Flexible DC cascade multi-terminal hierarchical system optimization method, apparatus and device, and storage medium

Abstract

The invention provides a flexible DC cascade multi-terminal hierarchical system optimization method, apparatus and device, and a storage medium. The method comprises the steps of determining a coordination control strategy including upper-layer total scheduling and lower-layer regionalization distribution and voltage support according to a cascade structure of an extra-high voltage DC trunk and a hierarchical branch; and determining a power distribution coefficient representing the power distribution proportion of the converter station to each layered area. And calculating the short-circuit current by adopting a linear approximation method based on the short-circuit sensitivity coefficient, and representing the short-circuit current as a linear function of the reference value and the power change. And determining a fault condition set containing a plurality of fault working conditions, and setting a current limiting proportion for limiting the power of the converter station during the fault. And integrating the power distribution coefficient, the short-circuit current and the current limiting proportion, executing optimization calculation, and generating optimized active and reactive power injection parameters of the converter station. According to the invention, through extra-high voltage flexible direct current cascade multi-terminal layered access and comprehensive optimization, flexible layered evacuation and customized distribution of power are realized, and the operation characteristics of the system are effectively improved.

Description

Technical Field

[0001] This application belongs to the field of power grid optimization, and in particular relates to a method, apparatus, equipment and storage medium for optimizing a flexible DC cascaded multi-terminal hierarchical system. Background Technology

[0002] Traditional ultra-high voltage direct current (UHVDC) transmission and flexible direct current (VSC-HVDC) transmission are used for long-distance, high-capacity power transmission and to improve the operating characteristics of the receiving-end power grid, such as power distribution and voltage support.

[0003] Traditional DC transmission adopts a two-end transmission or single-point access structure, with the receiving end naturally distributing power through the AC system; flexible DC transmission independently controls active and reactive power through converter stations, achieving effects such as fast response and black start, thereby improving the flexibility and stability of the power grid.

[0004] However, most existing flexible DC projects are two-end structures. During the receiving end connection process, due to the limited number of connection points, it is difficult to achieve flexible hierarchical distribution and customized allocation of DC power. Summary of the Invention

[0005] The purpose of this application is to overcome the deficiencies in the prior art and provide an optimization method, apparatus, device and storage medium for a flexible cascaded multi-terminal hierarchical system.

[0006] This application provides an optimization method for a flexible cascaded multi-terminal hierarchical system, including:

[0007] Based on the cascaded structure of the UHVDC main trunk and hierarchical DC branches, a coordinated control strategy is determined, which includes upper-level DC power total scheduling and lower-level regional allocation and voltage support.

[0008] Based on the coordinated control strategy, a power allocation coefficient is determined, which represents the power allocation ratio of the converter station to the hierarchical region.

[0009] Short-circuit parameters are obtained from the UHV flexible DC cascaded multi-terminal hierarchical access system, and the short-circuit current is calculated using a linear approximation method based on the short-circuit sensitivity coefficient in the short-circuit parameters. The short-circuit current is expressed as a linear function of the reference value and the power change based on the short-circuit sensitivity coefficient.

[0010] A set of fault conditions is determined, which includes multiple fault conditions, and a current limiting ratio is determined for the power limitation of the converter station under the fault conditions.

[0011] Based on the power allocation coefficient, the short-circuit current, and the current limiting ratio, a comprehensive optimization calculation is performed to generate optimized active power injection parameters and reactive power injection parameters for the converter station.

[0012] Optionally, the power allocation coefficient is determined according to the coordinated control strategy, including:

[0013] The power allocation coefficient represents the allocation ratio of the converter station to the hierarchical region; the sum of the allocation ratios of the power allocation coefficient for all hierarchical regions is one.

[0014] Optionally, the step of calculating the short-circuit current using a linear approximation method based on the short-circuit sensitivity coefficient includes:

[0015] The linear approximation method is a linear function of the reference short-circuit current and the change in converter station power.

[0016] Wherein, the reference short-circuit current is the reference value of the node short-circuit current, the converter station power change is determined based on the converter station power change, and the linear function is weighted and summed by the short-circuit sensitivity coefficient.

[0017] Optionally, determining the current limiting ratio for power limiting of the converter station during the fault condition includes:

[0018] The rate limiting ratio is used as an optimization decision variable, and the value of the rate limiting ratio ranges from zero to one.

[0019] According to the current limiting ratio, the power of the converter station under fault conditions shall not exceed the product of the current limiting ratio and the rated power.

[0020] Optionally, after determining the power allocation coefficient according to the coordinated control strategy, the process includes:

[0021] At the cascade node, a power flow conservation constraint is applied so that the power allocated by the converter station to the stratified region is equal to the product of the power allocation coefficient and the total power.

[0022] Optionally, short-circuit parameters can be obtained from the UHV flexible DC cascaded multi-terminal hierarchical access system, including:

[0023] The short-circuit sensitivity coefficient is pre-calculated. The pre-calculation estimates the short-circuit sensitivity matrix using a standard short-circuit calculation method, and the short-circuit sensitivity coefficient is determined using the short-circuit sensitivity matrix.

[0024] Optionally, perform comprehensive optimization calculations, including:

[0025] A robust minimization method is adopted, and an auxiliary variable is introduced to represent the power supply in the worst case.

[0026] Maximize the auxiliary variable and constrain the total power supply under all fault conditions to be no less than the auxiliary variable.

[0027] This application also provides an optimization device for a flexible DC cascaded multi-terminal hierarchical system, comprising:

[0028] The strategy module determines a coordinated control strategy based on the cascaded structure of the UHVDC main trunk and hierarchical DC branches. The coordinated control strategy includes upper-level DC power total scheduling and lower-level regional allocation and voltage support.

[0029] The power module determines the power allocation coefficient according to the coordination control strategy. The power allocation coefficient is used to represent the power allocation ratio of the converter station to the hierarchical region.

[0030] The short-circuit module obtains short-circuit parameters from the UHV flexible DC cascaded multi-terminal hierarchical access system, and calculates the short-circuit current using a linear approximation method based on the short-circuit sensitivity coefficient in the short-circuit parameters. The short-circuit current is expressed as a linear function of a reference value and power change based on the short-circuit sensitivity coefficient.

[0031] The scenario module determines a set of fault conditions, which includes multiple fault conditions, and determines a current limiting ratio for power limiting of the converter station under the fault conditions.

[0032] The calculation module performs comprehensive optimization calculations based on the power allocation coefficient, the short-circuit current, and the current limiting ratio to generate optimized active power injection parameters and reactive power injection parameters for the converter station.

[0033] This application also provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described above.

[0034] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the above-described method.

[0035] The beneficial effects of this application are:

[0036] This application provides an optimization method for a flexible DC cascaded multi-terminal hierarchical system, comprising: determining a coordinated control strategy based on the cascaded structure of the UHVDC main trunk and hierarchical DC branches, wherein the coordinated control strategy includes upper-level DC power total scheduling and lower-level regional allocation and voltage support; determining a power allocation coefficient based on the coordinated control strategy, wherein the power allocation coefficient is used to represent the power allocation ratio of the converter station to the hierarchical region; obtaining short-circuit parameters from the UHV flexible DC cascaded multi-terminal hierarchical access system, and calculating the short-circuit current using a linear approximation method based on the short-circuit sensitivity coefficient in the short-circuit parameters, wherein the short-circuit current is expressed as a linear function of a reference value and power change based on the short-circuit sensitivity coefficient; determining a set of fault conditions, wherein the set of fault conditions includes multiple fault conditions, and determining a current limiting ratio for power limitation of the converter station under the fault conditions; and performing a comprehensive optimization calculation based on the power allocation coefficient, the short-circuit current, and the current limiting ratio to generate optimized active power injection parameters and reactive power injection parameters for the converter station. This application adopts an ultra-high voltage flexible DC cascaded multi-terminal hierarchical access structure, and performs comprehensive optimization calculations based on coordinated control strategies, power allocation coefficients, short-circuit current linear approximation, and fault scenario optimization. This achieves flexible hierarchical evacuation and customized allocation of DC power, overcoming the shortcomings of the limited receiving-end access points in the existing dual-terminal structure. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the optimized process of the flexible DC cascaded multi-terminal hierarchical system in this application;

[0038] Figure 2 This is a schematic diagram of the UHV flexible DC cascaded multi-terminal hierarchical access structure in this application. Detailed Implementation

[0039] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is to be understood that various forms of implementation of the present disclosure are intended and should not be limited to the embodiments set forth herein. Rather, the embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0040] Please refer to Figure 1 This application provides an optimization method for a flexible DC cascaded multi-terminal hierarchical system, applied in the field of ultra-high voltage direct current (UHVDC) transmission, to solve problems such as uneven power flow distribution, high short-circuit current, and insufficient voltage support at the receiving end of the power grid in high load density areas. The method includes:

[0041] S101. Based on the cascaded structure of the UHVDC main trunk and the hierarchical DC branches, determine the coordination control strategy, which includes upper-level DC power total scheduling and lower-level regional allocation and voltage support.

[0042] Referring to Figure 2, the UHVDC backbone adopts an UHV level such as ±800kV or ±660kV, connecting to the remote sending system as the main power channel; the hierarchical DC branches are branched from the backbone DC through intermediate converter nodes to form secondary DC networks such as ±400kV or ±320kV, extending into high load density areas in the form of DC cables; the coordinated control strategy includes the upper layer being responsible for the total DC power scheduling, and the lower layer being responsible for regional distribution and voltage support, thus forming a hierarchical cascade architecture of "backbone-branch-terminal" in physical structure, and a multi-layered coordinated control system of "total power-regional power-local voltage" in control structure.

[0043] This strategy is implemented through a coordinated control system for each converter. The upper-level dispatcher sets the total power target, and the lower-level controller allocates and regulates the voltage according to the regional demand. For example, multiple flexible converter stations are set up at the receiving end and connected to AC systems of different voltage levels, such as 500kV, 220kV, and 110kV, to form a hierarchical evacuation and multi-point power supply system.

[0044] S102. Determine the power allocation coefficient according to the coordination control strategy. The power allocation coefficient is used to represent the power allocation ratio of the converter station to the hierarchical region.

[0045] The power allocation coefficient is defined as , representing the allocation ratio of the k-th converter station to the r-th layer region, satisfying that the sum of the allocation ratios for all layer regions is one, i.e.:

[0046]

[0047] The power distribution formula is:

[0048]

[0049] Among them, the The power allocation coefficient represents the allocation ratio of the k-th converter station to the r-th layer region; The active power allocated to the r-th layer region by the k-th converter station; Let be the total active power of the k-th converter station.

[0050] This coefficient The upper-level scheduler optimizes decisions or presets to achieve flexible hierarchical distribution and customized allocation of DC power. For example, power flow conservation constraints are applied at cascade nodes to balance the DC bus and ensure that the allocated power is equal to the product of the allocation coefficient and the total power.

[0051] Let the system contain N AC nodes (main network) and M DC converter terminals (multiple terminals), with subscripts:

[0052] i, j represent communication nodes (bus), set ;

[0053] k represents the DC terminal, and the set ;

[0054] Indicates a set of communication lines. .

[0055] The main variables and parameters include:

[0056] : Active / reactive power injection from conventional generators on AC bus (known or adjustable);

[0057] AC bus load (known);

[0058] : Active / reactive power injected into the AC network by converter station k (decision variable, can be positive / negative);

[0059] AC bus voltage amplitude and phase angle (decision variables);

[0060] : Active power flow of AC line (i,j);

[0061] : Rated capacity of converter station (active or apparent, parameter);

[0062] : Calculated short-circuit current (auxiliary quantity) of node i under operating condition s (which may include faults);

[0063] : The upper limit of the allowable short-circuit current of i (circuit breaker / equipment limit).

[0064] Several sensitivity / equivalent matrices (for linear approximation):

[0065] B: Admittance matrix of AC network (used for AC power flow linearization or Newton iteration);

[0066] PTDF: Power Flow Transmission Sensitivity Matrix (Linearized mapping of active power flow with respect to injection variations);

[0067] : Reactive power sensitivity matrix to voltage ( ).

[0068] Decision variables include continuous variables:

[0069]

[0070] Optional, converter current limiting / mode switching parameters such as (Indicates the current limiting ratio during a fault), or the hierarchical power allocation coefficient. (Distribute the power from the upper stage to different areas at the lower stage).

[0071] S103. Obtain short-circuit parameters from the UHV flexible DC cascaded multi-terminal hierarchical access system, and calculate the short-circuit current using a linear approximation method based on the short-circuit sensitivity coefficient in the short-circuit parameters. The short-circuit current is expressed as a linear function of a reference value and power change based on the short-circuit sensitivity coefficient.

[0072] The short-circuit parameters include the system rated voltage Unom and the node equivalent impedance. and short-circuit sensitivity coefficient The short-circuit sensitivity matrix is ​​estimated by pre-calculation using standard short-circuit calculation methods such as IEC 60909, and the short-circuit sensitivity coefficient is determined.

[0073] The linear approximation expression for short-circuit current is:

[0074]

[0075] Among them, the The short-circuit current at node i; The system's rated voltage; The equivalent impedance of node i; The short-circuit sensitivity coefficient from converter station k to node i; Injecting active power into converter station k; This is the equivalent internal resistance / reactance of the converter station.

[0076] This linear approximation method expresses the short-circuit current as a linear function of the reference short-circuit current and the change in converter station power. The reference short-circuit current is the reference value of the node short-circuit current, and the change in converter station power is determined based on the change in converter station power. The linear function is weighted and summed using the short-circuit sensitivity coefficient, which is used to quickly estimate the short-circuit current in the optimization process.

[0077] Furthermore, the short-circuit current Isc,i is usually obtained in engineering by using the equivalent Thevenin impedance method for nodes.

[0078] To ensure equipment safety, the following constraints are applied:

[0079]

[0080] in,

[0081] Engineering practice recommends performing calculations in advance under reference operating conditions using short-circuit calculation tools (IEC / ANSI method). The sensitivity matrix SI is used as the basis for the optimization problem, which is then substituted into the problem as linear constraints.

[0082] In highly nonlinear scenarios, a quadratic cone / linearized iteration (outer loop updates sensitivity, inner loop solves linear programming) can be used to ensure accuracy. The linear approximation method is a linear function of the reference short-circuit current and the change in converter station power; wherein, the reference short-circuit current is the reference value of the node short-circuit current, the change in converter station power is determined based on the change in converter station power, and the linear function is a weighted summation using short-circuit sensitivity coefficients.

[0083] S104. Determine a set of fault conditions, which includes multiple fault conditions, and determine the current limiting ratio for power limiting of the converter station under the fault conditions.

[0084] The set of fault conditions is denoted as It includes the normal operating condition s=0 and multiple fault operating conditions s=1,…,S.

[0085] The current limiting ratio is defined as follows: As an optimization decision variable, its value ranges from zero to one, and it is used to constrain the power of the converter station under fault conditions to not exceed the product of the current limiting ratio and the rated power, that is:

[0086]

[0087] in, The active power injected into the AC network by converter station k is... This is a set of fault conditions; s is a condition index, where s=0 represents normal operating conditions, and s=1,…,S represents fault conditions; The current limiting ratio of converter station k under condition s; This represents the rated active power of converter station k.

[0088] This current limiting ratio achieves a trade-off between local current limiting and global stability during faults. For example, under severe faults such as three-phase short circuits in the AC near-zone, it can be optimized... Improve fault tolerance capability.

[0089] The goal of fault ride-through and optimization modeling is to improve the ride-through capability of DC systems under severe faults such as AC "near-zone three-phase short circuit". Mathematically, this can be addressed through case constraints or robust / minimize worst-case objectives.

[0090] Capabilities can be optimized in two ways:

[0091] Method A (Robust Minimization of Worst-Case Loss) aims to maximize the minimum total power supply (or minimum DC active power retention) under all scenarios:

[0092]

[0093] Among them, the This is a set of fault conditions; s is a condition index, where s=0 represents normal operating conditions, and s=1,…,S represents fault conditions. The active power of the conventional generator on the AC bus is given by case s.

[0094] This is often transformed into introducing an auxiliary variable t:

[0095]

[0096] Method B (weighted expected value with penalty) aims to be the weighted sum of efficiency under normal operating conditions (e.g., minimizing losses) and losses under fault conditions.

[0097]

[0098] in, λ is the short-circuit default penalty weight, which is set according to the probability or importance of the operating condition.

[0099] The rate limiting ratio is used as an optimization decision variable, and the value of the rate limiting ratio ranges from zero to one.

[0100] According to the current limiting ratio, the power of the converter station under fault conditions shall not exceed the product of the current limiting ratio and the rated power.

[0101] S105. Based on the power allocation coefficient, the short-circuit current, and the current limiting ratio, perform comprehensive optimization calculations to generate optimized active power injection parameters and reactive power injection parameters for the converter station.

[0102] The comprehensive optimization calculation is based on a mathematical optimization procedure, and the decision variables include... The objective function adopts a hybrid objective, such as minimizing the weighted sum of losses under normal operating conditions and losses under fault conditions, while also considering the penalty for short-circuit current failure.

[0103] The optimization constraints include power balance constraints, line power flow constraints, converter station capacity constraints, short-circuit current upper limit constraints, hierarchical allocation constraints, current limiting strategy constraints, and voltage range constraints.

[0104] The power balance constraint is:

[0105]

[0106]

[0107] Among them, the Active power injection for the conventional generator of AC bus i; the Reactive power injection for the conventional generator of AC bus i; the The active power demand of AC bus i; The reactive power demand of AC bus i; For the active power injection of converter station k; the For reactive power injection into converter station k; the The voltage amplitude of AC bus i; For the active power flow of AC line (i,j); the For the reactive power flow of AC line (i,j); the This is the set of DC terminals connected to bus i.

[0108] Line power flow relationships can be modeled using nonlinear models or linear approximations. For example, a linear approximation could be:

[0109]

[0110]

[0111] The capacity constraint of the converter station is:

[0112]

[0113] Among them, the The upper limit of active power for converter station k; The upper limit of reactive power for converter station k; Let k be the rated apparent power of converter station k.

[0114] The upper limit constraint for short-circuit current is:

[0115]

[0116] Among them, the Let be the short-circuit current of node i under case s; the Let i be the upper limit of the allowable short-circuit current.

[0117] The hierarchical allocation constraint is:

[0118]

[0119] The rate limiting strategy is constrained as follows:

[0120]

[0121] The pressure range constraint is:

[0122]

[0123] The optimization method adopts a hierarchical iterative approach. First, a linear approximation is used to form a convex optimization problem for solution. Then, a nonlinear model is used for refinement. A robust minimization method is adopted, and an auxiliary variable t is introduced to represent the power supply under the worst case. The goal is to maximize t and constrain the total power supply under all fault conditions to be no less than 1%.

[0124] After generating optimized parameters, they are used to control the converter station in real time, enabling flexible power regulation, short-circuit current suppression, and enhanced reactive power support.

[0125] Furthermore, the set of decision variables for the comprehensive optimization mathematical program is as follows:

[0126]

[0127] Example of a standard function for a mixed objective:

[0128]

[0129] in, This refers to the system's active power loss or unmet load (which can be defined as unsupplied power or load reduction). The power supply quality or economic benefit under normal operating conditions (the higher the better); For operating condition probabilities or weights; For weights.

[0130] Solution suggestions and numerical implementation details include:

[0131] If the problem type uses the full AC power flow and short-circuit nonlinear expression, it is nonlinear nonconvex optimization (NLP). To improve solvability, a hierarchical / iterative method can be used, such as using linear / convex approximation to solve the main problem, and then using nonlinear backtracking to check and correct (Sequential Linear Programming or internal and external iterations that gradually update sensitivity).

[0132] The recommended solution strategy initially calculates the PTDF, VQ_sens, and short-circuit sensitivity matrix SI based on baseline power flow results; replaces the nonlinear components with linear constraints, forming an LP / QP / SOCP problem; and uses Gurobi / CPLEX to solve a rapid prototype. For refinement, the LP / QP results are used as initial values, and the nonlinear model is solved using IPOPT / KNITRO, or relaxed using SDP / SOCP.

[0133] For multi-case (N-1) handling, if the number of cases is large, reduction techniques (critical condition screening), Benders decomposition, or column generation are used to solve the cases as subproblems in parallel. Engineering the optimization of through-capacity by explicitly incorporating the maximization of the "minimum residual DC injection power in the worst-case scenario" into the objective can significantly improve power supply continuity under critical faults; through constraints... This is then used as a controllable variable to optimize how power is distributed across different terminals during a fault, achieving a trade-off between "local current limiting and global stability." Sensitivity / parameter preprocessing is recommended to be estimated using short-circuit calculations (IEC 60909 or specialized software) before implementation. , The PTDF / VSENS is calculated using power flow linearization; if higher accuracy is required, the sensitivity can be updated in each iteration to capture nonlinear effects.

[0134] Performance metrics are used to evaluate optimization results, including total power loss under normal operating conditions (MW), power supply coverage, DC active power distribution deviation (the difference from the target distribution); and the remaining DC power supply (MW) under worst-case fault conditions and the current limiting ratio at each terminal. Maximum short-circuit current at critical nodes Stability / robustness metrics: minimum / average voltage margin (V), N-1 acceptability (how many cases satisfy all constraints); Reliability metrics: the proportion and duration at which the system maintains output at other terminals under single-ended failure (obtainable through simulation).

[0135] For teaching implementation, a simplified model is used, employing a linearized model of an N-node network with M converter terminals, approximated by DC power flow. The voltage amplitude is fixed (or approximated by a first-order VQ); the short-circuit constraint is expressed as linear sensitivity. The objective is to minimize the loss under normal operating conditions + λ × (the load without power supply under fault conditions).

[0136] The comprehensive optimization calculation adopts a robust minimization method, introducing an auxiliary variable to represent the power supply under the worst case; the auxiliary variable is maximized, and the total power supply under all fault conditions is constrained to be no less than the auxiliary variable.

[0137] This application also provides an optimization device for a flexible DC cascaded multi-terminal hierarchical system, comprising:

[0138] The strategy module determines a coordinated control strategy based on the cascaded structure of the UHVDC main trunk and hierarchical DC branches. The coordinated control strategy includes upper-level DC power total scheduling and lower-level regional allocation and voltage support.

[0139] The power module determines the power allocation coefficient according to the coordination control strategy. The power allocation coefficient is used to represent the power allocation ratio of the converter station to the hierarchical region.

[0140] The short-circuit module obtains short-circuit parameters from the UHV flexible DC cascaded multi-terminal hierarchical access system, and calculates the short-circuit current using a linear approximation method based on the short-circuit sensitivity coefficient in the short-circuit parameters. The short-circuit current is expressed as a linear function of a reference value and power change based on the short-circuit sensitivity coefficient.

[0141] The scenario module determines a set of fault conditions, which includes multiple fault conditions, and determines a current limiting ratio for power limiting of the converter station under the fault conditions.

[0142] The calculation module performs comprehensive optimization calculations based on the power allocation coefficient, the short-circuit current, and the current limiting ratio to generate optimized active power injection parameters and reactive power injection parameters for the converter station.

[0143] This application also provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described above.

[0144] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the above-described method.

[0145] The above description of the embodiments is provided to enable those skilled in the art to understand and apply this application. Those skilled in the art will readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without inventive effort. Therefore, this application is not limited to the above embodiments, and any improvements and modifications made to this application based on the disclosure thereof should be within the scope of protection of this application.

Claims

1. An optimization method for a flexible cascaded multi-terminal hierarchical system, characterized in that, include: Based on the cascaded structure of the UHVDC main trunk and hierarchical DC branches, a coordinated control strategy is determined, which includes upper-level DC power total scheduling and lower-level regional allocation and voltage support. Based on the coordinated control strategy, a power allocation coefficient is determined, which represents the power allocation ratio of the converter station to the hierarchical region. Short-circuit parameters are obtained from the UHV flexible DC cascaded multi-terminal hierarchical access system, and the short-circuit current is calculated using a linear approximation method based on the short-circuit sensitivity coefficient in the short-circuit parameters. The short-circuit current is expressed as a linear function of the reference value and the power change based on the short-circuit sensitivity coefficient. A set of fault conditions is determined, which includes multiple fault conditions, and a current limiting ratio is determined for the power limitation of the converter station under the fault conditions. Based on the power allocation coefficient, the short-circuit current, and the current limiting ratio, a comprehensive optimization calculation is performed to generate optimized active power injection parameters and reactive power injection parameters for the converter station.

2. The method according to claim 1, characterized in that, Based on the aforementioned coordinated control strategy, the power allocation coefficient is determined, including: The power allocation coefficient represents the allocation ratio of the converter station to the hierarchical region; the sum of the allocation ratios of the power allocation coefficient for all hierarchical regions is one.

3. The method according to claim 1, characterized in that, The calculation of the short-circuit current using a linear approximation method based on the short-circuit sensitivity coefficient includes: The linear approximation method is a linear function of the reference short-circuit current and the change in converter station power. Wherein, the reference short-circuit current is the reference value of the node short-circuit current, the converter station power change is determined based on the converter station power change, and the linear function is weighted and summed by the short-circuit sensitivity coefficient.

4. The method according to claim 1, characterized in that, Determining the current limiting ratio for power limiting of the converter station under the aforementioned fault conditions includes: The rate limiting ratio is used as an optimization decision variable, and the value of the rate limiting ratio ranges from zero to one. According to the current limiting ratio, the power of the converter station under fault conditions shall not exceed the product of the current limiting ratio and the rated power.

5. The method according to claim 1, characterized in that, After determining the power allocation coefficients according to the aforementioned coordinated control strategy, the following steps are included: At the cascade node, a power flow conservation constraint is applied so that the power allocated by the converter station to the stratified region is equal to the product of the power allocation coefficient and the total power.

6. The method according to claim 1, characterized in that, Short-circuit parameters are obtained from the UHV flexible DC cascaded multi-terminal hierarchical access system, including: The short-circuit sensitivity coefficient is pre-calculated. The pre-calculation estimates the short-circuit sensitivity matrix using a standard short-circuit calculation method, and the short-circuit sensitivity coefficient is determined using the short-circuit sensitivity matrix.

7. The method according to claim 1, characterized in that... Perform comprehensive optimization calculations, including: A robust minimization method is adopted, and an auxiliary variable is introduced to represent the power supply in the worst case. Maximize the auxiliary variable and constrain the total power supply under all fault conditions to be no less than the auxiliary variable.

8. A flexible, cascaded, multi-terminal, hierarchical system optimization device, characterized in that, include: The strategy module determines a coordinated control strategy based on the cascaded structure of the UHVDC main trunk and hierarchical DC branches. The coordinated control strategy includes upper-level DC power total scheduling and lower-level regional allocation and voltage support. The power module determines the power allocation coefficient according to the coordination control strategy. The power allocation coefficient is used to represent the power allocation ratio of the converter station to the hierarchical region. The short-circuit module obtains short-circuit parameters from the UHV flexible DC cascaded multi-terminal hierarchical access system, and calculates the short-circuit current using a linear approximation method based on the short-circuit sensitivity coefficient in the short-circuit parameters. The short-circuit current is expressed as a linear function of a reference value and power change based on the short-circuit sensitivity coefficient. The scenario module determines a set of fault conditions, which includes multiple fault conditions, and determines a current limiting ratio for power limiting of the converter station under the fault conditions. The calculation module performs comprehensive optimization calculations based on the power allocation coefficient, the short-circuit current, and the current limiting ratio to generate optimized active power injection parameters and reactive power injection parameters for the converter station.

9. An electronic device, characterized in that, It includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method as described in claim 8.

10. A computer-readable storage medium, characterized in that, It stores a computer program that, when executed in a computer, causes the computer to perform the method of claim 8.

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