Method and system for calculating power grid impedance based on sliding window

Abstract

The invention provides a method and a system for calculating power grid impedance based on a sliding window. The method comprises the following steps: setting a signal category and a signal length of a disturbance signal to be injected into an access power grid by a new energy station; according to the signal category, the new energy field station injects orthogonal signals with the same amplitude and frequency into a d axis and a q axis of an access power grid at the same time as disturbance signals; acquiring three-phase current data and voltage data of the signal length at a grid connection point; and calculating the power grid impedance at the target frequency based on a sliding window according to the three-phase current data and the voltage data. According to the method and the system, the electric energy quality during the disturbance injection period is improved, the noise interference resistance of impedance calculation is improved, and it is well ensured that an impedance measurement result with rapidness and accuracy is obtained within a wide frequency range.

Description

Technical Field

[0001] This invention relates to the field of new energy access and control in power grids, and more specifically, to a method and system for calculating power grid impedance based on a sliding window. Background Technology

[0002] Impedance analysis is a commonly used method for stability analysis of grid-connected inverters in new energy sources. It treats the grid-connected inverter and the grid as equivalent subsystems capable of independent and stable operation. After obtaining the impedances of both the inverter and the grid, the stability of the grid-connected system is analyzed using impedance stability criteria. However, due to the large number of devices and lines connected to the grid, it is difficult to model the impedance of each device, and the real-time status of each device is unavailable. Therefore, grid impedance is difficult to obtain through modeling and is generally obtained through measurement.

[0003] Based on the requirements for real-time and rapid measurement of power grid impedance, online measurement methods are currently developing rapidly. Depending on whether a disturbance signal is injected into the power grid, online measurement methods can be divided into passive and active measurement. Passive online measurement methods do not inject disturbances; they only utilize the inherent harmonics or noise signals of the system to measure the power grid impedance. Therefore, they have no impact on the power quality of the power grid, but they are generally difficult to accurately measure the power grid impedance information, and it is impossible to independently design the spectral distribution of the disturbance signal. Active online measurement measures the power grid impedance by injecting a disturbance signal to excite the power grid response. Depending on the type of disturbance signal injected, it can be divided into single-frequency signal injection and wide-frequency signal injection methods. Single-frequency signals contain only harmonics of one frequency, resulting in concentrated signal power and a high signal-to-noise ratio, thus achieving high measurement accuracy. However, to measure impedance over a wide frequency range, disturbances need to be injected sequentially, consuming a long measurement time. Wide-frequency signal injection injects a signal with rich frequency components at once, allowing for the simultaneous measurement of power grid impedance over a wider frequency range, resulting in higher measurement efficiency. Discrete Interval Binary Sequences (DIBS) are wide-frequency signals with controllable spectrum, offering high flexibility and suitability for wide-frequency grid impedance measurements with a specified spectral distribution. However, because the perturbation power of the DIBS signal is not zero at frequencies outside the specified range, it is unsuitable for scenarios such as low frequencies where high perturbation amplitude is required but harmonic current content is strictly controlled. Therefore, using a single perturbation signal makes it difficult to achieve both speed and accuracy across a wide frequency range. Furthermore, considering that the harmonic current injected during active online measurement can impact power quality, the design of the injected signal should aim to minimize this impact.

[0004] In impedance calculation, there are two commonly used methods. One is to acquire and extract the target frequency f after applying the perturbation. t Positive and negative sequence currents and voltage phasors I at the locationa (f t )=|I a (f t )|∠I a (f t V a (f t )=|V a (f t )|∠V a (f t ), and according to Calculate the positive and negative sequence impedances, where a = pos represents the positive sequence component and a = neg represents the negative sequence component. This method assumes there are no background harmonics at the target frequency before the perturbation is applied, therefore it will have a large error when background harmonics are present. Another approach is to separately acquire and extract the target frequency f before and after the perturbation is applied. t Positive and negative sequence currents and voltage phasors I at the location a,before (f t ), I a,after (f t V a,before (f t V a,after (f t To reduce the impact of background harmonics, the current and voltage phasors before the perturbation are applied are used. Where a = pos represents the positive sequence component, a = neg represents the negative sequence component, the subscript "before" represents the phasor before the perturbation is applied, and "after" represents the phasor after the perturbation is applied; this method reduces the influence of background harmonics to a certain extent, but when the background harmonics change before and after the perturbation is applied or when the noise of the collected data is large, this single-point calculation method may introduce large errors and has poor anti-interference ability. Summary of the Invention

[0005] To address the technical challenges of existing methods for measuring the equivalent impedance of renewable energy grid connections, which, while passive online measurement methods do not affect the power quality of the grid, generally struggle to accurately measure the grid's impedance information and cannot independently design the spectral distribution of disturbance signals, and active online measurement methods, which rely solely on single-frequency or wideband disturbances, fail to achieve both speed and accuracy across a wide frequency range, this invention provides a method and apparatus for calculating grid impedance based on a sliding window.

[0006] According to one aspect of the present invention, the present invention provides a method for calculating grid impedance based on a sliding window, comprising:

[0007] The signal type and signal length of the disturbance signal to be injected into the grid by the new energy power station are set, wherein the disturbance signal is a current signal or a voltage signal;

[0008] According to the aforementioned signal category, the new energy power station simultaneously injects orthogonal signals with the same amplitude and frequency into the grid on both the d-axis and q-axis as disturbance signals. The amplitude of the injected disturbance signal is limited by the harmonic current generated at the grid connection point, and the frequency is determined based on the target frequency of the grid impedance to be calculated and the grid frequency.

[0009] Three-phase current and voltage data of the signal length are collected at the grid connection point;

[0010] Based on the three-phase current and voltage data, the grid impedance at the target frequency is calculated using a sliding window.

[0011] According to another aspect of the present invention, the present invention provides a system for calculating grid impedance based on a sliding window, the system comprising:

[0012] The signal setting module is used to set the signal type and signal length of the disturbance signal that the new energy power station intends to inject into the grid, wherein the disturbance signal is a current signal or a voltage signal;

[0013] The disturbance injection module is used to inject orthogonal signals with the same amplitude and frequency into the grid connection at the new energy power station simultaneously on the d-axis and q-axis as disturbance signals according to the signal category. The amplitude of the injected disturbance signal is limited by the harmonic current generated at the grid connection point, and the frequency is determined according to the target frequency of the grid impedance to be calculated and the grid frequency.

[0014] The data acquisition module is used to acquire three-phase current and voltage data of the signal length at the grid connection point;

[0015] The impedance calculation module is used to calculate the grid impedance at the target frequency based on the three-phase current data and voltage data using a sliding window.

[0016] According to another aspect of the present invention, a computer-readable storage medium is provided, the storage medium storing a computer program for performing the methods described in any of the above aspects of the present invention.

[0017] According to another aspect of the present invention, an electronic device is provided, the electronic device comprising: a processor; a memory for storing executable instructions of the processor; the processor being configured to read the executable instructions from the memory and execute the instructions to implement the method described in any of the preceding aspects of the present invention.

[0018] The present invention discloses a method and system for calculating grid impedance based on a sliding window. The method includes setting the signal type and length of a disturbance signal to be injected into the grid by a renewable energy power plant; injecting orthogonal signals with the same amplitude and frequency simultaneously along the d-axis and q-axis as disturbance signals according to the signal type; collecting three-phase current and voltage data of the specified signal length at the grid connection point; and calculating the grid impedance at the target frequency based on the three-phase current and voltage data using a sliding window. The method and system inject different types of disturbance signals depending on the frequency band of the target frequency, and the disturbance signal injection method involves simultaneously injecting orthogonal signals with the same amplitude and frequency along the d-axis and q-axis. Furthermore, by employing a sliding window algorithm and using multi-point calculation to determine the impedance at the target frequency, the power quality during disturbance injection and the impedance calculation's resistance to noise interference are improved, effectively ensuring that impedance measurement results with both speed and accuracy are obtained over a wide frequency range. Attached Figure Description

[0019] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0020] Figure 1 This is a flowchart of a method for calculating grid impedance based on a sliding window according to a preferred embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the signal length of the injected disturbance signal according to a preferred embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of a system for calculating grid impedance based on a sliding window according to a preferred embodiment of the present invention;

[0023] Figure 4 This is a schematic diagram of the structure of an electronic device according to a preferred embodiment of the present invention. Detailed Implementation

[0024] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0025] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0026] Exemplary methods

[0027] Figure 1 This is a flowchart of a method for calculating grid impedance based on a sliding window according to a preferred embodiment of the present invention. Figure 1 As shown, the method for calculating grid impedance based on a sliding window according to this preferred embodiment starts from step 101.

[0028] In step 101, the signal type and signal length of the disturbance signal to be injected into the grid by the new energy power station are set, wherein the disturbance signal is a current signal or a voltage signal.

[0029] In this preferred embodiment, when a new energy power station applies a disturbance signal to the grid in the current control loop, the disturbance signal is generally a current signal; when the disturbance signal is applied in the voltage control loop, the disturbance signal is generally a voltage signal.

[0030] Preferably, the step of setting the signal type and signal length of the disturbance signal to be injected into the grid by the new energy power station includes:

[0031] Based on the target frequency for calculating the grid impedance, determine the signal type of the disturbance signal to be injected, where:

[0032] When the target frequency is within the first frequency range and the second frequency range, let the signal type of the injected disturbance signal be a single sine wave, where the first frequency range is [0.1, f1] and the second frequency range is [f...]. b -f2,f b +f2],f b f1 and f2 are positive numbers not greater than 10, where f1 is the fundamental frequency.

[0033] When the target frequency is located in the third frequency range [f1, f2] b -f2] and the fourth frequency range [f b +f2,f max When the injected disturbance signal is classified as a discrete-interval binary sequence signal, f max The target frequency maximum value of the grid impedance is to be calculated;

[0034] The signal length of the disturbance signal to be injected is determined based on the set frequency resolution, the sliding window time interval, and the number of sliding windows. The formula for calculating the signal length is as follows:

[0035] T2 = T1 + Δt

[0036]

[0037] Δt=Δw*(N-1)

[0038] In the formula, T1 is the sliding window length, T2 is the signal length of the disturbance signal to be injected, x is the set frequency resolution, Δw is the sliding window time interval, and N is the number of sliding windows.

[0039] A single sinusoidal signal, containing only one frequency, concentrates all the power of the disturbance signal at that frequency, resulting in a high signal-to-noise ratio and high measurement accuracy. However, it has low measurement efficiency because it can only measure impedance at a single frequency point at a time. Discrete-interval binary sequence signals (DIBS signals), designed from a frequency domain perspective based on a specified frequency, allow for flexible designation of multiple target frequency points, concentrating power primarily at the specified frequency. Furthermore, the time-domain amplitude of the signal does not increase with the number of target frequency points, leading to higher measurement efficiency. However, DIBS signals also have power at other frequencies outside the target frequency. Considering that a larger disturbance is needed to obtain accurate results in low-frequency impedance measurements, and to avoid the risk of oscillation from injected harmonic currents, the harmonic current in the low-frequency range needs to be maintained at a low level. Therefore, a single sinusoidal signal injection method is used for impedance measurement in the low-frequency range. Impedance near the fundamental frequency also requires a larger disturbance to obtain accurate results; therefore, a single sinusoidal signal injection method is also used for impedance measurement near the fundamental frequency. To improve measurement efficiency, impedance measurements in the sub / supersynchronous and high-frequency bands are performed by injecting DIBS disturbance signals. Therefore, this invention selects the signal category based on the target frequency range when setting the signal category of the injected disturbance signal. Single sinusoidal signals are injected in the first and second frequency ranges corresponding to the low-frequency band and the fundamental frequency, while DIBS signals are injected in the third and fourth frequency ranges corresponding to the sub / supersynchronous and high-frequency bands excluding the fundamental frequency. For DIBS signals, the more target frequencies injected at once, the lower the power at each frequency. To ensure measurement accuracy, the number of frequencies injected at once needs to be limited. Considering the attenuation effect of control and sampling on high-frequency signals, the higher the frequency, the larger the amplitude of the injected signal needs to be. Therefore, as the frequency increases, the number of frequencies injected at once needs to be reduced.

[0040] Figure 2 This is a schematic diagram illustrating the signal length of the injected disturbance signal according to a preferred embodiment of the present invention. Figure 2As shown, in order to improve the accuracy of impedance calculation, the present invention increases the length of the injected disturbance signal from the length T1 calculated according to the frequency resolution to T2 = T1 + Δt, and uses a sliding window to obtain a series of current and voltage frequency-domain data of the target frequency within the time of Δt, where Δt is determined according to the set sliding window time interval Δw and the number of sliding windows N. The sliding window time interval is determined according to the target frequency of the impedance to be calculated. For low-frequency data that changes slowly with time, a larger sliding window time interval can be set, while for high-frequency data that changes quickly, a smaller sliding window time interval can be set. The more the number of sliding windows set, the stronger the anti-noise interference ability of the impedance calculation method based on the sliding window, but the longer the required impedance measurement time. Therefore, when setting the number of sliding windows N, it is necessary to comprehensively consider the requirements of calculation accuracy and measurement time to determine.

[0041] In step 102, according to the signal category, the new energy power station injects orthogonal signals with the same amplitude and frequency in the d-axis and q-axis into the grid connected to the power grid as disturbance signals. Among them, the amplitude of the injected disturbance signal is limited by the harmonic current generated at the grid connection point, and the frequency is determined according to the target frequency of the power grid impedance to be calculated and the power grid frequency.

[0042] Preferably, the step of injecting orthogonal signals with the same amplitude and frequency in the d-axis and q-axis into the grid connected to the power grid as disturbance signals according to the signal category includes:

[0043] When the target frequency f p > f0 and calculating the positive sequence impedance of the target frequency, inject disturbance signals with the same amplitude and a frequency of f p - f0, and the phase of the q-axis lags behind the d-axis in the d-axis and q-axis simultaneously, where f0 is the power grid frequency;

[0044] When the target frequency f p < f0 and calculating the positive sequence impedance of the target frequency, inject disturbance signals with the same amplitude and a frequency of f0 - f p , and the phase of the d-axis lags behind the q-axis in the d-axis and q-axis simultaneously;

[0045] When calculating the negative sequence impedance of the target frequency f p , inject disturbance signals with the same amplitude and a frequency of f p + f0, and the phase of the d-axis lags behind the q-axis in the d-axis and q-axis simultaneously.

[0046] In renewable energy grid-connected inverters or static var generators configured in power plants, after acquiring three-phase signals, coordinate transformation and decoupling are performed for separate control on the d-axis and q-axis. When performing impedance calculations, the acquired three-phase signals are typically converted to positive and negative sequence for calculation. To obtain the target frequency disturbance signal in the positive and negative sequence components, taking the application of a disturbance current in the current control loop as an example, this illustrates the specific situation where a renewable energy power plant simultaneously injects orthogonal signals of the same amplitude and frequency into the grid along both the d-axis and q-axis.

[0047] The transformation formula from the dq coordinate system to the abc three-phase stationary coordinate system is:

[0048]

[0049] Among them, i a i b i c The currents of the three phases a, b, and c are respectively, and θ grid Let i be the phase angle of the power grid. d i q Let be the d-axis current and the q-axis current, respectively. Assuming the initial phase of the power grid is θ0 and the grid frequency is f0, then we have...

[0050] θ grid =2πf0t+θ0 (2)

[0051] The formula for calculating the positive and negative sequence components from the three-phase stationary coordinate system abc is:

[0052]

[0053] Among them, i pos i neg These are the positive-sequence current component and the negative-sequence current component. j is the imaginary number sign, j 2 =-1.

[0054] By combining equations (1), (2), and (3), we can obtain:

[0055]

[0056] According to equation (4), if an amplitude of I is applied on the d-axis... d The frequency is f d Disturbance signal An amplitude of [value] will be generated in the positive sequence current. Frequency f d A disturbance of +f0 is generated simultaneously in the negative sequence current with an amplitude of... Frequency f d -f0 perturbation. If, in addition to applying a perturbation along the d-axis, a perturbation with the same amplitude and frequency but a phase lag along the q-axis is also applied... perturbation Then, a perturbation of magnitude I d and frequency f d + f0 will be generated on the positive-sequence current, and no perturbation will be generated on the negative-sequence current.

[0057] Therefore, in order to measure the positive- and negative-sequence impedances at frequency f p while minimizing the impact of perturbations on power quality to the greatest extent, the specific method of simultaneously injecting orthogonal signals of the same magnitude and frequency on the d-axis and q-axis in this preferred embodiment is as follows:

[0058] When the target frequency f p > f0 and calculating the positive-sequence impedance of the target frequency, a perturbation current of the same magnitude and frequency f p - f0 and with the q-axis phase lagging the d-axis is simultaneously injected on the d-axis and q-axis;

[0059] When the target frequency f p < f0 and calculating the positive-sequence impedance of the target frequency, a perturbation current of the same magnitude and frequency f0 - f p and with the d-axis phase lagging the q-axis is simultaneously injected on the d-axis and q-axis;

[0060] When calculating the negative-sequence impedance of the target frequency f p a perturbation current of the same magnitude and frequency f p + f0 and with the d-axis phase lagging the q-axis is simultaneously injected on the d-axis and q-axis.

[0061] Preferably, the magnitude of the injected perturbation signal is limited by the harmonic current generated at the point of common coupling, including:

[0062] The harmonic current generated when the target frequency is in the first frequency range is not greater than 1% of the fundamental current, and the harmonic current generated when the target frequency is in the second to fourth frequency ranges is not greater than 2% of the fundamental current.

[0063] In step 103, three-phase current data and voltage data of the signal length are collected at the point of common coupling.

[0064] In this preferred embodiment, the collection of three-phase current data and voltage data of the signal length at the point of common coupling occurs after the new energy power station injects a perturbation signal into the connected power grid.

[0065] In step 104, based on the three-phase current data and voltage data, the grid impedance at the target frequency is calculated using a sliding window.

[0066] Preferably, the step of calculating the grid impedance at the target frequency based on the three-phase current data and voltage data using a sliding window includes:

[0067] Calculate the positive / negative sequence current and voltage data based on the three-phase current and voltage data;

[0068] With a sliding window length of T1 seconds and a sliding window time interval of Δw seconds, a Fast Fourier Transform is performed on the positive / negative sequence current data and voltage data to obtain N sets of positive / negative sequence current frequency domain data I at the target frequency. k =[I k,1 ,I k,2 ,...,I k,N ] T and voltage frequency domain data V k =[V k,1 V k,2 ,...,V k,N ] T Where k = pos represents the positive sequence component, and k = neg represents the negative sequence component. Each set of current frequency domain data contains positive / negative sequence current data at M target frequencies. Each set of voltage frequency domain data contains positive / negative sequence voltage data at M target frequencies. 1≤i≤N, This represents the positive / negative sequence current at the m-th target frequency obtained after performing an FFT on the data within the i-th sliding window. This represents the positive / negative sequence voltage of the m-th target frequency obtained after performing FFT on the data within the i-th sliding window;

[0069] Based on the positive / negative sequence current frequency domain data I at N sets of target frequencies k and voltage frequency domain data V k Calculate the positive / negative sequence current increment data and voltage increment data at the target frequency respectively;

[0070] Based on the positive / negative sequence current increment data and voltage increment data at the target frequency, the positive / negative sequence grid impedance at the target frequency is calculated using a sliding window.

[0071] Preferably, the calculation formulas for the positive and negative sequence current data and voltage data based on the three-phase current data and voltage data are as follows:

[0072]

[0073] In the formula, i pos i neg These represent the positive-sequence current component and the negative-sequence current component, i a i b and i cThese are the three-phase currents, u, collected at the grid connection point after the injection of the disturbance signal. pos u neg These are the positive-sequence voltage component and the negative-sequence voltage component, respectively. a u b and u c These are the three-phase voltages collected at the grid connection point after the injection of the disturbance signal. j is the imaginary number sign, j 2 =-1.

[0074] Preferably, the step of using N sets of positive / negative sequence current frequency domain data I at the target frequency... k and voltage frequency domain data V k The positive / negative sequence current increment and voltage increment data at the target frequency are calculated separately using the following formulas:

[0075]

[0076] In the formula, and These are the positive / negative sequence current increment data and voltage increment data at the m-th target frequency, respectively.

[0077] In this preferred embodiment, considering that noise accompanies the sampling process of current and voltage signals, calculating impedance using only the perturbation increment of a single voltage and current signal can easily introduce errors caused by sampling noise. Therefore, to improve the accuracy of the calculation results, this preferred embodiment uses an impedance calculation method based on a sliding window. A series of perturbed current and voltage frequency domain data are obtained using a sliding window, and impedance calculation is performed based on this series of data to minimize the impact of noise.

[0078] Preferably, the step of calculating the positive / negative sequence grid impedance at the target frequency based on the incremental data using a sliding window includes:

[0079] The moving average method is used to calculate the positive / negative sequence grid impedance at the m-th target frequency. The formula is as follows:

[0080]

[0081] In the formula, The positive / negative sequence grid impedance at the m-th target frequency; or

[0082] The positive / negative grid impedance at the m-th target frequency is calculated using the least squares method, and the formula is as follows:

[0083]

[0084] In the formula, This represents the estimated positive / negative sequence grid impedance at the m-th target frequency.

[0085] In this preferred embodiment, when calculating the positive / negative grid impedance at the m-th target frequency using the least squares method, the relationship between the grid impedance at the m-th target frequency and the current and voltage increments is as follows:

[0086]

[0087] In the formula, e is the error matrix. Let be the positive / negative sequence grid impedance at the m-th target frequency. Then, according to least squares theory, we can obtain... The estimated values ​​are as follows:

[0088]

[0089] The preferred embodiment of the method for calculating grid impedance based on a sliding window involves new energy power plants injecting different types of disturbance signals into the grid connection based on the target frequency range in which the grid impedance to be calculated is located. After the disturbance signal is injected, the grid impedance at the target frequency is calculated based on the sliding window averaging method or the least squares method, using the three-phase current and voltage data collected at the grid connection point. This improves the power quality during the disturbance injection period and the impedance calculation's ability to resist noise interference, effectively ensuring that impedance measurement results with both speed and accuracy are obtained over a wide frequency range.

[0090] Exemplary System

[0091] Figure 3 This is a schematic diagram of a system for calculating grid impedance based on a sliding window according to a preferred embodiment of the present invention. Figure 3 As shown, the system 300 for calculating grid impedance based on a sliding window according to this preferred embodiment includes:

[0092] The signal setting module 301 is used to set the signal type and signal length of the disturbance signal that the new energy power station intends to inject into the grid, wherein the disturbance signal is a current signal or a voltage signal;

[0093] The disturbance injection module 302 is used to inject orthogonal signals with the same amplitude and frequency into the grid connection at the new energy power station according to the signal category. The amplitude of the injected disturbance signal is limited by the harmonic current generated at the grid connection point, and the frequency is determined according to the target frequency of the grid impedance to be calculated and the grid frequency.

[0094] Data acquisition module 303 is used to acquire three-phase current data and voltage data of the signal length at the grid connection point;

[0095] Impedance calculation module 304 is used to calculate the grid impedance at the target frequency based on the three-phase current data and voltage data using a sliding window.

[0096] Preferably, the signal setting module 301 sets the signal type and signal length of the disturbance signal to be injected by the new energy power station into the grid, including:

[0097] Based on the target frequency for calculating the grid impedance, determine the signal type of the disturbance signal to be injected, where:

[0098] When the target frequency is within the first frequency range and the second frequency range, let the signal type of the injected disturbance signal be a single sine wave, where the first frequency range is [0.1, f1] and the second frequency range is [f...]. b -f2,f b +f2],f b f1 and f2 are positive numbers not greater than 10, where f1 is the fundamental frequency.

[0099] When the target frequency is located in the third frequency range [f1, f2] b -f2] and the fourth frequency range [f b +f2,f max When the injected disturbance signal is classified as a discrete-interval binary sequence signal, f max The target frequency maximum value of the grid impedance is to be calculated;

[0100] The signal length of the disturbance signal to be injected is determined based on the set frequency resolution, the sliding window time interval, and the number of sliding windows. The formula for calculating the signal length is as follows:

[0101] T2 = T1 + Δt

[0102]

[0103] Δt=Δw*(N-1)

[0104] In the formula, T1 is the sliding window length, T2 is the signal length of the disturbance signal to be injected, x is the set frequency resolution, Δw is the sliding window time interval, and N is the number of sliding windows.

[0105] Preferably, the disturbance injection module 302, according to the signal category, allows the new energy power station to simultaneously inject orthogonal signals with the same amplitude and frequency on both the d-axis and q-axis as disturbance signals into the grid connection, including:

[0106] When the target frequency f p >f0, and when calculating the positive sequence impedance at the target frequency, simultaneously inject the same amplitude and frequency f on both the d-axis and q-axis. p -f0, and the q-axis phase lags the d-axis. perturbation signal, where f0 is the grid frequency;

[0107] When the target frequency f p < f0, and when calculating the positive sequence impedance of the target frequency, a perturbation signal with the same amplitude and a frequency of f0 - f is injected simultaneously on the d-axis and the q-axis p , and the phase of the d-axis lags behind the q-axis ;

[0108] When calculating the negative sequence impedance of the target frequency f p , a perturbation signal with the same amplitude and a frequency of f p + f0 is injected simultaneously on the d-axis and the q-axis, and the phase of the d-axis lags behind the q-axis .

[0109] Preferably, the amplitude of the perturbation signal injected by the perturbation injection module 302 is limited by the harmonic current generated at the point of common coupling, including:

[0110] The harmonic current generated when the target frequency is in the first frequency range is not greater than 1% of the fundamental current, and the harmonic current generated when the target frequency is in the second to fourth frequency ranges is not greater than 2% of the fundamental current.

[0111] Preferably, the impedance calculation module 304 calculates the grid impedance at the target frequency based on the three-phase current data and voltage data using a sliding window, including:

[0112] Calculating the positive / negative sequence current data and voltage data based on the three-phase current data and voltage data;

[0113] Performing a fast Fourier transform on the positive / negative sequence current data and voltage data with a sliding window length of T1 seconds and a sliding window time interval of Δw seconds to obtain N sets of positive / negative sequence current frequency domain data I k = [I k,1 , I k,2 ,..., I k,N T and voltage frequency domain data V k = [V k,1 , V k,2 ,..., V k,N T , where when k = pos, it represents the positive sequence component, and when k = neg, it represents the negative sequence component. Each set of current frequency domain data contains M positive / negative sequence current data of the target frequency Each set of voltage frequency domain data contains M positive / negative sequence voltage data of the target frequency 1 ≤ i ≤ N, This represents the positive / negative sequence current at the m-th target frequency obtained after performing an FFT on the data within the i-th sliding window. This represents the positive / negative sequence voltage of the m-th target frequency obtained after performing FFT on the data within the i-th sliding window;

[0114] Based on the positive / negative sequence current frequency domain data I at N sets of target frequencies k and voltage frequency domain data V k Calculate the positive / negative sequence current increment data and voltage increment data at the target frequency respectively;

[0115] Based on the positive / negative sequence current increment data and voltage increment data at the target frequency, the positive / negative sequence grid impedance at the target frequency is calculated using a sliding window.

[0116] Preferably, the impedance calculation module 304 calculates the positive and negative sequence current data and voltage data based on the three-phase current data and voltage data, and the calculation formulas are as follows:

[0117]

[0118] In the formula, i pos i neg These are the positive-sequence current component and the negative-sequence current component, i a i b and i c These are the three-phase currents, u, collected at the grid connection point after the injection of the disturbance signal. pos u neg These are the positive-sequence voltage component and the negative-sequence voltage component, respectively. a u b and u c These are the three-phase voltages collected at the grid connection point after the injection of the disturbance signal. j is the imaginary number sign, j 2 =-1.

[0119] Preferably, the impedance calculation module 304 calculates the impedance based on N sets of positive / negative sequence current frequency domain data I at the target frequency. k and voltage frequency domain data V k The positive / negative sequence current increment and voltage increment data at the target frequency are calculated separately using the following formulas:

[0120]

[0121] In the formula, and These are the positive / negative sequence current increment data and voltage increment data at the m-th target frequency, respectively.

[0122] Preferably, the impedance calculation module 304 calculates the positive / negative sequence grid impedance at the target frequency based on the incremental data and a sliding window, including:

[0123] The moving average method is used to calculate the positive / negative sequence grid impedance at the m-th target frequency. The formula is as follows:

[0124]

[0125] In the formula, The positive / negative sequence grid impedance at the m-th target frequency; or

[0126] The positive / negative grid impedance at the m-th target frequency is calculated using the least squares method, and the formula is as follows:

[0127]

[0128] In the formula, This represents the estimated positive / negative sequence grid impedance at the m-th target frequency.

[0129] The system for calculating grid impedance based on a sliding window described in this preferred embodiment and the method for calculating grid impedance based on a sliding window are identical in that, according to the set signal category, the new energy power station simultaneously injects orthogonal signals with the same amplitude and frequency into the grid along the d-axis and q-axis as disturbance signals, collects three-phase current and voltage data of a set signal length at the grid connection point, and calculates the grid impedance at the target frequency based on the three-phase current and voltage data using a sliding window. The technical effects achieved are also the same, and will not be repeated here.

[0130] Exemplary electronic devices

[0131] Figure 4 This is a schematic diagram of an electronic device according to a preferred embodiment of the present invention. The electronic device may be either or both of a first device and a second device, or a standalone device independent of them. The standalone device may communicate with the first device and the second device to receive the collected input signals from them. Figure 4 A block diagram of an electronic device according to an embodiment of the present disclosure is shown. Figure 4 As shown, the electronic device includes one or more processors 401 and memory 402.

[0132] The processor 401 may be a central processing unit (CPU) or other form of processing unit with data processing and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions.

[0133] Memory 402 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and processor 401 may execute the program instructions to implement the sliding window-based method for calculating grid impedance of the various embodiments disclosed above, and / or other desired functions. In one example, the electronic device may also include an input device 403 and an output device 404, which are interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0134] In addition, the input device 403 may also include, for example, a keyboard, a mouse, etc.

[0135] The output device 404 can output various information to the outside. The output device 404 may include, for example, a display, a speaker, a printer, and a communication network and its connected remote output devices, etc.

[0136] Of course, for the sake of simplicity, Figure 4 Only some of the components of the electronic device relevant to this disclosure are shown, omitting components such as buses, input / output interfaces, etc. In addition, the electronic device may include any other suitable components depending on the specific application.

[0137] Exemplary computer program products and computer-readable storage media

[0138] In addition to the methods and apparatus described above, embodiments of this disclosure may also be computer program products comprising computer program instructions that, when executed by a processor, cause the processor to perform the steps in the methods for calculating grid impedance based on a sliding window according to various embodiments of this disclosure as described in the "Exemplary Methods" section above.

[0139] The computer program product can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments of this disclosure. The programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on a user's computing device, partially on a user's computing device, as a standalone software package, partially on a user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0140] Furthermore, embodiments of this disclosure may also be computer-readable storage media storing computer program instructions that, when executed by a processor, cause the processor to perform the steps in the methods for calculating grid impedance based on a sliding window according to various embodiments of this disclosure as described in the "Exemplary Methods" section above.

[0141] The computer-readable storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may, for example, include, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatuses, or devices, or any combination thereof. More specific examples of readable storage media (a non-exhaustive list) include: electrical connections having one or more wires, portable disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0142] The basic principles of this disclosure have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this disclosure are merely examples and not limitations, and should not be considered as essential features of each embodiment of this disclosure. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the scope of this disclosure to the necessity of employing the aforementioned specific details for implementation.

[0143] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system embodiments, since they largely correspond to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0144] The block diagrams of devices, apparatuses, devices, and systems disclosed herein are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0145] The apparatus and methods of this disclosure may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the methods is for illustrative purposes only, and the steps of the methods of this disclosure are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, this disclosure may also be implemented as a program recorded on a recording medium, the program including machine-readable instructions for implementing the methods according to this disclosure. Thus, this disclosure also covers recording media storing programs for performing the methods according to this disclosure.

[0146] It should also be noted that in the apparatus, devices, and methods of this disclosure, the components or steps are decomposable and / or recombinable. Such decomposition and / or recombination should be considered equivalent to the present disclosure. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0147] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this disclosure to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A method for calculating grid impedance based on a sliding window, characterized in that: The method comprises: Setting the signal type and signal length of the disturbance signal to be injected by the new energy station into the access power grid, wherein the disturbance signal is a current signal or a voltage signal; According to the signal category, the new energy station simultaneously injects orthogonal signals with the same amplitude and frequency into the access grid on the d-axis and q-axis as disturbance signals, wherein the amplitude of the injected disturbance signal is limited by the harmonic current generated at the grid connection point, and the frequency is determined according to the target frequency of the grid impedance to be calculated and the grid frequency; Collect three-phase current data and voltage data of the signal length at the grid connection point; According to the three-phase current data and voltage data, the grid impedance at the target frequency is calculated based on a sliding window.

2. The method according to claim 1, characterized in that The signal type and signal length of the disturbance signal to be injected by the new energy station into the access power grid are set, including: According to the target frequency of the grid impedance to be calculated, the signal type of the disturbance signal to be injected is determined, where: When the target frequency is between the first frequency interval and the second frequency interval, the signal type of the injected disturbance signal is set to a single sine signal, wherein the first frequency interval is [0.1, f1], and the second frequency interval is [f b -f2,f b +f2],f b is the fundamental frequency, f1 and f2 are positive numbers not greater than 10; When the target frequency is in the third frequency interval [f1, f b -f2] and the fourth frequency interval [f b +f2,f max ], let the signal type of the injected disturbance signal be a discrete interval binary sequence signal, where f max The maximum value of the target frequency for calculating the grid impedance; The signal length of the disturbance signal to be injected is determined according to the set frequency resolution, sliding window time interval and number of sliding windows. The calculation formula of the signal length is: T2=T1+Δt Δt=Δw*(N-1) Where T1 is the sliding window length, T2 is the signal length of the disturbance signal to be injected, x is the set frequency resolution, Δw is the sliding window time interval, and N is the number of sliding windows.

3. The method according to claim 2, characterized in that According to the signal category, the new energy station simultaneously injects orthogonal signals with the same amplitude and frequency into the access grid on the d-axis and q-axis as disturbance signals, including: When the target frequency f p >f0, and when calculating the positive sequence impedance of the target frequency, the same amplitude is injected on the d-axis and q-axis at the same time, and the frequency is f p -f0, and the q-axis phase lags behind the d-axis The disturbance signal is: f0 is the grid frequency; When the target frequency is f p < f0, and when calculating the positive-sequence impedance of the target frequency, a perturbation signal with the same amplitude and a frequency of f0 - f is injected simultaneously on the d-axis and the q-axis p , and the phase of the d-axis lags behind that of the q-axis ; When calculating the target frequency f p When the negative sequence impedance is , the same amplitude and frequency f are injected into the d-axis and q-axis at the same time p +f0, and the d-axis phase lags behind the q-axis of the disturbance signal.

4. The method according to claim 2, characterized in that: The amplitude of the injected disturbance signal is limited by the harmonic current generated at the grid connection point, including: When the target frequency is in the first frequency interval, the harmonic current generated is no greater than 1% of the fundamental current; when the target frequency is in the second to fourth frequency intervals, the harmonic current generated is no greater than 2% of the fundamental current.

5. The method according to claim 2, characterized in that: The step of calculating the grid impedance at the target frequency based on a sliding window according to the three-phase current data and voltage data comprises: Calculate positive / negative sequence current data and voltage data according to the three-phase current data and voltage data; With a sliding window length of T1 seconds and a sliding window time interval of Δw seconds, the positive / negative sequence current data and voltage data are subjected to fast Fourier transform to obtain N groups of positive / negative sequence current frequency domain data I at the target frequency. k =[I k，1 , I k，2 ,…,I k，N ] T And voltage frequency domain data V k =[V k，1 , V k，2 , …, V k，N ] T , where when k = pos, it represents the positive sequence component, and when k = neg, it represents the negative sequence component. Each set of current frequency domain data contains M positive / negative sequence current data of the target frequency. Each set of voltage frequency domain data contains positive / negative sequence voltage data of M target frequencies It represents the positive / negative sequence current of the mth target frequency obtained after FFT of the data in the i-th sliding window. represents the positive / negative sequence voltage of the mth target frequency obtained after performing FFT on the data in the i-th sliding window; According to the positive / negative sequence current frequency domain data I of N groups at the target frequency k And voltage frequency domain data V k respectively calculating the positive / negative sequence current increment data and voltage increment data at the target frequency; According to the positive / negative sequence current increment data and voltage increment data at the target frequency, the positive / negative sequence grid impedance at the target frequency is calculated based on a sliding window.

6. The method according to claim 5, characterized in that The positive and negative sequence current data and voltage data are calculated according to the three-phase current data and voltage data, and the calculation formulas are: In the formula, i pos 、i neg are the positive sequence current component and the negative sequence current component respectively, i a 、i b and i c They are the three-phase currents collected at the grid connection point after the disturbance signal is injected, u pos 、u neg are the positive sequence voltage component and the negative sequence voltage component, respectively, u a 、u b and u c They are the three-phase voltages collected at the grid connection point after the disturbance signal is injected, j is the imaginary number symbol, j 2 =-1.

7. The method according to claim 5, characterized in that According to the N groups of positive / negative sequence current frequency domain data I at the target frequency k And voltage frequency domain data V k The positive / negative sequence current increment data and voltage increment data at the target frequency are calculated respectively, and the calculation formula is: In the formula, and They are respectively the positive / negative sequence current increment data and voltage increment data at the mth target frequency.

8. The method according to claim 7, characterized in that The step of calculating the positive / negative sequence grid impedance at the target frequency based on the sliding window according to the incremental data includes: The moving average method is used to calculate the positive / negative sequence grid impedance at the mth target frequency, and the calculation formula is: In the formula, is the positive / negative sequence grid impedance at the mth target frequency; or The least square method is used to calculate the positive / negative grid impedance at the mth target frequency, and the calculation formula is: In the formula, is the estimated value of the positive / negative sequence grid impedance at the mth target frequency.

9. A system for calculating grid impedance based on a sliding window, characterized in that: The system comprises: A signal setting module, used to set the signal type and signal length of the disturbance signal to be injected by the new energy station into the access power grid, wherein the disturbance signal is a current signal or a voltage signal; A disturbance injection module, for injecting orthogonal signals with the same amplitude and frequency as disturbance signals into the access grid on the d-axis and q-axis simultaneously according to the signal category, wherein the amplitude of the injected disturbance signal is limited by the harmonic current generated at the grid connection point, and the frequency is determined according to the target frequency of the grid impedance to be calculated and the grid frequency; A data acquisition module, used for collecting three-phase current data and voltage data of the signal length at the grid connection point; The impedance calculation module is used to calculate the grid impedance at the target frequency based on the sliding window according to the three-phase current data and voltage data.

10. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and the computer program is used to execute the method according to any one of claims 1 to 8.

11. An electronic device, characterized in that: The electronic device comprises: processor; a memory for storing instructions executable by the processor; The processor is used to read the executable instructions from the memory and execute the instructions to implement the method described in any one of claims 1 to 8.

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