A method for evaluating the minimum inertia requirement of power systems

Abstract

The present application proposes a method for evaluating the minimum inertia demand of an electric power system. First, the regional system load level and the detailed parameters of each installed unit are obtained. Next, the search difference with the initial expected kinetic energy satisfies the first preset condition as the objective function, and a feasible inertia operating point optimization search model for the electric power system is constructed. Then, based on the model, a feasible inertia operating point that meets the objective function and constraint conditions is searched, and a multi-machine frequency response model is constructed. Through this model, the dynamic change process of the frequency under the expected disturbance is simulated and calculated to obtain the calculation result of the dynamic process of the disturbed frequency. If the result meets the frequency requirements, the evaluation result of the minimum inertia demand of the electric power system is determined based on this; if not, the initial expected kinetic energy is adaptively corrected to obtain the first expected kinetic energy, which is substituted into the steps and repeated iterative calculations are performed. This method accurately evaluates the minimum inertia demand of the electric power system through continuous optimization and adjustment to ensure stable operation of the system.

Description

Technical Field

[0001] The present application relates to the field of power system operation technology, and in particular to the field of power system operation control technology. Background Art

[0002] The traditional power system dominated by synchronous generating sets is gradually transforming into a new power system with a high proportion of converters. Under this transformation, wind and solar power sources and inter-regional DC transmission will be developed with emphasis, and their access number and installed capacity will continue to grow substantially in the future, further squeezing the output space of synchronous power sources, resulting in a significant decrease in the inertia constant of the power system, weakening the frequency support capacity of the power system, and seriously reducing the frequency stability of the power system under large disturbances, bringing unprecedented challenges to the safe and stable operation of low-inertia power systems.

[0003] At present, the evaluation of the minimum inertia requirement of power systems is mainly based on the construction of frequency time domain analytical expressions and simulation iteration methods based on equivalent SFR models. Such methods generally have problems such as considering the inertia constant as an independent variable and considering the frequency regulation capability unchanged when evaluating the minimum inertia requirement. It is difficult to intuitively reflect the actual operation mode of the system, the safety critical value of inertial resources, and the frequency stability boundary. Therefore, how to accurately calculate the frequency dynamic response of the power system under different operation modes and different expected faults, accurately find the minimum inertia requirement and its unit combination method that meet the safety operation constraints, realize the online evaluation of the frequency stability of the power system under large disturbances, and specify the emergency control strategy based on the minimum inertia requirement is still an important challenge facing the new power system. Summary of the invention

[0004] The present application provides a method for evaluating the minimum inertia requirement of an electric power system, which solves the problem that the minimum inertia requirement evaluation of an electric power system in the prior art cannot accurately calculate the frequency dynamic response of the electric power system under different operating modes and different expected faults.

[0005] To achieve the above objectives, the present application provides a method for evaluating the minimum inertia requirement of a power system, comprising the following steps:

[0006] S1: Obtain the regional system load level and detailed parameters of each installed unit;

[0007] S2: Based on the regional system load level and detailed parameters of each installed generating unit, a power system feasible inertia operation point optimization search model is constructed with the difference between the search and the initial expected kinetic energy satisfying the first preset condition as the objective function;

[0008] S3: Based on the power system feasible inertia operation point optimization search model, search for a feasible inertia operation point that meets the objective function and constraint conditions; and construct a multi-machine frequency response model corresponding to the feasible inertia operation point;

[0009] S4: Based on the multi-machine frequency response model, a simulation calculation is performed on the frequency dynamic change process under the expected disturbance to obtain a calculation result of the disturbed frequency dynamic process;

[0010] S5: Based on the calculation result of the disturbed frequency dynamic process, judging whether the disturbed frequency dynamic process meets the frequency requirement;

[0011] If yes, go to step S6;

[0012] If not, the initial expected kinetic energy is adaptively corrected by simulating the feasible inertia running points according to the ascending order of kinetic energy to obtain the first expected kinetic energy, and the first expected kinetic energy is substituted into step S2 as the initial expected kinetic energy for the next round of calculation, and steps S2 to S5 are repeated for iterative calculation;

[0013] S6: Determine an evaluation result of the minimum inertia requirement of the power system based on the calculation result of the disturbed frequency dynamic process.

[0014] Optionally, the steps S1 and S2 include:

[0015] The feasible inertia operating point is defined as all operating points in the power system that satisfy the power flow equation and the operation safety constraints, representing an operation mode of the power system, which is determined by the system inertia constant , Unit combination Composition, including the combination of units The unit operation state vector , Unit active power output vector , Unit active power reserve vector Composition, that is ; Wherein, the system inertia constant calculation formula is:

[0016] ,

[0017] In the formula, For the The rotational kinetic energy of a generator set, in ; For the The rated capacity of the generator set is ; For the The startup status of the generator sets, Indicates startup. Power off.

[0018] Optionally, the method of constructing an optimization search model for a feasible inertia operation point of a power system with the difference between the searched and expected kinetic energy satisfying a first threshold as an objective function comprises:

[0019] The startup status, active output power and active reserve capacity of each unit are taken as optimization variables, and the square of the difference between the rotation function of the unit combination mode and the expected value of the equivalent kinetic energy satisfies the first preset condition as the objective function:

[0020] ,

[0021] In the formula, The rotational kinetic energy of the unit combination ， is the total number of generators within the regional system; For the The rotational kinetic energy of a generator set, in ; For the The startup status of the generator sets, Indicates boot ， Power off.

[0022] Optionally, the constructing of a power system feasible inertia operating point optimization search model with the difference between the searched and expected kinetic energy satisfying a first threshold as an objective function further includes:

[0023] From the system level, the optimization search model for the feasible inertia operation point of the power system is set with constraints including active power balance constraint, active power reserve constraint, and net load reserve constraint, and their expressions are as follows:

[0024] , , ,

[0025] in, is the number of synchronous units within the regional system; For the The steady-state active output of each synchronous unit; is the number of new energy stations within the regional system; For the The steady-state active power output of each new energy station; The number of DC transmission lines with a single-side access point located within the regional system; For the The steady-state active power of the DC transmission line is Indicates that the access point is the power receiving side. Indicates that the access point is the power transmission side; is the number of AC transmission lines with single-side access points located inside the regional system, i.e., the number of external network equivalent machines; For the The steady-state active power of the AC tie line, Indicates that the access point is the power receiving side. Indicates that the access point is the power transmission side; is the load level of the system in the area; is the regional system network loss rate; is the expected disturbance power; For the The spare capacity of each generator set; For the Reserve capacity for power modulation of DC lines; For the Spare capacity of check-in machines in Taiwan's overseas network; is the load reserve ratio of the regional system, which represents the equivalent scale of load power fluctuation and expected deviation; For the The output limit of each generator set; For the The active power output of each generator set; It is the unplanned load variation;

[0026] Among them, the constraints set for the units participating in frequency regulation in the synchronous units within the regional system are:

[0027] , ,

[0028] ,

[0029] In the formula, For the The startup status of the synchronous units participating in frequency regulation, Indicates startup. Shut down the device; For the The lower output limit of the generator sets participating in frequency regulation; For the The active power output of the synchronous units participating in frequency regulation; For the The output limit of synchronous units participating in frequency regulation; For all synchronous units participating in frequency regulation; For the The upper limit of the spinning reserve capacity of synchronous units participating in frequency regulation.

[0030] Optionally, the optimizing search model based on the feasible inertia operating point of the power system, searching for a feasible inertia operating point that satisfies an objective function and constraint conditions; and constructing a multi-machine frequency response model corresponding to the feasible inertia operating point, comprises:

[0031] Based on the power system feasible inertia operating point optimization search model, searching for a feasible inertia operating point that meets the objective function and constraint conditions;

[0032] Based on the feasible inertia operating point, determining detailed parameters of the regional system and frequency dynamic response parameters of each frequency modulation;

[0033] Based on the detailed parameters of the regional system and the frequency dynamic response parameters of each frequency modulation, a multi-machine frequency response model corresponding to the feasible inertia operation point is constructed; wherein the multi-machine frequency response model includes the power-on status and frequency response characteristics of all frequency modulation resources in the feasible inertia operation point.

[0034] Optionally, based on the multi-machine frequency response model, a simulation calculation is performed on the frequency dynamic change process under the expected disturbance to obtain a calculation result of the disturbed frequency dynamic process, specifically:

[0035] The detailed parameters of the regional system and the frequency dynamic response parameters of each frequency modulation are input into the multi-machine frequency dynamic response model, and the frequency dynamic change process under the expected disturbance is simulated and calculated to obtain the calculation result of the disturbed frequency dynamic process.

[0036] Optionally, if not, after adaptively correcting the expected kinetic energy by simulating feasible inertia running points in ascending order of kinetic energy, steps S2 to S5 are repeated for iterative calculation;

[0037] The process of adaptively correcting the expected kinetic energy is as follows:

[0038] Arrange the powered-on units in the current unit combination mode and unpowered units ;

[0039] Determine if the unit is not turned on Is the empty set, if so, the iteration operation ends, executing step S6;

[0040] If not, determine the difference matrix of rotational kinetic energy between the started units and the unstarted units;

[0041] Based on the elements in the difference matrix that are greater than the correction threshold, a judgment set is formed;

[0042] Based on the elements in the difference matrix and the correction threshold, determining whether the determination set is an empty set;

[0043] If so, determine the correction amount to be the generator set with the smallest non-zero rotational kinetic energy among the non-started generator sets;

[0044] Based on the minimum rotational kinetic energy of the current number of startups, determine the expected value of the rotational kinetic energy of the next iteration process;

[0045] The expected value of the rotational kinetic energy is used as the first expected kinetic energy, and steps S2 to S5 are executed;

[0046] If not, select the minimum value in the judgment set as the correction amount;

[0047] Based on the rotational kinetic energy level of the current unit combination mode, the expected value of the rotational kinetic energy of the next iteration process is corrected;

[0048] The expected value of the rotational kinetic energy is used as the first expected kinetic energy, and steps S2 to S5 are executed.

[0049] Optionally, the correction threshold may be corrected in two ways, specifically:

[0050] Method 1: The correction threshold is set to 0 to achieve accurate correction;

[0051] Mode 2: The correction threshold is set as a piecewise function of the frequency index to achieve rough correction.

[0052] Optionally, the evaluation result of the minimum inertia requirement of the power system includes:

[0053] The evaluation result of the minimum inertia requirement of the power system includes: the minimum inertia requirement and the corresponding unit combination mode, the system inertia kinetic energy ratio, and the system inertia kinetic energy critical ratio of the preset fault;

[0054] Wherein, the calculation formula of the system inertia kinetic energy ratio is: ,

[0055] In the formula, is the system inertia kinetic energy ratio, is the expected disturbance power, is the frequency extreme time; is the equivalent kinetic energy of the system.

[0056] This application has the following beneficial effects:

[0057] The present invention comprehensively considers the coupling relationship between the system inertia constant and the unit combination mode, constructs a feasible operating point optimization search model and a multi-machine frequency response model, proposes a minimum inertia demand evaluation method based on the feasible operating point, and proposes a forward correction algorithm for simulating the unit combination mode in ascending order of kinetic energy for the evaluation method, and realizes adaptive correction in iterative calculation. The method effectively solves the defect that the existing method assumes that the inertia constant and the frequency regulation capability are independent variables, and does not consider the coupling change of the frequency regulation capability with the inertia constant when calculating and obtaining the minimum inertia demand of the power system. The system minimum inertia demand can be evaluated without relying on a simplified synchronous generator primary frequency regulation structure and a complex algorithm that takes too long to calculate, effectively improving the accuracy of the minimum inertia demand evaluation, providing a basis for the refined optimization and regulation of the inertia and frequency regulation capability of the low-inertia power system, avoiding as much as possible the system instability caused by large-capacity active impacts such as DC locking and new energy grid disconnection due to insufficient system inertia level and frequency regulation capability, and providing an effective evaluation tool for the safe and stable operation and reasonable planning and design of the low-inertia power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In addition to the above-described purposes, features and advantages, the present application also has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings.

[0059] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0060] Figure 1 It is a flowchart of a method for evaluating the minimum inertia requirement of a power system according to an embodiment of the present application.

[0061] Figure 2 This is a structural diagram of a multi-machine frequency response model according to an optional embodiment of the present application.

[0062] Figure 3 Schematic diagram of a minimum inertia requirement evaluation framework based on feasible inertia operating points proposed in an optional embodiment of the present application.

[0063] Figure 4 It is a flow chart of an adaptive correction algorithm of an optional embodiment of the present application.

[0064] Figure 5 It is a schematic diagram of an improved IEEE-39 node calculation example system of an optional embodiment of the present application.

[0065] Figure 6 It is a frequency dynamic curve diagram corresponding to the minimum inertia requirement and the operating inertia constant of an optional embodiment of the present application.

[0066] Figure 7 This is a diagram of the system inertia-kinetic energy ratio evaluation results of an optional embodiment of the present application. DETAILED DESCRIPTION

[0067] The embodiments of the present application are described in detail below with reference to the accompanying drawings; however, the present application can be implemented in many different ways as defined and covered by the claims.

[0068] In response to the "dual carbon" goal, the traditional power system is transformed into a new power system. The development of non-synchronous power sources such as wind and solar power generation has continuously reduced the system inertia. The current system minimum inertia requirement assessment method has shortcomings, and it is necessary to find an assessment method that can accurately assess the system minimum inertia requirement to ensure the safe and stable operation of the system frequency under large disturbances.

[0069] Therefore, in order to solve the above problems, an evaluation method for the minimum inertia requirement of a power system is provided in an embodiment of the present application, such as Figure 1 As shown, the following steps are included:

[0070] S1: Obtain the regional system load level and detailed parameters of each installed unit;

[0071] The regional system load level refers to the total load power of power users in a specific area at the same time. It includes the power load of various types of users such as industry, commerce, and residents, and also covers some special loads such as data centers and specific production equipment in large factories. The detailed parameters of the installed units vary depending on the installed units, and are determined according to the specific conditions of the installed units on site, so they will not be elaborated here.

[0072] The regional system load level and the parameters of each installed unit are crucial in calculating the minimum inertia requirement of the power system. The load level affects the active output and spare capacity of each installed unit in the system due to the active power balance. As a frequency regulation resource, the detailed parameters of each installed unit are mainly the detailed parameters of each link of the frequency response, which directly affects the primary frequency regulation dynamic characteristics of each unit and indirectly affects the system frequency support capacity and the dynamic change process of the disturbed frequency. Therefore, comprehensive consideration of the regional system load level and the parameters of each installed unit helps to accurately evaluate the minimum inertia requirement of the system to ensure the stable operation of the power system.

[0073] It should be noted that the minimum inertia requirement in this application is a key indicator for maintaining the frequency stability of the power system. It refers to the minimum rotational inertia required for the system to ensure that the system frequency does not exceed the allowable range when facing various possible disturbances (such as generator tripping, sudden load changes, etc.).

[0074] In the power system, the feasible inertia operating point refers to the operating state point where the system can operate stably under various operating constraints (such as power balance, voltage limit, unit output range, network security, etc.). These state points are determined by the combination of operating parameters of various components in the system (including generators, loads, transmission lines, etc.). In this application, the feasible inertia operating point is defined as is all the operating points in the power system that satisfy the power flow equation and operation safety constraints, representing an operation mode of the power system, which is determined by the system inertia constant , Unit combination Composition, including the combination of units The unit operation state vector (1 means the unit is in the on state; 0 means the unit is in the off state), the unit active power output vector , Unit active power reserve vector Composition, that is ; Wherein, the system inertia constant calculation formula is:

[0075] System inertia constant The calculation formula is: (1), where For the The rotational kinetic energy of a generator set, in ; For the The rated capacity of the generator set is ; For the The startup status of the generator sets, Indicates startup. Power off.

[0076] S2: Based on the regional system load level and detailed parameters of each installed generating unit, a power system feasible inertia operation point optimization search model is constructed with the difference between the search and the initial expected kinetic energy satisfying the first preset condition as the objective function;

[0077] After obtaining the regional system load level and the parameters of each installed unit, the startup status, active output power, and active reserve capacity of each unit are used as optimization variables, and the square of the difference between the rotation function of the unit combination mode and the expected value of the equivalent kinetic energy that satisfies the first preset condition is used as the objective function:

[0078] (2)

[0079] In the formula, is the expected equivalent kinetic energy value, is the total number of generators within the regional system; For the The rotational kinetic energy of a generator set, in ; For the The startup status of the generator sets, Indicates startup. Shut down. For renewable energy power plants, the corresponding rotational kinetic energy should be zero or the virtual rotational kinetic energy provided by the virtual inertia. It should be noted that in the first iteration, the expected kinetic energy is selected as the lower boundary of the equivalent kinetic energy of the power system. Starting from the second iteration, the expected kinetic energy is selected as the correction result of the correction algorithm. The correction process will be explained later and will be omitted here.

[0080] The first preset condition here can be set as the square of the difference between the rotational kinetic energy of the unit combination and the expected value of the equivalent kinetic energy is minimized. Specifically, during the operation of the power system, the rotational kinetic energy of the unit combination represents the equivalent rotational kinetic energy provided by each rotating device and virtual inertia in the system under the current actual operating state.

[0081] When the square of the difference between the rotational kinetic energy of the unit combination and the expected value of the equivalent kinetic energy is minimized, it means that the gap between the actual operating state and the ideal state has been minimized to some extent, which provides a clear goal and direction for the optimal scheduling and control of the system, allowing the dispatching personnel to reasonably arrange the unit combination according to this condition and adjust the operating parameters of each equipment to achieve the optimal operating state of the system.

[0082] From the system level, the present application sets constraints including active power balance constraint, active power reserve constraint and net load reserve constraint for the feasible operation power optimization search model of the power system, and the expressions thereof are as follows:

[0083] (3) (4)

[0084] (5), where is the number of synchronous units within the regional system; For the The steady-state active output of each synchronous unit; is the number of new energy stations within the regional system; For the The steady-state active power output of each new energy station; The number of DC transmission lines with a single-side access point located within the regional system; For the The steady-state active power of the DC transmission line is Indicates that the access point is the power receiving side. Indicates that the access point is the power transmission side; is the number of AC transmission lines with single-side access points located inside the regional system, i.e., the number of external network equivalent machines; For the The steady-state active power of the AC tie line, Indicates that the access point is the power receiving side. Indicates that the access point is the power transmission side; is the load level of the system in the area; is the regional system network loss rate; is the expected disturbance power; For the The spare capacity of each generator set; For the Reserve capacity for power modulation of DC lines; For the The reserve capacity of the equivalent value machine in the Taiwan external network. Since it is believed that new energy does not participate in frequency response, the active power reserve capacity of new energy is not considered; is the load reserve ratio of the regional system, which represents the equivalent scale of load power fluctuation and expected deviation; For the The output limit of each generator set; For the The active power output of each generator set; It is the unplanned load variation.

[0085] The output constraints of the generator sets are set at the unit level. In order to rationally utilize power resources and reduce power generation and operating costs, each synchronous unit is divided into two categories according to its frequency regulation characteristics: participating in frequency regulation and not participating in frequency regulation, which are represented as and Taking nuclear power plants as an example, the decommissioning and recommissioning of reactors and steam turbine units are time-consuming and increase energy consumption, and are not suitable for participating in frequency support after disturbances. Therefore, nuclear power plants have the characteristic of full power generation when they are dispatched and operated. Photovoltaic and other new energy generating units do not arrange primary frequency regulation reserve capacity, which is expressed as For synchronous units participating in frequency regulation , its output must meet the upper and lower limit constraints at the same time. The active power reserve capacity of the unit has a maximum limit. When the unit participates in frequency response, its output should not exceed the maximum technical output. Therefore, the constraint condition is:

[0086] (6)

[0087] in, For the The startup status of the synchronous units participating in frequency regulation, Indicates startup. Shut down the device; For the The lower output limit of the generator sets participating in frequency regulation; For the The active power output of the synchronous units participating in frequency regulation; For the The output limit of synchronous units participating in frequency regulation; For all synchronous units participating in frequency regulation; For the The upper limit of the spinning reserve capacity of synchronous units participating in frequency regulation.

[0088] S3: Based on the power system feasible inertia operation point optimization search model, search for a feasible inertia operation point that meets the objective function and constraint conditions; and construct a multi-machine frequency response model corresponding to the feasible inertia operation point;

[0089] For synchronous units not participating in frequency regulation and new energy units , its output is uniformly set by the dispatcher, and no active power reserve capacity is reserved:

[0090] (7)

[0091] in, For the The output setting value of each generator set.

[0092] After determining the optimization search model of the feasible inertia operation point of the power system, a feasible inertia operation point that satisfies the objective function and constraint conditions is searched. That is to say, when the optimization search model of the feasible inertia operation point of the power system is constructed, according to the objective function constructed by formula (2), under the conditional constraints of formulas (3)-(6), a feasible inertia operation point is determined, and then according to the feasible inertia operation point, according to the regional system installed unit information table provided in Table 1, the unit name, power type, installed capacity, rotation kinetic energy, upper and lower limits of active output, and frequency response mode information of each installed unit in the regional system are obtained, wherein the frequency response mode includes, and then according to the detailed parameters of the regional system and the frequency dynamic response parameters of each frequency regulation resource, a multi-machine frequency response model for the searched feasible inertia operation point is constructed. The constructed model ignores the grid structure and spatiotemporal distribution characteristics of the power system, and includes the startup status and frequency response characteristics of all frequency regulation resources in the feasible inertia operation point. It should be noted that the multi-machine frequency response model here can be understood as a simulation model.

[0093] ,

[0094] It should be noted that in actual application, the corresponding data in Table 1 will be different depending on the actual installed capacity of power grids in different regions.

[0095] S4: Based on the multi-machine frequency response model, a simulation calculation is performed on the frequency dynamic change process under the expected disturbance to obtain a calculation result of the disturbed frequency dynamic process;

[0096] Frequency stability is crucial in the operation of power systems. When the system is disturbed, the frequency will change, and its dynamic process reflects many factors such as the system's inertia, frequency regulation capability, and load characteristics. The goal of calculating the dynamic process of the disturbed frequency is to establish a mathematical model to simulate the change of the system's frequency over time under various disturbances, providing a basis for evaluating the stability of the system and formulating control strategies.

[0097] In this application, based on the constructed multi-machine frequency response model, the frequency dynamics of the expected limit fault is simulated and calculated. The simulation calculation process is as follows: Figure 2 As shown, the formula used in the simulation process is the rotor motion equation, as shown below:

[0098] (8)

[0099] In the formula, is the system operating inertia level; For time; is the frequency deviation; is the sum of the power frequency modulation power; is the sum of the modulated power of the DC transmission line; is the system damping coefficient; is the expected disturbance power; It is the frequency modulation function of the DC line, that is, the frequency response mode of the DC line.

[0100] The calculation result of the disturbed frequency dynamic process is generally a frequency change curve, among which the main frequency indicators of concern are the maximum frequency change rate, the maximum frequency deviation, and the extreme value time.

[0101] This application sets the constraint conditions of the optimization model based on the various safe operation constraints of the power system, and obtains the feasible inertia operation point that meets the safe operation constraints and the objective function. The multi-machine frequency response model includes a detailed frequency response model of each frequency regulation resource, which effectively solves the current assumption that the inertia constant and the frequency regulation capacity are independent variables, and when calculating the minimum inertia demand of the power system, the defect of not considering the coupling change of the frequency regulation capacity with the inertia constant is not considered. It provides a basis for accurately simulating and calculating the dynamic process of the disturbed frequency, effectively improves the calculation credibility of the minimum inertia demand evaluation method of the power system, makes the minimum inertia demand evaluation more in line with the actual operation situation, and avoids the introduction of evaluation errors due to model assumptions and simplified processing.

[0102] S5: Based on the calculation result of the disturbed frequency dynamic process, judging whether the disturbed frequency dynamic process meets the frequency requirement;

[0103] If yes, go to step S6;

[0104] If not, the initial expected kinetic energy is adaptively corrected according to the ascending order of kinetic energy to obtain the first expected kinetic energy, which is substituted into step S2, and steps S2 to S5 are repeated for iterative calculation, wherein the ascending order of kinetic energy is obtained by the combination mode of the simulated unit;

[0105] After obtaining the calculation results of the dynamic process of the disturbed frequency, extract the key frequency indicators, including the maximum frequency deviation and the maximum frequency change rate, to determine whether the maximum frequency deviation indicator is between the upper and lower limits of the system's maximum frequency deviation constraint limit, and whether the maximum frequency change rate indicator is between the upper and lower limits of the system's maximum frequency change rate limit, that is, to determine whether the key frequency indicators simultaneously meet the requirements of the system's frequency stability constraints, wherein the upper and lower limits of the maximum frequency deviation constraint limit are respectively taken as the first round of action values ​​of the high-frequency machine cutting and low-frequency load reduction safety automatic devices, and the upper and lower limits of the maximum frequency change rate limit are specifically taken according to the trigger value of the frequency change rate protection device configured in the actual power grid. If so, it means that the inertia constant that currently makes the key frequency indicators of the disturbed frequency meet the frequency stability constraint requirements is the so-called minimum inertia requirement, and the calculation of step S6 can be directly performed. If not, it means that the current inertia constant does not meet the definition of the minimum inertia requirement. For the specific correction process, see Figure 3 , by simulating the feasible inertia running points in ascending order of kinetic energy, the first expected kinetic energy is obtained, which is substituted into step S2 as the initial expected kinetic energy for the next round of calculation, and steps S2 to S5 are repeated for iterative calculation.

[0106] It should be noted that the first expected kinetic energy here is the corrected expected kinetic energy obtained after correcting the initial kinetic energy expectation each time. In other words, the value of the first expected kinetic energy changes each time according to different calculation processes.

[0107] In a simple power system, different unit combinations correspond to different inertia constants, and the feasible inertia operating point is used to characterize the coupling relationship between the unit combination and the inertia constant. After sorting, the kinetic energy values ​​corresponding to these operating points can reflect the change law of the system inertia, that is, the change from low inertia (low kinetic energy) operating state to high inertia (high kinetic energy) operating state. According to the unit combination mode, the correction algorithm is designed in ascending order of kinetic energy, which can accurately obtain the correction amount suitable for the current feasible inertia operating point, solve the evaluation error caused by excessive correction, and realize adaptive correction.

[0108] like Figure 4 As shown, the correction process of the initial kinetic energy expectation adaptive adjustment in this application is described in more detail:

[0109] For the feasible inertia operating points that need to be corrected, sort out the started units in the current unit combination mode and unpowered units , determine that the unit is not turned on Is it an empty set? If it is an empty set, it means that all installed units in the system have been turned on, and the equivalent inertia constant has reached the upper boundary of the inertia range, so the iterative calculation ends with no result; if it is a non-empty set, the difference matrix of the rotational kinetic energy between the turned-on units and the unturned units is determined. , the calculation expressions of each element are: (9), where For the The unused unit and the The difference in rotational kinetic energy between the units that have been started is the matrix The components of ; For the The rotational kinetic energy of the started units, ; For the The rotational kinetic energy of the unused units, ;

[0110] Extract the elements in the difference matrix that are greater than the correction threshold to form a judgment set , the expression is: (10), where is the correction threshold; from the expression, it can be seen that the judgment set is based on the elements in the difference matrix and the correction threshold. to judge Is it an empty set? If is a non-empty set, indicating that the rotational kinetic energy needs to be increased by replacing the unit. Too large a correction will skip several feasible solutions for the rotational kinetic energy. To ensure the accuracy of the correction, the minimum value in the judgment set is selected as the correction. , and based on the rotational kinetic energy level of the current unit combination , correct the expected value of the rotational kinetic energy in the next iteration process ; Take the expected value of the rotational kinetic energy as the first expected kinetic energy and execute steps S2~S5.

[0111] like If it is an empty set, it means that the current unit combination mode is the maximum startup mode with the startup number n. , the number of starts needs to be increased to continue to increase the rotational kinetic energy, and the correction amount should be the minimum start-up mode with the start-up number n The generator set with the smallest and non-zero rotational kinetic energy among the non-starting sets, and based on the number of started sets n The minimum rotational kinetic energy , correct the expected value of the rotational kinetic energy in the next iteration process ; Correction Then, taking the expected value of the rotational kinetic energy as the first expected kinetic energy, performing iterative calculations of steps S2 to S5 to search for a feasible inertia operating point that is closer to the desired result;

[0112] The implementation path 1 of the correction method is: Correction threshold λ Set to 0 to achieve accurate correction; the implementation path 2 of the correction method is: Correction threshold Set it as a piecewise function about the frequency index to achieve a rough correction, and its expression is:

[0113] (11), where Generally, they are two larger values, which need to be set manually and satisfy the relationship .

[0114] S6: Determine an evaluation result of the minimum inertia requirement of the power system based on the calculation result of the disturbed frequency dynamic process.

[0115] The evaluation result of the minimum inertia requirement of the power system includes: the minimum inertia requirement and the corresponding unit combination mode, the system inertia kinetic energy ratio, and the system inertia kinetic energy critical ratio of the preset fault;

[0116] Output the minimum inertia requirement and the corresponding unit combination method, use the calculated inertia-kinetic energy critical ratio as the safety threshold, judge whether the inertia-kinetic energy ratio of the actual operation mode of the regional system can meet the frequency stability requirements, and use it as a reference indicator to guide frequency regulation resource scheduling and planning.

[0117] Calculate the system inertia-kinetic energy ratio , which represents the ratio between the inertial kinetic energy consumed by the regional system in response to active disturbances and the system equivalent kinetic energy. The smaller the value of this indicator, the stronger the frequency support capability of the regional system. Its expression is:

[0118] (12) , where is the expected disturbance power, is the extreme time; is the equivalent kinetic energy of the system; it should be noted that the extreme time It is obtained by simulation calculation, the equivalent kinetic energy of the system It is obtained by optimizing the search model for feasible inertia operating points. The disturbance power is set and is the same value as the disturbance set in the previous minimum inertia requirement evaluation process.

[0119] Calculate the minimum inertia requirement based on the above steps and calculate the critical ratio of the system inertia kinetic energy of the system in this area for the set expected fault , whose expression is: (13) , where It is the extreme time corresponding to the minimum inertia requirement; It is the system equivalent kinetic energy corresponding to the minimum inertia requirement. The adequacy of the frequency support capability is evaluated by comparing the system inertia-kinetic energy ratio and the system inertia-kinetic energy critical ratio; the adequacy of the frequency support capability is evaluated by comparing the system inertia-kinetic energy ratio and the system inertia-kinetic energy critical ratio; if the system inertia-kinetic energy ratio is less than the system inertia-kinetic energy critical ratio, it means that the system has sufficient frequency support capability to ensure the system frequency stability; if the system inertia-kinetic energy ratio is greater than the system inertia-kinetic energy critical ratio, it means that the system has insufficient frequency support capability and needs to supplement inertia resources and frequency modulation resources to deal with the hidden danger of frequency instability. To be precise, the system inertia-kinetic energy ratio is calculated based on the system inertia constant operating kinetic energy inertia constant, and the system inertia-kinetic energy critical ratio is calculated based on the minimum inertia requirement.

[0120] The present invention comprehensively considers the coupling relationship between the system inertia constant and the unit combination mode, constructs a feasible operating point optimization search model and a multi-machine frequency response model, proposes a minimum inertia demand evaluation method based on a feasible inertia operating point, and proposes a forward correction algorithm for simulating the unit combination mode in ascending order of kinetic energy for the evaluation method, and realizes adaptive correction in iterative calculation. The method effectively solves the defect that the existing method assumes that the inertia constant and the frequency regulation capability are independent variables, and does not consider the coupling change of the frequency regulation capability with the inertia constant when calculating and obtaining the minimum inertia demand of the power system. The system minimum inertia demand can be evaluated without relying on a simplified synchronous generator primary frequency regulation structure and a complex algorithm that takes too long to calculate, effectively improving the accuracy of the minimum inertia demand evaluation, providing a basis for the refined optimization and regulation of the inertia and frequency regulation capability of the low-inertia power system, avoiding as much as possible the system instability caused by large-capacity active impacts such as DC locking and new energy grid disconnection due to insufficient system inertia level and frequency regulation capability, and providing an effective evaluation tool for the safe and stable operation and reasonable planning and design of the low-inertia power system.

[0121] In order to verify the effectiveness of the evaluation method of this application, the following verification method is used:

[0122] Simulation condition configuration: The computer configuration used is CPU Intel Core i5 and memory 16 GB. The proposed power system minimum inertia requirement evaluation method is implemented in MATLAB software, and the simulation calculation is completed through MATLAB / Simulink.

[0123] like Figure 5As shown, based on the improved IEEE-39 node example system verification, the accuracy of the scheme of a method for evaluating the minimum inertia requirement of a power system as described above in the present invention. In the improved IEEE-39 node example system, nodes 31, 32, 33, 35, and 38 are connected to thermal power generating sets with steam turbines as prime movers, nodes 37 and 39 are connected to hydropower generating sets with water turbines as prime movers, node 21 is connected to a DC transmission line via a converter, node 30 is connected to a wind farm via a converter, node 34 is connected to a photovoltaic power plant via a converter, and node 36 is connected to an energy storage unit via a converter. In order to simulate the inertia shortage scenario, the wind and solar power sources and energy storage units are set to zero inertia mode and do not participate in the frequency response. The inertia of the test system is only provided by the synchronous generator set. All synchronous generator sets are equipped with speed regulators to participate in the primary frequency modulation response, and the DC transmission lines are equipped with DC modulation functions. The unit information of the above nodes is shown in Table 1.

[0124] Please refer to Table 2 for the main parameters of the tested new energy power system. First, set the following example. The maximum disturbance that may occur under the current operation mode of the test system is a sudden disconnection of the wind farm at node 30, resulting in a power supply loss of 460MW. Secondly, in order to determine whether the system frequency of the example is safe after the fault, the following frequency safety boundary conditions under low-frequency faults are set: the maximum frequency deviation of the system after the fault does not exceed -0.5Hz, and the maximum frequency change rate does not exceed -1Hz / s.

[0125] ,

[0126] Based on Table 1 and Table 2, the optimization search model of the feasible inertia operation point of the power system is constructed, and the input equivalent kinetic energy expected value is optimized and searched to obtain a feasible inertia operation point corresponding to the input value. The multi-machine frequency response model is constructed in combination with the frequency response mode of each unit in Table 1, and the dynamic process simulation calculation of the disturbed frequency is performed to obtain the disturbed frequency change curve. The maximum frequency deviation and the maximum frequency change rate are extracted from the curve as the key frequency indicators and compared with the frequency safety boundary conditions in Table 2. If none of the key frequency indicators exceeds the limit, the system inertia constant of the current feasible inertia operation point is the minimum inertia requirement of the evaluated system; if one or more key frequency indicators exceed the limit, the equivalent kinetic energy expected value is corrected and the feasible inertia operation point is optimized again to realize iterative calculation.

[0127] The current inertia constant of the test system is 4.3840s. The proposed method can be used to iteratively calculate the minimum inertia requirement of the test system to be 3.4898s. The calculation time is 2.4730s, and the calculation is iterated 5 times. Figure 6, which is the frequency change process of the test system when the maximum possible disturbance occurs under the operating inertia constant and the minimum inertia requirement. The maximum frequency deviation of the disturbance under the operating inertia level is -0.45Hz, and the maximum frequency change rate is -0.43Hz / s. Compared with the frequency stability constraint, it can be seen that the maximum frequency deviation and the maximum frequency change rate are far from the constraint value, indicating that the test system is in a state of sufficient inertia. The current operating inertia constant is greater than the minimum inertia requirement of the test system. It is necessary to solve the minimum inertia requirement of the system according to the frequency stability constraint. The maximum frequency deviation of the same disturbance occurring at the operating point corresponding to the minimum inertia requirement is -0.50Hz, which is at the critical position of the maximum frequency deviation constraint, and can safely cope with the occurrence of the possible maximum disturbance. The number of startups of the test system at the operating point corresponding to the minimum inertia requirement of 3.4898s is 9, and the number of startups at the operating point corresponding to the operating inertia constant of 4.3840s is 10. Therefore, in order to ensure the frequency stability of the test system, the minimum critical value of the operating inertia level is 3.4898s, that is, the minimum inertia requirement of the system, and the corresponding inertia kinetic energy critical ratio is 2.834%.

[0128] Figure 7 The inertia kinetic energy ratio of all feasible inertia operating points of the test system is shown, where the red scattered points represent the feasible inertia operating points that meet the frequency stability constraint, the black scattered points represent the feasible inertia operating points that do not meet the frequency stability constraint, and the red solid scattered points represent the feasible inertia operating points corresponding to the minimum inertia requirement. Figure 7 It can be seen that the inertia-kinetic energy critical ratio is the safety critical value of the inertia-kinetic energy ratio index. Therefore, the minimum inertia requirement and the inertia-kinetic energy ratio index can well evaluate the strength and adequacy of the frequency support capacity of the power system.

[0129] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for evaluating the minimum inertia requirement of a power system, characterized in that: The following steps are involved: S1: Obtain the regional system load level and detailed parameters of each installed unit; S2: Based on the regional system load level and detailed parameters of each installed generating unit, a power system feasible inertia operation point optimization search model is constructed with the difference between the search and the initial expected kinetic energy satisfying the first preset condition as the objective function; S3: based on the power system feasible inertia operation point optimization search model, searching for a feasible inertia operation point that satisfies the objective function and constraint conditions, and constructing a multi-machine frequency response model corresponding to the feasible inertia operation point; S4: Based on the multi-machine frequency response model, a simulation calculation is performed on the frequency dynamic change process under the expected disturbance to obtain a calculation result of the disturbed frequency dynamic process; S5: Based on the calculation result of the disturbed frequency dynamic process, judging whether the disturbed frequency dynamic process meets the frequency requirement; If yes, go to step S6; If not, the initial expected kinetic energy is adaptively corrected by simulating the feasible inertia running points according to the ascending order of kinetic energy to obtain the first expected kinetic energy, and the first expected kinetic energy is substituted into step S2 as the initial expected kinetic energy for the next round of calculation, and steps S2 to S5 are repeated for iterative calculation; S6: Determine an evaluation result of the minimum inertia requirement of the power system based on the calculation result of the disturbed frequency dynamic process.

2. The method according to claim 1, characterized in that The steps S1 and S2 include: The feasible inertia operating point is defined as all operating points in the power system that satisfy the power flow equation and the operation safety constraints, representing an operation mode of the power system, which is determined by the system inertia constant , Unit combination Composition, including the combination of units The unit operation state vector , Unit active power output vector , Unit active power reserve vector Composition, that is ; Wherein, the system inertia constant calculation formula is: ； In the formula, For the The rotational kinetic energy of a generator set, in ; For the The rated capacity of the generator set is ; For the The startup status of the generator sets, Indicates startup. Power off.

3. The method according to claim 1, characterized in that The method takes the difference between the searched and expected kinetic energy satisfying the first threshold as the objective function and constructs an optimization search model for the feasible inertia operation point of the power system, including: The startup status, active output power and active reserve capacity of each unit are taken as optimization variables, and the square of the difference between the rotation function of the unit combination mode and the expected value of the equivalent kinetic energy satisfies the first preset condition as the objective function: ； In the formula, is the rotational kinetic energy of the unit combination, is the total number of generators within the regional system; For the The rotational kinetic energy of a generator set, in ; For the The startup status of the generator sets, Indicates startup. Power off.

4. The method according to claim 2, characterized in that: The method takes the difference between the searched and expected kinetic energy satisfying the first threshold as the objective function, constructing the power system feasible inertia operation point optimization search model, and further includes: From the system level, the optimization search model for the feasible inertia operation point of the power system is set with constraints including active power balance constraint, active power reserve constraint, and net load reserve constraint, and their expressions are as follows: ， ， ， in, is the number of synchronous units within the regional system; For the The steady-state active output of each synchronous unit; is the number of new energy stations within the regional system; For the The steady-state active power output of each new energy station; The number of DC transmission lines with a single-side access point located within the regional system; For the The steady-state active power of the DC transmission line is Indicates that the access point is the power receiving side. Indicates that the access point is the power transmission side; is the number of AC transmission lines with single-side access points located inside the regional system, i.e., the number of external network equivalent machines; For the The steady-state active power of the AC tie line, Indicates that the access point is the power receiving side. Indicates that the access point is the power transmission side; is the load level of the system in the area; is the regional system network loss rate; is the expected disturbance power; For the The spare capacity of each generator set; For the Reserve capacity for power modulation of DC lines; For the The spare capacity of check-in machines in Taiwan's overseas network, is the load reserve ratio of the regional system, which represents the equivalent scale of load power fluctuation and expected deviation; For the The output limit of each generator set; For the The active power output of each generator set; It is the unplanned load variation; Among them, the constraints set for the units participating in frequency regulation in the synchronous units within the regional system are: ， ， ， In the formula, For the The startup status of the synchronous units participating in frequency regulation, Indicates startup. Shut down the device; For the The lower output limit of the generator sets participating in frequency regulation; For the The active power output of the synchronous units participating in frequency regulation; For the The output limit of synchronous units participating in frequency regulation; For all synchronous units participating in frequency regulation; For the The upper limit of the spinning reserve capacity of synchronous units participating in frequency regulation.

5. The method according to claim 1, characterized in that The method of optimizing the search model for the feasible inertia operation point of the power system, searching for a feasible inertia operation point that satisfies the objective function and the constraint conditions, and constructing a multi-machine frequency response model corresponding to the feasible inertia operation point, includes: Based on the power system feasible inertia operating point optimization search model, searching for a feasible inertia operating point that meets the objective function and constraint conditions; Based on the feasible inertia operating point, determining detailed parameters of the regional system and frequency dynamic response parameters of each frequency modulation; Based on the detailed parameters of the regional system and the frequency dynamic response parameters of each frequency modulation, a multi-machine frequency response model corresponding to the feasible inertia operation point is constructed; wherein the multi-machine frequency response model includes the power-on status and frequency response characteristics of all frequency modulation resources in the feasible inertia operation point.

6. The method according to claim 5, characterized in that Based on the multi-machine frequency response model, the frequency dynamic change process under the expected disturbance is simulated and calculated to obtain the calculation result of the disturbed frequency dynamic process, which is specifically: The detailed parameters of the regional system and the frequency dynamic response parameters of each frequency modulation are input into the multi-machine frequency dynamic response model, and the frequency dynamic change process under the expected disturbance is simulated and calculated to obtain the calculation result of the disturbed frequency dynamic process.

7. The method according to claim 6, wherein the calculation result of the disturbed frequency dynamic process includes a maximum frequency deviation and a maximum frequency change rate, characterized in that: Based on the calculation result of the disturbed frequency dynamic process, judging whether the disturbed frequency dynamic process meets the frequency requirement includes: Determine whether the maximum frequency deviation index is between the upper and lower limits of the system maximum frequency deviation constraint limit and whether the maximum frequency change rate index is between the upper and lower limits of the system maximum frequency change rate limit; If so, the disturbed frequency dynamic process meets the frequency requirement.

8. The method according to claim 1, if not, after adaptively correcting the expected kinetic energy by simulating the feasible inertia running points according to the ascending order of kinetic energy, repeating steps S2 to S5 for iterative calculation; in, The process of adaptively correcting the expected kinetic energy is as follows: Arrange the powered-on units in the current unit combination mode and unpowered units ; Determine if the unit is not turned on Is the empty set, if so, the iteration operation ends, executing step S6; If not, determine the difference matrix of rotational kinetic energy between the started units and the unstarted units; Based on the elements in the difference matrix that are greater than the correction threshold, a judgment set is formed; Based on the elements in the difference matrix and the correction threshold, determining whether the determination set is an empty set; If so, determine the correction amount to be the generator set with the smallest non-zero rotational kinetic energy among the non-started generator sets; Based on the minimum rotational kinetic energy of the current number of startups, determine the expected value of the rotational kinetic energy of the next iteration process; The expected value of the rotational kinetic energy is used as the first expected kinetic energy, and steps S2 to S5 are executed; If not, select the minimum value in the judgment set as the correction amount; Based on the rotational kinetic energy level of the current unit combination mode, the expected value of the rotational kinetic energy of the next iteration process is corrected; The expected value of the rotational kinetic energy is used as the first expected kinetic energy, and steps S2 to S5 are executed.

9. The method according to claim 8, characterized in that The correction method of the correction threshold includes two methods, specifically: Method 1: The correction threshold is set to 0 to achieve accurate correction; Mode 2: The correction threshold is set as a piecewise function of the frequency index to achieve rough correction.

10. The method according to claim 1, characterized in that The evaluation results of the minimum inertia requirement of the power system include: Minimum inertia requirement and corresponding unit combination, system inertia kinetic energy ratio, and system inertia kinetic energy critical ratio for preset faults; Wherein, the calculation formula of the system inertia kinetic energy ratio is: , In the formula, is the system inertia kinetic energy ratio, is the expected disturbance power, is the frequency extreme time; is the system equivalent kinetic energy; Based on the system inertia-kinetic energy ratio and the system inertia-kinetic energy critical ratio of the preset fault, the minimum inertia requirement of the power system is evaluated.

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