A diesel generator load fluctuation safety domain evaluation method based on sweep frequency identification

Abstract

This invention provides a method for assessing the safe domain of diesel generator load fluctuations based on frequency sweep identification, belonging to the field of operational safety assessment. Under the steady-state operation of the diesel generator, a small-amplitude frequency sweep power disturbance that does not change its steady-state operating point is applied to the generator, and the frequency sweep power disturbance signal and the corresponding frequency deviation response signal are simultaneously acquired. Based on the frequency sweep power disturbance signal and the frequency deviation response signal, a general frequency response function for the power-frequency channel, independent of the internal structure and control parameters of the diesel generator, is obtained through frequency domain identification. The load fluctuation signal to be assessed is acquired, converted to the frequency domain to obtain the load disturbance spectrum, and a predicted frequency deviation spectrum is obtained. The time-domain frequency deviation response of the diesel generator under the action of the load fluctuation signal is reconstructed. The maximum frequency deviation and the maximum frequency change rate are extracted and compared with the corresponding preset safety thresholds to determine whether the load fluctuation is within the safe domain of the diesel generator.

Description

Technical Field

[0001] This invention belongs to the technical field of diesel generator frequency response analysis and operation safety assessment, specifically involving a method for assessing the load fluctuation safety domain of a diesel generator based on frequency sweep identification. Background Technology

[0002] Diesel generators are widely used in marine power systems, isolated microgrids, emergency power systems, and distributed power supply scenarios. In these applications, the load is often fluctuating, which can easily cause deviations in the speed and frequency of the diesel generator. When the load disturbance is large, problems such as excessively low frequency minimums, excessively large frequency change rates, and excessively long recovery times may occur, which can even lead to a decline in power quality or unit instability in severe cases. Therefore, accurately assessing the tolerable range of diesel generators under different load fluctuation conditions is of great significance for ensuring their safe and stable operation.

[0003] Existing methods for assessing load disturbances in diesel generators mainly include experimental testing and modeling simulation. Experimental testing methods typically employ step loading tests or ramp loading tests, which require applying significant power disturbances to the actual generator set. This approach suffers from high testing costs, high testing risks, and significant impact on equipment. Modeling simulation methods, on the other hand, rely on the precise structural and control parameters of the diesel engine, governor, generator, and load. However, in actual engineering projects, the structures of generator sets from different manufacturers are complex, and some key parameters are difficult to obtain, making it difficult to directly apply modeling analysis methods.

[0004] Furthermore, existing methods mostly focus on time-domain analysis under single disturbance conditions. Although they can obtain the frequency response process of diesel generators under specific disturbances, they are difficult to extend to multiple disturbance forms with limited experimental data. When analyzing different forms of load disturbances, conducting time-domain tests or full-model simulations one by one is not only labor-intensive but also inefficient.

[0005] Therefore, there is an urgent need for a diesel generator load fluctuation safety domain assessment method that does not rely on detailed internal structural parameters of the diesel generator, has low testing risk, and can be efficiently applied to various load disturbance forms to meet the needs of safety analysis and operation assessment in engineering applications. Summary of the Invention

[0006] To address the shortcomings of existing diesel generator load fluctuation safety assessment methods, which rely on large disturbance tests or detailed structural parameters, resulting in high testing risks and limited applicability, this invention provides a diesel generator load fluctuation safety domain assessment method and system based on frequency sweep identification. This method injects a small-amplitude frequency sweep power disturbance under steady-state operation of the diesel generator, simultaneously acquiring the disturbance signal and frequency deviation response signal. Through frequency domain identification, a universal frequency response function for the power-frequency channel, independent of internal structure and control parameters, is obtained. This universal frequency response function is then multiplied point-by-point in the frequency domain with the spectrum of any load fluctuation signal to be assessed. The time-domain frequency deviation response is reconstructed through inverse transformation, and the maximum frequency deviation and maximum frequency change rate are extracted. These are compared with a preset safety threshold to determine the load fluctuation safety domain. This invention enables batch safety assessment of various forms of load fluctuations with a single frequency sweep identification, resulting in low testing risk, strong applicability, and no need for complex modeling or large disturbance tests, significantly improving assessment efficiency and safety.

[0007] The technical solutions adopted by this invention to solve its technical problems include:

[0008] I. Methodology and Scheme

[0009] A method for assessing the safety domain of diesel generator load fluctuations based on frequency sweep identification includes the following steps:

[0010] Under the steady-state operation of the diesel generator, a small-amplitude sweep frequency power disturbance that does not change its steady-state operating point is applied to the diesel generator, and the sweep frequency power disturbance signal and the corresponding frequency deviation response signal are collected simultaneously. The key to this step is that the applied power disturbance amplitude is small enough to ensure that the operating point of the diesel generator does not shift significantly, thereby satisfying the linear time-invariant assumption of the power-frequency channel and laying the foundation for subsequent frequency domain identification.

[0011] Based on the swept-frequency power disturbance signal and frequency deviation response signal, a universal frequency response function for the power-frequency channel, independent of the internal structure and control parameters of the diesel generator, is obtained through frequency domain identification. This universal frequency response function is a non-parametric description of the dynamic characteristics of the diesel generator's power-frequency channel, reflecting the system's gain and phase response under different frequency disturbances. Since this function is directly identified from experimental data, it does not require knowledge of the structural and control parameters of internal subsystems such as the diesel engine, governor, and generator, fundamentally solving the problem that existing modeling and simulation methods are difficult to apply directly due to the difficulty in obtaining parameters.

[0012] The load fluctuation signal to be evaluated in any form is acquired and converted to the frequency domain to obtain the load disturbance spectrum. This load disturbance spectrum is then multiplied point-by-point in the frequency domain by the general frequency response function to obtain the predicted frequency deviation spectrum. This step utilizes the fundamental frequency domain relationship of linear systems: the system output spectrum equals the product of the input spectrum and the frequency response function. Since the aforementioned general frequency response function fully characterizes the power-frequency channel of the diesel generator, this multiplication operation can predict the frequency deviation output spectrum of the system under any input.

[0013] An inverse Fourier transform is performed on the predicted frequency deviation spectrum to reconstruct the time-domain frequency deviation response of the diesel generator under the load fluctuation signal. This step allows for the direct calculation of the dynamic curve of the diesel generator's time-domain frequency deviation based on the frequency response function obtained through frequency sweep identification and the load fluctuation signal to be evaluated, without conducting actual large-disturbance loading tests.

[0014] The maximum frequency deviation and maximum frequency change rate are extracted based on the time-domain frequency deviation response. These are then compared to their corresponding preset safety thresholds to determine whether the load fluctuation is within the safe operating range of the diesel generator. The maximum frequency deviation reflects the degree of frequency drop, and the maximum frequency change rate reflects the degree of dynamic impact; together, they constitute the core indicator system for determining the safe operating range. When neither exceeds its respective preset allowable threshold, the load fluctuation is determined to be within the safe operating range; if either indicator exceeds the limit, the load fluctuation is determined to be outside the safe operating range.

[0015] Furthermore, the small-amplitude sweep frequency power disturbance is achieved by injecting d-axis and q-axis disturbance currents in a synchronous rotating coordinate system into the diesel generator. The sweep frequency power disturbance signal is calculated from the synchronously acquired d-axis voltage, q-axis voltage, d-axis disturbance current, and q-axis disturbance current. This dq-axis injection method is a preferred implementation for three-phase diesel generator systems, capable of generating a sweep frequency excitation signal in the power-frequency channel without changing the steady-state operating point of the equipment.

[0016] Furthermore, the frequency deviation response signal is determined by the difference between the real-time output frequency of the diesel generator and the steady-state operating reference frequency, which can be obtained by measuring the generator speed signal.

[0017] Furthermore, the general frequency response function is obtained through the following steps: performing Fourier transforms on the swept power disturbance signal and the frequency deviation response signal respectively to obtain the corresponding input spectrum and output spectrum, and calculating the ratio of the output spectrum to the input spectrum. This ratio method identification is the core operation of the frequency domain identification in this scheme, which can eliminate the influence of the input signal spectral characteristics on the identification results and obtain the inherent frequency response characteristics of the system.

[0018] Furthermore, when the general frequency response function is discrete frequency data, linear interpolation is performed on the discrete frequency data to ensure that the interpolated general frequency response function corresponds one-to-one with the frequency points of the load disturbance spectrum. This processing method solves the engineering problem that the frequency domain point-by-point multiplication method cannot be directly executed when the frequency sweep test frequency points are limited and the frequency components of the load fluctuation signal to be evaluated may not be completely consistent with the frequency sweep frequency points.

[0019] Furthermore, the maximum frequency deviation is the maximum absolute value of the time-domain frequency deviation response, and the maximum frequency change rate is the maximum absolute value of the time-domain frequency deviation response after taking the derivative with respect to time.

[0020] Furthermore, the arbitrary form of the load fluctuation signal to be evaluated includes any one of the following: step load disturbance signal, ramp load disturbance signal, periodic load disturbance signal, and load power fluctuation signal collected under actual operating conditions. This demonstrates the versatility of the method of the present invention, eliminating the need to conduct separate experiments or remodel for different types of disturbances.

[0021] Furthermore, the preset safety thresholds include a maximum allowable frequency deviation threshold and a maximum allowable frequency change rate threshold, which are set based on the operating requirements of the diesel generator. Operating requirements may include diesel generator capacity, operating conditions, power grid specifications, or industry standards, etc., and engineers can flexibly set them according to actual conditions.

[0022] Furthermore, by utilizing the general frequency response function obtained from a single frequency sweep identification, frequency domain mapping and safety domain determination are performed on multiple different load fluctuation signals to be evaluated, thereby achieving batch evaluation of the safety domain of diesel generators. This "one-time identification, multiple evaluations" characteristic is one of the key advantages of this scheme compared to existing methods, and it is also the key to achieving efficient construction of the safety domain.

[0023] II. System Solution

[0024] This invention also provides a diesel generator load fluctuation security domain assessment system based on frequency sweep identification. This system corresponds one-to-one with the method scheme and includes:

[0025] The frequency sweep test module is used to apply a small frequency sweep power disturbance under the steady-state operation of the diesel generator and simultaneously acquire the frequency sweep power disturbance signal and the frequency deviation response signal.

[0026] The frequency response identification module is used to identify the general frequency response function of the diesel generator power-frequency channel based on the swept-frequency power disturbance signal and the frequency deviation response signal. This module implements the function of the frequency domain identification step in the above method and outputs a general frequency response function that can be directly used for subsequent response prediction.

[0027] The response prediction module is used to convert the load fluctuation signal to be evaluated to the frequency domain, perform frequency domain operations with the general frequency response function, and then inversely transform it to the time domain to reconstruct the time-domain frequency deviation response. This module is the specific implementation of the frequency domain reconstruction method.

[0028] The security assessment module extracts assessment indicators based on the time-domain frequency deviation response and compares them with preset thresholds to output a security domain determination result. This module automates the determination of dual-indicator security constraints.

[0029] The four modules described above are interconnected, forming a complete technical architecture from frequency sweep testing to safety domain determination. This system can rapidly assess the safety domain of a diesel generator under various load fluctuation conditions without acquiring the internal structural parameters of the diesel generator or conducting large disturbance tests.

[0030] Compared to existing technologies, this invention and its preferred solutions can complete the evaluation without obtaining the internal structural and control parameters of the diesel generator, solving the problems of difficult acquisition of key parameters and insufficient modeling accuracy in existing modeling and simulation methods. It uses small-amplitude frequency sweep disturbances instead of traditional large-disturbance loading tests, avoiding the impact and safety risks to the unit during the test process and reducing testing costs. The universal frequency response function obtained through a single frequency sweep identification is applicable to various forms of load fluctuation evaluation, eliminating the need for separate tests or simulations for each disturbance, significantly improving the efficiency of safety domain evaluation. The combination of frequency domain mapping and time domain reconstruction accurately predicts the frequency dynamic response process of the diesel generator under arbitrary load fluctuations, ensuring reliable evaluation results. The safety domain determination using dual indicators—maximum frequency deviation and maximum frequency change rate—comprehensively reflects the impact of load fluctuations on the operational stability of the diesel generator, meeting the needs of practical engineering applications. Attached Figure Description

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0032] Figure 1 This is a flowchart illustrating the overall implementation of the solution in this embodiment of the invention;

[0033] Figure 2 This is a schematic diagram of the diesel generator frequency sweep test and small-signal equivalent model in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of frequency response extraction in an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the frequency domain point-by-point multiplication and inverse Fourier transform process in an embodiment of the present invention;

[0036] Figure 5This is a power-frequency Bode plot of a diesel generator in an embodiment of the present invention;

[0037] Figure 6 This is a time-domain response diagram of the frequency deviation of a diesel generator under a step load disturbance in an embodiment of the present invention. Detailed Implementation

[0038] To make the features and advantages of the present invention more apparent and understandable, specific embodiments are described below in detail:

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0040] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0041] This invention proposes a method for evaluating the load fluctuation safety domain of a diesel generator based on frequency sweep identification. Without requiring detailed knowledge of the diesel generator's internal structure and control parameters, it achieves rapid evaluation of the load fluctuation safety domain by sweeping the generator's power-frequency channels. Compared to other methods, this invention has low testing risk, strong applicability, requires minimal complex modeling and large-disturbance testing, and is simple and easy to implement.

[0042] To address the challenges of rapidly and accurately assessing the frequency dynamic response of existing diesel generators under load fluctuations through traditional tests, and the safety risks associated with large disturbance tests, this invention proposes a method for frequency sweep identification of diesel generators followed by safety domain assessment. By acquiring frequency response data of the diesel generator's power-frequency channel through frequency sweep testing, the method can reconstruct the time-domain frequency deviation response under load fluctuations without knowing the detailed internal structure and control parameters of the diesel generator, thereby achieving safety domain assessment of load fluctuations.

[0043] Specifically, it includes: (1) Designing a frequency sweep identification structure for a diesel generator, obtaining power disturbance input and frequency deviation output data through frequency sweep experiments, using these as the input and output signals for system identification, and obtaining the frequency response function of the diesel generator. (2) Based on the obtained frequency response function, performing a Fourier transform on the load fluctuation signal to obtain its spectrum, and multiplying it point-by-point with the frequency response function in the frequency domain, and then reconstructing the time-domain frequency deviation response of the diesel generator under load disturbance through an inverse Fourier transform. (3) Analyzing whether the frequency fluctuation is within the allowable range based on indicators such as the lowest frequency point and the rate of frequency change, and determining the load fluctuation safety domain of the diesel generator. This invention is particularly suitable for analyzing the frequency stability of diesel generator sets and similar power equipment under load fluctuation. Compared with traditional step test and time-domain simulation methods, the method of this invention is simple, easy to implement, and highly safe.

[0044] The implementation process of this solution will be further described below with reference to the accompanying drawings and through embodiments:

[0045] The method of this invention generally includes four steps: frequency sweep identification, frequency response extraction, frequency domain deviation response reconstruction, and security domain evaluation. Figure 1 As shown.

[0046] First, such as Figure 2 As shown, a frequency sweep test and data acquisition were performed on the diesel generator. Under stable operating conditions, a small d-axis and q-axis disturbance current was injected into the system through the frequency sweep module, denoted as i0, i1, i2, i3, i4, i5, i6, i7, i d (t) and i q (t), and simultaneously acquire the corresponding d-axis and q-axis voltage signals, denoted as u respectively. d (t) and u q (t). Based on the active power calculation relationship in the synchronous rotating coordinate system, the power disturbance signal caused by the frequency sweep disturbance can be obtained:

[0047] (1)

[0048] in p(t) is the power disturbance input signal, and 1.5 is the power calculation coefficient of the three-phase system.

[0049] Simultaneously, the actual output frequency signal f of the diesel generator is collected. m (t), and using the frequency f0 under stable operating conditions as a reference value, the frequency deviation signal in the frequency sweep test is obtained:

[0050] (2)

[0051] Where f m (t) represents the measured actual output frequency of the diesel generator, which can be obtained by measuring the generator speed. f m (t) represents the measured frequency deviation signal. Therefore, p(t) is used as the input signal for frequency sweep identification. f m (t) serves as the output signal for frequency sweep identification.

[0052] Secondly, such as Figure 3 As shown, frequency response extraction is performed on the power-frequency channel of the diesel generator based on the acquired time-domain input and output signals. First, the power disturbance input signal is analyzed... p(t) and frequency deviation output signal f m Perform a Fourier transform on (t) to obtain the corresponding frequency domain signal:

[0053] (3)

[0054] here, P(jω) is the input disturbance power spectrum. F m (jω) represents the output frequency deviation spectrum. This represents the Fourier transform operator, where ω is the angular frequency, t is the time variable, and j is the imaginary unit.

[0055] If we consider the diesel generator power-frequency channel as a linear time-invariant system, then its input-output relationship in the frequency domain can be expressed as:

[0056] (4)

[0057] Therefore, the frequency response function H(jω) of the diesel generator power-frequency channel can be obtained as follows:

[0058] (5)

[0059] H(jω) reflects the frequency deviation response characteristics caused by power disturbance at different frequencies.

[0060] Furthermore, the amplitude and phase of the frequency response function can be expressed as follows:

[0061] (6)

[0062] Where |H(jω)| is the amplitude-frequency response, This represents the phase frequency characteristic.

[0063] Furthermore, the frequency response function obtained from the frequency sweep test is typically discrete data at a finite number of frequency points. If the frequency axis of the load fluctuation signal to be analyzed subsequently does not perfectly match the frequency points of the frequency sweep, the obtained discrete frequency response data can be interpolated to make H(jω) consistent with the load disturbance input spectrum. P L (jω) corresponds one-to-one at the same frequency points. Linear interpolation can be used for interpolation.

[0064] After obtaining the frequency response function of the diesel generator, the load fluctuation signal is... p L (t) is subjected to a Fourier transform, transformed to the frequency domain, such as Figure 4 As shown, its spectral expression is obtained as follows:

[0065] (7)

[0066] For example, the Fourier transform of a typical step power load can be expressed as:

[0067] (8)

[0068] Where A is the amplitude of the step disturbance, and t0 is the step time. It is a unit impulse function.

[0069] According to equation (4), the output frequency deviation spectrum of a diesel generator under load fluctuation is... Y(jω) is the product of the input power spectrum and the frequency response function, i.e.:

[0070] (9)

[0071] in, Y(jω) is the output spectrum of the frequency deviation response of the diesel generator.

[0072] By performing an inverse Fourier transform on the output spectrum, the time-domain frequency deviation response of the diesel generator under this load disturbance can be reconstructed.

[0073] (10)

[0074] in, f r (t) represents the time-domain frequency deviation response of the diesel generator.

[0075] In obtaining f r After (t), extract the maximum frequency deviation value. f max Maximum rate of change of frequency r max These indicators are defined as follows:

[0076] (11)

[0077] When the above indicators meet the preset safety constraints, the corresponding load fluctuation is considered to be within the safe domain of the diesel generator, that is:

[0078] (12)

[0079] in, F set r set These are the maximum permissible frequency deviation threshold and the maximum frequency change rate threshold, respectively. If either condition is not met, the load fluctuation is determined to exceed the safe range.

[0080] Based on the above design, the steps for assessing the safety domain of diesel generator load fluctuations in this embodiment are as follows:

[0081] Step one: First, conduct a diesel generator frequency sweep test and data acquisition. After the diesel generator starts and runs stably, inject small d-axis and q-axis disturbance currents into the system through the frequency sweep module. The frequency of the disturbance current changes point by point according to the preset frequency sweep range. Since this invention is mainly used to extract the dynamic response characteristics of the diesel generator's power-frequency, the amplitude of the injected disturbance current should be small to avoid significant deviations in the diesel generator's operating point.

[0082] During the frequency sweep process, the d-axis and q-axis voltage and current signals are acquired synchronously, and the power disturbance input signal caused by the frequency sweep disturbance is calculated according to equation (1). p(t). Simultaneously, the diesel generator output frequency f is collected based on the rotor speed. m (t), and calculate the measurement frequency deviation signal according to equation (2). f m (t). Among them p(t) serves as the input signal for power-frequency sweep identification of the diesel generator. f m (t) serves as the output signal for frequency sweep identification.

[0083] In practice, the power disturbance input signal and the frequency deviation output signal are synchronously acquired using the same sampling frequency. After acquisition, the signal is filtered, invalid values ​​are removed, and outliers are eliminated to reduce the impact of noise and non-steady-state data on the subsequent frequency response extraction results.

[0084] Step two: Extract the response function of the diesel generator's power-frequency channel based on the collected data. This is derived from the power disturbance input signal obtained in step one. p(t) and the measured frequency deviation signal f m (t), respectively, are subjected to Fourier transform according to Equation (3) to obtain the power disturbance input spectrum. P(jω) and frequency deviation output spectrum F m(jω). In discrete implementation, the Fast Fourier Transform can be used to obtain the discrete spectrum data at each swept frequency point.

[0085] At each swept frequency point, the frequency response function H(jω) of the diesel generator power-frequency channel is calculated according to equations (4) and (5). The output spectrum is then... F m (jω) and input spectrum Using P(jω) as the quotient, the complex frequency response data at that frequency point is obtained. Thus, the power-frequency response of the diesel generator at different frequency points can be obtained. Furthermore, according to equation (6), the frequency response function is expressed in amplitude and phase form, yielding the amplitude-frequency characteristic |H(jω)| and phase-frequency characteristic of the power-frequency channel. The frequency response function H(jω) is used to represent the dynamic characteristics of the frequency deviation response of a diesel generator under power disturbances at different frequencies.

[0086] Step 3: Reconstruct the time-domain frequency response of the diesel generator under load disturbance based on its frequency domain characteristics. Apply load power fluctuations according to the operating condition to be evaluated. p L (t). The load fluctuation signal can be a step load disturbance, a ramp load disturbance, a periodic load disturbance, etc., or it can be a load power fluctuation curve collected under actual working conditions. The load fluctuation signal is subjected to Fourier transform according to equation (7) to obtain its input spectrum. P L (jω). For example, when the load disturbance is in the form of a step, the frequency domain expression of the step load disturbance can be obtained according to equation (8).

[0087] Subsequently, according to equation (9), the load disturbance is input to the spectrum. P L Multiplying (jω) by the diesel generator power-frequency channel frequency response function H(jω) obtained in step two at the corresponding frequency points yields the output spectrum of the diesel generator frequency deviation response. Y(jω). This calculation process simultaneously considers the amplitude variation and phase lag of the diesel generator power-frequency channel at each frequency point.

[0088] Obtain the output spectrum After Y(jω), perform an inverse Fourier transform on it according to Equation (10) to reconstruct the time-domain frequency deviation response of the diesel generator under the load disturbance. f r (t). Using this frequency domain reconstruction method, the dynamic curve of frequency deviation of diesel generator under different load fluctuations can be obtained based on the frequency response function obtained by frequency sweep identification without conducting actual large disturbance loading tests.

[0089] Step four involves a safety domain assessment of the diesel generator's dynamic response. This is based on the time-domain frequency deviation response obtained in step three. f r (t) is the maximum frequency deviation value extracted after the load disturbance occurs. f max and the maximum rate of change of frequency r max Its definition is shown in equation (11). Wherein, f max Depend on f r (t) is obtained by taking the maximum absolute value within the time interval after the disturbance, and is used to reflect the degree of frequency drop of the diesel generator under load disturbance; r max Depend on f r (t) is obtained by differentiating it with respect to time and taking the maximum absolute value, which is used to reflect the rate of change of diesel generator frequency and the degree of dynamic impact.

[0090] After obtaining the above indicators, safety constraints are determined according to equation (12). If the maximum frequency deviation value... f max Not exceeding the preset allowable threshold F set And the maximum frequency change rate r max Not exceeding the preset threshold r set If the load disturbance is within the safe operating range of the diesel generator, then the load disturbance is considered to be within the safe operating range; if any indicator does not meet the corresponding threshold requirement, then the load disturbance is determined to be outside the safe range.

[0091] In practical applications, the settings can be determined based on the diesel generator capacity, operating conditions, and engineering standard requirements. F set and r set For example, the allowable frequency deviation range and the maximum frequency change rate threshold can be set by referring to relevant industry standards and engineering practices regarding the constraints on frequency deviation and frequency change rate. By changing the load disturbance amplitude, disturbance duration, or disturbance change rate, and repeating steps three and four, the safe or unsafe judgment results under different load disturbance conditions can be obtained, thereby forming the safe domain boundary of the diesel generator load fluctuation.

[0092] By adopting the above implementation steps, it is possible to predict the frequency dynamic response and assess the safety domain under load fluctuations of a diesel generator without knowing the detailed internal structural and control parameters of the diesel generator or conducting large-scale disturbance measurements.

[0093] Based on the above method, Figure 6The typical load step disturbance signal shown is used to calculate the frequency deviation response of the diesel generator, where the disturbance is injected at t0 = 20 s. Based on the power-frequency channel frequency response function of the diesel generator obtained from the frequency sweep test, its Bode plot is plotted as follows. Figure 5 As shown, the Bode plot reflects the amplitude and phase characteristics of the system across different frequency ranges. Specifically, the system amplitude is larger in the low-frequency range, indicating that the diesel generator has a strong response capability to low-frequency disturbances. The frequency corresponding to the position of maximum gain is ω. c As the frequency increases, the amplitude gradually decreases, demonstrating a significant suppression characteristic of the system against high-frequency disturbances. Based on this, the time-domain frequency deviation response is reconstructed using a point-by-point multiplication and inverse Fourier transform method in the frequency domain, as shown in the results. Figure 6 As shown. By Figure 6 It can be seen that, under the effect of this step load disturbance, the maximum frequency deviation of the diesel generator is... f max The maximum frequency change rate is approximately 0.4850 Hz. max It is approximately 8.4771 Hz / s.

[0094] Referring to the frequency deviation constraints in relevant IEEE standards and the commonly used limits for frequency change rate in engineering practice, the maximum permissible frequency deviation is set to 1 Hz, and the maximum frequency change rate is set to 10 Hz / s. The extracted indicators are compared with the above safety thresholds; when the conditions are met... f max ≤ 1 Hz and r max When the disturbance amplitude is ≤ 10 Hz / s, it is determined that the disturbance condition is within the safe operating range of the diesel generator. In this embodiment, all indicators meet the above constraints, indicating that the system operates safely under this disturbance amplitude.

[0095] Therefore, the method of the present invention can accurately predict the frequency dynamic response of a diesel generator under load fluctuations without the need for large-disturbance field measurements, and achieve effective assessment of the load fluctuation safety domain.

[0096] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

[0098] This invention is not limited to the preferred embodiment described above. Anyone inspired by this invention can derive other forms of a diesel generator load fluctuation safety domain assessment method based on frequency sweep identification. All equivalent variations and modifications made within the scope of the claims of this invention shall fall within the scope of this invention.

Claims

1. A method for diesel generator load fluctuation safety domain assessment based on frequency sweep identification, characterized in that, Includes the following steps: Under the steady-state operation of the diesel generator, a small sweep frequency power disturbance that does not change its steady-state operating point is applied to the diesel generator, and the sweep frequency power disturbance signal and the corresponding frequency deviation response signal are collected simultaneously. Based on the swept frequency power disturbance signal and frequency deviation response signal, a general frequency response function for the power-frequency channel, independent of the internal structure and control parameters of the diesel generator, is obtained by frequency domain identification. Obtain any form of load fluctuation signal to be evaluated, convert it to the frequency domain to obtain the load disturbance spectrum, and multiply the load disturbance spectrum with the general frequency response function point by point in the frequency domain to obtain the predicted frequency deviation spectrum; The predicted frequency deviation spectrum is subjected to inverse Fourier transform to reconstruct the time-domain frequency deviation response of the diesel generator under the load fluctuation signal. The maximum frequency deviation and the maximum frequency change rate are extracted based on the time-domain frequency deviation response. The two are then compared with the corresponding preset safety thresholds to determine whether the load fluctuation is within the safety range of the diesel generator. The small-amplitude sweep frequency power disturbance is achieved by injecting d-axis and q-axis disturbance currents in a synchronous rotating coordinate system into the diesel generator. The sweep frequency power disturbance signal is calculated from the synchronously acquired d-axis voltage, q-axis voltage, d-axis disturbance current, and q-axis disturbance current. The frequency deviation response signal is determined by the difference between the real-time output frequency of the diesel generator and the steady-state operating reference frequency.

2. The method for assessing the load fluctuation security domain of a diesel generator based on frequency sweep identification according to claim 1, characterized in that: The general frequency response function is obtained through the following steps: performing Fourier transforms on the swept power disturbance signal and the frequency deviation response signal respectively to obtain the corresponding input spectrum and output spectrum, and calculating the ratio of the output spectrum to the input spectrum.

3. The method for assessing the load fluctuation security domain of a diesel generator based on frequency sweep identification according to claim 1, characterized in that: When the general frequency response function is discrete frequency data, linear interpolation is performed on the discrete frequency data so that the interpolated general frequency response function corresponds one-to-one with the frequency points of the load disturbance spectrum.

4. The method for assessing the load fluctuation security domain of a diesel generator based on frequency sweep identification according to claim 1, characterized in that: The maximum frequency deviation is the maximum absolute value of the time-domain frequency deviation response, and the maximum frequency change rate is the maximum absolute value of the time-domain frequency deviation response after taking the derivative with respect to time.

5. The method for assessing the load fluctuation security domain of a diesel generator based on frequency sweep identification according to claim 1, characterized in that: The load fluctuation signal to be evaluated in any form includes one of the following: step load disturbance signal, ramp load disturbance signal, periodic load disturbance signal, and load power fluctuation signal collected under actual operating conditions.

6. The method for assessing the load fluctuation security domain of a diesel generator based on frequency sweep identification according to claim 1, characterized in that: The preset safety thresholds include the maximum allowable frequency deviation threshold and the maximum allowable frequency change rate threshold, which are set based on the operating requirements of the diesel generator.

7. The method for assessing the load fluctuation security domain of a diesel generator based on frequency sweep identification according to claim 1, characterized in that: By utilizing the general frequency response function obtained from a single frequency sweep identification, frequency domain mapping and safety domain determination are performed on multiple different load fluctuation signals to be evaluated, thereby realizing batch evaluation of the safety domain of diesel generators.

8. A diesel generator load fluctuation security domain assessment system based on frequency sweep identification, characterized in that, For implementing the method as described in any one of claims 1-7, comprising: The frequency sweep test module is used to apply a small frequency sweep power disturbance under the steady-state operation of the diesel generator and simultaneously acquire the frequency sweep power disturbance signal and the frequency deviation response signal. The frequency response identification module is used to identify the general frequency response function of the diesel generator power-frequency channel based on the swept frequency power disturbance signal and the frequency deviation response signal. The response prediction module is used to convert the load fluctuation signal to be evaluated to the frequency domain, perform frequency domain operations with the general frequency response function, and inversely transform it to the time domain to reconstruct the time domain frequency deviation response. The security assessment module is used to extract assessment indicators based on the time-domain frequency deviation response and compare them with preset thresholds to output the security domain determination result.

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