Planning method of wind power AC / DC power transmission network under short-circuit current constraint

Abstract

The invention discloses a planning method of a wind power AC / DC power transmission network under short-circuit current constraint in the technical field of electrical information. The method comprises the following steps: constructing a short-circuit current calculation model comprising wind power plant feed-in, an AC power transmission line, a traditional DC power transmission line and a fault current limiter; according to the method, wind power plant feed-in short-circuit currents of different forming mechanisms are calculated through the established short-circuit current calculation model, a unified node short-circuit current function is formed, the short-circuit currents of various forming mechanisms are described in a unified mode, constraint conditions for solving the alternating-current and direct-current power transmission network stochastic programming model are formed, and the method has the advantages of being simple in structure and convenient to operate. And the stochastic programming model of the AC / DC power transmission network is solved by combining preset constraints, an AC / DC power transmission network planning scheme including an AC power transmission line planning scheme, a traditional DC power transmission line planning scheme and a current limiter configuration scheme is obtained, and an optimal balance point of economy and reliability is found in multi-scene analysis.

Description

Technical Field

[0001] This invention relates to the field of electrical information technology, specifically a planning method for wind power AC / DC transmission networks under short-circuit current constraints. Background Technology

[0002] Excessive short-circuit current is one of the key challenges restricting the development of power systems, especially in areas with dense construction of high-voltage AC lines, thermal synchronous generators, and wind farms. The system's short-circuit current level is increasingly approaching safety limits, posing a serious threat to grid operation. As a classic research area, transmission line expansion planning aims to find the optimal investment scheme that meets various operating conditions and economic requirements, and has been extensively studied.

[0003] High-voltage direct current (HVDC) transmission technology, as an economical and efficient power transmission method, has gradually attracted the attention of scholars and experts both domestically and internationally in recent years. Existing research on AC / DC transmission network planning methods mainly focuses on alleviating transmission congestion, optimizing control strategies for DC transmission systems, and promoting wind power integration. It is worth noting that advanced HVDC transmission technology offers new possibilities for short-circuit current suppression, but this potential has not yet been systematically evaluated and utilized in transmission network planning.

[0004] Furthermore, with the large-scale grid connection of wind farms, their contribution to short-circuit current has significantly increased, and their impact on the system's short-circuit current level cannot be ignored. Although some studies have focused on faults within DC systems or the short-circuit characteristics of doubly-fed wind farms, research on short-circuit current modeling under grid-connected wind farm conditions and its impact on system short-circuit current safety is still relatively lacking, and no complete conclusions have been reached.

[0005] Traditional power grid planning methods often ignore the impact of wind power feed-in on short-circuit current and do not comprehensively consider the coordinated planning of AC lines, DC lines and fault current limiters, making it difficult to implement the planning scheme under the constraint of short-circuit current. Summary of the Invention

[0006] The purpose of this invention is to provide a planning method for wind power AC / DC transmission networks under short-circuit current constraints, in order to solve the problem mentioned above that the planning scheme is difficult to implement under short-circuit current constraints because it does not comprehensively consider the coordinated planning of AC lines, DC lines and fault current limiters.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A planning method for wind power AC / DC transmission networks under short-circuit current constraints includes: S1: Construct a short-circuit current calculation model that includes wind farm feed-in, AC transmission lines, traditional DC transmission lines, and fault current limiters; S2: Establish a stochastic programming model for AC / DC transmission networks with the objective of minimizing total cost, where total cost includes planning cost and operating cost; S3: Based on the input power grid system parameters, the AC / DC transmission network stochastic programming model is optimized and solved using the short-circuit current calculation model and preset constraints as constraints, to obtain an AC / DC transmission network planning scheme that includes AC lines, traditional DC lines and current limiters.

[0008] As a further aspect of the present invention: S1 includes: Establish a piecewise function model of the short-circuit current fed into the wind farm under different fault voltage drop conditions; Establish an AC line admittance change model that causes changes in the power grid admittance matrix due to the construction of AC transmission lines; Establish a dynamic correction model for the change in the grid admittance matrix caused by the configuration of current limiters; A short-circuit current calculation model is formed based on the piecewise function model of the wind farm feed-in short-circuit current, the AC line admittance variation model, and the dynamic correction model. A unified nodal short-circuit current function is obtained based on the short-circuit current calculation model.

[0009] As a further aspect of the present invention: the establishment of a piecewise function model of the short-circuit current fed into the wind farm under different fault voltage drop conditions includes: The piecewise function model is expressed as follows:

[0010] in, This refers to the short-circuit current when the voltage drops significantly. This refers to the short-circuit current when the voltage drops slightly. This is the short-circuit current when the voltage drops slightly.

[0011] As a further aspect of the present invention: the short-circuit current of a wind farm when the voltage drops significantly. Controlled by the crowbar protection circuit, short-circuit current The calculation formula is: ; in, This refers to the voltage at the grid connection point after the fault. It is the equivalent impedance that includes the stator, rotor, crowbar, and excitation branch; Short-circuit current of a wind farm when the voltage drops slightly Controlled by the rotor-side converter, short-circuit current The calculation formula is: ; in, This is the reference value for the d-axis current on the stator side. This is the reference value for the q-axis current on the stator side;

[0012] ; In the formula, This is the stator-side limiting value. Set to the maximum value controlled by the pry bar protection circuit. This is the rated current value of the wind farm. This is the reactive power compensation coefficient, and ≥1.5; The short-circuit current of the wind farm during a slight voltage drop is controlled by the outer loop. Take the value of the rated current of the wind farm.

[0013] As a further aspect of the present invention: the establishment of the AC line admittance change model caused by the construction of AC transmission lines to alter the power grid admittance matrix includes: The AC line admittance variation model is expressed as follows:

[0014] ; Where Y0 is the original admittance matrix. This is the admittance change matrix caused by the planning and construction of the line. l For AC transmission lines, For the collection of communication lines, For line association vectors, 1 represents the first endpoint of the line, and -1 represents the last endpoint of the line. For line admittance, If it is a binary variable, =1 indicates the planned construction of AC transmission lines; otherwise, it is 0. The establishment of a dynamic correction model for the change in the grid admittance matrix caused by the configuration of the current limiter includes: The dynamic correction model is expressed as follows:

[0015] ; Where Y0 is the original admittance matrix. The admittance change matrix caused by the current limiter. A collection of AC transmission lines with configurable current limiters. A collection of current limiters AC transmission line l The model number is i The equivalent parallel admittance of the current limiter; It is a binary variable, if =1 indicates an AC transmission line l The model number is i The current limiter is planned and installed; otherwise, the value is 0.

[0016] As a further aspect of the present invention: the piecewise function model of the wind farm feed-in short-circuit current, the AC line admittance variation model, and the dynamic correction model form a short-circuit current calculation model. Based on this short-circuit current calculation model, a unified nodal short-circuit current function is obtained, including: Based on the linear superposition of grid short-circuit currents by grid composition, a unified nodal short-circuit current function is obtained. At node n of the power grid for; ; in, The voltage per unit value of node n before the fault; Let n be the set of electrical devices connected to node n. is the location vector, and 1 represents the position of node n.

[0017] As a further aspect of the present invention: the establishment of a stochastic programming model for AC / DC transmission networks with the objective of minimizing total cost, wherein the total cost includes planning cost and operating cost, including: Initial scenarios are generated using Latin hypercube sampling, and forward reduction techniques are employed to shrink the scenarios, thereby constructing a representative scenario set with probability weights. ; The objective function of the stochastic programming model for the AC / DC transmission network is:

[0018]

[0019] ; in, For the context The probability is given by IC, where IC is the planning cost and OC is the operating cost. The unit cost of a traditional DC line; The unit cost of an AC line; The configuration cost of the current limiter for model i; It is a collection of thermal power units.

[0020] As a further aspect of the present invention: the preset constraints include node balance constraints, DC power flow constraints, DC line planning constraints, AC line planning constraints, current limiter planning constraints, and maximum planning quantity constraints for current limiters. A unified nodal short-circuit current function is obtained using a short-circuit current calculation model. Obtain the constraint of short-circuit current; Based on the input power grid system parameters, the stochastic programming model of the AC / DC transmission network is optimized and solved by means of node balance constraints, DC power flow constraints, DC line planning constraints, AC line planning constraints, current limiter planning constraints, maximum planning quantity constraints of current limiters, and short-circuit current constraints, so as to obtain an AC / DC transmission network planning scheme that includes AC lines, traditional DC lines, and current limiters.

[0021] As a further aspect of the present invention: the constraint on the short-circuit current is expressed as follows: ; In the formula, The maximum permissible short-circuit current threshold. Let ξ be the effective value of the short-circuit current under node n, time period h, and scenario ξ.

[0022] As a further aspect of the present invention: the planning constraint of the DC line plans a certain DC line, whose state is set to 1 for the remaining time. The planning constraints of an AC line plan a certain AC line, whose state is set to 1 for the remaining time. The planning constraints of the current limiter plan a current limiter whose state is set to 1 for the remaining time.

[0023] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, a short-circuit current calculation model is established to calculate the short-circuit current fed into wind farms with different formation mechanisms separately. A unified and accurate short-circuit current modeling system is established, treating the wind farm as a controlled current source. This achieves a unified short-circuit current representation for traditional synchronous generators, AC lines, and new energy power electronic equipment, effectively solving the problem of incompatibility between AC equipment and power electronic equipment models in existing short-circuit current expressions. It overcomes the limitations of traditional modeling methods, accurately reflecting the short-circuit current characteristics of wind farms under different voltage drop levels, and characterizing the impact of newly built AC lines on the network's equivalent impedance. Simultaneously, it incorporates the current limiter in the existing... During the fault period, factors that suppress short-circuit current are added to form a unified nodal short-circuit current function, thereby enabling a unified description of short-circuit currents with various formation mechanisms. This forms the constraint conditions for solving the stochastic programming model of the AC / DC transmission network. When inputting power grid system parameters, the stochastic programming model of the AC / DC transmission network is solved together with the preset constraints, resulting in an AC / DC transmission network planning scheme that includes AC transmission line planning schemes, traditional DC transmission line planning schemes, and current limiter configuration schemes. This not only accurately assesses the impact of wind farm access on grid stability but also finds the optimal balance between economy and reliability in multi-scenario analysis.

[0024] 2. In this invention, a stochastic programming model for AC / DC transmission networks with the objective of minimizing total cost is established to characterize planning and operating costs. Planning costs, operating costs, short-circuit current constraints, and wind power output are tightly coupled. When generating AC / DC transmission network planning schemes, these factors are comprehensively considered to ensure that investment and operating costs are minimized while satisfying multiple constraints. This planning method, which comprehensively considers short-circuit current safety and investment economy, achieves a breakthrough in multi-objective optimization. It optimizes the configuration schemes of traditional DC transmission, AC lines, and current limiters, effectively controls short-circuit current levels, and overcomes the shortcomings of traditional planning that only focuses on economy or absorption capacity. It achieves multi-objective synergy of short-circuit current safety, investment economy, and operational reliability, providing theoretical support for the construction of new power systems.

[0025] 3. In this invention, the impact of newly constructed AC lines on the network's equivalent impedance is characterized by an AC line admittance variation model, while a dynamic correction model describes the suppression effect of different types of current limiters on short-circuit current after they are put into operation during a fault. This approach can more accurately reflect the impact of changes in the power grid structure on overall performance. The AC line admittance variation model mainly focuses on the static parameter adjustments brought about by line construction, while the dynamic correction model focuses on the real-time response characteristics after the current limiter is configured. By combining these two models, the specific impact of different planning schemes on power grid stability, transmission efficiency, and short-circuit current distribution can be effectively analyzed, providing a theoretical basis for subsequent optimization decisions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 Verification diagrams are provided for the wind farm short-circuit current modeling method of Embodiment 1 of the present invention; Figure 3 This invention provides short-circuit current distribution diagrams related to all calculation examples in Embodiment 1. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example: This invention, based on a unified short-circuit current analysis framework for power transmission networks, integrates short-circuit current models for traditional AC transmission lines and synchronous generators, as well as a wind farm model based on equivalent current sources. This forms a unified characterization method for the short-circuit current of various key power equipment, laying a solid foundation for accurate short-circuit current assessment in AC / DC hybrid systems. Supported by this modeling framework, a planning method for AC / DC power transmission networks is further proposed, comprehensively considering the stochasticity of wind power, short-circuit current safety constraints, and the coordinated configuration of current-limiting devices. This method establishes a stochastic model of wind power output and uses mixed-integer linear programming for efficient solution. It integrates traditional DC transmission lines, AC transmission lines, and current limiters into a unified collaborative optimization system, constructing an explicit correlation between these facilities and the system's short-circuit current level. Under the premise of meeting short-circuit current safety constraints and system operational reliability requirements, a long-term coordinated planning model for AC / DC power transmission networks is established with the goal of minimizing overall investment and operating costs. Ultimately, this results in a systematic short-circuit current suppression and planning scheme covering traditional DC transmission construction, AC line expansion, and current limiter configuration.

[0029] Furthermore, the planning model established in this invention is a mixed-integer linear programming (MILP) problem, which can be solved by mature commercial solvers. In this invention, the commercial solver Gurobi is called in the MATLAB environment for optimization and solution operations.

[0030] Please see Figure 1 In this embodiment of the invention, a planning method for a wind power AC / DC transmission network under short-circuit current constraints includes: S1: Construct a short-circuit current calculation model that includes wind farm feed-in, AC transmission lines, traditional DC transmission lines, and fault current limiters. Among them, the short-circuit current value of the wind farm fed into the grid is considered according to the different voltage drop nozzles under different short-circuit faults. S2: Establish a stochastic programming model for the AC / DC transmission network with the objective of minimizing total cost. The total cost includes planning cost and operating cost. The planning cost considers the planning cost of AC / DC transmission lines and the configuration cost of current limiters. The operating cost includes the power generation cost of traditional thermal power units and DC line losses. Furthermore, in the stochastic optimization model, by introducing multiple scenarios of wind power output and their corresponding probabilities, the uncertainty of wind power is quantitatively analyzed, which can effectively capture the impact of wind power fluctuations on system operation, thereby improving the robustness of the planning scheme. S3: Based on the input power grid system parameters, the stochastic programming model of the AC / DC transmission network is optimized and solved using the short-circuit current calculation model and preset constraints. This yields an AC / DC transmission network planning scheme that includes AC lines, traditional DC lines, and current limiters. The power grid system parameters are IEEE standard system example data, which includes key information such as node voltage, line impedance, load demand, and wind farm output. The IEEE standard system example data provides a fundamental support for the accuracy and reliability of the model, and also ensures that the planning scheme can adapt to the actual operation requirements of the power grid.

[0031] Specifically, by establishing a short-circuit current calculation model, the short-circuit current fed into wind farms with different formation mechanisms is calculated separately. A unified and accurate short-circuit current modeling system is established, treating wind farms as equivalent controlled current sources. This achieves a unified short-circuit current representation for traditional synchronous generators, AC lines, and new energy power electronic equipment, effectively solving the problem of incompatibility between AC equipment and power electronic equipment models in existing short-circuit current expressions. It overcomes the limitations of traditional modeling methods, accurately reflecting the short-circuit current characteristics of wind farms under different voltage drop levels, and characterizing the impact of newly built AC lines on the network's equivalent impedance. Simultaneously, it incorporates the current limiter's fault... During this period, factors that suppress short-circuit current are added to form a unified node short-circuit current function, thereby enabling a unified description of short-circuit currents with various formation mechanisms. This forms the constraint conditions for solving the AC / DC transmission network stochastic programming model. When inputting grid system parameters, the AC / DC transmission network stochastic programming model is solved together with preset constraints, resulting in AC / DC transmission network planning schemes that include AC transmission line planning schemes, traditional DC transmission line planning schemes, and current limiter configuration schemes. This not only accurately assesses the impact of wind farm access on grid stability but also finds the optimal balance between economy and reliability in multi-scenario analysis. Furthermore, this method comprehensively considers the impact of wind power feed-in on short-circuit current, AC lines, DC lines and fault current limiters, and uses the short-circuit current obtained from the short-circuit current calculation model as one of the optimization calculation constraints to perform optimization and solve the problem. The resulting AC / DC transmission network planning scheme includes AC lines, traditional DC lines and current limiters, which can effectively cope with the changes in short-circuit current brought about by wind farm access and has good performance. Furthermore, this method establishes a stochastic programming model for AC / DC transmission networks with the objective of minimizing total cost, characterizing planning and operating costs. It tightly couples planning costs, operating costs, short-circuit current constraints, and wind power output. When generating AC / DC transmission network planning schemes, these factors are comprehensively considered, ensuring that investment and operating costs are minimized while satisfying multiple constraints. This planning method, which comprehensively considers short-circuit current safety and investment economy, achieves a breakthrough in multi-objective optimization. It optimizes the configuration schemes of traditional DC transmission lines, AC lines, and current limiters, effectively controlling short-circuit current levels. It overcomes the shortcomings of traditional planning that only focuses on economy or absorption capacity, achieving multi-objective synergy of short-circuit current safety, investment economy, and operational reliability, providing theoretical support for the construction of new power systems.

[0032] Preferably, S1 includes: Establish a piecewise function model of the short-circuit current fed into the wind farm under different fault voltage drop conditions; Establish an AC line admittance change model that causes changes in the power grid admittance matrix due to the construction of AC transmission lines; Establish a dynamic correction model for the change in the grid admittance matrix caused by the configuration of current limiters; The piecewise function model of the short-circuit current fed into the wind farm, the AC line admittance variation model, and the dynamic correction model form the short-circuit current calculation model. Based on the short-circuit current calculation model, a unified nodal short-circuit current function is obtained.

[0033] Specifically, the piecewise function model of the short-circuit current fed into the wind farm, the AC line admittance variation model, and the dynamic correction model effectively reflect the short-circuit current characteristics of the wind farm under different operating conditions, ensuring that the established short-circuit current calculation model has high adaptability and reliability, and providing accurate basic data support for the formulation of subsequent AC and DC transmission network planning schemes.

[0034] Preferably, a piecewise function model of the short-circuit current fed into the wind farm under different fault voltage drop conditions is established, including: The piecewise function model is represented as follows:

[0035] in, This refers to the short-circuit current when the voltage drops significantly. This refers to the short-circuit current when the voltage drops slightly. This refers to the short-circuit current when the voltage drops slightly. A significant voltage drop is defined as a voltage drop exceeding 50% of the rated voltage; a slight voltage drop is defined as a voltage drop between 20% and 50%; and a minor voltage drop is defined as a voltage drop less than 20%.

[0036] Short-circuit current in wind farms when voltage drops significantly Controlled by the crowbar protection circuit, short-circuit current The calculation formula is: ; in, This refers to the voltage at the grid connection point after the fault. It is the equivalent impedance that includes the stator, rotor, crowbar, and excitation branch; Specifically, when the voltage drops significantly, the crowbar protection circuit activates during the low-voltage ride-through to prevent inrush current. This is in response to the short-circuit current fed into the wind farm. The calculation is performed using the following formula.

[0037]

[0038] ( +j )+( +j )+ [( ) +j ] In the formula, This refers to the voltage at the grid connection point after the fault. The equivalent impedance is ()s / cr / r / m, which are the relevant parameters of stator / crowbar protection / rotor / excitation. / It is the leakage inductance reactance of the stator / rotor The above formula describes the short-circuit current. Amplitude and post-fault voltage The linear relationship between them can be directly expressed as shown in the following formula:

[0039] In the formula, This is a proportional parameter; Short-circuit current of a wind farm when the voltage drops slightly Controlled by the rotor-side converter, short-circuit current The calculation formula is: ; in, This is the reference value for the d-axis current on the stator side. This is the reference value for the q-axis current on the stator side;

[0040] ; In the formula, This is the stator-side limiting value. Set to the maximum value controlled by the pry bar protection circuit. This is the rated current value of the wind farm. This is the reactive power compensation coefficient, and ≥1.5; Specifically, when the voltage drops slightly, rotor-side converter control is used instead of crowbar protection circuit control. Taking typical d-axis voltage-oriented control as an example, this can be achieved through the stator's d / q axis reference values. / This indicates the short-circuit current fed into the wind farm under this condition. ; j

[0041]

[0042] , ∈[0.2pu,0.9pu] In the formula, / This is the stator-side limiting value / the wind farm's rated current value, and under normal circumstances... It is generally set to the maximum value for pry bar protection; (≥1.5) is the reactive power compensation coefficient; The short-circuit current of the wind farm during a slight voltage drop is controlled by the outer loop. Take the value of the rated current of the wind farm; When the voltage drop is small, wind farms typically use outer-loop control. In this case, The variation is minimal, and the value of the rated current of the wind farm is usually taken as the value. Therefore, the short-circuit current fed from a wind farm into the transmission network can be expressed as a piecewise function. Furthermore, the short-circuit current is a piecewise function. The maximum value is used to obtain the piecewise function model. As shown in the following formula; =max{ , , }

[0043] Specifically, this paper analyzes the short-circuit current provided by the wind farm after grid connection. Given that the contribution of the grid-side converter to the short-circuit current is usually insignificant, the focus is mainly on the short-circuit current fed into the transmission network from the stator side. Based on the degree of voltage drop at the grid connection point after a fault, three control scenarios are discussed: control using a crowbar protection circuit, control solely by the rotor-side converter, and outer-loop control. In the case of crowbar protection circuit control, the crowbar circuit effectively suppresses rotor current overshoot and also limits the stator-side short-circuit current. In this case, the crowbar impedance and the system equivalent impedance jointly determine the short-circuit current. The magnitude and trend of the short-circuit current are important factors. When controlled solely by the rotor-side converter, the short-circuit current component output from the stator side can be flexibly adjusted by regulating the control strategy of the rotor-side converter. In particular, the reference values ​​of the d-axis and q-axis currents directly affect the amplitude and phase characteristics of the short-circuit current. For the case under outer-loop control, since it is mainly designed for operating conditions with slight voltage drops, more emphasis is placed on reactive power support and system stability. The current command value is dynamically adjusted by the outer-loop controller to achieve effective management of the short-circuit current. The selection of the three control scenarios requires a comprehensive judgment based on the actual fault characteristics and system operating requirements.

[0044] Preferably, an AC line admittance change model is established to reflect the change in the power grid admittance matrix caused by the construction of AC transmission lines, including: The AC line admittance variation model is expressed as follows:

[0045] ; Where Y0 is the original admittance matrix. This is the admittance change matrix caused by the planning and construction of the line. l For AC transmission lines, For the collection of communication lines, For line association vectors, 1 represents the first endpoint of the line, and -1 represents the last endpoint of the line. For line admittance, If it is a binary variable, =1 indicates the planned construction of AC transmission lines; otherwise, it is 0. Furthermore, consider the initial state of the transmission network as having no planned lines. The transmission network admittance matrix Y after the construction of AC transmission lines is decomposed into the original admittance matrix Y0 and the admittance change matrix caused by line planning and construction. The sum of these two expressions yields the following expression: Y=Y0+

[0046]

[0047] In the formula, 1 / -1 represent the beginning and end points of the line, respectively; A collection of communication lines; It is a binary variable, if =1 indicates the planned construction of AC transmission lines; otherwise, it is 0. Traditional DC transmission systems typically do not feed short-circuit current into the power grid because both the DC rectifier side uses constant current and the inverter side uses constant DC voltage control. Therefore, the short-circuit current calculation for AC / DC transmission networks only needs to consider the increase in short-circuit current in the power grid after the planning and construction of AC transmission lines. A dynamic correction model is established to address the changes in the grid admittance matrix caused by the configuration of current limiters, including: The dynamic correction model is represented as follows:

[0048] ; Where Y0 is the original admittance matrix. The admittance change matrix caused by the current limiter. A collection of AC transmission lines with configurable current limiters. A collection of current limiters AC transmission line l The model number is i The equivalent parallel admittance of the current limiter; It is a binary variable, if =1 indicates an AC transmission line l The model number is i The value is 0 if the current limiter is planned and deployed; otherwise, it is 0. Furthermore, the current limiter operates based on real-time sensing and fault response of the configured AC line current. During a fault, it engages a series reactor, essentially dynamically increasing the impedance of the branch. Therefore, within the mathematical framework of representing short-circuit current using an admittance matrix, the current limiter's operation can be analogous to the planning and construction of AC transmission lines, specifically manifested as a modification of certain elements in the matrix, as shown in the following equation.

[0049] Y=Y0+

[0050]

[0051] In the formula, The admittance change matrix caused by the current limiter; A collection of AC transmission lines with configurable current limiters; A collection of current limiters; AC transmission linel The model number is i The equivalent parallel admittance of the current limiter; It is a binary variable, if =1 indicates an AC transmission line l The model number is i The current limiter is planned and installed; otherwise, the value is 0.

[0052] Specifically, an AC line admittance change model is established to reflect the changes in the grid admittance matrix caused by the construction of AC transmission lines, and a dynamic correction model is established to reflect the changes in the grid admittance matrix caused by the configuration of current limiters. Through these two models, it is shown that AC transmission lines and current limiters themselves do not constitute new sources of short-circuit current, but they significantly affect the magnitude of the short-circuit current. The AC line admittance change model characterizes the impact of newly constructed AC lines on the network's equivalent impedance, while the dynamic correction model describes the suppression effect of different types of current limiters on short-circuit current after their activation during a fault. This model can more accurately reflect the impact of changes in the grid structure on overall performance. The AC line admittance change model mainly focuses on the static parameter adjustments brought about by line construction, while the dynamic correction model emphasizes the real-time response characteristics after the current limiter configuration. By combining these two models, the specific impacts of different planning schemes on grid stability, transmission efficiency, and short-circuit current distribution can be effectively analyzed, providing a theoretical basis for subsequent optimization decisions.

[0053] Preferably, the piecewise function model of the wind farm feed-in short-circuit current, the AC line admittance variation model, and the dynamic correction model form the short-circuit current calculation model. Based on this model, a unified nodal short-circuit current function is obtained, including: Based on the linear superposition of grid short-circuit currents by grid composition, a unified nodal short-circuit current function is obtained. At node n of the power grid for; ; in, The voltage per unit value of node n before the fault; Let n be the set of electrical devices connected to node n. is the location vector, and 1 represents the position of node n.

[0054] Specifically, by using a unified nodal short-circuit current function to accurately assess the distribution of short-circuit current in the power grid, the influence of different factors on the current distribution can be comprehensively considered, thereby improving the accuracy of the calculation results. By incorporating wind farm feed-in characteristics, line admittance changes, and dynamic response characteristics into a unified framework, the behavior patterns of complex power grids under fault conditions can be analyzed more comprehensively.

[0055] Preferably, a stochastic programming model for the AC / DC transmission network is established with the objective of minimizing total cost. Total cost includes planning cost and operating cost, including: Initial scenarios are generated using Latin hypercube sampling, and forward reduction techniques are employed to shrink the scenarios, thereby constructing a representative scenario set with probability weights. ; The objective function of the stochastic programming model for AC / DC transmission networks is:

[0056]

[0057] ; in, For the context The probability is given by IC, where IC is the planning cost and OC is the operating cost. The unit cost of a traditional DC line; The unit cost of an AC line; The configuration cost of the current limiter for model i; It is a collection of thermal power units.

[0058] Specifically, to characterize stochastic wind energy and ensure coverage of all sampling areas, a large number of stochastic scenarios were generated using Latin hypercube sampling. A forward slashing method was then used to simplify the scenarios, and the scenarios in the set were preserved. The most likely scenario is that the overall cost is to minimize the total cost of planning and operation, within the timeframe. and its duration The cost, including both AC / DC planning costs and current limiter planning costs, is taken into account. These costs are defined as planning costs, while operating costs are the losses of thermal power generating units. By comprehensively considering the probability weights under different scenarios, the adaptability and robustness of the model can be effectively improved. In practical applications, this method not only helps reduce the overall system cost but also provides a reliable guarantee for the long-term stable operation of the power grid.

[0059] Furthermore, by accurately modeling the configuration cost of the current limiter, the resource allocation strategy was further optimized, thereby maximizing economic objectives while meeting technical constraints.

[0060] Preferably, the preset constraints include node balance constraints, DC power flow constraints, DC line planning constraints, AC line planning constraints, current limiter planning constraints, and maximum planning quantity constraints for current limiters. A unified nodal short-circuit current function is obtained using a short-circuit current calculation model. Obtain the constraint of short-circuit current; Based on the input power grid system parameters, the stochastic programming model of AC / DC transmission network is optimized and solved by means of node balance constraints, DC power flow constraints, DC line planning constraints, AC line planning constraints, current limiter planning constraints, maximum planning quantity constraints of current limiters, and short-circuit current constraints, so as to obtain an AC / DC transmission network planning scheme that includes AC lines, traditional DC lines, and current limiters.

[0061] Preferably, the constraint on the short-circuit current is expressed as follows: ; In the formula, The maximum permissible short-circuit current threshold. Let ξ be the effective value of the short-circuit current under node n, time period h, and scenario ξ.

[0062] Preferably, the planning constraint of the DC line plans a certain DC line, whose state is set to 1 for the remaining time. The planning constraints of an AC line plan a certain AC line, whose state is set to 1 for the remaining time. The planning constraints of the current limiter plan a current limiter whose state is set to 1 for the remaining time.

[0063] Specifically, the constraints of the stochastic programming model for AC / DC transmission networks are as follows: 1) Node balance constraints

[0064] In the formula, Indicates the output of the thermal power unit; Power flow on DC lines; Current flow on the communication line; in this constraint d For load parameters; For load.

[0065] 2) DC power flow constraints are as follows:

[0066]

[0067] In the formula, and For the line l The phase angle between the first and last endpoints; It is a sufficiently large real number.

[0068] 3) The planning constraints for DC lines are as follows, which describe that once a DC line is planned, its state must be set to 1 for the remaining time: ;

[0069] 4) The planning constraints for AC lines are as follows, describing how, once an AC line is planned, its state must be set to 1 for the remaining time:

[0070] 5) The planning constraints for current limiters are as follows, describing how, once a current limiter is planned, its state must be set to 1 for the remaining time:

[0071] 6) The maximum planned number of current limiters is as follows:

[0072] In the formula, Plan the maximum number of current limiters.

[0073] 7) The constraint on short-circuit current is as follows:

[0074] In the formula, This is the maximum permissible short-circuit current threshold.

[0075] Based on the input power grid system parameters, where the power grid system parameters are IEEE standard system example data; By inputting IEEE standard system example data, the proposed stochastic programming model for AC / DC transmission networks that takes into account wind power inflow and short-circuit current constraints is optimized and solved, resulting in an AC / DC transmission network planning scheme that includes the construction of AC / DC transmission lines, expansion of AC lines, and configuration of current limiters.

[0076] Furthermore, in the MATLAB environment, the commercial solver Gurobi is called to perform optimization calculations and obtain the planning scheme.

[0077] Example 1: An example of short-circuit current modeling for wind farms. Simulations are conducted in PSCAD by setting different voltage drop amplitudes. For example... Figure 2 As shown, the simulation results are presented. IU Curves, along with short-circuit fault waveform data from the engineering site, were used to verify the feasibility of the equivalent current source model. Simultaneously, theoretical curves were obtained through point-by-point plotting. Slight errors were observed between the different curves, primarily due to differences between actual engineering parameters and simulation modeling parameters. Based on... IU Characteristics, based on Obtain the proportionality coefficient proportionality coefficient The calculated value is 3.72, and the critical voltage for switching the control strategy is 0.405 pu. And consider... Retain sufficient computational margin. Take its maximum value, 1.5 As the short-circuit current value fed into the wind farm, a piecewise function model for modeling the short-circuit current fed into the wind farm is derived. The value is: max{3.72 1.5 , }

[0078] An example of an AC / DC transmission network planning model considering wind power inflow and short-circuit current constraints is presented. Examples 1-5, using a modified IEEE-118 system, demonstrate the advantages of this model, as shown in Table 1. Initialization parameters are as follows: maximum short-circuit current threshold is 27kA; planning period is 5 years; there are 9 candidate transmission lines; current limiter impedance types are 15 / 25 / 35Ω, corresponding to prices of $1.8M / $2.4M / $3M respectively; unit costs for AC and DC lines are $1M / km and $1.5M / km respectively.

[0079] Table 1

[0080] Table notes: Y# represents the planning year; Wn: wind farm located at node n; SGn: thermal power generator located at node n.

[0081] Table 2 lists the detailed data for each example, with example 5 being the model object proposed in this study.

[0082] Table 2

[0083] Table Notes: A (m-n) / D (m-n) For the node m and nodes n AC / DC lines between them. F (m-n) - i Located at node m and nodes n Between i Model current limiter.

[0084] Table 3 reports the corresponding economic expenditures. The short-circuit current distribution of each calculation at the end of the planning period is as follows: Figure 3 As shown, the nodes with excessive short-circuit current and the transmission lines connected to them are marked.

[0085] Table 2

[0086] Example 1 uses a traditional transmission line expansion planning model as a baseline example. Five AC transmission lines were constructed around the synchronous generators and wind farms to alleviate transmission pressure. This scheme significantly increased the system's short-circuit current level, causing short-circuit currents to exceed limits at nine nodes, such as... Figure 3 (See the boxed section). In particular, the short-circuit current at nodes 5 and 80 exceeded 27kA due to the wind farm connection, verifying the effect of the wind farm on increasing the system's short-circuit current. Figure 3 The diagram (in the arc section) further illustrates that the dense connection of AC lines weakens short-circuit current safety, especially in the areas where nodes 61, 64, 65 and 69 are located, where the short-circuit current reaches its maximum value.

[0087] Example 2 introduces short-circuit current constraints based on Example 1, employing current limiters to suppress excessively high short-circuit currents caused by AC lines and wind farms. Compared to Example 1, the three candidate lines are adjusted to accommodate the current limiter configuration: the original A(49–62) is replaced by A(51–62), and two additional current limiters, F(49–66)-2 and F(61–64)-2, are added. This indicates that the initial line A(49–62) requires higher current limiter investment. Similarly, in Example 5, A(81–75) and A(98–108) replace A(81–69) and A(107–99) in Example 1, respectively, to alleviate the economic pressure caused by current limiter investment.

[0088] Example 3 replaces the same line in Example 1 with a DC transmission line. It is noteworthy that in this example, the short-circuit current exceedance only occurs at nodes 5 and 80, consistent with Example 1, further illustrating the effect of wind power grid connection on short-circuit current. No short-circuit current exceedances were observed on the other busbars, indicating that DC transmission contributes significantly less to the system's short-circuit current than AC lines, demonstrating a greater advantage in short-circuit current safety.

[0089] Example 4 further verifies the benefits of DC transmission in terms of short-circuit current friendliness: the number of current limiters is reduced from 6 in Example 2 to 2. Except for D(107–99) being adjusted to D(107–98) to balance the investment in current limiters, the other transmission lines are basically the same as in Examples 1 and 3. Compared to Example 2, where the generation cost increased significantly due to the non-optimal line, Example 4 retains a more economical dispatch scheme due to the short-circuit current safety friendliness of DC transmission, reducing the generation cost by nearly $30M. It can be seen that although the single AC line scheme has better overall economic efficiency, it requires more current limiter resources to suppress short-circuit current; while DC transmission, although more expensive, can achieve more effective transmission planning and dispatch while ensuring short-circuit current safety.

[0090] Example 5: In the AC / DC transmission network planning model proposed in this study, to address the high cost of current limiters, the planning scheme is designed with a combination of two AC lines and three DC lines. Notably, due to the increase in short-circuit current caused by the construction of line A(49–62), an additional current limiter is added in this example compared to Example 4; two more current limiters are used to suppress the increase in short-circuit current caused by wind farm grid connection. The results show that, under this configuration, the total cost of the combined investment in AC lines and current limiters is still lower than the scheme using only DC lines. Economic comparisons show that the cost difference between Example 2 and Example 4 is much smaller than that between Example 1 and Example 3, indicating that the planning costs saved by using AC lines are reallocated to current limiter investment. Furthermore, among Examples 2, 4, and 5 considering short-circuit current constraints, Example 5 has the lowest total cost. Therefore, the planning model proposed in this paper can achieve an effective balance between cost control, increased transmission capacity, and suppression of excessively high short-circuit currents, thus obtaining the optimal AC / DC transmission network planning scheme.

[0091] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for planning a wind power AC / DC power transmission network under short circuit current constraint, characterized in that, The application relates to a method for planning an AC / DC power transmission network, comprising the following steps: S1: constructing a short-circuit current calculation model comprising a wind farm feed-in, an AC transmission line and a traditional DC transmission line and a fault current limiter; S2: establishing an AC / DC power transmission network random planning model with the minimum total cost as the target, wherein the total cost comprises a planning cost and an operation cost; S3: based on the input power grid system parameters, the short-circuit current calculation model and preset constraints as constraint conditions, the AC / DC power transmission network random planning model is solved to obtain an AC / DC power transmission network planning scheme comprising an AC line, a traditional DC line and a limiter.

2. The method for planning a wind power AC / DC power transmission network under short circuit current constraint according to claim 1, characterized in that, The S1 comprises: a segmented function model of a wind farm feed-in short-circuit current under different fault voltage drop degrees is established; an AC line admittance change model of a change of a power grid admittance matrix caused by the construction of an AC transmission line is established; a dynamic correction model of a change of a power grid admittance matrix caused by the configuration of a limiter is established; a short-circuit current calculation model is formed based on the segmented function model of the wind farm feed-in short-circuit current, the AC line admittance change model and the dynamic correction model, and a unified node short-circuit current function is obtained according to the short-circuit current calculation model.

3. The method for planning a wind power AC / DC power transmission network under short circuit current constraint according to claim 2, characterized in that, The segmented function model of the wind farm feed-in short-circuit current under different fault voltage drop degrees is established, and the segmented function model is represented as: The AC line admittance change model of the change of the power grid admittance matrix caused by the construction of the AC transmission line is established, and the AC line admittance change model is represented as: wherein is the short circuit current at a large voltage drop, is the short circuit current at a small voltage drop, is the short circuit current at a slight voltage drop.

4. The method for planning a wind power AC / DC power transmission network under short circuit current constraint according to claim 3, characterized in that, Short circuit current of a wind farm at a significant voltage drop Short circuit current controlled by crowbar protection circuit The calculation formula is: ； wherein, is the post-fault point of common coupling voltage, is the equivalent impedance containing the stator, rotor, crowbar, and excitation branches; Short circuit current of a wind farm at a small voltage drop Short circuit current controlled by a rotor-side converter The calculation formula is: ； wherein, is a stator-side d-axis current reference value, is a stator-side q-axis current reference value; ； In the formula, is a stator-side limiting value, is set as the maximum value controlled by the crowbar protection circuit, is a wind farm rated current value, is a reactive power compensation coefficient, and ≥1.5; The short circuit current of the wind farm at a slight voltage drop is controlled by the outer loop, the short circuit current The value of the rated current of the wind farm is taken.

5. The method for planning a wind power AC / DC power transmission network under short circuit current constraint according to claim 4, characterized in that, The dynamic correction model of the change of the power grid admittance matrix caused by the configuration of the limiter is established, and the dynamic correction model is represented as: The short-circuit current calculation model is formed based on the segmented function model of the wind farm feed-in short-circuit current, the AC line admittance change model and the dynamic correction model, and a unified node short-circuit current function is obtained according to the short-circuit current calculation model, and the method comprises the following steps: ； where Y0is the original admittance matrix, is the admittance variation matrix caused by the planning and construction of transmission lines, l is an AC transmission line, is a set of AC transmission lines, is a line incidence vector, 1 represents the first end point of the line, -1 represents the end point of the line respectively, is the admittance of the line, is a binary variable, if =1 indicates the planning and construction of AC transmission lines, otherwise 0; The AC / DC power transmission network random planning model with the minimum total cost as the target is established, wherein the total cost comprises a planning cost and an operation cost, and the method comprises the following steps: The objective function of the AC / DC power transmission network random planning model is: ； where Y0is the original admittance matrix, is the admittance variation matrix caused by the current limiter, is the set of AC transmission lines equipped with the configurable current limiter, is the set of current limiters, is the AC transmission line l is the equivalent parallel admittance of the current limiter of type i is the equivalent parallel admittance of the current limiter of type is a binary variable, if = 1, it indicates that the AC transmission line l is the planning construction of the current limiter of type i , otherwise 0.

6. The method for planning a wind power AC / DC power transmission network under short circuit current constraint according to claim 5, characterized in that, The preset constraints comprise a node balance constraint, a DC power flow constraint, a DC line planning constraint, an AC line planning constraint, a limiter planning constraint and a maximum planning number constraint of the limiter; Based on the linear superposition of the power grid composition for the short-circuit current of the power grid, the unified node short-circuit current function is obtained At the node n of the power grid is; ； wherein, is the voltage unit of the node n before the fault; is the set of electrical devices connected to the node n; is the location vector, 1 is the location of the node n.

7. The method for planning a wind power AC / DC power transmission network under short circuit current constraint according to claim 6, characterized in that, Based on the input power grid system parameters, the node balance constraint, the DC power flow constraint, the DC line planning constraint, the AC line planning constraint, the limiter planning constraint, the maximum planning number constraint of the limiter and the short-circuit current constraint, the AC / DC power transmission network random planning model is solved to obtain an AC / DC power transmission network planning scheme comprising an AC line, a traditional DC line and a limiter. Generating initial scenarios based on Latin hypercube sampling and reducing the scenarios using forward pruning techniques to construct a representative set of scenarios with probabilistic weights ; The short-circuit current constraint is represented as: ； wherein, is the probability of the scenario, IC is the planning cost, OC is the operation cost, is the unit cost of the traditional DC line; is the unit cost of the AC line; is the configuration cost of the current limiter of type i; is the set of thermal power units.

8. The method for planning a wind power AC / DC power transmission network under short circuit current constraint according to claim 7, characterized in that, The DC line planning constraint sets the state of a certain DC line as 1 in the remaining time; A unified node short circuit current function is obtained by a short circuit current calculation model Constraints for obtaining short circuit current are obtained; The AC line planning constraint sets the state of a certain AC line as 1 in the remaining time; 9. The method of claim 8, wherein the method further comprises: The limiter planning constraint sets the state of a certain limiter as 1 in the remaining time. ； wherein is the maximum allowed short circuit current threshold, is the short circuit current root mean square value at node n, time period h, scenario ξ.

10. The method of claim 9, wherein the method further comprises: ​ ​ ​

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