A method for optimizing division of an urban multi-level local power grid disaster island boundary

Abstract

The application provides a kind of urban multi-level local power grid disaster island boundary optimization division method.The method comprises the following steps: analyzing the characteristics of urban multi-level local power grid from the source network load three angles, based on the existence of power flow transmission limit between different voltage levels in urban multi-level local power grid, the boundary division principle of urban multi-level local power grid is established;The constraint condition of the boundary optimization division model of urban multi-level local power grid is set, based on the principle of local power grid boundary division, linearization branch power flow constraint and dynamic response ability demand constraint, the boundary optimization division model of urban multi-level local power grid is established;The boundary optimization division model is solved by using the solver, and the boundary division result of urban multi-level local power grid is obtained.The application combines the limit of power flow transmission between different voltage levels of urban local power grid, and formulates the boundary optimization division strategy of multi-resource cooperation, to ensure that urban local power grid forms the optimal partition after extreme event.

Description

Technical Field

[0001] This invention relates to the field of power grid boundary delineation technology, and in particular to an optimized delineation method for island boundaries in urban multi-level local power grid disasters. Background Technology

[0002] Urban power grids are typically load centers with high load density. To limit system short-circuit currents and other factors, urban power grids are generally operated in zones. These zoned grids are usually centered around 500kV substations and supplied power through a 220kV network. These zoned grids rely on the 500kV grid for power and transmit power through the 220kV network. A 220kV ring network is formed within each zone, with a certain number of generating units and mutual power supply capabilities. Each level of local grid has independent operating capabilities. When extreme events cause severe faults, a zone can be switched to islanded operation mode based on the actual situation, providing multiple power supply guarantees for critical loads through flexible islanded operation of local grids.

[0003] Currently, existing research methods for active disconnection of large power grids and flexible islanding of active distribution networks include: active disconnection research mainly targets the generator grouping problem caused by out-of-synchronization oscillations, focusing on transmission networks with voltage levels above 220kV; active distribution network islanding research focuses on distribution networks with voltage levels of 110kV and below. The drawbacks of these existing methods include: they focus on single-voltage-level power grids, while urban local power grids cover multiple voltage levels, and there are mutual influences between lines and power flow transmission at different voltage levels. Summary of the Invention

[0004] The embodiments of the present invention provide a method for optimizing the delineation of island boundaries in urban multi-level local power grid disasters, so as to effectively optimize the delineation of island boundaries in urban multi-level local power grid disasters.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] A method for optimizing the boundary delineation of isolated power grid islands during urban multi-level local power grid disasters includes:

[0007] This paper analyzes the characteristics of urban multi-level local power grids from the perspectives of source, grid, and load. Based on the power transmission constraints between different voltage levels in urban multi-level local power grids, it establishes the boundary delineation principle for urban multi-level local power grids.

[0008] The constraints of the boundary optimization partitioning model of the urban multi-level local power grid are set. These constraints include dynamic response capability requirement constraints, branch power flow constraints considering interruption, node power balance constraints, line capacity constraints, node voltage constraints, and unit output constraints.

[0009] Based on the principles of local power grid boundary delineation, linearized branch power flow constraints, and dynamic response capability requirements, a boundary optimization delineation model for urban multi-level local power grids based on an AC power flow model is established with the goal of minimizing load control costs.

[0010] The boundary optimization partitioning model is solved using a solver to obtain the boundary partitioning results of the urban multi-level local power grid.

[0011] Preferably, the analysis of the characteristics of urban multi-level local power grids from the perspectives of source, grid, and load, based on the power flow transmission constraints existing between different voltage levels in urban multi-level local power grids, establishes boundary delineation principles for urban multi-level local power grids, including:

[0012] From the perspective of the power supply side of a multi-level urban local power grid, the steady-state and dynamic support capabilities of the internal power supply required for emergency control of the local power grid are considered. From the perspective of the power grid, the backbone network connecting multiple source-load pairs is considered with differentiated reinforcement, and in principle, it is necessary to ensure that the distance between the power supply and the load is as close as possible. From the perspective of load measurement, important loads cannot be guaranteed by lower-level power supplies, and power supplies cannot be guaranteed through lines of the next higher voltage level. The multi-level power grid needs to meet the conditions of the number of connected lines and the direction of power flow transmission. The boundary delineation principles for the multi-level urban local power grid are as follows:

[0013] Condition 1: When the upstream substation is available, the downstream power grid can be powered by a maximum of one upstream substation;

[0014] Condition 2: When the upstream substation loses power, it is unable to transmit electrical energy to the downstream distribution network;

[0015] Condition 3: The lower-level substation is unable to supply power to the upper-level power grid;

[0016] Condition 4: The distribution network at all levels is operating in an open-loop manner.

[0017] Preferably, the dynamic response capability requirements constraints for the urban multi-level local power grid boundary optimization partitioning model include:

[0018]

[0019] In the formula: f RoCoF , ROCOF represents the rate of change of frequency after disturbance and the safety limit; f0 is the frequency reference value; ΔP e，m For the power deficit of local power grid m; ΔP L，m Let H be the load shedding power of local power grid m; H be the equivalent inertia of local power grid m; H i H n These represent the inertial constants of the synchronous generator unit G and the inverter interface power supply E, respectively. These indicate whether synchronous generator unit i and inverter interface power supply n belong to the local power grid m, respectively. The power-frequency regulation response power of synchronous machine i; The fast frequency response power of the inverter interface power supply n; Δf max Indicates the maximum allowable frequency deviation of the system; t E t G These represent the complete response time of the inverter interface power supply and the synchronous generator, respectively.

[0020] Equations (2)-(6) are used to evaluate whether the dynamic frequency support capability of the local power grid under each disconnectable line meets the frequency security constraints. The relationship shown in equations (2)-(6) is described by the BigM method, as shown in equations (7)-(11):

[0021]

[0022] -(1-β m )·M≤a m ≤(1-β m )·M (11)

[0023] Where: β m This is a 0-1 integer variable, representing whether the local power grid dynamic response capability under this boundary meets the safety constraints; a value of 1 indicates that it does not. m This represents the line state variables corresponding to the boundary of the local power grid m, and is related to a in the following text. ij They are the same variable; M is an integer.

[0024] Preferably, the branch power flow constraints considering disconnection in the urban multi-level local power grid boundary optimization partitioning model include:

[0025] The transformer line is configured to allow power flow only from the side with the higher voltage level to the side with the lower voltage level. The formula for the injected power at the AC power flow node is as follows:

[0026]

[0027] In the formula: P i Injecting active power into node i; Q i Inject reactive power into node i; G ij and B ij The elements Y of the nodal admittance matrix are respectively ij The real and imaginary parts; θ ij U represents the voltage phase difference between node i and node j, respectively; i The branch power expression for AC power flow represents the voltage magnitude at node i.

[0028]

[0029] When the line is open, the branch power is zero; when the line is closed, the branch power is calculated according to equation (13), and the branch power flow constraints are modeled based on the BigM method:

[0030] a ij =1,(i,j)∈S U (14)

[0031]

[0032] In the formula: a ij This indicates the open / closed state of the circuit; a value of 0 indicates the circuit is open, and a value of 1 indicates the circuit is closed. ij Q ij Let S be the active and reactive power of the line from node i to node j; M is a large positive integer; S U S C S T These represent the sets of serial numbers for non-disconnectable lines, disconnectable lines, and lines containing transformers, respectively.

[0033] Equation (14) indicates that for a non-disconnectable line, a ij The variable is preset to 1. For disconnectable lines, only equations (14)-(16) need to be satisfied. For lines with transformers, in addition to satisfying equations (15) and (15), the following also needs to be satisfied:

[0034]

[0035] Equation (17) indicates that for a transformer branch, the power flow direction can only flow from the side with a higher voltage level to the side with a lower voltage level.

[0036] Equation (15) is modeled using a linearized power flow model, as shown in Equation (18):

[0037]

[0038] Preferably, the node power balance constraints, line capacity constraints, node voltage constraints, and unit output constraints of the urban multi-level local power grid boundary optimization partitioning model include:

[0039] For actual transformer branches, a configuration is constructed including adjustable ratio coefficient t and phase shift angle θ. s The model, using Y ij The line admittance parameter is represented by t, the actual transformer ratio coefficient is represented by θ. s The phase adjustment amount generated by the phase shifter is represented by the voltage vector of node i in the original model being equivalently replaced by the voltage parameter of node A. By substituting into equation (18), a branch power analytical model including the dynamic characteristics of the phase-shifting transformer is constructed, which characterizes the relationship between the turns ratio adjustment (t) and the phase shift angle (θ).s The active / reactive power transmission equations under coupling are shown in equation (19):

[0040]

[0041] For lines that do not contain transformers, equation (15) can ultimately be linearized to equation (20) for calculation:

[0042]

[0043] Set the node power balance constraint as follows:

[0044]

[0045] In the formula: P G，i，0 Q G，i，0 Let ΔP be the initial active and reactive power of the distributed power source or power plant connected to node i, respectively. G，i ΔQ G，i These represent the active and reactive power generated by the distributed power source or power plant at access node i, respectively; P L，i Q L，i These represent the active and reactive loads at node i, respectively; ΔQ L，i This represents the reactive power of the load removed from node i.

[0046] Set the line capacity constraint as follows:

[0047]

[0048] In the formula: P ij，max P ij，min Q ij，max Q ij，min These are the upper and lower limits for active power flow and reactive power flow, respectively.

[0049] Set the node voltage and phase angle constraints as follows:

[0050] U i,min ≤U i ≤U i,max (twenty three)

[0051] θ i,min ≤θ i ≤θ i,max (twenty four)

[0052] In the formula: U i，max U i，min These are the upper and lower limits of the voltage amplitude at node i, respectively; θ i，max θ i，min These are the upper and lower limits of the voltage phase angle at node i, respectively;

[0053] Set the unit output constraint as follows:

[0054] P G,i,min ≤P G,i,0 +ΔP G,i ≤P G,i,max (25)

[0055] Q G,i,min ≤Q G,i,0 +ΔQ G,i ≤Q G,i,max (26)

[0056] In the formula: P Gi，max P Gi，min Q Gi，max Q Gi，min These represent the upper and lower limits of active and reactive power output of power generation resources, respectively.

[0057] Preferably, the boundary optimization partitioning model based on the principle of local power grid boundary division, linearized branch power flow constraints, and dynamic response capability demand constraints, with the objective of minimizing load control costs, and based on the AC power flow model, includes:

[0058] With the goal of minimizing load control costs, the objective function of the boundary optimization partitioning model for a multi-level urban local power grid is set as follows:

[0059]

[0060] In the formula: ω i =100, 10, 0.2 represent different load weights, with larger values ​​indicating higher weights; ΔP L,i N represents the active power of the load removed from node i; L The number of loads in the system;

[0061] Based on the principles of local power grid boundary delineation, linearized branch power flow constraints, dynamic response capability requirement constraints, and objective function, a boundary optimization delineation model based on the AC power flow model is established with the goal of minimizing load control costs, as follows:

[0062]

[0063] The decision variables of the boundary optimization partitioning model include:

[0064] 1) Line open / closed state (a);

[0065] 2) Emergency load shedding (ΔP) L ΔQ L );

[0066] 3) Power flow variables (P, Q) of the line;

[0067] 4) Active and reactive power adjustment of the unit (ΔP) G ΔQ G );

[0068] 5) Auxiliary variables (β) for assessing dynamic response capability;

[0069] 6) Node voltage magnitude and phase angle variables (U, θ), where 1) and 5) are 0-1 variables, and the rest are continuous variables.

[0070] As can be seen from the technical solutions provided by the embodiments of the present invention above, the present invention combines the limitations of power flow transmission between different voltage levels of the urban local power grid with the dynamic response capability of the local power grid, and formulates a boundary optimization partitioning strategy with multi-resource coordination to ensure that the urban local power grid forms the optimal partition after extreme events.

[0071] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0072] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0073] Figure 1 The flowchart illustrates a method for optimizing the delineation of isolated boundaries during urban multi-level local power grid disasters, as provided in an embodiment of the present invention.

[0074] Figure 2 This is a schematic diagram of a multi-level local power grid provided in an embodiment of the present invention;

[0075] Figure 3 This is a schematic diagram of an ideal transformer model provided for an embodiment of the present invention.

[0076] Figure 4 A topology diagram of a local power grid in a city established for an embodiment of the present invention;

[0077] Figure 5 This is a schematic diagram of boundary division in the operating state of a local power grid after it enters islanded operation, provided by an embodiment of the present invention.

[0078] Figure 6 This is a schematic diagram illustrating the division of the lower boundary of multiple faults in the operating state after a local power grid enters islanded operation, as provided in an embodiment of the present invention. Detailed Implementation

[0079] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0080] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or couplings. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0081] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0082] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments. These embodiments do not constitute a limitation on the embodiments of the present invention.

[0083] The processing flow of the method for optimizing the delineation of island boundaries in a multi-level local power grid disaster in an urban area provided by this invention is as follows: Figure 1 As shown, the processing steps include the following:

[0084] Step S10: Analyze the characteristics of urban multi-level local power grids from the perspectives of source, grid, and load. Based on the power flow transmission constraints between different voltage levels in the multi-level local power grid, establish the principle for delineating the local power grid boundaries of the urban multi-level local power grid.

[0085] Step S20: For the grid topology of multi-level urban local power grid, consider the turns ratio and phase shift angle of the ideal transformer model to establish linearized branch power flow constraints considering line interruption, and consider the maximum frequency change rate and the minimum frequency point index to establish dynamic response capability requirement constraints.

[0086] Step S30: Based on the principle of the local power grid boundary division, the linearized branch power flow constraints and the dynamic response capability requirement constraints, establish a boundary optimization division model based on the AC power flow model with the goal of minimizing load control costs.

[0087] Step S40: Use a solver to solve the above boundary optimization partitioning model to obtain the boundary partitioning results of the urban multi-level local power grid.

[0088] Finally, the effectiveness of the proposed island boundary optimization partitioning method was verified in a local urban power grid example.

[0089] A schematic diagram of a multi-level local power grid provided in this embodiment of the invention is shown below. Figure 2 As shown, it includes a three-tiered local power grid system consisting of "urban zone power grid - local distribution network - microgrid (group)", covering voltage levels from 220kV to 380V. Nodes and lines of different voltage levels are represented by different colors, and the power grids at each level are connected via transformers.

[0090] Figure 2 In this system, power sources include gas-fired power plants, oil-fired power plants, and coal-fired power plants connected to 220kV; thermal power plants, energy storage power stations, wind farms, and photovoltaic power stations connected to 110kV or 35kV; and distributed power sources connected to 10kV or 380V. Each line in the power system is equipped with protective switches or circuit breakers. These switches or circuit breakers automatically cut off current in the event of a fault (such as a short circuit or overload) to prevent equipment damage or a wider system failure. Normal, non-faulty interruptions are typically performed by personnel or automated systems according to dispatch commands. Modern power systems employ automation technology for control and monitoring. When a system fault occurs or requires adjustment, intelligent devices can automatically detect the problem and disconnect the circuit, reducing the risk of human intervention. Figure 2 The sections indicated by the different colored boxes represent local power grids of different voltage levels with islanding capabilities. Solid rectangles represent circuit breakers; disconnecting these circuit breakers creates an islanded local power grid. Islanding switching boundaries are pre-determined based on the multi-level local power grid partitioning and defense resource deployment results, primarily including the connection channels between different power grid levels, and pre-assessing whether the lower-level power grid can survive independently as an island after the channel is disconnected. After extreme events occur, the optimal zoning control scheme needs to first... Figure 2 The system makes decisions about whether to disconnect each circuit breaker, specifically determining whether islanding is necessary and the appropriate islanding switch location. Emergency control measures are required to ensure safety after a circuit breaker disconnects. Figure 2 The local power grid within the colored box can be successfully switched to islanded operation.

[0091] The boundary delineation principles for the established multi-level local power grid in the city are as follows: First, from the power supply side, it is necessary to consider the internal power supply steady-state support capacity and dynamic support capacity required for emergency control of the local power grid; from the power grid side, it is necessary to consider the differentiated reinforcement of the backbone network connecting multiple source-load pairs, and in principle, it is necessary to ensure that the distance between the power supply and the load is as close as possible. From the load measurement perspective, the local robust grid of the regional power grid needs to cover all important loads. In addition, important loads may be connected to different voltage levels. Considering the differences in power supply capacity and capability at different levels, the following principle is determined: important loads cannot be guaranteed by lower-level power supplies, that is, loads cannot be guaranteed through lines of the next lower voltage level, and power supplies cannot be guaranteed through lines of the next higher voltage level. Furthermore, to ensure that the multi-voltage level power grid maintains radial operation, the multi-level power grid also needs to meet the conditions of the number of connected lines and the direction of power flow transmission, specifically:

[0092] Condition 1: When the upstream substation is available, the downstream power grid can be powered by a maximum of one upstream substation;

[0093] Condition 2: When the upstream substation loses power, it is unable to transmit electrical energy to the downstream distribution network;

[0094] Condition 3: The lower-level substation is unable to supply power to the upper-level power grid;

[0095] Condition 4: The distribution network at all levels is operating in an open-loop manner.

[0096] The characteristics of urban power grids at various levels are summarized below:

[0097] 1: Overview of the characteristics of urban 220kV transmission networks

[0098] On the source side: The 220kV transmission network is located in the middle of the urban power grid, connecting large generating units from the upper-level transmission network and distributed power sources from the lower-level regional power grid. The types of power sources it connects to include gas turbine units, coal-fired units, and offshore wind power. Gas turbine units have an installed capacity of over 100MW and feature rapid start-up and shutdown, capable of completing start-up and shutdown operations within minutes, providing flexible peak-shaving and frequency regulation services to the grid and effectively responding to short-term load fluctuations. Coal-fired units continue to play a role in stabilizing loads in some areas, with individual synchronous turbine units typically having capacities in the hundreds of MW range.

[0099] On the grid side: The urban 220kV power grid structure presents two forms: radial, ring, and a combination of radial. Power is supplied by one or more upstream 500kV substations. Each 220kV zone operates normally and independently, with balanced internal power supply, and can transfer power in case of a fault. Due to short-circuit current limitations, the 220kV topology of the city center zone is radial. Other zone power grids, due to their relatively vast geographical areas, operate with a ring + radial configuration.

[0100] Load side: The 220kV transmission network is mainly used to transmit electricity from power plants or large substations to regional load centers or urban power grids. Load types mainly include medium-sized industrial loads and commercial loads. Individual load demand typically ranges from 50MW to 300MW, primarily consisting of medium-sized industrial parks, large commercial areas, and residential areas. The 220kV power grid experiences significant load fluctuations, influenced not only by common diurnal load variations but also by seasonal changes. For example, during peak summer air conditioning and winter heating periods, grid load demand increases dramatically. Simultaneously, with the grid integration of distributed renewable energy sources (such as wind and solar power), the 220kV transmission network must also cope with fluctuating loads from renewable energy sources, posing new challenges to grid stability.

[0101] 2: Overview of the characteristics of urban 110 / 35kV distribution networks

[0102] Source side: Centralized power sources connected to the 110 / 35kV high-voltage distribution network include small gas-fired power plants, coal-fired power plants and combined heat and power plants, while distributed power sources include gas-fired power plants, combined heat and power plants, wind farms, photovoltaic power stations, energy storage power stations, user-provided power sources, mobile emergency power generation vehicles, mobile energy storage vehicles, electric vehicles, etc.

[0103] On the grid side: The typical architecture of urban 110 / 35kV high-voltage distribution networks mainly includes three topologies: radial, ring, and chain. The radial structure (single-source power supply mode) connects to the substation busbar (or bridging device) via a single / double-circuit line from the upstream power supply hub. It is divided into single-line radial and double-line radial types based on line configuration. This architecture exhibits good scalability due to its simplified wiring, but the single-source power supply characteristic limits system reliability. It is typically used in areas with low energy demand or moderate power supply reliability requirements, and can also serve as a transitional solution for insufficient power supply points in the early stages of grid construction. The ring topology adopts a single-side power supply multi-level series connection mode, connecting multiple substations sequentially through the ring network lines before closing the loop to the starting power source. In actual operation, open-loop management is often implemented at the central node of the ring network. This structure can be divided into single-ring / double-ring configurations, offering advantages such as flexible power supply point deployment and strong scalability. However, it is limited by the single-source power supply characteristic of N-power-one-backup wiring (N cable lines connected to form a cable ring network, with another line serving as a common backup line), which can be summarized as a composite series power supply form. Chain topology employs a dual-power, multi-node interconnection mode, distributing power from different power hubs to the substation busbars via multiple circuits, and achieving a closed loop of multiple power supply points at the end through tie lines. Based on the number of tie lines, it can be divided into single-chain, double-chain, and multi-chain structures. Its significant features are flexible operation and outstanding power supply reliability, but the need for more outgoing circuits leads to higher infrastructure investment costs. Therefore, it is mostly deployed in key areas with high load density and stringent power supply reliability requirements, such as commercial core areas and administrative centers.

[0104] Load side: The 110 / 35kV high-voltage distribution network mainly consists of medium-sized industrial users, commercial users, large public facilities, and some residential areas. The capacity of a single load center is generally between 10MW and 100MW. For example, the electricity demand of medium-sized industrial parks (such as food processing plants, chemical plants, and small machinery manufacturing plants) and large commercial complexes (such as shopping malls, supermarkets, and office buildings) is concentrated at this voltage level. At the same time, this grid also provides power support for some infrastructure, such as large hospitals, data centers, and transportation hubs, whose electricity demand is also relatively stable and large.

[0105] The load fluctuations of the 110 / 35kV distribution network are significantly affected by seasonality and weekday / holiday electricity consumption patterns, especially during the high temperatures of summer when the use of equipment such as air conditioners leads to a sharp increase in load. The differences in demand between industrial loads and commercial and residential electricity consumption at different times result in obvious peak-valley fluctuations in the distribution network load.

[0106] 3: Overview of the characteristics of urban 10kV distribution networks

[0107] On the source side: The 10kV medium-voltage distribution network primarily serves urban commercial, residential, and some small and medium-sized enterprise users. The power sources connected at this voltage level are mainly energy storage, electric vehicle charging and battery swapping stations, and flexible loads. Energy storage is a key component of the 10kV distribution network, possessing peak-shaving and valley-filling capabilities. By storing electrical energy during off-peak periods and releasing it during peak periods, it smooths the power load curve. Electric vehicle charging and battery swapping stations are gradually becoming important loads in the 10kV distribution network, and also possess vehicle-to-grid (V2G) capabilities, further enhancing the grid's flexibility by transmitting power back to the grid when needed. Flexible loads, through demand response management, balance supply and demand by flexibly adjusting electricity demand when load fluctuations are significant.

[0108] On the grid side: Medium-voltage distribution network structures are divided into two types: overhead grid structure and cable grid structure. These two grid structures can be summarized into three connection methods: single-power supply, series supply, and composite series supply. The radial type of overhead grids and the single-radial and double-radial types (single-radial type with an additional circuit) of cable grids can be classified as single-power supply structures. The multi-segment single-tie of overhead grids and the through-beam, single-loop (with a break at a point forming an open loop), and double-loop (with an additional circuit on top of the single-loop) connections of cable grids can be classified as series supply structures. The multi-segment moderate-tie of overhead grids and the N-supply-one-backup connection of cable grids (N cable lines connected to form a cable ring network, with another line serving as a common backup line) can be summarized as composite series supply forms.

[0109] On the load side: The 10kV medium-voltage distribution network serves small and medium-sized commercial users, residential users, and small industrial users. The load capacity is relatively dispersed and varies considerably. The capacity of each load point typically ranges from several hundred kW to several MW. Specifically, the load capacity of small commercial users is generally 0.5MW to 3MW, such as shopping malls, catering facilities, and offices; the load capacity of small industrial users is typically 1MW to 5MW, such as small manufacturing plants and processing plants; the load capacity of residential areas is generally 2MW to 10MW, and some large residential areas or communities can reach over 20MW. The load connected to the 10kV voltage level exhibits strong diurnal fluctuations. For example, residential and commercial electricity loads mainly peak during the day and evening peak hours, while industrial loads differ between weekdays and weekends. In winter and summer, load fluctuations are more pronounced due to the use of heating and air conditioning equipment. Simultaneously, the 10kV distribution network is increasingly connecting to more distributed energy sources, such as rooftop photovoltaics. These clean energy sources are unstable and may lead to reverse feedback, thus increasing the difficulty of load management for the power grid.

[0110] In summary, Table 1 summarizes the main characteristics of the power grid source, grid, and load sides at various levels of the city.

[0111] Table 1 Summary of the characteristics of urban power grids at different levels

[0112]

[0113]

[0114] Boundary optimization partitioning model for urban multi-level local power grids

[0115] objective function

[0116] The objective function takes into account the importance of active power load and aims to minimize the weighted sum of active power load shelving amounts, i.e.:

[0117]

[0118] In the formula: ω i =100, 10, 0.2 represent different load weights, with larger values ​​indicating higher weights; ΔP L,i N represents the active power of the load removed from node i; L This represents the number of loads in the system.

[0119] Constraints

[0120] The constraints of the urban multi-level local power grid boundary optimization partitioning model include dynamic response capability requirement constraints, branch power flow constraints considering interruption, node power balance constraints, line capacity constraints, node voltage constraints, and unit output constraints.

[0121] Dynamic response capability requirements of local power grid

[0122] The key frequency security indicators for urban local power grids considered during boundary delineation include the rate of frequency change and the frequency minimum. Different types of power sources can be deployed in a coordinated and optimized manner to ensure the system's ability to maintain frequency stability even under extreme conditions.

[0123]

[0124] In the formula: f RoCoF , The ROCOF (Rate of Change of Frequency) after disturbance and the safety limit; f0 is the frequency reference value; ΔP e，m For the power deficit of local power grid m; ΔP L，m Let H be the load shedding power of local power grid m; H be the equivalent inertia of local power grid m; H i H n These represent the inertial constants of the synchronous generator unit G and the inverter interface power supply E, respectively. These indicate whether synchronous generator unit i and inverter interface power supply n belong to the local power grid m, respectively. The power-frequency regulation response power of synchronous machine i; The fast frequency response power of the inverter interface power supply n; Δf max Indicates the maximum allowable frequency deviation of the system; t E t G These represent the complete response time of the inverter interface power supply and the synchronous unit, respectively.

[0125] Equations (2)-(6) can evaluate whether the dynamic frequency support capability of the local power grid under each disconnectable line meets the frequency safety constraints, ensuring that each local power grid can meet the dynamic frequency safety operation of the system. If the above safety constraints are not met, the line cannot be disconnected, which means that it is impossible to form a local power grid from that point. The above relationship can be described by the BigM method, as shown in equations (7)-(11):

[0126]

[0127] -(1-β m )·M≤a m ≤(1-β m )·M (11)

[0128] Where: β m This is a 0-1 integer variable, representing whether the local power grid dynamic response capability under this boundary meets the safety constraints; a value of 1 indicates that it does not. m This represents the line state variables corresponding to the boundary of the local power grid m, and is related to a in the following text.ij They are the same variable; M is a very large integer.

[0129] This invention classifies and models whether a line can be disconnected. Whether a line can be disconnected is predetermined by the divisible boundaries of a multi-level local power grid plan; not every line can be disconnected to form a local power grid. For lines that can be disconnected, further classification is needed based on whether a transformer exists. A transformer determines whether the power flow can flow upwards on that line. This invention assumes that lines with transformers only allow power flow from the higher voltage level side to the lower voltage level side. First, the formula for the AC power flow node injection power is established as follows:

[0130]

[0131] In the formula: P i Injecting active power into node i; Q i Inject reactive power into node i; G ij and B ij The elements Y of the nodal admittance matrix are respectively ij The real and imaginary parts; θ ij U represents the voltage phase difference between node i and node j, respectively; i Let represent the voltage magnitude at node i. Correspondingly, the branch power expression for AC power flow is:

[0132]

[0133] When the line is open, the branch power is zero; when the line is closed, the branch power is calculated according to equation (13). Utilizing the if…then… logic of line opening and closing, this invention models branch power flow constraints based on the Big M method:

[0134] a ij =1,(i,j)∈S U (14)

[0135]

[0136] In the formula: a ij This indicates the open / closed state of the circuit; a value of 0 indicates the circuit is open, and a value of 1 indicates the circuit is closed. ij Q ij Let S be the active and reactive power of the line from node i to node j; M is a large positive integer; S U S C S T These represent the sets of serial numbers for non-disconnectable lines, disconnectable lines, and lines with transformers, respectively.

[0137] Equation (14) indicates that for a non-disconnectable line, a ijThe variable is preset to 1. For disconnectable lines, only equations (14)-(16) need to be satisfied. For lines with transformers, in addition to satisfying equations (15) and (15), the following also needs to be satisfied:

[0138]

[0139] Equation (17) indicates that for a transformer branch, the power flow direction can only flow from the side with a higher voltage level to the side with a lower voltage level.

[0140] Since equation (15) is nonlinear, in order to improve the computational efficiency of the model, this invention adopts a linearized power flow model for modeling, as shown in equation (18):

[0141]

[0142] The following extends the general transformer modeling method based on the linear power flow model. The original model sets the transformer turns ratio to a constant per-unit value and ignores the phase shift angle. A schematic diagram of an ideal transformer model provided in this embodiment of the invention is shown below. Figure 3 As shown. This invention constructs a transformer branch with adjustable transformation ratio coefficient t and phase shift angle θ. s A refined model. For example... Figure 3 The improved branch topology shown is given, where Y ij Characterizing the line admittance parameter, t represents the actual transformer turns ratio coefficient, θ s This refers to the phase adjustment amount generated by the phase shifter. This modeling method, by introducing a turns ratio adjustment factor and a phase compensation term, can accurately describe the dynamic adjustment characteristics of a real transformer to the power flow distribution of the system.

[0143] To introduce the turns ratio parameters and phase angle offset of an ideal phase shifter into the existing linearized power flow model framework, it is only necessary to replace the voltage vector of node i in the original model with the voltage parameter of node A. By substituting into equation (18), a branch power analytical model including the dynamic characteristics of the phase-shifting transformer can be constructed, accurately characterizing the turns ratio adjustment (t) and phase angle (θ). s The active / reactive power transmission equations under coupling are shown in equation (19):

[0144]

[0145] In summary, for any line, whether or not it includes a transformer, equation (15) can ultimately be linearized into equation (20) for calculation:

[0146]

[0147] Node power balance constraints

[0148]

[0149] In the formula: P G，i，0 Q G，i，0 These represent the initial active and reactive power of the distributed power source or power plant connected to node i, respectively. ΔP G，i ΔQ G，i These represent the active and reactive power generated by the distributed power source or power plant at access node i, respectively; P L，i Q L，i These represent the active and reactive loads at node i, respectively; ΔQ L，i This represents the reactive power of the load removed from node i.

[0150] Line capacity constraints

[0151]

[0152] In the formula: P ij，max P ij，min Q ij，max Q ij，min These are the upper and lower limits for active power flow and reactive power flow, respectively.

[0153] Node voltage and phase angle constraints

[0154] U i,min ≤U i ≤U i,max (twenty three)

[0155] θ i,min ≤θ i ≤θ i,max (twenty four)

[0156] In the formula: U i，max U i，min These are the upper and lower limits of the voltage amplitude at node i, respectively; θ i，max θ i，min These are the upper and lower limits of the voltage phase angle at node i, respectively.

[0157] Unit output constraints

[0158] P G,i,min ≤P G,i,0 +ΔP G,i ≤P G,i,max (25)

[0159] Q G,i,min ≤Q G,i,0 +ΔQ G,i ≤Q G,i,max (26)

[0160] In the formula: P Gi，max P Gi，min Q Gi，max Q Gi，minThese represent the upper and lower limits of active and reactive power output of power generation resources, respectively.

[0161] The boundary optimization partitioning model for the multi-level local power grid in the city is now complete. The decision variables for this model include:

[0162] 1) Line open / closed state (a);

[0163] 2) Emergency load shedding (ΔP) L ΔQ L );

[0164] 3) Power flow variables (P, Q) of the line;

[0165] 4) Active and reactive power adjustment of the unit (ΔP) G ΔQ G );

[0166] 5) Auxiliary variables (β) for assessing dynamic response capability;

[0167] 6) Node voltage magnitude and phase angle variables (U, θ). Among them, 1) and 5) are 0-1 variables, and the rest are continuous variables. The overall model is shown below.

[0168]

[0169] Since the control variables in the aforementioned robust local power grid emergency frequency control model involve both continuous and 0-1 variables, and the objective function and constraints are all linear, it is a mixed-integer linear programming problem. This model can be solved efficiently using mature commercial solvers.

[0170] This invention uses the Julia language's JuMP optimization toolkit in the VS Code compilation environment to model the optimization model, and calls the Gurobi (version v11.2) solver to solve it. The final solution mainly includes 1) line interruption state (a); 2) emergency load shedding amount (ΔP) L ΔQ L ); 3) Active and reactive power adjustment of the unit (ΔP) G ΔQ G ); 4) Auxiliary variables for assessing dynamic response capability (β).

[0171] Case Study: Based on the typical operation mode and topology of large urban power grids in my country, this invention establishes a case study of a local urban power grid to verify the feasibility of the proposed method. This invention uses the Julia language's JuMP optimization toolkit in the VS Code compilation environment to model the optimization model and calls the Gurobi (version v11.2) solver for the solution. The computer's CPU is an Intel Core i7-8750H with a clock speed of 2.2GHz and 16GB of memory.

[0172] The topology of a local power grid in a certain city established by this invention is as follows: Figure 4 As shown, it includes three levels: 220kV transmission network, 110 / 35kV high-voltage distribution network and 10kV medium-voltage distribution network. The power sources, lines, busbars and loads of each voltage level are distinguished by different colors.

[0173] In this local power grid example, the 220kV transmission network contains 6 substations. Substations 2, 3, and 4 are connected to the downstream power grid via three-winding transformers. The downstream power grids of the remaining 220kV substations 1, 5, and 6 are all equivalent to loads. The transmission network is connected to 2 gas turbine units. The 110 / 35kV high-voltage distribution network contains 22 substations. Each substation has loads connected via direct supply lines and downstream power grids connected via transformers. The high-voltage distribution network is connected to 2 medium-capacity gas turbine units and 1 energy storage power station. The 10kV medium-voltage distribution network contains 74 substations, connected to 3 distributed power sources and 3 energy storage power stations. Figure 3 In the diagram, SG, ES, and DG represent synchronous generators, energy storage, and distributed power sources, respectively.

[0174] Table 2 Capacity parameters of each power supply

[0175]

[0176] In this local power grid example, the total load capacity is 2400MW. It is assumed that each node contains only one type of load. The distribution of primary, secondary, and tertiary loads in the system is as follows: Figure 3 As shown.

[0177] Boundary delineation strategy analysis: The fault scenario set in this example is as follows: When an extreme event occurs, the local power grid is disconnected from the upper-level power grid at point 5 of the 220kV substation. At this time, the external power received is 1248MW, which is equivalent to the local power grid being subjected to an initial power disturbance of 1248MW at the moment of the fault.

[0178] To ensure a smooth transition of the local power grid into islanded operation mode, the output power of each distributed power source and power plant rapidly increases to its rated power. All primary and secondary loads in the system can survive, with a total survivable load capacity of 1388.97MW. The boundary delineation diagram of the local power grid after entering islanded operation, provided in this embodiment of the invention, is shown below. Figure 5 As shown.

[0179] Simulation data shows that the distributed power sources successfully maintained a continuous power supply of 1388.97MW of survivable load (including 623.4MW of primary load and 765.57MW of secondary load), reaching 57.87% of the total load capacity. In spatial analysis, the 220kV red area forms the backbone network through the boundary optimization partitioning technology proposed in this invention; the 35kV green area is independently divided to form a regional grid mainly composed of a 110kV distribution network; due to the priority given to critical load operation by upstream power transmission, and influenced by power flow transmission limitations, the 10kV blue area (including 5 microgrids) is independently divided into islanded operations. Figure 2-5 In order to improve the overall disturbance rejection capability, all levels of the power grid can be interconnected under the premise of satisfying power balance, as shown in the red background area. However, not all loads in this area can survive. In order to ensure the survival of important loads, some nodes will perform emergency load shedding. In order to improve the voltage of the end nodes and reduce unnecessary power transmission losses, the system will prioritize disconnecting loads that are far from the power source. The blue background area with independent operation contains 10kV distributed power sources, which can independently maintain the power supply of critical loads. Distributed power sources of medium and high voltage levels will prioritize supplying power to critical loads that do not have distributed power sources nearby, so as to ensure the survival of more loads.

[0180] Multiple fault scenario analysis: The fault scenario set in this example is as follows: When an extreme event occurs, the entire urban local power grid is disconnected from the upper-level power grid at point 5 of the 220kV substation, and the synchronizing machine at node 3 also goes out of operation due to a fault. At this time, the power deficit reaches 74%. The schematic diagram of the lower boundary division of multiple faults in the operating state after the local power grid enters islanded operation is shown below. Figure 6 As shown.

[0181] exist Figure 6 In the red-background area, the gas turbine unit at node 2 can only guarantee the operation of a smaller portion of the load under its substation. Since the load at node 6 has a higher weight than that at node 1, the excess power of the gas turbine unit at node 2 is used to ensure the power supply to the critical load at node 6. The secondary loads at node 1 cannot survive, but node 6 still cuts off 198MW of load. Because the gas turbine unit at node 2 has no spare power, compared to... Figure 2-5 The high-voltage distribution network under line 2-104 is independently disconnected and relies on the gas turbine unit at node 26 for independent survival. The yellow background area is the 110kV voltage level, which is the main area for independently disconnectable load power supply. This area mainly relies on the gas turbine unit at node 17 for power supply. Compared with a fault where only the upstream power transmission channel is disconnected, the power shortage is more severe in this scenario. Since the upstream grid cannot provide power, by forming a zoned grid with different voltage levels, the remaining distributed power sources, with the additional disconnection of some secondary loads, ensure that all primary loads survive, with a total surviving load of 728.97MW.

[0182] In summary, this invention has introduced the characteristics of urban 220kV transmission networks, 110 / 35kV high-voltage distribution networks, and 10kV medium-voltage distribution networks from the perspectives of source, grid, and load. Considering the differences in power capacity and capability at different levels within a multi-level local power grid, and the power flow transmission limitations between different voltage levels, a principle for delineating the boundaries of the local power grid is proposed. Then, a boundary optimization delineation model is established, taking into account dynamic capacity requirements and aiming to minimize load control costs. Finally, the effectiveness of the proposed boundary optimization delineation method is verified under multiple fault scenarios in a case study of an urban local power grid.

[0183] This invention systematically analyzes the differentiated operational characteristics of urban transmission networks and medium- and high-voltage distribution networks from three dimensions: power source type, network architecture, and load characteristics. It establishes a method for optimizing the boundary partitioning of grid islands considering voltage level coupling. Addressing the power flow transmission constraints between multi-voltage level grids, this invention innovatively proposes boundary partitioning principles, constructs a linearized power flow model, and employs linearized branch power flow modeling technology considering line interruption scenarios. By introducing the turns ratio and phase shift angle parameters of an ideal transformer model, the adaptability of the model to the actual power grid is improved. This invention innovatively incorporates the maximum rate of frequency change and the lowest frequency point as dual constraints, establishing a comprehensive constraint framework that balances static security and dynamic response. A mixed-integer programming model with the goal of minimizing load control costs is constructed to achieve efficient solutions under the AC power flow model. Finally, the effectiveness of the proposed boundary optimization partitioning method is verified in a case study of an urban local power grid.

[0184] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of one embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing the present invention.

[0185] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that the present invention can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of the present invention.

[0186] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for apparatus or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The apparatus and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0187] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for optimizing the delineation of island boundaries in urban multi-level local power grid disasters, characterized in that, include: This paper analyzes the characteristics of urban multi-level local power grids from the perspectives of source, grid, and load. Based on the power transmission constraints between different voltage levels in urban multi-level local power grids, it establishes the boundary delineation principle for urban multi-level local power grids. The constraints of the boundary optimization partitioning model of the urban multi-level local power grid are set. These constraints include dynamic response capability requirement constraints, branch power flow constraints considering interruption, node power balance constraints, line capacity constraints, node voltage constraints, and unit output constraints. Based on the principles of local power grid boundary delineation, linearized branch power flow constraints, and dynamic response capability requirements, a boundary optimization delineation model for urban multi-level local power grids based on an AC power flow model is established with the goal of minimizing load control costs. The boundary optimization partitioning model is solved using a solver to obtain the boundary partitioning results of the urban multi-level local power grid; The analysis of the characteristics of urban multi-level local power grids from the perspectives of source, grid, and load, and the establishment of boundary delineation principles for urban multi-level local power grids based on the power transmission constraints between different voltage levels, including: From the perspective of the power supply side of a multi-level urban local power grid, the internal power supply steady-state support capability and dynamic support capability required for emergency control of the local power grid are considered. From the power grid side, the backbone network connecting multiple source-load pairs is considered to be reinforced in a differentiated manner, and in principle, it is necessary to ensure that the distance between the power supply and the load is less than a set value. From the perspective of load measurement, important loads cannot be guaranteed by lower-level power supplies, and power supplies cannot be guaranteed through lines of the next higher voltage level. The multi-level power grid needs to meet the conditions of the number of connected lines and the direction of power flow transmission. The boundary delineation principle of the multi-level urban local power grid is as follows: Condition 1: When the upstream substation is available, the downstream power grid can be powered by a maximum of one upstream substation; Condition 2: When the upstream substation loses power, it is unable to transmit electrical energy to the downstream distribution network; Condition 3: The lower-level substation is unable to supply power to the upper-level power grid; Condition 4: The distribution network at all levels is operating in an open-loop manner; The dynamic response capability requirements constraints for the urban multi-level local power grid boundary optimization partitioning model include: (2) (3) (4) (5) (6) In the formula: The ROCOF (Rate of Frequency Change) after disturbance and safety limits; This is the frequency reference value; For local power grid The power deficit; For local power grid The load shedding power; For local power grid The equivalent inertia; , They represent synchronous generator units. and inverter interface power supply The inertial constant; , They represent synchronous generator units. and inverter interface power supply Does it belong to a local power grid? ; The power-frequency regulation response power of synchronous machine i; The fast frequency response power of the inverter interface power supply n; Indicates the maximum allowable frequency deviation of the system; , These represent the complete response time of the inverter interface power supply and the synchronous generator, respectively. Using equations (2)-(6), we can evaluate whether the dynamic frequency support capability of the local power grid under each disconnectable line meets the frequency security constraints. The relationship shown in equations (2)-(6) is described using the BigM method, as shown in equations (7)-(11): （7） （8） （9） （10） （11） In the formula: This is an integer variable between 0 and 1, representing whether the local power grid dynamic response capability under this boundary meets the safety constraints. If it is 1, it does not meet the constraints. This represents the line state variables corresponding to the boundary of the local power grid m, as described below. They are the same variable; M is an integer.

2. The method according to claim 1, characterized in that, The branch power flow constraints considering disconnection are set in the boundary optimization partitioning model of a multi-level local power grid in a city, including: The transformer line is configured to allow power flow only from the side with the higher voltage level to the side with the lower voltage level. The formula for the injected power at the AC power flow node is as follows: （12） In the formula: P i Injecting active power into node i; Q i Inject reactive power into node i; G ij and B ij The elements Y of the nodal admittance matrix are respectively ij The real and imaginary parts; θ ij U represents the voltage phase difference between node i and node j, respectively; i The branch power expression for AC power flow represents the voltage magnitude at node i. （13） When the line is open, the branch power is zero; when the line is closed, the branch power is calculated according to equation (13), and the branch power flow constraints are modeled based on the BigM method: （14） ； （15） 16） In the formula: a ij This indicates the open / closed state of the circuit; a value of 0 indicates the circuit is open, and a value of 1 indicates the circuit is closed. ij Q ij Let S be the active and reactive power of the line from node i to node j; M is a positive integer; S is the reactive power of the line from node i to node j. U S C S T These represent the sets of serial numbers for non-disconnectable lines, disconnectable lines, and lines containing transformers, respectively. Equation (14) indicates that for a non-disconnectable line, a ij The variable is preset to 1. For disconnectable lines, only equations (14)-(16) need to be satisfied. For lines with transformers, in addition to satisfying equations (15) and (16), the following also needs to be satisfied: （17） Equation (17) indicates that for a transformer branch, the power flow can only flow from the high voltage level side to the low voltage level side; The linearized power flow model is used to model equation (15), as shown in equation (18): （18）。 3. The method according to claim 1, characterized in that, The nodal power balance constraints, line capacity constraints, nodal voltage constraints, and generator output constraints for the boundary optimization partitioning model of a multi-level local power grid in a city include: For actual transformer branches, a configuration is constructed including adjustable ratio coefficient t and phase shift angle θ. s The model, using Y ij The line admittance parameter is represented by t, the actual transformer ratio coefficient is represented by θ. s The phase adjustment amount generated by the phase shifter is represented by the voltage vector of node i in the original model, which is equivalently replaced by the voltage parameter of node A. By substituting into equation (18), a branch power analytical model including the dynamic characteristics of the phase-shifting transformer is constructed, which characterizes the relationship between the turns ratio adjustment t and the phase shift angle θ. s The active / reactive power transmission equations under coupling are shown in equation (19): （19） For lines that do not contain transformers, equation (15) can ultimately be linearized to equation (20) for calculation: （20） Set the node power balance constraint as follows: （21） In the formula: P G，i，0 Q G，i，0 Let ΔP be the initial active and reactive power of the distributed power source or power plant connected to node i, respectively. G，i ΔQ G，i These represent the active and reactive power generated by the distributed power source or power plant at access node i, respectively; P L，i Q L，i These represent the active and reactive loads at node i, respectively; ΔQ L，i This represents the reactive power of the load removed from node i. Set the line capacity constraint as follows: （22） In the formula: P ij，max P ij，min Q ij，max Q ij，min These are the upper and lower limits for active power flow and reactive power flow, respectively. Set the node voltage and phase angle constraints as follows: （23） （24） In the formula: U i，max U i，min These are the upper and lower limits of the voltage amplitude at node i, respectively; θ i， max θ i， min These are the upper and lower limits of the voltage phase angle at node i, respectively; The unit output constraint is set as follows: （25） （26） In the formula: P Gi，max P Gi，min Q Gi，max Q Gi，min These represent the upper and lower limits of active and reactive power output of power generation resources, respectively.

4. The method according to claim 3, characterized in that, The aforementioned boundary optimization partitioning model, based on the principles of local power grid boundary division, linearized branch power flow constraints, and dynamic response capability demand constraints, aims to minimize load control costs and is based on an AC power flow model. This model includes: With the goal of minimizing load control costs, the objective function of the boundary optimization partitioning model for a multi-level urban local power grid is set as follows: (1) In the formula: =100, 10, 0.2 represent different load weights, with larger values ​​indicating higher weights; This represents the active power of the load removed from node i. The number of loads in the system; Based on the principles of local power grid boundary delineation, linearized branch power flow constraints, dynamic response capability requirement constraints, and objective function, a boundary optimization delineation model based on the AC power flow model is established with the goal of minimizing load control costs, as follows: （27） The decision variables of the boundary optimization partitioning model include: 1) Line open / closed status ; 2) Emergency load shedding ( , ); 3) Line power flow variables ( , ); 4) Active and reactive power adjustment of the unit ( , ); 5) Auxiliary variables for assessing dynamic response capability ; 6) Node voltage magnitude and phase angle variables ( , ), where 1) and 5) are 0-1 variables, and the rest are continuous variables.

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