Harmonic detection method of energy storage power station

Abstract

The invention relates to the technical field of harmonic detection, and discloses a harmonic detection method of an energy storage power station, compared with the prior art, the harmonic detection method of the energy storage power station has the remarkable advantages that the detection precision is greatly improved, the frequency measurement precision reaches + / -0.001 Hz, the harmonic amplitude detection error is as low as 0.2%, and the phase measurement precision is + / -0.5 degree, which is far better than that of a traditional method; the dynamic performance is improved, the response time is shortened to be within 20ms, and a dynamic window function selection mechanism and an innovative harmonic decoupling algorithm enable the system to be excellent in a complex environment; the engineering applicability is high, the algorithm calculation amount is reduced by 40%, 100-order harmonic real-time detection is supported, and integration is facilitated through modular design; the economic benefit is obvious, the frequency regulation efficiency is improved by more than 15%, and the investment of filtering equipment is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of harmonic detection, and particularly relates to a harmonic detection method for an energy storage power station. BACKGROUND

[0002] Under the background of current energy transformation, with the large-scale grid connection of high-proportion new energy and the wide and large-scale application of power electronic equipment in the power system, the harmonic parameter detection of the energy storage power station, including the accurate detection of key parameters such as frequency, amplitude and phase, is facing extremely severe challenges.

[0003] From the perspective of frequency detection, the large-scale access of intermittent power sources such as photovoltaic and wind power makes the frequency fluctuation of the power grid more complex and intensified. The traditional zero-crossing detection technology and phase-locked loop technology have obvious limitations in dealing with such complex and variable frequency fluctuations. Specifically, under the requirement of achieving an accuracy standard of less than ±0.01 Hz, the traditional technology is difficult to achieve this accuracy requirement within a relatively short time window of 100 ms, thereby affecting the accuracy and timeliness of the frequency parameter detection of the energy storage power station.

[0004] In terms of harmonic amplitude and phase detection, a series of complex harmonic problems will be generated in the switching process of the converter. Among them, the broadband harmonic up to 100 times brings great difficulties to the detection work. The existing fast Fourier transform (FFT) method will produce high errors in the process of harmonic amplitude detection and phase detection due to the constraints of inherent problems such as spectrum leakage and fence effect. With the increasing demand of the power system for high-order harmonic detection, regional standards are becoming increasingly stringent. The existing FFT method obviously cannot meet these increasingly strict standard requirements, resulting in that the detection result is difficult to truly reflect the actual harmonic condition of the energy storage power station.

[0005] In addition, when the energy storage power station adopts a parallel operation mode of multiple power conversion systems (PCS), the background noise and inter-harmonic interference problems in the system are more prominent. These interference factors will further reduce the reliability of harmonic parameter detection, causing the detection result to deviate. Such deviation may trigger a series of chain reactions, such as causing the control error of automatic generation control (AGC) to be amplified, thereby affecting the power balance and stable operation of the power system; at the same time, it will also cause the reduction of primary frequency modulation qualification rate, weaken the ability of the power system to respond to frequency fluctuations, and pose a potential threat to the safe and stable operation of the power grid.

[0006] In summary, in view of the many severe challenges currently faced by energy storage power station harmonic parameter detection and the series of adverse effects that may be caused thereby, it is urgent to comprehensively and deeply improve and optimize the existing harmonic parameter detection technology to improve the accuracy, reliability and timeliness of the detection, and to ensure the safe and stable operation of the energy storage power station and the entire power system.

[0007] The above information is presented as background information only to assist with an understanding of the present disclosure. No determination or admission is made as to any portion of the above information as having predictive value in relation to the adequacy or existence of prior art with respect to the present disclosure. SUMMARY

[0008] The present application provides a harmonic detection method of energy storage power station to solve the problems in the prior art.

[0009] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0010] A harmonic detection method of energy storage power station, the method comprising:

[0011] S101, collecting voltage and current signals of the power grid;

[0012] S102, selecting a Nuttall window function, the Nuttall window function being a four-term Nuttall window function or a six-term Nuttall window function;

[0013] S103, performing windowing processing on the collected signals using the Nuttall window function, and performing fast Fourier transform to obtain an FFT spectrum;

[0014] S104, in the FFT spectrum, determining the positions of three spectral lines with the largest amplitudes near the target harmonic using three-spectral-line interpolation to estimate the frequency, amplitude and phase of the harmonic;

[0015] S105, performing harmonic coupling compensation to output a high-precision harmonic detection result.

[0016] Further, in the harmonic detection method of the energy storage power station, after S101, the method further comprises:

[0017] S101.5, pre-processing the collected signals.

[0018] Further, in the harmonic detection method of the energy storage power station, the preprocessing is wavelet denoising.

[0019] Further, in the harmonic detection method of the energy storage power station, S102 comprises:

[0020] S1021, determining whether SNR> 50dB, and ; wherein SNR is a signal-to-noise ratio estimation value, is the highest harmonic number to be detected; if yes, S1022 is executed; if no, S1023 is executed;

[0021] S1022, a four-term Nuttall window function is selected;

[0022] S1023, a six-term Nuttall window function is selected.

[0023] Further, in the harmonic detection method of the energy storage power station, the time domain expression of the Nuttall window function is:

[0024] ;

[0025] wherein, is a window function coefficient vector; m is an order; N is a sampling point number; n is a sampling point serial number, .

[0026] Further, in the harmonic detection method of the energy storage power station, the coefficient vector of the four-term Nuttall window function and the coefficient vector of the six-term Nuttall window function are:

[0027] .

[0028] Further, in the harmonic detection method of the energy storage power station, in the S104, the position positioning formula of the three spectral lines is:

[0029] ;

[0030] wherein, is a coarse estimation spectral line position corresponding to a target harmonic, is an FFT spectrum, is a position of the three spectral lines positioned, and .

[0031] Further, in the harmonic detection method of the energy storage power station, after the S104, the method further comprises:

[0032] S104.5, based on a theoretical model of a Nuttall window function spectrum main lobe and amplitudes of the three spectral lines, a normalized frequency offset is solved by least square fitting :

[0033] ;

[0034] wherein, is an amplitude of the three spectral lines;

[0035] S104.6, introducing a quadratic correction term Compensate for the asymmetry of the main lobe of the Nuttall window function, the quadratic correction term The expression is:

[0036] ;

[0037] S104.7, joint And Calculate the accurate frequency:

[0038] ;

[0039] Wherein, The intermediate spectral line position, The sampling frequency, N is the number of sampling points.

[0040] Further, the harmonic detection method of the energy storage power station, the S105 includes:

[0041] S1051, construct a harmonic coupling compensation model:

[0042] ;

[0043] Wherein, , the measured harmonic amplitude vector; , the real amplitude vector after compensation; The coupling matrix, the element is The Nuttall window function side lobe leakage leads to mutual interference between harmonics, Quantitatively describes the interference intensity of the jth harmonic on the ith harmonic;

[0044] S152, solve by using Tikhonov regularization to control the amplitude detection error of the harmonic:

[0045] ;

[0046] Wherein, The diagonal weighting matrix, Adaptive regularization parameter.

[0047] Further, the harmonic detection method of the energy storage power station, after the S105, the method further includes:

[0048] The harmonic detection result is transmitted to the energy storage power station coordination controller.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] (1) significantly improve the detection accuracy

[0051] The frequency measurement accuracy is improved by two orders of magnitude, and the ultra-high precision detection of ±0.001 Hz is realized, which fully meets the strict monitoring requirements of the energy storage power station on the power grid frequency. Compared with the ±0.05 Hz error of the traditional method, the accuracy is improved by 50 times; the harmonic amplitude detection error is reduced from the conventional 5% to within 0.2%, and the advantage is obvious especially in the detection of high-order harmonics (>35 times), and the harmonic components below 1500 Hz can be accurately identified; the phase measurement accuracy reaches ±0.5 degrees, which provides a reliable phase synchronization reference for accurate power control of the energy storage power station.

[0052] (2) Improve dynamic performance

[0053] The response time is shortened to within 20 ms, ensuring that the energy storage system can quickly respond when the power grid frequency suddenly changes. The dynamic window function selection mechanism is adopted, which can automatically adjust the algorithm parameters according to the signal characteristics, and still maintain stable detection in a harsh environment with SNR<40dB; the innovative harmonic decoupling algorithm effectively suppresses the influence of PCS switch noise, and shows stronger robustness in complex electromagnetic environment.

[0054] (3) Enhance engineering applicability

[0055] The algorithm calculation amount is reduced by 40% compared with the traditional method, which can be realized on the existing hardware platform without additional equipment cost; supports real-time detection of up to 100 harmonics, meeting the needs of future power grid development for wide frequency domain monitoring; modular design is convenient for integration into various energy storage control systems, and the actual THD detection error is stable within 0.1%.

[0056] (4) Create significant economic benefits

[0057] By improving the detection accuracy, the frequency regulation efficiency of the energy storage power station can be improved by more than 15%, the resonance risk can be accurately identified, and the filter equipment investment can be reduced.

[0058] The present application has other characteristics and advantages, which will be apparent or will be described in detail in the accompanying drawings and subsequent specific embodiments incorporated herein, which together serve to explain the specific principles of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiment or prior art description will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0060] Figure 1 is a flowchart of a harmonic detection method of an energy storage power station provided by an embodiment of the present application;

[0061] Figure 2 is a comparison chart of sidelobe attenuation of different window functions provided by an embodiment of the present application;

[0062] Figure 3 is a decision plane chart of dynamic window function selection provided by an embodiment of the present application;

[0063] Figure 4 is a frequency tracking performance chart provided by an embodiment of the present application;

[0064] Figure 5 is a harmonic coupling compensation detection comparison chart provided by an embodiment of the present application. DETAILED DESCRIPTION

[0065] To explain possible application scenarios, technical principles, specific schemes that can be implemented, purposes and effects that can be achieved, etc. of the present application in detail, the following will be described in detail in combination with specific embodiments listed and with reference to the drawings. The embodiments described in the present text are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot be used to limit the protection scope of the present application.

[0066] In the present text, the term “embodiment” means that the specific features, structures or characteristics described in combination with the embodiment can be contained in at least one embodiment of the present application. The term “embodiment” appearing at various positions in the specification does not necessarily refer to the same embodiment, and does not particularly limit the independence or association between other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, each technical feature mentioned in each embodiment can be combined in any way to form a corresponding implementable technical solution.

[0067] Unless otherwise defined, the meanings of the technical terms used in the present text are the same as those commonly understood by the person skilled in the art to which the present application belongs; the use of related terms in the present text is only for the purpose of describing specific embodiments, and is not intended to limit the present application.

[0068] In the description of the present application, the phrase “and / or” is a description of the logical relationship between the objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases: A exists, B exists, and A and B exist at the same time. In addition, the character “ / ” in the present text generally represents that the associated objects before and after are a kind of “or” logical relationship.

[0069] In the present application, the phrases such as “first” and “second” are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantity, primary and secondary or order relationship between the entities or operations.

[0070] In the present application, the "including", "containing", "having" or other similar expressions used in the statements are intended to cover the non-exclusive inclusion, and the expressions do not exclude the presence of additional elements in the process, method or product comprising the elements, so that the process, method or product comprising a series of elements can not only include those limited elements, but also include other elements not explicitly listed, or also include the elements inherent to such process, method or product.

[0071] In the present application, the expressions such as "greater than", "less than", "exceed" are understood as not including the number; the expressions such as "above", "below", "within" are understood as including the number. In addition, in the description of the embodiments of the present application, the meaning of "multiple" is more than two (including two), and similar expressions related to "multiple" are also understood in this way, for example, "multiple groups", "multiple times", etc., unless otherwise explicitly specified.

[0072] In the description of the embodiments of the present application, the spatial-related expressions used, such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. The indicated orientation or position relationship is based on the orientation or position relationship shown in the specific embodiment or the drawing, and is only for the convenience of describing the specific embodiments of the present application or for the reader to understand, and does not indicate or imply that the indicated device or component must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0073] Unless otherwise explicitly specified or limited, in the description of the embodiments of the present application, the terms "mounting", "connecting", "connecting", "fixing", "setting" and the like should be interpreted broadly. For example, the "connection" can be a fixed connection, or a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be directly connected, or indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art to which the present application belongs, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0074] Please refer to Figure 1 , a flowchart of a harmonic detection method of an energy storage power station provided by Embodiment One of the present application. The method specifically comprises the following steps:

[0075] S101, collect the voltage and current signals of the power grid.

[0076] It should be noted that the voltage and current signals in the power grid contain a wealth of information, including harmonic information. Through professional signal acquisition equipment such as voltage transformers, current transformers, etc., the voltage and current signals in the power grid are converted into electrical signals suitable for subsequent processing. These signals are the basis data for subsequent harmonic detection, and their accuracy and integrity directly affect the reliability of the final detection results.

[0077] Obtain the original power grid signal to provide data source for subsequent harmonic analysis. Only by collecting voltage and current signals that accurately reflect the actual operating state of the power grid can effective harmonic detection and analysis be performed.

[0078] S102, select a Nuttall window function, the Nuttall window function is a four-term Nuttall window function or a six-term Nuttall window function.

[0079] It should be noted that the window function plays an important role in signal processing. When performing Fast Fourier Transform (FFT), due to signal truncation, spectral leakage phenomenon occurs, resulting in a decrease in spectral analysis accuracy. The Nuttall window function is a window function with good characteristics, which can effectively suppress spectral leakage. The four-term and six-term Nuttall window functions differ in spectral characteristics, and can be selected according to specific detection requirements and signal characteristics.

[0080] By selecting the appropriate Nuttall window function, the influence of spectral leakage on harmonic detection can be reduced, and the accuracy of spectral analysis can be improved, laying a foundation for subsequent accurate estimation of the frequency, amplitude and phase of harmonics.

[0081] S103, window processing is performed on the collected signal using the Nuttall window function, and Fast Fourier Transform is performed to obtain the FFT spectrum.

[0082] It should be noted that window processing is to multiply the selected Nuttall window function with the collected voltage and current signals, so that the change at the truncated point of the signal is smoother, thereby reducing spectral leakage. Then the windowed signal is subjected to Fast Fourier Transform to convert the time domain signal to the frequency domain signal, and the FFT spectrum is obtained. The FFT spectrum can directly show the distribution of each frequency component in the signal.

[0083] This step converts the time domain voltage and current signals into frequency domain FFT spectrum, which facilitates harmonic analysis and detection in the frequency domain, and extracts the frequency, amplitude and phase information of the harmonics.

[0084] S104. In the FFT spectrum, three-spectrum-line interpolation is used to determine the positions of three spectrum lines with the largest amplitudes near the target harmonic to estimate the frequency, amplitude and phase of the harmonic.

[0085] It should be noted that in the FFT spectrum, due to the effects of spectrum leakage and fence effect, the energy of the harmonic will be dispersed to the adjacent spectrum lines. The three-spectrum-line interpolation method selects three spectrum lines with the largest amplitudes near the target harmonic, uses the amplitude and phase information of the three spectrum lines, and through a specific interpolation algorithm, the frequency, amplitude and phase of the harmonic can be more accurately estimated.

[0086] This step can improve the accuracy of harmonic parameter estimation, overcome the errors caused by spectrum leakage and fence effect, and obtain more accurate harmonic frequency, amplitude and phase information.

[0087] S105. Harmonic coupling compensation is performed, and a high-precision harmonic detection result is output.

[0088] It should be noted that in the actual power grid, there may be a coupling relationship between harmonics, which will affect the accuracy of harmonic detection. Harmonic coupling compensation analyzes the detected harmonic signals, identifies the coupling relationship between harmonics, and uses a corresponding compensation algorithm to correct the detection result to eliminate the influence of coupling effect.

[0089] This step can further improve the precision of harmonic detection and output a high-precision harmonic detection result to provide accurate and reliable harmonic information for the operation control of the energy storage power station.

[0090] In one embodiment of the present embodiment, after S101, the method further comprises:

[0091] S101.5. The collected signal is preprocessed.

[0092] Optionally, the preprocessing is wavelet denoising.

[0093] It should be noted that in the signal collection process, it is inevitable to be disturbed by various noises. These noises may come from the internal equipment operation of the power grid, such as electromagnetic noise of transformers, operating noise of switching devices, etc.; or from the external environment, such as electromagnetic interference, lightning, etc. The existence of noise will mask the useful information in the signal, reduce the quality of the signal, and thus affect the accuracy of subsequent harmonic detection.

[0094] Wavelet denoising is a signal processing method based on wavelet transform. Wavelet transform has the characteristics of multi-resolution analysis, which can decompose the signal into different frequency subbands. In the decomposition process, the useful information (such as harmonic signals) and noise signals in the signal show different characteristics at different wavelet scales. By selecting a suitable threshold, the wavelet coefficients are processed, the coefficients less than the threshold are set to zero, and the coefficients greater than the threshold are retained. Then, the processed wavelet coefficients are reconstructed to obtain the denoised signal.

[0095] On the one hand, wavelet denoising can effectively remove noise interference in the collected signal, improve the signal-to-noise ratio of the signal, make the signal clearer and more accurate, and provide high-quality input signal for subsequent harmonic detection.

[0096] On the other hand, the interference of noise on the harmonic detection algorithm is reduced, and problems such as spectral leakage and misjudgment caused by noise are avoided, thereby improving the accuracy of parameter estimation such as harmonic frequency, amplitude and phase.

[0097] In an embodiment of the embodiment, S102 can be further refined to include the following steps:

[0098] S1021, judge whether SNR> 50dB, and ; wherein SNR is the signal-to-noise ratio estimate (dB), is the highest harmonic order to be detected; if yes, execute S1022; if no, execute S1023;

[0099] S1022, select four-term Nuttall window function;

[0100] S1023, select six-term Nuttall window function.

[0101] It should be noted that the time domain expression of the Nuttall window function is:

[0102] ;

[0103] wherein, is the window function coefficient vector; m is the order; N is the number of sampling points; n is the sampling point number, .

[0104] The Nuttall window function is composed of a linear combination of cosine functions, and it can be verified that , the expression embodies symmetry, ensuring that the FFT result has no phase distortion, , which meets the amplitude detection requirements, and Balancing main lobe width and side lobe attenuation. The four Nuttall window functions currently have a good effect, and the side lobe attenuation is-98dB. Compared with the traditional Hanning window and Blackman-Harris window, the four Nuttall window functions have great improvement in the problems of spectrum leakage, main lobe width and noise sensitivity, but still have deficiencies in dealing with high harmonics.

[0105] The embodiment of the present application introduces six Nuttall window functions, and the side lobe attenuation is ensured by the optimized design of the coefficient For the m-order window, according to the side lobe attenuation theorem of Fourier transform, the side lobe attenuation satisfies:

[0106] ;

[0107] wherein, is the main lobe boundary frequency, The solution can be converted into the following convex optimization problem, and there is a unique global optimal solution.

[0108] ;

[0109] By solving the constrained optimization problem, the side lobe attenuation is further improved from-98dB to-120dB, which is suitable for high harmonic detection. Compared with the traditional method and the side lobe attenuation of the four Nuttall window functions, as shown in Figure 2 .

[0110] The coefficient vector of the four Nuttall window functions and the coefficient vector of the six Nuttall window functions are:

[0111] .

[0112] It can be understood that under the condition of high signal-to-noise ratio SNR>50dB, the influence of noise is small, and the spectrum leakage is the main contradiction. At the same time, in the low harmonic scene of the maximum harmonic number , the frequency interval between low harmonics is large, and the influence of spectrum leakage is small. In combination with the above working conditions: when SNR≤50dB or >25, the six Nuttall window functions are used to enhance the side lobe suppression ability. The design window function dynamic switching function is:

[0113] ;

[0114] The decision plane of dynamic switching is as shown in Figure 3As shown, the red dotted line is the demarcation line, when the working point is located in the lower left area, six Nuttall window functions are selected, and four Nuttall window functions are selected in the upper right area. The turning point (50dB, 25 times) of the demarcation line is determined by a large amount of experimental data statistics, which ensures that the optimal detection performance can be maintained under various working conditions

[0115] In an embodiment of the present embodiment, in S104, the position positioning formula of the three spectral lines is:

[0116] ;

[0117] Wherein, is the coarse estimated spectral line position corresponding to the target harmonic, is the FFT spectrum, is the position of the three spectral lines positioned, and . The design ensures that the three continuous spectral lines with the maximum amplitude in the main lobe of the target harmonic are selected, which provides a reliable data basis for subsequent interpolation. Compared with the traditional double spectral line method, one spectral line is added to effectively suppress the influence of noise.

[0118] In an embodiment of the present embodiment, after S104, the method further comprises:

[0119] S104.5, based on the theoretical model of the main lobe of the Nuttall window function spectrum and the amplitude of the three spectral lines, the normalized frequency offset is solved by least squares fitting :

[0120] ;

[0121] Wherein, is the amplitude of the three spectral lines.

[0122] It should be noted that the frequency domain discretization characteristics of the signal will produce a fence effect, and when the actual frequency deviates from the frequency point, energy will be dispersed to the adjacent frequency points, causing amplitude measurement error and phase information distortion, and a frequency correction model needs to be constructed. According to the windowed FFT theory and the energy conservation principle, the frequency correction model is established, assuming that the actual frequency is located between DFT frequency points and , the normalized frequency offset is α∈(-0.5, 0.5), then:

[0123] f = (k + α)Δf;

[0124] Wherein, is the frequency resolution, according to the spectrum characteristics of the window function, the amplitudes of three adjacent spectral lines contain frequency offset information, and an energy center equation is constructed based on this:

[0125] ;

[0126] wherein, is the amplitude of the three spectral lines, is the theoretical model of the main lobe of the window function spectrum, and the frequency offset can be accurately estimated by least square fitting the main lobe of the theoretical window function with the actual spectral line distribution The theoretical model is determined by the spectral characteristics of the window function:

[0127] ;

[0128] In the formula, A is the true value of the harmonic amplitude, and W is the spectrum of the window function.

[0129] S104.6, introducing a quadratic correction term to compensate for the asymmetry of the main lobe of the Nuttall window function, the quadratic correction term is:

[0130] .

[0131] It should be noted that the quadratic correction term is used to compensate for the energy center shift caused by the asymmetry of the main lobe of the window function, and when the main lobe is completely symmetrical ; When the main lobe is left-leaning , right-leaning , the correction can eliminate the system error of 0.01 Hz level. S104.7, joint and

[0132] to calculate the accurate frequency: ;

[0133] wherein, is the position of the intermediate spectral line,

[0134] is the sampling frequency, and N is the number of sampling points. It should be noted that the joint and

[0135] double correction can obtain a high-precision frequency parameter, which provides an accurate frequency reference for the coordinated control of the energy storage power station. The accuracy is increased by 5 times compared with the single parameter method, and the frequency estimation error is reduced to ±0.001 Hz. The frequency following performance is shown in . Figure 4 In one embodiment of the present embodiment, the S105 can be further refined to include the following steps:

[0136] In one embodiment of the present embodiment, the S105 can be further refined to include the following steps:

[0137] ​S1051, construct a harmonic coupling compensation model:

[0138] ;

[0139] wherein, is a measured harmonic amplitude vector; is a real amplitude vector after compensation; is a coupling matrix, and the element is The side lobe leakage of the Nuttall window function causes mutual interference between harmonics, quantitatively describes the interference intensity of the jth harmonic on the ith harmonic;

[0140] It should be noted that the power electronic equipment such as photovoltaic inverters and wind power converters generates harmonic wide frequency domain distribution up to 2 kHz, and high switching frequency modulation will cause harmonic migration, and the sideband harmonic spectrum generated by PWM modulation is dense, and harmonic analysis needs to eliminate the coupling interference term in the side lobe characteristics of the window function spectrum, and needs to solve the convolution of the actual measurement spectrum and the window function spectrum, and construct a harmonic coupling compensation model:

[0141] ;

[0142] Through matrix inverse operation, each harmonic can be decoupled, and the detection accuracy of high-order harmonics can be significantly improved.

[0143] S152, solve by Tikhonov regularization to control the amplitude detection error of the harmonic:

[0144] ;

[0145] wherein, is a diagonal weighting matrix (high frequency component weight increases), is an adaptive regularization parameter, which is adaptively determined by L-curve method.

[0146] It should be noted that the amplitude detection error of the 100th harmonic can be controlled within 0.5% by this method, and the compensation effect of the system is shown in Figure 5 .

[0147] In one embodiment of the embodiment, after the S105, the method further comprises:

[0148] transmitting the harmonic detection result to a energy storage power station coordinated controller.

[0149] It should be noted that the high-precision harmonic detection result output by S105 is packaged and transmitted according to a certain communication protocol (such as Modbus, IEC 61850) through wired communication (such as Ethernet, field bus) or wireless communication (such as Wi-Fi, 4G / 5G) and the like, to ensure that the data can be accurately and timely reached to the energy storage power station coordinated controller.

[0150] The purpose of this step is to enable the energy storage power station coordinated controller to obtain real-time harmonic information in the power grid, to provide a basis for subsequent control decisions, so as to realize effective control and optimized operation of the energy storage power station.

[0151] Although the terms such as window function, fast Fourier transform are used more in this application, the possibility of using other terms is not excluded. The use of these terms is only to facilitate the description and explanation of the essence of the application; any additional limitation is contrary to the spirit of the application.

[0152] The harmonic detection method for the energy storage power station provided by the embodiment of the application has the following beneficial effects:

[0153] (1) Significantly improve the detection accuracy

[0154] The frequency measurement accuracy is improved by two orders of magnitude, realizing ultra-high precision detection of ±0.001Hz, fully meeting the stringent monitoring requirements of the energy storage power station on the power grid frequency. Compared with the ±0.05Hz error of the traditional method, the accuracy is improved by 50 times; the harmonic amplitude detection error is reduced from the conventional 5% to within 0.2%, especially in high-order harmonic (>35 times) detection, the advantage is obvious, and the harmonic components below 1500Hz can be accurately identified; the phase measurement accuracy reaches ±0.5 degrees, providing a reliable phase synchronization reference for accurate power control of the energy storage power station.

[0155] (2) Improve dynamic performance

[0156] The response time is shortened to within 20ms, ensuring that the energy storage system can quickly respond when the power grid frequency suddenly changes. The dynamic window function selection mechanism is adopted, which can automatically adjust the algorithm parameters according to the signal characteristics, and still maintain stable detection in a harsh environment with SNR<40dB; the innovative harmonic decoupling algorithm effectively suppresses the influence of PCS switch noise, and shows stronger robustness in complex electromagnetic environment.

[0157] (3) Enhance engineering applicability

[0158] The algorithm reduces the calculation amount by 40% compared with the traditional method, can be implemented on the existing hardware platform, and does not need to increase the equipment cost; supports real-time detection of up to 100 harmonics, meets the demand of future power grid development on wide frequency domain monitoring; and the modular design is convenient for integration into various energy storage control systems, and the measured THD detection error is stable within 0.1%.

[0159] (4) Create significant economic benefits

[0160] By improving the detection accuracy, the frequency regulation efficiency of the energy storage power station can be improved by more than 15%, the resonance risk can be accurately identified, and the filter equipment investment can be reduced.

[0161] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of the present application, the patent protection scope of the present application should not be limited. Any technical solution obtained by replacing or modifying the equivalent structure or equivalent flow based on the essential concept of the present application, using the content described in the specification and drawings, and directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, etc. are all included in the patent protection scope of the present application.

Claims

1. A harmonic detection method for an energy storage power station, characterized in that, The method includes: S101. Acquire voltage and current signals from the power grid; S102. Select the Nuttall window function, wherein the Nuttall window function is a four-term Nuttall window function or a six-term Nuttall window function; S103. The acquired signal is windowed using the Nuttall window function and then subjected to Fast Fourier Transform to obtain the FFT spectrum. S104. In the FFT spectrum, the positions of the three spectral lines with the largest amplitude near the target harmonic are determined by three-line interpolation in order to estimate the frequency, amplitude and phase of the harmonic. S105. Perform harmonic coupling compensation and output high-precision harmonic detection results.

2. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, Following S101, the method further includes: S101.

5. Preprocess the acquired signals.

3. The harmonic detection method for an energy storage power station according to claim 2, characterized in that, The preprocessing is wavelet denoising.

4. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, S102 includes: S1021. Determine whether SNR > 50dB, and Where SNR is the estimated signal-to-noise ratio. The highest harmonic order to be detected; if yes, proceed to S1022; otherwise, proceed to S1023. S1022. Select four Nuttall window functions; S1023. Select one of the six Nuttall window functions.

5. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, The time-domain expression of the Nuttall window function is: ； in, Here, m is the coefficient vector of the window function; N is the order; and n is the number of sampling points. .

6. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, The coefficient vectors of the four Nuttall window functions and the coefficient vector of the six Nuttall window functions for: 。 7. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, In S104, the formula for locating the positions of the three spectral lines is as follows: ； in, To roughly estimate the spectral line position corresponding to the target harmonic, For FFT spectrum, The positions of the three spectral lines are determined, and .

8. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, Following S104, the method further includes: S104.5 Theoretical Model of the Spectral Main Lobe Based on Nuttall Window Function The normalized frequency offset is obtained by solving the amplitudes of the three spectral lines using least squares fitting. : ； in, The amplitudes of the three spectral lines; S104.6, Introducing a quadratic correction term Compensation for the main lobe asymmetry of the Nuttall window function, quadratic correction term The expression is: ； S104.7, Joint and Calculate the precise frequency: ； in, This indicates the position of the middle spectral line. Where N is the sampling frequency and N is the number of sampling points.

9. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, S105 includes: S1051. Constructing a harmonic coupling compensation model: ； in, , is the measured harmonic amplitude vector; , which is the true amplitude vector after compensation; Let be the coupling matrix, with elements of: Sidelobe leakage in the Nuttall window function leads to mutual interference between harmonics. The interference intensity of the j-th harmonic on the i-th harmonic is quantitatively described; S152. Tikhonov regularization is used to solve the problem to control the amplitude detection error of harmonics: ； in, It is a diagonal weighted matrix. For adaptive regularization parameters.

10. The harmonic detection method for an energy storage power station according to claim 1, characterized in that, Following S105, the method further includes: The harmonic detection results are transmitted to the energy storage power station coordination controller.

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