Overvoltage early warning method and system in state of new energy accessing power distribution network

Abstract

The invention relates to the technical field of electric data measurement, and provides an overvoltage early warning method and system in a state that new energy accesses a power distribution network, and the method comprises the steps: collecting the voltage data of each capacitive voltage divider of the power distribution network; setting a measurement period and a power frequency period, determining a voltage disturbance coefficient of the capacitive voltage divider in the power frequency period, and determining a distortion estimation value of the capacitive voltage divider in the power frequency period; obtaining a harmonic sequence of the capacitive voltage divider in the power frequency period, and determining the capacitance interference degree of the capacitive voltage divider in the target power frequency period according to the distortion estimation value of the capacitive voltage divider in the target power frequency period and the difference between the harmonic sequences of all capacitive voltage dividers in the target power frequency period; and determining the optimal measurement voltage of the power frequency period according to the capacitance interference degree of the power frequency period, and realizing overvoltage early warning in the state that the new energy accesses the power distribution network according to voltage data acquired by the optimal measurement voltage in the power frequency period and all corresponding root-mean-square values. According to the invention, the accuracy of overvoltage early warning can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical data measurement, and particularly relates to an overvoltage early warning method and system under the condition of new energy access to the distribution network. Background Art

[0002] Overvoltage refers to the phenomenon that the voltage in the power system instantaneously or continuously rises above the rated value, which is a precursor and important warning information of power system faults. Overvoltage will pose a potential threat to the power equipment operating normally, and may cause serious consequences such as equipment damage, power interruption, and even fire. Therefore, it is necessary to timely warn of the overvoltage existing in the distribution network, and perform maintenance and repair on the power equipment according to the warning results to ensure the safe and stable operation of the power system. After new energy is accessed to the distribution network, due to the intermittency and uncertainty of new energy power generation, the voltage of the power system will be affected by new energy and fluctuate frequently, resulting in the distribution network being prone to overvoltage and power safety accidents. In addition, the access of new energy to the distribution network will cause additional harmonics to be introduced into the power system, making the voltage contain more frequency components, and the frequency components change very rapidly.

[0003] The capacitive voltage division measurement method can attenuate the high voltage at the measured end to a low voltage within the safety threshold through a voltage division circuit to achieve the measurement of the distribution network voltage. However, when the capacitive voltage division measurement method measures high-frequency voltage signals, the frequency response of the capacitive voltage divider will introduce measurement errors, and the rapid change of the voltage frequency components will further exacerbate the expansion of the errors, affecting the detection accuracy of the power system voltage, and further resulting in insufficient accuracy of overvoltage early warning. Summary of the Invention

[0004] The present invention provides an overvoltage early warning method and system under the condition of new energy access to the distribution network to solve the problem that the measurement errors introduced when new energy is accessed to the distribution network affect the detection accuracy of the power system voltage, resulting in insufficient accuracy of overvoltage early warning. The specific technical solutions adopted are as follows: In a first aspect, an embodiment of the present invention provides an overvoltage early warning method under the condition of new energy access to the distribution network, and the method includes the following steps: Collect the voltage data of each capacitive voltage divider set in the distribution network; Denote any power frequency period divided from a preset measurement period as the target power frequency period. Determine all root mean square values corresponding to the target power frequency period of the same capacitive voltage divider according to all voltage data collected within adjacent power frequency periods divided from the measurement period by the same capacitive voltage divider. Determine the voltage disturbance coefficient of the same capacitive voltage divider in the target power frequency period according to the differences between all root mean square values corresponding to the target power frequency period of the same capacitive voltage divider. Combine the differences between the values corresponding to the ideal change trend of all voltage data collected in the target power frequency period by the same capacitive voltage divider and the voltage data to determine the distortion estimation value of the same capacitive voltage divider in the target power frequency period; Obtain the harmonic sequence of the same capacitive voltage divider in the target power frequency period according to the spectrum corresponding to the voltage data. Determine the capacitive interference degree of the capacitive voltage divider in the target power frequency period according to the distortion estimation value of the capacitive voltage divider in the target power frequency period and the differences between the harmonic sequences of all capacitive voltage dividers in the target power frequency period; Determine the optimal measurement voltage of the power frequency period according to the capacitive interference degree of the power frequency period. Implement overvoltage warning under the condition of new energy accessing the distribution network according to the voltage data collected in the power frequency period at the optimal measurement voltage and the corresponding all root mean square values.

[0005] Furthermore, the method for determining the root mean square value is as follows: Denote the measurement window formed by the target power frequency period and the M - 1 adjacent power frequency periods before the target power frequency period as the measurement window of the target power frequency period, where M is the second preset threshold; Calculate the root mean square value of all voltage data collected by the same capacitive voltage divider within each half power frequency period in the measurement window of the target power frequency period.

[0006] Furthermore, the method for determining the voltage disturbance coefficient of the same capacitive voltage divider in the target power frequency period according to the differences between all root mean square values corresponding to the target power frequency period of the same capacitive voltage divider includes the following specific method: Arrange all root mean square values corresponding to the measurement window of the target power frequency period of the same capacitive voltage divider in the order of the sequence of the power frequency periods corresponding to the root mean square values, and obtain the root mean square value sequence of the same capacitive voltage divider in the target power frequency period; Determine the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period according to the differences between all root mean square values included in the root mean square value sequence of the capacitive voltage divider in the target power frequency period.

[0007] Furthermore, the method for determining the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period according to the differences between all root mean square values included in the root mean square value sequence of the capacitive voltage divider in the target power frequency period includes the following specific method: The ratio of the maximum value to the minimum value of the root mean square values included in the root mean square value sequence of the capacitive voltage divider in the target power frequency period is denoted as the first ratio of the capacitive voltage divider in the target power frequency period; The ratio of the standard deviation to the average value of all the root mean square values included in the root mean square value sequence of the capacitive voltage divider in the target power frequency period is denoted as the second ratio of the capacitive voltage divider in the target power frequency period; According to the first ratio and the second ratio of the capacitive voltage divider in the target power frequency period, determine the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period. The voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period is positively correlated with the first ratio of the capacitive voltage divider in the target power frequency period and the second ratio of the capacitive voltage divider in the target power frequency period respectively.

[0008] Furthermore, the method for determining the distortion estimation value of the same capacitive voltage divider in the target power frequency period is as follows: Perform curve fitting on all the voltage data corresponding to the measurement window of the same capacitive voltage divider in the target power frequency period to obtain a fitting curve, and obtain the corresponding voltage data fitting values of all the voltage data corresponding to the measurement window of the same capacitive voltage divider in the target power frequency period on the fitting curve. Denote the cumulative sum of the absolute values of the differences between all the voltage data corresponding to the measurement window of the same capacitive voltage divider in the target power frequency period and the voltage data fitting values as the fitting deviation of the same capacitive voltage divider in the target power frequency period; Denote the average value of the voltage disturbance coefficients of all the capacitive voltage dividers in the target power frequency period as the average value of the voltage disturbance coefficients in the target power frequency period. Denote any one capacitive voltage divider as the target capacitive voltage divider, and denote the ratio of the voltage disturbance coefficient of the target capacitive voltage divider in the target power frequency period to the average value of the voltage disturbance coefficients in the target power frequency period as the third ratio of the target capacitive voltage divider in the target power frequency period; According to the third ratio of the target capacitive voltage divider in the target power frequency period and the fitting deviation of the target capacitive voltage divider in all the power frequency periods, determine the distortion estimation value of the target capacitive voltage divider in the target power frequency period. The distortion estimation value of the target capacitive voltage divider in the target power frequency period is positively correlated with the third ratio of the target capacitive voltage divider in the target power frequency period and the fitting deviation of the target capacitive voltage divider in all the power frequency periods respectively.

[0009] Furthermore, the specific method for obtaining the harmonic sequence of the same capacitive voltage divider in the target power frequency period according to the spectrum corresponding to the voltage data includes: Obtain the spectrum sequence of all the voltage data corresponding to the measurement window of the target capacitive voltage divider in the target power frequency period, and obtain the spectrum peak value in the spectrum sequence; Reduce all the values in the spectrum sequence by the same value until the spectrum peak value drops to 3 dB to obtain the harmonic sequence of the target capacitive voltage divider in the target power frequency period.

[0010] Further, the method for determining the capacitance interference degree of the capacitance voltage divider in the target power frequency period is as follows: Denote the average value of the DTW distances between the target capacitance voltage divider and the harmonic sequences of all other capacitance voltage dividers in the target power frequency period as the first difference of the target capacitance voltage divider in the target power frequency period. Denote the average value of the DTW distances between the harmonic sequences of all different capacitance voltage dividers in the target power frequency period as the second difference of the target power frequency period. Denote the ratio of the first difference of the target capacitance voltage divider in the target power frequency period to the second difference of the target power frequency period as the fourth ratio of the target capacitance voltage divider in the target power frequency period; Denote the product of the sum of all values included in the harmonic sequence of the target capacitance voltage divider in the target power frequency period, the fourth ratio of the target capacitance voltage divider in the target power frequency period, and the distortion estimation value as the capacitance interference degree of the target capacitance voltage divider in the target power frequency period.

[0011] Further, the method for determining the optimal measurement voltage of the power frequency period according to the capacitance interference degree of the power frequency period includes the following specific method: Take the voltage data of the capacitance voltage divider corresponding to the minimum value among all the capacitance interference degrees corresponding to the same power frequency period as the optimal measurement voltage of the same power frequency period.

[0012] Further, the method for realizing overvoltage warning under the condition of new energy access to the distribution network according to the voltage data collected in the power frequency period based on the optimal measurement voltage and the corresponding all root mean square values includes the following specific method: Calculate the absolute value of the difference between the extreme values of two adjacent root mean square values included in the root mean square value sequence corresponding to the optimal measurement voltage in the target power frequency period. Denote the maximum value of all the absolute values of the differences corresponding to the same power frequency period as the maximum voltage change of the power frequency period; When the two adjacent voltage data collected in the power frequency period are not equal, convert the number of voltage changes occurring in the power frequency period into the number of voltage changes per hour, and denote the number of voltage changes per hour as the voltage change frequency of the power frequency period; When the values of the maximum voltage change and the voltage change frequency of the power frequency period conform to one of the overvoltage conditions, it is determined that there is overvoltage in the power frequency period; when the values of the maximum voltage change and the voltage change frequency of the power frequency period do not conform to any of the overvoltage conditions, it is determined that there is no overvoltage in the power frequency period.

[0013] In a second aspect, an overvoltage warning system for new energy access to the distribution network according to an embodiment of the present invention further includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of the method described in any one of the above are implemented.

[0014] The beneficial effects of the present invention are as follows: After new energy is connected to the distribution network, the high-frequency harmonic voltage changes rapidly. There are differences in the distribution of stray capacitances in different capacitive voltage dividers and different frequency responses at high frequencies. Therefore, different capacitive voltage dividers have different voltage division capabilities for high-frequency harmonic voltages of different frequencies. In order to make full use of the discreteness of the stray capacitances in multiple capacitive voltage dividers and reduce the error introduced into voltage measurement due to the frequency response of the capacitive voltage divider, it is necessary to select the voltage data corresponding to the capacitive voltage divider with the least interference from the frequency response of the capacitive voltage divider as the optimal measurement voltage according to the characteristics of the voltage data of each capacitive voltage divider in the time domain and frequency domain. Specifically: First, evaluate the degree of disturbance of the distribution network voltage by the injected harmonics of new energy, and analyze the change of the degree of disturbance of the distribution network voltage by the injected harmonics of new energy over time, so as to obtain the probability evaluation of voltage distortion generated by the capacitive voltage divider in the target power frequency cycle, that is, obtain the voltage disturbance coefficient. Combine the difference between the value corresponding to the ideal change trend of all voltage data collected by the same capacitive voltage divider in the target power frequency cycle and the voltage data to determine the distortion estimation value of the same capacitive voltage divider in the target power frequency cycle. The distortion estimation value is an evaluation of the relative distortion degree of the target capacitive voltage divider in measuring the current distribution network voltage. Further, analyze the frequency domain characteristics of the voltage data collected by the capacitive voltage divider, evaluate the degree of interference of the target capacitive voltage divider due to the influence of stray capacitance when measuring voltage, improve the accuracy of measuring high-frequency harmonics injected into the distribution network by new energy, and obtain the capacitive interference degree of each capacitive voltage divider in each power frequency cycle. The greater the capacitive interference degree of the target capacitive voltage divider in the target power frequency cycle, the greater the degree of interference of the target capacitive voltage divider due to the influence of stray capacitance when measuring voltage. Finally, determine the optimal measurement voltage in the power frequency cycle according to the capacitive interference degree in the power frequency cycle, and realize overvoltage warning in the state of new energy connected to the distribution network based on the voltage data collected in the power frequency cycle by the optimal measurement voltage and the corresponding all root mean square values, so as to solve the problem that the measurement error introduced when new energy is connected to the distribution network affects the detection accuracy of the power system voltage and results in insufficient accuracy of overvoltage warning, and improve the accuracy of overvoltage warning. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1 It is a schematic flowchart of a method for overvoltage warning in the state of new energy connected to the distribution network provided by an embodiment of the present invention; Figure 2 Flowchart for obtaining voltage disturbance coefficient provided by an embodiment of the present invention. Detailed implementation manners

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Please refer to Figure 1 , which shows a flowchart of an overvoltage warning method in the state of new energy accessing the distribution network provided by an embodiment of the present invention. The method includes the following steps: Step S001, collect the voltage data of each capacitive voltage divider set in the distribution network.

[0019] When measuring the voltage of the distribution network using the capacitive voltage division measurement method, the frequency response of the capacitive voltage divider has a stronger voltage division ability in the low-frequency band of the voltage. Since the capacitance impedance in the voltage division circuit decreases with the increase of frequency, the voltage division ability of the capacitive voltage divider is relatively weak in the high-frequency band. In the state of new energy accessing the distribution network, more high-frequency harmonics are introduced into the corresponding power system of the distribution network, and the measurement error of the capacitive voltage divider will increase.

[0020] There are certain differences in the production process of electrical components of the same model and the same specification, and there is a certain degree of dispersion in the electrical parameters of different electrical components, resulting in the discreteness of electrical components. Therefore, the discreteness of the circuit structure and parasitic capacitance in the capacitive voltage divider will cause differences in the distribution of stray capacitance in the capacitive voltage divider of the same model. The capacitance values of the high-voltage arm capacitor and the low-voltage arm capacitor in the capacitive voltage divider are very small, usually in the pF range. For low-frequency voltages, the influence of stray capacitance on the voltage division circuit is small, and the voltage division of the capacitive voltage divider is relatively stable; for high-frequency voltages, small changes in the electrical structure will cause a large change in the voltage division ratio of the capacitive voltage divider. Therefore, the differences in the distribution of stray capacitance in different capacitive voltage dividers will cause changes in the measurement error of the capacitive voltage divider.

[0021] To reduce the measurement error caused by the frequency response of the capacitive voltage divider, at the distribution network bus, install K capacitive voltage dividers of the same model, use the capacitive voltage divider to complete the voltage division and analog-to-digital conversion of the voltage data, and obtain the voltage data of each capacitive voltage divider after voltage division.

[0022] Among them, in this embodiment, a coaxial capacitive voltage divider is used as the capacitive voltage divider. The voltage division ratio of the coaxial capacitive voltage divider is 10000:1. The sampling rate of the voltage data of the capacitive voltage divider is 10 kHz. K is the first preset threshold, and the value of the first preset threshold in this embodiment is 5. As other implementation manners, the implementer can select the type and number of capacitive voltage dividers according to the specific operating state of the distribution network power system.

[0023] Thus, the voltage data of each capacitive voltage divider is obtained.

[0024] Step S002: Denote any power frequency cycle divided in the preset measurement period as the target power frequency cycle. According to all the voltage data collected in adjacent power frequency cycles divided in the measurement period by the same capacitive voltage divider, determine all the root mean square values corresponding to the target power frequency cycle of the same capacitive voltage divider. According to the difference between all the root mean square values corresponding to the target power frequency cycle of the same capacitive voltage divider, determine the voltage disturbance coefficient of the same capacitive voltage divider in the target power frequency cycle. Combine the difference between the value corresponding to the ideal change trend of all the voltage data collected in the target power frequency cycle of the same capacitive voltage divider and the voltage data to determine the distortion estimation value of the same capacitive voltage divider in the target power frequency cycle.

[0025] After the new energy is connected to the distribution network, the high-frequency harmonic voltage changes rapidly. There are differences in the distribution of stray capacitances in different capacitive voltage dividers, and the frequency responses at high frequencies are different. Therefore, different capacitive voltage dividers have different voltage division capabilities for high-frequency harmonic voltages of different frequencies.

[0026] In order to make full use of the discreteness of the stray capacitances in multiple capacitive voltage dividers and reduce the error introduced into the voltage measurement due to the frequency response of the capacitive voltage divider, it is necessary to select the voltage data corresponding to the capacitive voltage divider with the least interference from the frequency response of the capacitive voltage divider as the optimal measurement voltage according to the time-domain and frequency-domain characteristics of the voltage data of each capacitive voltage divider. The process of determining the optimal measurement voltage is as follows.

[0027] Preferably, in an embodiment of the present application, 100 seconds is used as a measurement period, and the optimal measurement voltage is determined according to all the voltage data within one measurement period. In the actual application process, as other implementation manners, the implementer can determine the value of the measurement period by himself according to the actual situation, and the present application does not make special restrictions.

[0028] It should be noted that the power frequency of the power system where the distribution network is located is 50 Hz. Therefore, one measurement period contains a total of 5000 power frequency cycles.

[0029] Denote any power frequency cycle in the measurement period as the target power frequency cycle, and denote the measurement window composed of the target power frequency cycle and the M-1 power frequency cycles adjacent to the target power frequency cycle before it as the measurement window of the target power frequency cycle. Calculate the root mean square value of all voltage data collected by the same capacitor voltage divider within each half power frequency cycle in the measurement window of the target power frequency cycle, and arrange all the root mean square values corresponding to the same capacitor voltage divider in the measurement window of the target power frequency cycle in the order of the power frequency cycles corresponding to the root mean square values, so as to obtain the root mean square value sequence of the same capacitor voltage divider in the target power frequency cycle.

[0030] Among them, M is the second preset threshold, and the value of the second preset threshold in this embodiment is 100; the calculation of the root mean square value is a well-known technology. Specifically, it is to calculate the average value of the squares of all voltage data and then take the square root of the average value, which will not be elaborated here. It can be understood that when the number of power frequency cycles adjacent to the target power frequency cycle before it in the measurement period where the target power frequency cycle is located is less than M-1, take the power frequency cycles in the previous adjacent measurement period of the measurement period where the target power frequency cycle is located. When the power frequency cycles in the previous adjacent measurement period of the measurement period where the target power frequency cycle is located are also insufficient, this power frequency cycle will not be analyzed; the root mean square value sequence of the target power frequency cycle contains 200 root mean square values.

[0031] The root mean square values included in the root mean square value sequence of the target power frequency cycle can reflect the degree of disturbance of the distribution network voltage by the harmonics injected by new energy. Since the disturbance of the high-frequency harmonic voltage to the distribution network is manifested on different time scales, therefore, calculate the root mean square value of all voltage data included in each half power frequency cycle, and arrange the root mean square values in order to facilitate the analysis of the change of the degree of disturbance of the distribution network voltage by the harmonics injected by new energy over time.

[0032] According to the same method, obtain the root mean square value sequence of each capacitor voltage divider in each power frequency cycle. That is to say, for each capacitor voltage divider, there is a corresponding root mean square value sequence in each power frequency cycle.

[0033] Determine the voltage disturbance coefficient of the capacitor voltage divider in the target power frequency cycle according to the difference between all the root mean square values included in the root mean square value sequence of the capacitor voltage divider in the target power frequency cycle.

[0034] Denote the ratio of the maximum value to the minimum value of the root mean square values included in the root mean square value sequence of the capacitor voltage divider in the target power frequency cycle as the first ratio of the capacitor voltage divider in the target power frequency cycle, and denote the ratio of the standard deviation to the average value of all the root mean square values included in the root mean square value sequence of the capacitor voltage divider in the target power frequency cycle as the second ratio of the capacitor voltage divider in the target power frequency cycle.

[0035] Determine the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period according to the first ratio and the second ratio of the capacitive voltage divider in the target power frequency period. The voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period is positively correlated with the first ratio of the capacitive voltage divider in the target power frequency period and the second ratio of the capacitive voltage divider in the target power frequency period, respectively.

[0036] It can be understood that the positive correlation relationship and the negative correlation relationship in this application refer to the relationship between the independent variable and the dependent variable. The positive correlation relationship means that the dependent variable increases (decreases) as the independent variable increases (decreases), and it can be an additive relationship, a multiplicative relationship, etc.

[0037] Preferably, as an embodiment of this application, the product of the first ratio and the second ratio of the capacitive voltage divider in the target power frequency period is denoted as the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period.

[0038] The first ratio of the capacitive voltage divider in the target power frequency period is used to evaluate the maximum instantaneous interference degree of the high-frequency harmonics introduced by new energy into the distribution network on the overvoltage measured by the capacitive voltage divider; the second ratio of the capacitive voltage divider in the target power frequency period is used to evaluate the average interference degree of the high-frequency harmonics on the distribution network voltage, so as to reduce the influence of the frequency response difference of different capacitive voltage dividers on the voltage disturbance estimation; the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency period is used to evaluate the disturbance degree of the high-frequency harmonics introduced by new energy into the distribution network on the voltage measured by the capacitive voltage divider. The larger the voltage disturbance coefficient, the greater the disturbance degree of the high-frequency harmonics introduced by new energy into the distribution network on the voltage measured by the capacitive voltage divider, and the greater the probability of voltage distortion generated by the capacitive voltage divider in the target power frequency period. In addition, since the frequency of the ideal power frequency voltage of the power system where the distribution network is located is fixed, the greater the voltage data fluctuation measured by the capacitive voltage divider, the weaker the voltage division ability of the capacitive voltage divider for high-frequency voltage, and the greater the voltage distortion degree. At this time, the voltage disturbance coefficient is greater.

[0039] The flowchart for obtaining the voltage disturbance coefficient is as Figure 2 shown.

[0040] Use the three-parameter sine curve fitting method to perform curve fitting on all voltage data corresponding to the measurement window of the same capacitive voltage divider in the target power frequency period, obtain the fitting curve of the same capacitive voltage divider in the target power frequency period, obtain the corresponding voltage data fitting values of all voltage data corresponding to the measurement window of the same capacitive voltage divider in the target power frequency period on the fitting curve, and record the cumulative sum of the absolute values of the differences between all voltage data corresponding to the measurement window of the same capacitive voltage divider in the target power frequency period and the voltage data fitting values as the fitting deviation of the same capacitive voltage divider in the target power frequency period.

[0041] The fitting deviation of the capacitive voltage divider in the target power frequency period is an estimate of the distortion of the voltage data measured by the capacitive voltage divider.

[0042] According to the differences between the voltage disturbance coefficients of all capacitive voltage dividers in the target power frequency period and the fitting deviations of all capacitive voltage dividers in the target power frequency period, the distortion estimation value of each capacitive voltage divider in the target power frequency period is determined respectively.

[0043] The mean value of the voltage disturbance coefficients of all capacitive voltage dividers in the target power frequency period is denoted as the mean value of the voltage disturbance coefficients of the target power frequency period. Any one capacitive voltage divider is denoted as the target capacitive voltage divider. The ratio of the voltage disturbance coefficient of the target capacitive voltage divider in the target power frequency period to the mean value of the voltage disturbance coefficients of the target power frequency period is denoted as the third ratio of the target capacitive voltage divider in the target power frequency period.

[0044] The third ratio of the target capacitive voltage divider in the target power frequency period is used to evaluate the disturbance degree of high-frequency harmonics on the measured voltage of the target capacitive voltage divider. The larger the third ratio, the relatively larger the fluctuation degree of the voltage data obtained by the target capacitive voltage divider, the worse the voltage division ability of the frequency response of the target capacitive voltage divider to the current high-frequency harmonics, and the greater the degree of voltage distortion caused.

[0045] According to the third ratio of the target capacitive voltage divider in the target power frequency period and the fitting deviation of the target capacitive voltage divider in all power frequency periods, the distortion estimation value of the target capacitive voltage divider in the target power frequency period is determined. The distortion estimation value of the target capacitive voltage divider in the target power frequency period is positively correlated with the third ratio of the target capacitive voltage divider in the target power frequency period and the fitting deviation of the target capacitive voltage divider in all power frequency periods respectively.

[0046] Preferably, as an embodiment of the present application, the product of the normalized value of the mean value of the fitting deviations of the target capacitive voltage divider in all power frequency periods and the third ratio of the target capacitive voltage divider in the target power frequency period is denoted as the distortion estimation value of the target capacitive voltage divider in the target power frequency period.

[0047] It should be noted that in this embodiment, the Z-Score standard normalization method is used to calculate the normalized value. In the actual application process, implementers can use other methods of existing technologies such as the maximum-minimum normalization method, sigmoid function, etc. to calculate the normalized value, which is not limited here.

[0048] The normalized value of the mean value of the fitting deviations of the target capacitive voltage divider in all power frequency periods is used to evaluate the degree of voltage distortion presented by the voltage data obtained by the target capacitive voltage divider. The distortion estimation value of the target capacitive voltage divider in the target power frequency period is used to evaluate the relative distortion degree of the target capacitive voltage divider in measuring the current distribution network voltage.

[0049] In the same way, the distortion estimation value of each capacitive voltage divider in each power frequency cycle is obtained. That is to say, for each capacitive voltage divider, there is a corresponding distortion estimation value in each power frequency cycle.

[0050] Thus, the distortion estimation value of each capacitive voltage divider in each power frequency cycle is obtained.

[0051] Step S003: According to the spectrum corresponding to the voltage data, obtain the harmonic sequence of the same capacitive voltage divider in the target power frequency cycle. According to the distortion estimation value of the capacitive voltage divider in the target power frequency cycle and the difference between the harmonic sequences of all capacitive voltage dividers in the target power frequency cycle, determine the capacitive interference degree of the capacitive voltage divider in the target power frequency cycle.

[0052] Considering that when the stray capacitance forms a resonant circuit with the high-voltage arm capacitance, the low-voltage arm capacitance, and the rest of the capacitive voltage divider, it will have an amplifying or reducing effect on the voltage of a specific frequency. Further analyze the frequency-domain characteristics of the voltage data collected by the capacitive voltage divider to improve the accuracy of the high-frequency harmonic measurement of the new energy injected into the distribution network.

[0053] Use the spectrum analysis method to obtain the spectrum sequence of all voltage data corresponding to the measurement window of the target capacitive voltage divider in the target power frequency cycle, and obtain the spectrum peak in the spectrum sequence. The peak in the spectrum sequence reflects the power frequency component in the voltage data. Since the high-frequency component introduced by the new energy into the distribution network is lower than the power frequency component, reduce all values in the spectrum sequence by the same value until the spectrum peak drops to 3 dB to obtain the harmonic sequence of the target capacitive voltage divider in the target power frequency cycle.

[0054] The spectrum analysis method in this embodiment uses a 2048-point fast Fourier transform.

[0055] According to the distortion estimation value of the target capacitive voltage divider in the target power frequency cycle and the difference between the harmonic sequences of all capacitive voltage dividers in the target power frequency cycle, determine the capacitive interference degree of the target capacitive voltage divider in the target power frequency cycle.

[0056] The mean of the DTW distances between the target capacitive voltage divider and all other capacitive voltage dividers in the harmonic sequences of the target power frequency cycle is denoted as the first difference of the target capacitive voltage divider in the target power frequency cycle. The mean of the DTW distances between the harmonic sequences of all different capacitive voltage dividers in the target power frequency cycle is denoted as the second difference of the target power frequency cycle. The ratio of the first difference of the target capacitive voltage divider in the target power frequency cycle to the second difference of the target power frequency cycle is denoted as the fourth ratio of the target capacitive voltage divider in the target power frequency cycle. The sum of all the values included in the harmonic sequence of the target capacitive voltage divider in the target power frequency cycle, multiplied by the fourth ratio and the distortion estimation value of the target capacitive voltage divider in the target power frequency cycle, is denoted as the capacitive interference degree of the target capacitive voltage divider in the target power frequency cycle.

[0057] Among them, calculating the DTW distance between sequences is a well-known technology and will not be elaborated here. When the DTW distance between harmonic sequences is smaller, the harmonic sequences are more similar, and the high-frequency harmonic components of different capacitive voltage dividers in the target power frequency cycle are closer. Ideally, the cut-off frequency of the bode plot is fixed. Any increase or decrease in impedance caused by stray capacitance will result in a shift in the cut-off frequency. When the resonant circuit formed by the stray capacitance of the capacitive voltage divider has a relatively large or small impedance to the high-frequency harmonic voltage introduced by new energy into the distribution network, the DTW distance between the harmonic sequence of the capacitive voltage divider and the harmonic sequences of the other capacitive voltage dividers is larger, and the current measurement interference on the capacitive voltage divider is greater. At this time, the capacitive interference degree of the target capacitive voltage divider in the target power frequency cycle is greater.

[0058] The fourth ratio of the target capacitive voltage divider in the target power frequency cycle is used to evaluate the similarity degree of the voltage data collected by the target capacitive voltage divider and other capacitive voltage dividers at the harmonic frequencies in the target power frequency cycle, that is, the degree of measurement interference suffered by the target capacitive voltage divider at high frequencies due to the influence of stray capacitance. At the same time, the fourth ratio of the target capacitive voltage divider in the target power frequency cycle can control the value range of the capacitive interference degree. The sum of all the values included in the harmonic sequence of the target capacitive voltage divider in the target power frequency cycle is used to reflect the proportion of the harmonic components of the target capacitive voltage divider in the target power frequency cycle in the measured voltage. The capacitive interference degree of the target capacitive voltage divider in the target power frequency cycle is used to evaluate the degree of interference suffered by the target capacitive voltage divider when measuring voltage due to the influence of stray capacitance. The greater the capacitive interference degree of the target capacitive voltage divider in the target power frequency cycle, the greater the degree of interference suffered by the target capacitive voltage divider when measuring voltage due to the influence of stray capacitance.

[0059] According to the same method, the capacitive interference degree of each capacitive voltage divider in each power frequency cycle is obtained. That is to say, for each capacitive voltage divider, there is a corresponding capacitive interference degree in each power frequency cycle.

[0060] Thus far, the capacitive interference degree of each capacitive voltage divider in each power frequency cycle is obtained.

[0061] Step S004: Determine the optimal measurement voltage for the power frequency period according to the capacitance interference degree of the power frequency period, and realize overvoltage warning under the condition of new energy access to the distribution network based on the voltage data collected during the power frequency period according to the optimal measurement voltage and the corresponding all root mean square values.

[0062] The stray capacitance of the capacitive voltage divider is greatly affected by the environment, and the high-frequency harmonic voltage injected into the distribution network by new energy has strong time-variability. Therefore, the frequency response of the capacitive voltage divider is different in different time periods, and the measurement errors of different frequency harmonics are also different in different time periods.

[0063] To increase the redundancy of the capacitive voltage division measurement method, it is necessary to dynamically select the optimal measurement voltage. Specifically, the voltage data of the capacitive voltage divider corresponding to the minimum value among all the capacitance interference degrees corresponding to the same power frequency period is used as the optimal measurement voltage for the same power frequency period.

[0064] Thus, the optimal measurement voltage for each power frequency period is determined.

[0065] Calculate the absolute value of the difference between the extreme values of two adjacent root mean square values included in the root mean square value sequence corresponding to the optimal measurement voltage in the target power frequency period, and record the maximum value of the absolute values of all the differences corresponding to the same power frequency period as the maximum voltage change of the power frequency period. When two adjacent voltage data collected during the power frequency period are not equal, it is considered that there is a voltage change during the power frequency period. Convert the number of voltage changes that occur during the power frequency period into the number of voltage changes per hour, and record the number of voltage changes per hour as the voltage change frequency of the power frequency period.

[0066] Respectively judge whether the values of the maximum voltage change and the voltage change frequency of the power frequency period meet one of the following four overvoltage situations. When it meets one of the following four overvoltage situations, it is determined that there is overvoltage during the power frequency period, and the alarm signal is transmitted to the audible and visual alarm, and overvoltage warning is carried out through audible and visual alarms to remind the staff to conduct further maintenance of the distribution network; when the values of the maximum voltage change and the voltage change frequency of the power frequency period do not meet any of the following four overvoltage situations, it is determined that there is no overvoltage during the power frequency period.

[0067] Among them, the four overvoltage situations are respectively: Situation 1: The voltage change frequency is less than or equal to 1 and the maximum voltage change is greater than 4%.

[0068] Situation 2: The voltage change frequency is less than or equal to 10 and greater than 1, and at the same time, the maximum voltage change is greater than 3%.

[0069] Situation 3: The voltage change frequency is less than or equal to 100 and greater than 10, and at the same time, the maximum voltage change is greater than 2%.

[0070] Case 4: The voltage change frequency is greater than 100 and the maximum voltage change is greater than 1.25%.

[0071] Thus, accurate overvoltage early warning under the condition of new energy access to the distribution network is realized.

[0072] Based on the same inventive concept as the above method, an overvoltage early warning system for new energy access to the distribution network provided by an embodiment of the present invention includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above overvoltage early warning methods for new energy access to the distribution network state are implemented.

[0073] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. An overvoltage warning method when new energy is connected to a distribution network, characterized in that: The method comprises the following steps: Collect voltage data of each capacitive voltage divider set in the distribution network; Record any power frequency cycle divided in a preset measurement cycle as a target power frequency cycle, determine all root mean square values ​​corresponding to the target power frequency cycle of the same capacitive voltage divider according to all voltage data collected in adjacent power frequency cycles divided in the measurement cycle, determine the voltage disturbance coefficient of the same capacitive voltage divider in the target power frequency cycle according to the difference between all root mean square values ​​corresponding to the target power frequency cycle of the same capacitive voltage divider, and determine the distortion estimation value of the same capacitive voltage divider in the target power frequency cycle in combination with the difference between the values ​​corresponding to the ideal change trend of all voltage data collected by the same capacitive voltage divider in the target power frequency cycle and the voltage data; According to the frequency spectrum corresponding to the voltage data, a harmonic sequence of the same capacitor voltage divider in the target power frequency period is obtained, and according to the distortion estimation value of the capacitor voltage divider in the target power frequency period and the difference between the harmonic sequences of all the capacitor voltage dividers in the target power frequency period, the capacitance interference degree of the capacitor voltage divider in the target power frequency period is determined; The optimal measurement voltage of the power frequency cycle is determined according to the capacitance interference degree of the power frequency cycle, and the overvoltage warning is realized when the new energy is connected to the distribution network according to the voltage data collected in the power frequency cycle and the corresponding root mean square value of the optimal measurement voltage.

2. According to claim 1, the overvoltage early warning method in the state of new energy access to the distribution network is characterized in that: The method for determining the root mean square value is: The target power frequency cycle and the M-1 power frequency cycles adjacent to the target power frequency cycle together form a measurement window, which is recorded as the measurement window of the target power frequency cycle, where M is a second preset threshold; Calculate the RMS value of all voltage data collected by the same capacitive voltage divider within each half power frequency cycle in the measurement window of the target power frequency cycle.

3. The overvoltage early warning method when a new energy source is connected to a distribution network according to claim 2 is characterized in that: The method of determining the voltage disturbance coefficient of the same capacitor voltage divider in the target power frequency period according to the difference between all the root mean square values ​​corresponding to the same capacitor voltage divider in the target power frequency period includes: Arrange all RMS values ​​corresponding to the measurement window of the same capacitive voltage divider in the target power frequency cycle in the order of the power frequency cycles corresponding to the RMS values, and obtain a RMS value sequence of the same capacitive voltage divider in the target power frequency cycle; The voltage disturbance coefficient of the capacitor voltage divider in the target power frequency cycle is determined according to the difference between all root mean square values ​​contained in the root mean square value sequence of the capacitor voltage divider in the target power frequency cycle.

4. The overvoltage early warning method when a new energy source is connected to a distribution network according to claim 3 is characterized in that: The method of determining the voltage disturbance coefficient of the capacitor voltage divider in the target power frequency period according to the difference between all the root mean square values ​​contained in the root mean square value sequence of the capacitor voltage divider in the target power frequency period includes the following specific methods: Record the ratio of the maximum value to the minimum value of the root mean square value of the capacitor voltage divider in the root mean square value sequence of the target power frequency cycle as the first ratio of the capacitor voltage divider in the target power frequency cycle; The ratio of the standard deviation of all the root mean square values ​​contained in the root mean square value sequence of the capacitive voltage divider in the target power frequency period to the average value is recorded as the second ratio of the capacitive voltage divider in the target power frequency period; According to the first ratio and the second ratio of the capacitive voltage divider in the target power frequency cycle, the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency cycle is determined, and the voltage disturbance coefficient of the capacitive voltage divider in the target power frequency cycle is positively correlated with the first ratio of the capacitive voltage divider in the target power frequency cycle and the second ratio of the capacitive voltage divider in the target power frequency cycle, respectively.

5. The overvoltage early warning method when a new energy source is connected to a distribution network according to claim 2 is characterized in that: The method for determining the distortion estimation value of the same capacitive voltage divider in the target power frequency period is: Performing curve fitting on all voltage data corresponding to the measurement window of the target power frequency cycle of the same capacitive voltage divider, obtaining a fitting curve, obtaining corresponding voltage data fitting values ​​of all voltage data corresponding to the measurement window of the target power frequency cycle of the same capacitive voltage divider on the fitting curve, and accumulating the absolute values ​​of the differences between all voltage data corresponding to the measurement window of the target power frequency cycle of the same capacitive voltage divider and the voltage data fitting values, recording the fitting deviation of the same capacitive voltage divider in the target power frequency cycle; The average value of the voltage disturbance coefficients of all capacitor voltage dividers in the target power frequency cycle is recorded as the average value of the voltage disturbance coefficient of the target power frequency cycle, any capacitor voltage divider is recorded as the target capacitor voltage divider, and the ratio of the voltage disturbance coefficient of the target capacitor voltage divider in the target power frequency cycle to the average value of the voltage disturbance coefficient of the target power frequency cycle is recorded as the third ratio of the target capacitor voltage divider in the target power frequency cycle; According to the third ratio of the target capacitor voltage divider in the target power frequency cycle and the fitting deviation of the target capacitor voltage divider in all power frequency cycles, the distortion estimation value of the target capacitor voltage divider in the target power frequency cycle is determined, and the distortion estimation value of the target capacitor voltage divider in the target power frequency cycle is positively correlated with the third ratio of the target capacitor voltage divider in the target power frequency cycle and the fitting deviation of the target capacitor voltage divider in all power frequency cycles.

6. The overvoltage early warning method when a new energy source is connected to a distribution network according to claim 5 is characterized in that: The specific method of obtaining the harmonic sequence of the same capacitive voltage divider in the target power frequency period according to the frequency spectrum corresponding to the voltage data is as follows: Obtain a spectrum sequence of all voltage data corresponding to the target capacitor voltage divider within a measurement window of a target power frequency period, and obtain a spectrum peak in the spectrum sequence; All values ​​in the spectrum sequence are reduced by the same value until the spectrum peak drops to 3 dB, and the harmonic sequence of the target capacitor voltage divider in the target power frequency period is obtained.

7. The overvoltage early warning method when a new energy source is connected to a distribution network according to claim 5, characterized in that: The method for determining the capacitance interference degree of the capacitive voltage divider in the target power frequency period is: The average of the DTW distances between the target capacitor voltage divider and the harmonic sequences of all other capacitor voltage dividers in the target power frequency cycle is recorded as the first difference of the target capacitor voltage divider in the target power frequency cycle, the average of the DTW distances between the harmonic sequences of all different capacitor voltage dividers in the target power frequency cycle is recorded as the second difference of the target power frequency cycle, and the ratio of the first difference of the target capacitor voltage divider in the target power frequency cycle to the second difference of the target power frequency cycle is recorded as the fourth ratio of the target capacitor voltage divider in the target power frequency cycle; The cumulative sum of all values ​​contained in the harmonic sequence of the target capacitor voltage divider in the target power frequency period, the product of the fourth ratio of the target capacitor voltage divider in the target power frequency period and the distortion estimation value is recorded as the capacitor interference degree of the target capacitor voltage divider in the target power frequency period.

8. The overvoltage warning method when a new energy source is connected to a distribution network according to claim 1 is characterized in that: The specific method of determining the optimal measurement voltage of the power frequency cycle according to the capacitance interference degree of the power frequency cycle includes: The voltage data of the capacitive voltage divider corresponding to the minimum value of all the capacitive interferences corresponding to the same power frequency cycle is used as the optimal measurement voltage of the same power frequency cycle.

9. The overvoltage early warning method when a new energy source is connected to a distribution network according to claim 1 is characterized in that: The voltage data collected in the power frequency cycle according to the optimal measured voltage and the corresponding root mean square value are used to realize the overvoltage warning when the new energy is connected to the distribution network, and the specific method includes: Calculate the absolute value of the difference between two adjacent extreme values ​​of the root mean square value of the optimal measured voltage in the root mean square value sequence corresponding to the target power frequency cycle, and record the maximum value of the absolute values ​​of all differences corresponding to the same power frequency cycle as the maximum voltage change of the power frequency cycle; When two adjacent voltage data collected within the power frequency cycle are not equal, the number of voltage changes occurring within the power frequency cycle is converted into the number of voltage changes per hour, and the number of voltage changes per hour is recorded as the voltage change frequency of the power frequency cycle; When the values ​​of the maximum voltage change and the voltage change frequency in the power frequency cycle meet one of the overvoltage conditions, it is determined that there is overvoltage in the power frequency cycle; when the values ​​of the maximum voltage change and the voltage change frequency in the power frequency cycle do not meet the overvoltage conditions, it is determined that there is no overvoltage in the power frequency cycle.

10. An overvoltage warning system when a new energy source is connected to a distribution network, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 9 are implemented.

Images