Reactive power source hierarchical configuration method and system for power grid strength improvement

Abstract

The application discloses a reactive power source layered configuration method and system for power grid strength improvement, and mainly relates to the technical field of power system planning and operation control. The method comprises the following steps: dividing a power system into a high-voltage layer and a low-voltage layer according to voltage grades; taking the equivalent impedance of a dynamic reactive power source as a decision variable, taking the high-voltage layer stability constraint and the low-voltage layer stability constraint as constraint conditions, and taking the minimum total capacity of the dynamic reactive power source as an objective function to construct a dynamic reactive power source double-layer configuration model; and adopting a layered solving strategy of "upper layer optimization-lower layer correction" to solve the double-layer configuration model to obtain a dynamic reactive power source configuration scheme which meets the stability constraints of the high-voltage layer and the low-voltage layer. The application has the beneficial effect that the minimum configuration capacity of the dynamic reactive power source is realized under the premise of meeting the stability constraints of different layers.

Description

Technical Field

[0001] This invention relates to the field of power system planning and operation control technology, specifically a method and system for hierarchical configuration of reactive power sources based on the node strength requirements of different voltage levels. Background Technology

[0002] With the rapid development of new energy power generation, modern power systems are gradually evolving into new power systems dominated by new energy sources. Conventional generating units are being largely replaced by new energy sources, and the proportion of installed capacity of traditional synchronous generator units is continuously decreasing. Because new energy sources are integrated into the grid via power electronic devices, their ability to provide short-circuit current during grid faults is much smaller than that of synchronous generators due to limitations in control methods and device overcurrent capacity. This weakens the transient reactive power support capability of the power system and gradually reduces voltage stability. Optimizing the configuration of dynamic reactive power sources has become a crucial issue for new power systems to improve system transient voltage stability and enhance reactive power support capability. However, given the large scale and complex grid structure of power systems, it is essential to rationally plan the configuration of dynamic reactive power sources to fully leverage their support capability while ensuring economic efficiency.

[0003] The new power system is characterized by multiple DC feeds and a large number of renewable energy sources. The system voltage levels vary significantly across different regions, especially at key nodes such as DC feed points and renewable energy grid connection points. Correspondingly, the capacity of reactive power compensation equipment installed at these nodes also varies considerably. Directly applying the same baseline value to all these key nodes and configuring reactive power sources simultaneously is impractical. Furthermore, due to the different characteristics of DC feed points and renewable energy grid connection points, DC feed points typically have voltage levels greater than 500kV, are fewer in number, and their stability requirements are reflected in the DC system's stability needs. Renewable energy grid connection points typically have voltage levels less than 500kV, are more numerous in the grid, and their stability requirements are reflected in the renewable energy grid connection points' stability needs. This necessitates that dynamic reactive power source configuration must simultaneously ensure the stability needs of both high-voltage DC feed points and low-voltage renewable energy grid connection points.

[0004] Therefore, there is an urgent need for a method and system for hierarchical configuration of reactive power sources based on the node strength requirements of different voltage levels to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for hierarchical configuration of reactive power sources based on the node strength requirements of different voltage levels. Under the premise of satisfying the stability constraints of different levels, it achieves the minimization of dynamic reactive power source configuration capacity.

[0006] To achieve the above objectives, the present invention employs the following technical solution: On the one hand, this invention provides a method for hierarchical configuration of reactive power sources to enhance grid strength, comprising the following steps: The power system is divided into high-voltage and low-voltage layers according to voltage levels; Using the equivalent impedance of dynamic reactive power sources as the decision variable, the high-voltage layer stability constraints and the low-voltage layer stability constraints as the constraints, and the minimum total capacity of dynamic reactive power sources as the objective function, a two-layer configuration model for dynamic reactive power sources is constructed. The two-layer configuration model is solved by adopting a hierarchical solution strategy of "upper-layer optimization - lower-layer correction" to obtain a dynamic reactive power source configuration scheme that simultaneously satisfies the stability constraints of the high-voltage layer and the low-voltage layer.

[0007] Preferably, the high-voltage layer stability constraints include short-circuit ratio constraints and commutation failure risk constraints; for the first There are one DC feed point, and the short-circuit ratio constraint is: ; in, For nodes The short-circuit ratio, , Here is the system node impedance matrix. For nodes Self-impedance, To preset the lower limit of the short-circuit ratio; The commutation failure risk constraint is as follows: ; in, For nodes Commutation failure risk indicators , This represents the total number of nodes in the network. DC feed point and the point of failure mutual impedance between Fault point Self-impedance, This is the critical voltage for commutation failure.

[0008] Preferably, the low-pressure layer stability constraint is an improved multi-station short-circuit ratio constraint; for the first For each new energy grid connection point, the improved multi-station short-circuit ratio constraint is: ; in, For the first Improvements to the short-circuit ratio of multiple power stations at new energy grid connection points To preset and improve the lower limit of short-circuit ratio for multiple stations; Represented as: ; in, This represents the mutual impedance vector between the fault point and each renewable energy grid connection point. This represents the incremental output current vector at the new energy grid connection point during a fault. and The first The and the first The rated power of each new energy grid connection point For nodes With nodes The mutual impedance between them.

[0009] Preferably, the conversion relationship between the equivalent impedance of the dynamic reactive power source and its actual capacity is as follows: ; in, The equivalent impedance of a dynamic reactive power source. This refers to the internal impedance of the dynamic reactive power source under its own reference. As a power reference for the system node impedance matrix, Rated capacity of dynamic reactive power source; The objective function is: ; in, This represents the total number of dynamic reactive power sources. For the first The equivalent impedance of the dynamic reactive power source in Taiwan. For the first The internal impedance of the dynamic reactive power source under its own reference.

[0010] Preferably, the upper-level optimization model of the dual-layer configuration model uses the equivalent impedance of the dynamic reactive power source of the high-voltage layer. and installation location The decision variable is determined by the high-voltage layer stability constraint, and the objective function is to minimize the total capacity of dynamic reactive power sources. The lower-level optimization model of the two-layer configuration model uses the equivalent impedance of the dynamic reactive power source in the low-voltage layer. and installation location The decision variable is defined by the low-voltage layer stability constraint, and the objective function is to minimize the total capacity of dynamic reactive power sources. Both the upper-level optimization model and the lower-level optimization model satisfy the power flow equation constraint: ; ; in, , They are nodes The generator has active and reactive power outputs. , They are nodes Active and reactive loads, , They are nodes and nodes voltage amplitude, , They are nodes With nodes The conductivity and susceptance between them For nodes With nodes The voltage phase angle difference between them.

[0011] Preferably, the hierarchical solution strategy of "upper-level optimization - lower-level correction" includes: Set the low-voltage layer dynamic reactive power source configuration scheme to zero, solve the upper-layer optimization model, and obtain the dynamic reactive power source installation location and capacity scheme that satisfies the stability constraints of the high-voltage layer. The optimization results are incorporated into the system network model to update the system node impedance matrix; Based on the updated impedance matrix, the improved multi-station short-circuit ratio index of each new energy grid connection point is calculated. For new energy grid connection points where the short-circuit ratio of multiple power stations is lower than the preset threshold, dynamic reactive power sources with corresponding equivalent impedance are configured at the node according to the strength improvement requirements of the node, so that the short-circuit ratio of multiple power stations can meet the preset requirements. Recalculate the system node impedance matrix and improve the short-circuit ratio index of each new energy grid connection point for multiple power stations; If there are still new energy grid connection points that do not meet the intensity requirements, return to step four to continue the iteration; otherwise, end the calculation and output the final dynamic reactive power source configuration scheme.

[0012] Preferred, new energy grid connection points After configuring dynamic reactive power sources, this node improves the short-circuit ratio of multiple substations. The relationship of change is expressed as: ; in, For new energy grid connection points Improved short-circuit ratio in multiple substations after configuring dynamic reactive power sources. The equivalent impedance of the dynamic reactive power source configured at this point; according to The equivalent dynamic reactive power source impedance required for each non-compliant renewable energy grid connection point is obtained by reverse calculation. .

[0013] On the other hand, the present invention provides a reactive power source hierarchical configuration system for improving grid strength, used to implement the reactive power source hierarchical configuration method as described above, including: The hierarchical division module is used to divide the power system into high-voltage and low-voltage layers according to voltage levels. The model building module is used to construct a two-layer configuration model of dynamic reactive power sources with the equivalent impedance of dynamic reactive power sources as the decision variable, the high-voltage layer stability constraint and the low-voltage layer stability constraint as the constraint conditions, and the minimum total capacity of dynamic reactive power sources as the objective function. The model solving module is used to solve the two-layer configuration model using a hierarchical solution strategy of "upper-layer optimization - lower-layer correction" to obtain a dynamic reactive power source configuration scheme that simultaneously satisfies the stability constraints of the high-voltage layer and the low-voltage layer.

[0014] Preferably, the model solving module includes: The upper-level optimization unit is used to set the dynamic reactive power source configuration scheme of the low-voltage layer to zero, solve the upper-level optimization model, and obtain the dynamic reactive power source installation location and capacity scheme that meets the stability constraints of the high-voltage layer. The impedance matrix update unit is used to incorporate the upper-level optimization results into the system network model and update the system node impedance matrix. The index calculation unit is used to calculate the improved multi-site short-circuit ratio index of each new energy grid connection point based on the updated impedance matrix. The lower-level correction unit is used to improve the short-circuit ratio index of multiple power stations below the preset threshold for new energy grid connection points. Based on the strength improvement requirements of the node, the unit configures a dynamic reactive power source with corresponding equivalent impedance at the node so that the short-circuit ratio index of the multiple power stations reaches the preset requirements. The iterative judgment unit is used to recalculate the system node impedance matrix and the improved multi-site short-circuit ratio index of each new energy grid connection point. If there are still new energy grid connection points that do not meet the strength requirements, the lower-level correction unit is triggered to continue iterating; otherwise, the final dynamic reactive power source configuration scheme is output.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention integrates the stability requirements of high-voltage-level DC feed-in systems and the grid connection intensity requirements of low-voltage-level renewable energy sources into a two-layer configuration model of dynamic reactive power sources. By constructing stability indicators for nodes at different voltage levels, it achieves hierarchical collaborative optimization configuration of dynamic reactive power sources.

[0016] The high-voltage layer uses short-circuit ratio and commutation failure risk indicators to characterize the stability requirements of the AC / DC system, while the low-voltage layer uses indicators that consider the mutual influence between power stations and the support capacity of new energy sources. The indicator represents the demand for grid connection intensity of new energy sources.

[0017] Based on the mapping relationship between the equivalent impedance and actual capacity of dynamic reactive power sources, a hierarchical solution strategy of "upper-level optimization - lower-level correction" is adopted. Under the premise of satisfying the stability constraints at different levels, the configuration capacity of dynamic reactive power sources is minimized, which improves the rationality, economy and engineering practicality of the configuration scheme. Attached Figure Description

[0018] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is the equivalent model diagram of the dynamic reactive power source of the present invention; Figure 3 This is a model diagram of the dynamic reactive power source access system of the present invention; Figure 4 This is a schematic diagram of the system structure of the present invention; Figure 5 This is the reactive power source assembly node of the present invention. Comparison chart. Detailed Implementation

[0019] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0020] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0021] Example: like Figure 1 As shown, this embodiment provides a method for hierarchical configuration of reactive power sources to improve grid strength, including the following steps: The power system is divided into high-voltage and low-voltage layers according to voltage levels; Using the equivalent impedance of dynamic reactive power sources as the decision variable, the high-voltage layer stability constraints and the low-voltage layer stability constraints as the constraints, and the minimum total capacity of dynamic reactive power sources as the objective function, a two-layer configuration model for dynamic reactive power sources is constructed. A hierarchical solution strategy of "upper-level optimization - lower-level correction" is adopted to solve the two-level configuration model, and a dynamic reactive power source configuration scheme that simultaneously satisfies the stability constraints of the high-voltage layer and the low-voltage layer is obtained.

[0022] High-pressure layer stability indicators: The high-voltage level layer of the system mainly refers to the DC feed-in points of the ultra-high voltage direct current (UHVDC) transmission projects within the system. To meet the needs of DC feed-in, the voltage level of these nodes generally exceeds 500kV. The reactive power requirements of these DC feed-in points are mainly divided into system strength requirements to ensure the static voltage stability of the DC system under steady-state conditions, and transient voltage support requirements to effectively reduce the risk of commutation failure under transient faults. Dynamic reactive power sources provide reactive power support to the system under both steady-state and transient conditions; therefore, it is necessary to ensure that the requirements of the DC system under both transient and steady-state conditions are met simultaneously.

[0023] Under steady-state operation, DC systems are required to have an operating short-circuit ratio no lower than the critical short-circuit ratio and to maximize voltage stability margin. Therefore, the short-circuit ratio can be directly used as an indicator of steady-state strength. For the system's... A high-voltage layer is directly fed into the node, and the short-circuit ratio at this point is the reciprocal of its self-impedance in the node impedance matrix, as shown in equation (1): (1); Among them, subscript Representing the One DC feed point, For nodes The short-circuit ratio, Here is the nodal impedance matrix of the system. for The first of the matrix Line 1 Columns, i.e., nodes The self-impedance. Typically, the DC feed point requires a short-circuit ratio of not less than 3, therefore it can... As one of the stability constraints for the DC feed point of the high-voltage layer.

[0024] Under transient faults, DC systems also require reactive power sources to provide sufficient voltage support to suppress transient voltage drops and reduce the risk of commutation failure. Therefore, in addition to short-circuit ratio constraints, it is necessary to construct constraint indicators that reflect the commutation failure risk of the DC system. Next, the transient voltage drop at the DC feed point under faults is calculated based on the node impedance matrix, and the commutation failure risk indicator of the DC system is defined accordingly: Assuming DC feed point A three-phase ground fault occurs at point A, and the short-circuit impedance is _____. According to the superposition theorem, the system voltage drop and fault current at this time are related. The following relationship exists: (2); in, to For nodes The fault transient voltage drop, Let be the total number of nodes in the system. For a fault point, according to Kirchhoff's theorem, assuming the voltage before the fault is 1 p.u., the following equation holds: (3); Substituting it into equation (2), we have: (4); Based on this, the voltage drop and fault current at that point can be calculated: , (5); As can be seen from equation (5), under the same short-circuit impedance, The larger the self-impedance of a fault point, the smaller the voltage drop of the system. Therefore, under transient faults, the voltage drop at the fault point is actually determined by the self-impedance of that node, that is, the short-circuit ratio of that node, which is exactly the same as the static voltage stability index of the system. This also shows that the short-circuit ratio index reflects static stability and is also related to transient voltage drop.

[0025] However, in actual power systems, faults cannot occur only at the DC feed-in point. Therefore, it is necessary to extend equation (5) to the voltage drop at the DC feed-in point when a fault occurs at any node in the entire network, assuming that the fault occurs at any point in the system. Similarly, at this point, the system voltage drop and fault current have the following relationship: (6); and The fault current at the point remains: (7); Substituting into equation (6), we can obtain the DC feed point at this time. Voltage drop at point: (8); in DC feed point Point and Fault Point Mutual impedance between points.

[0026] Consider the most severe fault scenario, namely a three-phase metallic ground fault ( Assuming that all nodes in the network have the same probability of failure, the average voltage drop after all nodes fail can be used as a measure of the transient voltage drop of that node. (9); in The total number of nodes in the network is given. Considering that when an AC system failure occurs, the voltage at the DC feed point should not be lower than its commutation failure threshold voltage, this is taken into account. Otherwise, the DC system will experience an irreversible commutation failure. Therefore, the difference between the average voltage drop and the critical voltage drop for commutation failure in the DC system can be considered as an indicator reflecting the commutation failure risk (CFR) of the DC system. (10); The smaller the value of this indicator, the greater the risk of commutation failure in the DC system when a fault occurs on the AC side. When this indicator is less than the critical voltage for commutation failure, it means that the average voltage drop of the system has exceeded the critical voltage drop for commutation failure, and the risk of commutation failure in the system is extremely high.

[0027] Thus, we have obtained the optimization indicators reflecting the voltage stability of the AC / DC feed system at the high-voltage layer: the static stability margin (SCR) of the DC system and the commutation failure risk (CFR). The SCR mainly characterizes the role of reactive power sources in improving the static stability of the system, while the CFR mainly characterizes the transient support capability of reactive power sources. When optimizing the configuration of reactive power sources at the high-voltage layer, the combined impact of reactive power sources on the above two indicators should be considered.

[0028] Low-pressure layer stability indicators: The low-voltage level layer of the system refers to the level where the grid connection points of various new energy power stations in the system are located. The voltage level of this level is usually less than 500kV. In the low-voltage layer, the steady-state and transient requirements of the system strength are mainly reflected in the short-circuit ratio requirements of key nodes such as new energy grid connection points. However, there is a big difference in the calculation of the short-circuit ratio between the low-voltage layer new energy power station access system and the high-voltage layer DC feed-in system: First, most of the DC feed-in points are AC buses of converter stations, with fewer landing points and higher voltage levels, while the number of new energy grid connection points in the low-voltage layer is large and the voltage level is low, resulting in non-negligible mutual influence; Second, when a transient fault occurs, the new energy power station needs to actively provide fault reactive power to compensate for part of the reactive power loss of the collector lines inside the new energy power station and the external transmission lines. The traditional short-circuit ratio index shown in Equation (1) ignores the mutual influence between the new energy grid connection points and the reactive power output capability of the new energy power station itself, and it is difficult to accurately reflect the stability level of the new energy grid connection points in the low-voltage layer. Therefore, the short-circuit ratio (MRSCR) of multiple renewable energy stations is adopted as an indicator to measure the stability level of renewable energy grid connection points. Further consideration is given to the impact of the reactive power support capacity of the renewable energy stations themselves, ultimately leading to an improved MRSCR indicator, the specific derivation of which is as follows: For the For each new energy grid connection point, the MRSCR further considers the mutual influence between power stations based on the traditional SCR, and incorporates the influence of other nodes in the form of impedance. Point, as shown in equation (11): (11); In the formula: where, subscript Representing the One new energy grid connection point, and Representing the first and The rated power of each renewable energy grid connection point. The MRSCR takes into account the electrical distance and network coupling relationship between different access points. For renewable energy grid connection points in the low-voltage layer with a large number of access nodes, this indicator can more accurately reflect the actual system strength of each access point in the scenario of centralized access by multiple substations compared with the short-circuit ratio indicator. Therefore, it is more suitable as a stability indicator for renewable energy grid connection points.

[0029] However, while the MRSCR index considers mutual influences, it does not take into account the reactive power support capacity of renewable energy sources themselves during faults. Due to the overcurrent capacity limitations of power electronic devices in renewable energy grid connection, renewable energy power plants typically function as current sources during faults, inputting additional current into the system to provide reactive power support within the maximum overcurrent limit. Assuming there is a fault in the system... New energy grid connection points When a system fault occurs, each grid connection point reaches its maximum overcurrent capacity to support the power grid, and the output current increment of the new energy grid connection point during the fault period can be obtained. : (12); in, For the first The output current amplitude of a new energy power station is usually around 1.4-2 pu; For the first The steady-state output current of a new energy power station, assuming it was operating at the steady-state point before the fault, then After considering the current output of the renewable energy power plant, assume the renewable energy grid connection point... When a fault occurs at a point, the nodal voltage equations of the system will be rewritten as follows: (13); in, This is for the fault voltage drop at each renewable energy power station. Consideration is given to three-phase short-circuit faults. In consideration Afterwards, when the node When a three-phase short circuit occurs, the fault current emitted at the short circuit point for: (14); in, Let be the mutual impedance between the fault point and each renewable energy grid connection point. Therefore, based on the definition of the short-circuit ratio, the improved short-circuit ratio considering the current output of the renewable energy power station at the per-unit value is expressed as: (15); Replace (11) with (15) This yields an improved MRSCR index that simultaneously considers the mutual influence between stations and the fault current output of the station itself, denoted as: : (16); Thus, reactive power configuration optimization indicators reflecting the grid connection points of new energy sources at the low-voltage layer have been obtained.

[0030] Construction of decision variables: Dynamic reactive power sources refer to dynamic reactive power compensation elements such as synchronous condensers and grid-type SVG, as well as reactive power compensation devices with active support capabilities. During fault periods, they typically exhibit voltage source characteristics and can therefore be equivalent to a voltage source in series with internal impedance, such as... Figure 2 As shown.

[0031] In the picture, This represents the internal impedance of the dynamic reactive power source under its own reference. and Let V represent the amplitude and phase of the internal electromotive force (EMF) of the dynamic reactive power source. Assume the dynamic reactive power source is installed at... When considering the impact of dynamic reactive power sources on various stability indicators, the dynamic reactive power source should first be considered as follows: Figure 3 The form shown is incorporated into the system, including the internal impedance. The per-unit values ​​are converted to the equivalent impedance in the system node impedance matrix. This forms a node impedance matrix that considers the dynamic reactive power source support capability. Then, the stability index of each layer is calculated based on this. Therefore, this embodiment uses the equivalent impedance of the dynamic reactive power source. The decision variables for configuring reactive power sources in the model are related to the reactive power source capacity as follows: (17); in, As a power reference for the system node impedance matrix, This represents the rated capacity of the reactive power source. Equation (17) represents the model decision variables. and actual engineering variables The relationship. When the model concludes at a certain point... The equivalent impedance needs to be installed. When the PU is a dynamic reactive power source, it means that the actual installed capacity at that point is [missing information]. Dynamic reactive power source.

[0032] Dynamic reactive power source two-layer configuration model: The aforementioned constructs reactive power source configuration optimization indices applicable to high-voltage layer DC feed-in nodes and low-voltage layer renewable energy grid-connected nodes, respectively, and uses the equivalent impedance of reactive power sources. The decision variables are represented by [variable name]. The high-voltage layer focuses on the static voltage stability capability of the AC / DC system and the risk of commutation failure, while the low-voltage layer focuses on the system strength requirements of renewable energy grid connection points. Since dynamic reactive power sources in different voltage level regions are not completely independent, their configuration results will influence each other through the grid topology and node impedance coupling relationships. Therefore, when planning reactive power sources, it is necessary to consider the synergistic effects between different levels simultaneously.

[0033] If all nodes in the high-voltage and low-voltage layers are uniformly converted to the same benchmark for centralized optimization, it will be difficult to take into account the optimization objectives of different levels due to the significant differences between the two types of nodes in terms of voltage level, equipment capacity and operating requirements. If reactive power sources are configured completely independently for each layer, it will be impossible to reflect the role of reactive power sources in the high-voltage layer in improving the strength of the low-voltage layer system, as well as the impact of reactive power sources in the low-voltage layer on the local power grid operation status.

[0034] Considering that the dynamic reactive power source capacity configured in the high-voltage layer is usually large, it has a significant impact on the impedance characteristics of the low-voltage layer nodes and the system strength; while the dynamic reactive power source capacity configured in the low-voltage layer is relatively small, and its impact on the operating state of the high-voltage layer system is limited. Therefore, the high-voltage layer optimization model is used as the upper-level problem of the two-level optimization model, and the low-voltage layer optimization model is used as the lower-level problem. The upper-level optimization results are used to determine the installation location and capacity of the large-capacity dynamic reactive power source, and serve as the input parameters for the lower-level optimization; the lower-level optimization further modifies the overall configuration scheme based on the upper-level optimization results. The overall mathematical model is shown in equations (18) - (19).

[0035] (18); (19); in, For upper-level decision variables, The equivalent impedance of the upper-level large-capacity dynamic reactive power source. Location for installing upper-level reactive power sources; For lower-level decision variables, The equivalent impedance of the lower-level small-capacity dynamic reactive power source. Location for installing the lower-level reactive power source; , , The objective function, equality constraints, and inequality constraints of the upper-level mathematical model; , , The objective function, equality constraints, and inequality constraints of the lower-level mathematical model.

[0036] The optimization objective is to minimize the total capacity of the assembled dynamic reactive power sources. Based on the conversion relationship between reactive power source capacity and equivalent impedance shown in equation (17), the upper and lower optimization layers share the same objective function: minimizing the sum of the capacities of all dynamic reactive power sources. (20); subscripts in the formula Representing the Taiwan dynamic reactive power source.

[0037] For the upper-level DC feed point, according to the previous analysis, its inequality constraints consist of the short-circuit ratio index and the commutation failure risk index. For the first... One DC feed point: (twenty one); subscripts in the formula Representing the One DC feed point.

[0038] For lower-level renewable energy grid connection points, based on the previous analysis, the inequality constraints are constituted by the improved multi-site short-circuit ratio index. For the first... One new energy grid connection point: (twenty two) Furthermore, both-layer optimizations must satisfy the equality power flow constraint. That is, for both the upper and lower layers, the following equality constraint applies: (twenty three); Equations (18)-(23) together constitute the reactive power source hierarchical configuration optimization model based on the node strength requirements of different voltage levels.

[0039] Solution steps: Since the established two-layer optimization model includes the installation location and capacity decision variables of dynamic reactive power sources in both high-voltage and low-voltage layers, direct solution has high computational complexity. To balance solution efficiency and configuration accuracy, this invention simplifies the model solution by adopting a hierarchical solution strategy of "upper-layer optimization - lower-layer correction" to gradually complete the optimized configuration of dynamic reactive power sources in different voltage level regions.

[0040] First, with the minimum dynamic reactive power source configuration capacity as the optimization objective, the optimization model for the high-voltage layer is solved under the conditions of satisfying system strength constraints and commutation failure risk constraints. Specifically, the dynamic reactive power source configuration scheme for the low-voltage layer is first set... Considering only the decision variables of the high-voltage layer, the upper-level optimization model shown in equation (18) is solved to obtain the dynamic reactive power source installation location and capacity scheme that meets the operation requirements of the DC feed-in system. .

[0041] Subsequently, the results of the upper-level optimization were... The system network model is incorporated, the impedance matrix of the system nodes is updated, and based on the updated impedance matrix, the improvements for each renewable energy grid connection point in the low-voltage layer are calculated one by one. Indicators. For Below the preset threshold For the new energy grid connection point i, based on the required strength enhancement demand of this node, a dynamic reactive power source with corresponding equivalent impedance is directly configured at this node, so that it... The target parameters have been met. The specific method for calculating the equivalent impedance of a dynamic reactive power source can be derived based on the branch addition method: When new energy grid connection point Point-to-point equivalent model such as Figure 1 When the dynamic reactive power source is shown, it can be considered as being in The point is connected to a line with an impedance of The grounding link branch. According to the branch addition method, in... After the grounding link is connected, the elements in the system impedance matrix will change as shown in the equation: , (twenty four); In the formula, For no source of power The increment of the nodal impedance matrix elements after point installation This is the node impedance matrix after the reactive power source is installed. Combining equation (16), we can obtain... After the reactive power source is installed at this node Changes: (25); Equation (25) establishes The analytical correspondence between indicators and the equivalent impedance of dynamic reactive power sources. This applies to the grid connection points of new energy sources in the low-voltage layer. We can deduce the solution that makes each point possible by working backward from equation (25). The equivalent impedance of the reactive power source Finally, a configuration scheme for the dynamic reactive power source in the low-voltage layer was derived. .

[0042] After completing the dynamic reactive power source configuration of the low-voltage layer, the system node impedance matrix and the grid connection points of each new energy source are recalculated. Then, it is determined again whether there are still new energy grid connection points that do not meet the intensity requirements. If there are still nodes that do not meet the requirements, then continue to add reactive power sources to the nodes based on equation (25); if all new energy grid connection points meet the intensity requirements, then the iteration process ends.

[0043] The final result is a dynamic reactive power source configuration scheme that simultaneously meets the stable operation requirements of the high-voltage layer DC feed-in system and the grid connection intensity requirements of the low-voltage layer renewable energy. This enables coordinated and optimized configuration of dynamic reactive power sources in regions with different voltage levels.

[0044] The above solution process can be summarized into the following steps: (1) Solve the high-voltage layer optimization model to obtain the dynamic reactive power source installation location and capacity configuration scheme that meets the operation requirements of the DC feed-in node; (2) Update the system node impedance matrix based on the upper-level optimization results; (3) Calculate the grid connection points of each new energy source index; (4) For For the new energy grid connection point, a dynamic reactive power source is directly configured at the original node for reinforcement, and the equivalent impedance of the reactive power source is obtained according to equation (25); (5) Recalculate the node impedance matrix and improve it index; (6) If there are still nodes that do not meet the strength requirements, return to step (4) to continue the iteration; otherwise, end the calculation and output the final dynamic reactive power source configuration scheme.

[0045] like Figure 4 As shown, this embodiment also provides a reactive power source hierarchical configuration system for improving grid strength, including: The hierarchical division module is used to divide the power system into high-voltage and low-voltage layers according to voltage levels. The model building module is used to construct a two-layer configuration model of dynamic reactive power sources with the equivalent impedance of dynamic reactive power sources as the decision variable, the high-voltage layer stability constraints and the low-voltage layer stability constraints as the constraints, and the minimum total capacity of dynamic reactive power sources as the objective function. The model solving module is used to solve the two-layer configuration model using a hierarchical solution strategy of "upper-layer optimization - lower-layer correction" to obtain a dynamic reactive power source configuration scheme that simultaneously satisfies the stability constraints of the high-voltage layer and the low-voltage layer.

[0046] The model solution module includes: The upper-level optimization unit is used to set the dynamic reactive power source configuration scheme of the low-voltage layer to zero, solve the upper-level optimization model, and obtain the dynamic reactive power source installation location and capacity scheme that meets the stability constraints of the high-voltage layer. The impedance matrix update unit is used to incorporate the upper-level optimization results into the system network model and update the system node impedance matrix. The index calculation unit is used to calculate the improved multi-site short-circuit ratio index of each new energy grid connection point based on the updated impedance matrix. The lower-level correction unit is used to improve the short-circuit ratio index of multiple power stations below the preset threshold for new energy grid connection points. Based on the strength improvement requirements of the node, the unit configures a dynamic reactive power source with corresponding equivalent impedance at the node so that the short-circuit ratio index of the multiple power stations reaches the preset requirements. The iterative judgment unit is used to recalculate the system node impedance matrix and the improved multi-site short-circuit ratio index of each new energy grid connection point. If there are still new energy grid connection points that do not meet the strength requirements, the lower-level correction unit is triggered to continue iterating; otherwise, the final dynamic reactive power source configuration scheme is output.

[0047] Furthermore, this embodiment uses actual data from a provincial power grid as an example to perform optimized calculations for the hierarchical configuration of reactive power sources. This power grid comprises three DC lines with a rated voltage of 500kV; 14 renewable energy nodes with a rated voltage of 220kV; and a total of 1860 nodes of 220kV and above, with a total synchronous machine installed capacity of 10000MW and a renewable energy installed capacity of 12600MW. Specifically, the names, data, and initial indicators of each DC and renewable energy node are shown in Tables 1 and 2.

[0048] Table 1 DC Node Information and Indicators

[0049] Table 2 New Energy Node Information and Indicators

[0050] First, calculate the upper-level model, i.e., the reactive power source configuration of the three DC nodes in the system, and take the lower limit of the short-circuit ratio of the DC nodes. commutation failure critical voltage Clearly, all three DC nodes meet the commutation failure risk constraint, but none meet the short-circuit ratio constraint, requiring the installation of reactive power sources to improve their short-circuit ratio. Let the upper-level model (18)... Optimization solution The equivalent impedances of the reactive power sources that meet the requirements of the upper-level constraints and their configuration methods are shown in Table 3: Table 3. Results of Equivalent Impedance Requirements of Upper-Level Reactive Sources

[0051] Subsequently, the reactive power source configuration results given in the table above are substituted into the original system and the impedance matrix is ​​updated. Then, the equivalent impedance of the reactive power source that satisfies the MRSCRRE constraint of the lower-level new energy grid connection point is solved step by step according to steps (3) to (6). The results are shown in Table 4.

[0052] Table 4. Results of Equivalent Impedance Requirements of Lower Layer Reactive Sources

[0053] The results in the table above show the locations of reactive power sources and their required equivalent impedances in the lower-level model. Combining Tables 1, 2, and 3, we obtain the required reactive power source configuration nodes and their equivalent impedances for the entire system. To verify the effectiveness of this configuration scheme, the SCR / MRSCRRE of each DC / new energy node before and after reactive power source configuration were calculated, and the results are as follows: Figure 5 As shown: As shown in the figure, after assembling the reactive power source according to the dual-layer optimization configuration model, the SCR at the upper DC feed point and the MRSCRRE at the lower DC feed point of the system are precisely reinforced, and the system strength is effectively improved.

[0054] The above is a detailed description of the preferred embodiments of the present invention, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method for hierarchical configuration of reactive power sources for improving grid strength, characterized in that, Includes the following steps: The power system is divided into high-voltage and low-voltage layers according to voltage levels; Using the equivalent impedance of dynamic reactive power sources as the decision variable, the high-voltage layer stability constraint and the low-voltage layer stability constraint as the constraint conditions, and the minimum total capacity of dynamic reactive power sources as the objective function, a two-layer configuration model for dynamic reactive power sources is constructed. The two-layer configuration model is solved by adopting a hierarchical solution strategy of "upper-layer optimization - lower-layer correction" to obtain a dynamic reactive power source configuration scheme that simultaneously satisfies the stability constraints of the high-voltage layer and the low-voltage layer.

2. The method for hierarchical configuration of reactive power sources for grid strength enhancement according to claim 1, characterized in that, The high-voltage layer stability constraints include short-circuit ratio constraints and commutation failure risk constraints; for the first There are one DC feed point, and the short-circuit ratio constraint is: ； in, For nodes The short-circuit ratio, , Here is the system node impedance matrix. For nodes Self-impedance, To preset the lower limit of the short-circuit ratio; The commutation failure risk constraint is as follows: ； in, For nodes Commutation failure risk indicators , This represents the total number of nodes in the network. DC feed point and the point of failure mutual impedance between Fault point Self-impedance, This is the critical voltage for commutation failure.

3. The method for hierarchical configuration of reactive power sources for grid strength enhancement according to claim 1, characterized in that, The low-pressure layer stability constraint is an improved multi-station short-circuit ratio constraint; for the first... For each new energy grid connection point, the improved multi-station short-circuit ratio constraint is: ； in, For the first Improvements to the short-circuit ratio of multiple new energy grid connection points To preset and improve the lower limit of short-circuit ratio for multiple stations; Represented as: ； in, This represents the mutual impedance vector between the fault point and each renewable energy grid connection point. This represents the incremental output current vector at the new energy grid connection point during a fault. and The first The and the first The rated power of each new energy grid connection point For nodes With nodes The mutual impedance between them.

4. A method for hierarchical configuration of reactive power sources for grid strength enhancement according to claim 1, characterized in that, The conversion relationship between the equivalent impedance of the dynamic reactive power source and its actual capacity is as follows: ； in, The equivalent impedance of a dynamic reactive power source. This represents the internal impedance of the dynamic reactive power source under its own reference. As a power reference for the system node impedance matrix, Rated capacity of dynamic reactive power source; The objective function is: ； in, This represents the total number of dynamic reactive power sources. For the first The equivalent impedance of the dynamic reactive power source in Taiwan. For the first The internal impedance of the dynamic reactive power source under its own reference.

5. A method for hierarchical configuration of reactive power sources for grid strength enhancement according to claim 1, characterized in that, The upper-level optimization model of the two-layer configuration model uses the equivalent impedance of the dynamic reactive power source of the high-voltage layer. and installation location The decision variable is determined by the high-voltage layer stability constraint, and the objective function is to minimize the total capacity of dynamic reactive power sources. The lower-level optimization model of the two-layer configuration model uses the equivalent impedance of the dynamic reactive power source in the low-voltage layer. and installation location The decision variable is defined by the low-voltage layer stability constraint, and the objective function is to minimize the total capacity of dynamic reactive power sources. Both the upper-level optimization model and the lower-level optimization model satisfy the power flow equation constraint: ； ； in, , They are nodes The generator has active and reactive power outputs. , They are nodes Active and reactive loads, , They are nodes and nodes voltage amplitude, , They are nodes With nodes The conductivity and susceptance between them For nodes With nodes The voltage phase angle difference between them.

6. A method for hierarchical configuration of reactive power sources for grid strength enhancement according to claim 1, characterized in that, The hierarchical solution strategy of "upper-level optimization - lower-level correction" includes: Set the low-voltage layer dynamic reactive power source configuration scheme to zero, solve the upper-layer optimization model, and obtain the dynamic reactive power source installation location and capacity scheme that satisfies the stability constraints of the high-voltage layer. The optimization results are incorporated into the system network model to update the system node impedance matrix; Based on the updated impedance matrix, the improved multi-station short-circuit ratio index of each new energy grid connection point is calculated. For new energy grid connection points where the short-circuit ratio of multiple power stations is lower than the preset threshold, dynamic reactive power sources with corresponding equivalent impedance are configured at the node according to the strength improvement requirements of the node, so that the short-circuit ratio of multiple power stations can meet the preset requirements. Recalculate the system node impedance matrix and improve the short-circuit ratio index of each new energy grid connection point for multiple power stations; If there are still new energy grid connection points that do not meet the intensity requirements, return to step four to continue the iteration; otherwise, end the calculation and output the final dynamic reactive power source configuration scheme.

7. A method for hierarchical configuration of reactive power sources for grid strength enhancement according to claim 6, characterized in that, New energy grid connection points After configuring dynamic reactive power sources, this node improves the short-circuit ratio of multiple substations. The relationship of change is expressed as: ； in, For new energy grid connection points Improved short-circuit ratio in multiple substations after configuring dynamic reactive power sources. The equivalent impedance of the dynamic reactive power source configured at this point; according to The equivalent dynamic reactive power source impedance required for each non-compliant renewable energy grid connection point is obtained by reverse calculation. .

8. A reactive power source hierarchical configuration system for improving grid strength, used to implement the reactive power source hierarchical configuration method as described in any one of claims 1-7, characterized in that, include: The hierarchical division module is used to divide the power system into high-voltage and low-voltage layers according to voltage levels. The model building module is used to construct a two-layer configuration model of dynamic reactive power sources with the equivalent impedance of dynamic reactive power sources as the decision variable, the high-voltage layer stability constraints and the low-voltage layer stability constraints as the constraints, and the minimum total capacity of dynamic reactive power sources as the objective function. The model solving module is used to solve the two-layer configuration model using a hierarchical solution strategy of "upper-layer optimization - lower-layer correction" to obtain a dynamic reactive power source configuration scheme that simultaneously satisfies the stability constraints of the high-voltage layer and the low-voltage layer.

9. A reactive power source hierarchical configuration system for grid strength enhancement according to claim 8, characterized in that, The model solving module includes: The upper-level optimization unit is used to set the dynamic reactive power source configuration scheme of the low-voltage layer to zero, solve the upper-level optimization model, and obtain the dynamic reactive power source installation location and capacity scheme that meets the stability constraints of the high-voltage layer. The impedance matrix update unit is used to incorporate the upper-level optimization results into the system network model and update the system node impedance matrix. The index calculation unit is used to calculate the improved multi-site short-circuit ratio index of each new energy grid connection point based on the updated impedance matrix. The lower-level correction unit is used to improve the short-circuit ratio index of multiple power stations below the preset threshold for new energy grid connection points. Based on the strength improvement requirements of the node, the unit configures a dynamic reactive power source with corresponding equivalent impedance at the node so that the short-circuit ratio index of the multiple power stations reaches the preset requirements. The iterative judgment unit is used to recalculate the system node impedance matrix and the improved multi-site short-circuit ratio index of each new energy grid connection point. If there are still new energy grid connection points that do not meet the strength requirements, the lower-level correction unit is triggered to continue iterating; otherwise, the final dynamic reactive power source configuration scheme is output.

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