Method and device for evaluating frequency coupling characteristic measurement accuracy of grid-connected inverter

Abstract

The invention relates to a grid-connected inverter frequency coupling characteristic measurement precision evaluation method and device. Comprising the steps of estimating average noise amplitude distribution in a preset frequency interval based on a first port voltage set and a first current set of a tested grid-connected inverter; injecting a preset multi-sine disturbance signal into the tested grid-connected inverter, obtaining a second port voltage set and a second current set, carrying out Fourier analysis on the second port voltage set and the second current set, and selecting a first voltage component group and a first current component group corresponding to a first preset frequency based on an obtained first analysis result, the second voltage component group and the second current component group correspond to a second preset frequency; according to the first voltage component group, the second voltage component group, the first current component group, the second current component group and the average noise amplitude, the frequency coupling characteristic measurement precision is quantitatively evaluated based on the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement obtained through estimation. Therefore, the problem that the frequency coupling characteristic measurement precision under noise interference is difficult to evaluate in the prior art is solved.

Description

Technical Field

[0001] The present application relates to the technical field of inverter grid-connected technology, and in particular to a method and device for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter. Background Art

[0002] With the increasing penetration rate of renewable energy power generation, grid-connected inverters, as the main port for outputting power of renewable energy equipment, have been widely used in power grids. The large-scale access of grid-connected inverters based on power electronics technology has led to the risk of oscillation and instability in the interconnected system between renewable energy equipment and the power grid. The oscillation phenomenon will cause the system's ability to absorb renewable energy to decrease or even cause local power grid collapse. The reason for this is that the stability margin of the interconnected system composed of grid-connected inverters and the power grid is insufficient. Therefore, it is necessary to conduct stability analysis on the grid-connected operation system of renewable energy power generation to ensure that the interconnected system has sufficient stability margin.

[0003] In the related technology, it is proposed to use pseudo-random binary sequence and discrete interval binary sequence to realize grid impedance measurement; an improved disturbance energy distribution method is also proposed, which additionally considers the signal-to-noise ratio of the response signal, and derives the mathematical relationship between the impedance measurement error and the signal-to-noise ratio of the disturbance signal and the response signal, thereby realizing measurement accuracy evaluation by estimating the signal-to-noise ratio.

[0004] However, the above method is only applicable to the single-input single-output impedance model and does not consider the frequency coupling effect. It is difficult to evaluate the measurement accuracy of the frequency coupling characteristics under noise interference, which may lead to misjudgment of small signal stability and needs to be solved urgently. Summary of the invention

[0005] The present application provides a method and device for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter, so as to solve the problem that it is difficult to evaluate the measurement accuracy of the frequency coupling characteristics under noise interference in the prior art, effectively avoid the stability misjudgment caused by impedance measurement errors, and improve the reliability of impedance measurement results in actual system stability analysis.

[0006] To achieve the above-mentioned purpose, the first embodiment of the present application proposes a method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter, comprising the following steps:

[0007] Acquire a first port voltage set and a first current set of the tested grid-connected inverter, and estimate an average noise amplitude of each frequency within a preset frequency range based on the first port voltage set and the first current set;

[0008] Injecting a preset multi-sinusoidal disturbance signal into the tested grid-connected inverter, and obtaining a second port voltage set and a second current set of the tested grid-connected inverter, performing Fourier analysis on the second port voltage set and the second current set, and selecting a first voltage component group and a first current component group corresponding to a first preset frequency, and a second voltage component group and a second current component group corresponding to a second preset frequency based on the first analysis result obtained;

[0009] A generalized signal-to-noise ratio index for frequency coupling characteristic measurement is estimated based on the first voltage component group, the first current component group, the second voltage component group, the second current component group and the average noise amplitude of each frequency, and the frequency coupling characteristic measurement accuracy is quantitatively evaluated based on the generalized signal-to-noise ratio index.

[0010] According to an embodiment of the present application, the quantitative evaluation of the frequency coupling characteristic measurement accuracy based on the generalized signal-to-noise ratio indicator includes:

[0011] Inputting the generalized signal-to-noise ratio index into a preset impedance measurement error model to obtain a possible distribution range of the measurement error;

[0012] Based on the possible distribution range of the measurement error, the measurement accuracy of the frequency coupling characteristics is quantitatively evaluated.

[0013] According to one embodiment of the present application, the preset impedance measurement error model is:

[0014]

[0015] Among them, ΔM 11 is the amplitude error, S Gi , S Gv are the generalized signal-to-noise ratio indicators, ΔP 11 is the phase error.

[0016] According to an embodiment of the present application, estimating an average noise amplitude of each frequency within a preset frequency range based on the first port voltage set and the first current set includes:

[0017] Grouping the first port voltage set and the first current set according to a preset grouping standard and then performing Fourier analysis to obtain a second analysis result;

[0018] According to the second analysis result, a preset kernel density estimation method is used to perform probability modeling on the noise amplitude data of each frequency to obtain the average noise amplitude of each frequency.

[0019] According to one embodiment of the present application, the generalized signal-to-noise ratio indicator is:

[0020]

[0021] Among them, I G is the equivalent current signal when calculating the frequency coupling characteristics, V G is the equivalent voltage signal when calculating the frequency coupling characteristics, E i 、E v All of them are signals containing noise components.

[0022] According to the evaluation method of the measurement accuracy of the frequency coupling characteristics of the grid-connected inverter proposed in the embodiment of the present application, by obtaining the first port voltage set and the first current set of the measured grid-connected inverter, the average noise amplitude distribution within the preset frequency range can be estimated; by injecting a preset multi-sinusoidal disturbance signal into the measured grid-connected inverter and obtaining the second port voltage set and the second current set, the second port voltage set and the second current set can be subjected to Fourier analysis, and the first voltage component group and the first current component group corresponding to the first preset frequency, and the second voltage component group and the second current component group corresponding to the second preset frequency are selected based on the first analysis result obtained; according to the first and second voltage component groups, the first and second current component groups and the average noise amplitude, the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement obtained based on the estimation is used to quantitatively evaluate the measurement accuracy of the frequency coupling characteristic. Thus, the problem that the prior art is difficult to evaluate the measurement accuracy of the frequency coupling characteristic under noise interference is solved, the stability misjudgment caused by the impedance measurement error is effectively avoided, and the reliability of the impedance measurement result in the actual system stability analysis is improved.

[0023] To achieve the above-mentioned purpose, a second embodiment of the present application proposes a device for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter, comprising:

[0024] An estimation module, used for acquiring a first port voltage set and a first current set of the tested grid-connected inverter, and estimating an average noise amplitude of each frequency within a preset frequency range based on the first port voltage set and the first current set;

[0025] A selection module, used for injecting a preset multi-sinusoidal disturbance signal into the tested grid-connected inverter, and obtaining a second port voltage set and a second current set of the tested grid-connected inverter, performing Fourier analysis on the second port voltage set and the second current set, and selecting a first voltage component group and a first current component group corresponding to a first preset frequency, and a second voltage component group and a second current component group corresponding to a second preset frequency based on the first analysis result obtained;

[0026] An evaluation module is used to estimate a generalized signal-to-noise ratio index for frequency coupling characteristic measurement based on the first voltage component group, the first current component group, the second voltage component group, the second current component group and the average noise amplitude of each frequency, and quantitatively evaluate the frequency coupling characteristic measurement accuracy based on the generalized signal-to-noise ratio index.

[0027] According to one embodiment of the present application, the evaluation module is specifically used for:

[0028] Inputting the generalized signal-to-noise ratio index into a preset impedance measurement error model to obtain a possible distribution range of the measurement error;

[0029] Based on the possible distribution range of the measurement error, the measurement accuracy of the frequency coupling characteristics is quantitatively evaluated.

[0030] According to one embodiment of the present application, the preset impedance measurement error model is:

[0031]

[0032] Among them, ΔM 11 is the amplitude error, S Gi , S Gv are the generalized signal-to-noise ratio indicators, ΔP 11 is the phase error.

[0033] According to one embodiment of the present application, the estimation module is specifically used for:

[0034] Grouping the first port voltage set and the first current set according to a preset grouping standard and then performing Fourier analysis to obtain a second analysis result;

[0035] According to the second analysis result, a preset kernel density estimation method is used to perform probability modeling on the noise amplitude data of each frequency to obtain the average noise amplitude of each frequency.

[0036] According to one embodiment of the present application, the generalized signal-to-noise ratio indicator is:

[0037]

[0038] Among them, I G is the equivalent current signal when calculating the frequency coupling characteristics, V G is the equivalent voltage signal when calculating the frequency coupling characteristics, E i 、E v All of them are signals containing noise components.

[0039] According to the evaluation device for measuring the frequency coupling characteristics of the grid-connected inverter proposed in the embodiment of the present application, by obtaining the first port voltage set and the first current set of the measured grid-connected inverter, the average noise amplitude distribution within the preset frequency range can be estimated; by injecting a preset multi-sinusoidal disturbance signal into the measured grid-connected inverter and obtaining the second port voltage set and the second current set, the second port voltage set and the second current set can be subjected to Fourier analysis, and the first voltage component group and the first current component group corresponding to the first preset frequency, and the second voltage component group and the second current component group corresponding to the second preset frequency are selected based on the first analysis result obtained; according to the first and second voltage component groups, the first and second current component groups and the average noise amplitude, the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement obtained by estimation is used to quantitatively evaluate the frequency coupling characteristic measurement accuracy. Thus, the problem that the prior art is difficult to evaluate the frequency coupling characteristic measurement accuracy under noise interference is solved, the stability misjudgment caused by the impedance measurement error is effectively avoided, and the reliability of the impedance measurement result in the actual system stability analysis is improved.

[0040] To achieve the above-mentioned objectives, the third aspect embodiment of the present application proposes an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter as described in the above-mentioned embodiment.

[0041] To achieve the above objectives, the fourth aspect of the present application proposes a computer-readable storage medium having a computer program stored thereon, which is executed by a processor to implement the method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter as described in the above embodiments.

[0042] To achieve the above objectives, a fifth aspect of the present invention proposes a computer program product, including a computer program, which, when executed by a processor, is used to implement the method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter as described in the above embodiments.

[0043] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0045] Figure 1 A flowchart of a method for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter provided according to an embodiment of the present application;

[0046] Figure 2A schematic diagram of the maximum value analysis principle of impedance phase measurement error according to an embodiment of the present application;

[0047] Figure 3 A schematic diagram of a control hardware-in-the-loop experimental platform according to an embodiment of the present application;

[0048] Figure 4 A circuit connection diagram of an impedance measurement system according to an embodiment of the present application;

[0049] Figure 5 A schematic diagram of three-phase voltage, current and output power waveforms of a grid-connected inverter port according to an embodiment of the present application;

[0050] Figure 6 is the positive sequence admittance Y according to one embodiment of the present application 11 Schematic diagram of measurement results and error range evaluation results;

[0051] Figure 7 A block diagram of a device for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter provided according to an embodiment of the present application;

[0052] Figure 8 It is a schematic diagram of the structure of an electronic device provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0053] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0054] The following describes a method and device for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter proposed in an embodiment of the present application with reference to the accompanying drawings.

[0055] Figure 1 It is a flow chart of a method for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter according to an embodiment of the present application.

[0056] Before introducing the evaluation method for measuring the frequency coupling characteristics of a grid-connected inverter proposed in an embodiment of the present application, the relevant technical background is first introduced.

[0057] Impedance-based stability analysis is a reliable method for evaluating the stability of renewable energy grid-connected systems. The impedance model of the grid-connected inverter and the power grid is a key parameter for stability analysis. The impedance model is a single-input single-output model with positive and negative sequence decoupling. At present, the impedance modeling method has been widely studied. In addition, existing studies have shown that renewable energy power generation equipment based on power electronics technology usually exhibits frequency coupling effects.

[0058] The frequency coupling effect is mainly manifested as the generation of a coupling frequency component that is twice the fundamental frequency of the disturbance frequency, which transforms the impedance model from a single-input single-output to a multi-input multi-output model, and needs to be characterized by a two-dimensional admittance matrix. In order to perform stability analysis, the frequency coupling effect needs to be considered to ensure the reliability of the stability analysis. Impedance measurement is an effective method to obtain the impedance model of a renewable energy power generation device by injecting small signal disturbances, and its impedance can be calculated based on the port information of the device. When considering the frequency coupling characteristics in impedance measurement, two sets of linearly independent disturbance injections are required, and the components of the disturbance frequency and the coupling frequency need to be extracted from the sampled signal to calculate the elements of the two-dimensional matrix.

[0059] Noise is an important factor affecting the accuracy of impedance measurement. A lot of research has been done to reduce the measurement error caused by noise. The signal-to-noise ratio is a key indicator for evaluating and ensuring measurement accuracy. It has been proven that the use of single sinusoidal signal injection for frequency sweeping has a high signal-to-noise ratio. In order to improve the efficiency of impedance measurement, the application of broadband signals containing multiple harmonic components in impedance measurement has been widely studied. However, the limited disturbance energy is distributed on multiple harmonic components, which reduces the overall signal-to-noise ratio and becomes the main factor restricting the measurement accuracy.

[0060] In the related technology, it is proposed to use pseudo-random binary sequence and discrete interval binary sequence to realize grid impedance measurement; an improved disturbance energy distribution method is also proposed, which additionally considers the signal-to-noise ratio of the response signal, and derives the mathematical relationship between the impedance measurement error and the signal-to-noise ratio of the disturbance signal and the response signal, thereby realizing measurement accuracy evaluation by estimating the signal-to-noise ratio.

[0061] However, the above-mentioned accuracy evaluation method based on signal-to-noise ratio is only applicable to the single-input single-output impedance model, and the frequency coupling effect is not considered. In the process of measuring the frequency coupling characteristics, injecting two sets of linearly independent perturbations will generate 8 measurement signals. When calculating the frequency coupling matrix, multiple measurement signals will produce complex interactions. Therefore, the signal-to-noise ratio defined in the single-input single-output impedance measurement scenario cannot accurately quantify the accuracy level of the frequency coupling characteristic measurement. At present, there is a lack of signal-to-noise ratio indicators suitable for frequency coupling characteristics, making it difficult to evaluate the measurement accuracy of frequency coupling characteristics under noise interference, and it is impossible to evaluate the reliability of impedance measurement results, which may lead to misjudgment of small signal stability.

[0062] Precisely based on the above-mentioned problems, an embodiment of the present application proposes a method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter. By obtaining the first port voltage set and the first current set of the measured grid-connected inverter, the average noise amplitude distribution within a preset frequency range can be estimated; by injecting a preset multi-sinusoidal disturbance signal into the measured grid-connected inverter and obtaining the second port voltage set and the second current set, the second port voltage set and the second current set can be subjected to Fourier analysis, and the first voltage component group and the first current component group corresponding to the first preset frequency, as well as the second voltage component group and the second current component group corresponding to the second preset frequency are selected based on the first analysis result obtained; according to the first and second voltage component groups, the first and second current component groups and the average noise amplitude, the frequency coupling characteristic measurement accuracy is quantitatively evaluated based on the generalized signal-to-noise ratio indicator of the estimated frequency coupling characteristic measurement.

[0063] Compared with the existing frequency coupling impedance characteristic measurement method, the method proposed in the embodiment of the present application realizes the quantitative evaluation of the uncertainty domain of the frequency coupling impedance measurement result, solves the problem that the existing technology is difficult to evaluate the measurement accuracy of the frequency coupling characteristic under noise interference, effectively avoids the stability misjudgment caused by impedance measurement errors, and improves the reliability of the impedance measurement results in the actual system stability analysis.

[0064] For example, Figure 1 As shown, the method for evaluating the measurement accuracy of the frequency coupling characteristics of the grid-connected inverter includes the following steps:

[0065] In step S101, a first port voltage set and a first current set of a tested grid-connected inverter are obtained, and based on the first port voltage set and the first current set, an average noise amplitude of each frequency in a preset frequency range is estimated.

[0066] That is to say, when the grid-connected inverter under test is in a stable operating state, a suitable data acquisition device (such as a high-precision oscilloscope, etc.) can be used to sample the port voltage and current signals of the grid-connected inverter under test for 50 seconds to obtain a first port voltage set and a first current set. The sampling process needs to ensure that the sampling frequency is high enough to accurately estimate the noise amplitude distribution characteristics within a preset frequency range (such as 1 to 2000 Hz) (that is, the average noise amplitude of each frequency).

[0067] The following describes in detail how to estimate the average noise amplitude of each frequency within the preset frequency range based on the first port voltage set and the first current set.

[0068] As a possible implementation method, in some embodiments, based on the first port voltage set and the first current set, the average noise amplitude of each frequency within a preset frequency range is estimated, including: grouping the first port voltage set and the first current set according to a preset grouping standard and then performing Fourier analysis to obtain a second analysis result; based on the second analysis result, using a preset kernel density estimation method to probabilistically model the noise amplitude data of each frequency to obtain the average noise amplitude of each frequency.

[0069] Specifically, after the first port voltage set and the first current set are acquired, the first port voltage set and the first current set can be grouped according to a preset grouping standard. For example, the first port voltage set and the first current set are divided into 50 groups, each group of 1s, to ensure that each group of data can cover the frequency range of the entire preset frequency interval, to obtain multiple groups of voltage and current samples, and to perform Fourier transform on the voltage and current samples of each group to obtain its spectrum information (i.e., the second analysis result). For each frequency point (within the preset frequency interval, from 1Hz to 2000Hz, with an interval of 1Hz), the noise amplitude data corresponding to the frequency point in all groups can be extracted from the second analysis result, and then, the preset kernel density estimation method (Kernel Density Estimation) is used. KDE (KDE is a non-parametric probability density estimation method that estimates the entire probability density function based on the data points themselves. KDE can be used to obtain the distribution characteristics of the noise amplitude at each frequency, including its mean, standard deviation, peak value, etc.) to perform probability modeling on these noise amplitude data and obtain a probability density function, which describes the distribution of the noise amplitude at each frequency point. The average noise amplitude at each frequency point can be obtained by calculating the mean of the probability density function.

[0070] It should be noted that in order to ensure that the noise amplitude at each integer frequency point can be accurately obtained, the second analysis result can be interpolated or resampled, but under normal circumstances, if the sampling frequency is large enough, the closest Fourier transform result can also be directly selected as the amplitude estimate of the frequency point.

[0071] In step S102, a preset multi-sinusoidal disturbance signal is injected into the grid-connected inverter under test, and the second port voltage set and the second current set of the grid-connected inverter under test are obtained, and Fourier analysis is performed on the second port voltage set and the second current set, and based on the first analysis result obtained, a first voltage component group and a first current component group corresponding to a first preset frequency, and a second voltage component group and a second current component group corresponding to a second preset frequency are selected.

[0072] Specifically, by injecting a preset multi-sinusoidal disturbance signal into the grid-connected inverter under test, the frequency-coupled impedance characteristics of the grid-connected inverter can be measured, that is, by injecting two sets of linearly independent three-phase multi-sinusoidal disturbance signals into the grid-connected inverter under test through a signal generator, and using a suitable data acquisition device to sample the port voltage and current signals of the grid-connected inverter under test for 1 s, respectively, the second port voltage set and the second current set can be obtained, and the second port voltage set and the second current set are subjected to Fourier analysis to obtain their spectrum information (i.e., the first analysis result). According to the first analysis result, the frequency f is determined. p Hz (i.e., the first preset frequency) of the first voltage component group V p 、V n and the first current component group I p ,I n ; and frequency f p -2f1Hz (i.e., the second preset frequency) second voltage component group V p2 、V n2 and the second current component group I p2 ,I n2 Among them, V p 、V p2 ,I p ,I p2 is the measured signal obtained when the multi-sine signal is injected for the first time, V n 、V n2 ,I n ,I n2 This is the measured signal obtained when the multi-sine signal is injected for the second time.

[0073] Among them, the expression of the multi-sinusoidal disturbance signal sequence is shown in formula (1):

[0074]

[0075] Among them, x(t) is a multi-sine wave signal, a m is the amplitude of the mth sinusoidal component of the multi-sine wave signal, f m is the frequency of the mth sinusoidal component of the multi-sine wave signal, is the initial phase of the mth sinusoidal component of the multi-sine wave signal, N is the number of sinusoidal waves in the multi-sine wave signal (usually 20 to 40), and t is time.

[0076] When the first multi-sinusoidal disturbance signal is injected, f m The logarithmic distribution is uniform within the measurement frequency range, and the phase sequence of the three-phase multi-sinusoidal disturbance signal is positive sequence. m Taking the same value, the phase of the frequency components contained in the multi-sinusoidal disturbance signal can be determined by relevant technical means (such as peak shearing method), and then a is determined. m , am The principle of selecting the value is to ensure that the peak value of the multi-sinusoidal disturbance signal is not higher than 10% of the rated value of the fundamental voltage; when the multi-sinusoidal disturbance signal is injected for the second time, the three-phase multi-sinusoidal signal becomes a frequency of (f m -2f1) negative sequence signal, a m The value of remains unchanged, and the phase of the frequency components contained in the multi-sinusoidal disturbance signal can also be determined by using relevant technical means (such as the peak clipping method).

[0077] In step S103, a generalized signal-to-noise ratio index for frequency coupling characteristic measurement is estimated based on the first voltage component group, the first current component group, the second voltage component group, the second current component group and the average noise amplitude of each frequency, and the frequency coupling characteristic measurement accuracy is quantitatively evaluated based on the generalized signal-to-noise ratio index.

[0078] That is to say, based on the average noise amplitude of each frequency obtained in step S101 and the first voltage component group, the first current component group, the second voltage component group, and the second current component group obtained in step S102, the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement can be estimated, and the frequency coupling characteristic measurement accuracy can be quantitatively evaluated based on the generalized signal-to-noise ratio index.

[0079] The definition and calculation process of generalized signal-to-noise ratio will be introduced below.

[0080] The calculation formula of the frequency-coupled admittance characteristic matrix is ​​shown in formula (2):

[0081]

[0082] The frequency coupling characteristic measurement requires two sets of linearly independent perturbation injections, where V p [f p ] and V p2 [f p -2f1] respectively represent the frequency obtained when the multi-sinusoidal disturbance signal is injected for the first time as f p Hz and (f p -2f1)Hz voltage signal, I p [f p ] and I p2 [f p -2f1] respectively represent the frequency obtained when the multi-sinusoidal disturbance signal is injected for the first time as f p Hz and (f p -2f1)Hz current signal, V n [f p ] and V n2 [f p -2f1] respectively represent the frequency obtained when the multi-sinusoidal disturbance signal is injected for the first time as f p Hz and (f p-2f1)Hz voltage signal, I n [f p ] and I n2 [f n -2f1] respectively represent the frequency obtained when the multi-sinusoidal disturbance signal is injected for the second time as f p Hz and (f p -2f1)Hz current signal, where the frequency is omitted for simplicity.

[0083] Taking into account the existence of noise in actual measurement, the measurement results of frequency coupling characteristics under noise interference can be expressed as:

[0084]

[0085] Among them, Y 11m , Y 12m , Y 21m , Y 22m is the measurement result of the four elements of the frequency coupling admittance characteristic matrix under noise interference, I pe For I p The superimposed current noise component, V pe For V p The superimposed voltage noise component, I ne For I n The superimposed current noise component, V ne For V n The superimposed voltage noise component, I p2e For I p2 The superimposed current noise component, V p2e For V p2 The superimposed voltage noise component, I n2e For I n2 The superimposed current noise component, V n2e For V n2 Superimposed voltage noise component.

[0086] Y 11m Take the measurement results as an example:

[0087]

[0088] Among them, I S is the current value calculated from the sampled signal containing noise components, V S is the voltage value calculated from the sampled signal containing the noise component, E i 、E v is a signal containing noise components.

[0089] Further:

[0090]

[0091] Among them, in some embodiments, the generalized signal-to-noise ratio indicator is:

[0092]

[0093] Among them, I G is the equivalent current signal when calculating the frequency coupling characteristics, V G It is the equivalent voltage signal when calculating the frequency coupling characteristics.

[0094] From the definition of generalized signal-to-noise ratio, we can know that this indicator reflects the influence of the noise component on the effective measurement signal.

[0095] Next, we will explain in detail how to quantitatively evaluate the measurement accuracy of frequency coupling characteristics based on the generalized signal-to-noise ratio indicator.

[0096] As a possible implementation method, in some embodiments, the measurement accuracy of the frequency coupling characteristics is quantitatively evaluated based on a generalized signal-to-noise ratio indicator, including: inputting the generalized signal-to-noise ratio indicator into a preset impedance measurement error model to obtain a possible distribution range of the measurement error; based on the possible distribution range of the measurement error, quantitatively evaluating the measurement accuracy of the frequency coupling characteristics.

[0097] Among them, the amplitude of the impedance measurement error under noise interference (ΔM 11 ) and phase (ΔP 11 ) can be expressed by equation (7), which is defined as the impedance measurement error model. From this model, it can be seen that when the generalized signal-to-noise ratio tends to positive infinity, the measurement error tends to 0.

[0098] In some embodiments, the preset impedance measurement error model is:

[0099]

[0100] Among them, ΔM 11 is the amplitude error, S Gi , S Gv Both are generalized signal-to-noise ratio indicators, ΔP 11 is the phase error.

[0101] Specifically, in order to evaluate the frequency coupling characteristic measurement accuracy (i.e., impedance measurement accuracy), it is necessary to analyze the possible distribution range of the measurement error based on the measurement signal, that is, input the estimated generalized signal-to-noise ratio index into the preset impedance measurement error model, and the possible distribution range of the measurement error can be obtained. The size of the distribution range is negatively correlated with the measurement accuracy, thereby achieving a quantitative evaluation of the impedance frequency coupling characteristic measurement accuracy. Since the noise characteristics are changeable and difficult to predict, it is impossible to directly calculate S Gi and S GvTherefore, the specific value of S in the extreme case can be calculated. Gi and S Gv The minimum value of is used as the basis for evaluating the measurement accuracy of frequency coupling characteristics.

[0102] First, the maximum value of the impedance amplitude measurement error is calculated.

[0103] (1) Calculate the noise component E i 、E v The possible maximum value of is shown in formula (8):

[0104]

[0105] (2) When E i 、E v When the maximum value is taken, calculate I G 、V G The minimum value of the following two extreme cases is taken as I G 、V G The minimum value of .

[0106] 1) When I G With E i have the same phase, and V G With E v When they have the same phase, I G With V G has a minimum value, as shown below:

[0107]

[0108] 2) When the phase difference between each noise component and the corresponding measurement signal is 0rad, I G 、V G The minimum value of can be calculated by formula (10):

[0109]

[0110] Finally, I G 、V G The minimum values ​​of and The larger value in .

[0111] 3) The minimum value of the generalized signal-to-noise ratio is determined by the following formula:

[0112]

[0113]

[0114] Substituting the minimum value of the generalized signal-to-noise ratio into the impedance measurement error model, the maximum value of the impedance amplitude measurement error is calculated as shown in the following formula:

[0115]

[0116] Secondly, following a similar principle, the maximum value of the impedance phase measurement error can also be calculated.

[0117] (1) Calculate S Gi With S Gv The minimum value of Figure 2 As shown, when I G and V G When tangent to the circle, the impedance phase measurement error is defined as

[0118]

[0119] (2) and The value of can be obtained by the following formula:

[0120]

[0121] in,

[0122]

[0123] The above steps are for the positive sequence admittance Y 11 To evaluate the measurement accuracy of the frequency coupling characteristics, the impedance calculation expressions of the remaining three elements of the frequency coupling admittance matrix are as follows:

[0124]

[0125] From the above formula, we can see that Y 11 The calculation method is similar to the other three elements. The calculation steps for the generalized signal-to-noise ratio index and the measurement accuracy evaluation are the same, except that I G 、E i By adjusting the definition of accordingly and keeping the other steps unchanged, the measurement accuracy evaluation of the remaining three elements of the frequency-coupled admittance matrix can be achieved.

[0126] Therefore, according to the sampling signal of the measurement process, the maximum value of the measurement error in the extreme case is calculated ( and ), the possible distribution range of the estimated error is negatively correlated with the measurement accuracy, thereby achieving a quantitative evaluation of the measurement accuracy of the frequency coupling characteristics.

[0127] In order to facilitate those skilled in the art to further understand the evaluation method for measuring the frequency coupling characteristics of the grid-connected inverter proposed in this application, the following is combined with Figure 3 to Figure 6 For further elaboration.

[0128] Taking the measurement of frequency-coupled impedance / admittance characteristics of grid-connected inverter as an example, the design and implementation are carried out according to the following steps:

[0129] Step 1: Collect the port voltage and current signals of the grid-connected inverter under test during the stable operation stage, and estimate the noise amplitude distribution characteristics in the range of 1 to 2000 Hz.

[0130] Specifically, the Typhoon control hardware-in-the-loop platform can be used to establish an impedance measurement control hardware-in-the-loop model to measure the frequency coupling characteristics of the grid-connected inverter. 11 Taking the measurement of 200V as an example, the grid-connected inverter parameters are shown in Table 1. The control hardware is changed to the experimental platform. Figure 3 As shown, a megawatt-class grid-connected inverter model is built in Typhoon 602+, with a time step of 1 μs. The controller of the grid-connected inverter can be executed on the TMS320F28335 / Spartan 6XC6SLX16DSP+FPGA control board, and the sampling frequency is set to 5 kHz.

[0131] Table 1

[0132] variable Variable meaning Numeric <![CDATA[U s ]]> Rated voltage 690V <![CDATA[P s ]]> Rated Power 1.5MW <![CDATA[f1]]> Baseband 50Hz Vdc DC bus voltage 1200V kpp Phase-locked loop proportional control parameters 44 KPIs Phase-locked loop integral control parameters 500 kip Current loop proportional control parameters 3.35 kii Current loop integral control parameters 315

[0133] Furthermore, the impedance measurement system circuit diagram is shown in Figure 4. The grid-connected inverter is kept running stably, and its port voltage and current signals are collected for a total of 50 seconds. The signals are divided into 50 groups, each with a length of 1 second. Fourier analysis is performed, and the average noise amplitude at each frequency is estimated.

[0134] Step 2: Measure the frequency-coupled impedance characteristics of the grid-connected inverter by injecting multi-sinusoidal disturbance signals, collect the voltage and current signals at the grid-connected inverter ports, and use Fourier analysis to obtain their spectrum characteristics.

[0135] The measurement frequency is set to: [10, 13, 16, 21, 27, 35, 41, 47, 51, 55, 61, 71, 89, 115, 144, 183, 234, 298, 379, 483, 616, 785, 990] Hz. The disturbance amplitude is set to 10 V for the first measurement, and the measurement accuracy index is ΔM tar =2dB, ΔP tar =15°. Design two sets of linearly independent three-phase multi-sinusoidal signals according to the steps and inject them into the grid-connected inverter under test.

[0136] like Figure 5 As shown, the normal operation of the grid-connected inverter can be maintained during the injection of the multi-sinusoidal disturbance signal. In addition, when the injection of the multi-sinusoidal disturbance signal stops, the system can still resume normal operation.

[0137] During the two linearly independent disturbance injection processes, the port voltage and current signals of the tested grid-connected inverter are sampled for 1 s respectively, and the sampled signals are subjected to Fourier analysis. According to the Fourier analysis results, the frequency f is determined. p V in Hz p 、V n ,I p ,I n , and the frequency is f p -2f1Hz V p2 、V n2 ,I p2 ,I n2 .

[0138] Step 3: Calculation of generalized signal-to-noise ratio index and evaluation of impedance measurement accuracy.

[0139] According to V p 、V n ,I p ,I n 、V p2 、V n2 ,I p2 ,I n2 The value of and the average value of the noise amplitude are substituted into equations (8) to (11) and (14) to estimate the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement. This index is substituted into the mathematical model of the frequency coupling characteristic measurement error (the preset impedance measurement error model), and the possible distribution range of the measurement error is determined according to equations (12) and (13), thereby obtaining the quantitative evaluation result of the frequency coupling characteristic measurement accuracy.

[0140] The error bar characterizes the possible distribution range of the error obtained by the evaluation, such as Figure 6 As shown in the figure, the error bars can represent the upper and lower limits of the measurement error, and the range of the error bars is negatively correlated with the measurement accuracy. Therefore, a quantitative evaluation of the impedance measurement accuracy under the frequency coupling effect is achieved. According to the accuracy evaluation results, the measurement accuracy of [35, 41, 47, 51, 55, 61] Hz has not yet reached the standard, and its amplitude needs to be redesigned for further measurement.

[0141] In summary, the method for evaluating the measurement accuracy of the frequency coupling characteristics of the grid-connected inverter proposed in the present application, compared with the existing signal-to-noise ratio index, the generalized signal-to-noise ratio index takes into account the interaction between multiple coupled frequency components caused by the frequency coupling characteristics, thereby accurately reflecting the measurement accuracy; in view of the uncertainty of the actual measurement noise amplitude and phase, based on the generalized signal-to-noise ratio index, a frequency coupling impedance characteristic measurement error model is established, and the possible maximum value of the error is used as a quantitative indicator of measurement accuracy. This indicator can reflect the possible distribution range of the measurement error, which is negatively correlated with the measurement accuracy level, thereby realizing the quantitative evaluation of the frequency coupling impedance measurement accuracy.

[0142] According to the evaluation method of the measurement accuracy of the frequency coupling characteristics of the grid-connected inverter proposed in the embodiment of the present application, by obtaining the first port voltage set and the first current set of the measured grid-connected inverter, the average noise amplitude distribution within the preset frequency range can be estimated; by injecting a preset multi-sinusoidal disturbance signal into the measured grid-connected inverter and obtaining the second port voltage set and the second current set, the second port voltage set and the second current set can be subjected to Fourier analysis, and the first voltage component group and the first current component group corresponding to the first preset frequency, and the second voltage component group and the second current component group corresponding to the second preset frequency are selected based on the first analysis result obtained; according to the first and second voltage component groups, the first and second current component groups and the average noise amplitude, the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement obtained based on the estimation is used to quantitatively evaluate the measurement accuracy of the frequency coupling characteristic. Thus, the problem that the prior art is difficult to evaluate the measurement accuracy of the frequency coupling characteristic under noise interference is solved, the stability misjudgment caused by the impedance measurement error is effectively avoided, and the reliability of the impedance measurement result in the actual system stability analysis is improved.

[0143] Next, a device for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter proposed in an embodiment of the present application will be described with reference to the accompanying drawings.

[0144] Figure 7 It is a block diagram of a device for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter according to an embodiment of the present application.

[0145] like Figure 7 As shown, the evaluation device 10 for measuring the frequency coupling characteristic of a grid-connected inverter includes: an estimation module 100 , a selection module 200 and an evaluation module 300 .

[0146] The estimation module 100 is used to obtain a first port voltage set and a first current set of the tested grid-connected inverter, and estimate the average noise amplitude of each frequency within a preset frequency range based on the first port voltage set and the first current set;

[0147] A selection module 200 is used to inject a preset multi-sinusoidal disturbance signal into the grid-connected inverter under test, and obtain a second port voltage set and a second current set of the grid-connected inverter under test, perform Fourier analysis on the second port voltage set and the second current set, and select a first voltage component group and a first current component group corresponding to a first preset frequency, and a second voltage component group and a second current component group corresponding to a second preset frequency based on the first analysis result obtained;

[0148] The evaluation module 300 is used to estimate the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement based on the first voltage component group, the first current component group, the second voltage component group, the second current component group and the average noise amplitude of each frequency, and quantitatively evaluate the frequency coupling characteristic measurement accuracy based on the generalized signal-to-noise ratio index.

[0149] According to one embodiment of the present application, the evaluation module 300 is specifically used for:

[0150] The generalized signal-to-noise ratio index is input into a preset impedance measurement error model to obtain a possible distribution range of the measurement error;

[0151] Based on the possible distribution range of measurement errors, the measurement accuracy of frequency coupling characteristics is quantitatively evaluated.

[0152] According to one embodiment of the present application, the preset impedance measurement error model is:

[0153]

[0154] Among them, ΔM 11 is the amplitude error, s Gi , S Gv Both are generalized signal-to-noise ratio indicators, ΔP 11 is the phase error.

[0155] According to one embodiment of the present application, the estimation module 100 is specifically configured to:

[0156] Grouping the first port voltage set and the first current set according to a preset grouping standard and then performing Fourier analysis to obtain a second analysis result;

[0157] According to the second analysis result, a preset kernel density estimation method is used to perform probability modeling on the noise amplitude data of each frequency to obtain the average noise amplitude of each frequency.

[0158] According to one embodiment of the present application, the generalized signal-to-noise ratio index is:

[0159]

[0160] Among them, I G is the equivalent current signal when calculating the frequency coupling characteristics, V G is the equivalent voltage signal when calculating the frequency coupling characteristics, E i 、E v All of them are signals containing noise components.

[0161] It should be noted that the aforementioned explanation of the embodiment of the method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter is also applicable to the device for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter of this embodiment, and will not be repeated here.

[0162] According to the evaluation device for measuring the frequency coupling characteristics of the grid-connected inverter proposed in the embodiment of the present application, by obtaining the first port voltage set and the first current set of the measured grid-connected inverter, the average noise amplitude distribution within the preset frequency range can be estimated; by injecting a preset multi-sinusoidal disturbance signal into the measured grid-connected inverter and obtaining the second port voltage set and the second current set, the second port voltage set and the second current set can be subjected to Fourier analysis, and the first voltage component group and the first current component group corresponding to the first preset frequency, and the second voltage component group and the second current component group corresponding to the second preset frequency are selected based on the first analysis result obtained; according to the first and second voltage component groups, the first and second current component groups and the average noise amplitude, the generalized signal-to-noise ratio index of the frequency coupling characteristic measurement obtained by estimation is used to quantitatively evaluate the frequency coupling characteristic measurement accuracy. Thus, the problem that the prior art is difficult to evaluate the frequency coupling characteristic measurement accuracy under noise interference is solved, the stability misjudgment caused by the impedance measurement error is effectively avoided, and the reliability of the impedance measurement result in the actual system stability analysis is improved.

[0163] Figure 8 A schematic diagram of the structure of an electronic device provided in an embodiment of the present application. The electronic device may include:

[0164] A memory 801 , a processor 802 , and a computer program stored in the memory 801 and executable on the processor 802 .

[0165] When the processor 802 executes the program, the method for evaluating the measurement accuracy of the frequency coupling characteristics of the grid-connected inverter provided in the above embodiment is implemented.

[0166] Furthermore, the electronic device further comprises:

[0167] The communication interface 803 is used for communication between the memory 801 and the processor 802 .

[0168] The memory 801 is used to store computer programs that can be executed on the processor 802 .

[0169] The memory 801 may include a high-speed RAM (Random Access Memory) memory, and may also include a non-volatile memory, such as at least one disk memory.

[0170] If the memory 801, the processor 802 and the communication interface 803 are implemented independently, the communication interface 803, the memory 801 and the processor 802 can be connected to each other through a bus and communicate with each other. The bus can be an ISA (Industry Standard Architecture) bus, a PCI (Peripheral Component Interconnect) bus or an EISA (Extended Industry Standard Architecture) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Figure 8 Only one thick line is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0171] Optionally, in a specific implementation, if the memory 801, the processor 802 and the communication interface 803 are integrated on a chip, the memory 801, the processor 802 and the communication interface 803 can communicate with each other through an internal interface.

[0172] The processor 802 may be a CPU (Central Processing Unit), or an ASIC (Application Specific Integrated Circuit), or one or more integrated circuits configured to implement the embodiments of the present application.

[0173] An embodiment of the present application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter.

[0174] An embodiment of the present invention further provides a computer program product, including a computer program, which, when executed by a processor, implements the above method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter.

[0175] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0176] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0177] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter, characterized in that: The following steps are involved: Acquire a first port voltage set and a first current set of the tested grid-connected inverter, and estimate an average noise amplitude of each frequency within a preset frequency range based on the first port voltage set and the first current set; Injecting a preset multi-sinusoidal disturbance signal into the tested grid-connected inverter, and obtaining a second port voltage set and a second current set of the tested grid-connected inverter, performing Fourier analysis on the second port voltage set and the second current set, and selecting a first voltage component group and a first current component group corresponding to a first preset frequency, and a second voltage component group and a second current component group corresponding to a second preset frequency based on the first analysis result obtained; A generalized signal-to-noise ratio index for frequency coupling characteristic measurement is estimated based on the first voltage component group, the first current component group, the second voltage component group, the second current component group and the average noise amplitude of each frequency, and the frequency coupling characteristic measurement accuracy is quantitatively evaluated based on the generalized signal-to-noise ratio index.

2. The method according to claim 1, characterized in that The quantitative evaluation of the frequency coupling characteristic measurement accuracy based on the generalized signal-to-noise ratio indicator includes: Inputting the generalized signal-to-noise ratio index into a preset impedance measurement error model to obtain a possible distribution range of the measurement error; Based on the possible distribution range of the measurement error, the measurement accuracy of the frequency coupling characteristics is quantitatively evaluated.

3. The method according to claim 2, characterized in that The preset impedance measurement error model is: Among them, ΔM 11 is the amplitude error, S Gi and S Gv are the generalized signal-to-noise ratio indicators, ΔP 11 is the phase error.

4. The method according to claim 1, characterized in that The estimating an average noise amplitude of each frequency within a preset frequency range based on the first port voltage set and the first current set includes: Grouping the first port voltage set and the first current set according to a preset grouping standard and then performing Fourier analysis to obtain a second analysis result; According to the second analysis result, a preset kernel density estimation method is used to perform probability modeling on the noise amplitude data of each frequency to obtain the average noise amplitude of each frequency.

5. The method according to claim 1, characterized in that The generalized signal-to-noise ratio index is: Among them, I G is the equivalent current signal when calculating the frequency coupling characteristics, V G is the equivalent voltage signal when calculating the frequency coupling characteristics, E i and E v All of them are signals containing noise components.

6. A device for evaluating the measurement accuracy of frequency coupling characteristics of a grid-connected inverter, characterized in that: include: An estimation module, used for acquiring a first port voltage set and a first current set of the tested grid-connected inverter, and estimating an average noise amplitude of each frequency within a preset frequency range based on the first port voltage set and the first current set; A selection module, used for injecting a preset multi-sinusoidal disturbance signal into the tested grid-connected inverter, and obtaining a second port voltage set and a second current set of the tested grid-connected inverter, performing Fourier analysis on the second port voltage set and the second current set, and selecting a first voltage component group and a first current component group corresponding to a first preset frequency, and a second voltage component group and a second current component group corresponding to a second preset frequency based on the first analysis result obtained; An evaluation module is used to estimate a generalized signal-to-noise ratio index for frequency coupling characteristic measurement based on the first voltage component group, the first current component group, the second voltage component group, the second current component group and the average noise amplitude of each frequency, and quantitatively evaluate the frequency coupling characteristic measurement accuracy based on the generalized signal-to-noise ratio index.

7. The device according to claim 6, characterized in that The evaluation module is specifically used for: Inputting the generalized signal-to-noise ratio index into a preset impedance measurement error model to obtain a possible distribution range of the measurement error; Based on the possible distribution range of the measurement error, the measurement accuracy of the frequency coupling characteristics is quantitatively evaluated.

8. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter as described in any one of claims 1 to 5.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: The program is executed by a processor to implement the method for evaluating the measurement accuracy of the frequency coupling characteristics of a grid-connected inverter as described in any one of claims 1 to 5.

10. A computer program product, characterized in that It comprises a computer program, which, when executed by a processor, is used to implement the method for evaluating the measurement accuracy of the frequency coupling characteristics of the grid-connected inverter according to any one of claims 1 to 5.

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