Sweep frequency measurement method and system

Abstract

The invention discloses a frequency sweep measurement method and system. The method comprises the following steps: acquiring a fundamental frequency reference phase of each measured equipment access point at a measurement moment; executing rough scanning of the first-stage injection; analyzing the coarse scanning response data to identify a target frequency band which needs to be subjected to second preset resolution measurement; executing fine scanning of second-stage injection for the target frequency band; and analyzing the fine scanning response data, and obtaining a stability contribution evaluation result of each tested device to the power grid system based on an analysis result of the fine scanning response data and an analysis result of the coarse scanning response data. According to the scheme of the invention, the method can achieve the quick recognition of the potential key frequency region in a broadband range through the hierarchical rough scanning and fine scanning strategies, and avoids the time-consuming high-resolution measurement in a whole frequency band. And then, high-resolution fine scanning is performed on the identified target frequency bands in a targeted manner, so that accurate and detailed response data can be obtained in the key region.

Description

Technical Field

[0001] This application generally relates to the field of frequency domain testing technology for power systems. More specifically, this application relates to a sweep frequency measurement method and system. Background Technology

[0002] As the penetration rate of renewable energy sources such as wind and solar power in the power grid continues to rise, the dynamic characteristics of power systems are becoming increasingly complex. Impedance-based stability analysis, which divides the system into two subsystems—source and load—and determines system stability based on their impedance ratio, has become a core tool in research and engineering applications. The frequency sweep method is a key experimental technique for obtaining the impedance characteristics of various parts of the system. It identifies the frequency characteristics of the system by injecting disturbance signals of different frequencies into the system and measuring its response.

[0003] However, existing frequency sweep measurement techniques suffer from the following major drawbacks when applied to modern large-scale power electronic grids: First, large-scale application is difficult: For large power grids, it is necessary to obtain the impedance of all or a large number of IBR (Inverter-Based Resource) units and key nodes in the network. Traditional single-point, serial frequency sweep methods involve huge computational loads and high measurement costs, making them difficult to apply efficiently to large-scale practical systems. Second, measurement accuracy is limited: Traditional frequency sweep methods are mostly performed in dq or αβ synchronous rotating / stationary coordinate systems, which have inherent mirror frequency coupling and phase dependence problems. This leads to blind zones and errors when measuring the frequency coupling characteristics of the system, especially the off-diagonal elements of the impedance matrix, thus affecting the accuracy of stability analysis. Third, measurement efficiency is low and operating conditions are difficult to maintain: To obtain sufficient low-frequency resolution, the frequency sweep process is often very time-consuming. Moreover, during long-term measurement, the system is susceptible to other background disturbances, affecting the reliability of the measurement results. Fourth, the lack of fault location and diagnosis capabilities: When the frequency sweep results indicate that the system has potential instability risks, the existing methods are difficult to quickly and accurately reverse locate which IBR unit(s) contribute the most to the deterioration of system stability, and therefore cannot provide clear guidance for the formulation of targeted suppression and optimization strategies.

[0004] In view of this, there is an urgent need to provide a frequency sweep measurement scheme to solve the above problems, adapt to the testing needs of large-scale power grids, and perform efficient and accurate frequency sweep measurements. Summary of the Invention

[0005] In order to at least solve one or more of the technical problems mentioned above, this application proposes a frequency sweep measurement scheme in several aspects.

[0006] In a first aspect, this application provides a frequency sweep measurement method, comprising: acquiring the fundamental frequency reference phase of each access point of the device under test at the measurement time; performing a first-level injection coarse sweep, injecting disturbances within a preset frequency band at a first preset resolution and acquiring coarse sweep response data; analyzing the coarse sweep response data in conjunction with the acquired fundamental frequency reference phase to identify a target frequency band that needs to be measured at a second preset resolution; performing a second-level injection fine sweep for the target frequency band, injecting disturbances within the target frequency band at a second preset resolution and acquiring fine sweep response data; analyzing the fine sweep response data in conjunction with the acquired fundamental frequency reference phase, and obtaining an evaluation result of the contribution of each device under test to the stability of the power grid system based on the analysis results of the fine sweep response data and the analysis results of the coarse sweep response data.

[0007] In some embodiments, during the process of acquiring the power grid base frequency reference phase at each device under test access point, the following steps are performed: determining whether the phase output by the programmable logic controller (PLC) or phase-locked loop (PLL) device within a preset time period is within a preset phase range under stable power grid conditions; in response to the PLC or PLL device outputting the phase within the preset time period being within the preset phase range, acquiring the base frequency reference phase of the device under test access point at the measurement time through the PLC or PLL device; in response to the PLC or PLL device outputting the phase within the preset time period not being within the preset phase range, based on the principle of no disturbance to the device under test access point. The fundamental frequency reference phase of the device under test (DUT) access point at the measurement time is obtained by acquiring the steady-state three-phase voltage signal during injection. Specifically, in the process of obtaining the fundamental frequency reference phase of the DUT access point at the measurement time based on the steady-state three-phase voltage signal acquired during undisturbed injection, the following steps are performed: transforming the steady-state three-phase voltage signal acquired during undisturbed injection to the αβ stationary coordinate system; performing a discrete Fourier transform on the voltage signal transformed to the αβ stationary coordinate system to obtain the positive-sequence complex voltage phasor at the fundamental frequency; and extracting the angle of the positive-sequence complex voltage phasor at the fundamental frequency as the fundamental frequency reference phase of the DUT access point at the measurement time.

[0008] In some embodiments, during the coarse scanning process of the first-level injection, for multiple coarse scanning frequency points covering a preset frequency band and exhibiting a logarithmic distribution within the preset frequency band, a first basis vector injection and a second basis vector injection are performed respectively in the αβ stationary coordinate system; wherein, during the execution of the first basis vector injection, at frequency f k A first perturbation signal corresponding to the first component is injected at a certain point; during the second basis vector injection process, at frequency |f k A second disturbance signal corresponding to the second component is injected at -2f0|, where f0 is the base frequency of the power grid.

[0009] In some embodiments, the second component is the conjugate complex number of the first component or the product of the first component and the phase rotation operator; wherein, in f k When -2f0≥0, the second component is the conjugate of the first component; in f k When -2f0 < 0, the second component is the product of the first component and the phase rotation operator, where the phase rotation operator is... The fundamental frequency reference phase of the device under test at the measurement time is the access point of the device under test.

[0010] In some embodiments, the coarse scan response data includes time-domain response waveform data; during the analysis of the coarse scan response data, the following steps are performed: performing a discrete Fourier transform on the coarse scan response data to extract the corresponding voltage spectrum and current spectrum; calculating a complex impedance matrix based on the extracted voltage spectrum and current spectrum; and identifying the target frequency band that needs to be measured at a second preset resolution based on the complex impedance matrix.

[0011] In some embodiments, during the calculation of the complex impedance matrix based on the extracted voltage and current spectra: the voltage and current components at each coarse-sweep injection frequency and its corresponding image frequency are extracted from the extracted voltage and current spectra, wherein the image frequency is calculated using the formula: Image frequency = f i -2f0, where f0 is the base frequency of the power grid, f i Let the i-th coarse scan injection frequency be used. The voltage and current components at each coarse scan injection frequency are combined into corresponding positive-sequence response vectors, and the voltage and current components at each mirror frequency are combined into corresponding negative-sequence response vectors or negative-sequence response vectors after phase compensation. The positive-sequence response vectors and their corresponding negative-sequence response vectors or negative-sequence response vectors after phase compensation are integrated to obtain corresponding voltage response column vectors and current response column vectors. All voltage response column vectors are combined into a voltage response matrix, and all current response column vectors are combined into a current response matrix. The voltage response matrix is ​​right-multiplied by the inverse of the current response matrix to obtain the admittance matrix. The inverse of the admittance matrix is ​​then used to obtain the complex impedance matrix. During the process of combining the voltage and current components at each mirror frequency into corresponding negative-sequence response vectors, the following steps are performed: Determine if the mirror frequency is less than 0; if the mirror frequency is not less than 0, no phase compensation is performed on the negative-sequence response vector; if the mirror frequency is less than 0, a complex multiplication operation is performed on the negative-sequence response vector using a phase rotation operator to obtain a negative-sequence response vector after phase compensation. The phase rotation operator is... The fundamental frequency reference phase of the device under test at the measurement time is the access point of the device under test.

[0012] In some embodiments, during the process of identifying the target frequency band requiring a second preset resolution measurement based on the complex impedance matrix, the following steps are performed: sequentially determining whether the change of each complex impedance vector in the complex impedance matrix between its corresponding two adjacent coarse sweep frequency points satisfies the linear resonance condition; in response to a complex impedance vector not satisfying the linear resonance condition between its corresponding two adjacent coarse sweep frequency points, no action is performed; in response to a complex impedance vector satisfying the linear resonance condition between its corresponding two adjacent coarse sweep frequency points, the frequency interval between its corresponding two adjacent coarse sweep frequency points is taken as a candidate frequency interval; all candidate frequency intervals are summarized into a target frequency band; wherein, the linear resonance condition includes: the amplitude change of the complex impedance vector between its corresponding two adjacent coarse sweep frequency points exceeds a first preset difference value; the phase difference change of the complex impedance vector between its corresponding two adjacent coarse sweep frequency points exceeds a second preset difference value.

[0013] In some embodiments, during the process of obtaining the stability contribution assessment results of each device under test to the power grid system based on the analysis results of the fine-scan response data and the coarse-scan response data, the following steps are performed: constructing the impedance matrix of the device under test based on the analysis results of the fine-scan response data and the coarse-scan response data; obtaining the node modal impedance matrix and loop gain matrix based on the impedance matrix of the device under test and the equivalent impedance matrix of the power grid system, respectively; obtaining the system resonant frequency and the damping ratio corresponding to the system resonant frequency based on the node modal impedance matrix; and plotting the eigenvalues ​​of the loop gain matrix on the complex plane. The Nyquist trajectory is calculated, and the number of encirclements of the Nyquist trajectory around the critical point is obtained; the changes in the system resonant frequency and damping ratio before and after the removal of the device under test are calculated, and the minimum critical distance between the Nyquist trajectory and the critical point is calculated; based on the changes in the system resonant frequency before and after the removal of the device under test, the changes in the damping ratio before and after the removal of the device under test, the number of encirclements of the Nyquist trajectory around the critical point, and the minimum critical distance between the Nyquist trajectory and the critical point, a modal impact report for each access point of the device under test is generated; based on the modal impact reports of each access point of the device under test, a priority list indicating the contribution of each device under test to the system stability is generated.

[0014] In some embodiments, during the coarse scan of the first-stage injection and the fine scan of the second-stage injection, the injected voltage or current is monitored in real time, and it is determined whether the injected voltage or current exceeds the corresponding preset safety threshold. In response to the injected voltage or current not exceeding the corresponding preset safety threshold, no action is taken. In response to the injected voltage or current exceeding the corresponding preset safety threshold, the injection is stopped, and the injection amplitude is reduced or switched to a split measurement scheme. The split measurement scheme includes: temporarily disconnecting the device under test from the power grid system and measuring the impedance of the device under test and the impedance of the power grid respectively.

[0015] In a second aspect, this application provides a frequency sweep measurement system, employing the frequency sweep measurement method as described in any embodiment of the first aspect. The system includes: a fundamental frequency reference phase acquisition module, used to acquire the fundamental frequency reference phase of each device under test (DUT) access point at the measurement time; a coarse sweep module, used to perform a first-level injection coarse sweep, injecting disturbances within a preset frequency band at a first preset resolution and acquiring coarse sweep response data; a target frequency band acquisition module, used to analyze the coarse sweep response data in conjunction with the acquired fundamental frequency reference phase to identify the target frequency band requiring measurement at a second preset resolution; a fine sweep module, used to perform a second-level injection fine sweep for the target frequency band, injecting disturbances within the target frequency band at a second preset resolution and acquiring fine sweep response data; and a stability contribution evaluation module, used to analyze the fine sweep response data in conjunction with the acquired fundamental frequency reference phase, and based on the analysis results of the fine sweep response data and the analysis results of the coarse sweep response data, obtain an evaluation result of the stability contribution of each DUT to the power grid system.

[0016] Using the frequency sweep measurement scheme provided above, this embodiment employs a tiered coarse and fine sweep strategy. This method first rapidly identifies potential critical frequency regions across a wide frequency band, thus avoiding time-consuming high-resolution measurements across the entire band and significantly improving measurement efficiency. Subsequently, a high-resolution fine sweep is performed specifically on these identified target frequency bands, ensuring accurate and detailed response data in the critical regions. Combined with the fundamental frequency reference phase, both coarse and fine sweep data analysis guarantee phase accuracy, which is crucial for subsequently constructing accurate impedance models and conducting stability assessments. Finally, by integrating the results of coarse and fine sweeps, a more comprehensive and accurate assessment of the contribution of each device under test to the stability of the power grid system can be achieved, providing more reliable system stability assessment results and helping to identify potential harmonic problems or oscillation risks.

[0017] Furthermore, in some embodiments, during the coarse scan of the first-stage injection, by performing a specific bibasic vector injection in the αβ stationary coordinate system, the frequency coupling characteristics of the device under test between positive and negative sequences can be accurately and completely identified. By injecting a corresponding compensation signal at the theoretical coupling frequency simultaneously with the main perturbation frequency injection, this method can actively and completely excite the frequency coupling dynamics of the system, thereby decoupling the positive and negative sequence responses. This eliminates the measurement errors and uncertainties in traditional methods and can accurately identify the complete impedance / admittance matrix. An accurate impedance model including coupling terms is obtained, making subsequent stability analysis more comprehensive and reliable.

[0018] Furthermore, in some embodiments, the voltage and current spectra are extracted by performing a Discrete Fourier Transform on the time-domain response waveform data. This innovatively addresses the frequency coupling effect caused by the power grid fundamental frequency, extracting not only the response at the injected frequency but also considering the response at its corresponding mirror frequency. By combining these positive-sequence and negative-sequence response vectors into complete voltage and current response matrices, and further calculating the admittance matrix and its inverse to obtain the complex impedance matrix, the constructed model accurately reflects the true behavior of the device under test under asymmetric or dynamic conditions, thus providing extremely accurate and comprehensive device impedance characteristics. Simultaneously, the phase compensation mechanism for the negative mirror frequency eliminates potential errors in low-frequency measurements, ensuring measurement consistency and accuracy across the entire frequency band.

[0019] Furthermore, in some embodiments, by monitoring the injected voltage or current in real time and comparing it with a preset safety threshold, this method can effectively prevent damage to the device under test or the power grid due to excessive injected disturbances. When a potential risk is detected, the method does not simply stop the test, but provides two intelligent response strategies. First, it attempts to reduce the injection amplitude, a preferred approach designed to find an injection level that is both safe and yields a valid signal without interrupting online measurements. If reducing the injection amplitude still fails to meet safety requirements, the method switches to a split measurement scheme. This provides a foolproof backup plan, measuring the device under test and the power grid separately after decoupling. While sacrificing the convenience of online measurements, it ensures that regardless of the system's coupling strength or stability, the impedance data required for evaluation can ultimately be safely obtained. Attached Figure Description

[0020] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein:

[0021] Figure 1 An exemplary flowchart of the sweep frequency measurement method according to an embodiment of this application is shown;

[0022] Figure 2 An exemplary flowchart illustrating an embodiment of this application is provided for obtaining the fundamental frequency reference phase of each access point of the device under test at the measurement time.

[0023] Figure 3 An exemplary flowchart of an embodiment of this application is shown, which illustrates the acquisition of the fundamental frequency reference phase of the access point of the device under test at the measurement time based on the steady-state three-phase voltage signal acquired when there is no disturbance injection at the access point of the device under test;

[0024] Figure 4 An exemplary flowchart illustrating the analysis of coarse scan response data according to an embodiment of this application is shown;

[0025] Figure 5 An exemplary flowchart illustrating the calculation of the complex impedance matrix based on the extracted voltage and current spectra of this application is shown.

[0026] Figure 6 An exemplary flowchart illustrating how voltage and current components at various mirror frequencies are combined into a corresponding negative-order response vector is shown in an embodiment of this application.

[0027] Figure 7 An exemplary flowchart illustrating an embodiment of this application is shown, which identifies a target frequency band requiring a second preset resolution measurement based on a complex impedance matrix.

[0028] Figure 8 An exemplary flowchart illustrating the process involved in the injection protection mechanism of this application embodiment is shown;

[0029] Figure 9 An exemplary flowchart illustrating an embodiment of this application is provided for obtaining the evaluation results of the contribution of each device under test to the stability of the power grid system.

[0030] Figure 10 An exemplary structural block diagram of a sweep frequency measurement system according to an embodiment of this application is shown. Detailed Implementation

[0031] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0033] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0034] Figure 1 An exemplary flowchart of a sweep frequency measurement method 100 according to an embodiment of this application is shown.

[0035] like Figure 1 As shown, in step S110, the fundamental frequency reference phase of each device under test access point is obtained at the measurement time.

[0036] In the embodiments of this application, the device under test is an inverter or the like, and this application does not impose any restrictions.

[0037] In the embodiments of this application, the specific process involved in step S110 can be found in [reference needed]. Figure 2 .

[0038] Figure 2 An exemplary flowchart illustrating an embodiment of this application is shown, showing the acquisition of the fundamental frequency reference phase of each access point of the device under test at the measurement time.

[0039] like Figure 2 As shown, in step S210, it is determined whether the phase output by the programmable logic controller (PLC) or phase-locked loop (PLL) device within a preset time period is within a preset phase range under stable grid conditions. In response to the PLC or PLL device outputting a phase within the preset time period being within the preset phase range, in step S220, the fundamental frequency reference phase of the device under test (DUT) connection point at the measurement time is obtained through the PLC or PLL device. In response to the PLC or PLL device outputting a phase outside the preset phase range within the preset time period, in step S230, the fundamental frequency reference phase of the DUT connection point at the measurement time is obtained based on the steady-state three-phase voltage signal acquired when no disturbance is injected into the DUT connection point.

[0040] The specific process involved in step S230 in the embodiments of this application can be found in [reference needed]. Figure 3 .

[0041] Figure 3 An exemplary flowchart of an embodiment of this application is shown, which illustrates the acquisition of the fundamental frequency reference phase of the access point of the device under test at the measurement time based on the steady-state three-phase voltage signal acquired when the device under test is injected without disturbance.

[0042] like Figure 3 As shown, in step S310, the steady-state three-phase voltage signal acquired during undisturbed injection at the access point of the device under test is transformed to the αβ stationary coordinate system. In step S320, a discrete Fourier transform is performed on the voltage signal transformed to the αβ stationary coordinate system to obtain the positive-sequence complex voltage phasor at the fundamental frequency. In step S330, the angle of the positive-sequence complex voltage phasor at the fundamental frequency is extracted as the fundamental frequency reference phase of the access point of the device under test at the measurement time.

[0043] Specifically, the steady-state three-phase voltage signal v collected when the connection point of the device under test is undisturbed is injected. a (t), v b (t) and v c (t) is transferred to the αβ stationary coordinate system to obtain v α (t) and v β (t). Next, based on the grid fundamental frequency f0, the voltage signal v transformed into the αβ stationary coordinate system is... α (t) and v β (t) is subjected to discrete Fourier transform to obtain V α =FFT{v α (t)}|{f0},V β =FFT{v β (t)}|{f0}. Then, based on the discrete Fourier transform, the positive-sequence complex voltage phasor V is obtained. pos =V α +jV β Extract the angle of the positive-sequence complex voltage phasor at the fundamental frequency. The fundamental frequency reference phase of the access point of the device under test at the measurement time.

[0044] Step S110 ensures that the fundamental frequency reference phase of the device under test (DUT) connection point at the measurement time can be obtained with extremely high accuracy under any circumstances. Under normal and stable operation, the phase information is primarily provided directly by the system's built-in, typically highly accurate, programmable logic controller (PLC) or phase-locked loop (PLL). These devices are usually carefully designed and calibrated to provide a very reliable phase reference when the power grid is stable. When the PLC / PLL is unavailable or unreliable, the fundamental frequency reference phase is extracted from the original voltage waveform by acquiring the steady-state three-phase voltage signal under undisturbed injection and performing rigorous signal processing. This method is independent of the PLC / PLL's performance and can stably and accurately calculate the fundamental frequency reference phase even under conditions of large power grid fluctuations and potential loss of lock-in or decreased accuracy of traditional PLL devices. By ensuring high-precision acquisition of the fundamental frequency reference phase, errors in subsequent phase correction stages are avoided at the source, greatly improving the accuracy of the entire impedance measurement and model construction.

[0045] After step S110 is completed, in step S120, a coarse scan of the first-level injection is performed, and a disturbance is injected within a preset frequency band at a first preset resolution and coarse scan response data is collected.

[0046] In the embodiments of this application, during the coarse scan of the first-level injection, for multiple coarse scan frequency points that cover a preset frequency band and are logarithmically distributed within the preset frequency band, the first basis vector injection and the second basis vector injection are respectively performed in the αβ stationary coordinate system.

[0047] By using a coarse frequency sweep with a logarithmic distribution, the entire preset frequency band can be quickly covered with minimal measurement cost. This allows it to efficiently locate potential resonance points or impedance amplitude-phase abrupt change ranges, providing clear guidance for subsequent fine frequency sweeps and avoiding blind and time-consuming comprehensive detailed scans.

[0048] Specifically, the preset frequency band range is set according to actual needs and historical experience, and this application does not impose any restrictions on it. For example, it can range from tens of hertz to thousands of hertz.

[0049] Specifically, the first preset resolution is set according to actual needs and historical experience, and this application does not impose any restrictions. The first preset resolution is achieved by selecting multiple coarsely scanned frequency points with a logarithmic distribution. This means that more frequency points are selected for measurement in the low-frequency region, while they are relatively sparse in the high-frequency region. This effectively covers a wide frequency range, while focusing on the low- and mid-frequency bands where resonance is more likely to occur, in order to quickly preset the frequency band range to locate potential resonance or amplitude-phase transition intervals. For example, 40-80 logarithmically distributed frequency points may be selected.

[0050] In the embodiments of this application, during the execution of the first basis vector injection, at frequency f k A first disturbance signal corresponding to the first component is injected at the location.

[0051] In some embodiments, the amplitude of the injected first disturbance signal is 0.5%–1% of the rated voltage of the device under test. In other embodiments, to obtain a clearer response signal, it may be appropriately increased to 1%–3%.

[0052] In the embodiments of this application, during the second basis vector injection process, at frequency |f k A second disturbance signal corresponding to the second component is injected at -2f0|, where f0 is the base frequency of the power grid.

[0053] In embodiments of this application, the second component is the conjugate complex number of the first component or the product of the first component and the phase rotation operator.

[0054] Specifically, in f kWhen -2f0≥0, the second component is the complex conjugate of the first component. k When -2f0 < 0, the second component is the product of the first component and the phase rotation operator, where the phase rotation operator is... The fundamental frequency reference phase of the device under test at the measurement time is the access point of the device under test.

[0055] In f k When -2f0 < 0, multiply by the fundamental frequency reference phase. Related rotation operators This ensures that even when the physical measuring device maps a negative frequency signal to a positive frequency for display, its phase information can still be accurately corrected and recovered. This avoids phase errors caused by negative frequency mapping, thus guaranteeing the mathematical accuracy and physical authenticity of impedance measurement results in the low-frequency and even negative frequency regions.

[0056] By injecting a dual-basis vector, in the αβ stationary coordinate system, a first basis vector (corresponding to the positive-sequence component) is injected at the target frequency, and a second basis vector (corresponding to the negative-sequence component or a phase-corrected negative-sequence component) is simultaneously injected at the mirror frequency. This method can actively excite and accurately decouple the frequency coupling phenomenon commonly found in power electronic devices. This solves the problem that traditional single-frequency injection cannot accurately identify and quantify the coupling effect between positive and negative sequences, thus enabling a more comprehensive and realistic characterization of the device's impedance characteristics.

[0057] In the embodiments of this application, voltage injection or current injection can be performed during the execution of the first and second basis vector injections. Voltage injection is preferred, while current injection is used when the injection point impedance is extremely low or when protection restrictions apply.

[0058] In the embodiments of this application, during the execution of the first and second basis vector injections, each injection point is held for a period of time, which typically depends on the frequency. For example, for low frequencies (f < 10 Hz), the holding time is long, typically greater than or equal to 10 periods of the currently injected perturbation signal. For mid-frequency frequencies (10 Hz–100 Hz), the holding time is 5–10 periods of the currently injected perturbation signal. For high frequencies (> 100 Hz), the holding time is 2–5 periods of the currently injected perturbation signal. During the holding time of each injection point, the original time-domain waveform data of the entire period is captured and recorded. The recorded data includes v αk (t)(α-axis voltage), v βk (t)(β-axis voltage), i αk (t)(α-axis current), i βk Response data such as (t)(β-axis current) and dc_k(t)(DC-side voltage). Simultaneously, the fundamental frequency reference phase... It will also be acquired and recorded.

[0059] After step S120 is completed, in step S130, the coarse scan response data is analyzed in conjunction with the acquired fundamental frequency reference phase to identify the target frequency band that needs to be measured at the second preset resolution.

[0060] In the embodiments of this application, the second preset resolution is greater than the first preset resolution.

[0061] In the embodiments of this application, the aforementioned coarse scan response data includes time-domain response waveform data.

[0062] The specific process involved in step S130 in the embodiments of this application can be found in [reference needed]. Figure 4 .

[0063] Figure 4 An exemplary flowchart illustrating the analysis of coarse scan response data according to an embodiment of this application is shown.

[0064] like Figure 4 As shown, in step S410, a discrete Fourier transform is performed on the coarse scan response data to extract the corresponding voltage and current spectra. In step S420, a complex impedance matrix is ​​calculated based on the extracted voltage and current spectra. In step S430, the target frequency band requiring a second preset resolution measurement is identified based on the complex impedance matrix.

[0065] Specifically, for the coarse scan response data v αk (t)(α-axis voltage), v βk (t)(β-axis voltage), i αk (t)(α-axis current), i βk The voltage spectrum and current spectrum are obtained by performing a discrete Fourier transform on (t)(β-axis current).

[0066] The specific process involved in step S420 in the embodiments of this application can be found in the following documents. Figure 5 .

[0067] Figure 5 An exemplary flowchart illustrating the calculation of the complex impedance matrix based on the extracted voltage and current spectra according to an embodiment of this application is shown.

[0068] like Figure 5As shown, in step S510, voltage and current components at each coarse-scan injection frequency and its corresponding mirror frequency are extracted from the extracted voltage and current spectra. In step S520, the voltage and current components at each coarse-scan injection frequency are combined into a corresponding positive-sequence response vector, and the voltage and current components at each mirror frequency are combined into a corresponding negative-sequence response vector or a negative-sequence response vector after phase compensation. In step S530, the positive-sequence response vector and its corresponding negative-sequence response vector or the negative-sequence response vector after phase compensation are integrated to obtain corresponding voltage response column vectors and current response column vectors. All voltage response column vectors are combined into a voltage response matrix, and all current response column vectors are combined into a current response matrix. In step S540, the voltage response matrix is ​​right-multiplied by the inverse of the current response matrix to obtain the admittance matrix. In step S550, the inverse operation of the admittance matrix is ​​performed to obtain the complex impedance matrix.

[0069] Specifically, the formula for calculating the image frequency is: Image frequency = f i -2f0, where f0 is the base frequency of the power grid, f i Let be the injection frequency for the i-th coarse scan.

[0070] In the embodiments of this application, the specific process of combining the voltage and current components at each mirror frequency into the corresponding negative-order response vector can be found in [reference needed]. Figure 6 .

[0071] Figure 6 An exemplary flowchart illustrating an embodiment of this application is shown, which combines the voltage and current components at each mirror frequency into a corresponding negative-order response vector.

[0072] like Figure 6 As shown, in step S610, it is determined whether the image frequency is less than 0. If the image frequency is not less than 0, in step S620, no phase compensation is performed on the negative-order response vector. If the image frequency is less than 0, in step S630, a complex multiplication operation is performed on the negative-order response vector using a phase rotation operator to obtain a phase-compensated negative-order response vector.

[0073] Specifically, the phase rotation operator is The fundamental frequency reference phase of the device under test at the measurement time is the access point of the device under test.

[0074] Specifically, the frequency f is obtained from the voltage spectrum and the current spectrum. k The corresponding voltage component V αk (f k ) and V βk (f k ), frequency f k The corresponding current component I αk(f k ) and I βk (f k ), frequency f k The voltage component V corresponding to -2f0 αk (f k -2f0) and V βk (f k -2f0), frequency f k The current component I corresponding to -2f0 αk (f k -2f0) and I βk (f k -2f0). Next, construct the frequency f. k The positive order response vector: V pos (f k ) = V αk (f k )+jV βk (f k ) and I pos (f k ) = I αk (f k )+jI βk (f k ), construct frequency f k Negative-order response vector under -2f0: V neg (f k -2f0)=V αk (f k -2f0)+jV βk (f k -2f0) and I neg (f k -2f0)=I αk (f k -2f0)+jI βk (f k -2f0). And when the image frequency is less than 0, the phase-compensated negative-order response vector is obtained: as well as Then, combine all the voltage response column vectors into a voltage response matrix, and combine all the current response column vectors into a current response matrix. Next, multiply the voltage response matrix by the inverse of the current response matrix to obtain the admittance matrix, and then inverse the admittance matrix to obtain the complex impedance matrix.

[0075] By integrating all positive-sequence and negative-sequence (or compensated) response vectors, voltage response column vectors and current response column vectors are formed. Then, all column vectors are combined into voltage response matrices and current response matrices. Finally, the admittance matrix is ​​obtained by right-multiplying the voltage response matrix by the inverse of the current response matrix, and then the complex impedance matrix is ​​obtained by inverting the admittance matrix. This matrix operation-based method possesses high systematicity, robustness, and parallelism. It can simultaneously process response data from multiple frequency points and multiple injection conditions, and through matrix inversion, effectively calculates the multi-port complex impedance matrix describing the impedance relationships between all input and output ports of the device. This not only improves computational efficiency but also makes the obtained impedance model more comprehensive and accurate, providing precise mathematical tools for subsequent system stability analysis, harmonic mitigation, and control parameter optimization.

[0076] The specific process involved in step S430 in the embodiments of this application can be found in [reference needed]. Figure 7 .

[0077] Figure 7 An exemplary flowchart illustrating an embodiment of this application is shown, which identifies a target frequency band requiring a second preset resolution measurement based on a complex impedance matrix.

[0078] like Figure 7 As shown, in step S710, it is sequentially determined whether the change of each complex impedance vector in the complex impedance matrix between its two corresponding adjacent coarse sweep frequency points satisfies the linear resonance condition. In response to a complex impedance vector not satisfying the linear resonance condition between its two corresponding adjacent coarse sweep frequency points, no action is performed in step S720. In response to a complex impedance vector satisfying the linear resonance condition between its two corresponding adjacent coarse sweep frequency points, the frequency interval between its two corresponding adjacent coarse sweep frequency points is selected as a candidate frequency interval in step S730. Then, in step S740, all candidate frequency intervals are summarized into a target frequency band.

[0079] In the embodiments of this application, the linear resonance condition includes: the amplitude change of the complex impedance vector between its two corresponding adjacent coarse sweep frequency points exceeds a first preset difference value; and the phase difference change of the complex impedance vector between its two corresponding adjacent coarse sweep frequency points exceeds a second preset difference value.

[0080] In the embodiments of this application, the first and second preset difference values ​​are set according to actual needs and historical experience, and this application does not impose any limitations on them. For example, in some embodiments, the first preset difference value is 3dB–6dB, and the second preset difference value is 20°.

[0081] In some embodiments of this application, the short-time nonlinear frequency response (NFP) scan results can be used to determine whether there are signs of resonance in the corresponding frequency band, and the frequency band showing signs of resonance can be used as the target frequency band.

[0082] By determining whether the change in the complex impedance vector between adjacent coarse sweep frequency points satisfies a preset linear resonance condition (i.e., the amplitude or phase difference change exceeds a threshold), frequency ranges that may exhibit resonance, anti-resonance, or drastic changes in dynamic characteristics are automatically identified. This significantly saves measurement time and computational resources. By focusing subsequent finer frequency sweeps on these selected candidate frequency ranges, measurement efficiency can be greatly improved, avoiding wasted resources in regions with gentle impedance changes. The design of the linear resonance condition (considering both amplitude and phase difference changes) effectively captures various forms of resonance or potential instability regions. These regions typically correspond to drastic changes in system impedance, which are crucial to system stability and performance. This ensures that these critical dynamic characteristics are not overlooked in subsequent fine frequency sweeps. By performing higher resolution measurements within these target frequency bands, the resonant frequency, damping characteristics, and abrupt phase changes can be characterized more accurately, resulting in a more accurate and complete device impedance model, which is essential for system stability analysis and control parameter design.

[0083] After step S130 is completed, in step S140, a second-level fine scan is performed for the target frequency band, and perturbation injection is performed in the target frequency band at a second preset resolution and fine scan response data is collected.

[0084] In the embodiments of this application, the specific process involved in step S140 is the same as that involved in step S120, and will not be described again here.

[0085] In the embodiments of this application, during the execution of steps S120 and S140, the injected voltage or current is monitored in real time, and the specific process involved in the injection protection mechanism is described. The specific process involved in the injection protection mechanism can be found in [reference needed]. Figure 8 .

[0086] Figure 8 An exemplary flowchart illustrating the process involved in the injection protection mechanism of this application embodiment is shown.

[0087] like Figure 8 As shown, in step S810, it is determined whether the injected voltage or current exceeds the corresponding preset safety threshold. If the injected voltage or current does not exceed the corresponding preset safety threshold, no action is performed in step S820. If the injected voltage or current exceeds the corresponding preset safety threshold, in step S830, the injection is stopped, and the injection amplitude is reduced or switched to a split measurement scheme.

[0088] In the embodiments of this application, during the process of reducing the injection amplitude, a preset amplitude is reduced each time, and a minimum amplitude value is set. The preset amplitude can be set according to actual needs and historical experience. For example, it can be reduced by 0.5% each time.

[0089] In the embodiments of this application, the initial approach is to reduce the injection amplitude, a preferred method designed to find an injection level that is both safe and yields a valid signal without interrupting online measurements. If the injection amplitude is reduced to its minimum value, a split measurement scheme is switched to. This provides a foolproof backup plan, measuring the device under test and the power grid separately after decoupling. While sacrificing the convenience of online measurements, this ensures that regardless of the system's coupling strength or stability, the impedance data required for evaluation can ultimately be safely obtained.

[0090] In embodiments of this application, the split measurement scheme includes: temporarily disconnecting the device under test (DUT) from the power grid system and measuring the impedance of the DUT side and the impedance of the power grid side separately. By obtaining the impedance of the DUT side and the impedance of the power grid side and comparing the two, potential instability modes and resonance points can be predicted. If it is found that there is poor impedance matching or mutual cancellation between the two at a certain frequency point, measures can be taken to adjust control parameters, design filters, or optimize system topology to avoid power grid system instability.

[0091] After completing step S140, in step S150, the fine-scan response data is analyzed in conjunction with the acquired fundamental frequency reference phase, and the evaluation results of the contribution of each device under test to the stability of the power grid system are obtained based on the analysis results of the fine-scan response data and the analysis results of the coarse-scan response data.

[0092] In the embodiments of this application, the process of analyzing the fine scan response data is the same as the process of analyzing the coarse scan response data, and will not be described again here. That is, the result of analyzing the fine scan response data is the same as its corresponding complex impedance matrix.

[0093] The specific process involved in step S150 in the embodiments of this application can be found in [reference needed]. Figure 9 .

[0094] Figure 9 An exemplary flowchart illustrating an embodiment of this application is shown, demonstrating the acquisition of evaluation results of the contribution of each device under test to the stability of the power grid system.

[0095] like Figure 9As shown, in step S910, the impedance matrix of the device under test (DUT) is constructed based on the analysis results of the fine-scan response data and the coarse-scan response data. The nodal modal impedance matrix and loop gain matrix are obtained based on the impedance matrix of the DUT and the equivalent impedance matrix of the power grid system, respectively. In step S920, the system resonant frequency and the corresponding damping ratio are obtained based on the nodal modal impedance matrix. In step S930, the Nyquist trajectory of the eigenvalues ​​of the loop gain matrix is ​​plotted on the complex plane, and the number of encirclements of the Nyquist trajectory around the critical point is obtained. In step S940, the changes in the system resonant frequency and damping ratio before and after removing the DUT are calculated, and the minimum critical distance between the Nyquist trajectory and the critical point is calculated. In step S950, a modal impact report for each DUT access point is generated based on the changes in the system resonant frequency before and after removing the DUT, the changes in the damping ratio before and after removing the DUT, the number of encirclements of the Nyquist trajectory around the critical point, and the minimum critical distance between the Nyquist trajectory and the critical point. In step S960, a priority list indicating the contribution of each device under test to system stability is generated based on the modal impact reports of each device under test access point.

[0096] In the embodiments of this application, the impedance matrix of the device under test is obtained by using the complex impedance matrix corresponding to the coarse scan response data and the complex impedance matrix corresponding to the fine scan response data. Specifically, the complex impedance matrix corresponding to the coarse scan response data is used as the basic framework for the entire preset frequency band. In the target frequency band covered by the fine scan, the data points of the coarse scan are replaced with the complex impedance matrix obtained by the fine scan, thereby forming a discrete impedance matrix dataset. Then, a system identification technique, such as vector fitting (VF), is used to find a matrix Zi(s) that best fits the discrete impedance matrix dataset in terms of frequency response. This matrix Zi(s) is the impedance matrix of the device under test.

[0097] In the embodiments of this application, during the process of obtaining the node mode impedance matrix and loop gain matrix based on the impedance matrix of the device under test (DUT) and the equivalent impedance matrix of the power grid system, the equivalent impedance Zg(s) on the power grid side is first obtained. Zg(s) represents the equivalent impedance at the DUT connection point, looking towards the power grid. The equivalent impedance Zg(s) on the power grid side is obtained by performing a frequency sweep injection on the connection point when no DUT is connected and measuring its impedance. Next, the loop gain matrix L(s) is obtained using the DUT impedance matrix Zi(s) and the power grid equivalent impedance Zg(s), where L(s) = Zg(s) / Zi(s). Simultaneously, for analysis in the frequency domain, the DUT impedance matrix Zi(jω) and the power grid equivalent impedance Zg(jω) are obtained at s = jω, and the node mode impedance matrix Zn(jω) = Zg(jω) + Zi(jω) is obtained.

[0098] After obtaining the nodal modal impedance matrix, its eigenvalues ​​can be calculated for each frequency point ω. Then, peak detection is performed on the amplitude-frequency curve of the eigenvalues ​​to identify one or more system resonant frequencies. For each identified resonant frequency, the corresponding damping ratio is estimated using the half-power point method (peak picking).

[0099] Then, the eigenvalues ​​of the loop gain matrix L(s) are calculated, and the Nyquist trajectory of the eigenvalues ​​is plotted on the complex plane. The generalized Nyquist criterion is applied by counting the number of loops the Nyquist trajectory encircles the critical point to determine the closed-loop stability of the system when the device under test is removed or retained. The minimum critical distance between the Nyquist trajectory and the critical point is also calculated. Specifically, the critical point is the point (-1, 0) on the complex plane.

[0100] Subsequently, the aforementioned methods for obtaining the system resonant frequency and damping ratio were used to obtain the system resonant frequency and damping ratio after removing the device under test. The changes in the system resonant frequency and damping ratio before and after removing the device under test were then calculated.

[0101] Finally, the changes in system resonant frequency, damping ratio, number of Nyquist trajectory loops around the critical point, and minimum critical distance between the Nyquist trajectory and the critical point are recorded before and after the removal of the device under test (DUT) to generate modal impact reports for each DUT access point. The weighted sums of these values ​​are then applied to the modal impact reports for each DUT access point to obtain a ranking of the DUTs. Specifically, the weights corresponding to the changes in system resonant frequency, damping ratio, number of Nyquist trajectory loops around the critical point, and minimum critical distance between the Nyquist trajectory and the critical point are set according to actual needs and historical experience; this application does not impose any restrictions on these weights.

[0102] Through step S150, combining coarse and fine scan data, multi-dimensional stability index analysis, and comparative analysis before and after equipment removal, a detailed modal impact report can be generated. It accurately identifies and quantifies the impact of each device connected to the grid on the system's inherent resonance and damping characteristics, and provides intuitive stability margin information. More importantly, by weighted summing of key indicators and generating a priority list, it can clearly identify the devices that pose the greatest risk to system stability or offer the greatest potential for improvement. This guides fault diagnosis, optimization of equipment design, adjustment of control strategies, or development of effective system modification plans, ultimately significantly improving the operational stability, reliability, and power quality of the power grid system.

[0103] In summary, through the frequency sweep measurement scheme provided above, this embodiment of the application employs a hierarchical coarse and fine sweep strategy. This method can first rapidly identify potential critical frequency regions within a wide frequency band, thereby avoiding time-consuming high-resolution measurements across the entire frequency band and significantly improving measurement efficiency. Subsequently, targeted high-resolution fine sweeps are performed on these identified target frequency bands, ensuring accurate and detailed response data in the critical regions. Combined with the fundamental frequency reference phase, both coarse and fine sweep data analysis can guarantee phase accuracy, which is crucial for subsequently constructing accurate impedance models and conducting stability assessments. Finally, by integrating the results of coarse and fine sweeps, the contribution of each device under test to the stability of the power grid system can be assessed more comprehensively and accurately, providing more reliable system stability assessment results and helping to identify potential harmonic problems or oscillation risks.

[0104] Furthermore, in some embodiments, during the coarse scan of the first-stage injection, by performing a specific bibasic vector injection in the αβ stationary coordinate system, the frequency coupling characteristics of the device under test between positive and negative sequences can be accurately and completely identified. By injecting a corresponding compensation signal at the theoretical coupling frequency simultaneously with the main perturbation frequency injection, this method can actively and completely excite the frequency coupling dynamics of the system, thereby decoupling the positive and negative sequence responses. This eliminates the measurement errors and uncertainties in traditional methods and can accurately identify the complete impedance / admittance matrix. An accurate impedance model including coupling terms is obtained, making subsequent stability analysis more comprehensive and reliable.

[0105] Furthermore, in some embodiments, the voltage and current spectra are extracted by performing a Discrete Fourier Transform on the time-domain response waveform data. This innovatively addresses the frequency coupling effect caused by the power grid fundamental frequency, extracting not only the response at the injected frequency but also considering the response at its corresponding mirror frequency. By combining these positive-sequence and negative-sequence response vectors into complete voltage and current response matrices, and further calculating the admittance matrix and its inverse to obtain the complex impedance matrix, the constructed model accurately reflects the true behavior of the device under test under asymmetric or dynamic conditions, thus providing extremely accurate and comprehensive device impedance characteristics. Simultaneously, the phase compensation mechanism for the negative mirror frequency eliminates potential errors in low-frequency measurements, ensuring measurement consistency and accuracy across the entire frequency band.

[0106] Furthermore, in some embodiments, by monitoring the injected voltage or current in real time and comparing it with a preset safety threshold, this method can effectively prevent damage to the device under test or the power grid due to excessive injected disturbances. When a potential risk is detected, the method does not simply stop the test, but provides two intelligent response strategies. First, it attempts to reduce the injection amplitude, a preferred approach designed to find an injection level that is both safe and yields a valid signal without interrupting online measurements. If reducing the injection amplitude still fails to meet safety requirements, the method switches to a split measurement scheme. This provides a foolproof backup plan, measuring the device under test and the power grid separately after decoupling. While sacrificing the convenience of online measurements, it ensures that regardless of the system's coupling strength or stability, the impedance data required for evaluation can ultimately be safely obtained.

[0107] This application also provides a frequency sweep measurement system, which can perform frequency sweep measurement using the aforementioned frequency sweep measurement method 100, or other methods, which are not limited herein.

[0108] Figure 10 An exemplary structural block diagram of a sweep frequency measurement system according to an embodiment of this application is shown.

[0109] like Figure 10 As shown, the system 1000 includes a fundamental frequency reference phase acquisition module 1010, a coarse scan module 1020, a target frequency band acquisition module 1030, a fine scan module 1040, and a stability contribution evaluation module 1050. In the embodiments of this application, the fundamental frequency reference phase acquisition module 1010, the coarse scan module 1020, the target frequency band acquisition module 1030, the fine scan module 1040, and the stability contribution evaluation module 1050 may be individual units or integrated into the same controller; this application does not impose any restrictions here.

[0110] Specifically, the fundamental frequency reference phase acquisition module 1010 is used to acquire the fundamental frequency reference phase of each device under test access point at the measurement time.

[0111] Specifically, the coarse scan module 1020 is used to perform the first-level injection coarse scan, injecting disturbances within a preset frequency band at a first preset resolution and collecting coarse scan response data.

[0112] Specifically, the target frequency band acquisition module 1030 is used to analyze the coarse scan response data in conjunction with the acquired fundamental frequency reference phase in order to identify the target frequency band that needs to be measured at a second preset resolution.

[0113] Specifically, the fine scan module 1040 is used to perform a second-level injection fine scan for the target frequency band, injecting disturbances within the target frequency band at a second preset resolution and collecting fine scan response data.

[0114] Specifically, the stability contribution assessment module 1050 is used to analyze the fine-scan response data in conjunction with the acquired fundamental frequency reference phase, and to obtain the stability contribution assessment results of each device under test to the power grid system based on the analysis results of the fine-scan response data and the coarse-scan response data.

[0115] When the system 1000 performs frequency sweep measurement using the aforementioned frequency sweep measurement method 100, the fundamental frequency reference phase acquisition module 1010 executes the aforementioned step S110, the coarse sweep module 1020 executes the aforementioned step S120, the target frequency band acquisition module 1030 executes the aforementioned step S130, the fine sweep module 1040 executes the aforementioned step S140, and the stability contribution evaluation module 1050 executes the aforementioned step S150. The specific execution process can be found above and will not be repeated here.

[0116] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A sweep frequency measurement method, characterized in that, include: Obtain the fundamental frequency reference phase of each device under test at the measurement time; Perform the first-level injection coarse scan, injecting disturbances within a preset frequency band at a first preset resolution and collecting coarse scan response data; The coarse scan response data is analyzed in conjunction with the acquired fundamental frequency reference phase to identify the target frequency band that needs to be measured at a second preset resolution. For the target frequency band, a second-level injection fine scan is performed, and perturbation injection is performed in the target frequency band at a second preset resolution and fine scan response data is collected; By combining the obtained fundamental frequency reference phase, the fine-scan response data is analyzed, and the evaluation results of the contribution of each tested device to the stability of the power grid system are obtained based on the analysis results of the fine-scan response data and the analysis results of the coarse-scan response data.

2. The sweep frequency measurement method according to claim 1, characterized in that, During the process of obtaining the power grid fundamental frequency reference phase at each access point of the tested equipment, the following steps are performed: Determine whether the phase output by the programmable logic controller or phase-locked loop device is within a preset phase range within a preset time period under stable power grid conditions; In response to the fact that the phase output by the programmable logic controller or phase-locked loop device is within a preset phase range within a preset time period, the fundamental frequency reference phase of the access point of the device under test at the measurement time is obtained through the programmable logic controller or phase-locked loop device. In response to the fact that the phase output by the programmable logic controller or phase-locked loop device is not within the preset phase range within a preset time period, the fundamental frequency reference phase of the device under test at the measurement time is obtained based on the steady-state three-phase voltage signal collected when there is no disturbance injection at the device under test access point. In the process of obtaining the fundamental frequency reference phase of the device under test (DUT) at the measurement time based on the steady-state three-phase voltage signal acquired when there is no disturbance injection at the DUT's connection point, the following steps are performed: The steady-state three-phase voltage signal acquired when the connection point of the device under test is undisturbed is transformed into the αβ stationary coordinate system; Perform a discrete Fourier transform on the voltage signal transformed to the αβ stationary coordinate system to obtain the positive-sequence complex voltage phasor at the fundamental frequency; The angle of the positive sequence complex voltage phasor at the fundamental frequency is extracted as the fundamental frequency reference phase of the device under test at the measurement time.

3. The sweep frequency measurement method according to claim 1, characterized in that, During the coarse scan of the first-level injection, for multiple coarse scan frequency points that cover a preset frequency band and are logarithmically distributed within the preset frequency band, the first basis vector injection and the second basis vector injection are performed respectively in the αβ stationary coordinate system. During the execution of the first basis vector injection, at frequency f k A first perturbation signal corresponding to the first component is injected at the location; During the second basis vector injection process, at frequency |f k A second disturbance signal corresponding to the second component is injected at -2f0|, where f0 is the base frequency of the power grid.

4. The sweep frequency measurement method according to claim 3, characterized in that, The second component is the complex conjugate of the first component or the product of the first component and the phase rotation operator; where, in f k When -2f0≥0, the second component is the conjugate of the first component; in f k When -2f0 < 0, the second component is the product of the first component and the phase rotation operator, where the phase rotation operator is... The fundamental frequency reference phase of the device under test at the measurement time is the access point of the device under test.

5. The sweep frequency measurement method according to claim 1, characterized in that, The coarse scan response data includes time-domain response waveform data; The following steps are performed during the analysis of the coarse scan response data: The coarse scan response data is subjected to discrete Fourier transform to extract the corresponding voltage and current spectra. The complex impedance matrix is ​​calculated based on the extracted voltage and current spectra; The target frequency band requiring a second preset resolution measurement is identified based on the complex impedance matrix.

6. The sweep frequency measurement method according to claim 5, characterized in that, In the process of calculating the complex impedance matrix based on the extracted voltage and current spectra: The voltage and current components at each coarse-scan injection frequency and their corresponding image frequencies are extracted from the extracted voltage and current spectra. The image frequency is calculated using the formula: Image frequency = f i -2f0, where f0 is the base frequency of the power grid, f i Let i be the injection frequency for the i-th coarse scan; The voltage and current components at each coarse sweep injection frequency are combined into a corresponding positive-sequence response vector, and the voltage and current components at each mirror frequency are combined into a corresponding negative-sequence response vector or a negative-sequence response vector after phase compensation. The positive-sequence response vector and its corresponding negative-sequence response vector or the negative-sequence response vector after phase compensation are integrated to obtain the corresponding voltage response column vector and current response column vector. All voltage response column vectors are combined into a voltage response matrix, and all current response column vectors are combined into a current response matrix. The admittance matrix is ​​obtained by right-multiplying the voltage response matrix by the inverse of the current response matrix. The complex impedance matrix is ​​obtained by inverting the admittance matrix. In the process of combining the voltage and current components at each mirror frequency into the corresponding negative-order response vector, the following steps are performed: Determine if the mirror frequency is less than 0; When the image frequency is not less than 0, no phase compensation is performed on the negative-order response vector; In response to a mirror frequency less than 0, a complex multiplication operation is performed on the negative-order response vector using a phase rotation operator to obtain a phase-compensated negative-order response vector, wherein the phase rotation operator is... The fundamental frequency reference phase of the device under test at the measurement time is the access point of the device under test.

7. The sweep frequency measurement method according to claim 5 or 6, characterized in that, In the process of identifying the target frequency band requiring a second preset resolution measurement based on the complex impedance matrix, the following steps are performed: Determine in turn whether the changes of each complex impedance vector in the complex impedance matrix between its two adjacent coarse sweep frequency points satisfy the linear resonance condition. If the change of a complex impedance vector between its two adjacent coarse sweep frequencies does not satisfy the linear resonance condition, no action is taken. If the change of a certain complex impedance vector between its two adjacent coarse sweep frequency points satisfies the linear resonance condition, the frequency interval between its two adjacent coarse sweep frequency points is taken as the candidate frequency interval. All candidate frequency ranges are aggregated into the target frequency band; The linear resonance condition includes: The amplitude variation of the complex impedance vector between its two adjacent coarse sweep frequency points exceeds the first preset difference value. The phase difference between the complex impedance vector and its corresponding two adjacent coarse sweep frequency points exceeds the second preset difference value.

8. The sweep frequency measurement method according to claim 1, characterized in that, In the process of obtaining the evaluation results of the stability contribution of each tested device to the power grid system based on the analysis results of the fine scan response data and the coarse scan response data, the following steps are performed: Based on the analysis results of the fine scan response data and the coarse scan response data, the impedance matrix of the device under test is constructed. Based on the impedance matrix of the device under test and the equivalent impedance matrix of the power grid system, the node mode impedance matrix and the loop gain matrix are obtained respectively. Based on the nodal modal impedance matrix, the system resonant frequency and the damping ratio corresponding to the system resonant frequency are obtained; Plot the Nyquist trajectory of the eigenvalues ​​of the loop gain matrix on the complex plane, and obtain the number of encirclements of the Nyquist trajectory around the critical point; Calculate the changes in the system's resonant frequency and damping ratio before and after removing the tested equipment, and calculate the minimum critical distance between the Nyquist trajectory and the critical point; Modal impact reports for each access point of the tested device are generated based on the changes in the system resonant frequency before and after the removal of the tested device, the changes in the damping ratio before and after the removal of the tested device, the number of encirclements of the critical point by the Nyquist trajectory, and the minimum critical distance between the Nyquist trajectory and the critical point. Based on the modal impact reports of each device under test (DUT) access point, a priority list is generated to indicate the contribution of each DUT to system stability.

9. The sweep frequency measurement method according to claim 1, characterized in that, During the coarse scan of the first-level injection and the fine scan of the second-level injection, the injected voltage or current is monitored in real time, and it is determined whether the injected voltage or current exceeds the corresponding preset safety threshold. No action is taken if the injected voltage or current does not exceed the corresponding preset safety threshold. In response to the injected voltage or current exceeding the corresponding preset safety threshold, the injection is stopped, and the injection amplitude is reduced or the measurement scheme is switched to a split measurement scheme. The split measurement scheme includes: temporarily disconnecting the device under test from the power grid system and measuring the impedance of the device under test and the impedance of the power grid.

10. A sweep frequency measurement system, characterized in that, The system comprises: Frequency sweep measurement performed using the frequency sweep measurement method as described in any one of claims 1-9 The fundamental frequency reference phase acquisition module is used to acquire the fundamental frequency reference phase of each device under test access point at the measurement time; The coarse scan module is used to perform the first-level injection coarse scan, injecting disturbances within a preset frequency band at a first preset resolution and collecting coarse scan response data; The target frequency band acquisition module is used to analyze the coarse scan response data in conjunction with the acquired fundamental frequency reference phase in order to identify the target frequency band that needs to be measured at a second preset resolution. The fine scan module is used to perform a second-level injection fine scan for the target frequency band, injecting disturbances within the target frequency band at a second preset resolution and collecting fine scan response data; The stability contribution assessment module is used to analyze the fine-scan response data in conjunction with the acquired fundamental frequency reference phase, and to obtain the stability contribution assessment results of each device under test to the power grid system based on the analysis results of the fine-scan response data and the analysis results of the coarse-scan response data.

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