New energy grid-connected system operation mode optimization method and device based on oscillation stability margin, equipment and medium

Abstract

The present application relates to the field of new energy grid connection technology, especially to a new energy grid connection system operation mode optimization method, device, equipment and medium based on oscillation stability margin, the method comprises the following steps: constructing a small signal state space model of a new energy grid connection system; determining the dominant oscillation mode of the system and identifying the system instability mode, constructing a stability boundary based on the new energy output level and short circuit ratio, and calculating the system oscillation stability margin under the current operating condition; adjusting the system operation mode, increasing the short circuit capacity at the new energy grid connection point, thereby increasing the system oscillation stability margin, ensuring the stable operation of the system, providing a means for real-time evaluation of the system operating state, optimizing the system operation mode based on the oscillation stability margin to reduce the system wide frequency oscillation risk, which can evaluate the system oscillation risk, and in actual power grid operation, the new energy wide frequency oscillation risk early warning system can be combined to optimize the system operation mode online, ensuring the safe and stable operation of the new energy grid connection system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy grid-connected technology, and particularly relates to a new energy grid-connected system operation mode optimization method and device based on oscillation stability margin, equipment and medium. BACKGROUND

[0002] With the transformation of global energy structure, the proportion of clean energy continues to rise, especially the new energy dominated by wind power and photovoltaic power generation is rapidly developing worldwide. As of 2023, China's cumulative installed capacity of wind power has reached 441GW, and the cumulative installed capacity of photovoltaic power has reached 609GW, accounting for 36% of the total installed capacity of national power generation. In northwest, north and northeast China, a number of large new energy power generation bases have been formed, and power is transmitted to other regions through ultra-high voltage direct current transmission technology. These new energy bases lack the support of conventional thermal power and hydropower synchronous generating units, and the grid strength is relatively weak, facing problems of transient voltage instability, wideband oscillation and other stability problems, and the accommodation and delivery capacity of new energy is restricted. With the further expansion of new energy installed capacity, the proportion of traditional synchronous units is declining, and the lack of grid strength in new energy grid-connected areas will become a common problem.

[0003] At present, new energy grid-connected systems are mainly realized through alternating current and flexible direct current, and dynamic reactive power compensation devices (such as SVG) are widely used to enhance grid-connected stability. However, due to the large use of power electronic devices with multi-time scale control characteristics in grid-connected systems, the stability of the system, especially the wideband oscillation problem, becomes more prominent. There have been many oscillation accidents related to new energy grid connection at home and abroad, which has affected the safe operation of the power grid on a large scale.

[0004] The existing new energy grid-connected system operation mode optimization method can control the oscillation risk to a certain extent, but it relies on the adjustment and addition of equipment, which is high in cost and complex to implement. This optimization method fails to fully utilize the original system structure, and it is difficult to achieve efficient oscillation suppression and system stability improvement without significantly modifying the equipment.

[0005] The information disclosed in this BACKGROUND section is only intended to enhance the understanding of the general background of the application, and should not be considered as recognition or implicit acknowledgment in any form that this information constitutes prior art known to those skilled in the art. SUMMARY

[0006] The present application provides a new energy grid-connected system operation mode optimization method, device, equipment and medium based on oscillation stability margin, thereby effectively solving the problems in the background art.

[0007] In order to achieve the above object, the technical scheme adopted by the present application is: a new energy grid-connected system operation mode optimization method based on oscillation stability margin, comprising the following steps:

[0008] S10: According to the control structure and control parameters of the actual new energy grid-connected system, a small signal state space model of the new energy grid-connected system is constructed;

[0009] S20: Based on the small signal state space model, the full-dimensional eigenvalues of the system under the current operating condition are calculated, and the dominant oscillation mode of the system is determined by using the eigenvalue analysis method, wherein the dominant oscillation mode refers to the oscillation mode close to the virtual axis and having low damping, and the oscillation mode is easy to cause system instability, and based on the dominant oscillation mode, the mode causing system instability is identified;

[0010] S30: For the instability mode, a stability boundary based on the new energy output level and short-circuit ratio is constructed, and the system oscillation stability margin under the current operating condition is calculated;

[0011] S40: According to the oscillation stability margin, the system operation mode is adjusted, the short-circuit capacity at the new energy grid-connected point is improved, so as to improve the system oscillation stability margin and ensure the stable operation of the system.

[0012] Further, in step S10, the small signal state space model includes a continuous space state model, which includes:

[0013]

[0014] In the formula, X s represents a continuous state vector, U xy and i xy represent input and output vectors respectively, A cs , B cs , C cs and D cs are coefficient matrices, which can be obtained by linearizing the differential equation or transfer function of the dynamic characteristics of electrical elements, and p represents a differential operator.

[0015] Further, the continuous space state model is discretized by a specific integration rule to obtain a discrete state space model, which is used to describe the behavior of the system through a set of discrete-time equations, and the discrete state space model includes:

[0016]

[0017] In the formula, h s (t) represents a state vector in the current discrete state space, A ds , B ds , C dsand D ds is calculated from a coefficient matrix, At represents a discrete time step, t represents time, U xy and i xy represent input and output vectors, respectively.

[0018] Further, in step S20, based on the small signal state space model, the full-dimensional eigenvalues of the system under the current operating condition are calculated, the dominant oscillation mode of the system is determined using the eigenvalue analysis method, and the mode that may cause the system to lose stability is identified, and the step includes:

[0019] S21: Calculate the full-dimensional eigenvalues of the system and the corresponding left and right eigenvectors;

[0020] S22: Calculate the participation factor of the oscillation mode of the system according to the left and right eigenvectors, and determine the main link affecting the oscillation mode based on the participation factor;

[0021] S23: Calculate the oscillation frequency and damping ratio of each oscillation mode according to the full-dimensional eigenvalues, and define the oscillation mode with smaller or negative damping ratio as the dominant oscillation mode of the system;

[0022] S24: Based on the dominant oscillation mode, adjust the short-circuit ratio of the system and the output level of the new energy, and analyze the influence of the change of the system operating mode on the dominant oscillation mode by observing the change of the root locus;

[0023] S25: When the root locus is observed to change, if the conjugate eigenvalue crosses the imaginary axis into the right half of the complex plane, it is identified that the system has an oscillation instability risk;

[0024] S26: Based on the oscillation instability risk, determine the critical output level and critical short-circuit ratio of the system, and identify the oscillation instability risk of the system below the critical short-circuit ratio.

[0025] Further, in step S30, for the instability mode, a stability boundary based on the new energy output level and the short-circuit ratio is constructed, and the step of constructing the stability boundary includes:

[0026] S31: Calculate the eigenvalue corresponding to the system instability mode under the current output;

[0027] S32: Based on the eigenvalue, search and calculate the critical short-circuit ratio under the current output level by adjusting the short-circuit ratio of the new energy station grid connection point;

[0028] S33: Based on the critical short-circuit ratio, gradually increase the output level of the new energy station, and calculate the critical short-circuit ratio of the system under the corresponding output level;

[0029] S34: According to the system critical short-circuit ratio under the corresponding output level and the output level of the corresponding new energy field station, the critical stable operation point of each system is calibrated, and the stable boundary is drawn in the short-circuit ratio-new energy power space.

[0030] Further, in step S40, according to the oscillation stability margin, the system operation mode is adjusted, and the step includes:

[0031] S41: Calculate the oscillation stability margin of the current operating point of the system, which includes the oscillation stability margin under normal condition and N-1 / N-2 fault condition;

[0032] S42: Based on the oscillation stability margin, determine the optimization strategy of the system operation mode, and the optimization strategy dynamically adjusts the system parameters according to the oscillation stability margin of the system;

[0033] S43: Implement the optimization strategy, and recalculate the oscillation stability margin of the optimized system operating point, which includes the oscillation stability margin under normal condition and N-1 / N-2 fault condition;

[0034] S44: Check whether the oscillation stability margin of the optimized system operating point meets the predetermined stable operation requirement under normal condition and N-1 / N-2 fault condition, if yes, end the process; if not, return to step S42, adjust the optimization strategy and recalculate until the oscillation stability margin under normal condition and N-1 / N-2 fault condition meets the requirement.

[0035] Further, in step S41, the oscillation stability margin model under normal condition includes:

[0036]

[0037] In the formula, OSM SCR represents the oscillation stability margin under normal condition, SCR represents the short-circuit ratio of the new energy field station grid connection point, and CSCR represents the critical corresponding to the current output level of the new energy.

[0038] Further, in step S41, the oscillation stability margin model under N-1 / N-2 fault condition includes:

[0039]

[0040] In the formula, OSM SCR(N-1 / N-2) represents the oscillation stability margin under N-1 / N-2 fault condition, SCR N-1 / N-2 is the short-circuit ratio of the new energy field station grid connection point when the system is operated in N-1 / N-2 mode, and CSCR represents the critical corresponding to the current output level of the new energy.

[0041] The application also comprises a new energy grid-connected system operation mode optimization device based on oscillation stability margin, which uses the method as described above, comprising:

[0042] A small-signal state space model construction unit is configured to construct a small-signal state space model of the new energy grid-connected system according to the control structure and control parameters of the actual new energy grid-connected system;

[0043] An eigenvalue calculation and oscillation mode analysis unit is configured to calculate full-dimensional eigenvalues of the system under the current operation condition based on the small-signal state space model, and determine the dominant oscillation mode of the system by using eigenvalue analysis method, wherein the dominant oscillation mode refers to an oscillation mode close to the imaginary axis and having low damping, and the oscillation mode is prone to cause system instability, and the system instability mode is identified based on the dominant oscillation mode;

[0044] A stability boundary construction and oscillation stability margin calculation unit is configured to construct a stability boundary based on the new energy output level and short-circuit ratio for the system instability mode, and calculate the oscillation stability margin of the system under the current operation condition;

[0045] A system operation mode adjustment unit is configured to adjust the system operation mode according to the oscillation stability margin, increase the short-circuit capacity at the new energy grid-connected point, and thus increase the oscillation stability margin of the system, so as to ensure stable operation of the system.

[0046] The application also comprises a computer device, which comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the method as described above when executing the computer program.

[0047] The application also comprises a storage medium having a computer program stored thereon, and the computer program is executable on the processor to implement the method as described above.

[0048] The application has the following beneficial effects:

[0049] The stability margin index based on the oscillation stability boundary is proposed, and the oscillation stability margin index defined in the application can monitor the output level of the new energy field station and the short-circuit ratio of the grid-connected point, evaluate the current state of the system and the oscillation risk after the N-1 / N-2 fault.

[0050] The system operation mode optimization method based on the stability margin is proposed, which can adjust the system operation mode by optimizing the start-up mode and output of synchronous machines, reconstructing the power transmission network, optimizing the power flow distribution, and the like, so as to ensure that the new energy grid-connected point has sufficient short-circuit capacity and ensure stable operation of the system. BRIEF DESCRIPTION OF DRAWINGS

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 A flowchart of an optimization method for the operation mode of a new energy grid-connected system based on oscillation stability margin;

[0053] Figure 2 A schematic diagram of a new energy grid-connected system;

[0054] Figure 3 This is the discrete-time equivalent circuit diagram of the power element;

[0055] Figure 4 This is a schematic diagram of the system's oscillation stability margin.

[0056] Figure 5 A flowchart illustrating the specific process for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin;

[0057] Figure 6 The system structure diagram A1 in the implementation case;

[0058] Figure 7 To implement the system oscillation stability boundary diagram in the case study;

[0059] Figure 8 The diagram shows the time-domain simulation results of the system in the implementation case.

[0060] Figure 9 A schematic diagram of the structure of a device for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin;

[0061] Figure 10 This is a schematic diagram of the structure of a computer device. Detailed Implementation

[0062] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0063] Example 1:

[0064] like Figures 1 to 5 As shown: A method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin, comprising the following steps:

[0065] S10: According to the control structure and control parameters of the actual new energy grid-connected system, a small signal state space model of the new energy grid-connected system is constructed; according to the system topology, control structure and control parameters in the research system, the continuous space state model of the power element is discretized to obtain a discrete state space model, and then a single element equivalent circuit model is obtained from the discrete state space model, and finally all single discrete time equivalent circuit models of components are connected according to the research system topology structure, so that the complex target system is represented as a discrete time equivalent circuit network, and a state space model and an equivalent circuit network of the new energy grid-connected system containing new energy station, SVG, synchronous generator and other elements are obtained;

[0066] S20: Based on the small signal state space model, the full-dimensional eigenvalues of the system under the current operating condition are calculated, and the dominant oscillation mode of the system is determined by using the eigenvalue analysis method, wherein the dominant oscillation mode refers to the oscillation mode close to the virtual axis and having low damping, and the oscillation mode is easy to cause system instability, and based on the dominant oscillation mode, the mode that may cause system instability is identified; secondly, by changing the system operation mode, i.e. the grid strength and the new energy output level, the influence law of the system operation mode on the dominant oscillation mode of the system and the instability scenario are determined;

[0067] S30: For the instability mode, a stability boundary based on the new energy output level and the short-circuit ratio is constructed, and the system oscillation stability margin under the current operating condition is calculated; on the basis of determining the influence law of the system operation mode on the dominant oscillation mode of the system and the instability scenario, by changing the new energy output level, the critical short-circuit ratio at the land centralized control station under each output level is calculated, thereby the system oscillation stability boundary based on the new energy output level and the short-circuit ratio is constructed, and on this basis, the oscillation stability margin of the current operating point of the system is calculated;

[0068] S40: According to the oscillation stability margin, the system operation mode is adjusted by optimizing the synchronous machine starting mode, the system power flow distribution, the transmission line reconstruction, the configuration of synchronous compensator and the like, the short-circuit capacity at the new energy grid-connected point is improved, so as to improve the system oscillation stability margin and ensure the stable operation of the system; in addition, after the oscillation occurs, the oscillation can also be suppressed from continuing to occur by increasing the number of synchronous machine starting tables, increasing the number of transmission line returns, and the like.

[0069] Based on the oscillation stability margin, the system operation mode is optimized to reduce the risk of system wideband oscillation, which can evaluate the system oscillation risk, and in actual power grid operation, the system operation mode can be optimized online in combination with the new energy wideband oscillation risk early warning system to ensure the safe and stable operation of the new energy grid-connected system.

[0070] Through eigenvalue analysis, the dominant oscillation mode and potential instability mode in the system can be accurately identified. Compared with the traditional optimization method, eigenvalue analysis provides a more scientific and accurate way to identify and prevent system instability in time, avoiding large-scale oscillation accidents, which effectively solves the wideband oscillation problem mentioned in the background.

[0071] Based on the new energy output level and short circuit ratio, the system oscillation stability boundary is constructed, and the oscillation stability margin is defined, providing a means for real-time evaluation of system operation state. This margin can dynamically reflect the stability of the system. Compared with the existing method in the background technology which relies on hardware adjustment, it is more flexible and low cost. At the same time, this method can adaptively adjust according to different new energy output levels and grid strength, ensuring that the system operates in a stable region.

[0072] By optimizing the operation mode of the system (such as generator start-up mode, power flow distribution, and transmission line reconstruction, etc.), the short circuit capacity of the new energy grid-connected point is improved without the need for large-scale modification of the system hardware. This method can improve the anti-oscillation ability of the system without adding additional hardware devices, solving the high cost and complex implementation problem mentioned in the background technology. In addition, this method can quickly respond to the dynamic changes of the system and maintain the stable operation of the power grid.

[0073] By calculating the oscillation stability margin of the system, an adaptive optimization scheme is provided. This scheme can adjust the system operation mode in real time according to the current working condition of the system, and adapt to changes in different new energy output levels and grid topology. This flexibility ensures that the new energy grid-connected system can cope with the problem of insufficient grid strength in different scenarios, solving the stability problem of new energy bases lacking traditional synchronous generator support in the background technology.

[0074] In the new energy grid-connected system, most common power elements are included, among which the power supply elements and reactive power compensation elements include new energy generators, supporting SVG, synchronous generators, etc., while the transmission side devices include transformers, AC lines, etc. After collecting electric energy, it is sent to the main grid or load center, as shown in Figure 2 .

[0075] If the grid-connected bus voltage and the current flowing into the grid are regarded as input and output variables, any power element in the above power system can be represented by the following continuous space state model:

[0076] As a preferred embodiment of the above, in step S10, the small signal state space model includes a continuous space state model, including:

[0077]

[0078] In the formula, Xs represents a continuous state vector, U xy and i xy represent input and output vectors, respectively, A cs , B cs , C cs and D cs are coefficient matrices, which can be obtained by a differential equation or a transfer function of linearizing the dynamic characteristics of electrical elements, and p represents a differential operator.

[0079] By introducing a continuous space state model, the dynamic behavior of each electrical element in a new energy grid-connected system can be accurately described. The model represents the relationship between the input, state and output of the electrical element through a linear equation, which can capture the complex dynamic characteristics of the system under small perturbations, and provide an accurate data basis for the oscillation mode analysis of the system.

[0080] The continuous space state model is discretized by a specific integration rule to obtain a discrete state space model, which is used to describe the behavior of the system through a set of discrete-time equations, and belongs to a processing method of a small-signal state space model. The discrete state space model includes:

[0081]

[0082] In the formula, h s (t) represents a state vector in the current discrete state space, which is of great significance in subsequent model modal analysis, A ds , B ds , C ds and D ds are coefficient matrices calculated, Δt represents a discrete time step, t represents time, U xy and i xy represent input and output vectors, respectively.

[0083] In addition, the second term in the discrete state space model can obtain the discrete-time equivalent circuit of the element, as shown in Figure 3 , which is equivalent to a Norton branch, where g s =-C ds is an equivalent conductance, D ds h s is an equivalent current source, and the representation of the discrete-time equivalent circuit is the key to the construction of the system state matrix.

[0084] By discretizing the continuous space state model, the model is adapted to the digital control environment in modern power systems. The discrete state space model can be applied to digital simulation, online monitoring and control systems, and is more suitable for actual new energy grid-connected system operation.

[0085] As a preferred embodiment of the above, in step S20, based on the small signal state space model, the full-dimensional eigenvalues of the system under the current operating condition are calculated, the dominant oscillation mode of the system is determined using the eigenvalue analysis method, and the mode that may cause the system to lose stability is identified, and the steps include:

[0086] S21: Calculate the full-dimensional eigenvalues of the system and the corresponding left and right eigenvectors;

[0087] S22: Calculate the participation factor of the oscillation mode of the system according to the left and right eigenvectors, and determine the main link affecting the oscillation mode based on the participation factor;

[0088] S23: Calculate the oscillation frequency and damping ratio of each oscillation mode according to the full-dimensional eigenvalues, and define the oscillation mode with smaller or negative damping ratio as the dominant oscillation mode of the system;

[0089] S24: Based on the dominant oscillation mode, adjust the short circuit ratio (SCR) of the system and the new energy output level, and analyze the influence of the change of the system operating mode on the dominant oscillation mode by observing the change of the root locus;

[0090] S25: When the root locus changes are observed, if the conjugate eigenvalue crosses the imaginary axis into the right half of the complex plane, it is identified that the system has an oscillation instability risk;

[0091] S26: Based on the oscillation instability risk, determine the critical output level and critical short circuit ratio of the system, and identify the oscillation instability risk of the system below the critical short circuit ratio.

[0092] Based on the construction of the discrete state space model of the new energy, the full-dimensional eigenvalues of the system and the corresponding left and right eigenvectors can be calculated under the given system operating condition. According to the left and right eigenvectors, the participation factor of the oscillation mode of the system can be calculated, and according to the participation factor, the main link affecting the oscillation mode can be determined. According to the full-dimensional eigenvalues of the system, the oscillation frequency and damping ratio of each oscillation mode of the system can be calculated, and the oscillation mode with smaller or negative damping ratio is considered as the dominant oscillation mode of the system. Based on the determination of the dominant oscillation mode of the system, the system operating mode, i.e. the grid strength and the new energy output level, can be changed, and in this case, the commonly used short circuit ratio (SCR) in the industry is used as an index to evaluate the grid strength of the new energy access point, which is equal to the short circuit capacity of the access point divided by the installed capacity of the grid-connected power electronic equipment.

[0093] By adjusting the short circuit ratio (SCR) and the new energy output level respectively, the changes in the root locus can be observed, which provides an important basis for analyzing the changes in system operation mode, especially when studying the influence law of the dominant oscillation mode. When the conjugate eigenvalue crosses the imaginary axis and enters the right half of the complex plane, it means that the damping characteristics of the oscillation mode related to the conjugate eigenvalue have changed significantly, specifically, the damping changes from positive to negative, which may lead to oscillation instability. Therefore, in-depth study of the influence of short circuit ratio and new energy output level on system oscillation characteristics and timely identification of potential instability risks are crucial for ensuring the stability and reliability of the power system.

[0094] In addition, according to existing domestic and foreign research results, there is a critical output level and a critical short circuit ratio for grid-connected new energy power plants with grid-type control. That is, at each output level, there is a corresponding critical short circuit ratio. When the actual operating short circuit ratio is lower than the critical short circuit ratio, the system may experience oscillation instability.

[0095] By calculating the full-dimensional eigenvalues and left and right eigenvectors, and combining with the participation factor, the dominant oscillation mode and influencing link in the system can be accurately determined. Compared with traditional empirical methods, this eigenvalue analysis method can more accurately identify the main oscillation mode that leads to system instability, providing a clear direction for subsequent optimization.

[0096] By adjusting the short circuit ratio (SCR) and the new energy output level, this method can monitor the system operating state in real time and observe the changes in the system root locus. Root locus analysis provides an intuitive representation of the system response as the parameters change, effectively identifying changes in system stability.

[0097] When the root locus shows that the eigenvalue crosses the imaginary axis and enters the right half of the complex plane, the system can identify the risk of oscillation instability in a timely manner. This mechanism provides an early warning function for the power grid system, allowing measures to be taken to prevent fault expansion before system instability, ensuring safe operation of the system.

[0098] Based on the risk of oscillation instability, the critical output level and critical short circuit ratio of the system can be accurately determined, and the risk of instability when the system is below the critical short circuit ratio can be identified. This helps to provide key references for system design and dispatch, ensuring that the system operates within the stable range.

[0099] Through the above series of calculations and adjustments, this method not only identifies potential oscillation instability risks, but also dynamically adjusts operating parameters to improve system stability margins, ensuring safe and stable operation of the system under complex and changing operating conditions.

[0100] By optimizing the system operation mode (such as short-circuit ratio adjustment and output level adjustment), instead of relying on hardware adjustment, the transformation cost can be effectively reduced, without the need for large-scale equipment changes or additional device installation, and the stability can be improved only by optimizing the system parameters.

[0101] On the basis of determining the typical instability scenarios of the new energy grid-connected system, the system operating point is first defined as the grid-connected point short-circuit ratio under the current system operation mode and the corresponding point in the corresponding short-circuit ratio-new energy power space under the new energy output level / output combination.

[0102] In this embodiment, in step S30, for the instability mode, a stability boundary based on the new energy output level and the short-circuit ratio is constructed, and the step of constructing the stability boundary includes:

[0103] S31: Calculate the eigenvalue corresponding to the system instability mode under the current output;

[0104] S32: Based on the eigenvalue, search and calculate the critical short-circuit ratio under the current output level by adjusting the grid-connected point short-circuit ratio of the new energy station; that is, the grid-connected point short-circuit ratio when the system instability oscillation mode enters the right half plane from the left half plane of the complex plane and the real part of the eigenvalue is exactly 0;

[0105] S33: Based on the critical short-circuit ratio, gradually increase the output level of the new energy station, and calculate the system critical short-circuit ratio under the corresponding output level; the interval between adjacent two output levels should not be too large to ensure the smoothness of the stability boundary, and at the same time, to reduce the calculation pressure, the output level interval should not be too small, and it is recommended to take 0.1 p.u. as the output interval;

[0106] S34: According to the system critical short-circuit ratio under the corresponding output level and the output level of the corresponding new energy station, the critical stable operating point of each system is calibrated, and the stability boundary is drawn in the short-circuit ratio-new energy power space. The new energy output level can be taken as the y-axis and the grid-connected point short-circuit ratio as the x-axis, the critical stable operating points of each system are marked in the two-dimensional short-circuit ratio-new energy power space, and then the points are connected to obtain the stability boundary of the new energy grid-connected system.

[0107] According to the above steps, the core idea of the construction method of the oscillation stability boundary of the new energy grid-connected system can be obtained, that is, by calculating the system critical short-circuit ratio under each output level, the system oscillation stability boundary is obtained.

[0108] By calculating the eigenvalue of the system under different output levels, the instability oscillation mode of the system can be accurately identified, the eigenvalue analysis can help to find the potential instability mode of the system, which is helpful to identify the stability risk of the system in advance. Compared with the traditional rough estimation method, the technical scheme ensures the accurate positioning of the oscillation instability point by accurately calculating the eigenvalue of the system.

[0109] The critical short-circuit ratio is calculated by adjusting the short-circuit ratio of the new energy station, which provides a means for flexible adjustment of the system operation mode. As an important indicator for evaluating the strength of the grid at the new energy grid-connected point, the short-circuit ratio can respond to grid changes in a timely manner and flexibly control the stability of the system through dynamic adjustment, avoiding the limitations of traditional systems relying on fixed parameters, and making the system more adaptable and resistant to disturbances.

[0110] By gradually increasing the output level of the new energy station, the critical short-circuit ratio at each output level is calculated and calibrated, and a system stability boundary based on new energy output and short-circuit ratio is constructed. This boundary not only comprehensively and intuitively shows the stability of the system under different operating conditions, but also provides a scientific basis for system operation optimization. Compared with traditional methods, system operators can more accurately assess the stability of the system under different load conditions based on the stability boundary.

[0111] By adjusting system parameters (such as short-circuit ratio, output level, etc.) within the stability boundary to ensure stable operation of the system, the high cost of hardware modification or additional equipment installation is avoided. This software and algorithm-based optimization method can fully utilize existing system resources, avoid significant hardware investment, and reduce the cost of system upgrade and maintenance.

[0112] As a preferred embodiment of the above, in step S40, the system operation mode is adjusted according to the oscillation stability margin, such as Figure 5 As shown, the steps include:

[0113] S41: Calculate the oscillation stability margin of the current operating point of the system, which includes the oscillation stability margin under normal operating conditions and N-1 / N-2 fault operating conditions;

[0114] S42: Based on the oscillation stability margin, determine the optimization strategy for the system operation mode, which dynamically adjusts system parameters such as synchronous machine startup mode, reactive power compensation, etc., according to the oscillation stability margin of the system;

[0115] S43: Implement the optimization strategy and recalculate the oscillation stability margin of the optimized system operating point, which includes the oscillation stability margin under normal operating conditions and N-1 / N-2 fault operating conditions;

[0116] Wherein, N-1 / N-2 is a commonly used symbol in power systems, representing the number of all devices in the normal operating state of the power system; N-1 / N-2 fault operating condition refers to the assumption that one or two devices (such as generators, transformers, or transmission lines) in the power system are disconnected due to failure. By checking the oscillation stability margin under N-1 / N-2 fault operating conditions, the power system can better respond to emergencies and improve the reliability and stability of operation;

[0117] S44: Whether the oscillation stability margin of the optimized system operating point meets the predetermined stable operation requirements under normal operating conditions and N-1 / N-2 fault operating conditions. If yes, the process ends; if no, return to step S42 to adjust the optimization strategy and recalculate until the oscillation stability margin under normal operating conditions and N-1 / N-2 fault operating conditions meets the requirements.

[0118] The system operating mode optimization method based on stability margin is proposed, which can adjust the system operating mode by optimizing the synchronous machine start-up mode and output, reconfiguring the transmission network, and optimizing the power flow distribution, to ensure sufficient short-circuit capacity at the new energy grid connection point and ensure stable operation of the system.

[0119] By calculating the oscillation stability margin under normal operating conditions and N-1 / N-2 fault operating conditions, the stability of the system under different operating conditions can be comprehensively evaluated, whether it is in normal operation or single-point or multi-point fault, the stability of the system can be analyzed and evaluated.

[0120] According to the oscillation stability margin, the system can dynamically adjust the operating mode and parameters, such as the synchronous machine start-up mode and reactive power compensation, according to the real-time monitoring of the system state, the system can flexibly respond to the current operating conditions, avoiding the stability problems caused by fixed settings.

[0121] The system is not only optimized under normal operating conditions, but also evaluated under N-1 / N-2 fault operating conditions to ensure stability in single-point or multi-point fault, this multi-condition evaluation mechanism reduces the possibility of system instability in fault; by calculating the stability margin under normal operating conditions and N-1 / N-2 operating conditions, the system avoids the instability judgment of only focusing on a single condition, which ensures that the system can meet the stability requirements under multiple potential operating modes, avoiding unnecessary risks caused by ignoring specific fault conditions.

[0122] Based on the construction of the system oscillation stability boundary, the system stability margin requirements under normal operation can be defined, such as 20%, and the N-1 stability margin, such as 10%, the reasonable value range can be discussed in actual application.

[0123] 1) Oscillation stability margin definition

[0124] Under the current operating conditions of the system, the short-circuit ratio SCR of the new energy station grid connection point minus the critical CSCR corresponding to the current output level of the new energy, divided by the current SCR, is defined as the oscillation stability margin based on the short-circuit ratio:

[0125] Wherein, in step S41, the oscillation stability margin model of normal operating conditions includes:

[0126]

[0127] where OSM SCR represents the oscillation stability margin of normal operating condition, SCR represents the short circuit ratio of new energy station grid connection point, and CSCR represents the criticality corresponding to the current output level of new energy.

[0128] The oscillation stability margin model determines the stability margin quantification of the system in the normal operating condition, that is, the relationship between the system short circuit ratio (SCR) and the corresponding critical short circuit ratio (CSCR) is calculated, which can accurately describe the stability of the system in the current operating condition, and provides a quantitative basis for the safety evaluation of system operation.

[0129] 2) N-1 / N-2 oscillation stability margin

[0130] As a preferred embodiment of the above, in step S41, the oscillation stability margin under N-1 / N-2 fault condition, the model includes:

[0131] In order to reasonably evaluate the oscillation risk of the system under N-1 / N-2 operating mode, the system N-1 / N-2 stability margin index can also be defined based on this, which is defined as the distance between the system operating point after N-1 / N-2 and the system stability boundary under the current operating condition of the system, and the calculation formula is as follows:

[0132]

[0133] where OSM SCR(N-1 / N-2) represents the oscillation stability margin of normal operating condition, SCR represents the short circuit ratio of new energy station grid connection point, and CSCR represents the criticality corresponding to the current output level of new energy. N-1 / N-2 The system oscillation stability margin diagram is shown in Figure 4 .

[0134] By calculating the oscillation stability margin under N-1 / N-2 condition, the possible oscillation instability risk can be timely warned when the fault occurs or in the fault simulation, and the model clearly describes whether the operating margin of the system is sufficient under the fault condition. If the oscillation stability margin is too low, it indicates that the system has instability risk.

[0135] When the oscillation stability margin of the system under N-1 / N-2 condition is insufficient, the system can dynamically adjust the operating mode according to the model results, take necessary emergency response measures, and ensure that the system will not fall into instability when the fault occurs. Through the model, it can be accurately determined when the emergency response needs to be started.

[0136] Based on the system oscillation stability margin, the short-circuit capacity at the new energy grid connection point can be improved by optimizing the synchronous machine starting mode, system power flow distribution, transmission line reconstruction, and configuring synchronous compensators, so as to improve the system oscillation stability margin and ensure the safe and stable operation of the system. In addition, after oscillation occurs, the oscillation can also be suppressed from continuing to occur by increasing the number of synchronous machine starting units, increasing the number of transmission line returns, and the like.

[0137] Embodiment 2:

[0138] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and examples.

[0139] The single offshore wind farm through AC transmission access to the 10-machine 39-node system example provided by the embodiment case of the present application:

[0140] 1. Example introduction: Figure 6 The example shown is modified from the 10-machine 39-node system of IEEE, wherein the 300MW wind farm is transmitted to the land control station through a step-up transformer and a submarine cable, and then transmitted to the bus 23 of the 10-machine 39-node system through a certain distance overhead transmission line. At the land control station, a SVG is configured for dynamic reactive power compensation according to 20% of the new energy installed capacity.

[0141] Initial operating condition introduction: the wind farm WF output level is 0.1pu, and the short-circuit ratio of the land control station is 2.89.

[0142] 2. Eigenvalue calculation: calculate the full-dimensional eigenvalues of the system under the given power flow initial value condition. According to the calculation results, the damping ratio of each oscillation mode is determined, wherein the smaller the damping ratio, the more dominant the oscillation mode. Part of the calculation results are shown in Table 1.

[0143] Table 1 System dominant oscillation mode

[0144]

[0145] Among them, the participation factor analysis can be carried out on each oscillation mode, and according to the different participation factors, it can be mainly divided into four categories: electrical resonance mode, wind power control mode, SVG control mode and synchronous machine low-frequency oscillation mode. On this basis, by changing the system operation mode, it can be found that under the condition of low short-circuit ratio and low output level, the sub-synchronous oscillation mode λ 158，159 may occur oscillation instability, so the subsequent stability boundary is constructed around this instability mode.

[0146] 3. Stability boundary construction and system stability margin calculation:

[0147] The new energy grid-connected system is subjected to comprehensive evaluation of oscillation risk: first, the sub-synchronous oscillation mode λ dominated by the wind power current control which is likely to be unstable 158，159 The system oscillation stability boundary based on short-circuit ratio and output level is constructed, as shown in Figure 7

[0148] Secondly, the stability margin of the system basic operation condition can be calculated according to the oscillation stability margin definition as shown in the first row of Table 2, at this time, the oscillation stability margin OSM SCR is less than 0, which indicates that the system is likely to be unstable at this time.

[0149] Further, considering that the short-circuit ratio of the initial time set control station is 3.0, the wind power output is 0.4pu, and the single-circuit line operation of the wind farm outgoing overhead line, the system oscillation stability margin is 12.3% at this time, which can maintain stable operation. At 5s, the wind power output is reduced to 0.1pu, and the oscillation stability margin is reduced to-7.67%, which is less than 0 and is likely to be unstable, and the time domain simulation is carried out by combining PSCAD / EMTDC as shown in Figure 8 It can be seen that the system has sub-synchronous oscillation instability at this time, which is consistent with the analysis result. In order to suppress the oscillation, the outgoing overhead line of the wind farm is adjusted from single-circuit line operation to double-circuit line operation, and the system oscillation stability margin is increased to 7.7%>0, the system oscillation converges, and the stable operation is restored, and the time domain simulation combined with PSCAD / EMTDC is consistent with the analysis result.

[0150] Table 2 System operating point change and stability margin

[0151] Wind power output Control station short circuit ratio Critical control station short circuit ratio Oscillation stability margin OSM SCR ]]> 0.1 pu 2.89 3.40 -17.6％ 0.4 pu 3.0 2.63 12.3％ 0.14 pu 3.0 3.23 -7.67％ 0.14 pu 3.5 3.23 7.7％

[0152] Therefore, the effectiveness of the new energy grid-connected system operation mode optimization method based on the oscillation stability margin provided by the present application is verified.

[0153] The present application also includes a new energy grid-connected system operation mode optimization device based on the oscillation stability margin, which uses the method as described above, as shown in Figure 9 , comprising:

[0154] A small signal state space model construction unit is configured to construct a small signal state space model of the new energy grid-connected system according to the control structure and control parameters of the actual new energy grid-connected system.

[0155] An eigenvalue calculation and oscillation mode analysis unit is configured to calculate full-dimensional eigenvalues of the system under the current operating condition based on the small signal state space model, and determine the dominant oscillation mode of the system by using the eigenvalue analysis method, wherein the dominant oscillation mode refers to the oscillation mode close to the virtual axis and having low damping, and the oscillation mode is easy to cause system instability, and the mode which is likely to cause system instability is identified based on the dominant oscillation mode. ​

[0156] A stable boundary construction and oscillation stability margin calculation unit is configured to, for an unstable mode, construct a stable boundary based on a new energy output level and a short-circuit ratio, and calculate a system oscillation stability margin under a current operating condition;

[0157] A system operation mode adjustment unit is configured to adjust a system operation mode according to the oscillation stability margin, increase short-circuit capacity at a new energy grid-connected point, and thus increase the system oscillation stability margin, to ensure stable operation of the system.

[0158] See Figure 10 The computer device provided by the embodiment of the application is shown in a structural schematic diagram. The computer device 400 provided by the embodiment of the application comprises a processor 410 and a memory 420, the memory 420 stores a computer program executable by the processor 410, and the computer program is executed by the processor 410 to perform the method as above.

[0159] The embodiment of the application further provides a storage medium 430, the storage medium 430 stores a computer program, and the computer program is executed by the processor 410 to perform the method as above.

[0160] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as a static random access memory (SRAM), an electrically erasable programmable read-only memory (EEPROM), an erasable programmable read-only memory (EPROM), a programmable read-only memory (PROM), a read-only memory (ROM), a magnetic memory, a flash memory, a magnetic disk or an optical disk.

[0161] In the description of the application, the terms “first” and “second” are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with “first” and “second” can explicitly or implicitly include one or more of the features. The meaning of “a plurality of” is two or more, unless otherwise specifically limited.

[0162] In the present application, unless specifically defined otherwise, the terms "mounting", "connected", "connecting", "fixed", "fixedly connected", "connection", "joint", "jointly connected", "jointly connected" and the like should be construed broadly, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be direct connection, can also be indirect connection through an intermediate medium, can be internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0163] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms is not necessarily for the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0164] Any process or method descriptions in flow charts or otherwise described herein represent embodiments of examples that can be implemented by computer executable code or instructions, and the scope of the preferred embodiments of the present application includes additional implementation involving other processes or methods that can be performed according to the claimed subject matter. As such, the processes presented in a given example are illustrative in nature and can be modified or otherwise varied when implementing the application by those skilled in the art.

[0165] The logic and / or steps represented in flow diagrams or otherwise described herein, for example, can be considered as a sequence of instructions to implement logic functions, and can be realized in any computer-readable medium for use by an instruction execution system, apparatus, or device, such as a computer-based system, processor- containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this specification, a "computer-readable medium" can be any means that can contain, store, communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium include an electronic connection (an electronic device), a portable computer diskette (a magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CDROM). Further, the computer-readable medium can even be paper or other suitable medium upon which the program is printed, as the program can be electronically captured, for example, by optically scanning the paper or other suitable medium, then electronically converted into a form that is suitable for use by the instruction execution system, apparatus, or device, and then stored in computer memory.

[0166] It should be understood that aspects of the application can be implemented in hardware, software, firmware or combinations thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, and in another embodiment, any of the following technologies, known in the art, or combinations thereof, can be used: discrete logic circuitry having logic gates for implementing logic functions on data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), etc.

[0167] Those skilled in the art of the present technology can understand that all or part of the steps carried out by the above-mentioned embodiments can be completed by programs instructing related hardware, and the programs can be stored in a computer-readable storage medium. When the program is executed, it includes one of the steps of the method embodiments or a combination thereof.

[0168] The storage medium mentioned above can be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. A method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin, characterized in that, Includes the following steps: S10: Construct a small-signal state-space model of the new energy grid-connected system based on the control structure and control parameters of the actual new energy grid-connected system; S20: Based on the small-signal state-space model, calculate the full-dimensional eigenvalues ​​of the system under the current operating conditions, and use the eigenvalue analysis method to determine the dominant oscillation mode of the system. The dominant oscillation mode refers to the oscillation mode that is close to the imaginary axis and has low damping. The oscillation mode is prone to causing system instability. Based on the dominant oscillation mode, identify the mode that causes system instability. S30: For the aforementioned instability mode, construct a stability boundary based on the power output level of new energy sources and the short-circuit ratio, and calculate the system oscillation stability margin under the current operating conditions; S40: Based on the aforementioned oscillation stability margin, adjust the system operation mode to increase the short-circuit capacity at the new energy grid connection point, thereby increasing the system oscillation stability margin and ensuring stable system operation.

2. The method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin according to claim 1, characterized in that, In step S10, the small-signal state-space model includes a continuous-space state model, comprising: In the formula, X s U represents a continuous state vector. xy and i xy Let A represent the input and output vectors, respectively. cs B cs C cs and D cs It is a coefficient matrix, obtained by linearizing the differential equations or transfer functions of the dynamic characteristics of electrical components, where p represents the differential operator.

3. The method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin according to claim 2, characterized in that, The continuous-space state model is discretized using a specific integration rule to obtain a discrete-space state model. This discrete-space state model describes the system's behavior using a set of discrete-time equations. The discrete-space state model includes: In the formula, h s (t) represents the state vector in the current discrete state space, A ds B ds C ds and D ds It is calculated from the coefficient matrix, where Δt represents the discrete time step, t represents time, and U xy and i xy These represent the input and output vectors, respectively.

4. The method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin according to claim 1, characterized in that, In step S20, based on the small-signal state-space model, the full-dimensional eigenvalues ​​of the system under the current operating conditions are calculated. The dominant oscillation mode of the system is determined using eigenvalue analysis, and potential instability modes are identified. The steps include: S21: Calculate the full-dimensional eigenvalues ​​of the system and the corresponding left and right eigenvectors; S22: Calculate the participation factor of the system oscillation mode based on the left and right eigenvectors, and determine the main factors affecting the oscillation mode based on the participation factor; S23: Based on the full-dimensional eigenvalues, calculate the oscillation frequency and damping ratio of each oscillation mode, and define the oscillation mode with a small or negative damping ratio as the dominant oscillation mode of the system; S24: Based on the dominant oscillation mode, adjust the short-circuit ratio and the output level of new energy sources in the system, and analyze the impact of the change in the system operation mode on the dominant oscillation mode by observing the changes in the root locus; S25: When the change in the root locus is observed, if the conjugate eigenvalue crosses the imaginary axis and enters the right half of the complex plane, the risk of oscillation and instability in the system is identified. S26: Based on the oscillation instability risk, determine the critical output level and critical short-circuit ratio of the system, and identify the oscillation instability risk that occurs when the system is below the critical short-circuit ratio.

5. The method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin according to claim 1, characterized in that, In step S30, for the instability mode, a stability boundary is constructed based on the power output level of the new energy source and the short-circuit ratio. The step of constructing the stability boundary includes: S31: Calculate the eigenvalues ​​corresponding to the system instability modes under the current output; S32: Based on the aforementioned characteristic values, by adjusting the short-circuit ratio of the grid connection point of the new energy power station, search and calculate the critical short-circuit ratio under the current power output level; S33: Based on the critical short-circuit ratio, gradually increase the output level of the new energy power station and calculate the critical short-circuit ratio of the system under the corresponding output level; S34: Based on the critical short-circuit ratio of the system at the corresponding power output level and the corresponding power output level of the new energy power station, calibrate the critical stable operating point of each system, and draw the stability boundary in the short-circuit ratio-new energy power space.

6. The method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin according to claim 1, characterized in that, In step S40, the system operating mode is adjusted according to the oscillation stability margin. The steps include: S41: Calculate the oscillation stability margin at the current operating point of the system, wherein the oscillation stability margin includes the oscillation stability margin under normal operating conditions and N-1 / N-2 fault conditions; S42: Based on the oscillation stability margin, determine the optimization strategy for the system operation mode, and dynamically adjust the system parameters according to the oscillation stability margin of the system; S43: Implement the optimization strategy and recalculate the oscillation stability margin of the optimized system operating point. The oscillation stability margin includes the oscillation stability margin under normal operating conditions and N-1 / N-2 fault conditions. S44: Verify whether the oscillation stability margin of the optimized system operating point meets the predetermined stable operation requirements under normal operating conditions and N-1 / N-2 fault conditions. If yes, end the process; if not, return to step S42, adjust the optimization strategy and recalculate until the oscillation stability margin under normal operating conditions and N-1 / N-2 fault conditions meets the requirements.

7. The method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin according to claim 6, characterized in that, In step S41, the oscillation stability margin model under normal operating conditions includes: In the formula, OSM SCR The SCR indicates the oscillation stability margin under normal operating conditions, the CSCR indicates the short-circuit ratio at the grid connection point of the new energy power station, and the CSCR indicates the critical level corresponding to the current output level of the new energy power station.

8. The method for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin according to claim 6, characterized in that, In step S41, the oscillation stability margin under fault conditions N-1 / N-2 is modeled as follows: In the formula, OSM SCR(N-1 / N-2) SCR represents the oscillation stability margin under N-1 / N-2 fault conditions. N-1 / N-2 CSCR represents the short-circuit ratio of the grid connection point of the new energy power station when the system operates in N-1 / N-2 mode, and represents the critical level corresponding to the current output level of the new energy.

9. A device for optimizing the operation mode of a new energy grid-connected system based on oscillation stability margin, characterized in that, Using the method as described in any one of claims 1 to 8, comprising: The small-signal state-space model construction unit is used to construct the small-signal state-space model of the new energy grid-connected system based on the control structure and control parameters of the actual new energy grid-connected system. The eigenvalue calculation and oscillation mode analysis unit is used to calculate the full-dimensional eigenvalues ​​of the system under the current operating conditions based on the small-signal state-space model, and to determine the dominant oscillation mode of the system using the eigenvalue analysis method. The dominant oscillation mode refers to the oscillation mode that is close to the imaginary axis and has low damping. The oscillation mode is prone to causing system instability. Based on the dominant oscillation mode, the unit also identifies modes that may cause system instability. The stability boundary construction and oscillation stability margin calculation unit is used to construct a stability boundary based on the power output level of new energy sources and the short-circuit ratio for the instability mode, and to calculate the system oscillation stability margin under the current operating conditions. The system operation mode adjustment unit is used to adjust the system operation mode according to the oscillation stability margin, increase the short-circuit capacity at the new energy grid connection point, thereby increasing the system oscillation stability margin and ensuring stable system operation.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 1-8.

11. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-8.

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