A broadband impedance modulation index calculation method

Abstract

The application provides a broadband impedance modulus index calculation method, comprising the following steps: S1, signal acquisition; S2, frequency band division; S3, calculation of sub-frequency band impedance; S4, stability index; the application breaks through the limitation of the traditional method through multi-dimensional parameter fusion and dynamic collaborative optimization; an improved wavelet packet decomposition algorithm is used to construct non-uniform frequency band division, and fine modeling of full-frequency band impedance characteristics is realized; the total impedance modulus is synthesized by fusing the regularization constraint, the sub-frequency band impedance and the phase data; the peak values of the total impedance modulus, the stability margin and the total impedance modulus curve are fused dynamically to construct a multi-dimensional stability evaluation model; and the multi-level response strategy is triggered based on the fusion index.

Description

Technical Field

[0001] This invention relates to the field of power system analysis technology, specifically a method for calculating broadband impedance modulus. Background Technology

[0002] With the continuous increase in the penetration rate of new energy power generation (wind power and photovoltaic), power systems dominated by power electronic converters exhibit significant wideband dynamic characteristics. The interaction between new energy power plants and the grid may induce novel stability problems such as subsynchronous oscillations (SSO) and high-frequency resonances in the 0.1Hz–3kHz frequency band. Traditional impedance analysis methods face two major challenges:

[0003] Insufficient frequency band coverage: The FFT method has limited resolution in the low frequency band (0.1–10Hz requires a time window of >10s), while the wavelet transform is slow to respond to high frequency transients (>1kHz band error >10%).

[0004] High noise sensitivity: Power electronic switch noise (IGBT switching frequency 2–20kHz) causes impedance phase calculation jitter (±5°), affecting stability margin assessment.

[0005] The existing technology, disclosed in CN117910846A, is entitled "A Method and System for Calculating Impedance Modulus Index of a Multi-Infeed Renewable Energy System." It relates to the fields of power grid flow calculation and impedance analysis, including: collecting transmission network data to define the impedance modulus index; constructing the equivalent impedance matrix of the multi-infeed renewable energy grid-connected system; constructing the node impedance matrix of the system after grid connection of unassessed renewable energy based on the system node voltage and current relationships and the unassessed renewable energy equivalent; obtaining the impedance modulus index at the renewable energy nodes based on the unassessed renewable energy equivalent; and selecting the renewable energy grid-connected capacity based on the impedance modulus index. The method for calculating the impedance modulus index of a multi-infeed renewable energy system provided by this invention accurately indicates the strength of the system's static voltage stability when renewable energy is fed into the system at different nodes. The calculation is achieved through the equivalent impedance matrix, which remains unchanged, eliminating the need for repeated iterations. This invention achieves better results in terms of accuracy and applicability.

[0006] While the aforementioned existing technologies calculate the impedance mode index of new energy nodes, they do not incorporate frequency domain characteristics and do not address issues such as the impact of introduced noise on stability margin assessment. Summary of the Invention

[0007] The purpose of this invention is to provide a method for calculating wideband impedance modulus, in order to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for calculating broadband impedance mode parameters includes the following steps:

[0010] S1. Signal Acquisition: Acquire the voltage signal in the time domain at the grid connection point. and current signal And the collected voltage signal Current signal and sampling rate Preprocessing is performed to obtain the processed signal;

[0011] S2. Frequency Band Allocation: A nonlinear scaling factor is applied to the processed signal. To achieve dynamic adjustment of bandwidth, the target frequency band is divided into at least two sub-bands, thus generating a low-frequency band. <1, at this time the bandwidth is 0.1-10Hz, high frequency band >1, at which point the bandwidth is 1-3kHz, and a sub-band is obtained;

[0012] S3. Calculate the sub-band impedance: The sub-band impedance is calculated using the regularized synchronous phasor method.

[0013] S4. Stability Index: A global stability index is generated by frequency domain feature fusion based on dynamic stability margin.

[0014] Furthermore, the sub-band impedance in S3 is calculated as follows:

[0015] Synchronization phasor extraction: Apply a sliding time window to perform a fast Fourier transform on each sub-band signal to extract the complex phasor at the fundamental frequency. and ;

[0016] Regularized impedance calculation: Constructing a linear equation and solving it through regularization optimization. ;

[0017] Parameter selection and noise suppression: Based on noise variance estimation, adaptive adjustment is performed, and the collected parameters are the noise variance and the attenuation coefficient of the exponential term;

[0018] Dynamic error calibration: phase delay compensation;

[0019] Sub-band impedance fusion and analysis: For each sub-band ,Record amplitude and phase Plot a wideband impedance mode curve, covering 0.1Hz to 3kHz.

[0020] Furthermore, based on global stability indicators The system stability is determined as follows:

[0021] The value range is 0.8 ≤ A value ≤1 indicates that the system is stable, and the criterion is the stability margin of all sub-bands. ≥0.2, and the peak total impedance does not exceed the reference value. ;

[0022] The value range is 0.5 ≤ A value <0.8 indicates a low risk in the system, determined by the following criteria: at least one sub-band. <0.2, or the peak total impedance is close to the reference value. ;

[0023] The range of values ​​is within A value <0.5 indicates a high-risk system, determined by the following criteria: any sub-frequency band <0, or the peak total impedance exceeds the reference value. .

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention overcomes the limitations of traditional methods by integrating multi-dimensional parameters and dynamic collaborative optimization.

[0026] An improved wavelet packet decomposition algorithm is used to construct a non-uniform frequency band division, through... Parameter optimization enables high-resolution analysis of key frequency bands, and a distributed impedance estimation algorithm based on synchronous phasor measurement enables refined modeling of impedance characteristics across the entire frequency band.

[0027] By integrating regularization constraints, sub-band impedance, and phase data, a total impedance modulus is synthesized. The dynamic stability margin is fused into the total impedance modulus, stability margin, and peak value of the total impedance modulus curve, thus constructing a multi-dimensional stability assessment model. Based on the fused index, a multi-level response strategy is dynamically triggered, forming a closed-loop control from parameter adjustment to emergency protection, significantly reducing the false alarm rate and false alarm rate. Breaking the traditional single-band analysis mode, a composite stability index is constructed through multi-dimensional feature fusion, improving the reliability of decision-making in complex scenarios and revealing the broadband coupled oscillation mechanism. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall method flow of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0030] Please see Figure 1 This invention provides a technical solution: a method for calculating broadband impedance mode, comprising the following steps:

[0031] S1. Signal Acquisition: Acquire the voltage signal in the time domain at the grid connection point. and current signal And the collected voltage signal Current signal and sampling rate Preprocessing is performed to obtain the processed signal;

[0032] S2. Frequency Band Allocation: A nonlinear scaling factor is applied to the processed signal. To achieve dynamic adjustment of bandwidth, the target frequency band is divided into at least two sub-bands, thus generating a low-frequency band. <1, at this time the bandwidth is 0.1-10Hz, high frequency band >1, at which point the bandwidth is 1-3kHz, and a sub-band is obtained;

[0033] S3. Calculate the sub-band impedance: The sub-band impedance is calculated using the regularized synchronous phasor method.

[0034] S4. Stability Index: A global stability index is generated by frequency domain feature fusion based on dynamic stability margin.

[0035] In this embodiment, preferably, the calculation and analysis of the processed signal in S1 is as follows;

[0036] ;

[0037] in, Represented as an improved non-uniform wavelet basis function, it indicates that under the scaling factor... The wavelet function below is the basis function for time-frequency decomposition of the signal, and its shape and frequency band characteristics are determined by... Parameters are dynamically adjusted. Represented as a normalization factor, ensuring the energy consistency of the wavelet function, through The scaling ratio is dynamically adjusted to ensure that the wavelet energy is equal across different frequency bands. This is expressed as a normalization constant, correcting the magnitude of the Gaussian envelope and satisfying the standardization conditions of the wavelet basis functions. Represented as a Gaussian window function, it controls the time-domain localization properties of the wavelet. Represented as a time variable, Represented as a complex exponential term, it indicates the frequency modulation of the wavelet. Represented as the dynamic center frequency, by control;

[0038] It should be noted that by dynamically adjusting the frequency and time width of the wavelet basis function through a nonlinear scaling factor, a long time window is used in the low-frequency band (e.g., 0.1–10Hz) to improve frequency resolution, and a short time window is used in the high-frequency band (e.g., 1–3kHz) to enhance transient capture capability. This enables adaptive and refined decomposition of wideband signals (0.1Hz–3kHz), and accurate separation of mixed signals such as subsynchronous oscillations (low-frequency slow changes) and high-frequency resonances (fast-changing transients). It avoids overlapping interference of signals with different dynamic characteristics in the frequency domain and improves the ability to extract local features. Nonlinear wavelet packet decomposition, through dynamic bandwidth optimization, noise immunity enhancement, and adaptive structural adjustment, solves the contradiction between resolution and real-time performance in wideband impedance analysis, becoming the core technical support for the stability monitoring of high-proportion new energy power grids.

[0039] ;

[0040] in, Represented as target feature frequency, and , indicating the first The theoretical center frequency of each sub-band This is expressed as the percentage of subband energy. =0.5, representing the shape adjustment factor.

[0041] In this embodiment, preferably, the dynamic center frequency The calculation is as follows:

[0042] ;

[0043] in, Represented as the baseline term, This is indicated by the system's lowest frequency of interest, with a set value of 0.1Hz. Represented as signal feature offset term, Represented as a noise compensation term;

[0044] The calculation is based on the voltage signal. Current signal and sampling rate Perform the calculation:

[0045] ;

[0046] in, These are respectively represented as voltage signals. Current signal Total harmonic distortion, It is expressed as the resonance risk coefficient of a sub-band. =0.05, representing the proportionality coefficient;

[0047] It should be noted that the dynamic center frequency The calculation method, through multi-parameter fusion and adaptive adjustment mechanisms, significantly improves the accuracy and robustness of broadband impedance analysis, and the static reference term... Ensure continuous monitoring of core low-frequency issues; dynamic offset terms To achieve adaptive tracking of high-frequency transients and noisy environments, a collaborative sensing framework of "anchor point + floating" is formed;

[0048] ;

[0049] in, Represented as noise variance, this is the signal variance estimate after high-pass filtering. This is expressed as the total variance of the signal. This is expressed as the sampling rate. Represented as the number of decomposition layers, Represented as the direction control factor, based on the scaling factor. The value determines the direction of compensation: >1: Take +1, to compensate for low frequencies; <1: Take -1, for high-frequency compensation; =1: Take 0, no compensation.

[0050] In this embodiment, preferably, the sub-frequency band division in S2 is as follows:

[0051] Formula for determining the number of sub-bands:

[0052] ;

[0053] in, This represents the highest frequency of the analysis. This represents the minimum required frequency band resolution. This is expressed as the number of sub-bands;

[0054] And combined with the set threshold, that is, when When <1, a low-frequency band is generated, with a bandwidth of 0.1-10Hz. When the value is greater than 1, a high-frequency band is generated, and the bandwidth is 1-3kHz.

[0055] It should be noted that the sub-band division method, through dynamic frequency band quantity calculation and threshold classification mechanism, significantly improves the efficiency and accuracy of broadband impedance analysis; through threshold... Distinguish between low-frequency and high-frequency bands, and allocate computing resources according to the characteristics of different frequency bands: Low-frequency band: Long time window ensures frequency resolution and suppresses spectral leakage; High-frequency band: Short time window quickly tracks transient harmonics and avoids aliasing distortion.

[0056] In this embodiment, preferably, the sub-band impedance in S3 is calculated as follows:

[0057] Synchronization phasor extraction: Apply a sliding time window to perform a fast Fourier transform on each sub-band signal to extract the complex phasor at the fundamental frequency. and ;

[0058] Regularized impedance calculation: Constructing a linear equation and solving it through regularization optimization. ;

[0059] Parameter selection and noise suppression: Based on noise variance estimation, adaptive adjustment is performed, and the collected parameters are the noise variance and the attenuation coefficient of the exponential term;

[0060] Dynamic error calibration: phase delay compensation;

[0061] Sub-band impedance fusion and analysis: For each sub-band ,Record amplitude and phase Plot wideband impedance mode curves, covering 0.1Hz to 3kHz;

[0062] It should be noted that, through nonlinear wavelet packet decomposition, regularization optimization and dynamic error compensation, high-precision impedance modeling of the entire frequency band from 0.1Hz to 3kHz is achieved, which has strong noise resistance and takes into account both low-frequency resolution and high-frequency transient response.

[0063] In this embodiment, preferably, the linear equation is calculated as follows:

[0064] ;

[0065] in, Represented as sub-band Voltage phasors in Represented as sub-band Current phasors in Let be the sub-band to be solved. The impedance, and satisfies the above linear relationship, Represented as a noise vector, it includes measurement error and high-frequency interference;

[0066] Regularization optimization solution The calculation is as follows:

[0067] ;

[0068] in, This is represented as the conjugate transpose of the current phasor. Represented as an identity matrix, with dimensions AND same, This is represented as matrix inversion, ensuring numerical stability;

[0069] It should be noted that regularization suppresses noise interference, enhances matrix invertibility, and ensures the numerical stability and accuracy of impedance solutions under high noise conditions.

[0070] ;in, Represented as the regularization coefficient, Represented as noise variance, this is the signal variance estimate after high-pass filtering. It is expressed as the total variance of the signal.

[0071] In this embodiment, preferably, the calculation for the sub-band impedance fusion and analysis is as follows:

[0072] Sub-band impedance fusion formula:

[0073] ;

[0074] in, Represented as the synthesized frequency The impedance magnitude at that point, Represented as sub-band In frequency Dynamic weights at the location, Represented as sub-band center frequency The amplitude at that point, Represented as an interpolation kernel function, associated with the sub-band center With target frequency ;

[0075] Phase data fusion:

[0076] ;

[0077] in, This is represented as phase unwinding, eliminating 2π jumps. Represented as the synthesized frequency Phase magnitude at that point, Represented as sub-band center frequency Phase at;

[0078] ;

[0079] in, Expressed as the combined total impedance modulus, This represents the total number of sub-bands. Represented as a frequency domain window function, used to suppress interpolation boundary effects, main frequency band: Transition zone: , Represented as all sub-bands in The sum of the impedance magnitude and phase magnitude at that point multiplied by their respective weights. Represented as all sub-bands in The sum of the weights at each location;

[0080] It should be noted that dynamic weighting optimizes the contribution of key frequency bands, interpolation kernels eliminate frequency band edge distortion, and phase unwrapping ensures continuity, achieving high-precision seamless fusion of impedance curves across the entire frequency range of 0.1Hz–3kHz.

[0081] ;

[0082] in, This is expressed as the broadening parameter of the Gaussian kernel, controlling the spread range of sub-band energy in the frequency domain. Represented as the center frequency of the sub-band, the first... The center frequency of each sub-band This represents the target frequency, the frequency point where the impedance modulus to be calculated, covering the entire analysis range. The decay coefficient, expressed as the exponential term, determines the descent rate and frequency domain resolution of the Gaussian kernel.

[0083] In this embodiment, preferably, the global stability index in S4 is calculated as follows:

[0084] ;

[0085] in, Represented as a global stability indicator, Represented as sub-band stability margin Represented as weight values, Represented as a compression function, it maps the stability margin to [-1, 1], thus amplifying the sensitive region. This is represented by the peak value of the total impedance mode curve. Represented as reference impedance;

[0086] ;

[0087] in, Represented as grid impedance, This is expressed as inverter impedance. =0.01, regularization factor, to prevent the denominator from being zero;

[0088] It should be noted that the dual-factor joint evaluation of stability margin and impedance amplitude, dynamic weighting focusing on risky frequency bands, compression function amplifying sensitive areas, and regularization resisting denominator singularities achieve high-sensitivity quantification of global stability.

[0089] In this embodiment, preferably, it is based on a global stability index. The system stability is determined as follows:

[0090] The value range is 0.8 ≤ A value ≤1 indicates that the system is stable, and the criterion is the stability margin of all sub-bands. ≥0.2, and the peak total impedance does not exceed the reference value. ;

[0091] The value range is 0.5 ≤ A value <0.8 indicates a low risk in the system, determined by the following criteria: at least one sub-band. <0.2, or the peak total impedance is close to the reference value. ;

[0092] The range of values ​​is within A value <0.5 indicates a high-risk system, determined by the following criteria: any sub-frequency band <0, or the peak total impedance exceeds the reference value. ;

[0093] It should be noted that by combining frequency domain stability margin and impedance peak as dual criteria, and employing a three-level dynamic threshold-based early warning system, the system balances sensitivity and reliability, accurately identifying local instability and global risks.

[0094] It should be noted that all calculation formulas in this application employ, but are not limited to, regression analysis from machine learning algorithms to deeply analyze the collected parameters and identify their natural trends and interrelationships. Specialized software, such as Python's Scikit-learn library or the R language, is used to automatically generate mathematical models that match the data. Then, cross-validation and other methods are used to objectively evaluate the model performance, and continuous feedback and optimization are combined to ensure that the created formulas truly reflect the inherent laws of the data, thereby guaranteeing their validity and accuracy, and ensuring that the calculation process conforms to the constraints of natural laws, rather than being based on artificially set rules.

[0095] The technical solution of this invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments of this invention.

[0096] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-including system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0097] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for calculating broadband impedance mode, characterized in that, Includes the following steps: S1. Signal Acquisition: Acquire the voltage signal in the time domain at the grid connection point. and current signal And the collected voltage signal Current signal and sampling rate Preprocessing is performed to obtain the processed signal; S2. Frequency Band Allocation: A nonlinear scaling factor is applied to the processed signal. To achieve dynamic adjustment of bandwidth, the target frequency band is divided into at least two sub-bands, thus generating a low-frequency band. <1, at this time the bandwidth is 0.1-10Hz, high frequency band >1, at which point the bandwidth is 1-3kHz, and a sub-band is obtained; S3. Calculate the sub-band impedance: The sub-band impedance is calculated using the regularized synchronous phasor method. S301. For each sub-band signal, the time-domain voltage and current signals within a sliding time window are segmented and processed. For each signal segment extracted within a time window, a fast Fourier transform is performed to convert it from the time domain to the frequency domain; a series of voltage and current phasor data that change with time are obtained. S302. The sub-band impedance is calculated by constructing and solving optimized linear equations; and regularization optimization techniques are introduced for the solution. S303. Adaptive adjustment based on noise variance estimation, the collected parameters are noise variance and attenuation coefficient of exponential term; Phase delay compensation; For each sub-band ,Record amplitude and phase Plot wideband impedance mode curves, covering 0.1Hz to 3kHz; S4. Stability Indicator: A global stability index is generated by frequency domain feature fusion based on dynamic stability margin.

2. The method for calculating broadband impedance mode index according to claim 1, characterized in that: The calculation of sub-band impedance in S3 also includes the following: Regularized synchronization phasor method: Apply a sliding time window to perform a fast Fourier transform on each sub-band signal to extract the complex phasor at the fundamental frequency. and .

3. The method for calculating broadband impedance mode index according to claim 2, characterized in that: The calculation of the sub-band impedance in S3 also includes the following: Regularized impedance calculation: Constructing a linear equation and solving it through regularization optimization. ; Regularization optimization solution The calculation is as follows: ； in, Let be the sub-band to be solved. impedance, This is represented as the conjugate transpose of the current phasor. Represented as an identity matrix, with dimensions AND same, It is represented as matrix inversion, ensuring numerical stability.

4. The method for calculating broadband impedance mode according to claim 1, characterized in that: Based on global stability indicators The system stability is determined as follows: The value range is 0.8 ≤ A value ≤1 indicates that the system is stable, and the criterion is the stability margin of all sub-bands. ≥0.2, and the peak total impedance does not exceed the reference value. ; The value range is 0.5 ≤ A value <0.8 indicates a low risk in the system, determined by the following criteria: at least one sub-band. <0.2, or the peak total impedance is close to the reference value. ; The range of values ​​is within A value <0.5 indicates a high-risk system, determined by the following criteria: any sub-frequency band <0, or the peak total impedance exceeds the reference value. .

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