Practical aggregation method of power system frequency model considering frequency space-time distribution

Abstract

The invention relates to a practical aggregation method of a power system frequency model, in particular to a practical aggregation method of a power system frequency model considering frequency space-time distribution. The method aims at solving the problem that no method can aggregate the whole frequency process of the power system without relying on electromechanical simulation under the condition that system parameters are incomplete at present. The method comprises the following steps: firstly, constructing a power disturbance set of a power system, and then calculating initial unbalanced power and initial steady-state frequency of each node of the power system under specific disturbance; based on the initial unbalanced power and the initial steady-state frequency of each node of the power system, alternately calculating the frequency difference and the unbalanced power of each node until each node reaches the uniform steady-state frequency, and obtaining a frequency difference track among the nodes of the power system under specific disturbance; and according to the calculated track of the frequency difference of each node, clustering is carried out according to the track of the frequency difference of each node in each step.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel power system modeling and control, and in particular relates to a practical aggregation method of a power system frequency model. Background Art

[0002] In recent years, renewable energy has developed rapidly, and the new power system has shown the "double high" characteristics of high degree of power electronics and high proportion of new energy. New energy power generation such as wind power and photovoltaic power generation is random and time-varying, and the electrical distance between new energy stations and the main grid is long, and large system interconnection and other factors have led to more obvious frequency and space distribution characteristics of the power system. In order to ensure the safe and stable operation of the new power system, it is a prerequisite for judging the frequency stability of the power system to partition the power system frequency and aggregate and reduce the frequency model.

[0003] At present, there have been many studies on the frequency and spatial distribution characteristics of power systems, such as:

[0004] 1. Pei Ming et al. published "Inertia Estimation Method for Renewable Energy Power System Considering Spatiotemporal Correlation of Frequency Response" Automation of Electric Power Systems: 53-66 [2024-04-25]. The article studies the calculation method of inertia for synchronous units and renewable energy generators. It uses the Granger causality test algorithm to dynamically analyze the correlation of frequencies between different nodes in the system, constructs a spatiotemporal causal correlation set of system frequencies that changes with time, and establishes a system inertia constant-frequency state space model based on the swing equation of the frequency response process of each node in the system. It designs an unscented Kalman filter and a fixed lag smoother, and proposes an inertia estimation method for a high proportion of renewable energy power systems. The study only considers the partitioning and estimation of inertia, but does not consider the entire process of system frequency response.

[0005] 2. Xu Taishan and Xue Yusheng published “Quantitative Analysis of Acceptability of Transient Frequency Excursions” Automation of Electric Power Systems: 7-10 [2002, 26(19)]. The article combines common frequency indicators and proposes a binary table evaluation indicator based on transient frequency excursion threshold and excursion duration to evaluate the global frequency stability of the power system. It does not consider the node frequency security indicators of the power system.

[0006] 3. Larbi ES et al., “Evaluation of key performance indices for frequency quality: a method for evaluating frequency stability in the Nordic power system”, Stockholm, Sverige: KTH Royal Institute of Technology

[2023] , took the Nordic power system as an example and used the correlation method to analyze and show that: frequency, standard deviation, frequency area, frequency limit times and R max The four standard deviation indicators can comprehensively measure the safety of node frequency. Only the node frequency indicator is considered, and there is a lack of analysis of the global frequency safety and stability indicators.

[0007] 4. “Analysis of Spatio-temporal Frequency Distribution Characteristics of New Energy Power System” published by Ma Ningjia et al. High Voltage Technology: 406-413 [2014-01-31]. This article established an analytical model of the frequency dynamic response of the new energy power system, and analyzed the influencing factors of the spatio-temporal frequency distribution characteristics and the impact mechanism of the new energy grid connection on this characteristic; the article discussed the necessity of studying the spatio-temporal frequency distribution characteristics and the quantitative indicators to describe this characteristic, and summarized the impact of the grid connection of new energy units on this characteristic, but did not consider the aggregation and reduction of the frequency response equation taking into account the spatio-temporal distribution characteristics.

[0008] In summary, the current research on the spatiotemporal distribution characteristics of frequency in power systems focuses on qualitative analysis of case studies and research on global or node frequency security judgment indicators, and lacks a practical method for aggregation and equivalence of the entire frequency response process. Summary of the invention

[0009] The present invention aims to solve the problem that there is currently no method that can aggregate the entire process of power system frequency without relying on electromechanical simulation when system parameters are incomplete.

[0010] A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency comprises the following steps:

[0011] S1. Constructing a power disturbance set of the power system, wherein the disturbances corresponding to the disturbance set include disturbance scenarios consisting of a single disturbance and disturbance scenarios consisting of a composite disturbance;

[0012] S2, calculate the initial unbalanced power and steady-state frequency of each node in the power system under a specific disturbance;

[0013] S3, based on the initial unbalanced power and steady-state frequency of each node in the power system, alternately calculate the frequency difference and unbalanced power of each node until each node reaches a uniform steady-state frequency, and obtain the frequency difference trajectory between each node in the power system under a specific disturbance;

[0014] S4. Clustering is performed according to the calculated trajectories of the frequency differences of each node and the trajectories of the frequency differences of each node at each step.

[0015] Furthermore, the disturbance types in the disturbance scenario of S1 include impact load, generator tripping, sudden change in the operating conditions of wind power or photovoltaic power station, and line tripping.

[0016] Furthermore, the calculation process of the initial unbalanced power in S2 includes:

[0017] For thermal power units, the node voltage equation is determined according to the admittance matrix of the power system before the impact load changes; the voltage vector of the grid connection point of the new energy station is expressed as V R The new energy station is represented as a controlled current source, and the equivalent current is I R , the node voltage equation corresponding to the extended thermal power unit is obtained:

[0018]

[0019] In the formula, the block diagonal matrix represents the self-admittance matrix, the off-diagonal block matrix represents the mutual-admittance matrix, and Y GG is the self-admittance matrix of the generator node of the thermal power unit, Y RR is the self-admittance matrix of the new energy station node, Y BB is the self-admittance matrix of the load node, Y GR , Y RG is the mutual admittance matrix of thermal power nodes and new energy station nodes, Y GB , Y BG is the mutual admittance matrix between thermal power nodes and load nodes, Y RB , Y BR is the mutual admittance matrix between the new energy station node and the load node; I G Generator injection current, V B is the node voltage of the load node; V G 、V L are the voltages of the generator busbars respectively;

[0020] According to V G ,I R Solution I G 、V R 、V B , and then according to V G ,I R And the solved I G 、VR 、V B The initial unbalanced power of each power node is calculated.

[0021] Furthermore, the admittance matrix of the power system before the impact load changes is:

[0022]

[0023] Among them, X d ' is the subsynchronous reactance of the generator, X T is the equivalent reactance of the line and transformer, Y T is the equivalent admittance of the line and transformer; Y L1 is the equivalent admittance before the sudden load increase.

[0024] Furthermore, the node voltage equation determined according to the admittance matrix of the power system before the impact load changes is as follows:

[0025]

[0026] Where V G 、V L are the voltages of the generator bus and load nodes respectively; E is the potential inside the synchronous machine.

[0027] Furthermore, the calculation process of the steady-state frequency described in S2 includes:

[0028] Firstly, an equivalent droop coefficient of the power system is determined, then a shift of a steady-state frequency of the power system is determined based on the equivalent droop coefficient, and a steady-state frequency under a specific disturbance is determined through the shift of the steady-state frequency of the power system;

[0029] The deviation of the steady-state frequency of the power system is:

[0030]

[0031] Where Δf ∞ is the deviation of the steady-state frequency of the power system after the disturbance; ΔP d is the disturbance power of the power system.

[0032] Furthermore, the equivalent droop coefficient of the power system is:

[0033]

[0034] In the formula, R i represents the droop coefficient of power supply i, R eq Represents the equivalent droop coefficient of the power system.

[0035] Furthermore, the process of alternately calculating the frequency difference and unbalanced power of each node in S3 includes the following steps:

[0036] The formula for calculating the frequency difference between nodes is determined according to the DC power flow method:

[0037]

[0038] Among them, Δf ij represents the difference in frequency between node i and node j, B RN is the system admittance matrix of node contraction, ΔP ij is the electromagnetic power increment transmitted from node i to node j; Δt represents the time change, which is used to represent the iteration step;

[0039] Then, based on the frequency difference formula between nodes, the frequency difference of each power node is iteratively calculated, and the unbalanced power of each node is updated according to the known inertia and droop coefficient of each node and the inter-machine transmission power;

[0040] Determine whether each node has reached a uniform steady-state frequency, and if so, stop the iteration.

[0041] Furthermore, the conditions for determining whether each node reaches a uniform steady-state frequency are as follows:

[0042]

[0043] Among them, f i is the frequency of node i, f ∞ is the steady-state frequency of the system; δ1 and δ2 represent tolerances;

[0044] When formula (17) is true, it means that each node reaches a uniform steady-state frequency.

[0045] Furthermore, the process of clustering the node frequency difference trajectories at each step according to the calculated trajectories of the node frequency differences in S4 includes:

[0046] Select the clustering condition interval [-ε,ε], ε is the clustering cutoff point, and the clustering condition is:

[0047]

[0048] When formula (18) is satisfied, the frequency trajectories of node i and node j are similar, and the frequency models of node i and node j are aggregated.

[0049] Beneficial effects of the present invention:

[0050] For the power system frequency model taking into account the temporal and spatial distribution of frequency, a method is proposed which is independent of electromechanical simulation. When the system parameters are incomplete, the frequencies are grouped for specific disturbances and the frequency model is clustered and reduced in order. This method can not only aggregate the entire frequency process of the power system without relying on electromechanical simulation, but also improve the speed of estimating the system frequency. It provides a practical reduction method for analyzing the power system frequency response model taking into account the temporal and spatial distribution of frequency, and provides theoretical and technical support for improving the frequency security of new power systems and the safe and stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a frequency response transfer function diagram of the single inertia center system of the present invention;

[0052] Figure 2 The system frequency response transfer function diagram of the present invention with time and space distribution;

[0053] Figure 3 It is the algorithm flow chart of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with the accompanying drawings.

[0055] The present invention is based on a practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency. The power system frequency model taking into account the temporal and spatial distribution of frequency includes a frequency response model of a thermal power unit, a frequency response model of a wind power unit, and a frequency response model of a photovoltaic unit; the power system frequency model taking into account the temporal and spatial distribution of frequency uses a DC power flow method to characterize the power system power flow. This method does not rely on large-scale electromechanical simulation, can partition and aggregate the frequency of the power system for specific disturbances, effectively simplify the power system frequency model taking into account the temporal and spatial distribution of frequency, provide a theoretical basis for analyzing the temporal and spatial distribution of power system frequency, and provide technical support for improving the safe operation level of the power grid. The following is a detailed description in conjunction with a specific implementation method.

[0056] The frequency response of the power system is mainly related to the system disturbance and the frequency response characteristics of each power source. The single inertia center power system refers to a power system with uniform system frequency, which does not have obvious time and space distribution characteristics. The model is relatively simple and easy to analyze. The frequency response transfer function diagram of the single inertia center power system is shown in the attached figure. Figure 1As shown. The single-inertia center power system frequency response model established by the present invention can characterize the frequency response characteristics of thermal power units, wind farms, and photovoltaic power stations. The prime mover part of the thermal power unit is characterized by a one-stage reheat steam turbine transfer function, and the synchronous generator is represented by a second-order model. The wind turbine model takes into account the load reduction control and frequency regulation functions, including virtual inertia control and droop control. The photovoltaic unit takes into account the overpressure load reduction and frequency regulation functions, including virtual inertia control and droop control of the photovoltaic unit. The model covers the common new energy station types and frequency control methods of the current power system and has universal significance.

[0057] The DC power flow method assumes that the phase angle difference of each node is small and the active power flow equation is linearized. When studying the frequency problem, the DC power flow can be used to incorporate the power oscillation between the single inertia center power system into the frequency model. The obtained power system frequency model taking into account the time and space distribution is shown in the attached figure. Figure 2 The power system frequency model considering the temporal and spatial distribution established by the present invention takes into account the frequency characteristics of thermal power units and new energy stations, and can effectively characterize the temporal and spatial distribution characteristics of the frequency of the power system. The power system model considering the temporal and spatial distribution of frequency is in the form of a state equation with a high order. To analyze the equation, the model needs to be aggregated and reduced in order.

[0058] The core idea of ​​a practical aggregation method for power system frequency model taking into account the temporal and spatial distribution of frequency is: calculate the initial unbalanced power of each power node for a specific disturbance, iteratively calculate the frequency difference between each node, cluster the power system according to the obtained frequency difference trajectory between each node, and establish a mapping relationship between disturbance and system frequency partition, so as to aggregate and reduce the order of the power system frequency model taking into account the temporal and spatial distribution.

[0059] The practical aggregation method of the power system frequency model considering the spatiotemporal distribution of frequency includes the following steps:

[0060] S1. Construct a power disturbance set of the power system. The disturbances corresponding to the disturbance set include disturbance scenarios consisting of a single disturbance and disturbance scenarios consisting of a composite disturbance. Specific disturbance types include impact load, generator tripping, sudden changes in the working conditions of wind power or photovoltaic power stations, line tripping, etc.

[0061] S2, calculate the initial unbalanced power and steady-state frequency of each node in the power system under a specific disturbance;

[0062] The calculation process of the initial unbalanced power is as follows:

[0063] Considering a single machine-load system, the power system consists of a synchronous generator and a static load, and the load equivalent admittance is Y L The equivalent admittances before and after the sudden load increase are Y L1 , Y L2, the Norton equivalent injection current of the synchronous generator is E / X d ', E is the potential inside the synchronous machine, X d ' is the subsynchronous reactance of the generator, X T is the equivalent reactance of the line and transformer, Y T is the equivalent admittance of the line and transformer;

[0064] Line and transformer equivalent reactance Where X TR is the equivalent reactance of the transformer, R and X are the equivalent resistance and reactance of the line respectively, and j represents an imaginary number;

[0065] The admittance matrix of the power system before the impact load changes is:

[0066]

[0067] According to the node voltage equation:

[0068]

[0069] Where V G 、V L are the voltages of the generator busbar and load node respectively;

[0070] The calculated generator bus voltage is:

[0071]

[0072] The electromagnetic power P output by the generator without automatic voltage control device e for:

[0073]

[0074] The electromagnetic power P output by the generator with automatic voltage control device e The expression is:

[0075]

[0076] Formula (4) is for the case without automatic voltage control device, and formula (5) is for the case with automatic voltage control device.

[0077] It is necessary to obtain formula (5) based on formula (4); from formula (4), it can be obtained that in the case of no automatic generator voltage control device, in the case of power loss such as power system impact load or power system generator tripping, the output electromagnetic power of the generator decreases. For a simple generator and load system with an automatic voltage control device, the impact load suddenly increases, and the admittance corresponding to the load increases. The automatic voltage control device maintains the generator bus voltage V G unchanged, at VG Under the condition of no change, the electromagnetic power emitted by the generator increases.

[0078] Generally, the time from the occurrence of a fault to the restoration of bus voltage by an automatic voltage control device is 0.1 to 0.3 seconds.

[0079] From the occurrence of the fault to the process of the automatic voltage control device maintaining the bus voltage, the electromagnetic power of the generator first decreases and then increases. When the dynamics of the automatic voltage control device are ignored and the bus voltage is assumed to be unchanged, the electromagnetic power output by the generator increases immediately after the impact load increases. Currently, all thermal power units have automatic voltage regulating devices. Therefore, assuming that the terminal voltage of the thermal power unit remains unchanged before and after the fault, the initial unbalanced power of the thermal power unit can be obtained through the node voltage equation.

[0080] The above only considers the situation of thermal power units. The grid-connected new energy units do not have the ability to maintain terminal voltage similar to the excitation control device. The voltage vector of the grid-connected point of the new energy station is V R The new energy station is represented as a controlled current source, and the equivalent current is I R , the current value cannot change suddenly, and the extended formula (2) is:

[0081]

[0082] In the formula, the block diagonal matrix represents the self-admittance matrix, the off-diagonal block matrix represents the mutual-admittance matrix, and Y GG is the self-admittance matrix of the generator node of the thermal power unit, Y RR is the self-admittance matrix of the new energy station node, Y BB is the self-admittance matrix of the load node, Y GR , Y RG is the mutual admittance matrix of thermal power nodes and new energy station nodes, Y GB , Y BG is the mutual admittance matrix between thermal power nodes and load nodes, Y RB , Y BR It is the mutual admittance matrix between the new energy station nodes and the load nodes.

[0083] V G ,I R For known quantities, solve for I G 、V R 、V B :

[0084]

[0085] σ1=Y BB Y GG Y RR -Y BB Y GR Y RG-Y BG Y GB Y RR +Y BG Y GR Y RB +Y BR Y GB Y RG -Y BR Y GG Y RB (7)

[0086] I G =Y GG V G +Y GR V R +Y GB V B

[0087] Among them, I G Generator injection current, V B is the node voltage of the load node;

[0088] According to V G ,I R And the solved I G 、V R 、V B , the unbalanced power of each power node, that is, the initial unbalanced power, can be calculated.

[0089] Calculate the steady-state frequency of the power system. The frequency of each node in the system tends to a uniform steady-state frequency, which depends on the droop coefficient of each power source. The equivalent droop coefficient of the power system is:

[0090]

[0091] In the formula, R i represents the droop coefficient of power supply i, R eq It represents the equivalent droop coefficient of the power system;

[0092] The deviation of the steady-state frequency of the power system is:

[0093]

[0094] Where Δf ∞ is the deviation of the steady-state frequency of the power system after the disturbance; ΔP d is the disturbance power of the power system;

[0095] The steady-state frequency under a specific disturbance is then determined by the deviation of the steady-state frequency of the power system.

[0096] S3. Determine the time iteration step, start from the initial state, alternately calculate the frequency difference and unbalanced power of each node until each node reaches a uniform steady-state frequency, stop the iteration, and obtain the frequency difference trajectory between each node of the power system under a specific disturbance.

[0097] The basic idea of ​​obtaining the frequency difference trajectory between nodes in the power system under a specific disturbance is to highlight the admittance matrix of the power system, that is, the role of the spatiotemporal distribution characteristics in the power transfer between nodes in the power system after the disturbance occurs, and to simplify the frequency response of each power source; using the initial unbalanced power distribution after the disturbance as the initial condition, the frequency difference trajectory of each node is iteratively calculated.

[0098] The dynamic process of the frequency of the power system is not only determined by the unbalanced power of the system, but also by the frequency response characteristics of each power source. Since the parameters of each power source are incomplete, in order to highlight the influence of the spatiotemporal distribution of frequency, each power source is simplified with a model containing only inertia and droop (precondition, known in the art). The example shows that this simplification does not affect the frequency partitioning of the power system, and the inertia of each node can be estimated online through a wide-area measurement device. The power system eventually reaches a uniform steady-state frequency, which is determined by the droop coefficient of each power source. The specific iterative method of the practical aggregation method of the power system frequency model considering the spatiotemporal distribution.

[0099] Combined with Figure 3 , the principle and process of the iterative process are as follows:

[0100] The admittance matrix Y1 of the power system before and after the disturbance and the equivalent inertia K of each node are known. ii , the power of the disturbance ΔP d , the droop coefficient K of each thermal power unit and new energy station di , the alternating iterative calculation process of the frequency difference and unbalanced power between nodes is as follows:

[0101] S301. Derive a formula for calculating frequency differences between nodes according to a DC power flow method;

[0102] The inter-machine oscillation power determined by the DC power flow equation is:

[0103]

[0104] Among them, ΔP ei represents the change in electromagnetic power emitted by node i, B RNij is the contraction mutual admittance between nodes i and j, Δω i is the change in electrical angular velocity of node i, Δω j is the change in electrical angular velocity of node j, n g is the number of power nodes in the system;

[0105] Express the above formula in matrix form:

[0106]

[0107] Where Δf ij represents the difference in frequency between node i and node j, B RN is the system admittance matrix of node contraction, ΔP ij is the electromagnetic power increment transmitted from node i to node j; Δt represents the time change, that is, the iteration step.

[0108] Discretize the above formula to get the calculation method of the frequency difference between nodes:

[0109]

[0110] S302, iteratively calculate the frequency difference of each power supply node, determine the iteration step length Δt, and start the first iteration:

[0111]

[0112] Among them, ΔP ij 0 ΔP ij The initial value of , the superscript 0 indicates the number of iterations;

[0113] Update the unbalanced power of each node based on the known inertia and droop coefficient of each node and the inter-machine transmission power:

[0114]

[0115] Among them, ΔP i 1 , Δf i 1 The superscript 1 indicates the number of iterations, that is, the ΔP corresponding to the first iteration i , Δf i , ΔP i is the unbalanced power at node i, Δf i is the frequency offset of node i; K ii is the equivalent inertia constant of node i or the virtual inertia coefficient of the new energy station, K di is the equivalent droop coefficient of node i or the droop control coefficient of the virtual station; P ji is the electromagnetic power transmitted by node i under the influence of the connected node j, and Ω represents the set of all node numbers connected to node i.

[0116] S303, k-th iteration, calculate the node frequency difference matrix of k+1 step:

[0117]

[0118] Update the unbalanced power of each node:

[0119]

[0120] S304, based on the set iteration termination condition, determine whether the iteration is terminated; that is, when it is determined that each node reaches a uniform steady-state frequency, stop the iteration;

[0121] Select tolerances δ1 and δ2, calculate the 2-norm of the frequency difference matrix, and the iteration termination condition is:

[0122]

[0123] Among them, f i is the frequency of node i, f ∞ is the steady-state frequency of the system;

[0124] If the above equations are all true, it means that each node reaches a uniform steady-state frequency. If the conditions are not met, continue to iterate until the conditions are met and terminate the iteration.

[0125] S4. According to the calculated frequency difference trajectory of each node, the clustering conditions are defined, and clustering is performed according to the frequency difference trajectory of each step of the nodes.

[0126] Select the clustering condition interval [-ε,ε], ε is the clustering cutoff point, and the clustering condition is:

[0127]

[0128] The frequency trajectories of nodes i and j are similar and are classified into the same category, which means that under this disturbance, the frequency models of nodes i and j can be aggregated.

[0129] Thus, a practical aggregation method for the power system frequency model taking into account the temporal and spatial distribution of frequency has been formed.

[0130] The above calculation examples of the present invention are only used to explain the calculation model and calculation process of the present invention in detail, and are not intended to limit the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency, characterized in that: The following steps are involved: S1. Constructing a power disturbance set of the power system, wherein the disturbances corresponding to the disturbance set include disturbance scenarios consisting of a single disturbance and disturbance scenarios consisting of a composite disturbance; S2, calculate the initial unbalanced power and steady-state frequency of each node in the power system under a specific disturbance; S3, based on the initial unbalanced power and steady-state frequency of each node in the power system, alternately calculate the frequency difference and unbalanced power of each node until each node reaches a uniform steady-state frequency, and obtain the frequency difference trajectory between each node in the power system under a specific disturbance; S4. Clustering is performed according to the calculated trajectories of the frequency differences of each node and the trajectories of the frequency differences of each node at each step.

2. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 1, characterized in that: The disturbance types in the disturbance scenarios of S1 include impact load, generator tripping, sudden changes in the operating conditions of wind power or photovoltaic power plants, and line tripping.

3. The practical aggregation method of a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 1 is characterized in that: The calculation process of the initial unbalanced power in S2 includes: For thermal power units, the node voltage equation is determined according to the admittance matrix of the power system before the impact load changes; the voltage vector of the grid connection point of the new energy station is expressed as V R The new energy station is represented as a controlled current source, and the equivalent current is I R , the node voltage equation corresponding to the extended thermal power unit is obtained: In the formula, the block diagonal matrix represents the self-admittance matrix, the off-diagonal block matrix represents the mutual-admittance matrix, and Y GG is the self-admittance matrix of the generator node of the thermal power unit, Y RR is the self-admittance matrix of the new energy station node, Y BB is the self-admittance matrix of the load node, Y GR , Y RG is the mutual admittance matrix of thermal power nodes and new energy station nodes, Y GB , Y BG is the mutual admittance matrix between thermal power nodes and load nodes, Y RB , Y BR is the mutual admittance matrix between the new energy station node and the load node; I G Generator injection current, V B is the node voltage of the load node; V G 、V L are the voltages of the generator busbars respectively; According to V G ,I R Solution I G 、V R 、V B , and then according to V G ,I R And the solved I G 、V R 、V B The initial unbalanced power of each power node is calculated.

4. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 3, characterized in that: The admittance matrix of the power system before the impact load changes is: Among them, X d ' is the subsynchronous reactance of the generator, X T is the equivalent reactance of the line and transformer, Y T is the equivalent admittance of the line and transformer; Y L1 is the equivalent admittance before the sudden load increase.

5. The practical aggregation method of a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 3, characterized in that: The node voltage equation determined by the admittance matrix of the power system before the impact load changes is as follows: Where V G 、V L are the voltages of the generator bus and load nodes respectively; E is the potential inside the synchronous machine.

6. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 1, characterized in that: The calculation process of the steady-state frequency described in S2 includes: Firstly, an equivalent droop coefficient of the power system is determined, then a shift of a steady-state frequency of the power system is determined based on the equivalent droop coefficient, and a steady-state frequency under a specific disturbance is determined through the shift of the steady-state frequency of the power system; The deviation of the steady-state frequency of the power system is: Where Δf ∞ is the deviation of the steady-state frequency of the power system after the disturbance; ΔP d is the disturbance power of the power system.

7. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 6, characterized in that: The equivalent droop coefficient of the power system is: In the formula, R i represents the droop coefficient of power supply i, R eq Represents the equivalent droop coefficient of the power system.

8. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency according to any one of claims 1 to 7, characterized in that: The process of alternately calculating the frequency difference and unbalanced power of each node in S3 includes the following steps: The formula for calculating the frequency difference between nodes is determined according to the DC power flow method: Among them, Δf ij represents the difference in frequency between node i and node j, B RN is the system admittance matrix of node contraction, ΔP ij is the electromagnetic power increment transmitted from node i to node j; Δt represents the time change, which is used to represent the iteration step; Then, based on the frequency difference formula between nodes, the frequency difference of each power node is iteratively calculated, and the unbalanced power of each node is updated according to the known inertia and droop coefficient of each node and the inter-machine transmission power; Determine whether each node has reached a uniform steady-state frequency, and if so, stop the iteration.

9. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 8, characterized in that: The conditions for determining whether each node reaches a uniform steady-state frequency are as follows: Among them, f i is the frequency of node i, f ∞ is the steady-state frequency of the system; δ1 and δ2 represent tolerances; When formula (17) is true, it means that each node reaches a uniform steady-state frequency.

10. A practical aggregation method for a power system frequency model taking into account the temporal and spatial distribution of frequency according to claim 9, characterized in that: The process of clustering the frequency difference trajectories of each node according to the calculated frequency difference trajectories of each node in S4 includes: Select the clustering condition interval [-ε,ε], ε is the clustering cutoff point, and the clustering condition is: When formula (18) is satisfied, the frequency trajectories of node i and node j are similar, and the frequency models of node i and node j are aggregated.

Images