A method for collaborative planning of AC-DC hybrid power grid based on secure cut set feedback

Abstract

The application provides a kind of AC-DC hybrid power grid cooperative planning method based on secure cut set feedback, it is related to power system planning and operation technical field, including: obtaining the system parameter of receiving end power grid, determine DC candidate drop point set and AC to be expanded corridor set, set the security threshold and investment budget limit of system operation;Establish a multi-dimensional security and stability constraint index system of AC-DC coupling containing static security constraint, transient voltage stability constraint and frequency stability constraint;Construct a three-layer nested optimization model, the three-layer nested optimization model includes the upper model for site selection and expansion decision, the middle model for capacity configuration and the lower model for safety check;When the lower model is checked and it is found that the security constraint is out of limit, the sensitivity of the out-of-limit quantity to the decision variable is extracted and a security cut set is constructed, until the optimal planning scheme is output when all security constraints are met and the investment cost change is less than the preset threshold.

Description

Technical Field

[0001] This invention relates to the field of power system planning and operation technology, and in particular to a collaborative planning method for AC / DC hybrid power grids based on secure cut set feedback. Background Technology

[0002] With the accelerated construction of new power systems, provincial receiving-end power grids are facing the dual challenges of continuously increasing load density and large-scale centralized feeding of high-voltage direct current (HVDC). The characteristics of AC / DC hybrid interconnection are becoming increasingly prominent. However, the traditional capacity expansion model relying on the construction of new AC lines is limited by the scarcity of transmission corridor resources and excessive short-circuit current. Although embedded DC technology has become an important means of strengthening the power grid due to its advantages such as large transmission capacity, flexible control, and no increase in short-circuit current, existing AC / DC hybrid power grid planning methods still generally suffer from defects such as the separation of planning and operational safety, insufficient quantification of AC / DC coupling safety boundaries, and lack of collaborative optimization configuration of AC / DC multi-channel capacity. It is difficult to directly incorporate multi-dimensional coupled safety and stability constraints covering static safety, transient voltage stability, and frequency stability into the optimization model during the planning stage, making it difficult to unify the economy and safety of the planning scheme. There is an urgent need for a collaborative planning method that can overcome the above-mentioned technical bottlenecks.

[0003] However, existing AC / DC hybrid power grid planning methods generally suffer from several defects, such as the separation of planning and operational safety, insufficient quantification of AC / DC coupling safety boundaries, the simple decomposition of AC / DC planning into independent sub-problems without deep coordination, and reliance on manual experience for verification and correction without an automated closed-loop feedback mechanism. These defects lead to difficulties in unifying the economy and safety of planning schemes, prominent risks to voltage support and frequency stability under large disturbances, the inability to globally optimize the capacity ratio of AC / DC channels, and low iteration efficiency with difficulty in guaranteeing convergence. Summary of the Invention

[0004] To address the shortcomings of existing AC / DC hybrid power grid planning methods, such as the disconnect between planning and operational safety, insufficient quantification of AC / DC coupling safety boundaries, the simplistic decomposition of AC / DC planning into independent sub-problems lacking deep coordination, and reliance on manual experience for verification and correction without an automated closed-loop feedback mechanism, these problems lead to difficulties in unifying the economic efficiency and safety of planning schemes, significant risks to voltage support and frequency stability under large disturbances, the inability to globally optimize the capacity ratio of AC / DC channels, and low iteration efficiency with difficulty in guaranteeing convergence. This invention provides a collaborative planning method for AC / DC hybrid power grids based on safety cut set feedback.

[0005] The technical solutions provided by the embodiments of the present invention are as follows: First aspect This invention provides a collaborative planning method for AC / DC hybrid power grids based on secure cut set feedback, comprising: S1: Obtain the system parameters of the receiving-end power grid, determine the set of DC candidate landing points and the set of AC corridors to be expanded, and set the safety threshold and investment budget for system operation; S2: Establish a multi-dimensional safety and stability constraint index system for AC / DC coupling that includes static safety constraints, transient voltage stability constraints, and frequency stability constraints; S3: Construct a three-layer nested optimization model, which includes an upper-layer model for site selection and expansion decisions, a middle-layer model for capacity configuration, and a lower-layer model for security verification. S4: When the lower-level model verification finds that the safety constraints are exceeded, extract the sensitivity of the exceeded quantity to the decision variables and construct a safety cut set. The safety cut set is then fed back to the upper-level and middle-level models as a new constraint for iterative solution until all safety constraints are met and the change in investment cost is less than the preset threshold, at which point the optimal planning scheme is output.

[0006] Second aspect

[0007] This invention provides a collaborative planning system for AC / DC hybrid power grids based on secure cut set feedback, comprising: processor; A memory storing computer-readable instructions, which, when executed by the processor, implement the AC / DC hybrid power grid collaborative planning method based on secure cut set feedback as described in the first aspect.

[0008] Third aspect

[0009] The present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the AC / DC hybrid power grid collaborative planning method based on secure cut set feedback as described in the first aspect.

[0010] The beneficial effects of the technical solutions provided by the embodiments of the present invention include at least the following: In this embodiment of the invention, by transforming multi-dimensional dynamic physical responses such as static safety, transient voltage, and frequency stability into algebraic constraints that can be directly invoked by the optimization model, the grid structure scheme is endowed with the technical gene of "born safe" from the planning source. At the same time, the constructed three-layer nested architecture effectively solves the problem of solving high-dimensional mixed integer nonlinear programming. The safety cut set feedback mechanism can quantify the simulation limit-breaking information into sensitivity cut sets and automatically feed them back to the upper-layer site selection and middle-layer capacity model, driving the scheme to automatically converge to the solution that is both safe and economically optimal within a finite number of iterations. This achieves deep synergy between embedded DC landing point selection, capacity quota, and AC channel expansion, eliminating blind investment and asset idleness. The final output planning scheme has the engineering characteristics of "withstanding large disturbances, having the best investment cost within the budget, and being able to directly guide construction". While significantly shortening the planning cycle and reducing labor costs, it effectively curbs the risk of transient overvoltage and low-frequency load shedding caused by DC blocking, providing an integrated decision-making tool with broad application value for the construction of new AC / DC hybrid receiving-end grids in power systems. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0012] Figure 1 A flowchart illustrating a collaborative planning method for AC / DC hybrid power grids based on secure cut set feedback, provided in an embodiment of the present invention; Figure 2 A flowchart illustrating the fault prediction and remaining lifetime estimation of a collaborative planning method for AC / DC hybrid power grids based on secure cut set feedback, provided in an embodiment of the present invention. Detailed Implementation

[0013] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0014] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0015] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0016] Reference manual attached Figure 1 The diagram illustrates a flowchart of a collaborative planning method for AC / DC hybrid power grids based on secure cut set feedback, provided by an embodiment of the present invention.

[0017] Reference manual attached Figure 2 The diagram illustrates a fault prediction and remaining lifetime estimation flowchart of a collaborative planning method for AC / DC hybrid power grids based on secure cut set feedback, provided by an embodiment of the present invention.

[0018] This invention provides a collaborative planning method for AC / DC hybrid power grids based on secure cut set feedback. The processing flow of this method may include the following steps: S1: Obtain the system parameters of the receiving-end power grid, determine the set of DC candidate landing points and the set of AC corridors to be expanded, and set the safety threshold and investment budget for system operation; In one possible implementation, the acquisition of system parameters of the receiving-end power grid specifically includes: acquiring the grid topology data of the receiving-end power grid, including the geographical distribution of each node, voltage level, impedance parameters of existing AC lines, and thermal stability limits; acquiring the upper and lower limits of active power output, upper and lower limits of reactive power output, speed governor and excitation system parameters of each generator; acquiring the predicted values ​​of active and reactive power of each load node; and acquiring the system reference frequency and reference capacity.

[0019] The determination of the DC candidate landing point set and the AC corridor to be expanded set specifically includes: based on the load distribution of the receiving-end power grid, the existing grid structure and the resource conditions of the transmission corridor, selecting several nodes in the load center area and the restricted area of ​​the transmission corridor as candidate landing points for embedded DC, and determining the converter type that can be selected for each candidate landing point; selecting key AC corridors whose current load rate exceeds a preset heavy load threshold as candidate corridors to be expanded, and obtaining the unit length cost of each candidate AC line to be expanded.

[0020] The safety thresholds and investment budget for setting system operation specifically include: the upper and lower limits of the normal operating range of node voltages, the transmission thermal stability limits of each AC line, the minimum allowable effective short-circuit ratio of multiple DC feeders, the maximum allowable transient overvoltage, the maximum allowable frequency change rate of the system, the minimum steady-state frequency limit, the minimum safe transient frequency limit, and the total investment budget.

[0021] Optionally, the system parameters also include the rotational inertia time constant of each generator, the droop coefficient and response time constant of the speed governor, and the frequency regulation effect coefficient of the load.

[0022] The heavy load threshold can be set to 70% to 80% of the rated transmission capacity of the line according to the power grid operation regulations.

[0023] It should be noted that the converter types mentioned include at least voltage source converters (VSC) and grid-commutated converters (LCC). Different types of converters have different investment costs, reactive power compensation requirements, and fault ride-through characteristics, and participate in the optimization as discrete selection variables in the subsequent location decision of the upper-level model.

[0024] S2: Establish a multi-dimensional safety and stability constraint index system for AC / DC coupling that includes static safety constraints, transient voltage stability constraints, and frequency stability constraints; Specifically, the static safety constraints include: under normal operation and anticipated fault set, the apparent power of each AC line does not exceed its thermal stability limit, and the voltage amplitude of each node is kept within the preset safe upper and lower limits.

[0025] In one possible implementation, the transient voltage stability constraint includes a multi-DC-feed effective short-circuit ratio constraint and a transient overvoltage constraint: The effective short-circuit ratio constraint for multiple DC feeds is: the effective short-circuit ratio of multiple DC feeds at each DC landing point is not lower than a preset minimum limit. The transient overvoltage constraint is: the extreme value of transient overvoltage of AC bus voltage of each converter station within a specified time window after the fault is cleared does not exceed the preset maximum limit.

[0026] The frequency stability constraints include initial frequency change rate constraints, steady-state frequency deviation constraints, and transient extremely low frequency constraints. The initial frequency change rate constraint is: the absolute value of the initial frequency change rate of the system at the instant of disturbance does not exceed the preset maximum allowable value; The steady-state frequency deviation constraint is: when the system enters steady state after a frequency modulation operation is completed after the disturbance, the steady-state frequency shall not be lower than the preset minimum limit. The transient extremely low frequency constraint is as follows: the lowest point of the transient frequency after the fault is used as the verification object of the time domain simulation of the lower-level model. When the simulation shows that the lowest point of the transient frequency is lower than the preset safety bottom line, the sensitivity cut set of the system inertia and reserve capacity is constructed and fed into the upper-level model in step S4.

[0027] It is understandable that the aforementioned static safety constraints, transient voltage stability constraints, and frequency stability constraints together constitute a multi-dimensional safety and stability constraint index system for AC / DC coupling. Specifically, static safety constraints address the steady-state operating point under normal operating conditions and after anticipated faults; transient voltage stability constraints address the voltage response during the transient process after fault clearance; and frequency stability constraints address the dynamic frequency response under high-power deficit disturbances. These three types of constraints, from different time scales and physical dimensions, jointly ensure the comprehensive safety of the AC / DC hybrid receiving-end power grid.

[0028] More specifically, the static safety constraint is mathematically expressed as: For each fault scenario in the normal operating mode and the anticipated fault set. Any communication line Apparent power Not exceeding its thermal stability limit ,Right now ; any node voltage amplitude Maintain within the preset safe upper and lower limits, i.e. .

[0029] The effective short-circuit ratio constraint for multiple DC feeds is mathematically expressed as: for any DC landing point Its multi-DC feed effective short-circuit ratio Equal to the short-circuit capacity of the AC bus at that point Other DC power converted by coupling impedance The ratio must be no less than a preset minimum limit. ,Right now .

[0030] The transient overvoltage constraint is mathematically expressed as: for any converter station AC bus... Within a specified time window after the fault is cleared Internal, transient overvoltage extreme values ​​of bus voltage Not exceeding the preset maximum limit ,Right now .

[0031] The initial frequency change rate constraint is mathematically expressed as: the occurrence of the anticipated DC blocking power deficit. At that time, the absolute value of the initial frequency change rate of the system does not exceed the preset maximum allowable value. ,Right now ,in The equivalent inertia of the system, This represents the system's baseline capacity.

[0032] The steady-state frequency deviation constraint is mathematically expressed as: when the system enters steady state after a single frequency modulation operation following a disturbance, the steady-state frequency... Not lower than the preset minimum value ,Right now ,in The system's rated frequency, This is the load damping coefficient. The power adjustment unit for the primary frequency modulation of the system.

[0033] S3: Construct a three-layer nested optimization model, which includes an upper-layer model for site selection and expansion decisions, a middle-layer model for capacity configuration, and a lower-layer model for security verification. In one possible implementation, S3 specifically includes: S301: The upper-level model takes minimizing the overall investment cost as the objective function and the total investment not exceeding the preset limit as the constraint. The DC landing point location decision and the AC expansion decision are both represented by discrete variables. S302: The intermediate-level model takes minimizing system operation network loss and maximizing AC / DC combined transmission efficiency as its objective function. Its constraints include at least the active power balance constraints of each node and the upper and lower limits of the operating capacity of each DC channel. Specifically, the objective function of the mid-level capacity configuration model is to minimize system operation losses and maximize the combined AC / DC transmission efficiency. The constraints of the mid-level model include: active power balance constraints for each node, i.e. The left side is the node. The generator output minus the load; the right side represents the sum of the power flow out of the AC network and the DC power injected into this node; and the upper and lower limits of the operating capacity of each DC channel, i.e. .

[0034] S303: The lower-level model substitutes the schemes output by the upper-level model and the middle-level model into the expected fault scenario for time-domain simulation, including a set of state variables such as node voltage, system frequency and frequency change rate. When any state variable exceeds the limit, the limit penalty is calculated. Specifically, the lower-level model substitutes the planning schemes (including DC landing point selection scheme, DC channel rated capacity, and AC line expansion scheme) output by the upper and middle layers into the set of anticipated fault scenarios, and uses the time-domain simulation method to solve the differential-algebraic equations of the system to obtain the time-domain response curves of state variables such as node voltage, system frequency, and frequency change rate under each scenario. When the lower-level model verification finds that any safety constraint is exceeded, it records the time of exceedance, the magnitude of exceedance, and the duration of exceedance, and calculates the penalty for exceedance.

[0035] S304: When the lower-level model verification finds that the security constraints have exceeded the limit, the cut set feedback process in step S4 is triggered; More specifically, the anticipated fault scenarios include at least a DC bipolar blocking fault and an AC N-1 line interruption fault. The DC bipolar blocking fault simulates the power deficit and voltage fluctuations in the system after a certain embedded DC channel is shut down due to a fault. The AC N-1 line interruption fault simulates the power flow transfer and voltage redistribution in the system after a certain AC line is disconnected due to a fault.

[0036] Optionally, the active power balance constraint of the nodes in the middle layer model is specifically: the sum of the active power output of the generators and the DC injection power of each node is equal to the sum of the load power of the node and the power outflow from the AC network; the upper and lower limit constraints of the operating capacity of the DC channel are specifically: the actual transmission power of each DC channel does not exceed the maximum value of its rated capacity and is not lower than the minimum value of its allowed operation.

[0037] Optionally, the anticipated fault scenarios also include AC N-2 line interruption faults and DC unipolar blocking faults to cover more stringent operating conditions.

[0038] S4: When the lower-level model verification finds that the safety constraints are exceeded, extract the sensitivity of the exceeded amount to the decision variables and construct a safety cut set. Feed the safety cut set as a new constraint to the upper-level model and the middle-level model for iterative solution until all safety constraints are met and the change in investment cost is less than the preset threshold, and output the optimal planning scheme. In one possible implementation, S4 specifically includes: S401: The sensitivity is: when performing perturbation analysis on the over-limit safety index, the finite difference ratio obtained by slightly perturbing the decision variable and re-simulating and calculating, wherein the decision variable is a decision variable that has a significant impact on the over-limit safety index and is adjustable in the middle and upper level model; S402: The safe cut set is constructed by using the sensitivity to construct a linear effective inequality about the change of the decision variables by linearly superimposing the safety index value of the current iteration point with the product of the change of each decision variable and its sensitivity.

[0039] More specifically, let the first The planning scheme obtained in the next iteration is: (Including DC landing point) DC capacity Exchange expansion (and other decision variables). Time-domain simulation is performed under a given set of anticipated faults, for the first... One over-limit safety indicator (like , , (etc.), defining exceeding limits: when the constraint is an upper limit control type, When the constraint is a lower limit control type, .like A value greater than 0 indicates that the security constraint has been breached.

[0040] Select the pair Key decision variables that have a significant impact and are adjustable in the middle and upper levels of the model (including the system's equivalent inertia) DC power at nodes (such as the operational status of key communication lines), and perform small perturbations on each variable. Then, the simulation was repeated to calculate the finite difference sensitivity: .

[0041] Using the above sensitivity, construct a linear efficient inequality with respect to changes in the decision variable as a safe cut set: (Regarding upper limit constraints) or (Regarding the lower bound constraint), where It is the set of decision variables involved in regulation.

[0042] For discrete decision variables (such as railway construction) (∈{0,1}), the above linear security cut set can be transformed into a logical cut or expressed using the Big M method. For example, when sensitivity indicates that expanding a certain line can effectively reduce transient overvoltage, its construction status is forced to 1.

[0043] The aforementioned secure cut sets are added as new constraints to the mid-level capacity configuration model to limit... , The feasible region of continuous variables, and the addition of upper-level point layout models to directly lock or exclude the selection of certain DC access points or AC corridors when the cut set contains discrete variables.

[0044] Optionally, the convergence criterion for the iterative solution in step S4 is: the safety index exceeding the limit under all anticipated failure scenarios is not greater than zero, and the change in the comprehensive investment cost obtained from two consecutive iterations is less than a preset threshold.

[0045] Specifically, the anticipated fault scenarios include at least a DC bipolar blocking fault and an AC N-1 line interruption fault.

[0046] Optionally, after the algorithm converges, the current optimal planning scheme is output. The optimal planning scheme includes at least: the construction decision (yes / no) for each candidate DC landing point, the converter type of the selected DC landing point, the rated capacity of each DC channel, the expansion decision (yes / no) for each candidate AC corridor, and the recommended operating power range for each DC channel. The above output results can be directly used for subsequent power grid engineering design and construction drawing preparation.

[0047] For example, let's take a real 39-node AC / DC hybrid receiving-end system as an example. This receiving-end system includes 10 generators, with a total load capacity of 6000MW, a total system moment of inertia of 25000MW·s, a system reference frequency of 50Hz, and a maximum total investment budget of 5 billion yuan.

[0048] Step 1: Obtain basic data and initialize the candidate set

[0049] The planning model first reads the network topology parameters, generator parameters, and load data of the system. A candidate space is established: the embedded DC candidate landing point set selects nodes 16, 21, and 23 in the load center and corridor-restricted areas as alternative access points, with candidate converter types including VSC (Flexible DC) and LCC (Conventional DC); the AC expansion corridor candidate set selects five heavy-load AC corridors, L16-17, L21-22, and L23-24, as candidate expansion lines, and inputs the unit construction cost of each candidate device.

[0050] Safety thresholds are set as follows: normal node voltage fluctuation range is 0.95 pu to 1.05 pu, and maximum AC line load rate is limited to 80%; critical multi-DC feeder effective short-circuit ratio threshold. =1.5, transient overvoltage limit = 1.3 pu; Transient ultra-low frequency safety baseline = 49.5Hz, maximum permissible frequency change rate of the system = 2.0Hz / s.

[0051] Step 2: Establish a multi-dimensional safety and stability constraint index system for AC / DC coupling.

[0052] Based on the system parameters and safety thresholds obtained in step 1, mathematical expressions for static safety constraints (AC line power not exceeding limits, node voltage not exceeding limits), transient voltage stability constraints (MIESCR not less than 1.5, transient overvoltage not exceeding 1.3 pu), and frequency stability constraints (RoCoF not exceeding 2.0 Hz / s, steady-state frequency not less than 49.5 Hz, Nadir not less than 49.5 Hz) are established according to the method in step S2 of this invention.

[0053] Step 3: Construct a three-level nested optimization model and perform the first iteration to solve it.

[0054] A three-layer nested optimization model is constructed according to the method in step S3 of this invention. The upper-layer model aims to minimize the overall investment cost, and the decision variable is the DC landing point location. ∈{0,1} and communication extension The intermediate-level model aims to minimize the network loss during system operation, with the transmission power of each DC channel as the decision variable. The lower-level model performs time-domain simulation verification under the anticipated fault scenarios.

[0055] First iteration: The planning solver performs initial optimization with the goal of minimizing investment and network losses. Since node 23 is closest to the load center and has the lowest investment for new lines, the upper-level model initially decides to build a conventional DC (LCC) line at node 23. The middle-level model allocates a rated capacity of 1000MW for this DC channel based on power flow balance, without expanding the AC lines. The above scheme is then substituted into the lower-level model for time-domain simulation verification, simulating an extreme fault of "DC bipolar blocking". Simulation results show that the MIESCRI of node 23 is only 1.35 (below the threshold of 1.5), and the 1000MW power deficit causes the system transient frequency to drop to an extremely low value of 49.2Hz (below the threshold of 49.5Hz).

[0056] Step 4: Safe cut set feedback and second iteration solution

[0057] The lower-level model calculates the sensitivity of each limit-crossing quantity to the decision variable according to the method in step S4 of this invention based on the limit-crossing quantity (MIESCR limit-crossing 0.15, frequency limit-crossing 0.3Hz), constructs a linearized safe cut set, and feeds it back to the upper and middle-level models as a new constraint.

[0058] After receiving the safety cut set feedback, the upper-level model perceived that the "virtual penalty cost" of building the substation at node 23 was extremely high, and the original plan was rejected. The algorithm was re-optimized, and the upper-level decision shifted the DC landing point to node 21, which has stronger AC grid support, and adopted the VSC flexible DC technology with better voltage support capability; the middle-level model reduced the DC capacity to 800MW and made a collaborative decision to expand a 500kV AC line (L21-22). The new plan was substituted into the time domain simulation again. The simulation results showed that the MIESCR of node 21 increased to 1.72 (greater than 1.5), the transient overvoltage was 1.15pu (less than 1.3pu), and the system frequency remained at a very low value of 49.6Hz (greater than 49.5Hz). No constraint exceedance occurred in any dimension index, the penalty term converged to zero, and the model ended the iteration.

[0059] Step 5: Output the optimal collaborative planning scheme

[0060] The system ultimately outputs the optimal planning scheme that satisfies all AC / DC coupling safety and stability constraints: a new 800MW flexible embedded DC channel is built at node 21, and AC lines L21-22 are expanded simultaneously. Calculations show that, compared to the traditional methods of "only expanding AC" or "blindly connecting DC without considering coupling constraints," this scheme saves approximately 18.5% in overall investment costs and increases the total transmission capacity of the receiving-end system by approximately 22%, while ensuring that the system does not experience serious accidents such as low-frequency load shedding and continuous commutation failures.

[0061] The beneficial effects of the technical solutions provided by the embodiments of the present invention include at least the following: In this embodiment of the invention, by transforming multi-dimensional dynamic physical responses such as static safety, transient voltage, and frequency stability into algebraic constraints that can be directly invoked by the optimization model, the grid structure scheme is endowed with the technical gene of "born safe" from the planning source. At the same time, the constructed three-layer nested architecture effectively solves the problem of solving high-dimensional mixed integer nonlinear programming. The safety cut set feedback mechanism can quantify the simulation limit-breaking information into sensitivity cut sets and automatically feed them back to the upper-layer site selection and middle-layer capacity model, driving the scheme to automatically converge to the solution that is both safe and economically optimal within a finite number of iterations. This achieves deep synergy between embedded DC landing point selection, capacity quota, and AC channel expansion, eliminating blind investment and asset idleness. The final output planning scheme has the engineering characteristics of "withstanding large disturbances, having the best investment cost within the budget, and being able to directly guide construction". While significantly shortening the planning cycle and reducing labor costs, it effectively curbs the risk of transient overvoltage and low-frequency load shedding caused by DC blocking, providing an integrated decision-making tool with broad application value for the construction of new AC / DC hybrid receiving-end grids in power systems.

[0062] This invention also provides a cooperative planning system for AC / DC hybrid power grids based on secure cut set feedback, applied to the aforementioned cooperative planning method for AC / DC hybrid power grids based on secure cut set feedback, comprising: processor.

[0063] The memory stores computer-readable instructions, which, when executed by a processor, implement the AC / DC hybrid power grid collaborative planning method based on secure cut set feedback as described in the method embodiment.

[0064] The AC / DC hybrid power grid collaborative planning system 20 based on secure cut set feedback provided by this invention can execute the above-mentioned AC / DC hybrid power grid collaborative planning method based on secure cut set feedback and achieve the same or similar technical effects. To avoid repetition, this invention will not elaborate further.

[0065] This invention provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the AC / DC hybrid power grid collaborative planning method based on secure cut set feedback as described in the method embodiment.

[0066] The computer-readable storage medium provided by this invention can implement the steps and effects of the AC / DC hybrid power grid collaborative planning method based on secure cut set feedback in the above-described method embodiments. To avoid repetition, this invention will not elaborate further.

[0067] The above description is merely a specific 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.

[0068] The following points need to be explained: (1) The accompanying drawings of the embodiments of the present invention only involve the structures involved in the embodiments of the present invention. Other structures can refer to the general design.

[0069] (2) For clarity, the thickness of layers or regions is enlarged or reduced in the drawings used to describe embodiments of the invention, i.e., these drawings are not drawn to scale. It is understood that when an element such as a layer, film, region or substrate is referred to as being “above” or “below” another element, the element may be “directly” located “above” or “below” the other element or there may be intermediate elements.

[0070] (3) Where there is no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to obtain new embodiments.

[0071] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A collaborative planning method for AC / DC hybrid power grids based on secure cut-set feedback, characterized in that, include: S1: Obtain the system parameters of the receiving-end power grid, determine the set of DC candidate landing points and the set of AC corridors to be expanded, and set the safety threshold and investment budget for system operation; S2: Establish a multi-dimensional safety and stability constraint index system for AC / DC coupling that includes static safety constraints, transient voltage stability constraints, and frequency stability constraints; S3: Construct a three-layer nested optimization model, which includes an upper-layer model for site selection and expansion decisions, a middle-layer model for capacity configuration, and a lower-layer model for security verification. S4: When the lower-level model verification finds that the safety constraints are exceeded, extract the sensitivity of the exceeded quantity to the decision variables and construct a safety cut set. The safety cut set is then fed back to the upper-level and middle-level models as a new constraint for iterative solution until all safety constraints are met and the change in investment cost is less than the preset threshold, at which point the optimal planning scheme is output.

2. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 1, characterized in that, The static safety constraints include: under normal operation and anticipated fault set, the apparent power of each AC line does not exceed its thermal stability limit, and the voltage amplitude of each node is kept within the preset safe upper and lower limits.

3. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 1, characterized in that, 。 4. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 1, characterized in that, S3 specifically includes: S301: The upper-level model takes minimizing the overall investment cost as the objective function and the total investment not exceeding the preset limit as the constraint. The DC landing point location decision and the AC expansion decision are both represented by discrete variables. S302: The intermediate-level model takes minimizing system operation network loss and maximizing AC / DC combined transmission efficiency as its objective function. Its constraints include at least the active power balance constraints of each node and the upper and lower limits of the operating capacity of each DC channel. S303: The lower-level model substitutes the schemes output by the upper-level model and the middle-level model into the expected fault scenario for time-domain simulation, including a set of state variables such as node voltage, system frequency and frequency change rate. When any state variable exceeds the limit, the limit penalty is calculated. S304: When the lower-level model verification finds that the security constraints are exceeded, the cut set feedback process in step S4 is triggered.

5. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 1, characterized in that, S4 specifically includes: S401: The sensitivity is: when performing perturbation analysis on the over-limit safety index, the finite difference ratio obtained by slightly perturbing the decision variable and re-simulating and calculating, wherein the decision variable is a decision variable that has a significant impact on the over-limit safety index and is adjustable in the middle and upper level model; S402: The safe cut set is constructed by using the sensitivity to construct a linear effective inequality about the change of the decision variables by linearly superimposing the safety index value of the current iteration point with the product of the change of each decision variable and its sensitivity.

6. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 1, characterized in that, The frequency stability constraints include initial frequency change rate constraints, steady-state frequency deviation constraints, and transient extremely low frequency constraints: The initial frequency change rate constraint is: the absolute value of the initial frequency change rate of the system at the instant of disturbance does not exceed the preset maximum allowable value; The steady-state frequency deviation constraint is: when the system enters steady state after a frequency modulation operation is completed after the disturbance, the steady-state frequency shall not be lower than the preset minimum limit. The transient extremely low frequency constraint is as follows: the lowest point of the transient frequency after the fault is used as the verification object of the time domain simulation of the lower-level model. When the simulation shows that the lowest point of the transient frequency is lower than the preset safety bottom line, the sensitivity cut set of the system inertia and reserve capacity is constructed and fed into the upper-level model in step S4.

7. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 4, characterized in that, The active power balance constraint of the nodes in the mid-level model is as follows: the sum of the active power output of the generators and the DC injection power of each node is equal to the sum of the load power of the node and the power outflow from the AC network; the upper and lower limit constraints of the operating capacity of the DC channel are as follows: the actual transmission power of each DC channel does not exceed the maximum value of its rated capacity and is not lower than the minimum value of its allowed operation.

8. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 1, characterized in that, The convergence criterion for the iterative solution in step S4 is: the safety index exceeding the limit under all anticipated failure scenarios is not greater than zero, and the change in the comprehensive investment cost obtained from two consecutive iterations is less than a preset threshold.

9. The AC / DC hybrid power grid collaborative planning method based on secure cut set feedback according to claim 1, characterized in that, The anticipated fault scenarios include at least a DC bipolar blocking fault and an AC N-1 line interruption fault.

10. A collaborative planning system for AC / DC hybrid power grids based on secure cut-set feedback, characterized in that, include: processor; A memory storing computer-readable instructions, which, when executed by the processor, implement the AC / DC hybrid power grid collaborative planning method based on secure cut set feedback as described in any one of claims 1 to 9.

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