Power coordination method for direct current system and direct current system

Abstract

The application provides a power coordination method of a direct current system and the direct current system. The method comprises the following steps: setting an optimization target and a boundary condition, the optimization target being that an error between a direct current power support value and a direct current power expected value is minimum, and the boundary condition at least comprising a static voltage stability domain constraint condition, the static voltage stability domain constraint condition being a condition that active power injected by a plurality of target nodes into a receiving end alternating current power grid meets; constructing a power optimization model according to the optimization target and the boundary condition; if a generator set N-k fault is detected, determining a power curve of the direct current power support value changing over time by using the power optimization model, and issuing the power curve to a converter station controller to control an actual value of the direct current power to follow the direct current power support value. The application fills a technical blank in the related art that there is no effective power scheduling strategy for a hybrid multi-infeed direct current system when a generator set N-k fault occurs in a receiving end alternating current power grid.

Description

Technical Field

[0001] This application relates to the field of high voltage direct current transmission, and more specifically, to a power coordination method for a DC system and a DC system. Background Technology

[0002] In hybrid multi-infeed DC systems, existing power dispatch strategies mostly rely on fixed power reference values ​​or simple allocation mechanisms of each DC transmission system control unit. They cannot effectively coordinate the resources of each converter station when a generator Nk fault occurs in the receiving-end AC grid. Especially in scenarios where multiple types of converters (such as HCC, MMC, LCC) coexist, the lack of refined support strategies based on system voltage stability may lead to further deterioration of voltage fluctuations, or even trigger cascading failures, threatening system safety. Summary of the Invention

[0003] The main objective of this application is to provide a power coordination method and a DC system to address the lack of an effective power dispatch strategy for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid.

[0004] To achieve the above objectives, according to one aspect of this application, a power coordination method for a DC system is provided, wherein the DC system is a hybrid multi-infeed DC system, the hybrid multi-infeed DC system including multiple feeder links and a receiving-end AC grid, the method comprising: setting an optimization objective and boundary conditions, wherein the optimization objective is to minimize the error between a DC power support value and a DC power expected value, the boundary conditions including at least a static voltage stability domain constraint condition, wherein the DC power support value is a reference value of DC power set to compensate for a fault when a generator set Nk fault occurs in the receiving-end AC grid, and the DC power expected value is a reference value of DC power set at the receiving end AC grid. A reference value for DC power is set when the generator set of the AC grid is fault-free. The static voltage stability domain constraint is a condition that the active power injected into the receiving-end AC grid by multiple target nodes must satisfy. The target nodes are the nodes connected to the receiving-end AC grid by the feed-in link. A power optimization model is constructed based on the optimization objective and the boundary conditions. If a fault Nk of the generator set is detected in the receiving-end AC grid, the power optimization model is used to determine the power curve of the DC power support value changing over time, and the power curve is sent to the converter station controller to control the actual DC power value to follow the DC power support value.

[0005] Optionally, each of the feed-in links includes at least one type of converter station, which includes rectifier stations and inverter stations. The boundary conditions also include operational constraints and control constraints for multiple types of converter stations. Setting the boundary conditions includes: determining the corresponding operational constraints based at least on the power characteristics of each type of converter station, where the power characteristics include the active power injected by the converter station into the AC grid, and the AC grid includes the sending-end AC grid and the receiving-end AC grid; and determining the corresponding control constraints based on the converter station control mode.

[0006] Optionally, the converter station further includes a connecting transformer connected to the rectifier station. The converter station is an MMC converter station. The corresponding operating constraints are determined at least based on the power characteristics of each type of converter station, including: determining the operating constraints of the MMC converter station based on the active power injected into the AC grid by the MMC converter station, the DC-side active power of the MMC converter station, the active power loss of the MMC converter station, the AC-side current of the MMC converter station, the resistance of the connecting transformer, and the equivalent resistance of the MMC converter station. The active power loss of the MMC converter station is determined based on the AC-side current of the MMC converter station.

[0007] Optionally, the converter station is an MMC converter station. Determining the corresponding control constraints based on the converter station's control mode includes: determining the control constraints based on the active power control mode of the MMC converter station, wherein the active power control mode of the MMC converter station is one of constant active power control, constant DC voltage control, and DC voltage droop control; and determining the control constraints based on the reactive power control mode of the MMC converter station, wherein the reactive power control mode of the MMC converter station is one of constant reactive power control and constant AC voltage control.

[0008] Optionally, the converter station is an LCC converter station or an HCC converter station. The corresponding operating constraints are determined at least based on the power characteristics of each type of converter station, including: determining the operating constraints of the LCC converter station or HCC converter station based on the active and reactive power injected into the AC grid by the LCC converter station or HCC converter station, the DC-side active power of the LCC converter station or HCC converter station, the active power loss of the LCC converter station or HCC converter station, the AC-side current of the LCC converter station or HCC converter station, the commutation resistance and commutation reactance of the LCC converter station or HCC converter station, and the power factor angle of the LCC converter station or HCC converter station. The active power loss of the LCC converter station or HCC converter station is determined based on the AC-side current of the LCC converter station or HCC converter station.

[0009] Optionally, the converter station is an LCC converter station or an HCC converter station. Determining the corresponding control constraints based on the converter station control mode includes: determining the control constraints of the LCC converter station or the HCC converter station based on the control mode of the LCC converter station or the HCC converter station. The control mode of the LCC converter station or the HCC converter station is one of constant active power control mode, constant DC current control mode, constant DC voltage control mode, and constant firing angle / turn-off angle control mode.

[0010] Optionally, setting the boundary conditions further includes configuring the boundary conditions to include at least one of the following: total power support constraint conditions, new energy power generation node power constraint conditions, load node power constraint conditions, AC / DC node power balance constraint conditions, and DC converter station capacity constraint conditions.

[0011] Optionally, after sending the power curve to the converter station controller to control the actual DC power value to follow the DC power support value, the method further includes: monitoring the AC bus voltage, the system frequency of the receiving-end AC grid, and the actual DC power value; and generating a new power curve or delaying the recovery process if preset conditions are met. The preset conditions include at least one of the following: the AC bus voltage is not within a preset voltage range, the system frequency of the receiving-end AC grid is not within a preset frequency range, and the difference between the actual DC power value and the DC power support value is greater than a preset difference value.

[0012] According to another aspect of this application, a DC system is provided, which is a hybrid multi-infeed DC system, the hybrid multi-infeed DC system including multiple feed links, a receiving-end AC grid and a controller, the controller being used to execute any of the power coordination methods of the DC system described above.

[0013] Optionally, one of the feed-in links includes at least one type of converter station, which includes rectifier stations and inverter stations, and the multiple types of converter stations include MMC converter stations, LCC converter stations and HCC converter stations.

[0014] By applying the technical solution of this application, an optimization model is constructed based on the optimization objective and boundary conditions. If a generator Nk fault is detected in the receiving-end AC grid, the power optimization model is used to determine the power curve of the DC power support value changing over time, and the power curve is sent to the converter station controller to control the actual DC power value to follow the DC power support value. This fills the technical gap in related technologies where there is no effective power dispatch strategy for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid. More importantly, the static voltage stability domain constraint is taken into account, ensuring the voltage stability of the power system during power support. This ensures effective power coordination and dispatch for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0016] Figure 1 A schematic flowchart of a power coordination method for a DC system according to an embodiment of this application is shown;

[0017] Figure 2 A schematic diagram of a hybrid multi-feed DC system structure according to an embodiment of this application is shown. Detailed Implementation

[0018] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0019] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0020] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be an intermediate element present. Furthermore, in the specification and claims, when an element is described as being "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element via a third element.

[0021] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. It can be understood that "at least one" refers to one or more, and "multiple" refers to two or more.

[0022] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0023] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0024] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the word "part" is also intended to include the plural form unless the context clearly indicates otherwise.

[0025] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0026] As introduced in the background section, there is a lack of an effective power dispatch strategy for hybrid multi-infeed DC systems when generator Nk faults occur in the receiving-end AC grid. In order to solve the technical problem of the lack of an effective power dispatch strategy for hybrid multi-infeed DC systems when generator Nk faults occur in the receiving-end AC grid, this application proposes a power coordination method for DC systems and a DC system.

[0027] This embodiment provides a power coordination method for a DC system running on a mobile terminal, computer terminal, or similar computing device. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0028] Figure 1 This is a flowchart of a power coordination method for a DC system according to an embodiment of this application. Figure 2 A schematic diagram of a hybrid multi-feed DC system is shown. See also Figure 2 A hybrid multi-feed DC system includes multiple feeder links and a receiving-end AC grid (equivalent to...). Figure 2 (The receiving end communication system in the middle).

[0029] like Figure 1 As shown, the method includes the following steps:

[0030] Step S101: Set the optimization objective and boundary conditions. The optimization objective is to minimize the error between the DC power support value and the DC power expected value. The boundary conditions include at least the static voltage stability domain constraint condition. The DC power support value is a reference value of DC power set to compensate for the fault when the generator Nk fault occurs in the receiving-end AC grid. The DC power expected value is a reference value of DC power set when the generator in the receiving-end AC grid is fault-free. The static voltage stability domain constraint condition is the condition that the active power injected into the receiving-end AC grid by multiple target nodes must meet. The target nodes are the nodes connected to the receiving-end AC grid by the feed-in link.

[0031] The optimization objective is to minimize the error between the DC power support value and the DC power expected value. This can be represented by minimizing the sum of the squares of the differences between multiple sets of DC power support values ​​and DC power expected values; or by minimizing the sum of the absolute values ​​of the differences between multiple sets of DC power support values ​​and DC power expected values, with each set corresponding to one feed link.

[0032] The specific explanation of generator set Nk fault is as follows: Generator set Nk fault is a commonly used fault mode concept in AC power grid reliability analysis. Here, "N" and "k" have specific meanings: N usually refers to the total number of generator sets in the AC power grid. "N" is the theoretical maximum number of available generating units, which includes all operating generators capable of providing power output. K represents the number of generator sets that have failed in the receiving-end AC power grid.

[0033] See Figure 2 DC power refers to the power on the DC bus connecting the rectifier station and the inverter station.

[0034] See target node Figure 2 The PCC point is the node where the circulating transformer connects to the receiving-end AC system.

[0035] The technical advantage of step S101 is that:

[0036] By optimizing the target to minimize the error between the DC power support value and the expected DC power value, the optimization objective prompts the system to approach the expected power value as closely as possible during the support process, avoiding unnecessary power waste. This scheme ensures that the power support provided by the DC feed-in system is most accurate when an Nk fault occurs in the receiving-end AC grid. This means that the DC system can quickly identify and compensate for the power gap caused by generator failures, avoiding power surplus or deficiency, thereby effectively maintaining the balance between power supply and demand.

[0037] The introduction of static voltage stability domain constraints ensures the voltage stability of the power system during power support. Since grid voltage stability is crucial for power system operation, especially after large disturbances, this constraint prevents voltage collapse caused by inadequate power support, thus improving system safety and reliability.

[0038] After a fault occurs, the optimization target dynamically adjusts the DC power support value, while boundary conditions limit the support range, ensuring the feasibility and effectiveness of the optimization scheme. This adaptive optimization mechanism can handle faults of various scales and types, making the system more adaptable and robust.

[0039] By minimizing the error between the DC power support value and the expected DC power value, and combining this with static voltage stability domain constraints, this solution effectively avoids secondary faults caused by improper power support. In actual power systems, improper handling of a primary fault can lead to a cascading effect on other equipment or systems in the grid, thereby expanding the scale of the fault. This solution reduces this risk through preventative control.

[0040] In Nk fault scenarios, rapid and accurate power support is crucial for system recovery speed. This solution can quickly adjust DC power support and ensure a smooth and safe adjustment process, thus accelerating the recovery of the receiving-end AC grid and shortening the time for the grid to return to normal operation after a fault.

[0041] Step S102: Construct a power optimization model based on the optimization objective and boundary conditions;

[0042] Step S103: If a generator set Nk fault is detected in the AC grid at the receiving end, the power optimization model is applied to determine the power curve of the DC power support value changing over time, and the power curve is sent to the converter station controller to control the actual DC power value to follow the DC power support value.

[0043] The phrase "actual DC power value follows DC power support value" specifically means that in power system control, especially in hybrid multi-infeed DC systems, when the receiving-end AC grid encounters a fault in a generator (Nk) or other situations leading to power imbalance, the main control dispatch center or the corresponding control system will issue power adjustment commands to each converter station based on the optimal "DC power support value" (i.e., the specific power value that needs to be allocated or dispatched from the DC system to stabilize the AC grid) calculated using the aforementioned technical solution. Upon receiving these commands, the converter station controller will take measures to adjust its actual output DC power to match the calculated "DC power support value" as closely as possible—that is, "following" the power supply. This process typically requires fine-tuning of the converter's firing angle, converter current, and switching status using the converter station's power control execution unit, such as PI controllers or droop control, to ensure a smooth transition and precise control of the DC power. The purpose is to quickly and accurately draw additional power from the DC system to help the AC grid restore stability when it experiences significant disturbances, preventing voltage collapse, frequency anomalies, and other chain reactions, thereby ensuring the safe operation of the power system and power quality. This following process is dynamic and adjusts according to real-time changes in the AC grid status to ensure the real-time nature and effectiveness of power support.

[0044] Steps S102 and S103 demonstrate real-time response and dynamic control capabilities, and their technical advantages are as follows:

[0045] In step S103, once a generator Nk fault is detected in the receiving-end AC grid, the system immediately activates the power optimization model, demonstrating the scheme's high real-time response capability. In power systems, the suddenness and uncertainty of fault occurrence require the system to respond within seconds to minutes to avoid or mitigate the impact of the fault. This scheme, by assessing fault scenarios in real time and quickly determining the optimal power support strategy, meets the power system's requirement for immediate response.

[0046] The power optimization model can not only calculate the optimal DC power support value, but also generate a power curve that changes over time based on the current system state and predicted data. This dynamic power curve ensures that the converter station controller can follow a smooth power adjustment path, rather than abrupt changes, thereby reducing the impact on the power system and improving the stability and reliability of power adjustment.

[0047] The power curve is sent to the converter station controller, ensuring that the actual DC power value accurately follows the optimized DC power support value. This is crucial for ensuring power balance in the AC grid during Nk fault scenarios. Precise power control capabilities enable the DC system to provide timely and tailored support to the AC grid in emergency situations, preventing power supply and demand imbalances and maintaining grid stability.

[0048] By constructing a power optimization model, the system can comprehensively consider various constraints to determine the most reasonable power support allocation scheme. This not only maximizes the support effect of the DC feed-in system but also avoids resource waste and improves the overall economy of the power system.

[0049] This solution can quickly generate dynamic power recovery curves based on the current situation, providing clear operational guidance for the converter station controller. This is crucial for accelerating the recovery of the power system from a fault state to a stable state. After a system disturbance, it can rapidly formulate and execute recovery strategies, shortening the time for the system to return to normal operation and reducing economic losses caused by power outages.

[0050] Dynamic control and real-time response mechanisms enable power systems to exhibit greater robustness in the face of uncertainties and variable fault scenarios. By continuously monitoring system status and adjusting power curves as necessary, the system can adapt to various operating conditions, reduce cascading effects caused by single faults, and enhance the system's self-healing capabilities and safety.

[0051] This application discloses a power coordination method for DC systems, including steps S101, S102, and S103 as described above. By setting optimization objectives and boundary conditions, a power optimization model is constructed based on these objectives and boundary conditions. If a generator Nk fault is detected in the receiving-end AC grid, the power optimization model is applied to determine the power curve of the DC power support value over time, and this power curve is sent to the converter station controller to control the actual DC power value to follow the DC power support value. This fills the technical gap in related technologies regarding the lack of an effective power dispatch strategy for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid. More importantly, the static voltage stability domain constraint is considered, ensuring the voltage stability of the power system during power support. This ensures effective power coordination and dispatch for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid.

[0052] In a specific implementation, a feed-in link includes at least one type of converter station, which includes a rectifier station and an inverter station. Figure 2One feed link in the system includes one type of converter station. The first feed link includes an HCC rectifier station and an HCC inverter station. The second feed link includes an MMC rectifier station and an MMC inverter station. The third feed link includes an LCC rectifier station and an LCC inverter station. Of course, in some embodiments, one feed link includes multiple types of converter stations. For example, one feed link includes an HCC rectifier station and an MMC inverter station, and another feed link includes an LCC rectifier station and an MMC inverter station.

[0053] Boundary conditions also include various types of operational and control constraints for converter stations. Setting boundary conditions includes:

[0054] The corresponding operating constraints are determined based on the power characteristics of each type of converter station. These power characteristics include the active power injected by the converter station into the AC grid. The AC grid includes the sending-end AC grid and the receiving-end AC grid, wherein the sending-end AC grid and... Figure 2 The sending-end AC system is equivalent to the receiving-end AC power grid. Figure 2 The receiving-end communication system in the middle is equivalent.

[0055] The corresponding control constraints are determined based on the converter station control method.

[0056] The converter stations include various types such as MMC (Modular Multilevel Converter), LCC (Line-Commutated Converter), and HCC (Hybrid Line-Commutated Converter). MMC converters achieve multilevel output by combining multiple sub-modules in series and parallel, thereby improving the system's voltage level and control accuracy. LCC technology uses thyristors as the main switching elements, controlling the conduction and commutation of the thyristors to achieve AC-DC conversion. The advantages of this type of converter are its relatively simple structure and low cost, but its disadvantages include high harmonic content and the inability of the thyristors to automatically turn off, making it prone to commutation failure. HCC converters employ fully controlled RB-IGCT (Reverse-Blocking Integrated Gate-Commutated Thyristor) devices, possessing active turn-off capability, effectively mitigating commutation failure accidents in AC fault scenarios. Compared to MMC and LCC, HCC has both technical and economic advantages in high-power transmission scenarios and is suitable for ultra-high voltage and large-capacity DC transmission projects.

[0057] By setting specific operating and control constraints for the power characteristics and control methods of each converter station (including rectifier and inverter stations) in each feed-in link, the technical advantages are:

[0058] Each converter station, whether a rectifier or inverter station, has unique power characteristics, such as maximum power limits and power conversion efficiency. Setting operational constraints based on these characteristics allows the system to allocate power according to the actual capacity of the converter station, avoiding overload operation or insufficient power output, and improving the safety and effectiveness of system operation.

[0059] The control methods of converter stations, such as constant active power control and constant DC voltage control, directly affect their role in the power system. Determining control constraints based on the control methods of different converter stations enables the system to intelligently select the most suitable control strategy to cope with emergencies such as power imbalance and voltage fluctuations in the receiving-end grid, thereby improving the system's adaptability and control accuracy.

[0060] In multi-infeed DC systems, the power output and control requirements of different types of converter stations vary with changes in the grid conditions. By dynamically adjusting operating and control constraints, the system can optimize power support strategies in real time, ensuring that the power output of the converter stations can meet the grid's emergency needs while remaining within a safe operating range under different fault scenarios, thus enhancing the system's dynamic optimization capabilities.

[0061] The operational constraints take into account the maximum power output limit of the converter station, while the control constraints ensure that the power output and control commands of the converter station do not lead to voltage or frequency instability. These constraints help maintain system stability under Nk fault scenarios, prevent cascading failures, and ensure the safe operation of the power system.

[0062] By precisely matching the operating characteristics and control methods of the converter stations, the system can utilize power resources more efficiently. This means that in emergencies, the system can quickly mobilize available converter station resources to provide the necessary power support without wasting power or exceeding the converter station's processing capacity, thus improving resource utilization efficiency.

[0063] Hybrid multi-infeed DC systems may include various types of converter stations such as LCC, HCC, and MMC. This technical feature, by setting specific operating and control constraints, promotes compatibility and collaboration among different technologies, providing flexibility for diversified technology selection and future technology upgrades.

[0064] In the embodiments of this application, see Figure 2The converter station also includes a connecting transformer connected to the rectifier station. The converter station is an MMC converter station. The corresponding operating constraints are determined based on the power characteristics of each type of converter station, including:

[0065] Based on the active power injected into the AC grid by the MMC converter station, the active power on the DC side of the MMC converter station, the active power loss of the MMC converter station, the AC side current of the MMC converter station, the resistance of the connecting transformer, and the equivalent resistance of the MMC converter station, the operating constraints of the MMC converter station are determined.

[0066] The active power loss of the MMC converter station is determined based on the AC side current of the MMC converter station.

[0067] In some specific implementations, the rectifier station adopts: ;

[0068] The inverter station adopts: ;

[0069] The power loss is: ;

[0070] The active power injected into the AC grid by the MMC converter station; These are the resistances of the transformers connecting to the MMC converter station; The equivalent resistance of the MMC converter station; This refers to the active power on the DC side of the MMC converter station; For the active power loss of the MMC converter station; This refers to the AC side current of the MMC converter station; , , These are the coefficients of the quadratic, primary, and constant terms related to the power loss of the MMC converter station.

[0071] By clearly considering the active power injected into the AC grid by the MMC converter station, the active power on the DC side, and their losses, the system can accurately manage the power output and conversion efficiency of the converter station, avoid ineffective losses in the power support process, and ensure that the power output of the converter station meets the grid demand while maintaining operating efficiency.

[0072] The operating constraints of the MMC converter station include AC side current, the resistance of the connecting transformer, and the equivalent resistance of the converter station. These parameters directly affect the current management and voltage stability of the converter station. By setting these constraints, the system can ensure that the voltage and current of the MMC converter station remain within safe ranges during power support processes, thereby enhancing the stability and reliability of the system.

[0073] The active power loss of the MMC converter station is determined based on the AC side current. This characteristic introduces a loss model, allowing the system to consider actual energy losses during power optimization. This not only improves the practical feasibility of power support strategies but also helps the system calculate and adjust power output more accurately in emergency situations, reducing energy waste.

[0074] In this embodiment of the application, the converter station is an MMC converter station, and the corresponding control constraints are determined based on the converter station control method, including:

[0075] The control constraints of the MMC converter station are determined based on the active power control mode of the MMC converter station. The active power control mode of the MMC converter station is one of the following: constant active power control mode, constant DC voltage control mode, and DC voltage droop control mode.

[0076] The specific implementations of the active power control method, constant DC voltage control method, and DC voltage droop control method are described in the embodiments below.

[0077] The control constraints of the inverter station of the MMC converter station are determined based on the reactive power control mode of the MMC converter station. The reactive power control mode of the MMC converter station is one of the constant reactive power control mode and the constant AC voltage control mode.

[0078] The specific implementation of the constant reactive power control method and the constant AC voltage control method can be found in the embodiments described later.

[0079] By employing constant active power control, constant DC voltage control, or DC voltage droop control for active power operations at the MMC converter station, and constant reactive power control or constant AC voltage control for reactive power operations, the system can flexibly select the most suitable control strategy based on the real-time demands and fault scenarios of the receiving-end AC grid. This flexibility enhances the system's ability to cope with various situations, ensuring optimal power support and system stability.

[0080] The setting of control constraints, especially for active and reactive power control, enables the system to precisely adjust the power output of each converter station to maintain voltage and frequency stability in the receiving-end AC grid. This precise adjustment is crucial for rapidly restoring system balance under Nk fault scenarios.

[0081] The DC voltage droop control method can automatically adjust the output power of the MMC converter station to respond to voltage changes in the receiving-end grid without the need for immediate intervention from the central dispatcher. This provides the system with a more optimized dynamic response capability, enabling rapid stabilization of grid voltage and preventing voltage collapse and cascading failures.

[0082] By setting various control constraints, the system can cope with possible failures or inadequacies in the control methods of the MMC converter station, increasing the system's redundancy and robustness. Even under extreme conditions, it can maintain stable operation, reducing the impact of faults on the power grid.

[0083] If the converter station is an LCC converter station or an HCC converter station, in the specific implementation, at least the corresponding operating constraints should be determined based on the power characteristics of each type of converter station, including:

[0084] The operating constraints of an LCC or HCC converter station are determined based on the active and reactive power injected into the AC grid by the LCC or HCC converter station, the DC-side active power of the LCC or HCC converter station, the active power loss of the LCC or HCC converter station, the AC-side current of the LCC or HCC converter station, the commutation resistance and commutation reactance of the LCC or HCC converter station, and the power factor angle of the LCC or HCC converter station. Among these, the active power loss of the LCC or HCC converter station is determined based on the AC-side current of the LCC or HCC converter station.

[0085] In some specific implementations,

[0086] The organization station uses: ,

[0087] ,

[0088] ;

[0089] The inverter station adopts: ,

[0090] ,

[0091] ;

[0092] , These represent the active power and reactive power injected into the AC grid by the LCC / HCC converter station, respectively. , These are the commutation resistance and commutation reactance of the LCC / HCC converter station, respectively. This refers to the active power on the DC side of the LCC / HCC converter station. For the active power loss of the LCC / HCC converter station; This refers to the AC side current of the LCC / HCC converter station; , , φ represents the coefficients of the quadratic, primary, and constant terms related to the power loss of the LCC / HCC converter station; φ is the power factor angle of the LCC / HCC converter station.

[0093] Determining the active power loss of an LCC or HCC converter station based on the AC side current can more accurately reflect the actual operating status of the converter station, avoiding resource waste or equipment overload caused by inaccurate estimation, and improving the energy utilization efficiency of the system and the service life of the equipment.

[0094] The operating constraints comprehensively cover the injection of active and reactive power, as well as the management of active power on the DC side. This comprehensive power management strategy ensures that the power output of the converter station in different operating scenarios meets system requirements while remaining within a safe and efficient range.

[0095] By monitoring and controlling the power characteristics of the converter station in real time, the system can quickly adapt to the dynamic changes of the receiving-end AC power grid. Especially in the case of severe Nk faults, it can adjust the power support strategy in a timely manner and quickly restore grid stability.

[0096] Setting operating constraints, including commutation resistance and commutation reactance, can effectively prevent abnormalities during the commutation process, ensure the safe operation of the equipment, and reduce the risk of voltage fluctuations or equipment damage caused by commutation failure.

[0097] Including power factor angle control constraints, the system can optimize the power transmission efficiency of the converter station, reduce line losses, and improve the economy and efficiency of power transmission, which is especially important in long-distance, high-capacity power transmission.

[0098] If the converter station is an LCC converter station or an HCC converter station, in some embodiments, the corresponding control constraints are determined based on the converter station control method, including:

[0099] The control constraints of the rectifier station of the LCC or HCC converter station are determined based on the control mode of the LCC or HCC converter station. The control mode of the LCC or HCC converter station is one of the following: constant active power control mode, constant DC current control mode, constant DC voltage control mode, and constant firing angle / turn-off angle control mode.

[0100] The specific implementations of the constant active power control mode, constant DC current control mode, constant DC voltage control mode, and constant firing angle / turn-off angle control mode are described in the embodiments below.

[0101] By adopting a constant active power control method, the system can accurately control the active power transmitted from the LCC or HCC converter station to the receiving-end AC grid, ensuring accurate power support when the system needs it, and helping to quickly restore the voltage and frequency stability of the grid.

[0102] Setting constant DC current control and constant DC voltage control modes helps stabilize the current and voltage on the DC side, which is crucial for maintaining the stability of the entire DC transmission system. Especially in hybrid multi-infeed DC systems, stable control on the DC side can prevent commutation failure or equipment damage caused by DC current or voltage fluctuations.

[0103] Setting a fixed trigger angle / shutdown angle control mode can optimize the commutation process of LCC or HCC converter stations, effectively avoid commutation failure, reduce commutation losses, and improve system operating efficiency. At the same time, optimized commutation control can extend equipment lifespan and reduce maintenance costs.

[0104] The selective setting of the aforementioned control methods gives the system the flexibility to select the most suitable control strategy under different operating conditions. Whether it is fluctuations in grid load, intermittent access of new energy sources, or changes in the operating status of the DC transmission system itself, the system can respond and adapt quickly by adjusting the control method, thereby improving the overall adaptability and controllability of the system.

[0105] In addition, the power of the inverter station on the AC side of the LCC converter station / HCC converter station is determined based on its operating constraints.

[0106] To achieve better power support under fault conditions, the embodiments of this application include setting boundary conditions, which further include at least one of the following: total power support constraint conditions, new energy generation node power constraint conditions, load node power constraint conditions, AC / DC node power balance constraint conditions, and DC converter station capacity constraint conditions. Specific implementation methods of these boundary conditions can be found in the embodiments described below.

[0107] The total power support constraint ensures that, in the event of a fault, the power support provided by the entire system meets the power deficit requirements of the AC power grid, achieving the goal of globally optimized power support and avoiding system stability problems caused by insufficient support.

[0108] The power constraints of new energy power generation nodes take into account the actual output capacity of new energy power plants, ensuring that the predicted or actual available power limits are not exceeded during fault support. This can make full use of new energy resources and avoid system fluctuations or equipment damage caused by over-reliance, thereby improving the controllability of new energy and the grid's acceptance capacity.

[0109] The load node power constraint condition enables the system to manage the power consumption of the load node more accurately, ensuring that the load demand is met without exceeding the system's capacity under fault scenarios, which is conducive to the balance of power supply and demand and the continuity of user power consumption.

[0110] The AC / DC node power balance constraints are crucial for maintaining the power balance of each node in the system. In particular, when an Nk fault occurs in the receiving-end AC grid, the power output of each converter station is adjusted in real time to ensure that the system is in a dynamic balance state and to prevent voltage or frequency instability caused by power imbalance.

[0111] The capacity constraints of DC converter stations ensure that the power output of the converter station during fault support will not exceed its maximum capacity, preventing equipment overload, ensuring the safe operation of power equipment, and avoiding the waste of system resources.

[0112] The comprehensive setting of the above boundary conditions significantly improves the system's resilience and response capability in the face of sudden faults. By dynamically adjusting the power support strategy, the system can quickly respond to faults and return to a stable state, reducing the impact time and scope of faults on the power grid.

[0113] Boundary conditions, especially constraints on new energy power, help balance electricity costs and environmental benefits, promote the effective use of green energy, and meet the requirements of sustainable development.

[0114] In this embodiment of the application, after sending the power curve to the converter station controller to control the actual DC power value to follow the DC power support value, the method further includes:

[0115] Monitor the AC bus voltage, the system frequency of the receiving-end AC grid, and the actual value of DC power;

[0116] Under the condition that the preset conditions are met, a new power curve is generated or the recovery process is delayed. The preset conditions include that the AC bus voltage is not within the preset voltage range, the system frequency of the AC grid at the receiving end is not within the preset frequency range, and the difference between the actual DC power value and the DC power support value is greater than at least one of the preset differences.

[0117] In practice, the duration of the delayed recovery process is dynamically adjusted based on the deviation of the real-time monitored system status and preset conditions. The deviation of the preset conditions includes the degree of AC bus voltage deviation from the preset voltage range, the degree of system frequency deviation from the preset frequency range, and the degree of deviation of the actual DC power value from the DC power support value (i.e., the difference between the DC power support value and the actual value). The system status includes the system's dynamic characteristics, grid status, the complexity of the recovery strategy, and the predicted voltage and frequency recovery times.

[0118] The specific parameters included in the deviation between the real-time monitored system state and the preset conditions are explained as follows:

[0119] 1. AC bus voltage deviation: If the AC bus voltage deviates from the preset voltage range, the recovery delay time is related to the amount of voltage deviation and its rate of change. Larger voltage deviations or rapid changes require longer recovery delay times so that the system can stabilize the voltage without causing further fluctuations;

[0120] 2. System Frequency Deviation: When the system frequency of the receiving-end AC power grid deviates from the preset frequency range, the recovery delay time also depends on the degree of frequency deviation and the rate of change. Significant frequency deviations or rapid changes can cause system oscillations, requiring a longer delay to prevent control actions from exacerbating frequency instability;

[0121] 3. Difference between DC power support value and actual value: If the difference between the actual DC power value and the calculated DC power support value exceeds the preset difference, it means that the current recovery strategy has not been effectively implemented or needs to be adjusted. The larger the difference, the longer the required recovery delay time, so that the system can adjust the control parameters or recalculate the power support value to ensure a smooth and effective recovery process.

[0122] 4. Dynamic characteristics of the system: The dynamic characteristics of the power system, including system impedance, generator inertia, and load characteristics, also affect the setting of the delay recovery time. For example, power grids with greater system inertia require a longer delay recovery time to adapt to control changes.

[0123] 5. Grid Status: The overall status of the power grid, including generation capacity, load distribution, and network topology, is also a key factor determining the recovery time delay. In cases of unstable or fragile grid conditions, the recovery time delay is typically longer.

[0124] 6. Complexity of recovery strategy: If the control strategy that needs to be adjusted is relatively complex, such as involving the coordination of multiple converter stations or the redistribution of power reserves, the recovery time will be increased accordingly to ensure the accuracy of strategy adjustment and system stability.

[0125] 7. Predicted Voltage and Frequency Recovery Time: Based on the power grid model and the current fault conditions, the system estimates the time it will take for voltage and frequency to return to normal levels. If the estimated recovery time is long, the delayed recovery time will be set accordingly to avoid rapid power adjustments before full recovery, thereby preventing the generation of new instability factors.

[0126] In some implementations, based on the characteristics of the actual hybrid multi-infeed DC system, corresponding weights are assigned to the above-mentioned AC bus voltage deviation, system frequency deviation, difference between DC power support value and actual value, system dynamic characteristics, grid status, complexity of recovery strategy, and predicted voltage and frequency recovery time. The larger the weight, the greater the impact on the delayed recovery time. Finally, the delayed recovery time is determined by weighted averaging. That is, each parameter is given an initial delayed recovery time, which is multiplied by the corresponding weight and then added together to obtain the final delayed recovery time.

[0127] The above-mentioned abnormal situations include: the AC bus voltage not being within the preset voltage range; the system frequency of the receiving-end AC grid not being within the preset frequency range; and the difference between the actual DC power value and the DC power support value being greater than the preset difference. In other words, the actual DC power value is difficult to follow the DC power support value. Conversely, the actual DC power value can follow the DC power support value.

[0128] Real-time monitoring of AC bus voltage, system frequency, and actual DC power values ​​enables the system to respond quickly to changes in actual operating conditions, promptly correct or adjust the power curve, and enhance the system's dynamic adaptability and flexibility during fault recovery.

[0129] The delay in the power curve adjustment or recovery process under preset conditions helps to avoid voltage or frequency fluctuations caused by too rapid recovery, ensuring the stability of the system during the recovery phase and reducing the risk of equipment damage due to overload or improper operation.

[0130] To enable those skilled in the art to better understand the technical solution of this application, the implementation process of the power coordination method for DC systems of this application will be described in detail below with reference to specific embodiments.

[0131] This embodiment relates to a specific power coordination method for a DC system, including the following steps:

[0132] Step 1: Support Requirement Identification: The main control center detects grid faults and power shortages at the receiving end, triggers the support coordination mechanism, and generates a signal for the implementation of the power emergency coordination support strategy.

[0133] Step 2: Construct a power optimization model with the following optimization objective: ;

[0134] in, Represents the objective function value. This represents the DC power support value for the i-th feed link. This represents the expected DC power of the i-th feed link.

[0135] Its boundary conditions include:

[0136] 1) The total power support constraint (which needs to satisfy the AC system gap) is:

[0137] ,

[0138] in, This represents the DC power support value for the i-th feed link. The expected DC power of the i-th feed link. This refers to the active power gap following an Nk fault in the AC system.

[0139] 2) Static voltage stability domain constraints (calculated by calling the "Static Voltage Stability Domain Real-Time Calculation Module" based on real-time system topology and power flow data):

[0140] ,

[0141] in, It is the i-th coefficient of the j-th boundary surface in the static voltage stability domain. Let i be the active power injected into the receiving-end AC grid at PCC node i in the hybrid multi-feed DC system, where i = 1…N, and N is the total number of DC PCC points in the AC / DC hybrid system.

[0142] 3) Power constraints at renewable energy generation nodes (considering wind and solar curtailment, the actual output power of renewable energy shall not exceed the predicted value):

[0143] ,

[0144] in, This refers to the actual active power generated by the new energy power generation nodes. This represents the predicted power output of new energy sources.

[0145] 4) Load node power constraints:

[0146] ,

[0147] in, The active power consumed by the load node. This represents the predicted load power.

[0148] 5) Power balance constraints at AC / DC nodes:

[0149] The AC system includes pure AC nodes and PCC points. For a pure AC node i, i=1, …, n, the specific expression for its power balance constraint is:

[0150] ,

[0151] In the formula, and These represent the active power and reactive power generated by the generator set connected to the pure AC node i, respectively. and These represent the active power and reactive power consumed by the load connected to the pure AC node i, respectively. Let be the voltage phase angle difference between nodes i and j; , , i and j are the voltage amplitudes at nodes i and j, respectively; N is the number of nodes in the AC system; and Let be the conductance and susceptance between nodes i and j, respectively.

[0152] For converter PCC node k, the specific expression for its power balance constraint is:

[0153] ,

[0154] In the formula, and These represent the active power and reactive power injected into PCC node k, respectively. and These represent the active and reactive power injected by the converter station into node k of the PCC in the AC system, respectively.

[0155] 6) Operational constraints of the MMC converter station:

[0156] The rectifier station adopts: ;

[0157] The inverter station adopts: ;

[0158] The power loss is: ;

[0159] The active power injected into the AC grid by the MMC converter station; These are the resistances of the transformers connecting to the MMC converter station; The equivalent resistance of the MMC converter station; This refers to the active power on the DC side of the MMC converter station; For the active power loss of the MMC converter station; This refers to the AC side current of the MMC converter station; , , These are the coefficients of the quadratic, primary, and constant terms related to the power loss of the MMC converter station.

[0160] 7) Control constraints of the MMC converter station:

[0161] ①Constant active power control (DC side / active power type):

[0162] ;

[0163] in, This represents the actual active power on the DC side of the MMC. Set the active power setting for MMC.

[0164] ②Constant DC voltage control (DC side / active power):

[0165] ;

[0166] in, This represents the actual active power on the DC side of the MMC. This is the actual DC current of the MMC. Set the DC voltage value for the MMC.

[0167] ③ DC voltage droop control (DC side / active power):

[0168] ;

[0169] in, This represents the actual active power on the DC side of the MMC. and These are the set values ​​for the voltage and active power of the DC system, respectively, and k is the droop slope.

[0170] ④ Reactive power control (AC side / reactive power category):

[0171] ;

[0172] in, This represents the actual reactive power on the AC side of the MMC. Set the reactive power setting for MMC.

[0173] ⑤ Constant AC voltage control (AC side / reactive power):

[0174] ;

[0175] in, This represents the actual reactive power on the AC side of the MMC. Set AC voltage value. The phase angle of the AC voltage; , These represent the voltage amplitude and phase angle on the filter side of the MMC converter station, respectively. To connect the reactance of the transformer, This is the resistance of the transformer.

[0176] Based on the actual control methods adopted by the MMC converter station, one of the three control methods ① / ② / ③ on the DC side (active power type) is selected as the DC side control constraint of the MMC converter station, and one of the two control methods ④ / ⑤ on the AC side (reactive power type) is selected as the AC side control constraint of the MMC converter station.

[0177] 8) Operating constraints of LCC / HCC converter stations:

[0178] The rectifier station adopts:

[0179] ,

[0180] ,

[0181] ;

[0182] The inverter station adopts:

[0183] ,

[0184] ,

[0185] ;

[0186] , These represent the active power and reactive power injected into the AC grid by the LCC / HCC converter station, respectively. , These are the commutation resistance and commutation reactance of the LCC / HCC converter station, respectively. This refers to the active power on the DC side of the LCC / HCC converter station. For the active power loss of the LCC / HCC converter station; This refers to the AC side current of the LCC / HCC converter station; , , φ represents the coefficients of the quadratic, primary, and constant terms related to the power loss of the LCC / HCC converter station; φ is the power factor angle of the LCC / HCC converter station.

[0187] 9) Control constraints of LCC / HCC converter station:

[0188] ① Constant active power control:

[0189] ;

[0190] in, This refers to the actual active power on the DC side of the LCC / HCC. The active power setting value for LCC / HCC.

[0191] ② Constant DC current control:

[0192] ;

[0193] in, This refers to the actual active power on the DC side of the LCC / HCC. For LCC / HCC DC voltage settings, This represents the actual DC voltage of the LCC / HCC.

[0194] ③ Constant DC voltage control:

[0195] ;

[0196] in, This refers to the actual active power on the DC side of the LCC / HCC. This represents the actual DC current of the LCC / HCC. Set the DC voltage value for LCC / HCC.

[0197] ④ Fixed trigger angle / shutdown angle control:

[0198] ;

[0199] in, It is the cosine value of the LCC / HCC converter station's set firing angle / shutdown angle command. For the converter transformer ratio; The number of six-pulse converters per pole. Choose one of the above four control methods as the control constraint for LCC / HCC.

[0200] 10) Capacity constraints of DC converter stations:

[0201] ;

[0202] in, The active power transmitted by converter station i The minimum operating power of converter station i, The maximum operating power of converter station i.

[0203] Step 3: At each power source and load prediction point within a certain time window, according to the power optimization model in Step 2, and using optimization algorithms (such as gradient descent method) or commercial optimization solvers, obtain the optimal support power time series of each converter station, and fit the power recovery curve.

[0204] The specific process includes: obtaining ultra-short-term forecast data of new energy sources and loads within a preset time window (e.g., 15 minutes). Then, according to the forecast step size (e.g., 1 minute), at each forecast time, the corresponding forecast values ​​of new energy output and load are used as boundary conditions (constraints 3 and 4) of the power optimization model in step 2, combined with the static voltage stability domain boundary as constraint 2), and other constraints 5-10 mentioned above, to establish a complete power support and recovery optimization model (corresponding to step 2 of the scheme). Since the power of new energy sources and loads is different at each forecast point, the corresponding time-scaled optimization model is also different, resulting in a series of time-scaled optimization models. Solving each one yields the optimal power support and recovery curve that evolves over time.

[0205] Step 4: Power control implementation: The recovery curve is sent to the controller of each converter station, and the PI control loop of the converter station realizes real-time tracking control of the target curve.

[0206] Step 5: Feedback Correction: The main control system monitors the AC bus voltage, the system frequency of the receiving-end AC grid, and the DC power response in real time; if deviations from the target or system oscillations occur, the curve can be recalculated or the recovery process can be delayed to enhance the system robustness.

[0207] This application also provides a DC system, see details below. Figure 2 The DC system is a hybrid multi-infeed DC system, which includes multiple feed links, a receiving-end AC grid, and a controller. The controller is connected to the multiple feed links and the receiving-end AC grid (either by electrical connection or by communication connection). The controller is used to execute any one of the power coordination methods of the DC system.

[0208] In specific embodiments, see again Figure 2 A feed-in link includes at least one type of converter station, which includes rectifier stations and inverter stations. Multiple types of converter stations include MMC converter stations, LCC converter stations and HCC converter stations.

[0209] This application also provides a power coordination device for a DC system. It should be noted that the power coordination device for a DC system in this application can be used to execute the power coordination method for a DC system provided in this application. This device is used to implement the above embodiments and preferred embodiments; details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0210] The following describes the power coordination device for a DC system provided in an embodiment of this application. The DC system is a hybrid multi-infeed DC system, which includes multiple feeder links and a receiving-end AC grid. The device includes:

[0211] The setting unit is used to set the optimization objective and boundary conditions. The optimization objective is to minimize the error between the DC power support value and the DC power expected value. The boundary conditions include at least the static voltage stability domain constraint conditions. The DC power support value is a reference value of DC power set to compensate for the fault when the generator Nk fault occurs in the receiving-end AC grid. The DC power expected value is a reference value of DC power set when the generator in the receiving-end AC grid is fault-free. The static voltage stability domain constraint conditions are the conditions that the active power injected into the receiving-end AC grid by multiple target nodes must meet. The target nodes are the nodes connected to the receiving-end AC grid by the feed-in link.

[0212] Building units are used to construct power optimization models based on optimization objectives and boundary conditions;

[0213] The control unit is used to determine the power curve of the DC power support value changing over time by applying a power optimization model if a generator set Nk fault is detected in the AC grid at the receiving end, and to send the power curve to the converter station controller so as to control the actual DC power value to follow the DC power support value.

[0214] The power coordination device for DC systems disclosed in this application constructs a power optimization model by setting optimization objectives and boundary conditions. If a generator Nk fault is detected in the receiving-end AC grid, the power optimization model is used to determine the power curve of the DC power support value over time, and this power curve is sent to the converter station controller to ensure that the actual DC power value follows the DC power support value. This fills the technical gap in the related technology of lacking an effective power dispatch strategy for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid. More importantly, by taking into account the static voltage stability domain constraints, it achieves effective power coordination and dispatch for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid.

[0215] In this embodiment, a feed-in link includes at least one type of converter station, which includes rectifier stations and inverter stations. The boundary conditions also include operational and control constraints for various types of converter stations. The setting unit includes a first determining module and a second determining module. The first determining module is used to determine the corresponding operational constraints based at least on the power characteristics of each type of converter station. The power characteristics include the active power injected by the converter station into the AC grid, and the AC grid includes the sending-end AC grid and the receiving-end AC grid. The second determining module is used to determine the corresponding control constraints based on the converter station's control mode.

[0216] In the specific implementation, the converter station also includes a connecting transformer connected to the rectifier station. The converter station is an MMC converter station. The first determining module is specifically used to determine the operating constraints of the MMC converter station based on the active power injected into the AC grid by the MMC converter station, the DC-side active power of the MMC converter station, the active power loss of the MMC converter station, the AC-side current of the MMC converter station, the resistance of the connecting transformer, and the equivalent resistance of the MMC converter station. The active power loss of the MMC converter station is determined based on the AC-side current of the MMC converter station.

[0217] In the specific implementation, the converter station is an MMC converter station. The second determining module includes a first determining submodule and a second determining submodule. The first determining submodule is used to determine the control constraints of the MMC converter station based on the active power control mode of the MMC converter station. The active power control mode of the MMC converter station is one of constant active power control mode, constant DC voltage control mode, and DC voltage droop control mode. The second determining submodule is used to determine the control constraints of the MMC converter station based on the reactive power control mode of the MMC converter station. The reactive power control mode of the MMC converter station is one of constant reactive power control mode and constant AC voltage control mode.

[0218] In the specific implementation, the converter station is either an LCC converter station or an HCC converter station. The first determining module is specifically used to determine the operating constraints of the LCC converter station or HCC converter station based on the active and reactive power injected into the AC grid by the LCC converter station or HCC converter station, the DC-side active power of the LCC converter station or HCC converter station, the active power loss of the LCC converter station or HCC converter station, the AC-side current of the LCC converter station or HCC converter station, the commutation resistance and commutation reactance of the LCC converter station or HCC converter station, and the power factor angle of the LCC converter station or HCC converter station. Among them, the active power loss of the LCC converter station or HCC converter station is determined based on the AC-side current of the LCC converter station or HCC converter station.

[0219] In this embodiment of the application, the converter station is an LCC converter station or an HCC converter station. The second determining module is specifically used to determine the control constraints of the LCC converter station or HCC converter station based on the control mode of the LCC converter station or HCC converter station. The control mode of the LCC converter station or HCC converter station is one of the following: constant active power control mode, constant DC current control mode, constant DC voltage control mode, and constant firing angle / turn-off angle control mode.

[0220] The setting unit also includes a configuration module, which is used to configure boundary conditions including at least one of the following: total power support constraints, new energy generation node power constraints, load node power constraints, AC / DC node power balance constraints, and DC converter station capacity constraints.

[0221] In this embodiment, the device further includes a monitoring unit and a processing unit. The monitoring unit is used to monitor the AC bus voltage, the system frequency of the receiving-end AC grid, and the actual DC power value after sending the power curve to the converter station controller to control the actual DC power value to follow the DC power support value. The processing unit is used to generate a new power curve or delay the recovery process when preset conditions are met. The preset conditions include that the AC bus voltage is not within a preset voltage range, the system frequency of the receiving-end AC grid is not within a preset frequency range, and the difference between the actual DC power value and the DC power support value is greater than at least one of the preset differences.

[0222] The technical advantages of the method embodiments in this application are also applicable to the device embodiments of this solution.

[0223] The power coordination device of the DC system includes a processor and a memory. The aforementioned setting unit, construction unit, and control unit are all stored as program units in the memory, and the processor executes the aforementioned program units stored in the memory to achieve the corresponding functions. All of the above modules are located in the same processor; or, the above modules are located in different processors in any combination.

[0224] The processor contains a kernel, which retrieves the corresponding program units from memory. One or more kernels can be configured, and adjusting kernel parameters can address the technical problem of the lack of an effective power dispatch strategy for hybrid multi-infeed DC systems when a generator Nk fault occurs in the receiving-end AC grid.

[0225] The memory may include non-permanent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM, and the memory includes at least one memory chip.

[0226] This invention provides a computer-readable storage medium including a stored program, wherein the program, when executed, controls the device containing the computer-readable storage medium to perform a power coordination method for a DC system.

[0227] This invention provides a processor for running a program, wherein the program executes a power coordination method for a DC system.

[0228] This invention provides a device including a processor, a memory, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in a power coordination method for a DC system. The device described herein can be a server, PC, PAD, mobile phone, etc.

[0229] This application also provides a computer program product that, when executed on a data processing device, is adapted to perform the steps in a power coordination method for initializing a DC system.

[0230] It is obvious to those skilled in the art that the modules or steps of the present invention described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. They can be implemented using computer-executable program code, and thus can be stored in a storage device for execution by a computing device. In some cases, the steps shown or described can be performed in a different order than those described herein, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, the present invention is not limited to any particular combination of hardware and software.

[0231] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0232] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0233] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0234] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0235] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0236] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, like read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0237] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0238] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0239] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0240] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A power coordination method for a DC system, characterized in that, The DC system is a hybrid multi-infeed DC system, which includes multiple feed-in links and a receiving-end AC grid. The method includes: The optimization objective and boundary conditions are set. The optimization objective is to minimize the error between the DC power support value and the DC power expected value. The boundary conditions include at least the static voltage stability domain constraint condition. The DC power support value is a reference value of DC power set to compensate for the fault when the generator Nk fault occurs in the AC grid at the receiving end. The DC power expected value is a reference value of DC power set when the generator in the AC grid at the receiving end is fault-free. The static voltage stability domain constraint condition is a condition that the active power injected into the AC grid by multiple target nodes must satisfy. The target node is the node connected to the AC grid by the feed-in link. Construct a power optimization model based on the optimization objective and the boundary conditions; If a fault Nk of the generator set is detected in the AC grid at the receiving end, the power optimization model is used to determine the power curve of the DC power support value changing over time, and the power curve is sent to the converter station controller to control the actual DC power value to follow the DC power support value.

2. The power coordination method for a DC system according to claim 1, characterized in that, One of the feed-in links includes at least one type of converter station, the converter station including a rectifier station and an inverter station, and the boundary conditions also include various types of operating constraints and control constraints for the converter stations, the boundary conditions being set as follows: The corresponding operating constraints are determined at least based on the power characteristics of each type of converter station, the power characteristics including the active power injected by the converter station into the AC grid, the AC grid including the sending-end AC grid and the receiving-end AC grid; The corresponding control constraints are determined based on the converter station control method.

3. The power coordination method for a DC system according to claim 2, characterized in that, The converter station also includes a connecting transformer connected to the rectifier station. The converter station is an MMC converter station. The corresponding operating constraints are determined based on the power characteristics of each type of converter station, including: Based on the active power injected into the AC grid by the MMC converter station, the active power on the DC side of the MMC converter station, the active power loss of the MMC converter station, the AC side current of the MMC converter station, the resistance of the connecting transformer, and the equivalent resistance of the MMC converter station, the operating constraints of the MMC converter station are determined. The active power loss of the MMC converter station is determined based on the AC side current of the MMC converter station.

4. The power coordination method for a DC system according to claim 2, characterized in that, The converter station is an MMC converter station. The corresponding control constraints are determined based on the converter station control mode, including: The control constraints of the MMC converter station are determined based on the active power control mode of the MMC converter station. The active power control mode of the MMC converter station is one of constant active power control mode, constant DC voltage control mode, and DC voltage droop control mode. The control constraints of the MMC converter station are determined based on the reactive power control mode of the MMC converter station. The reactive power control mode of the MMC converter station is one of constant reactive power control mode and constant AC voltage control mode.

5. The power coordination method for a DC system according to claim 2, characterized in that, The converter station is either an LCC converter station or an HCC converter station. The corresponding operating constraints are determined based on the power characteristics of each type of converter station, including: The operating constraints of the LCC or HCC converter station are determined based on the active and reactive power injected into the AC grid by the LCC or HCC converter station, the DC-side active power of the LCC or HCC converter station, the active power loss of the LCC or HCC converter station, the AC-side current of the LCC or HCC converter station, the commutation resistance and commutation reactance of the LCC or HCC converter station, and the power factor angle of the LCC or HCC converter station. The active power loss of the LCC or HCC converter station is determined based on the AC-side current of the LCC or HCC converter station.

6. The power coordination method for a DC system according to claim 2, characterized in that, The converter station is either an LCC converter station or an HCC converter station. The corresponding control constraints are determined based on the converter station's control mode, including: The control constraints of the rectifier station of the LCC converter station or the HCC converter station are determined based on the control mode of the LCC converter station or the HCC converter station. The control mode of the LCC converter station or the HCC converter station is one of the following: constant active power control mode, constant DC current control mode, constant DC voltage control mode, and constant firing angle / turn-off angle control mode.

7. The power coordination method for a DC system according to claim 1, characterized in that, Setting the boundary conditions also includes: The boundary conditions also include at least one of the following: total power support constraints, power constraints for new energy generation nodes, power constraints for load nodes, power balance constraints for AC / DC nodes, and capacity constraints for DC converter stations.

8. The power coordination method for a DC system according to any one of claims 1 to 7, characterized in that, After sending the power curve to the converter station controller to control the actual DC power value to follow the DC power support value, the method further includes: Monitor the AC bus voltage, the system frequency of the receiving-end AC power grid, and the actual value of the DC power; Under preset conditions, a new power curve or a delayed recovery process is generated. The preset conditions include at least one of the following: the AC bus voltage is not within a preset voltage range, the system frequency of the receiving-end AC grid is not within a preset frequency range, and the difference between the actual DC power value and the DC power support value is greater than a preset difference value.

9. A DC system, characterized in that, The DC system is a hybrid multi-infeed DC system, which includes multiple feed links, a receiving-end AC grid, and a controller. The controller is used to execute the power coordination method of the DC system according to any one of claims 1 to 8.

10. The DC system according to claim 9, characterized in that, One of the feed-in links includes at least one type of converter station, which includes rectifier stations and inverter stations, and the multiple types of converter stations include MMC converter stations, LCC converter stations and HCC converter stations.

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