Power system small interference stability evaluation correction method and system considering N-1 operation mode

Abstract

The invention discloses an electric power system small interference stability evaluation correction method and system considering an N-1 operation mode, and relates to the field of artificial intelligence and electric power system static safety and stability online evaluation and optimization, and the method comprises the steps: obtaining the data of an electric power system in the N-1 operation mode; inputting the data into the power sensitivity calculation model, and outputting the minimum damping ratio of the system and the damping ratio sensitivity index of each generator; the model is obtained by adopting a random forest and gradient boosting decision tree algorithm; judging whether the minimum damping ratio is greater than or equal to a threshold value; if the sensitivity is smaller than the threshold value, taking the minimum sum of the active power variation of the generator as a target, and correcting the active power of the generator according to the sensitivity index and the constraint condition; and re-determining the minimum damping ratio of the system and the damping ratio sensitivity index of each generator until the minimum damping ratio is greater than or equal to a stable threshold value, and judging that the system is stable in small interference. Safe, stable and reliable operation of the power grid is ensured.

Description

Technical Field

[0001] The present application relates to the fields of artificial intelligence, online evaluation and optimization of static safety and stability of power systems, and in particular to a method and system for evaluating and correcting small disturbance stability of power systems taking into account an N-1 operating mode. Background Art

[0002] With the rapid and healthy development of the national economy, the demand for electricity in various industries has increased significantly, and the power system is developing in the direction of large-scale, large-capacity, ultra-high voltage and long-distance transmission. In recent years, the construction of power grids such as smart grids, new energy grid-connected AC / DC hybrids, the interconnection of regional power grids, and the access of new energy components to the power grid have made the power grid structure increasingly complex. Although the large-scale power grid can improve the operating efficiency of the power system, the structure of the system has become more and more complex, bringing many safety hazards to the system. Among them, the problem of small disturbance stability is becoming increasingly prominent. The emergence of power system oscillation will affect the normal transmission of the power grid. In severe cases, it may cause the system to be decoupled or even cause a major power outage. Therefore, studying the small disturbance stability of the power system, analyzing the damping level, timely discovering the weak damping mode, formulating a reasonable correction plan, and effectively avoiding the occurrence of weak damping oscillations are important conditions for ensuring the safe and stable operation of modern complex and diverse power systems.

[0003] The N-1 operation mode of the power system is a safety criterion used to ensure the reliability and stability of the power system. Specifically, the N-1 criterion means that under normal operation, when any component of the power system (such as generators, transmission lines, transformers, etc.) fails or needs to be disconnected for maintenance, the system should be able to maintain stable operation and normal power supply, other components will not be overloaded, and the system can continue to supply power without further failures. Under the N-1 operation mode, after the line in the power system is overloaded and cut off, the redistribution of power flow may cause internal chain failures of the transmission section, increasing the safety risk of the system. In order to ensure the stability of the power system with small disturbances, the power system should be promptly evaluated and corrected for safety and eliminate line overload. Summary of the invention

[0004] The purpose of this application is to provide a method and system for evaluating and correcting small disturbance stability of an electric power system taking into account an N-1 operating mode, which can prevent low-frequency oscillations that may occur in the operation of the evaluated electric power system, and can perform stability optimization calculations on the power grid of the evaluated electric power system, so as to achieve the power grid of the evaluated electric power system under any operating mode. The power grid operation mode optimization data required for the static safe and stable operation of the evaluated electric power system can be obtained, so as to ensure the safe, stable and reliable operation of the power grid.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a method for evaluating and correcting small disturbance stability of a power system considering an N-1 operation mode, comprising:

[0007] Real-time acquisition of power system operation data under N-1 operation mode;

[0008] According to the operation data, a power sensitivity calculation model is used to determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system; the power sensitivity calculation model is obtained by using a random forest algorithm and a gradient boosting decision tree algorithm; the damping ratio sensitivity index is the sensitivity of active power to the damping ratio;

[0009] Determining whether the minimum damping ratio is greater than or equal to a set stability threshold;

[0010] If the minimum damping ratio is greater than or equal to a set stability threshold, it is determined that the power system is small-disturbance stable;

[0011] If the minimum damping ratio is less than a set stability threshold, the active power of the generator in the power system is corrected according to the damping ratio sensitivity index and the constraint condition with the goal of minimizing the total amount of active power changes of the generator, and the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system are re-determined until the minimum damping ratio is greater than or equal to the set stability threshold; the constraint condition is the constraint condition that the line in the power system is not overloaded.

[0012] Optionally, the damping ratio sensitivity index of the generator is determined by the following formula:

[0013]

[0014] Where i is the generator number, j is the load node number, C i is the damping ratio sensitivity index of the i-th generator, ΔP ij is the active power change of the line between the i-th generator and the j-th load node, ΔP i is the active power change of the i-th generator, ΔP i The size of satisfies the upper and lower limits of the active power of the generator.

[0015] Optionally, the following formula is used to determine the active power change of the line between the i-th generator and the j-th load node:

[0016] ΔP ij =C1ΔP1+C2ΔP2+...+C n ΔP n ;

[0017] Where n is the total number of generators in the power system.

[0018] Optionally, the goal of correcting the active power of the generator in the power system according to the damping ratio sensitivity index and the constraint condition is:

[0019]

[0020] Among them, f(x) is the target value, min[·] is the minimum operator, is the positive value of the active power change of the i-th generator, is the negative value of the active power change of the i-th generator, and n is the total number of generators in the power system.

[0021] Optionally, the constraint conditions include: a damping ratio constraint, a constraint between a total damping ratio change of the power system and a change in active power of each generator, an equality constraint condition and an inequality constraint condition;

[0022] The equality constraints include power flow equations at each node in the power system;

[0023] The inequality constraints include node voltage constraints, unit output constraints, line flow constraints and transmission section constraints.

[0024] Optionally, the damping ratio constraint is:

[0025] ξ0+Δξ≥ξ limit ;

[0026] Among them, ξ0 is the minimum damping ratio corresponding to the power system under the initial operation mode, Δξ is the total damping ratio change of the power system, and ξli mit is the set threshold;

[0027] The constraint between the total damping ratio change of the power system and the active power change of each generator is:

[0028]

[0029] Where i is the generator number, C i is the damping ratio sensitivity index of the i-th generator, ΔP i is the change in active power of the i-th generator, Δξ is the change in the total damping ratio of the power system, and n is the total number of generators in the power system.

[0030] Optionally, the power flow equation of each node in the power system is:

[0031]

[0032] Where i is the generator number, j is the load node number, PGi is the active power of the i-th generator, Q Gi is the reactive power of the i-th generator, P Lj is the active power of the jth load node, Q Lj is the reactive power of the jth load node, V i is the voltage amplitude of the i-th generator, V j is the voltage amplitude of the jth load node, Y ij is the element amplitude of the admittance matrix between the i-th generator and the j-th load node, δ ij =δ i -δ j -α ij , δ i is the phase angle of the voltage of the i-th generator, δ j is the phase angle of the voltage at the jth load node, α ij is the element phase angle of the admittance matrix between the i-th generator and the j-th load node, S N is the system node set, the system node set S N It is the collection of generators and load nodes in the power system.

[0033] Optionally, the node voltage constraint is:

[0034] V i,min ≤V i ≤V i,max i∈S G ;

[0035] Among them, V i,max is the upper limit of the voltage amplitude of the i-th generator; V i,min is the lower limit of the voltage amplitude of the i-th generator, V i is the voltage amplitude of the i-th generator;

[0036] The unit output constraint is:

[0037] P Gi,min ≤P Gi ≤P Gi ,max i∈S G ;

[0038] P Lj,min ≤P Lj ≤P Lj ,max j∈S L ;

[0039] Among them, P Gi is the active power of the i-th generator, P Lj is the active power of the jth load node, P Gi,minis the lower limit of active power of the i-th generator, P Gi,max is the upper limit of active power of the ith generator, P Lj,min is the lower limit of the active power of the jth load node, P Lj,max is the upper limit of the active power of the jth load node, S G is the generator node set, the generator node set S G is the set of generators in the power system, S L is the load node set, load node set S L is the set of load nodes in the power system;

[0040] The line power flow constraint is:

[0041] P ij,min ≤P ij ≤P ij,max i∈S L ;

[0042] Among them, P ij,min is the lower limit of the line power between the i-th generator and the j-th load node, P i j,max is the upper limit of the line power between the i-th generator and the j-th load node, P i j is the active power of the line between the i-th generator and the j-th load node.

[0043] Optionally, the transmission section constraint is:

[0044]

[0045] ΔP l =C1ΔP1+C2ΔP2+...+C m ΔP m ;

[0046]

[0047] Among them, P l 0 is the active power of the line in the transmission section before the active power correction of the generator, P l is the active power of the line in the transmission section after the active power of the generator is corrected, Pl max is the maximum power flow allowed to pass through the transmission section when the power system is operating normally, m is the total number of lines in the transmission section, S m is the transmission section line set, the transmission section line set S m is the set of lines in the transmission section of the power system, ΔP lis the active power change of the line in the transmission section after the active power of the generator is corrected, l is the line included in the transmission section, C1, C2...C m is the damping ratio sensitivity index of the generator in the transmission section, ΔP1, ΔP2, … ΔP m It is the change of active power of the generator in the transmission section.

[0048] In a second aspect, the present application provides a power system small disturbance stability assessment and correction system considering N-1 operation mode, including:

[0049] Data acquisition module, used to obtain real-time operation data of the power system under N-1 operation mode;

[0050] A damping ratio calculation module, used to determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system according to the operating data and using a power sensitivity calculation model; the power sensitivity calculation model is obtained by using a random forest algorithm and a gradient boosting decision tree algorithm; the damping ratio sensitivity index is the sensitivity of active power to the damping ratio;

[0051] A judging module, used to judge whether the minimum damping ratio is greater than or equal to a set stability threshold;

[0052] A small disturbance stability evaluation module, configured to determine that the power system is stable with small disturbances if the minimum damping ratio is greater than or equal to a set stability threshold;

[0053] A correction control and damping ratio prediction module is used to correct the active power of the generators in the power system according to the damping ratio sensitivity index and constraint conditions with the goal of minimizing the total amount of active power changes of the generators if the minimum damping ratio is less than a set stability threshold, and to re-determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system until the minimum damping ratio is greater than or equal to the set stability threshold; the constraint condition is the constraint condition that the line in the power system does not overload.

[0054] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0055] The present application provides a method and system for evaluating and correcting the stability of a power system under small disturbances considering the N-1 operating mode. For a system in a weak damping mode under the N-1 operating mode, the active power of the generator is corrected according to the damping ratio sensitivity index and the constraint condition with the goal of minimizing the sum of the active power changes of the generator; the minimum damping ratio of the system can be increased so that the damping ratio reaches above the set stability threshold, thereby ensuring the stable operation of the power system. The obtained correction scheme is introduced into the RF-GBDT model, and the corrected damping ratio can be estimated more accurately. The present application can prevent the low-frequency oscillation that may occur during the operation of the evaluated power system, and can perform stable optimization calculations on the power grid of the evaluated power system, so that the power grid of the evaluated power system can obtain the power grid operation mode optimization data required for the static safe and stable operation of the evaluated power system through correction under any operating mode, and can use the power grid operation mode optimization data for automatic calculation and verification, and the verification results can be directly used to guide the compilation of the static safe and stable power grid operation mode of the evaluated power system to ensure the safe, stable and reliable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0057] Figure 1 This is a flow chart of a method for evaluating and correcting small disturbance stability of a power system considering an N-1 operation mode in an embodiment of the present application;

[0058] Figure 2 A functional module diagram of a power system small disturbance stability assessment and correction system considering N-1 operation mode provided in an embodiment of the present application;

[0059] Figure 3 A system structure topology diagram of IEEE-39 provided as a case in another embodiment of the present application;

[0060] Figure 4 A system correction control flow chart of IEEE-39 provided as another embodiment of the present application;

[0061] Figure 5 A scatter plot of system damping ratio prediction of IEEE-39, a case study provided as another embodiment of the present application. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0063] The terms used in this application are as follows:

[0064] Data-driven: It is to collect massive amounts of data through mobile Internet or other related software, organize the data into information, and then integrate and refine the relevant information. Based on the data, it forms an automated decision-making model through training and fitting. When new situations occur and new data is input, the system can use the previously established model to make decisions directly in an artificial intelligence way. It is closely integrated with digital transformation. The essence of digital transformation is to promote business growth through new technologies such as big data, artificial intelligence, cloud computing, and mobile Internet.

[0065] Artificial intelligence: It is a branch of computer science that attempts to understand the essence of intelligence and produce a new intelligent machine that can respond in a similar way to human intelligence. Research in this field includes robots, language recognition, image recognition, natural language processing and expert systems. Since the birth of artificial intelligence, the theory and technology have become increasingly mature, and the application field has continued to expand. It can be imagined that the technological products brought by artificial intelligence in the future will be the "container" of human wisdom. Artificial intelligence can simulate the information process of human consciousness and thinking. Artificial intelligence is not human intelligence, but it can think like humans and may also exceed human intelligence.

[0066] Machine learning: Use algorithms to learn from massive amounts of data, identify the rules contained therein, and use the data to predict development trends over the next period of time.

[0067] N-1 operation mode: When the total active power limit of the tie line is below a given limit, any line in the group of tie lines is disconnected, and the power flow of the other lines will not be overloaded.

[0068] RF-GBDT algorithm: A machine learning algorithm that combines Random Forest (RF) and Gradient Boosting Decision Tree (GBDT). Random Forest is an ensemble learning method that builds multiple decision trees and combines their predictions to improve the generalization and accuracy of the model. Gradient Boosting Decision Tree is a boosting method that improves the performance of the model by gradually adding trees to minimize the gradient of the loss function. The RF-GBDT algorithm can flexibly handle various types of data, including complex problems such as high dimensions, sparse features, and nonlinear relationships.

[0069] Power flow calculation: refers to the calculation of the voltage, current, direction and power distribution from the power source to the load in the power system under a certain operating mode and wiring method.

[0070] Flow constraint: refers to the flow in which static stability is used as a constraint in the flow constraint conditions.

[0071] With the development of artificial intelligence technology, more and more new algorithms have been proposed and applied to many fields of power systems. At present, the most widely used are machine learning algorithms represented by support vector machines and neural networks. In the prior art, a large number of machine learning algorithms have been applied to realize the conventional small disturbance stability assessment and correction of power systems. However, the small disturbance stability assessment and correction of power systems considering the N-1 operation mode mainly adopts the method of computer programming calculation, and the use of machine learning algorithms is relatively rare. The prior art solves the state equation of the system through computer programming to obtain the minimum damping ratio, which has the disadvantages of high requirements for computer memory, cumbersome programming, and large amount of calculation.

[0072] The technology to be solved by this application is a method and system for evaluating and correcting the small disturbance stability of an electric power system in an N-1 operating mode. By adjusting the active output of the generator to correct the electric power system operating in a weak damping mode, it is an important preventive control means in the actual operation of the power grid. This application adopts an artificial intelligence method to evaluate the small disturbance stability of the electric power system considering the N-1 operating mode. The vector measurement unit (Phasor Measurement Unit, PMU) can obtain the active and reactive power of the load, the active and reactive power output of the generator and other electrical quantities, providing reliable data support for the remote control of the power system safety and stability. After mining and processing the data, the machine learning algorithm can derive the potential rules and characteristics of the power grid operation and dynamically monitor the operation of the power system. This allows the machine learning algorithm to be used to evaluate the small disturbance stability of the power system, and then use the damping ratio sensitivity index to identify the key factors affecting the small disturbance stability, providing very valuable flow control guidance information for dispatchers, so a method based on sensitivity analysis is used to deal with the small disturbance stability correction problem. This method takes the minimum adjustment amount or power generation cost of the generator output as the objective function, and then calculates the sensitivity relationship between the line power and the generator under the premise of meeting the specified constraints. If the control variable exceeds the limit in the process of adjusting the active output of each generator, the control variable is redistributed according to the constraint conditions of the branch until the limit is eliminated, thereby realizing the small disturbance stability assessment and correction of the power system considering the N-1 operation mode.

[0073] First, a small disturbance stability assessment model for the power system in N-1 operation mode is established. It is necessary to obtain and construct a data set for analyzing the small disturbance stability of the system. By writing programs for power flow and small disturbance stability to generate data sets for artificial intelligence algorithms, this application uses the RF-GBDT algorithm with high prediction accuracy and fast convergence speed to perform nonlinear mapping on the system operating parameters and the minimum damping ratio, and estimate the minimum damping ratio when the system is running. Then, it is determined whether the system is in a weak damping operation state. If it is in a weak damping state, the sensitivity index between the minimum damping ratio of the system and the active output of the generator is reconstructed, and the damping ratio sensitivity index is used to determine the units involved in the regulation and the adjustment amount of the participating units. Active modulation uses the damping ratio sensitivity of each generator as a reference, and the adjustment amount is allocated to each generator according to the weight, or the number of adjustment units is controlled, and a combination of each generator is constructed to determine the upper and lower active power adjustment amounts of the generators, respectively, and the modulation amount is determined by taking the minimum active power change amount.

[0074] On the one hand, the present application can obtain the minimum damping ratio of the system without solving the state equation of the system. On the other hand, it overcomes the problem that the existing control method requires additional selection of other parameters (such as the existing control method may also require additional selection of load power, reactive compensation device and other parameters) for correction and is prone to limited adjustment.

[0075] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0076] In an exemplary embodiment, Figure 1 As shown, a power system small disturbance stability assessment and correction method considering N-1 operation mode is provided, including:

[0077] Obtain real-time operating data of the power system under N-1 operating mode.

[0078] According to the operating data, a power sensitivity calculation model is used to determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system; the power sensitivity calculation model is obtained by using a random forest algorithm and a gradient boosting decision tree algorithm; the damping ratio sensitivity index is the sensitivity of active power to the damping ratio.

[0079] It is determined whether the minimum damping ratio is greater than or equal to a set stability threshold.

[0080] If the minimum damping ratio is greater than or equal to a set stability threshold, it is determined that the power system is small-disturbance stable.

[0081] If the minimum damping ratio is less than a set stability threshold, the active power of the generator in the power system is corrected according to the damping ratio sensitivity index and the constraint condition with the goal of minimizing the total amount of active power changes of the generator, and the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system are re-determined until the minimum damping ratio is greater than or equal to the set stability threshold; the constraint condition is the constraint condition that the line in the power system is not overloaded.

[0082] In an exemplary embodiment, the active power of the line of the power system is obtained according to the load power and the generator power, that is, x=[P Lj ,Q Lj ,P Gi ,Q Gi ],y=[P ij ].

[0083] Among them, P Lj is the active power of the i-th load node, Q Lj is the reactive power of the jth load node, P Gi is the active power of the i-th generator, Q Gi is the reactive power of the i-th generator, P ij is the active power of the line between the i-th generator and the j-th load node.

[0084] In an exemplary embodiment, the damping ratio sensitivity index of the generator is determined using the following formula:

[0085]

[0086] Where i is the generator number, j is the load node number, C i is the damping ratio sensitivity index of the i-th generator, ΔP i j is the active power change of the line between the i-th generator and the j-th load node, ΔP i is the active power change of the i-th generator, ΔP i The size of satisfies the upper and lower limits of the active power of the generator.

[0087] In an exemplary embodiment, the following formula is used to determine the active power change of the line between the i-th generator and the j-th load node:

[0088] ΔP ij =C1ΔP1+C2ΔP2+…+C n ΔP n .

[0089] Where n is the total number of generators in the power system.

[0090] In an exemplary embodiment, the goal of correcting the active power of the generator in the power system according to the damping ratio sensitivity index and the constraint condition is:

[0091]

[0092] Among them, f(x) is the target value, min[·] is the minimum operator, is the positive value of the active power change of the i-th generator, is the negative value of the active power change of the i-th generator, and n is the total number of generators in the power system.

[0093] In an exemplary embodiment, the constraints include: damping ratio constraints, constraints between the total damping ratio change of the power system and the active power change of each generator, equality constraints and inequality constraints; the equality constraints include the flow equations of each node in the power system; the inequality constraints are network physical limitations and operating limitations, including node voltage constraints, unit output constraints, line flow constraints and transmission section constraints.

[0094] In an exemplary embodiment, when a small disturbance causes the system to oscillate at a low frequency, adjusting the active output of the generator can improve the stability of the system. To ensure the stable operation of the power system N-1 operation mode, an appropriate correction control method is used to increase the system operation damping ratio so that the system damping ratio is greater than the set threshold ξ limit , the damping ratio constraint is:

[0095] ξ0+Δξ≥ξ limit .

[0096] Among them, ξ0 is the minimum damping ratio corresponding to the power system under the initial operation mode, Δξ is the total damping ratio change of the power system, limit is the set threshold.

[0097] The constraint between the total damping ratio change of the power system and the active power change of each generator is:

[0098]

[0099] Where i is the generator number, C i is the damping ratio sensitivity index of the i-th generator, ΔP i is the change in active power of the i-th generator, Δξ is the change in the total damping ratio of the power system, and n is the total number of generators in the power system.

[0100] In an exemplary embodiment, the power flow equations of each node in the power system are:

[0101]

[0102] Where i is the generator number, j is the load node number, P Gi is the active power of the i-th generator, Q Gi is the reactive power of the i-th generator, P L j is the active power of the jth load node, QLj is the reactive power of the jth load node, V i is the voltage amplitude of the i-th generator, V j is the voltage amplitude of the jth load node, Y ij is the element amplitude of the admittance matrix between the i-th generator and the j-th load node, δ i j = δ i -δj-α i j, δ i is the phase angle of the voltage of the i-th generator, δ j is the phase angle of the voltage at the jth load node, α ij is the element phase angle of the admittance matrix between the i-th generator and the j-th load node, S Nis the system node set, the system node set S N It is the collection of generators and load nodes in the power system.

[0103] In an exemplary embodiment, the value of the node voltage constraint is related to the voltage level, the type of node, the region, or the normal or emergency condition of the node. The node voltage constraint is:

[0104] V i,min ≤V i ≤V i,max i∈S G .

[0105] Among them, V i,max is the upper limit of the voltage amplitude of the i-th generator; V i,min is the lower limit of the voltage amplitude of the i-th generator, V i is the voltage amplitude of the i-th generator.

[0106] The unit output limit includes active output limit and reactive output limit. The unit output constraint is:

[0107] P Gi,min ≤P Gi ≤P Gi ,max i∈S G .

[0108] P Lj,min ≤P Lj ≤P Lj ,max j∈S L .

[0109] Among them, P Gi is the active power of the i-th generator, P Lj is the active power of the jth load node, P Gi,min is the lower limit of active power of the i-th generator, P Gi,max is the upper limit of active power of the ith generator, P Lj,min is the lower limit of the active power of the jth load node, P Lj,max is the upper limit of the active power of the jth load node, S G is the generator node set, the generator node set S G is the set of generators in the power system, S L is the load node set, load node set S L It is the collection of load nodes in the power system.

[0110] The line power flow constraint is:

[0111] P ij,min ≤P ij ≤P ij,maxi∈S L .

[0112] Among them, P ij,min is the lower limit of the line power between the i-th generator and the j-th load node, P ij,max is the upper limit of the line power between the i-th generator and the j-th load node, P i j is the active power of the line between the i-th generator and the j-th load node.

[0113] In an exemplary embodiment, section management in a power system is one of the key links to ensure stable, safe and efficient operation of the power system. By constraining the section, the problem of small disturbance instability in the power system can be prevented and controlled. The transmission section constraint is:

[0114]

[0115] ΔP l =C1ΔP1+C2ΔP2+…+C m ΔP m .

[0116]

[0117] in, is the active power of the line in the transmission section before the active power correction of the generator, P l is the active power of the line in the transmission section after the active power of the generator is corrected, P lmax is the maximum power flow allowed to pass through the transmission section when the power system is operating normally, m is the total number of lines in the transmission section, S m is the transmission section line set, the transmission section line set S m is the set of lines in the transmission section of the power system, ΔP l is the active power change of the line in the transmission section after the active power of the generator is corrected, l is the line included in the transmission section, C1, C2…C m is the damping ratio sensitivity index of the generator in the transmission section, ΔP1, ΔP2, … ΔP m It is the change of active power of the generator in the transmission section.

[0118] The solution of this embodiment uses an artificial intelligence algorithm to quickly perform small disturbance stability assessment and correction control of the power system considering the N-1 operating mode, breaking through the problem of previous computer programming technology being limited by content capacity and long calculation time.

[0119] The overall workflow of the power system small disturbance stability assessment and correction method considering the N-1 operation mode in the above embodiment includes the following steps:

[0120] Step 1: Obtain the real-time operating data of the system under the N-1 operating mode, mainly the system state variables and control variables, including the amplitude and phase angle of the PQ node voltage, the reactive power and phase angle of the PV node, the active and reactive power of the load node, the voltage and phase angle of the balance node, etc.

[0121] Step 2: After determining the parameters of all nodes, the power flow program is used to calculate the real-time operation data, thereby obtaining the line power flow data (such as the transmission power of each line) of the system under the N-1 operation mode.

[0122] Step 3: Select an appropriate RF-GBDT algorithm model, and use the collected data to form an artificial intelligence model data set for training; use the calculated transmission power data of each line of the system to train the RF-GBDT algorithm model, and obtain the relationship between input and output in the data set as a power sensitivity calculation model. The input is the system state variable and control variable, and the output is the minimum damping ratio of the system. Adjust the parameters of the model to achieve a relatively accurate evaluation of the system damping ratio.

[0123] Step 4: According to the topological structure of the power system, an N-1 fault set is set to cover the impact of the disconnection of branches with larger currents on the changes in the network topology under normal conditions, so as to determine the transmission section of the system and the transmission limit of the transmission section.

[0124] Step 5: In the trained power sensitivity calculation model, the approximate sensitivity of power is estimated by using the numerical perturbation method. Under the determined operation mode, it is determined whether the remaining lines can be overloaded in the "N-1" case (the minimum damping ratio is less than the set stability threshold); if the line is overloaded, the correction control program is started.

[0125] Step six, start the correction control program. The objective function is to adjust the total active power of the generator to the minimum and the power generation cost to the minimum. The constraints include the upper and lower limits of the active power and reactive power of the generator and the upper and lower limits of the node voltage, and the section active power constraint. The active power of the generator is optimized to eliminate line overload and ensure that no new overload occurs.

[0126] Step seven, check the corrected calculation result file and output the calculation result report. The result can ensure that the active power flow of the transmission section of the evaluated power system under the N-1 static safety power flow constraint operates within a safe range and is in a safe and stable operation mode. The power grid operation mode is the safe and stable operation limit of the evaluated power system.

[0127] This application uses the machine learning RF-GBDT algorithm to process the real-time operating data of the current power system, establishes a mapping relationship between input and output, and uses an offline data-driven model to predict and evaluate the small disturbance stability of the power system under the N-1 operating mode, while estimating the approximate damping ratio sensitivity of each generator. If the damping ratio is greater than the set stability threshold, the system is stable with small disturbances; if the damping ratio is less than the set stability threshold, the system is in a weak damping or unstable operating state. The weak damping mode will affect the small disturbance stability of the power system, and the active power of the generator needs to be modulated. The adjustment amount of the active power is determined by the optimization algorithm to increase the damping ratio above the stability threshold. A correction control optimization model is established based on the set stability threshold and sensitivity, and the adjustment strategy after optimization calculation is obtained to adjust the active output of the generator to ensure safe and stable operation of the system.

[0128] Compared with the prior art, this application has the following beneficial effects:

[0129] 1. It can prevent the low-frequency oscillation that may occur in the operation of the evaluated power system, and can perform stable optimization calculations on the power grid of the evaluated power system, so that the power grid of the evaluated power system can obtain the power grid operation mode optimization data required for the static safe and stable operation of the evaluated power system under any operation mode, and can use the power grid operation mode optimization data for automatic calculation and verification. The verification results can be directly used to guide the preparation of the static safe and stable power grid operation mode of the evaluated power system, so as to ensure the safe, stable and reliable operation of the power grid.

[0130] 2. It can make the formulation of the static voltage stable operation mode of the power grid simple and easy, shorten the work process and formulation time, reduce the workload and pressure of operators, and comprehensively improve the voltage quality, safety and stability of the power grid operation.

[0131] Based on the same inventive concept, the embodiment of the present application also provides a system for evaluating and correcting small disturbances in a power system considering an N-1 operating mode for implementing the method for evaluating and correcting small disturbances in a power system considering an N-1 operating mode involved above. The implementation scheme for solving the problem provided by the system is similar to the implementation scheme recorded in the above method, so the specific limitations in one or more embodiments of the system for evaluating and correcting small disturbances in a power system considering an N-1 operating mode provided below can be referred to the limitations of the method for evaluating and correcting small disturbances in a power system considering an N-1 operating mode above, and will not be repeated here.

[0132] In an exemplary embodiment, Figure 2 As shown, a power system small disturbance stability assessment and correction system considering N-1 operation mode is provided, comprising:

[0133] The data acquisition module is used to obtain the operating data of the power system in the N-1 operating mode in real time.

[0134] A damping ratio calculation module is used to determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system according to the operating data and using a power sensitivity calculation model; the power sensitivity calculation model is obtained by using a random forest algorithm and a gradient boosting decision tree algorithm; the damping ratio sensitivity index is the sensitivity of active power to the damping ratio.

[0135] The judging module is used to judge whether the minimum damping ratio is greater than or equal to a set stability threshold.

[0136] The small disturbance stability evaluation module is used to determine whether the power system is stable with small disturbances if the minimum damping ratio is greater than or equal to a set stability threshold.

[0137] A correction control and damping ratio prediction module is used to correct the active power of the generators in the power system according to the damping ratio sensitivity index and constraint conditions with the goal of minimizing the total amount of active power changes of the generators if the minimum damping ratio is less than a set stability threshold, and to re-determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system until the minimum damping ratio is greater than or equal to the set stability threshold; the constraint condition is the constraint condition that the line in the power system does not overload.

[0138] This embodiment obtains operating data such as load power, line power, generator output and minimum damping ratio of a small hydropower system; forms a data set for training an artificial intelligence model based on the collected data; selects an appropriate artificial intelligence model to obtain the relationship between input and output in the data set, adjusts the parameters of the model so that the model evaluation achieves better results, estimates the minimum damping ratio of the system operation, and realizes small disturbance stability evaluation; adopts damping ratio constraints, power balance constraints, and constraints satisfied between the total damping ratio change of the system and the active power change of each generator as constraints, and takes the minimum sum of the adjusted generator active power (square) as the objective function, and optimizes and corrects the generator active power change; and predicts the corrected damping ratio based on the model established in the small disturbance stability evaluation module.

[0139] Taking the IEEE-39 node system as an example, the system structure topology diagram is as follows: Figure 3 As shown. The system is subjected to real-time low-frequency oscillation operation analysis and optimal correction control under the "N-1" condition. The analysis steps are as follows:

[0140] 1. The system has 39 busbars, 10 generators and 46 transmission lines. 1-39 are 39 busbar nodes and G is the generator.

[0141] 2. Obtain the system's generator output, load power output and other operating data.

[0142] 3. Make the system load fluctuate randomly between 70% and 130%, and the active power and reactive power output of the generator fluctuate by 30%, while ensuring the power balance of the system. Use the power flow program to perform power flow calculations, generate a large amount of raw data, and form a data set.

[0143] 4. Use the large amount of raw data generated to train the RF-GBDT algorithm model and adjust the model parameters to achieve better model evaluation results, obtain the relationship between generator output and line power, and accurately estimate the damping ratio sensitivity.

[0144] 5. Under a given operating mode, determine the line power situation after any line is disconnected in the "N-1" situation. If the line is overloaded, start the correction control program.

[0145] 6. Establishment of correction control optimization model (i.e. Figure 4 Small disturbance stability evaluation model and correction model in the process reference Figure 4 As shown, the active power of the controllable generator of the system is perturbed, the damping ratio sensitivity is calculated, and the active power of the generator is optimized.

[0146] 7. Check the corrected calculation result file and output the calculation result report. The result can ensure that the evaluated power system is in a safe and stable operation mode. The grid operation mode is the safe and stable operation limit of the evaluated power system.

[0147] An example is given below to illustrate: in the operation of the IEEE-39 node system, this embodiment has a very obvious effect on the active safety and correction control of the calculated power system.

[0148] This application uses the RF-GBDT algorithm to build a power sensitivity calculation model. According to the "N-1" principle, the expected fault of the transmission line disconnection is designed, and the fluctuation of the system generator and load power is considered to form 10,000 groups of different operating points considering various "N-1" disconnection faults, and then generate 10,000 groups of sample data sets. Use MAPE (Mean Absolute Error) and RMSE (Root Mean Square Error) as the fitting error to represent the accuracy of the prediction results, please refer to Figure 4 , the stability threshold is set to 0.03, using Figure 4 The correction process shown in the figure is used for correction, and the prediction results are shown in Table 1. In general, the error value of the model is still small, the accuracy is high, and it can be used to estimate the damping ratio sensitivity.

[0149] Table 1. Prediction of MAPE and RMSE

[0150] Model MAPE RMSE Maximum error RF-GBDT algorithm 1.56％ <![CDATA[4.59×10 -5 ]]> 5.41％

[0151] The given system initial state does not meet the small disturbance stability check under the N-1 operation mode. The damping ratio sensitivity results of each generator estimated by the RF-GBDT model are shown in Table 2, where the G1 unit is set as the balance unit of the system, does not participate in active power modulation, and has a sensitivity of 0.

[0152] Table 2 Results of damping ratio sensitivity of each generator estimated by RF-GBDT model

[0153]

[0154]

[0155] Then, the generator active power adjustment is obtained according to the estimated sensitivity, and the system optimization correction control is performed. The process and results of the generator active power modulation are shown in Table 3.

[0156] Table 3 Process and results of generator active power modulation

[0157] dynamo Adjustment amount / MW Actual damping ratio RF-GBDT predicts damping ratio G1 0 - - G30 9 - - G32 9 - - G33 13.44 - - G34 13.76 0.0335 0.03235 G35 16 - - G36 18.3 - - G37 9.8 - - G38 14.6 - - G39 2 - -

[0158] The above example illustrates that under the premise of a certain network structure, when the system cannot meet the small disturbance stability under the N-1 operation mode, in order to improve the small disturbance stability of the system, the active output of the generator set can be adjusted. For the system in the weak damping mode under the N-1 operation mode, the correction control method proposed in this application can be used to increase the minimum damping ratio of the system so that the damping ratio reaches above the set stability threshold, ensuring the stable operation of the power system. The obtained correction scheme is brought into the RF-GBDT algorithm, such as Figure 5 As shown, the corrected damping ratio can be estimated more accurately. The scheme can be formulated by using data-driven generation of real-time control strategy according to the specific input data.

[0159] The above describes the implementation of the present application in conjunction with the accompanying drawings, explores the application of generator output adjustment measures in active safety correction control, and makes some meaningful research on active operation risk correction control combining sensitivity method with operation risk assessment. However, due to the complexity of active operation risk control of the power grid, the implementation is not limited by the above implementation cases, and ordinary technicians in this field can make various changes or modifications within the scope of the attached claims.

[0160] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0161] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode, characterized in that: The power system small disturbance stability assessment and correction method considering the N-1 operation mode includes: Real-time acquisition of power system operation data under N-1 operation mode; According to the operation data, a power sensitivity calculation model is used to determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system; the power sensitivity calculation model is obtained by using a random forest algorithm and a gradient boosting decision tree algorithm; the damping ratio sensitivity index is the sensitivity of active power to the damping ratio; Determining whether the minimum damping ratio is greater than or equal to a set stability threshold; If the minimum damping ratio is greater than or equal to a set stability threshold, it is determined that the power system is small-disturbance stable; If the minimum damping ratio is less than a set stability threshold, the active power of the generator in the power system is corrected according to the damping ratio sensitivity index and the constraint condition with the goal of minimizing the total amount of active power changes of the generator, and the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system are re-determined until the minimum damping ratio is greater than or equal to the set stability threshold; the constraint condition is the constraint condition that the line in the power system is not overloaded.

2. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 1, characterized in that: The damping ratio sensitivity index of the generator is determined by the following formula: Where i is the generator number, j is the load node number, C i is the damping ratio sensitivity index of the i-th generator, ΔP ij is the active power change of the line between the i-th generator and the j-th load node, ΔP i is the active power change of the i-th generator, ΔP i The size of satisfies the upper and lower limits of the active power of the generator.

3. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 2, characterized in that: The following formula is used to determine the active power change of the line between the i-th generator and the j-th load node: ΔP ij =C1ΔP1+C2ΔP2+…+C n ΔP n ; Where n is the total number of generators in the power system.

4. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 1, characterized in that: The goal of correcting the active power of the generator in the power system according to the damping ratio sensitivity index and the constraint condition is: Among them, f(x) is the target value, min[·] is the minimum operator, is the positive value of the active power change of the i-th generator, is the negative value of the active power change of the i-th generator, and n is the total number of generators in the power system.

5. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 1, characterized in that: The constraint conditions include: damping ratio constraint, constraint between the total damping ratio change of the power system and the active power change of each generator, equality constraint condition and inequality constraint condition; The equality constraints include power flow equations for each node in the power system; The inequality constraints include node voltage constraints, unit output constraints, line flow constraints and transmission section constraints.

6. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 5, characterized in that: The damping ratio constraint is: ξ0+Δξ≥ξ limit ; Among them, ξ0 is the minimum damping ratio corresponding to the power system under the initial operation mode, Δξ is the total damping ratio change of the power system, limit is the set threshold; The constraint between the total damping ratio change of the power system and the active power change of each generator is: Where i is the generator number, C i is the damping ratio sensitivity index of the i-th generator, ΔP i is the change in active power of the i-th generator, Δξ is the change in the total damping ratio of the power system, and n is the total number of generators in the power system.

7. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 5, characterized in that: The power flow equations of each node in the power system are: Where i is the generator number, j is the load node number, P Gi is the active power of the i-th generator, Q Gi is the reactive power of the i-th generator, P Lj is the active power of the jth load node, Q Lj is the reactive power of the jth load node, V i is the voltage amplitude of the ith generator, V j is the voltage amplitude of the jth load node, Y ij is the element amplitude of the admittance matrix between the i-th generator and the j-th load node, δ ij =δ i -δ j -α ij , δ i is the phase angle of the voltage of the i-th generator, δ j is the phase angle of the voltage at the jth load node, α ij is the element phase angle of the admittance matrix between the i-th generator and the j-th load node, S N is the system node set, the system node set S N It is the collection of generators and load nodes in the power system.

8. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 5, characterized in that: The node voltage constraint is: In i,min ≤V i ≤V i,max i∈S G ; Among them, V i,max is the upper limit of the voltage amplitude of the i-th generator; V i,min is the lower limit of the voltage amplitude of the i-th generator, V i is the voltage amplitude of the i-th generator; The unit output constraint is: P Gi,min ≤P Gi ≤P Gi,max i∈S G ; P Lj,min ≤P Lj ≤P Lj,max j∈S L ; Among them, P Gi is the active power of the i-th generator, P Lj is the active power of the jth load node, P Gi,min is the lower limit of active power of the i-th generator, P Gi,max is the upper limit of active power of the ith generator, P Lj,min is the lower limit of the active power of the jth load node, P Lj,max is the upper limit of the active power of the jth load node, S G is the generator node set, the generator node set S G is the set of generators in the power system, S L is the load node set, the load node set S L is the set of load nodes in the power system; The line power flow constraint is: P ij,min ≤P ij ≤P ij,max i∈S L ; Among them, P ij,min is the lower limit of the line power between the i-th generator and the j-th load node, P ij,max is the upper limit of the line power between the i-th generator and the j-th load node, P ij is the active power of the line between the i-th generator and the j-th load node.

9. The method for evaluating and correcting small disturbance stability of a power system considering N-1 operation mode according to claim 5, characterized in that: The transmission section constraint is: ΔP l =C1ΔP1+C2ΔP2+…+C m ΔP m ; P l =P l 0 +ΔP l ; Among them, P l 0 is the active power of the line in the transmission section before the active power correction of the generator, P l is the active power of the line in the transmission section after the active power of the generator is corrected, P lmax is the maximum power flow allowed to pass through the transmission section when the power system is operating normally, m is the total number of lines in the transmission section, S m is the transmission section line set, the transmission section line set S m is the set of lines in the transmission section of the power system, ΔP l is the active power change of the line in the transmission section after the active power of the generator is corrected, l is the line included in the transmission section, C1, C2...C m is the damping ratio sensitivity index of the generator in the transmission section, ΔP1, ΔP2, … ΔP m It is the change of active power of the generator in the transmission section.

10. A power system small disturbance stability assessment and correction system considering N-1 operation mode, characterized in that: The power system small disturbance stability assessment and correction system considering the N-1 operation mode includes: Data acquisition module, used to obtain real-time operation data of the power system under N-1 operation mode; A damping ratio calculation module, used to determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system according to the operating data and using a power sensitivity calculation model; the power sensitivity calculation model is obtained by using a random forest algorithm and a gradient boosting decision tree algorithm; the damping ratio sensitivity index is the sensitivity of active power to the damping ratio; A judging module, used to judge whether the minimum damping ratio is greater than or equal to a set stability threshold; A small disturbance stability evaluation module, configured to determine that the power system is stable with small disturbances if the minimum damping ratio is greater than or equal to a set stability threshold; A correction control and damping ratio prediction module is used to correct the active power of the generators in the power system according to the damping ratio sensitivity index and constraint conditions with the goal of minimizing the total amount of active power changes of the generators if the minimum damping ratio is less than a set stability threshold, and to re-determine the minimum damping ratio of the power system and the damping ratio sensitivity index of each generator in the power system until the minimum damping ratio is greater than or equal to the set stability threshold; the constraint condition is the constraint condition that the line in the power system does not overload.

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