record the voltage and current signal monitoring data of each node. When the 35 kV line contains a 10 kV busbar section, if the transformer node position is in the 2nd row and 3rd column of the matrix, the corresponding connection data record is 2 and 3, forming a node coordinate pair. Each device node has an identification attribute, and when the load data is recorded, it is classified and stored according to the device type. Fourier transform is used to analyze the sampling data in the frequency domain. The signal with a fundamental frequency of 50 Hz is used as the standard. The frequency band is divided into units of 5 Hz. The length of each frequency band is 0.1 times the sampling frequency. The harmonic voltage and current amplitudes in the range of 25 Hz to 125 Hz are obtained. If the sampling frequency is 1000 Hz, the segment length is 100 Hz. Among the obtained harmonic components, the 50 Hz amplitude is the reference value 1.0, and the amplitudes of other frequency components are recorded as relative values. The impedance value corresponding to each frequency is calculated and filled in the corresponding position of the impedance matrix. Harmonic current injection is carried out from the circuit breaker on the low-voltage side of the transformer. The frequency of the injected harmonic current increases by 5 Hz in the range of 25 Hz to 125 Hz. The frequency component contains non-integer multiple frequencies to form a frequency scanning sequence. The length of the sampling time window is determined according to the inverse of the injection frequency. The number of sampling points is not less than 100 points in each cycle to ensure sampling accuracy. The voltage signal is synchronously collected at three nodes around the injection point, and the voltage amplitude and phase angle data at different frequencies are recorded. The impedance frequency curve fitting adopts piecewise linear interpolation. The slope between two adjacent points reflects the trend of impedance change with frequency. The slope in the range of 0.5 to 1.5 indicates that the impedance change is smooth.

[0090] When the slope of a certain frequency point exceeds the interval range, increase the number of sampling times at this point and take the average value until the slope meets the smoothing condition. If the voltage amplitude at a certain point is 100 volts and the phase angle is 30 degrees, the impedance value at this point is 1 ohm and the impedance angle is 30 degrees. Connect the sampling points in order from low to high frequency to form an impedance-frequency characteristic curve. When harmonic interference occurs on the 10 kV bus, the location of the harmonic source is determined by measuring the impedance response curve. When the impedance amplitude at a certain point has a valley value, it indicates that the point is the injection point of the harmonic source, and the impedance curve shows a low-resistance characteristic at this frequency. Compare the impedance curve shapes of different nodes, and determine the harmonic propagation path based on the amplitude and phase difference. In the impedance curve of the 35 kV bus section, the impedance value at the harmonic frequency is higher, indicating that the harmonic source is located on the low-voltage side.

[0091] It should be noted that the specific values ​​such as the adopted frequency, divided frequency bands and segment length provided in the above embodiments are all preferred application embodiments. In other embodiments provided by the present invention, the above parameters can be set or adjusted according to the actual application scenario.

[0092] In another embodiment provided by the present invention, when step S2 in the above embodiment is specifically implemented, the following steps are specifically performed:

[0093] Discretization is performed on the impedance frequency response curve at intervals of multiples of the fundamental frequency, and the coordinates of the inflection point of the impedance curve are obtained by calculating the difference between the maximum and minimum impedance values ​​in a fixed-length data window; an impedance difference matrix is ​​established according to the impedance complex values ​​of the inflection point coordinates, and the impedance change at adjacent frequency points is calculated using the ratio of the Fourier components of the voltage signal and the current signal, and the current frequency point is marked when the impedance value ratio between the reference frequency point and the current frequency point exceeds a preset threshold;

[0094] Construct a sliding window for the marked frequency point to calculate the cumulative product of the impedance value in the window, and if the maximum and minimum ratios of the cumulative products exceed a preset multiple, record the coordinates of the corresponding frequency point;

[0095] Wavelet transform is used to perform time-frequency analysis on the recorded frequency points. If the time interval between adjacent peak values ​​of the amplitude spectrum is less than a preset multiple of the sampling period, the adjacent frequency points are determined to be non-integer frequency components that cause amplification.

[0096] In a specific application, the impedance frequency response curve is numerically discretized at intervals of 0.5 times the fundamental frequency according to the sampling data.

[0097] The difference between the maximum and minimum impedance values ​​of the discrete point sequence in the window is calculated using a fixed-length data window. The inflection point coordinates of the impedance curve are obtained by the point position where the difference exceeds the preset index, and the position where the calculated difference is greater than the preset index is used as the inflection point coordinates of the impedance curve;

[0098] An impedance difference matrix with 4 rows and 4 columns is established according to the impedance complex values ​​of the obtained inflection point coordinates.

[0099] The ratio of the Fourier components of the voltage signal and the current signal is used to calculate the impedance value change of adjacent frequency points in the impedance difference matrix. The ratio of the impedance value of the reference frequency point to the impedance value of the current frequency point is recorded as the judgment standard. When the ratio exceeds 1.5 times, the current frequency point is marked, and the harmonic amplification frequency interval is extracted for the marked frequency point.

[0100] According to the frequency components contained in the marked frequency interval, a sliding window consisting of 5 frequency points is used to calculate the cumulative product of the impedance values ​​in the window. The amplification factor is calculated by the maximum and minimum ratio of the impedance cumulative product, and the corresponding frequency point is recorded when the amplification factor exceeds 2 times.

[0101] Wavelet transform is used to perform time-frequency analysis on the impedance sequence of marked frequency points, and the correlation degree of frequency components is determined by the position relationship of the amplitude peaks and valleys in the impedance spectrum.

[0102] When the time interval between adjacent peaks of the amplitude spectrum is less than 0.5 times the sampling period, the adjacent frequency points are determined to be non-integer frequency components that cause harmonic amplification. In the discretization processing of the impedance frequency response curve, when the fundamental frequency is 50 Hz, the sampling interval is set to 25 Hz, corresponding to 0.5 times the fundamental frequency, and 10 discrete sampling points are obtained in the frequency range of 0 to 250 Hz. Each sampling point records the impedance amplitude and phase angle at the corresponding frequency to form an impedance value expressed in complex form. A fixed window of 20 data points is used to calculate the degree of difference. When the maximum impedance value in the window is 2 ohms and the minimum impedance value is 1 ohm, the difference is 1, which exceeds the preset 0.5 index, and the point is determined to be an inflection point. The impedance difference matrix is ​​used to record the impedance change at the inflection point. The number of rows and columns of the matrix is ​​4, corresponding to the impedance values ​​of 4 frequency intervals. At the frequency point of 75 Hz, the voltage amplitude is 100 volts and the current amplitude is 50 amperes, and the impedance value is 2 ohms. The impedance value of the adjacent 100 Hz frequency point is 3 ohms, and the impedance change is 1 ohm. Compared with the impedance value of 1.5 ohms at the reference frequency of 50 Hz, the ratio is 2, which exceeds the criterion of 1.5 times, marking the frequency point as having harmonic amplification. The sliding window contains 5 adjacent frequency points, and the impedance values ​​in the window are 1.5, 2, 3, 2.5, and 1.8 ohms, respectively. The calculated cumulative product is 20.25. When the window moves to the next position, the new cumulative product is 15.3, and the product ratio of the two windows is 1.32, which does not exceed the criterion of 2 times, indicating that the harmonic amplification degree of this frequency interval is weak. At the 150 Hz frequency point, the cumulative product reaches 45.9, and the ratio with the previous window is 3, which exceeds the criterion, and the point is recorded as a harmonic amplification frequency point. After the wavelet transform decomposes the impedance sequence, the change characteristics of the impedance amplitude are presented on the time-frequency plane. At the two frequency points of 125 Hz and 137.5 Hz, the peaks of the impedance spectrum appear at 0.2 seconds and 0.3 seconds respectively, with a time interval of 0.1 seconds, which is less than 0.5 times the sampling period of 0.2 seconds. The amplitude peaks and valleys of these two frequency points appear alternately, showing significant correlation characteristics, and are determined to be the frequency components that cause harmonic amplification.

[0103] It should be noted that the specific values ​​of frequency, impedance, difference index, etc. provided in the above embodiments are all preferred application embodiments. In other embodiments provided by the present invention, the above parameters can be set or adjusted according to the actual application scenario.

[0104] In the power system, non-integer harmonic sources usually come from high-power inverters, which contain sideband components of the switching frequency in the output voltage. These components cause harmonic amplification at specific frequencies, resulting in significant changes in the system impedance characteristics. By identifying these characteristic frequencies, the source of harmonic amplification can be accurately located, providing a basis for subsequent harmonic suppression.

[0105] In another embodiment provided by the present invention, when the step S3 is implemented, it specifically includes the following steps:

[0106] The voltage signal is Fourier transformed using the fundamental wave period multiple as the sampling window, and the frequency offset sequence is obtained by the phase angle difference between the fundamental wave signal and the harmonic signal; the duration of the voltage fluctuation value being lower than the lower limit is calculated using the multiple of the reference voltage as the lower limit criterion;

[0107] In a specific application, according to the harmonic current value of the non-integer frequency component, a first preset multiple of the fundamental wave period is used as a sampling window to perform Fourier transform on the voltage signal of the power line, and the frequency offset is calculated by the difference between the phase angles of the fundamental wave signal and the harmonic signal;

[0108] A time domain distribution curve is constructed for the offset sequence in each sampling period, and the amplitude of the offset in the range of 0.1 to 0.5 times the fundamental frequency and its cumulative duration are recorded from the time domain distribution curve.

[0109] In another embodiment provided by the present invention, after determining the amplitude and duration of the frequency offset, the present case further includes the following steps:

[0110] For the frequency offset sequence, determining the occurrence time of the frequency offset according to the corresponding relationship between the load capacity and the offset;

[0111] A normal distribution function is established for the product term of the occurrence time of the frequency offset and the duration, and the occurrence probability of the frequency offset is calculated using the mean and variance of the normal distribution function.

[0112] In the specific implementation, according to the frequency offset in the time domain distribution curve, the load operation state of the power system is used as a criterion to classify the capacity ratio of the inverter, and the occurrence time and duration of the frequency offset are obtained through the corresponding relationship between the load capacity and the frequency offset. A normal distribution function is established for the product term of the occurrence time and the duration, and the probability of occurrence of the frequency offset is calculated using the mean and variance of the normal distribution function. According to the correlation between the probability of occurrence of the frequency offset and the voltage fluctuation amplitude, 0.9 times the reference voltage is used as the lower limit criterion to calculate the duration of the voltage fluctuation value below the lower limit, and the voltage deviation is determined by the proportion of the duration of the fluctuation within the fundamental period. The stability margin of the power line is judged based on the difference between the voltage deviation and the preset threshold. A convolutional neural network is used to learn the stability margin sequence in real time, and the stability reference value is calculated by the correlation coefficient between the stability margin and the frequency offset. The real-time impact of the frequency offset on the stability of the power line is judged against the preset classification standard for the reference value.

[0113] The propagation of non-integer frequency components in power lines manifests itself as distortion of the voltage waveform. When the fundamental frequency is 50 Hz, a frequency offset occurs in the range of 25 to 125 Hz. The waveform data is obtained by voltage sampling, and the sampling window is set to 4 times the fundamental period, that is, 0.08 seconds. The voltage signal is Fourier transformed in this interval to obtain the amplitude and phase of the fundamental and harmonic components. If the fundamental phase is 30 degrees and the harmonic phase is 45 degrees, the phase difference is 15 degrees, and the corresponding frequency offset is 0.3 times the fundamental frequency, that is, 15 Hz.

[0114] The higher the proportion of inverter load in the power line, the more significant the frequency offset phenomenon. Taking the 10 kV bus as an example, when the inverter capacity accounts for 30% of the total load capacity, the probability of frequency offset is low and the duration is within 0.1 second. When the inverter capacity accounts for more than 50%, the probability of frequency offset increases significantly and the duration is extended to 0.3 seconds. By recording the occurrence time and duration of frequency offset within 24 hours, a normal distribution curve is formed with a mean of 0.2 seconds and a standard deviation of 0.05 seconds, indicating that the frequency offset is mainly concentrated in the time interval of about 200 milliseconds. Voltage fluctuation is closely related to frequency offset. When the reference voltage is 10 kV, 9 kV is set as the lower limit of fluctuation. Within the fundamental wave period of 0.08 seconds, if the voltage is lower than 9 kV for more than 0.04 seconds, the voltage deviation is 0.5. By continuously monitoring the voltage deviation of 100 cycles, when the average deviation exceeds 0.4, the line stability margin is reduced, indicating that frequency offset has a significant impact on voltage stability. The convolutional neural network extracts stability margin features through a three-layer convolution structure, and the input data is a 100-cycle voltage deviation sequence. When the frequency offset is 15 Hz and the duration is 0.2 seconds, the corresponding stability reference value is 0.8, which is higher than the warning threshold of 0.6, indicating that the line is running stably. If the reference value drops to 0.5, which is lower than the warning threshold, it is determined that the frequency offset has a greater impact on the stability of the line. During the start-up and shutdown of production equipment in the industrial park, the working state of the inverter changes, resulting in voltage fluctuations and frequency offsets, and the continuous cumulative effect causes the power quality to deteriorate.

[0115] It should be noted that the specific values ​​of frequency, period, phase, etc. provided in the above embodiments are all preferred application embodiments. In other embodiments provided by the present invention, the above parameters can be set or adjusted according to the actual application scenario.

[0116] By real-time monitoring of the changing trend of frequency offset, combined with load type and operating conditions, a voltage stability assessment criterion is established to achieve early warning of harmonic interference.

[0117] In another embodiment provided by the present invention, step S4 in the above embodiment specifically includes the following steps:

[0118] Sampling the impedance frequency response curve according to the fundamental frequency period to construct an impedance frequency response matrix, wherein the impedance frequency response matrix is ​​obtained by using fixed-interval sampling points of the fundamental frequency period;

[0119] Adding a frequency offset to the impedance frequency response matrix to perform Fourier transform, and obtaining impedance frequency characteristic parameters by superimposing the amplitudes of the fundamental frequency and the frequency multiplication component;

[0120] The least square method is used to calculate the deformation amount of the impedance frequency characteristic parameter, and the distortion degree is obtained by the difference between the reference impedance frequency response curve and the response curve after the offset;

[0121] The distortion of the impedance frequency characteristic curve is fitted by support vector regression, and the harmonic amplification range is determined by the distribution of the distortion sequence on the frequency axis.

[0122] In the specific implementation, the impedance frequency response curve is sampled according to the fundamental frequency period based on the voltage and current sampling data, and an impedance frequency response matrix is ​​constructed using 100 sampling points at fixed intervals. The corrected impedance frequency component is obtained by complex division of the voltage value and the current value at the sampling point, and the frequency offset is added to the impedance frequency component to construct a new impedance frequency response matrix.

[0123] Fourier transform is used to perform spectrum analysis on the impedance frequency response matrix containing frequency offset, and the impedance frequency characteristic parameters are calculated by superimposing the amplitude of the fundamental frequency and the frequency components from 0.5 to 2.5 times;

[0124] A modified impedance frequency characteristic curve is constructed for the impedance frequency characteristic parameters to obtain the amplitude change after adding the frequency offset.

[0125] The deformation amount of the impedance frequency characteristic curve is calculated by the least square method according to the amplitude change, and the distortion degree is calculated by the difference between the reference impedance frequency response curve and the impedance frequency response curve after adding the frequency offset at the corresponding frequency point; the curve distortion amplitude is determined for the frequency point that exceeds the standard impedance value by 0.3 times.

[0126] Support vector regression is used to numerically fit the distortion of the impedance frequency characteristic curve. The amplitude change curve is obtained by the distribution of the distortion sequence on the frequency axis. The range and degree of harmonic amplification are determined for the frequency interval where the amplitude increases by more than 0.5 times the reference value. The impedance frequency characteristic curve is discretized and sampled at the fundamental frequency of 50 Hz. 100 sampling points are obtained at a fixed time interval of 0.2 milliseconds in one cycle. The instantaneous values ​​of voltage and current are obtained at each sampling point. When the voltage value at the sampling point is 100 volts and the current value is 50 amperes, the impedance value of the point is 2 ohms through complex number operation. The frequency offset increases by 0.1 times the fundamental frequency, and the impedance value is corrected in the range of 25 Hz to 125 Hz to form an impedance frequency response matrix with 4 rows and 4 columns. Spectral analysis reflects the characteristics of impedance value changing with frequency. The impedance value at the fundamental frequency of 50 Hz is the reference value, which is superimposed with the impedance values ​​at frequency points such as 75 Hz, 87.5 Hz, and 100 Hz. When the impedance value at 75 Hz is 3 ohms, the impedance frequency characteristic parameter of 5 ohms is obtained by superimposing it with the reference value of 2 ohms. In the distribution line of the industrial park, the frequency offset generated when the nonlinear load starts causes the impedance characteristics to change. The impedance valley value originally at 75 Hz is transferred to 87.5 Hz, forming a new impedance frequency characteristic curve. The deformation of the impedance frequency characteristic curve reflects the degree of distortion caused by the frequency offset. On the 10 kV bus, at the frequency point where the reference impedance value is 5 ohms, the impedance value increases to 6.5 ohms after adding the frequency offset, and the distortion is 0.3. The larger the load capacity, the more significant the distortion caused by the frequency offset. At the 35 kV incoming line switch, the impedance increases by more than 0.3 times the reference value, indicating that the harmonic distortion is serious at this point. When the inverter is operated in a group, the switching frequencies of inverters of different capacities affect each other, causing impedance characteristic distortion at the intermediate frequency point. Support vector regression uses Gaussian kernel function to fit the distortion data. The input features include frequency points, impedance values ​​and frequency offsets. In the frequency range of 50 to 75 Hz, the impedance value increases by more than 0.5 times the baseline value and lasts for more than 0.1 seconds, which indicates that harmonic amplification exists in this frequency range. The parallel capacitors and line inductors in the distribution line resonate at a specific frequency point, and the frequency shift causes the resonance point to shift, resulting in an expansion of the harmonic amplification range.

[0127] It should be noted that the specific values ​​of frequency, period, phase, etc. provided in the above embodiments are all preferred application embodiments. In other embodiments provided by the present invention, the above parameters can be set or adjusted according to the actual application scenario.

[0128] By monitoring the distortion degree and amplitude change trend of the impedance curve, the frequency range and severity of the harmonic amplification phenomenon can be identified, and targeted measures can be taken to eliminate harmonic resonance.

[0129] In another embodiment provided by the present invention, the step S5 specifically includes the following steps:

[0130] According to the voltage and current sampling data in the frequency interval, a second preset multiple of the fundamental wave period is used as the window length of the sampling window to perform Fourier decomposition on the voltage waveform and the current waveform;

[0131] The voltage distortion rate and the current distortion rate are calculated according to the root mean square value of the amplitude of the fundamental wave and the harmonic component, and the ratio of the distortion rate to the preset reference value is used to construct a hazard assessment matrix;

[0132] Perform support vector regression mapping according to the hazard assessment matrix, and obtain a hazard coefficient through the proportion of time when the voltage distortion rate exceeds the threshold value and the proportion of time when the current distortion rate exceeds the threshold value;

[0133] The hazard coefficient is divided into hazard level values.

[0134] In the specific implementation, for example, according to the voltage and current sampling data in the harmonic frequency interval, the voltage waveform and the current waveform are Fourier decomposed using 4 times the fundamental wave period as the window length, and the voltage distortion rate and the current distortion rate are calculated by the root mean square value of the fundamental wave and the 2nd to 13th harmonic component amplitudes, and a 4-row 4-column hazard assessment matrix is ​​constructed for the ratio of the distortion rate value to the preset reference value. Support vector regression is used to perform numerical mapping on the hazard assessment matrix, and the hazard coefficient is calculated by the time proportion when the voltage distortion rate exceeds the 5% threshold value and the time proportion when the current distortion rate exceeds the 10% threshold value. The hazard coefficient is divided into 4 hazard levels in the range of 0 to 1, and the hazard level value corresponding to each frequency interval is obtained.

[0135] Harmonic distortion in power lines is manifested as distortion of voltage and current waveforms. Based on the fundamental frequency of 50 Hz, waveform data is obtained within a sampling window of 4 cycles, i.e. 0.08 seconds. When the voltage fundamental amplitude is 10 kilovolts and the 2nd to 13th harmonic amplitudes are 200 volts, 150 volts, and 100 volts, respectively, the voltage distortion rate is 3% through RMS calculation. Similarly, when the current fundamental is 100 amperes and the harmonic components are 15 amperes, 10 amperes, and 8 amperes, the current distortion rate is 8%.

[0136] The calculated distortion rate values ​​are filled into the hazard assessment matrix, with rows representing voltage distortion and columns representing current distortion. After the hazard assessment matrix is ​​processed by support vector regression, the hazard coefficient reflecting the degree of distortion is obtained. In the industrial park distribution line, the voltage distortion rate exceeds 5% for a period of time, reaching 0.3 for 24 hours, and the current distortion rate exceeds 10% for a period of time of 0.5. The corresponding hazard coefficient is 0.7, which belongs to the third level of hazard level. The harmonic distortion generated by the inverter load during the start-stop process is more serious, with a hazard coefficient of 0.9, entering the fourth level of hazard level.

[0137] It should be noted that the specific numerical values ​​of frequency, voltage, current, threshold value, etc. provided in the above embodiments are all preferred application embodiments. In other embodiments provided by the present invention, the above parameters can be set or adjusted according to the actual application scenario.

[0138] In another embodiment provided by the present invention, when the above step S6 is implemented specifically, it specifically includes the following steps:

[0139] Obtain the hazard coefficient corresponding to each frequency interval;

[0140] Calculate the overlap between the hazard coefficients corresponding to different frequency intervals and the hazard coefficients of different types of equipment in the preset power equipment database;

[0141] The type of equipment whose overlap degree is not less than a preset threshold is determined as the harmonic source equipment type.

[0142] During the specific implementation of this embodiment, the hazard level value corresponding to each frequency interval is obtained.

[0143] The harmonic source characteristics are classified in advance according to the hazard level value, and the switching frequency, power level and load capacity are used as characteristic parameters to build a power equipment database with hazard coefficients of different types of equipment and different frequency ranges;

[0144] The matching coefficient is calculated by the degree of overlap between the measured harmonic frequency components and the hazard coefficient of the standard frequency range in the power equipment database, and the type of harmonic source equipment is determined for frequency combinations with matching coefficients exceeding 0.8.

[0145] The gradient boosting tree is used to train the recognition function of the characteristic parameters of the harmonic source equipment. By comparing the power spectra of the fundamental frequency component and the harmonic frequency component in the measured current, the operating status of the equipment is judged at the frequency point in the power spectrum where the amplitude exceeds the reference value by 5 times.

[0146] The power equipment database records the characteristic parameters of different types of equipment. The switching frequency of the inverter is between 2 and 16 kHz, the power level ranges from several kilowatts to several megawatts, and the load capacity accounts for 10% to 80%. When the measured harmonic frequency combination, the amplitudes of the three frequency points of 250 Hz, 350 Hz, and 450 Hz are significant, and the matching degree with the standard harmonic characteristics of the 6 kilovolt inverter in the database reaches 0.85, and the harmonic source is determined to be a medium-sized frequency conversion device. The equipment feature recognition process uses a gradient boosting tree for training, and the input parameters include harmonic frequency combinations, amplitude distribution, and phase relationships. For example, in the operating data of the machine tool load, the current amplitude at the fundamental frequency of 50 Hz is 50 amperes, and the amplitude at the harmonic frequency of 150 Hz reaches 300 amperes. The power spectrum shows that the amplitude at this frequency point is 6 times the baseline value, which exceeds the 3-fold limit under normal operating conditions. The reactive power compensation device of the distribution station amplifies the harmonic current at the resonant frequency point, causing the compensation capacitor to heat up and an overtemperature alarm to appear. The current distortion rate in the electric arc furnace workshop continued to exceed the standard during the smelting process. By identifying the characteristic frequency combination, it was found that the main harmonic sources came from the odd harmonics generated by the core saturation and the characteristic harmonics generated by the rectifier circuit.

[0147] In another embodiment of the present invention, the method further comprises the following steps:

[0148] Calculate the impact of interharmonics and harmonic amplification on the transmission efficiency, transmission capacity and transmission loss of the power system, as well as the impact on voltage distortion rate, voltage imbalance and voltage flicker. By comparing the changes in indicators before and after frequency offset, quantitatively evaluate the impact of harmonic amplification on the operation of the power system.

[0149] That is, a node admittance matrix is ​​used to obtain the frequency coupling characteristics, the impedance complex value is calculated according to the coupling characteristics to obtain the coupling transfer function, and a power loss matrix is ​​constructed for the coupling transfer function; the difference between the input point power and the output point power is calculated according to the power loss matrix, the transmission efficiency is obtained by dividing the difference by the input power, and the transmission capacity limited point is marked according to the transmission efficiency; three-phase voltage data is obtained for the transmission capacity limited point, the negative sequence component, the zero sequence component and the positive sequence component are obtained by symmetrical component transformation, and then the voltage imbalance and the harmonic voltage distortion rate are calculated, and the voltage disturbance index is calculated by the normalized weighted calculation of the short-time flicker value and the long-time flicker value; a deep neural network is used to fit the voltage disturbance index, and the deviation mean is calculated by the fitting result and the measured data. If the deviation mean exceeds the preset threshold, the harmonic amplification impact level is judged.

[0150] In the specific implementation, according to the ratio relationship between the fundamental frequency and the non-integer frequency component, a 10-dimensional node admittance matrix is ​​used to calculate the coupling characteristics between frequencies, and the coupling transfer function is calculated by the complex impedance values ​​of adjacent frequency points. A 4-row and 4-column power loss matrix is ​​constructed for the amplitude and phase angle of the transfer function, and the transmission power loss value of each frequency component is recorded in the power loss matrix.

[0151] Adaptive threshold judgment is used to perform numerical processing on the power loss matrix. The transmission efficiency is calculated by dividing the difference between the input point power and the output point power by the input power. The transmission capacity limited point is marked for the line section where the transmission efficiency drops by more than 0.5 times the reference value, and the limited points are graded according to the amplitude of the transmission efficiency reduction. According to the voltage and current data of the transmission capacity limited point, the three-phase voltage is transformed into a symmetrical component using the fundamental wave period data window, the three-phase voltage imbalance is calculated by the ratio of the zero-sequence component to the positive-sequence component, and the voltage distortion rate of each harmonic is calculated based on the ratio of the negative-sequence component to the positive-sequence component. The voltage disturbance index is calculated by the normalized weighted calculation of the 10-minute short-term flicker value and the 2-hour long-term flicker value.

[0152] A deep neural network is used to fit the voltage disturbance index sequence. The deviation mean in the 1-hour data window is calculated by the benchmark index sequence before the frequency offset and the measured index sequence after the offset. The intensity level of harmonic amplification on power transmission is determined for the period when the deviation mean exceeds the preset threshold. The frequency coupling phenomenon in the power system is reflected in the mutual influence between different frequency components. When the fundamental frequency is 50 Hz, the 25 Hz frequency division component and the 75 Hz frequency multiplication component will produce energy exchange. The 10-dimensional node admittance matrix contains frequency points from 0.5 times to 3 times the fundamental frequency, and the elements in the matrix represent the coupling strength between different frequencies. In the industrial park distribution line, if the impedance value at 75 Hz is 2 ohms and the phase angle is 30 degrees, the coupling transfer function amplitude with the 1 ohm impedance at 50 Hz is 1.5, and the phase angle difference is 45 degrees. The calculated power loss value is 0.3 times the input power. The calculation of transmission efficiency reflects the impact of harmonics on the line transmission capacity. In a 10 kV bus section, when the input power is 1000 kilowatts, the output power is reduced to 800 kilowatts and the transmission efficiency is 0.8.

[0153] When a large-capacity capacitor group is connected in parallel in the line, the harmonic current is amplified at the resonant frequency point, causing the transmission efficiency to drop to 0.6, which is 0.5 times lower than the baseline value of 0.8. The line section is marked as a transmission capacity-limited point. When the inverter group is running, the sideband components of the switching frequency cause increased power loss at the capacitor resonance point, forming multiple transmission-limited areas. The imbalance of the three-phase voltage is reflected by the symmetrical components, and the three-phase voltage is sampled and decomposed within 4 fundamental cycles. During normal operation, the positive sequence voltage is 10 kV, the zero sequence voltage is 100 V, and the imbalance is 0.01. Harmonic current increases the neutral point potential, the zero sequence voltage increases to 500 V, and the imbalance increases to 0.05. The voltage flicker phenomenon is obvious in the arc furnace workshop, with a short-term flicker value of 0.8 for 10 minutes and a long-term flicker value of 0.6 for 2 hours. The weighted voltage disturbance index is 0.7, which exceeds the power quality standard limit. The deep neural network extracts voltage disturbance features through a three-layer convolution structure, and the input data is a sequence of voltage disturbance indicators within 1 hour. The average value of the benchmark indicator before the frequency offset was 0.3, and the average value of the measured indicator after the offset rose to 0.8. The deviation value of 0.5 exceeded the preset threshold of 0.4. The start-stop process of medium-sized frequency conversion devices in the industrial zone produces frequency offsets, which leads to increased voltage fluctuations, and the harmonic amplification effect deteriorates the line impedance characteristics. The reactive power compensation device of the distribution station amplifies the harmonic current at the resonant frequency point, causing the voltage disturbance to worsen. The rectifier power supply in the metal processing workshop produces significant harmonics in the low-frequency band, which affects the impedance characteristics of adjacent frequency points through the frequency coupling effect, resulting in increased transmission losses.

[0154] This case also selects typical interharmonic frequencies, sets the phase adaptation amplitude ratio, and quantitatively analyzes the suppression effects of different interharmonics through the suppression degree of the reference frequency point.

[0155] An interharmonic point within a preset frequency range is selected according to the fundamental frequency, and impedance frequency response data is obtained by calculating the voltage and current complex values ​​of the interharmonic point; the voltage and current waveforms are Fourier decomposed using the impedance frequency response data, and the harmonic distortion rate is obtained by the ratio of the fundamental component to the harmonic component, and an evaluation matrix is ​​established for the harmonic distortion rate to obtain the frequency point suppression degree; for the suppression degree in the evaluation matrix, an improvement rate is calculated by the suppression degree of the reference frequency point, and if the slope change of the improvement rate exceeds the preset slope change value, the improvement rate value at the corresponding frequency position is determined; according to the improvement rate value at the frequency position, a characteristic vector is constructed by measuring the switching frequency of the inverter load, the rectification frequency of the rectifier load and the disturbance frequency of the arc furnace load, and the interharmonic effect is judged according to the response amplitude of the characteristic vector at the frequency point.

[0156] In the specific implementation, interharmonic points within the frequency range of 0.5 to 2.5 times the fundamental frequency are selected, and frequency points are selected in sequence using an interval of 0.1 times the frequency. The interharmonic amplitude is set by taking 0.1 times the fundamental amplitude as the starting point and increasing by 0.05 times the fundamental amplitude. The impedance frequency response is calculated for the complex values ​​of voltage and current at each frequency point to obtain the distribution data of power at each frequency point within the fundamental period. According to the impedance frequency response data, 4 times the fundamental period is used as the sampling window to perform Fourier decomposition on the voltage and current waveforms, and the harmonic distortion rate is calculated by the ratio of the fundamental component to the harmonic component. An evaluation matrix of 4 rows and 4 columns is established for the distortion rate change before and after the interharmonic is added and the ratio of the harmonic amplitude to obtain the suppression degree of each frequency point. According to the suppression degree value in the evaluation matrix, the suppression degree of the reference frequency point is used as the comparison standard to calculate the improvement rate, and the maximum value point and the inflection point where the slope change exceeds 0.5 are extracted from the curve of the improvement rate changing with frequency, and the improvement rate value is recorded for the frequency position corresponding to the maximum value point and the inflection point. A clusterer is used to group the operation data of different loads. The characteristic vector is constructed by measuring the switching frequency of the inverter load, the rectification frequency of the rectifier load and the disturbance frequency of the arc furnace load. The load correlation of the interharmonic effect is judged according to the response amplitude of the characteristic vector at each frequency point. The selection of interharmonic frequency is based on the fundamental frequency of the power system of 50 Hz, and a frequency point is selected every 5 Hz in the range of 25 Hz to 125 Hz. When the selected frequency is 75 Hz, the starting amplitude is set to 0.1 times the fundamental voltage, that is, 1000 volts, and different amplitude gears are set in increments of 500 volts. In the actual power line, the impedance value is obtained by measuring the voltage and current. The impedance amplitude at the 75 Hz point is 2 ohms, the phase angle is 30 degrees, and the power distribution at this frequency point is calculated to be 500 kilowatts. The calculation of the harmonic distortion rate uses a sampling window of 0.08 seconds, which contains data of 4 fundamental cycles. In the distribution lines of the industrial park, when the fundamental voltage is 10 kV, the 2nd to 13th harmonic voltages are 300 V, 200 V, and 150 V, respectively, and the total harmonic distortion rate is 4%. After adding 75 Hz interharmonics, the harmonic voltages are reduced to 200 V, 150 V, and 100 V, and the total harmonic distortion rate is reduced to 3%. The suppression degree of the 75 Hz frequency point recorded in the 2nd row and 3rd column of the evaluation matrix is ​​0.25, indicating that the harmonic content is reduced by 25%. The improvement rate curve reflects the suppression effect of interharmonics on harmonics of different frequencies, and the suppression degree of 0.2 at 50 Hz is selected as the benchmark value. In the range of 25 to 125 Hz, the improvement rate curve fluctuates, and a maximum value of 0.4 appears at 75 Hz, which is twice the benchmark value. The slope of the curve at 65 Hz and 85 Hz changes by more than 0.5, forming two inflection points, and the improvement rates at the inflection points are 0.3 and 0.35 respectively, indicating that the suppression effect of interharmonics in this frequency band is significant. The load characteristics are reflected in the frequency characteristics of the harmonic source. The switching frequency of the inverter load is between 2 and 16 kHz, generating sideband harmonics.The rectifier load generates characteristic harmonics at 6 times the rectification frequency, and the arc furnace load generates wide-band harmonics in the low frequency band. Cluster analysis divides the loads into 3 groups. The characteristic vector of the inverter group has the largest response amplitude at 75 Hz, reaching 3 times the baseline value. The rectifier group is significant at 150 Hz and 250 Hz, while the arc furnace group has a large response in the range of 25 to 75 Hz. This difference shows that there is a significant difference in the frequency range in which interharmonics play a role in different types of loads. When the reactive compensation device of the distribution station resonates with the harmonic source, the interharmonics change the impedance characteristics of the resonance point through frequency coupling, reducing the harmonic amplification factor. During the start-up and shutdown process of the medium-sized frequency conversion device in the metal processing workshop, the interharmonics suppress the switching frequency sideband components, reducing the degree of voltage waveform distortion.

[0157] It should be noted that the specific numerical values ​​of frequency, voltage, current, threshold value, etc. provided in the above embodiments are all preferred application embodiments. In other embodiments provided by the present invention, the above parameters can be set or adjusted according to the actual application scenario.

[0158] During the specific implementation of this case, in order to address the power system stability issues that may be caused by the harmonic amplification effect, dynamic simulation or small disturbance analysis methods were used to analyze the impact of frequency offset and harmonic amplification on the voltage and frequency stability of the power system. By simulating and analyzing the harmonic amplification amplitude and duration under the critical stable state, the critical frequency offset and harmonic amplification factor that caused the power system instability were determined.

[0159] Specifically, a fundamental wave period sampling window is used to obtain voltage and current sampling data of the transmission line, and a load power fluctuation sequence and a frequency offset are calculated based on the sampled data; a dynamic characteristic matrix is ​​constructed based on the power fluctuation sequence and the frequency offset, and the voltage amplitude change rate is recorded through the dynamic characteristic matrix; a frequency injector is used to inject harmonic current into the transmission line, and an impedance frequency response curve is obtained based on the harmonic current, and a voltage dynamic margin value is calculated through the impedance frequency response curve; if the voltage dynamic margin value is lower than a preset threshold and the voltage distortion rate exceeds a set value, the harmonic amplification factor is recorded, and a recursive neural network is trained through the harmonic amplification factor and the frequency offset to obtain an instability criterion.

[0160] According to the topological structure of the power transmission line, 20 fundamental cycles are used as sampling windows to dynamically collect voltage and current data. The load power fluctuation value is calculated by the voltage amplitude and frequency in each cycle. A 4-row and 4-column dynamic characteristic matrix is ​​constructed for the power fluctuation sequence and frequency offset in 20 cycles. The voltage amplitude change rate and the accumulated value of frequency offset between adjacent cycles are recorded in the dynamic characteristic matrix. According to the change trend recorded in the dynamic characteristic matrix, the voltage amplitude change rate is accumulated by proportional integral operation. The critical instability criterion is established by the frequency offset corresponding to the voltage amplitude lower than 0.7 times the rated value and the duration exceeds 0.2 seconds. The voltage amplitude with frequency offset change curve is plotted for the critical instability criterion to obtain the voltage dynamic response characteristics under different offsets. A frequency injector is used to inject harmonic current into the transmission line at intervals of 0.1 times the fundamental frequency. The impedance frequency response is obtained by increasing the harmonic current amplitude from 0.1 times to 1 times the fundamental current. The voltage dynamic margin is calculated for the impedance frequency response curve. The harmonic amplification factor is recorded when the margin value is lower than 0.3 and the voltage distortion rate exceeds 0.1. Recurrent neural network is used to train the dynamic response of recorded frequency offset and harmonic magnification. The instability criterion is constructed by the operating state parameters when the slope change rate of the voltage dynamic margin curve exceeds 0.5. The upper limit of frequency offset and the limit of harmonic magnification under critical stable state are determined according to the instability criterion. The dynamic characteristics of power lines are reflected by continuous sampling of voltage and current, and 20 fundamental wave cycles are included in the sampling window of 0.4 seconds. Taking the 10 kV bus as an example, the voltage fluctuation range is between 9.5 kV and 10.5 kV during normal operation, and the frequency is maintained at 49.5 Hz to 50.5 Hz. When high-power loads are put into operation, the bus voltage fluctuates, the voltage change rate of adjacent cycles reaches 5%, and the frequency offset accumulates to 1 Hz. These values ​​are recorded in the dynamic characteristic matrix for judging the operating state. The change trend of voltage amplitude reflects the system stability through cumulative calculation. When the voltage reduction of 7 kV lasts for more than 0.2 seconds, the corresponding frequency offset is 2 Hz, and the line enters a critical state. During the inverter load startup process, the voltage amplitude shows nonlinear characteristics as the frequency offset changes. A frequency offset of 1 Hz causes the voltage to drop by 1 kV, and the voltage drops sharply to 6 kV when the offset is 2 Hz. This nonlinearity exacerbates the dynamic response of the line, which is particularly obvious in the arc furnace workshop. Harmonic injection increases the frequency step by step from 5 Hz, and the injected current at each frequency point increases from 10 amperes to 100 amperes. When a harmonic current of 75 Hz and 50 amperes is injected, the line impedance value is 3 ohms, and the voltage distortion rate reaches 15%, exceeding the limit of 10%. At this time, the harmonic amplification factor is 3. In the industrial park, the parallel capacitor and the line inductance resonate at a specific frequency, causing the harmonic current to be amplified 5 times, reducing the voltage dynamic margin to 0.2.The recursive neural network is trained using 1,000 sets of frequency offset and harmonic amplification data, and the input features include voltage change rate, frequency deviation, and harmonic distortion rate. In the metal processing workshop, when the slope change rate of the voltage dynamic margin curve reaches 0.6, the frequency offset is 2.5 Hz and the harmonic amplification factor is 4 times, which exceeds the operating limit of the critical stable state. The reactive compensation device of the distribution station amplifies the harmonics at the resonant frequency point, which is superimposed on the frequency offset generated by the inverter load, accelerating the instability of the line. The switching process of the rectifier load causes voltage drop. Under the action of frequency offset, the voltage recovery time is prolonged, reducing the dynamic stability margin of the line. This instability process often occurs during the start-up and shutdown of large production lines. By monitoring the frequency offset and harmonic amplification factor, an early warning criterion for voltage stability is established.

[0161] The scheme of this application combines the frequency coupling effect to calculate the impact of interharmonics and harmonic amplification on various system indicators. Finally, the critical frequency offset and harmonic amplification factor that cause system instability are determined through dynamic simulation. The present invention can comprehensively evaluate the impact of harmonic amplification effects in power systems, provide a basis for stable system operation and harmonic suppression, and help improve power quality and system reliability.

[0162] An embodiment of the present invention further provides a harmonic amplification detection system for an electric power system, the system comprising a controller, the controller being used to execute the harmonic amplification detection method for an electric power system as described in any one of the above embodiments.

[0163] It should be noted that the computer program that can be run on the controller is, for example, a harmonic amplification detection program for a power system. When the controller executes the computer program, the steps in the above-mentioned harmonic amplification detection method embodiments for the power system are implemented, for example Figure 1 Steps S1 to S6 are shown.

[0164] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A harmonic amplification detection method for an electric power system, characterized in that: The method comprises: Obtain the topological structure and load distribution data of the power system, analyze the frequency response of the power system impedance including the interharmonic frequency components, and obtain the impedance frequency response curve; Calculating the difference between the impedance value at the inflection point in the impedance frequency response curve and the impedance value at the adjacent frequency point, and performing frequency component analysis of the harmonic amplification phenomenon based on the obtained difference; When a non-integer frequency component causing harmonic amplification is detected, it is determined that a frequency offset phenomenon occurs, and the amplitude and duration of the frequency offset are calculated according to the voltage signal of the power system and a preset fundamental wave period multiple; Analyzing the frequency response of the power system impedance according to the amplitude and the duration, simulating the change of the impedance frequency characteristic of the power system under the condition of frequency offset, and determining the impedance frequency response curve distortion caused by the frequency offset according to the impedance frequency characteristic change, and determining the frequency range of harmonic amplification by comparing the impedance frequency response curves before and after the frequency offset; Determining a voltage distortion rate and a current distortion rate caused by harmonics according to the frequency range, and calculating a harmonic hazard coefficient according to the voltage distortion rate and the current distortion rate; Determining the type of harmonic source equipment causing harmonic amplification according to the hazard coefficient; Determining the voltage distortion rate and the current distortion rate caused by the harmonics according to the frequency range, and calculating the harmonic hazard coefficient according to the voltage distortion rate and the current distortion rate, specifically includes: According to the voltage and current sampling data in the frequency interval, a second preset multiple of the fundamental wave period is used as the window length of the sampling window to perform Fourier decomposition on the voltage waveform and the current waveform; The voltage distortion rate and the current distortion rate are calculated based on the root mean square value of the harmonic component amplitude obtained by decomposition; Constructing a voltage hazard assessment matrix according to the ratio of the voltage distortion rate to a preset voltage reference value; Constructing a current hazard assessment matrix according to the ratio of the current distortion rate to a preset current reference value; Performing support vector regression mapping according to the voltage hazard assessment matrix and the current hazard assessment matrix, and calculating the hazard coefficient according to the proportion of time that the voltage distortion rate exceeds a preset voltage threshold value and the proportion of time that the current distortion rate exceeds a preset current threshold value; The type of harmonic source equipment causing harmonic amplification is determined according to the hazard coefficient, including: Obtain the hazard coefficient corresponding to each frequency interval; Calculate the overlap between the hazard coefficients corresponding to different frequency intervals and the hazard coefficients of different types of equipment in the preset power equipment database; The type of equipment whose overlap degree is not less than a preset threshold is determined as the harmonic source equipment type.

2. The harmonic amplification detection method for the power system according to claim 1, characterized in that: Obtain the topological structure and load distribution data of the power system, analyze the frequency response of the power system impedance including the interharmonic frequency components, and obtain the impedance frequency response curve, including: Determine the topological node coordinates and the connection relationship matrix between nodes according to the topological structure and load distribution data of the power system collected by the power distribution terminal; Reading node voltage values ​​and node current values ​​of different nodes in the node connection relationship matrix to construct a load distribution matrix; Decomposing node voltage values ​​and node current values ​​in the load distribution matrix by Fourier transform to obtain signal amplitudes of multiples of fundamental frequency, and calculating impedance frequency response vectors according to the signal amplitudes; Injecting a harmonic current with a non-integer frequency component into the circuit breaker position marked by the impedance frequency response vector to obtain the harmonic voltage amplitude and harmonic phase of the adjacent nodes of the circuit breaker position; The harmonic voltage amplitude and the harmonic phase are sequentially connected in time series by linear interpolation, and the slope of the connection point of the fitting curve is calculated according to the numerical deviation before and after the connection point; When the calculated connection point slope is not within the preset threshold interval, the number of linear interpolation sampling is increased, the connection point is re-determined, and the connection point slope of the fitting curve is calculated until the connection point slope is within the threshold interval; When the calculated connection point slope is within the threshold interval, the impedance frequency response curve is drawn according to the sampling points.

3. The harmonic amplification detection method for the power system according to claim 1, characterized in that: Calculating the difference between the impedance value at the inflection point in the impedance frequency response curve and the impedance value at the adjacent frequency point, and performing frequency component analysis of the harmonic amplification phenomenon according to the obtained difference, including: Discretizing the impedance frequency response curve at intervals of multiples of the fundamental frequency; The difference between the maximum and minimum impedance values ​​of the discrete point sequence in the window is calculated using a fixed-length data window, and the position where the calculated difference is greater than the preset index is used as the inflection point coordinate of the impedance curve; Establishing an impedance difference matrix according to the impedance complex values ​​of the inflection point coordinates; Calculating the impedance change at adjacent frequency points using the ratio of the Fourier components of the voltage signal and the current signal according to the impedance difference matrix, calculating the ratio of the impedance value of the preset reference frequency point to the current frequency point, and marking the frequency points whose ratios exceed the preset ratio threshold; Extracting the harmonic amplification frequency interval according to the marked frequency points, and calculating the cumulative product of the impedance values ​​in the window using a sliding window composed of a number of frequency points according to the frequency components contained in the harmonic amplification frequency interval; When the ratio of the maximum value to the minimum value of the cumulative product of the sliding window exceeds a preset multiple, the coordinates of the corresponding frequency point are recorded; Wavelet transform is used to perform time-frequency analysis on the impedance sequence of the recorded frequency points; When the time interval between adjacent peak values ​​of the amplitude spectrum is less than the product of a preset sampling period and a preset multiple, the adjacent frequency point is determined to be a non-integer frequency component of the harmonic amplification phenomenon.

4. The harmonic amplification detection method for the power system according to claim 1, characterized in that: Calculating the amplitude and duration of the frequency deviation according to the voltage signal of the power system and a preset fundamental wave period multiple, including: According to the harmonic current value of the non-integer frequency component, a first preset multiple of the fundamental wave period is used as a sampling window to perform Fourier transform on the voltage signal of the power system, and a difference in phase angle between the fundamental wave signal and the harmonic signal is calculated to obtain a frequency offset sequence; A time domain distribution curve is constructed based on the offset sequence in each sampling period; The amplitude and duration of the offset in the time domain distribution curve within a preset base frequency range are recorded as the amplitude and duration of the frequency offset.

5. The harmonic amplification detection method for the power system according to claim 4, characterized in that: The method further comprises: Using the load operating state of the power system as a criterion to determine the load capacity of the frequency converter; Determining the occurrence time of the frequency offset according to the corresponding relationship between the load capacity and the offset in the time domain distribution curve; A normal distribution function is established for the product term of the occurrence time of the frequency offset and the duration, and the occurrence probability of the frequency offset is calculated using the mean and variance of the normal distribution function.

6. The harmonic amplification detection method for the power system according to claim 1, characterized in that: Analyzing the frequency response of the power system impedance according to the amplitude and the duration, simulating the change of the impedance frequency characteristic of the power system under the condition of frequency offset, and determining the impedance frequency response curve distortion caused by the frequency offset according to the impedance frequency characteristic change, and determining the frequency range of harmonic amplification by comparing the impedance frequency response curves before and after the frequency offset, including: Sampling the impedance frequency response curve according to the fundamental frequency period to construct an impedance frequency response matrix; Using Fourier transform to perform spectrum analysis on the impedance frequency response matrix containing frequency offset, and obtaining impedance frequency characteristic parameters by superimposing and calculating the amplitude of the fundamental frequency and the frequency component of the preset multiple; Constructing a modified impedance-frequency revision curve according to the impedance-frequency characteristic parameters, and determining the amplitude change after adding the frequency offset; Calculating the deformation amount of the impedance frequency characteristic parameter by using the least square method according to the amplitude variation, and obtaining the distortion degree by the difference between the impedance frequency response curve and the impedance frequency revision curve; Support vector regression is used to perform numerical fitting on the obtained distortion degree, and the amplitude variation curve is determined according to the distribution of the obtained distortion degree sequence on the frequency axis; The frequency interval in the amplitude variation curve where the amplitude exceeds a preset reference value is determined as the frequency interval of harmonic amplification.

7. A harmonic amplification detection system for an electric power system, characterized in that: The system includes a controller, and the controller is used to execute the harmonic amplification detection method for the power system according to any one of claims 1 to 6.

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