Alternating current and direct current hybrid network rack optimization control method and device based on strong and weak balance

Abstract

The invention provides an alternating-current and direct-current hybrid grid optimization control method and device based on strong and weak balance. The method comprises the following steps: constructing an alternating-current and direct-current hybrid grid optimization model considering power flow constraint, short-circuit current constraint, channel and converter station capacity constraint and planning cost; based on the AC / DC hybrid network rack optimization model, optimizing a current AC / DC hybrid network rack structure to obtain an AC / DC hybrid network rack initial optimization scheme; performing voltage stability evaluation and system transient stability evaluation on the initial optimization scheme of the alternating current and direct current hybrid network rack, and judging whether the initial optimization scheme of the alternating current and direct current hybrid network rack meets a strong and weak balance requirement or not according to an evaluation result; adjusting the initial optimization scheme of the alternating-current and direct-current hybrid network rack which does not meet the strong and weak balance requirement until the optimal optimization scheme of the alternating-current and direct-current hybrid network rack which meets the strong and weak balance requirement is obtained; according to the method, the fault influence can be avoided to the greatest extent, and the robustness of the grid system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution networks, and in particular to an AC / DC hybrid network frame optimization control method and device based on strong / weak balance. Background Art

[0002] As China's energy mix transforms, installed capacity of renewable energy sources continues to increase annually. This increased penetration of renewable energy will lead to reduced system inertia, insufficient short-circuit capacity, and weakened frequency and voltage regulation capabilities of traditional synchronous generators. This will severely challenge the voltage and transient stability capabilities of the AC grid and place higher demands on the grid's transmission capacity. Due to grid short-circuit current constraints, AC transmission capacity is nearing saturation. Embedded DC systems are being considered to enhance grid transmission capacity. However, the introduction of embedded DC changes the operating characteristics of the AC grid. Due to the power flow coupling characteristics of hybrid AC / DC grids, capacity matching between the AC and DC systems is required to ensure normal power flow transmission under varying grid operating conditions. The introduction of DC lines increases the electrical distance between source and load nodes in the AC grid, weakening AC connections across transmission sections and reducing the grid's voltage support capacity. Furthermore, the reduced system inertia will affect the AC / DC hybrid grid's ability to withstand interference. When a short-circuit fault occurs, the system frequency will fluctuate significantly, the power angle curve will oscillate more, and transient stability will be weakened. It can be seen that the introduction of embedded DC will not only improve the current flow operation and short-circuit current, but will also bring challenges to the stability of the AC / DC hybrid network.

[0003] Given the complex operating characteristics of AC / DC hybrid grids, optimizing the grid structure topology while simultaneously balancing economic efficiency, safety, and stability, while also overcoming technical bottlenecks in grid development, is a pressing issue. However, existing research primarily considers single issues such as power flow and short-circuit current improvement, failing to fully mitigate the impact of faults. For example, Chinese patent application CN110875602A discloses a method for optimizing grid reconstruction schemes for multiple DC feed-in systems. The method comprises the following steps: I. Determining the grid reconstruction objective function for multiple DC feed-in systems: including a target grid optimization objective and a power source startup sequence optimization objective. II. Determining the constraints for the grid reconstruction of multiple DC feed-in systems: grid connectivity constraints, DC startup constraints, unit startup constraints, and power flow constraints. III. Solving the established model using a hybrid particle swarm algorithm in two steps: target grid optimization and unit startup sequence optimization. Each step involves particle initialization, fitness calculation, and iterative updates. The aforementioned method cannot fully mitigate the impact of faults and cannot effectively improve grid voltage stability. Summary of the Invention

[0004] The present invention provides an AC / DC hybrid grid optimization control method and device based on strong-weak balance to improve grid voltage stability.

[0005] An AC / DC hybrid grid optimization control method based on strong / weak balance includes: Construct an AC / DC hybrid grid optimization model that considers power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs; Based on the AC / DC hybrid grid optimization model, the current AC / DC hybrid grid structure is optimized to obtain an initial optimization solution for the AC / DC hybrid grid; Conducting voltage stability assessment and system transient stability assessment on the initial optimization scheme for the AC / DC hybrid grid, and determining whether the initial optimization scheme for the AC / DC hybrid grid meets the requirements for strong-weak balance based on the assessment results; The initial optimization scheme of the AC / DC hybrid grid that does not meet the strong-weak balance requirements is adjusted until the optimal AC / DC hybrid grid optimization scheme that meets the strong-weak balance requirements is obtained.

[0006] Furthermore, the AC / DC hybrid grid optimization model includes power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and an objective function to minimize planning costs.

[0007] Furthermore, based on the AC / DC hybrid grid optimization model, the current AC / DC hybrid grid structure is optimized to obtain an initial optimization solution for the AC / DC hybrid grid, including: At least one of adding a DC line, adding an AC line, and converting an AC line to a DC line is performed on the current AC / DC hybrid grid structure to obtain candidate solutions. Based on the candidate solutions, an optimization algorithm is used to calculate and obtain an initial optimization solution for the AC / DC hybrid grid that satisfies the power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and minimizes the planning cost.

[0008] Furthermore, a voltage stability assessment and a system transient stability assessment are performed on the initial optimization scheme of the AC / DC hybrid grid, and whether the initial optimization scheme of the AC / DC hybrid grid meets the requirements of strong and weak balance is determined based on the assessment results, including: Calculate the voltage stiffness of the corresponding node according to the voltage of the network-connected equipment corresponding to the node in the initial optimization scheme of the AC / DC hybrid network rack; If the voltage stiffness of all nodes in the initial optimization scheme of the AC / DC hybrid grid is greater than the first preset value, it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the voltage stability requirement; Calculate the AC / DC system strength ratio index based on the AC and DC channel capacities between all two nodes in the initial optimization plan of the AC / DC hybrid grid; If the AC / DC system strength ratio index of all two nodes in the AC / DC hybrid network rack initial optimization scheme is greater than a second preset value, it is determined that the AC / DC hybrid network rack initial optimization scheme meets the system transient stability requirements; If the initial optimization scheme of the AC / DC hybrid grid meets both the voltage stability requirement and the system transient stability requirement, then it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the strong-weak balance requirement; The initial optimization scheme of the AC / DC hybrid grid that meets the strong-weak balance requirements is determined as the optimal AC / DC hybrid grid optimization scheme.

[0009] Furthermore, the voltage stiffness is a ratio of a voltage modulus of a network port when a network-accessing device corresponding to the node is connected to a no-load voltage when the network-accessing device corresponding to the node is not connected.

[0010] Furthermore, the AC / DC system strength ratio index is the ratio between the AC channel capacity and the DC channel capacity between any two nodes.

[0011] Furthermore, the initial optimization scheme of the AC / DC hybrid grid that does not meet the requirements of strong and weak balance is adjusted until the optimal AC / DC hybrid grid optimization scheme that meets the requirements of strong and weak balance is obtained, including: For AC / DC hybrid grid initial optimization schemes that do not meet voltage stability requirements, static VAR compensation devices or VSC DC devices are introduced. The adjusted AC / DC hybrid grid initial optimization scheme is then re-evaluated and adjusted for voltage stability until voltage stability requirements are met. For the initial optimization plan of AC / DC hybrid grid that does not meet the system transient stability requirements, disconnect the AC lines between nodes and re-evaluate and adjust the system transient stability until the system transient stability requirements are met; The initial optimization scheme of the AC / DC hybrid grid that meets both the voltage stability requirements and the system transient stability requirements after adjustment is determined as the optimal AC / DC hybrid grid optimization scheme.

[0012] Furthermore, the initial optimization scheme for AC / DC hybrid grids that do not meet voltage stability requirements introduces static VAR compensation devices or VSC DC devices, including: Identifying nodes in an initial optimization scheme for an AC / DC hybrid grid that does not meet voltage stability requirements and in which voltage stiffness is less than or equal to a first preset value; A static VAR compensation device or a VSC direct current device is connected to a node where the voltage stiffness is less than or equal to a first preset value.

[0013] Furthermore, for the initial optimization scheme of AC / DC hybrid grids that do not meet the system transient stability requirements, the AC lines between nodes are disconnected, including: Determine a node in the initial optimization plan for the AC / DC hybrid grid that does not meet the system transient stability requirements and in which the AC / DC system strength ratio index is less than or equal to a second preset value; The AC lines in the transmission sections between two nodes whose AC / DC system strength ratio index is less than or equal to the second preset value are disconnected.

[0014] An AC / DC hybrid grid optimization control device based on strong / weak balance, comprising: A model building module is used to construct an AC / DC hybrid grid optimization model that considers power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs; An initial optimization module, configured to optimize the current AC / DC hybrid network rack structure based on the AC / DC hybrid network rack optimization model to obtain an initial optimization solution for the AC / DC hybrid network rack; An evaluation module is used to perform voltage stability evaluation and system transient stability evaluation on the initial optimization scheme of the AC / DC hybrid grid, and determine whether the initial optimization scheme of the AC / DC hybrid grid meets the requirements of strong and weak balance according to the evaluation results; The adjustment model is used to adjust the initial optimization scheme of the AC / DC hybrid network rack that does not meet the strong-weak balance requirements until the optimal AC / DC hybrid network rack optimization scheme that meets the strong-weak balance requirements is obtained.

[0015] Furthermore, the AC / DC hybrid grid optimization model includes power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and an objective function to minimize planning costs.

[0016] Furthermore, the initial optimization module optimizes the current AC / DC hybrid network frame structure based on the AC / DC hybrid network frame optimization model to obtain an initial optimization solution for the AC / DC hybrid network frame, including: At least one of adding a DC line, adding an AC line, and converting an AC line to a DC line is performed on the current AC / DC hybrid grid structure to obtain candidate solutions. Based on the candidate solutions, an optimization algorithm is used to calculate and obtain an initial optimization solution for the AC / DC hybrid grid that satisfies the power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and minimizes the planning cost.

[0017] Furthermore, the evaluation module performs voltage stability evaluation and system transient stability evaluation on the initial optimization scheme of the AC / DC hybrid grid, and determines whether the initial optimization scheme of the AC / DC hybrid grid meets the strong-weak balance requirement based on the evaluation results, including: Calculate the voltage stiffness of the corresponding node according to the voltage of the network-connected equipment corresponding to the node in the initial optimization scheme of the AC / DC hybrid network rack; If the voltage stiffness of all nodes in the initial optimization scheme of the AC / DC hybrid grid is greater than the first preset value, it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the voltage stability requirement; Calculate the AC / DC system strength ratio index based on the AC and DC channel capacities between all two nodes in the initial optimization plan of the AC / DC hybrid grid; If the AC / DC system strength ratio index of all two nodes in the AC / DC hybrid network rack initial optimization scheme is greater than a second preset value, it is determined that the AC / DC hybrid network rack initial optimization scheme meets the system transient stability requirements; If the initial optimization scheme of the AC / DC hybrid grid meets both the voltage stability requirement and the system transient stability requirement, then it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the strong-weak balance requirement; The initial optimization scheme of the AC / DC hybrid grid that meets the strong-weak balance requirements is determined as the optimal AC / DC hybrid grid optimization scheme.

[0018] Furthermore, the voltage stiffness is a ratio of a voltage modulus of a network port when a network-accessing device corresponding to the node is connected to a no-load voltage when the network-accessing device corresponding to the node is not connected.

[0019] Furthermore, the AC / DC system strength ratio index is the ratio between the AC channel capacity and the DC channel capacity between any two nodes.

[0020] Furthermore, the adjustment module adjusts the initial optimization scheme of the AC / DC hybrid network rack that does not meet the requirements of strong and weak balance until an optimal AC / DC hybrid network rack optimization scheme that meets the requirements of strong and weak balance is obtained, including: For AC / DC hybrid grid initial optimization schemes that do not meet voltage stability requirements, static VAR compensation devices or VSC DC devices are introduced. The adjusted AC / DC hybrid grid initial optimization scheme is then re-evaluated and adjusted for voltage stability until voltage stability requirements are met. For the initial optimization plan of AC / DC hybrid grid that does not meet the system transient stability requirements, disconnect the AC lines between nodes and re-evaluate and adjust the system transient stability until the system transient stability requirements are met; The initial optimization scheme of the AC / DC hybrid grid that meets both the voltage stability requirements and the system transient stability requirements after adjustment is determined as the optimal AC / DC hybrid grid optimization scheme.

[0021] Furthermore, the adjustment module introduces a static VAR compensation device or a VSC DC device into the initial optimization solution of the AC / DC hybrid grid that does not meet the voltage stability requirements, including: Identifying nodes in an initial optimization scheme for an AC / DC hybrid grid that does not meet voltage stability requirements and in which voltage stiffness is less than or equal to a first preset value; A static VAR compensation device or a VSC direct current device is connected to a node where the voltage stiffness is less than or equal to a first preset value.

[0022] Furthermore, the adjustment module disconnects the AC lines between nodes for the initial optimization scheme of the AC / DC hybrid network frame that does not meet the system transient stability requirements, including: Determine a node in the initial optimization plan for the AC / DC hybrid grid that does not meet the system transient stability requirements and in which the AC / DC system strength ratio index is less than or equal to a second preset value; The AC lines in the transmission sections between two nodes whose AC / DC system strength ratio index is less than or equal to the second preset value are disconnected.

[0023] An electronic device includes a processor and a storage device, wherein the storage device stores a plurality of instructions, and the processor is used to read the instructions and execute the above method.

[0024] A computer storage medium stores a plurality of instructions, wherein the plurality of instructions are used to execute the above method when read.

[0025] The AC / DC hybrid grid optimization control method and device based on strong / weak balance provided by the present invention have at least the following beneficial effects: (1) Propose an AC / DC hybrid grid optimization model based on power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs to ensure that the optimized grid can meet the power balance and voltage stability requirements in both normal operation and fault conditions, avoid overload or voltage exceeding the limit, and reduce network losses, improve transmission efficiency, and reduce operating costs by optimizing power flow distribution. Limit the short-circuit current level within the breaking capacity of equipment such as circuit breakers and transformers to avoid equipment damage, prevent the spread of short-circuit faults, and reduce the risk of cascading failures. In particular, when the DC system fails (such as phase change failure), the fault area can be quickly isolated to ensure that the grid can still meet the operating requirements under N-1 faults or extreme scenarios, minimize the impact of faults, and improve the robustness of the grid system; at the same time, consider economic efficiency; (2) Based on the obtained optimization scheme, the voltage stiffness and AC / DC system strength ratio indicators are used to verify whether the voltage and transient stability of the AC / DC hybrid grid after topology optimization meet the engineering standards. Finally, for the scenario that does not meet the engineering stability standards, a topology structure and adjustment strategy are proposed to achieve the construction of an AC / DC hybrid grid that takes into account both economy, safety and stability, so that the AC system and DC system in the optimized AC / DC hybrid grid meet the principle of strong and weak balance; (3) Introducing static VAR compensation devices or VSC DC devices into the initial optimization scheme for AC / DC hybrid grids that do not meet voltage stability requirements can effectively suppress voltage fluctuations, improve voltage stability, and further optimize AC / DC hybrid grids; (4) For the initial optimization scheme of the AC / DC hybrid grid that does not meet the system transient stability requirements, disconnecting the AC lines between nodes can optimize the power flow distribution, thereby improving the system transient stability and further optimizing the AC / DC hybrid grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention provides a flowchart of an embodiment of an AC / DC hybrid grid optimization control method based on strong-weak balance.

[0027] Figure 2 The present invention provides a flowchart of an embodiment of voltage stability assessment and system transient stability assessment in the AC / DC hybrid grid optimization control method based on strong-weak balance.

[0028] Figure 3 This is a schematic diagram of an embodiment of the relationship between short-circuit ratio and voltage stiffness in the AC / DC hybrid grid optimization control method based on strong-weak balance provided by the present invention.

[0029] Figure 4 The present invention provides a flowchart of an embodiment of adjusting the initial optimization scheme of the AC / DC hybrid network rack in the AC / DC hybrid network rack optimization control method based on strong and weak balance provided by the present invention.

[0030] Figure 5 A schematic diagram of a grid structure in an application scenario of the AC / DC hybrid grid optimization control method based on strong-weak balance provided by the present invention.

[0031] Figure 6 A schematic diagram of the optimized grid structure in an application scenario of the AC / DC hybrid grid optimization control method based on strong-weak balance provided by the present invention.

[0032] Figure 7 This is a structural schematic diagram of an embodiment of an AC / DC hybrid grid optimization control device based on strong-weak balance provided by the present invention. DETAILED DESCRIPTION

[0033] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0034] refer to Figure 1 In some embodiments, a method for optimizing and controlling an AC / DC hybrid network based on a balance of strength and weakness is provided, comprising: S1. Construct an AC / DC hybrid grid optimization model that considers power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs; S2. Based on the AC / DC hybrid grid optimization model, optimize the current AC / DC hybrid grid structure to obtain an initial optimization solution for the AC / DC hybrid grid; S3. Perform voltage stability evaluation and system transient stability evaluation on the initial optimization scheme of the AC / DC hybrid grid, and determine whether the initial optimization scheme of the AC / DC hybrid grid meets the requirements of strong and weak balance based on the evaluation results; S4. Adjust the initial optimization scheme of the AC / DC hybrid network rack that does not meet the strong-weak balance requirement until an optimal AC / DC hybrid network rack optimization scheme that meets the strong-weak balance requirement is obtained.

[0035] Specifically, in step S1, the AC / DC hybrid grid optimization model includes power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and an objective function of minimizing planning costs.

[0036] In view of the increase in the installed capacity and load of new energy in the national power grid, the adoption of new AC solutions in the AC / DC hybrid grid at the provincial level can effectively share the transmission load of existing lines by adding AC lines, thereby alleviating line overload pressure and improving the ability to absorb new energy. For the new DC solution, since the DC transmission system has the characteristics of flexible power regulation, the AC / DC hybrid transmission section can achieve power optimization distribution through coordinated control strategies. After the introduction of embedded DC, each transmission section in the grid must meet the load supply demand and power generation absorption demand under the new energy scenario in steady state. The power flow constraint conditions can be described as: ; (1) ; (2) in, is the total capacity of the newly added DC line between the i-th node and the j-th node, is the total capacity of the newly added AC line between the i-th node and the j-th node, is the existing total transmission capacity of the channel between the i-th node and the j-th node, It is expressed as the total capacity of the AC line in the scheme of converting the AC line between the i-th node and the j-th node into a DC line in the topology optimization process, r is the number of nodes in the AC / DC hybrid network, P G and P L They are the power generation and consumption demand and the node load supply demand, G represents the set of power output nodes in the sending-end power grid, and L represents the set of load power supply nodes in the receiving-end power grid.

[0037] In addition, the AC / DC hybrid network rack should also have a certain ability to resist fault risks. In the AC / DC hybrid network rack, after the AC or DC line N-1 fails, the steady-state power flow of the faulty line will be transferred to the remaining AC lines in the section, which will bring a greater impact to the AC line. The DC line will not participate in the power redistribution due to its power controllable characteristics. Therefore, in the process of AC / DC hybrid network rack planning, the power flow constraint under the line N-1 failure is also an important factor to be considered. The anti-N-1 impact strength index S of the channel between the i-th node and the j-th node of the system ac,dc_ijIt can accurately describe the ability of AC lines to withstand the impact of power flow transfer from fault lines under the planning scheme, providing a theoretical basis for power grid security assessment. Therefore, the power flow constraints also include: ; (3) Among them, S ac,dc_ij It is the N-1 impact strength index. is the total maximum transmission capacity of AC transmission lines in the AC / DC hybrid grid, is the sum of the steady-state transmission power of all AC lines in the AC / DC hybrid network under normal operating conditions, Transmit power for the kth DC line between the i-th node and the j-th node.

[0038] Due to the introduction of DC, the electrical distance between nodes in the AC / DC hybrid grid is increased compared to the all-AC grid, which will reduce the short-circuit current of the nodes. The AC grid has dense lines and a large transmission scale. The risk of exceeding the short-circuit current under fault conditions is high. Once the short-circuit current exceeds the standard, the heat and electric force generated will damage the performance of the equipment, causing the grid voltage to drop sharply, destroying the system stability, and even causing large-scale power outages. Therefore, short-circuit current is one of the key factors restricting the scale development of the grid. During planning, each node must meet the maximum allowable short-circuit current limit. Taking into account the different structures, equipment characteristics and operating modes of the grid, a certain short-circuit current safety margin must be guaranteed. Therefore, the short-circuit current constraint can be expressed as: ; (4) ; (5) in, is the maximum allowable short-circuit current of the i-th node in the AC / DC hybrid grid, is the actual short-circuit current peak value of the i-th node in the AC / DC hybrid grid, Z ii is the self-impedance value of the i-th node, γ i is the short-circuit current margin value of the i-th node, is the minimum short-circuit current margin required for the i-th node.

[0039] Furthermore, channel resource constraints are also a key issue that needs to be considered when planning the topology of AC / DC hybrid grids. Due to the relatively mature development of the existing AC grid and the dense transmission lines, the land, pipelines and other resources used to build transmission channels are close to saturation, which poses a challenge to the expansion of transmission channels. In addition, considering the capacity limitations of converter station units, in order to ensure stable and efficient power transmission, it is necessary to rationally utilize channel resources, meet channel transmission power constraints, and ensure that the converter station processing capacity covers the total line capacity. The following is the channel and converter station capacity constraint formula: ; (6) ; (7) in, is the maximum transmission power limit of the channel between the i-th node and the j-th node, N dc_ij is the number of DC converter stations in the channel between the i-th node and the j-th node, is the capacity limit of a single converter station, is the power transmitted by the kth DC line between the i-th node and the j-th node, m represents the number of DC lines, is the total capacity of the newly added DC line between the i-th node and the j-th node, is the total capacity of the newly added AC line between the i-th node and the j-th node, It is expressed as the total capacity of the AC line in the scheme of converting the AC line between the i-th node and the j-th node into a DC line in the topology optimization process, is the existing total transmission capacity of the channel between the i-th node and the j-th node.

[0040] The aforementioned power flow constraints, short-circuit current constraints, and channel and converter station capacity constraints restrict the capacity and location of AC / DC systems within the AC / DC hybrid grid. Given limited channel resources, DC may be introduced through an AC-to-DC conversion scheme. However, due to the potential for insufficient AC transmission margin at the grid transmission section, the ability to withstand power flow transfer shocks under N-1 faults is weak. To enhance the grid's fault resilience, AC may be reinforced at some nodes. The following summarizes the cost conditions of different schemes to construct a planning cost function: ; (8) Among them, L ij is the line length, c dc_ij The unit (MW km) cost of adding a DC solution to the channel between the i-th node and the j-th node, c ac_ij The unit cost of adding a communication scheme for the channel between the i-th node and the j-th node, c ac-dc_ij is the unit cost of the direct-to-interchange scheme between the i-th and j-th nodes, c 0_ij is the unit cost of the DC converter station, C total_ij is the AC / DC planning cost of the channel between the i-th node and the j-th node, which includes construction cost, operation and maintenance cost, depreciation cost, etc. dc_ij is the number of DC converter stations in the channel between the i-th node and the j-th node, is the total capacity of the newly added AC lines between the i-th node and the j-th node during the optimization process, The total capacity of the AC line in the AC line to DC line conversion scheme, is the total capacity of the newly added DC line between the i-th node and the j-th node.

[0041] Taking into account the above power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and aiming to minimize planning costs, an AC / DC hybrid grid optimization model is constructed: ; ; (9) Furthermore, in step S2, based on the AC / DC hybrid grid frame optimization model, the current AC / DC hybrid grid frame structure is optimized to obtain an initial optimization solution for the AC / DC hybrid grid frame, including: At least one of adding a DC line, adding an AC line, and converting an AC line to a DC line is performed on the current AC / DC hybrid grid structure to obtain candidate solutions. Based on the candidate solutions, an optimization algorithm is used to calculate and obtain an initial optimization solution for the AC / DC hybrid grid that satisfies the power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and minimizes the planning cost.

[0042] Among them, optimization algorithms can include particle algorithms, genetic algorithms, etc.

[0043] For example, a particle algorithm is used, and a candidate solution of a candidate solution is used as a particle. The candidate solution is a solution after performing at least one of the operations of adding a DC line, adding an AC line, and changing an AC line to a DC line on the current AC / DC hybrid network structure. The particle swarm is initialized, the fitness of each particle is calculated, and the individual optimum and the global optimum are updated according to the fitness of the particle. The speed and position of the ion are updated until the stopping condition is met, and the global optimal solution is used as the initial optimization solution of the AC / DC hybrid network.

[0044] Further, refer to Figure 2 In step S3, voltage stability evaluation and system transient stability evaluation are performed on the initial optimization scheme of the AC / DC hybrid grid, and whether the initial optimization scheme of the AC / DC hybrid grid meets the requirements of strong and weak balance is determined based on the evaluation results, including: S31. Calculate the voltage stiffness of the corresponding node according to the voltage of the network-connected device corresponding to the node in the initial optimization scheme of the AC / DC hybrid network rack; S32. If the voltage stiffness of all nodes in the initial optimization scheme for the AC / DC hybrid network rack is greater than a first preset value, determining that the initial optimization scheme for the AC / DC hybrid network rack meets the voltage stability requirement; S33. Calculate the AC / DC system strength ratio index based on the AC channel capacity and DC channel capacity between all two nodes in the initial optimization plan for the AC / DC hybrid network. S34. If the AC / DC system strength ratio indexes of all two nodes in the initial optimization scheme for the AC / DC hybrid network rack are greater than a second preset value, it is determined that the initial optimization scheme for the AC / DC hybrid network rack meets the system transient stability requirements; S35. If the initial optimization scheme for the AC / DC hybrid network rack satisfies both the voltage stability requirement and the system transient stability requirement, then determining that the initial optimization scheme for the AC / DC hybrid network rack satisfies the strong / weak balance requirement; S36. Determine the initial optimization scheme of the AC / DC hybrid grid that meets the strong-weak balance requirement as the optimal AC / DC hybrid grid optimization scheme.

[0045] Specifically, in step S31 , the voltage stiffness is the ratio of the voltage modulus of the network port when the node corresponding to the network access device is connected to the no-load voltage when the node corresponding to the network access device is not connected.

[0046] Compared to a fully AC grid, the introduction of DC will weaken the AC connections between nodes, reducing the AC system's ability to support the voltage and power of the hybrid grid, and degrading the system's voltage and transient stability. The following section examines whether the voltage and transient stability of the initial optimized AC / DC hybrid grid meet project requirements.

[0047] The first step is to verify grid voltage stability, which primarily depends on the strength of the AC system. Voltage stability can be verified using the voltage stiffness index, which measures AC system strength and is also applicable to AC / DC hybrid grids. This index defines the voltage support strength at any point in the grid as the ability to maintain the voltage modulus at that point close to the no-load voltage at that point. The voltage stiffness of a node can be calculated using the following formula: ; (10) Among them, K vtg is the voltage stiffness of the node, λ SCR is the short-circuit ratio of the node corresponding to the network device, U sys is the voltage modulus on the network port of the node corresponding to the network device, U sys0 is the no-load voltage at any point when the node corresponding to the network-connected device is not connected to the grid. The ratio of the two is the voltage stiffness.

[0048] According to the relationship between short-circuit ratio and voltage stiffness, Figure 3 As shown, it can be seen that when λ SCR >>1, U sys ≈U N ; When λ SCR =5, U sys =0.98U N ; When λ SCR =3, U sys =0.95U N ; When λ SCR =1, U sys =0.71U NTherefore, it can be considered that when the voltage stiffness is greater than 0.95, the system voltage support capability is strong and meets the voltage stability requirements. Therefore, the first preset value can be 0.95.

[0049] A global scan is performed on the voltage stiffness of all nodes in the initial optimization scheme of the AC / DC hybrid grid. If the voltage stiffness of all nodes in the initial optimization scheme of the AC / DC hybrid grid is greater than a first preset value, it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the voltage stability requirement.

[0050] Furthermore, in step S33, the AC / DC system strength ratio index is the ratio between the AC channel capacity and the DC channel capacity between any two nodes.

[0051] Specifically, when multiple DC circuits fail to commutate simultaneously due to a serious short-circuit fault in the receiving power grid or multiple lines are locked due to other reasons, whether the power balance of the sending and receiving systems can be maintained is a key assessment of transient stability. In order to accurately characterize the transient stability of the system, it is necessary to compare the strength of the AC system and the DC system. Only when the strength balance of the AC and DC systems is met can the power angle and frequency instability of the entire system be avoided. Therefore, the AC / DC system strength ratio index Q can be used. ac,dc_ij Conduct system transient stability assessment: ; (11) in, represents the communication channel capacity between the i-th node and the j-th node, represents the DC channel capacity between the i-th node and the j-th node, Q ac,dc_ij Indicates the AC / DC system strength ratio index.

[0052] In some embodiments, it is believed that when Q ac,dc_ij >0.5, the transient stability of the grid meets the requirements. ac,dc_ij When <0.5, it is considered that the system transient stability is insufficient to ensure the safety of grid operation, that is, the second preset value can be 0.5.

[0053] Specifically, in step S35, if the initial optimization scheme of the AC / DC hybrid grid meets both the stability requirement and the system transient stability requirement, the AC system and the DC system in the initial optimization scheme of the AC / DC hybrid grid are in a strong-weak balance.

[0054] Further, refer to Figure 4 In step S4, the initial optimization scheme of the AC / DC hybrid network rack that does not meet the requirements of strong and weak balance is adjusted until the optimal AC / DC hybrid network rack optimization scheme that meets the requirements of strong and weak balance is obtained, including: S41. For the initial optimization plan of the AC / DC hybrid grid that does not meet the voltage stability requirements, introduce a static VAR compensation device or a VSC DC device, and re-evaluate and adjust the voltage stability of the adjusted initial optimization plan of the AC / DC hybrid grid until the voltage stability requirements are met. S42: For the initial optimization plan of the AC / DC hybrid grid that does not meet the system transient stability requirements, disconnect the AC lines between the nodes and re-evaluate and adjust the system transient stability until the system transient stability requirements are met; S43. The initial optimization scheme of the AC / DC hybrid grid that meets both the voltage stability requirements and the system transient stability requirements after adjustment is determined as the optimal AC / DC hybrid grid optimization scheme.

[0055] In the above-mentioned grid voltage stability verification using the voltage stiffness index, if the voltage stiffness index is higher than 0.95, the voltage support capability is considered strong enough to meet the project requirements. Otherwise, the planning scheme is not feasible and the AC line capacity can be appropriately increased, or SVC / VSC DC devices can be installed to provide voltage support for the grid and improve grid voltage stability.

[0056] In the above-mentioned verification of the transient stability of the grid transmission section using the AC / DC system strength ratio index, if Q ac,dc_ij >0.5, the grid strength is large enough to meet the AC / DC strength balance principle and meet the engineering requirements; if Q ac,dc_ij <0.5, indicating insufficient transient stability. When a fault occurs, the power angle difference at both ends of the line may increase divergently, resulting in power angle instability. In this case, the AC line between the nodes in the section can be disconnected to achieve partitioned asynchronous operation.

[0057] Furthermore, in step S41, a static VAR compensation device or a VSC DC device is introduced into the initial optimization solution for the AC / DC hybrid grid that does not meet the voltage stability requirement, including: Identifying nodes in an initial optimization scheme for an AC / DC hybrid grid that does not meet voltage stability requirements and in which voltage stiffness is less than or equal to a first preset value; A static VAR compensation device or a VSC direct current device is connected to a node where the voltage stiffness is less than or equal to a first preset value.

[0058] Furthermore, in step S42, for the initial optimization scheme of the AC / DC hybrid network that does not meet the system transient stability requirements, disconnecting the AC lines between the nodes includes: Determine a node in the initial optimization plan for the AC / DC hybrid grid that does not meet the system transient stability requirements and in which the AC / DC system strength ratio index is less than or equal to a second preset value; The AC lines in the transmission sections between two nodes whose AC / DC system strength ratio index is less than or equal to the second preset value are disconnected.

[0059] The adjusted initial optimization scheme of the AC / DC hybrid grid meets both the stability requirements and the system transient stability requirements, and the AC system and the DC system in the adjusted initial optimization scheme of the AC / DC hybrid grid are in a strong and weak balance.

[0060] The method provided in the above embodiment is further illustrated below through specific application scenarios.

[0061] A four-zone AC network frame is used as an example. Its original AC / DC hybrid network frame structure is shown in the attached figure. Figure 5 As shown. The AC / DC hybrid grid structure includes two sending-end power grids and two receiving-end power grids, namely, sending-end power grid 1, sending-end power grid 2, receiving-end power grid 1 and receiving-end power grid 2. The sending-end power grid 1 includes synchronous machine 1, synchronous machine 2 and synchronous machine 3, the sending-end power grid 2 includes synchronous machine 4, synchronous machine 5 and synchronous machine 6, the receiving-end power grid 1 includes load 1 and load 2, and the receiving-end power grid 2 includes load 3 and load 4. The power generation of the sending-end power grid 1 and the sending-end power grid 2 are 532MW and 2840MW respectively, and the load power supply demand of the receiving-end power grid 1 and the receiving-end power grid 2 are 1466MW and 2580MW respectively. The key transmission sections between each partition are AC connections. The sending-end power grid 1 and the receiving-end power grid 1 are interconnected through channel 1 and channel 2, and the sending-end power grid 2 and the receiving-end power grid 2 are interconnected through channel 3 and channel 4. Numbers 1-30 represent node numbers. Using the AC / DC hybrid grid optimization model provided in this embodiment, the AC / DC hybrid grid structure is simulated and analyzed to obtain the initial optimization scheme of the AC / DC hybrid grid as shown in the attached figure. Figure 6 As shown in Figure 1, two DC lines, Line A and Line B, were added to Channel 3. Table 1 shows the changes in the grid's steady-state and N-1 fault state power flow parameters before and after structural optimization for the AC / DC hybrid grid. The short-circuit current margins at nodes 7 and 8 were 0.78% and 0.44%, respectively, before and after optimization. Regarding stability, grid node voltage stiffness values ​​ranged from 0.96 to 0.97, exceeding 0.95. The AC / DC system strength ratios for the interconnection channels between the sending and receiving grids and key transmission sections were both above 0.92, exceeding 0.5, meeting the AC / DC power balance standard. This validates the adaptability of the AC / DC hybrid grid optimization model.

[0062] Table 1 Power flow parameters of the grid in steady state and N-1 fault state before and after topology optimization

[0063] refer to Figure 7 In some embodiments, an AC / DC hybrid network optimization control device based on strong / weak balance is provided, comprising: A model building module 201 is used to build an AC / DC hybrid grid optimization model that takes into account power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs; An initial optimization module 202 is configured to optimize the current AC / DC hybrid network rack structure based on the AC / DC hybrid network rack optimization model to obtain an initial optimization solution for the AC / DC hybrid network rack; An evaluation module 203 is configured to perform voltage stability evaluation and system transient stability evaluation on the initial optimization scheme for the AC / DC hybrid grid, and determine whether the initial optimization scheme for the AC / DC hybrid grid meets the requirements of strong and weak balance based on the evaluation results; The adjustment model 204 is used to adjust the initial optimization scheme of the AC / DC hybrid grid that does not meet the strong-weak balance requirement until an optimal AC / DC hybrid grid optimization scheme that meets the strong-weak balance requirement is obtained.

[0064] Furthermore, the AC / DC hybrid grid optimization model includes power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and an objective function to minimize planning costs.

[0065] Furthermore, the initial optimization module 202 optimizes the current AC / DC hybrid network frame structure based on the AC / DC hybrid network frame optimization model to obtain an initial optimization solution for the AC / DC hybrid network frame, including: At least one of adding a DC line, adding an AC line, and converting an AC line to a DC line is performed on the current AC / DC hybrid grid structure to obtain candidate solutions. Based on the candidate solutions, an optimization algorithm is used to calculate and obtain an initial optimization solution for the AC / DC hybrid grid that satisfies the power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and minimizes planning costs.

[0066] Furthermore, the evaluation module 203 performs voltage stability evaluation and system transient stability evaluation on the initial optimization scheme of the AC / DC hybrid grid, and determines whether the initial optimization scheme of the AC / DC hybrid grid meets the strong-weak balance requirement based on the evaluation results, including: Calculate the voltage stiffness of the corresponding node according to the voltage of the network-connected equipment corresponding to the node in the initial optimization scheme of the AC / DC hybrid network rack; If the voltage stiffness of all nodes in the initial optimization scheme of the AC / DC hybrid grid is greater than the first preset value, it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the voltage stability requirement; Calculate the AC / DC system strength ratio index based on the AC and DC channel capacities between all two nodes in the initial optimization plan of the AC / DC hybrid grid; If the AC / DC system strength ratio index of all two nodes in the AC / DC hybrid network rack initial optimization scheme is greater than a second preset value, it is determined that the AC / DC hybrid network rack initial optimization scheme meets the system transient stability requirements; If the initial optimization scheme of the AC / DC hybrid grid meets both the voltage stability requirement and the system transient stability requirement, then it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the strong-weak balance requirement; The initial optimization scheme of the AC / DC hybrid grid that meets the strong-weak balance requirements is determined as the optimal AC / DC hybrid grid optimization scheme.

[0067] Furthermore, the voltage stiffness is a ratio of a voltage modulus of a network port when a network-accessing device corresponding to the node is connected to a no-load voltage when the network-accessing device corresponding to the node is not connected.

[0068] Furthermore, the AC / DC system strength ratio index is the ratio between the AC channel capacity and the DC channel capacity between any two nodes.

[0069] Furthermore, the adjustment module 204 adjusts the initial optimization scheme of the AC / DC hybrid network rack that does not meet the requirements of strong and weak balance until an optimal AC / DC hybrid network rack optimization scheme that meets the requirements of strong and weak balance is obtained, including: For AC / DC hybrid grid initial optimization schemes that do not meet voltage stability requirements, static VAR compensation devices or VSC DC devices are introduced. The adjusted AC / DC hybrid grid initial optimization scheme is then re-evaluated and adjusted for voltage stability until voltage stability requirements are met. For the initial optimization plan of AC / DC hybrid grid that does not meet the system transient stability requirements, disconnect the AC lines between nodes and re-evaluate and adjust the system transient stability until the system transient stability requirements are met; The initial optimization scheme of the AC / DC hybrid grid that meets both the voltage stability requirements and the system transient stability requirements after adjustment is determined as the optimal AC / DC hybrid grid optimization scheme.

[0070] Furthermore, the adjustment module 204 introduces a static VAR compensation device or a VSC DC device into the initial optimization solution for the AC / DC hybrid grid that does not meet the voltage stability requirement, including: Identifying nodes in an initial optimization scheme for an AC / DC hybrid grid that does not meet voltage stability requirements and in which voltage stiffness is less than or equal to a first preset value; A static VAR compensation device or a VSC direct current device is connected to a node where the voltage stiffness is less than or equal to a first preset value.

[0071] Furthermore, the adjustment module 204 disconnects the AC lines between nodes for the initial optimization solution of the AC / DC hybrid network frame that does not meet the system transient stability requirements, including: Determine a node in the initial optimization plan for the AC / DC hybrid grid that does not meet the system transient stability requirements and in which the AC / DC system strength ratio index is less than or equal to a second preset value; The AC lines in the transmission sections between two nodes whose AC / DC system strength ratio index is less than or equal to the second preset value are disconnected.

[0072] In some embodiments, an electronic device is also provided, including a processor and a storage device, wherein the storage device stores a plurality of instructions, and the processor is configured to read the instructions and execute the above method.

[0073] In some embodiments, a computer storage medium is further provided, storing a plurality of instructions, which are used to execute the above method when read.

[0074] The AC / DC hybrid grid optimization control method and device based on strong / weak balance provided in the above embodiment have at least the following beneficial effects: (1) Propose an AC / DC hybrid grid optimization model based on power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs to ensure that the optimized grid can meet the power balance and voltage stability requirements in both normal operation and fault conditions, avoid overload or voltage exceeding the limit, and reduce network losses, improve transmission efficiency, and reduce operating costs by optimizing power flow distribution. Limit the short-circuit current level within the breaking capacity of equipment such as circuit breakers and transformers to avoid equipment damage, prevent the spread of short-circuit faults, and reduce the risk of cascading failures. In particular, when the DC system fails (such as phase change failure), the fault area can be quickly isolated to ensure that the grid can still meet the operating requirements under N-1 faults or extreme scenarios, minimize the impact of faults, and improve the robustness of the grid system; at the same time, consider economic efficiency; (2) Use voltage stiffness and AC / DC system strength ratio indicators to verify whether the voltage and transient stability of the AC / DC hybrid grid after topology optimization meet the engineering standards. Finally, for scenarios that do not meet the engineering stability standards, propose topology structures and adjustment strategies to achieve the construction of AC / DC hybrid grids that take into account both economy, safety and stability, and meet the principle of strong-weak balance. (3) Introducing static VAR compensation devices or VSC DC devices into the initial optimization scheme for AC / DC hybrid grids that do not meet voltage stability requirements can effectively suppress voltage fluctuations, improve voltage stability, and further optimize AC / DC hybrid grids; (4) For the initial optimization scheme of the AC / DC hybrid grid that does not meet the system transient stability requirements, disconnecting the AC lines between nodes can optimize the power flow distribution, thereby improving the system transient stability and further optimizing the AC / DC hybrid grid.

[0075] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the invention. Thus, the present invention is intended to include such changes and modifications as fall within the scope of the claims and their equivalents.

Claims

1. An AC / DC hybrid grid optimization control method based on strong / weak balance, characterized in that: include: Construct an AC / DC hybrid grid optimization model that considers power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs; Based on the AC / DC hybrid grid optimization model, the current AC / DC hybrid grid structure is optimized to obtain an initial optimization solution for the AC / DC hybrid grid; Conducting voltage stability assessment and system transient stability assessment on the initial optimization scheme for the AC / DC hybrid grid, and determining whether the initial optimization scheme for the AC / DC hybrid grid meets the requirements for strong-weak balance based on the assessment results; The initial optimization scheme of the AC / DC hybrid grid that does not meet the strong-weak balance requirements is adjusted until the optimal AC / DC hybrid grid optimization scheme that meets the strong-weak balance requirements is obtained.

2. The method according to claim 1, characterized in that The AC / DC hybrid grid optimization model includes power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and an objective function to minimize planning costs.

3. The method according to claim 2, characterized in that Based on the AC / DC hybrid grid optimization model, the current AC / DC hybrid grid structure is optimized to obtain an initial optimization solution for the AC / DC hybrid grid, including: At least one of adding a DC line, adding an AC line, and converting an AC line to a DC line is performed on the current AC / DC hybrid grid structure to obtain candidate solutions. Based on the candidate solutions, an optimization algorithm is used to calculate and obtain an initial optimization solution for the AC / DC hybrid grid that satisfies the power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and minimizes the planning cost.

4. The method according to claim 1, wherein Performing voltage stability assessment and system transient stability assessment on the initial optimization scheme for the AC / DC hybrid grid, and judging whether the initial optimization scheme for the AC / DC hybrid grid meets the requirements for strong-weak balance based on the assessment results, including: Calculate the voltage stiffness of the corresponding node according to the voltage of the network-connected equipment corresponding to the node in the initial optimization scheme of the AC / DC hybrid network rack; If the voltage stiffness of all nodes in the initial optimization scheme of the AC / DC hybrid grid is greater than the first preset value, it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the voltage stability requirement; Calculate the AC / DC system strength ratio index based on the AC and DC channel capacities between all two nodes in the initial optimization plan of the AC / DC hybrid grid; If the AC / DC system strength ratio indexes of all two nodes in the initial optimization scheme of the AC / DC hybrid network rack are greater than the second preset value, it is determined that the initial optimization scheme of the AC / DC hybrid network rack meets the system transient stability requirements; If the initial optimization scheme of the AC / DC hybrid grid meets both the voltage stability requirement and the system transient stability requirement, then it is determined that the initial optimization scheme of the AC / DC hybrid grid meets the strong-weak balance requirement; The initial optimization scheme of the AC / DC hybrid grid that meets the strong-weak balance requirements is determined as the optimal AC / DC hybrid grid optimization scheme.

5. The method according to claim 4, characterized in that The voltage stiffness is the ratio of the voltage modulus of the network port when the node's corresponding network access device is connected to the no-load voltage when the node's corresponding network access device is not connected.

6. The method according to claim 4, characterized in that The AC / DC system strength ratio index is the ratio between the AC channel capacity and the DC channel capacity between any two nodes.

7. The method according to claim 4, characterized in that Adjust the initial optimization scheme of the AC / DC hybrid grid that does not meet the requirements of strong and weak balance until the optimal AC / DC hybrid grid optimization scheme that meets the requirements of strong and weak balance is obtained, including: For AC / DC hybrid grid initial optimization schemes that do not meet voltage stability requirements, static VAR compensation devices or VSC DC devices are introduced. The adjusted AC / DC hybrid grid initial optimization scheme is then re-evaluated and adjusted for voltage stability until voltage stability requirements are met. For the initial optimization plan of AC / DC hybrid grid that does not meet the system transient stability requirements, disconnect the AC lines between nodes and re-evaluate and adjust the system transient stability until the system transient stability requirements are met; The initial optimization scheme of the AC / DC hybrid grid that meets both the voltage stability requirements and the system transient stability requirements after adjustment is determined as the optimal AC / DC hybrid grid optimization scheme.

8. The method according to claim 7, characterized in that The initial optimization solution for AC / DC hybrid grids that do not meet voltage stability requirements introduces static VAR compensation devices or VSC DC devices, including: Identifying nodes in an initial optimization scheme for an AC / DC hybrid grid that does not meet voltage stability requirements and in which voltage stiffness is less than or equal to a first preset value; A static VAR compensation device or a VSC direct current device is connected to a node where the voltage stiffness is less than or equal to a first preset value.

9. The method according to claim 7, characterized in that The initial optimization plan for AC / DC hybrid grids that do not meet the system transient stability requirements is to disconnect the AC lines between nodes, including: Determine a node in the initial optimization plan for the AC / DC hybrid grid that does not meet the system transient stability requirements and in which the AC / DC system strength ratio index is less than or equal to a second preset value; The AC lines in the transmission sections between two nodes whose AC / DC system strength ratio index is less than or equal to the second preset value are disconnected.

10. An AC / DC hybrid grid optimization control device based on strong / weak balance, characterized in that: include: A model building module is used to construct an AC / DC hybrid grid optimization model that considers power flow constraints, short-circuit current constraints, channel and converter station capacity constraints, and planning costs; An initial optimization module, configured to optimize the current AC / DC hybrid network rack structure based on the AC / DC hybrid network rack optimization model to obtain an initial optimization solution for the AC / DC hybrid network rack; An evaluation module is used to perform voltage stability evaluation and system transient stability evaluation on the initial optimization scheme of the AC / DC hybrid grid, and determine whether the initial optimization scheme of the AC / DC hybrid grid meets the requirements of strong and weak balance according to the evaluation results; The adjustment model is used to adjust the initial optimization scheme of the AC / DC hybrid network rack that does not meet the strong-weak balance requirements until the optimal AC / DC hybrid network rack optimization scheme that meets the strong-weak balance requirements is obtained.

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