A stability online monitoring method and system based on an improved forbidden zone criterion

Abstract

The application discloses a kind of stability online monitoring method and system based on improved forbidden zone criterion, periodic current disturbance signal is injected at the point of common coupling of inverter and power grid;N cycle of grid-side current signal data and injected disturbance current signal data are collected respectively at the point of common coupling of inverter and power grid;The grid-side current signal data and the disturbance current signal data obtained are de-stabilized, and small signal disturbance and response information are extracted;The small signal information obtained is subjected to fast Fourier transform, and the relevant frequency domain signal of time domain signal is obtained;The relevant frequency domain signal obtained is substituted into improved forbidden zone criterion to determine stability, and the system stability online monitoring is completed by measuring grid-side current response and injected disturbance current.It realizes the stability determination precision equivalent to existing monitoring scheme or even better.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, specifically relating to an online stability monitoring method and system based on an improved restricted area criterion. Background Technology

[0002] With the widespread application of renewable energy sources (RESs), especially the rapid development of distributed energy sources such as solar and wind power, single-phase grid-connected inverters are becoming increasingly common in homes and small and medium-sized enterprises. These inverters convert direct current (DC) to alternating current (AC) and connect it to the grid, thereby enabling the efficient utilization of distributed power sources. However, when inverters are connected to the grid, especially under weak grid conditions, system stability faces many challenges.

[0003] In traditional strong power grid environments, the grid impedance is low, and the inverter's output voltage and current are driven by the grid voltage, resulting in a relatively stable system. However, in weak power grid conditions caused by long transmission lines or the extensive integration of distributed power sources, the impedance at the point of common coupling (PCC) increases, and the grid characteristics become complex and unstable. In such cases, the high bandwidth of the inverter controller makes it extremely sensitive to system fluctuations, easily leading to impedance mismatch with the grid, which can cause system instability or even oscillations.

[0004] To address these potential stability issues, the industry has proposed a series of online stability monitoring solutions aimed at timely detection and resolution of stability problems, ensuring long-term safe system operation. Some online monitoring solutions utilize frequency sweeping methods, measuring the system response and calculating the system impedance by continuously injecting sinusoidal signals into the system. However, these methods require long signal injection and data acquisition times, resulting in poor real-time performance. Therefore, more online monitoring solutions employ measurement schemes based on composite signal injection to improve real-time performance. These solutions rely on different stability criteria, but their principle is the same: monitoring the system's real-time impedance and other information, and then using the Nyquist criterion for stability assessment. However, the forbidden zone criteria currently used in the stability evaluation of these measurement schemes have certain shortcomings, making it difficult to achieve a good balance between measurement convenience and stability assessment accuracy, thus reducing their practicality.

[0005] Therefore, to improve the accuracy and real-time performance of online stability monitoring for single-phase grid-connected systems, an efficient and reliable monitoring method is urgently needed. This method should not only be able to accurately assess system stability under weak grid conditions, but also be able to quickly respond to dynamic changes in the system and possess good anti-interference capabilities in practical applications. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a stability online monitoring method and system based on an improved forbidden zone criterion, which addresses the shortcomings of the prior art and solves the technical problem of the difficulty in balancing the accuracy of stability determination and the convenience of measurement in the prior art.

[0007] The present invention adopts the following technical solution:

[0008] A stability online monitoring method based on an improved forbidden zone criterion includes the following steps:

[0009] Inject a periodic current disturbance signal at the common connection point between the inverter and the power grid;

[0010] At the common connection point between the inverter and the grid, N cycles of grid-side current signal data and injected disturbance current signal data are collected respectively.

[0011] The obtained grid-side current signal data and injected disturbance current signal data are subjected to destabilization processing to extract small-signal disturbance and response information;

[0012] The obtained small signal information is subjected to a fast Fourier transform to obtain the correlation frequency domain signal of the time domain signal;

[0013] The obtained relevant frequency domain signals are substituted into the improved forbidden zone criterion for stability determination, and the system stability is monitored online by measuring the grid-side current response and the injected disturbance current.

[0014] Preferredly, periodic current disturbance signals are injected using a pulse injection method.

[0015] Preferred, the disturbance signal is a bipolar sawtooth wave signal.

[0016] Preferably, N is 5 or 10.

[0017] Prioritize, the destabilization process specifically involves:

[0018] For multiple cycles of current signals obtained through continuous sampling, distinguish between periodic data containing disturbances and periodic data without disturbances;

[0019] Select periodic data that does not contain disturbances, calculate its average value or other statistical characteristics, and determine the steady-state reference signal;

[0020] The periodic data containing the disturbance is compared with the steady-state reference signal, and the steady-state reference signal is subtracted from the periodic data containing the disturbance to obtain the individual disturbance signal.

[0021] Preferably, the improved restricted area criterion includes a circular region centered at (-1,j0) and a fan-shaped region extending outward from the circular region.

[0022] Prior to this, the stability determination relationship is as follows:

[0023]

[0024] in, and These represent the small-signal forms of the point of common coupling voltage response, grid-side current response, and injected current disturbance, respectively. M is the small-loop gain, and Z... grid For the net side, Z inv On the inverter side, GM represents the gain margin that the system should have for stable operation.

[0025] Preferredly, the Bode plot is used as a tool for stability assessment. The upper half of the Bode plot represents the amplitude-frequency characteristic of the near-minimum loop gain, and the lower half represents the phase-frequency characteristic.

[0026] First, check whether the amplitude-frequency response curve in the Bode plot is always above the corresponding constraint boundary; check whether the phase-frequency response curve is always outside the defined phase forbidden zone; when both of the above conditions are met, the system is stable.

[0027] Secondly, embodiments of the present invention provide a stability online monitoring system based on an improved forbidden zone criterion, comprising:

[0028] The injection module injects a periodic current disturbance signal at the common connection point between the inverter and the power grid;

[0029] The acquisition module collects grid-side current signal data and injected disturbance current signal data for N cycles at the common connection point between the inverter and the grid.

[0030] The processing module performs destabilization processing on the grid-side current signal data and the injected disturbance current signal data, and extracts small-signal disturbance and response information;

[0031] The transformation module performs a fast Fourier transform on the small signal information to obtain the correlated frequency domain signal of the time domain signal;

[0032] The monitoring module substitutes relevant frequency domain signals into the improved restricted area criterion for stability determination, and completes online monitoring of system stability by measuring the grid-side current response and injected disturbance current.

[0033] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described online stability monitoring method based on the improved restricted area criterion.

[0034] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described online stability monitoring method based on the improved restricted area criterion.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] An online stability monitoring method based on an improved forbidden zone criterion is proposed. This method injects a periodic current disturbance signal at the common connection point between the inverter and the grid, and collects both the grid-side current signal and the injected disturbance current signal, thereby enabling real-time monitoring of system stability. This online monitoring approach can promptly detect and warn of potential stability problems, preventing system instability or failure. After injecting the periodic current disturbance signal, de-stabilization processing and Fast Fourier Transform (FFT) effectively extract small-signal disturbance and response information. Substituting this small-signal information into the improved forbidden zone criterion, the system stability can be quickly determined by measuring the grid-side current response and the injected disturbance current. The core of this method lies in utilizing the improved forbidden zone criterion, which improves the accuracy and efficiency of stability determination.

[0037] Furthermore, the pulse injection method can generate significant disturbance signals, making it easier to clearly observe the system response during monitoring. This method is simple to implement and is not easily affected by interference from other signals.

[0038] Furthermore, bipolar sawtooth wave signals contain multiple frequency components, enabling them to excite system responses over a wide frequency range. By analyzing these responses, a comprehensive understanding of the system's stability at different frequencies can be achieved, thereby improving the overall accuracy of monitoring.

[0039] Furthermore, choosing an appropriate N value can reduce the amount of data and computation while improving the efficiency and response speed of real-time monitoring, provided that sufficient signal data is collected to ensure monitoring accuracy. An N value of 5 or 10 is the result of comprehensive consideration of system response characteristics and computational resources.

[0040] Furthermore, by distinguishing between periodic data containing and excluding disturbances, and comparing the data containing disturbances with the steady-state reference signal, the steady-state component can be effectively removed, while retaining useful disturbance signal information. This processing method can significantly improve the detection capability of small signals, thereby improving the accuracy of system stability monitoring.

[0041] Furthermore, the improved exclusion zone criterion's circular region centered at (-1, j0) and its outwardly extending fan-shaped region can comprehensively cover potentially unstable areas of the system. By substituting the relevant frequency domain calculation results into this criterion, the stability of the system can be determined more accurately, improving the reliability and accuracy of monitoring results.

[0042] Furthermore, Bode plots clearly demonstrate the gain and phase characteristics of a system. By observing the amplitude-frequency response curves and phase-frequency response curves on the Bode plot, the stability of the system can be quickly determined. The system is considered stable when the amplitude-frequency response curve consistently remains above the corresponding constraint boundary and the phase-frequency response curve consistently stays outside the defined phase-free zone. The application of Bode plots simplifies the stability assessment process and improves the intuitiveness and accuracy of the assessment.

[0043] It is understandable that the beneficial effects of the second aspect mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0044] In summary, this invention optimizes the stability criterion and achieves stability determination accuracy equal to or even better than existing monitoring schemes by using only two current signals measured at the common connection point between the inverter and the power grid. It does not depend on specific hardware, and its core solution can be combined with any existing mature frequency response measurement equipment or converter.

[0045] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0046] Figure 1 This is a diagram of the online stability monitoring system architecture for a single-phase grid-connected system used in this invention.

[0047] Figure 2 This is a schematic diagram of the pulse injection signal used in this invention;

[0048] Figure 3 This is a flowchart illustrating the overall process of online stability monitoring in this invention.

[0049] Figure 4 This is a schematic diagram of the improved stability forbidden zone criterion proposed in this invention;

[0050] Figure 5 This is a Bode plot illustrating the real-time monitoring of system stability according to the present invention;

[0051] Figure 6 These are actual waveform diagrams from specific embodiments of the present invention, showing the system response waveforms under three different operating conditions. (a) is the operating condition where the system impedance ratio trajectory is far from the restricted area; (b) is the operating condition where the system impedance ratio trajectory is at the edge of the restricted area; and (c) is the operating condition where the system impedance ratio trajectory crosses the restricted area. These operating conditions are achieved by adjusting the magnitude of the grid impedance.

[0052] Figure 7 These are actual Bode plots from specific embodiments of the present invention used for stability testing, demonstrating the Bode plot determination results under three different operating conditions. Figure 6 Similarly, (a) represents the operating condition where the system impedance ratio trajectory is far from the restricted area, (b) represents the operating condition where the system impedance ratio trajectory is at the edge of the restricted area, and (c) represents the operating condition where the system impedance ratio trajectory crosses the restricted area.

[0053] Figure 8 A schematic diagram of a computer device provided in an embodiment of the present invention;

[0054] Figure 9 This is a block diagram of an electronic device according to an embodiment of the present invention;

[0055] Figure 10 This is a schematic diagram illustrating the effectiveness of the technical solution using two inverter modules as described in this invention. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention 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 the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] In the description of this invention, it should be understood that the terms "comprising" and "including" 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.

[0058] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0059] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0060] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0061] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0062] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0063] Please see Figure 1 This invention provides an online stability monitoring method based on an improved restricted area criterion. The stability criterion is optimized, and the stability determination accuracy is equal to or even better than that of existing monitoring schemes, provided that only two current signals are measured at the common connection point between the inverter and the power grid.

[0064] In the monitoring system, when the grid phase angle is detected to be equal to a predetermined value, the excitation signal generation module generates a periodic current disturbance signal reference. This disturbance signal is input to the closed-loop current controller to ensure that the actual current can better track the reference value, and is then injected into the point of common coupling (PCC). By measuring the current information at PCC and importing the data into the stability analysis module, the system stability can be analyzed and the system state determined using an algorithm based on an improved restricted area criterion. The results of the stability analysis will be used to determine the current operating state of the system, ensuring that the system can remain stable under different operating conditions, and providing online monitoring capabilities to prevent potential instability risks.

[0065] Please see Figure 2 This invention discloses an online stability monitoring method based on an improved restricted area criterion, comprising the following steps:

[0066] S1. Inject a periodic current disturbance signal at the common connection point between the inverter and the power grid;

[0067] The perturbation is performed by pulse injection, and the perturbation signal is determined to be a bipolar sawtooth wave signal. The injection period is usually 1 second or longer.

[0068] In a single-phase grid-connected system, a periodic current disturbance signal is injected at the point of common coupling (PCC) between the inverter and the grid via a controller. This invention uses a bipolar sawtooth waveform pulse signal as an example; please refer to the detailed waveform documentation. Figure 3 This pulse signal was chosen because of its short duration, strong real-time performance, and ability to complete measurements with minimal disruption to normal system operation. Furthermore, its suitable spectral characteristics facilitate subsequent frequency domain analysis after Fourier transform.

[0069] S2. Collect grid-side current signal and injected disturbance current signal data for N cycles at the common connection point between the inverter and the grid.

[0070] The number of sampling periods N is usually 5 or 10, and the sampling frequency is usually 10000 Hz or higher.

[0071] The data acquisition module collects grid-side current signals and injected disturbance current signals at the PCC. Data acquisition needs to cover N complete cycles to ensure that the acquired data fully reflects the system's dynamic and response characteristics.

[0072] S3. Destabilize the two sets of current data collected in step S2 and extract the small signal disturbance and response information.

[0073] The destabilization process specifically involves:

[0074] For multiple cycles of current signals obtained through continuous sampling, the periodic data containing disturbances and those without disturbances are distinguished. The periodic data without disturbances are selected, and their average value or other statistical characteristics are calculated to determine the steady-state reference signal. The periodic data containing disturbances is compared with the steady-state reference signal; that is, the steady-state reference signal is subtracted from the periodic data containing disturbances to obtain the individual disturbance signal.

[0075] It helps to eliminate the steady-state components in the system, allowing for a focus on analyzing the dynamic response caused by pulse injection.

[0076] S4. Perform a fast Fourier transform on the small signal information extracted in step S3 to obtain the correlation frequency domain signal of the time domain signal.

[0077] This helps to obtain the frequency response characteristics of the system, thereby enabling further stability analysis.

[0078] S5. Substitute the relevant frequency domain signal from step S4 into the improved restricted area criterion for calculation and perform relevant stability analysis.

[0079] For stability assessment of single-phase grid-connected systems, the harmonic linearization method is generally used. An impedance model of the single-phase grid-connected system is constructed within a linear time-varying periodic framework, dividing the system into grid-side (Z) and grid-side (Z) components. grid ) and inverter side (Z inv Two parts. If the grid-connected inverter exhibits stability under ideal grid conditions, then as long as the impedance ratio (Z) is... grid / Z inv If the minimum loop gain satisfies the Nyquist stability criterion, the stability of the system under weak grid conditions can also be guaranteed.

[0080] In other words, a system is generally considered stable as long as the minimum loop gain trajectory does not enclose the point (-1,j0) on the complex plane in the Nyquist plot.

[0081] Based on the above principles, a series of forbidden zone criteria are applied to single-phase systems to simplify stability analysis. A forbidden zone, as the name suggests, is a zone that should not be crossed by the trajectory of minimum loop gain; otherwise, the system is considered unstable. By constraining the trajectory of minimum loop gain outside the forbidden zone, the trajectory will never encircle the point (-1, j0), thus satisfying the Nyquist criterion and ensuring the stability of the system. For the Nyquist plot related to the improved stability forbidden zone criterion proposed in this invention, please refer to [link to Nyquist plot]. Figure 4 The improved forbidden zone criterion comprises two forbidden zones: a circular region and a sector region. In the diagram, GM and PM represent the gain margin and phase margin required for stable system operation, respectively. The constraint formula corresponding to the circular forbidden zone is as follows:

[0082]

[0083] Defining M in the above formula as the small-loop gain, we can obtain the constraint formula corresponding to the sector-shaped restricted area:

[0084]

[0085] Here, θ represents the phase of the small loop gain, with the upper and lower limits defined by the sector-shaped restricted area.

[0086] Furthermore, the circular restricted area constraint formula can be further simplified based on the relationship between the two impedances:

[0087]

[0088] in, and These represent the small-signal forms of the point of common coupling voltage response, the grid-side current response, and the injected current disturbance, respectively. Based on the simplified constraint formula, only two current parameters are needed to complete the system stability assessment.

[0089] In addition to the Nyquist plot and mathematical equations mentioned above, the corresponding Bode plot can also be used as a tool for stability assessment. Please refer to [link / reference needed]. Figure 5 The upper half of the Bode plot represents the amplitude-frequency response of a near-minimum loop gain, while the lower half represents the phase-frequency response.

[0090] To assess the stability of the system, follow these steps:

[0091] 1. Check whether the amplitude-frequency response curve in the Bode plot is consistently above the corresponding constraint boundary. This result reflects whether the minimum loop gain trajectory has intruded into the circular restricted area.

[0092] 2. Check whether the phase frequency response curve remains outside the defined phase forbidden zone. This reflects whether the minimum loop gain trajectory has intruded into the sector forbidden zone.

[0093] When both conditions are met, the system is stable; if either condition is violated, instability may occur.

[0094] S6. Repeat steps S1 to S5 to achieve continuous online stability monitoring of the system.

[0095] During system operation, pulse signals are continuously injected, and the system's response characteristics are acquired and analyzed in real time to ensure the stable operation of the power system.

[0096] Those skilled in the art will understand that various aspects of the present invention can be implemented as systems, methods, or program products. Therefore, various aspects of the present invention can be specifically implemented in the following forms: a completely hardware implementation, a completely software implementation (including firmware, microcode, etc.), or a combination of hardware and software aspects, collectively referred to herein as a "circuit," "module," or "platform."

[0097] In another embodiment of the present invention, a stability online monitoring system based on an improved restricted area criterion is provided. This system can be used to implement the above-mentioned stability online monitoring method based on the improved restricted area criterion. Specifically, the stability online monitoring system based on the improved restricted area criterion includes an injection module, an acquisition module, a processing module, a transformation module, and a monitoring module.

[0098] The injection module injects a periodic current disturbance signal at the common connection point between the inverter and the power grid.

[0099] The acquisition module collects grid-side current signal data and injected disturbance current signal data for N cycles at the common connection point between the inverter and the grid.

[0100] The processing module performs destabilization processing on the grid-side current signal data and the injected disturbance current signal data, and extracts small-signal disturbance and response information;

[0101] The transformation module performs a fast Fourier transform on the small signal information to obtain the correlated frequency domain signal of the time domain signal;

[0102] The monitoring module substitutes relevant frequency domain signals into the improved restricted area criterion for stability determination, and completes online monitoring of system stability by measuring the grid-side current response and injected disturbance current.

[0103] In another embodiment of the present invention, a terminal device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment can be used for the operation of an online stability monitoring method based on an improved restricted area criterion, including:

[0104] A periodic current disturbance signal is injected at the common connection point between the inverter and the grid. N cycles of grid-side current signal data and injected disturbance current signal data are collected at the common connection point. The grid-side current signal data and injected disturbance current signal data are destabilized to extract small-signal disturbance and response information. A fast Fourier transform is performed on the small-signal information to obtain the relevant frequency domain signal of the time domain signal. The relevant frequency domain signal is substituted into the improved forbidden zone criterion for stability determination. Online system stability monitoring is completed by measuring the grid-side current response and the injected disturbance current.

[0105] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium (Memory), which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). It should be noted that more specific examples (a non-exhaustive list) of the computer-readable storage medium include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0106] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, RF, etc., or any suitable combination thereof.

[0107] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0108] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the stability online monitoring method based on the improved forbidden zone criterion in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps:

[0109] A periodic current disturbance signal is injected at the common connection point between the inverter and the grid. N cycles of grid-side current signal data and injected disturbance current signal data are collected at the common connection point. The grid-side current signal data and injected disturbance current signal data are destabilized to extract small-signal disturbance and response information. A fast Fourier transform is performed on the small-signal information to obtain the relevant frequency domain signal of the time domain signal. The relevant frequency domain signal is substituted into the improved forbidden zone criterion for stability determination. Online system stability monitoring is completed by measuring the grid-side current response and the injected disturbance current.

[0110] Please see Figure 8 The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When executed by the processor 61, the computer program 63 implements the fluid composition calculation method in the reservoir stimulation wellbore of this embodiment. To avoid repetition, details are omitted here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the stability online monitoring system based on the improved restricted area criterion of this embodiment. To avoid repetition, details are omitted here.

[0111] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 8 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0112] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, CPUs, graphics processing units (GPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, quantum computing-based data processing logic units, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0113] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or RAM of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc. equipped on the computer device 60.

[0114] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0115] Any references to memory, databases, or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0116] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0117] Please see Figure 9 The terminal device 600 is an electronic device, which takes the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0118] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 2 The steps are shown in the figure.

[0119] Storage unit 620 may include a readable medium in the form of a volatile storage unit, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include a read-only memory (ROM) 6203.

[0120] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0121] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0122] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem, etc.). This communication can be performed via input / output (I / O) interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0123] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention 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 the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0124] Please see Figure 10 This invention uses two inverter modules to verify the effectiveness of the technical solution. One is used to simulate a normal grid-connected inverter system, while the other is used as the implementation carrier of the technical solution. The different components in the figure are (a) inverter unit, (b) LCL filter, (c) current sensor, (d) voltage sensor, (e) grid inductor, (f) host computer, (g) oscilloscope, and (h) grid simulator.

[0125] The relevant experimental results are as follows Figure 6 and Figure 7 As shown:

[0126] Please see Figure 6 In the first operating condition, the system impedance ratio trajectory is far from the restricted area, and the waveform exhibits stable response characteristics. The system recovers quickly after a disturbance without significant oscillations. In the second operating condition, the system impedance ratio trajectory is at the edge of the restricted area, and the waveform shows a certain oscillating trend, but still remains in a stable state. In the third operating condition, the system impedance ratio trajectory crosses the restricted area, and the waveform exhibits significant oscillating characteristics. At this point, the system is still in a stable state but has exceeded the predetermined stability margin boundary.

[0127] Please see Figure 7 When the system impedance ratio trajectory is far from the restricted area, both the amplitude-frequency response curve and the phase-frequency response curve shown in the Bode plot are within the safe range, indicating sufficient system stability margin. When the system impedance ratio trajectory is at the edge of the restricted area, the amplitude-frequency response curve approaches the constraint boundary, and the phase-frequency response curve also approaches the phase restricted area, indicating that the system stability margin is at a critical state. However, when the system impedance ratio trajectory crosses the restricted area, the Bode plot shows that the amplitude-frequency response curve enters the constraint boundary, and the phase-frequency response curve further approaches the phase restricted area. At this point, the system stability margin decreases significantly, requiring stabilization actions to prevent the system from becoming unstable.

[0128] The technical solution adopted in this invention has high versatility and can be implemented in various devices with programmable control systems. Whether it's an inverter, converter, or other power electronic device, as long as it possesses basic programmable control and signal acquisition functions, this method can be implemented through programming to monitor system stability in real time. This characteristic makes this invention widely adaptable and scalable in different application scenarios, providing an effective solution for the safety monitoring of various power systems.

[0129] In summary, the stability online monitoring method and system based on the improved restricted area criterion of the present invention has the following significant advantages compared with the prior art:

[0130] The monitoring requires a small amount of data:

[0131] The monitoring method of this invention injects a periodic current disturbance signal at the common connection point between the inverter and the grid, requiring only the acquisition of two key current signal data: the grid-side current signal and the injected disturbance current signal. Compared to traditional methods that require large amounts of data for complex analysis, this invention significantly reduces the amount of monitoring data needed, lowers the complexity of data processing, and improves the real-time monitoring efficiency of the system.

[0132] Stability determination is simple:

[0133] After acquiring the necessary current signals, small-signal disturbances and response information can be quickly extracted through simple destabilization processing and Fast Fourier Transform. Combined with the improved forbidden zone criterion, the stability of the system can be quickly determined by analyzing this small-signal information. This process does not rely on complex mathematical models or large amounts of computational resources, thus simplifying the stability determination process.

[0134] The judgment result is accurate:

[0135] This invention employs an improved restricted area criterion, combined with Bode plot analysis, to accurately determine the stability of a system under various operating conditions. Whether the system impedance ratio trajectory is far from the restricted area, on the edge of the restricted area, or crossing the restricted area, this invention provides reliable stability assessment, ensuring high accuracy of monitoring results, thereby effectively preventing potential instability risks and ensuring the safe operation of the power grid.

[0136] In summary, this invention not only reduces the amount of data required for monitoring by simplifying the data acquisition and processing process, but also ensures the accuracy of monitoring results through a precise stability determination method, significantly improving the efficiency and reliability of online system stability monitoring.

[0137] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0138] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0139] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0140] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0141] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0142] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0143] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0144] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0145] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0146] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0147] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A stability online monitoring method based on an improved forbidden zone criterion, characterized in that, Includes the following steps: Inject a periodic current disturbance signal at the common connection point between the inverter and the power grid; At the common connection point between the inverter and the grid, N cycles of grid-side current signal data and injected disturbance current signal data are collected respectively. The obtained grid-side current signal data and injected disturbance current signal data are subjected to destabilization processing to extract small-signal disturbance and response information; The obtained small signal information is subjected to a fast Fourier transform to obtain the correlation frequency domain signal of the time domain signal; The obtained relevant frequency domain signals are substituted into the improved forbidden zone criterion for stability determination. The system stability is monitored online by measuring the grid-side current response and the injected disturbance current. The improved forbidden zone criterion includes a circular region centered at (-1, j0) and a fan-shaped region extending outward from this circular region. The stability determination relationship is as follows: in, , and These represent the small-signal forms of the point of common coupling voltage response, the grid-side current response, and the injected current disturbance, respectively. For small loop gain, For the net side, For the inverter side, Gain margin that should be available for stable system operation.

2. The online stability monitoring method based on the improved restricted area criterion according to claim 1, characterized in that, Periodic current disturbance signals are injected using a pulse injection method.

3. The online stability monitoring method based on the improved restricted area criterion according to claim 2, characterized in that, The disturbance signal is a bipolar sawtooth wave signal.

4. The online stability monitoring method based on the improved restricted area criterion according to claim 1, characterized in that, N is 5 or 10.

5. The online stability monitoring method based on the improved restricted area criterion according to claim 1, characterized in that, The destabilization process specifically involves: For multiple cycles of current signals obtained through continuous sampling, distinguish between periodic data containing disturbances and periodic data without disturbances; Select periodic data that does not contain disturbances, calculate its average value, and determine the steady-state reference signal; The periodic data containing the disturbance is compared with the steady-state reference signal, and the steady-state reference signal is subtracted from the periodic data containing the disturbance to obtain the individual disturbance signal.

6. The online stability monitoring method based on the improved restricted area criterion according to claim 1, characterized in that, Bode plots are used as a stability assessment tool. The upper half of the Bode plot represents the amplitude-frequency response of the near-minimum loop gain, and the lower half represents the phase-frequency response.

7. The online stability monitoring method based on the improved restricted area criterion according to claim 6, characterized in that, Check whether the amplitude-frequency response curve in the Bode plot is always above the corresponding constraint boundary; check whether the phase-frequency response curve is always outside the defined phase forbidden zone; when both conditions are met, the system is stable.

8. A stability online monitoring system based on an improved restricted area criterion, characterized in that, include: The injection module injects a periodic current disturbance signal at the common connection point between the inverter and the power grid; The acquisition module collects grid-side current signal data and injected disturbance current signal data for N cycles at the common connection point between the inverter and the grid. The processing module performs destabilization processing on the grid-side current signal data and the injected disturbance current signal data, and extracts small-signal disturbance and response information; The transformation module performs a fast Fourier transform on the small signal information to obtain the correlated frequency domain signal of the time domain signal; The monitoring module substitutes relevant frequency domain signals into the improved restricted area criterion for stability determination, and completes online monitoring of system stability by measuring the grid-side current response and injected disturbance current. The improved forbidden zone criterion includes a circular region centered at (-1, j0) and a fan-shaped region extending outward from this circular region. The stability determination relationship is as follows: in, , and These represent the small-signal forms of the point of common coupling voltage response, the grid-side current response, and the injected current disturbance, respectively. For small loop gain, For the net side, For the inverter side, Gain margin that should be available for stable system operation.

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