A disengageable and engageable direct current operation mode control method and system

Abstract

This invention discloses a control method and system for DC operation modes that can be switched between on and off, applicable to the field of DC transmission control. The method includes: determining the system stability margin of the sending-end grid based on its operating data; determining the first DC in the off-grid ready state among the DC units based on the exchange power between each DC unit and the sending-end main grid; controlling the first DC to disconnect from the grid based on the system stability margin and the regulation attributes of the supporting power source, switching the DC transmission system corresponding to the first DC to islanded operation mode; and controlling the second DC in the grid-connected ready state to connect to the grid based on the system stability margin and the regulation attributes of the supporting power source, switching the DC transmission system corresponding to the second DC to grid-connected operation mode. This invention flexibly switches the operation modes of each DC according to the operating status of the sending-end grid, improving the operational flexibility and system resilience of the sending-end grid.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission control technology, and in particular to a control method and system for DC operation modes that can be switched on and off. Background Technology

[0002] Ultra-high voltage direct current (UHVDC) transmission enables long-distance and efficient power transmission. Current UHVDC operation modes primarily include grid-connected operation and islanded operation. However, these modes are relatively rigid, either fully integrated into the main grid or completely isolated from it. Therefore, there is a lack of a scheme for the planned and flexible switching of operation modes within the sending-end power grid based on its actual operating conditions and carrying capacity, thus improving the grid's operational flexibility and system resilience. Summary of the Invention

[0003] This invention provides a control method and system for DC operation modes that can be switched on and off, in order to solve the technical problem that the operation modes of existing UHVDC cannot be flexibly switched, thereby improving the operational flexibility and system resilience of the sending-end power grid.

[0004] To address the aforementioned technical problems, embodiments of the present invention provide a control method for a DC operating mode that can be switched on and off, comprising: Based on the operating data of the sending-end power grid, the system stability margin of the sending-end power grid is determined; the sending-end power grid includes the sending-end main grid and multiple DC transmission systems; each DC transmission system includes multiple supporting power sources and a DC main body; each DC main body is connected to the sending-end main grid; Based on the exchange power between each DC body and the sending-end main grid, determine the first DC body in the off-grid ready state among each DC body; Based on the system stability margin and the regulation properties of the supporting power supply, the first DC power is controlled to be disconnected from the grid, and the DC transmission system corresponding to the first DC power is switched to islanded operation mode. Based on the system stability margin and the regulation attributes of the supporting power supply, the second DC power transmission system, which is in the grid-ready state, is controlled to switch to grid-connected operation mode.

[0005] As one preferred embodiment, controlling the first DC transmission line to disconnect from the grid based on the system stability margin and the regulation attributes of the supporting power supply, and switching the DC transmission system corresponding to the first DC transmission line to islanded operation mode, includes: If the system stability margin does not meet the preset requirements and there is only one first DC, the first DC is controlled to disconnect from the grid, and the DC transmission system corresponding to the first DC is switched to islanded operation mode. When the system stability margin does not meet the preset requirements and there are multiple first DCs, determine the correlation degree between each first DC and the system stability margin; Based on the correlation between each of the first DC and the stability margin of the system, and the regulation attributes of the power supply corresponding to each of the first DC, a target DC is selected from each of the first DCs; If only one target DC exists, the target DC is controlled to be disconnected from the grid, and the DC transmission system corresponding to the target DC is switched to islanded operation mode.

[0006] As one preferred embodiment, the step of selecting the target DC from the first DC based on the correlation between each first DC and the system stability margin, and the regulation attributes of the corresponding power supply for each first DC, includes: Based on the correlation between each of the first DC and the stability margin of the system, the stability impact contribution of each of the first DC is ranked to obtain a first ranking result; Based on the regulation attributes of the matching power supply corresponding to each first DC, the regulation capabilities of each first DC are sorted to obtain a second sorting result. Based on the comparison between the first sorting result and the second sorting result, the target DC is selected from each of the first DCs.

[0007] As one preferred embodiment, the step of selecting a target DC from the first DC based on the correlation between each first DC and the system stability margin, and the regulation attributes of the corresponding power supply for each first DC, includes: Obtain the power demand of the receiving-end power grid; the receiving-end power grid is asynchronously connected to the sending-end power grid; When there are multiple target DCs, the system stability margin of the sending-end power grid and the operating status of the sending-end main grid are simulated and updated after each target DC is disconnected from the grid. Off-grid DC is selected from the target DC; the system stability margin updated after the off-grid DC is disconnected from the grid meets the preset requirements, and the operating status of the sending-end main grid updated meets the power receiving requirements; Control the off-grid DC to go off-grid, and switch the DC transmission system corresponding to the off-grid DC to islanded operation mode.

[0008] As one preferred embodiment, controlling the grid connection of the second DC power transmission system in the grid-ready state based on the system stability margin and the regulation attributes of the supporting power supply, and converting the DC transmission system corresponding to the second DC power transmission system into grid-connected operation mode, includes: When the system stability margin meets the preset requirements and there are multiple second DCs, determine the degree of influence of each island corresponding to the second DC on the system stability margin; Based on the degree of influence of each second DC and the regulation attributes of the power supply corresponding to each second DC, network DCs are selected from each second DC. The DC transmission system corresponding to the aforementioned DC network will be switched to network operation mode.

[0009] Another embodiment of the present invention provides a system comprising: The system stability margin determination module is used to determine the system stability margin of the sending-end power grid based on the operating data of the sending-end power grid; the sending-end power grid includes the sending-end main grid and multiple DC transmission systems; each DC transmission system includes multiple supporting power sources and a DC transmission body; each DC transmission body is connected to the sending-end main grid; The first DC determination module is used to determine the first DC in the off-grid ready state among the DC bodies based on the exchange power between each DC body and the sending-end main grid. The grid-connected module is used to control the first DC to disconnect from the grid and switch the DC transmission system corresponding to the first DC to islanded operation mode based on the system stability margin and the regulation attributes of the supporting power supply. The separation-to-connection module is used to control the second DC grid connection in the grid-ready state based on the system stability margin and the regulation attributes of the supporting power supply, and to switch the DC transmission system corresponding to the second DC to the grid-connected operation mode.

[0010] As one preferred embodiment, the closing / disclosing module includes: The first DC off-grid control unit is used to control the first DC off-grid and switch the DC transmission system corresponding to the first DC to islanded operation mode when the system stability margin does not meet the preset requirements and there is only one first DC. The correlation degree determination unit is used to determine the correlation degree between each of the first DC and the system stability margin when the system stability margin does not meet the preset requirements and there are multiple first DCs. The target DC filtering unit is used to filter out target DCs from each of the first DCs based on the correlation between each of the first DCs and the stability margin of the system, as well as the adjustment attributes of the matching power supply corresponding to each of the first DCs. The target DC off-grid control unit is used to control the target DC to go off-grid when there is only one target DC, and to switch the DC transmission system corresponding to the target DC to islanded operation mode.

[0011] As one preferred embodiment, the target DC screening unit includes: The first sorting unit is used to sort the stability impact contribution of each first DC based on the correlation degree between each first DC and the stability margin of the system, and obtain the first sorting result. The second sorting unit is used to sort the regulation capabilities of each first DC power supply based on the regulation attributes of the corresponding power supply of each first DC power supply, and obtain a second sorting result. The sorting comparison unit is used to select the target DC from each of the first DCs based on the comparison result of the first sorting result and the second sorting result.

[0012] As one preferred embodiment, the closing / disclosing module further includes: A power demand acquisition unit is used to acquire the power demand of the receiving-end power grid; the receiving-end power grid is asynchronously connected to the sending-end power grid; The simulation update unit is used to simulate and update the system stability margin of the sending-end power grid and the operating status of the sending-end main grid after each of the target DCs is disconnected from the grid when there are multiple target DCs. Off-grid DC screening unit is used to screen off-grid DC from each of the target DC; the system stability margin updated after the off-grid DC is disconnected from the grid meets the preset requirements, and the operating status of the main grid at the sending end meets the power receiving requirements. Off-grid DC control unit is used to control the off-grid DC to switch the DC transmission system corresponding to the off-grid DC to islanded operation mode.

[0013] As one preferred embodiment, the disengagement / engagement module includes: The influence degree determination unit is used to determine the influence degree of each island corresponding to the second DC on the system stability margin when the system stability margin meets the preset requirements and there are multiple second DCs. A networked DC filtering unit is used to filter out networked DCs from each of the second DCs based on the degree of influence of each of the second DCs and the adjustment attributes of the power supply corresponding to each of the second DCs; The networked DC control unit is used to switch the DC transmission system corresponding to the networked DC to network operation mode.

[0014] This invention provides a control method and system for DC operation modes that can be switched between isolated and connected modes. The system stability margin of the sending-end power grid is determined based on its operational data. This sending-end power grid includes a main grid and a DC transmission system. Each DC transmission system includes multiple supporting power sources and a DC main unit. The DC main unit is connected to the main grid. The system stability margin reflects the safe and stable operation of the sending-end power grid. Based on the exchange power between each DC main unit and the main grid, a first DC unit in an off-grid ready state is identified. When the DC unit is disconnected from the grid, the first DC unit is controlled to disconnect based on the system stability margin of the sending-end power grid and the regulation attributes of the supporting power sources, thereby switching the corresponding DC transmission system to an islanded operation mode. When the DC unit is connected to the grid, the second DC unit in a grid-connected ready state is controlled to connect to the grid based on the system stability margin of the sending-end power grid and the regulation attributes of the supporting power sources, thereby switching the corresponding DC transmission system to a grid-connected operation mode. This invention flexibly switches the operation modes of each DC unit according to the operating status of the sending-end power grid, improving the operational flexibility and system resilience of the sending-end power grid. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the DC operation mode control method that can be switched on and off as provided by the present invention. Figure 2 This is a schematic diagram of the operating framework of the sending-end power grid provided by the present invention; Figure 3 This is a schematic diagram of the DC operation mode control system that can be operated in both separate and combined modes, provided by the present invention.

[0016] Figure label: Among them, 301 is the system stability margin determination module; 302 is the first DC determination module; 303 is the closing-to-disconnecting module; and 304 is the disconnecting-to-closing module. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0019] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used herein are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0020] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] See Figure 1 , Figure 1 This is a flowchart illustrating one embodiment of the DC operation mode control method that can be switched on and off as provided by the present invention. Figure 1 As shown, this embodiment includes steps 100 to 400, and the specific steps are as follows: Step 100: Based on the operating data of the sending-end power grid, determine the system stability margin of the sending-end power grid; the sending-end power grid includes the sending-end main grid and multiple DC transmission systems; each DC transmission system includes multiple supporting power sources and a DC main body; each DC main body is connected to the sending-end main grid; Specifically, such as Figure 2As shown, the DC operation mode control method that can be separated and combined provided by the present invention is applied to the sending-end power grid, which includes the sending-end main grid and several DC transmission systems. Each DC transmission system includes multiple supporting power sources and a DC main unit. Each power source collection station is used to process (collect, integrate and regulate) the power from the supporting power sources (e.g., wind power, photovoltaic power, hydropower and thermal power) and then send it into the receiving-end power grid through the DC main unit. Multiple supporting power sources are sent into the receiving-end power grid through a single DC main unit.

[0022] The DC grid connection and off-grid control method provided by this invention realizes DC grid connection and off-grid control based on the system stability margin of the sending-end power grid. The system stability margin reflects the ability of the sending-end power grid to operate safely and stably. The calculation basis of the system stability margin is the operating data of the sending-end power grid. This operating data specifically includes monitoring parameters common to both operating modes (islanding operation mode and grid connection operation mode), monitoring parameters of islanding operation mode (reflecting the self-sufficiency of the islanded system), and monitoring parameters of the DC system itself. The general monitoring parameters include the power and voltage of the DC grid connection point, the short-circuit capacity of the converter bus of the sending-end converter station, the short-circuit current of the substation of the sending-end system, the active power / reactive power of the key transmission sections closely related to the DC electrical system, the voltage level of the key bus of the sending-end system and the system frequency, and the system broadband oscillation margin, etc.; the monitoring parameters of the islanded operation mode include the voltage and frequency of the sending-end island, the regulation capability of the supporting power supply, and the state of charge (SOC) of the energy storage, etc.; the monitoring parameters of the DC body include: AC and DC side power, DC voltage, DC current, and electrical angle, etc.

[0023] The fundamental principle behind this invention's ability to achieve both disconnection and connection of the sending-end grid (disconnection refers to the DC system being able to break its connection with the sending-end main grid; connection refers to the DC system being able to connect to the sending-end main grid) lies in assessing the "carry-over margin of the sending-end main grid for DC" and the "independent operation capability of the islanded system." The connection and disconnection are planned and controlled switching, and by rationally designing system monitoring parameters, power surges in the sending-end grid can be avoided. Regardless of whether it's in grid-connected or islanded operation mode, the monitoring parameters always reflect the interaction between the DC system and the sending-end main grid, and its impact on the safety and stability of the sending-end grid. In islanded operation mode, monitoring the islanded system's self-sufficiency capability is the basis for assessing independent islanded operation and the possibility of future safe DC grid connection.

[0024] Step 200: Based on the exchange power between each DC body and the sending-end main grid, determine the first DC body in the off-grid ready state among each DC body; Specifically, before controlling a networked DC transmission system to switch to islanded operation mode, it is necessary to determine the off-grid readiness status of each DC transmission line. The DC transmission line in the off-grid ready state is designated as the first DC transmission line in this embodiment. The off-grid readiness status determination criterion provided in this embodiment is the exchange power between each DC transmission line and the sending-end main grid. The objective of determining the off-grid ready DC transmission line is to ensure that the sending-end grid can restore or maintain stable operation (e.g., frequency and voltage stability) after the DC transmission line is disconnected from the grid; the impact caused by the DC disconnection must be less than the maximum tolerable power deficit of the sending-end grid. The exchange power between each DC transmission line and the sending-end main grid is a key indicator for measuring the magnitude of the off-grid impact. The decision on the off-grid readiness status is made by selecting the first DC transmission line, ensuring that the sum of the total power of the first DC transmission line after disconnection has a controllable impact on the sending-end grid and can maximize the solution to the problem of stable operation of the sending-end grid.

[0025] Step 300: Based on the system stability margin and the regulation attributes of the supporting power supply, control the first DC to disconnect from the grid and switch the DC transmission system corresponding to the first DC to islanded operation mode; Specifically, after determining the existence of a first DC power line in a grid-ready state, further comprehensive judgment is made using criteria such as short-circuit current, safety and stability, unplanned risk avoidance, and wideband oscillation. It also considers the impact of grid disconnection on the receiving-end grid (i.e., grid disconnection should not affect reliable power reception at the receiving end), where reliable power reception can be reflected by the regulation capability of the supporting power source. Therefore, this invention provides a method for determining a first DC power line that can be disconnected based on the system stability margin of the sending-end grid and the regulation attributes (representing regulation capability) of the supporting power source, and for switching the corresponding DC transmission system to islanded operation mode, such as... Figure 2 As shown, the first DC that can be disconnected from the grid is... Figure 2 Off-grid DC in the middle.

[0026] Step 400: Based on the system stability margin and the regulation attributes of the supporting power supply, control the second DC power transmission system in the grid-ready state to switch to grid-connected operation mode.

[0027] Specifically, after determining the existence of a second DC power line in a grid-ready state, further comprehensive judgment is made using short-circuit current criteria, safety and stability criteria, and wideband oscillation criteria, while also considering the impact of reliable power reception at the receiving end. Therefore, this invention provides a method for determining a second DC power line suitable for grid connection based on the system stability margin of the sending-end grid and the regulation capability of the supporting power source, and for converting the corresponding DC transmission system of the second DC power line into grid-connected operation mode, such as... Figure 2 As shown, the second DC that can be connected to the network is... Figure 2 Grid-connected DC in the middle.

[0028] This embodiment determines the system stability margin of the sending-end power grid by using operational data from the sending-end power grid. The sending-end power grid includes the sending-end main grid and a DC transmission system. The DC transmission system includes multiple supporting power sources and multiple DC transmission units. Each DC transmission unit is connected to the sending-end main grid. The system stability margin reflects the safe and stable operation of the sending-end power grid. Based on the exchange power between each DC transmission unit and the sending-end main grid, a first DC transmission unit in an off-grid ready state is identified. When the DC transmission unit is taken off-grid, the system stability margin of the sending-end power grid and the regulation attributes of the supporting power sources are used to control the first DC transmission unit to be taken off-grid, thereby switching the corresponding DC transmission system to an islanded operation mode. When the DC transmission unit is connected to the grid, the system stability margin of the sending-end power grid and the regulation attributes of the supporting power sources are used to control the second DC transmission unit in a grid-connected ready state to be connected to the grid, thereby switching the corresponding DC transmission system to a grid-connected operation mode. This invention flexibly switches the operation modes of each DC transmission unit according to the operating status of the sending-end power grid, improving the operational flexibility and system resilience of the sending-end power grid.

[0029] In another embodiment of the detachable and combinable DC operation mode control method provided by the present invention, step 300 specifically includes: Step 310: If the system stability margin does not meet the preset requirements and there is only one first DC, control the first DC to disconnect from the grid and switch the DC transmission system corresponding to the first DC to islanded operation mode. Step 320: When the system stability margin does not meet the preset requirements and there are multiple first DCs, determine the correlation between each first DC and the system stability margin. Step 330: Based on the correlation between each first DC and the stability margin of the system, and the adjustment attributes of the matching power supply corresponding to each first DC, select the target DC from each first DC. Step 340: If there is only one target DC, control the target DC to go offline and switch the DC transmission system corresponding to the target DC to islanded operation mode.

[0030] Specifically, when the system stability margin of the sending-end power grid does not meet the preset requirements (i.e., the safe and stable operation of the sending-end power grid system may be affected), the number of first DC lines in the off-grid ready state is further determined. If the system stability margin does not meet the preset requirements and there is only one first DC line, the first DC line is controlled to disconnect from the grid, and the DC transmission system corresponding to the first DC line is switched to islanded operation mode. Whether the system stability margin meets the preset requirements is determined by conditions such as short-circuit current criteria, safety and stability criteria, unplanned risk avoidance criteria, and broadband oscillation criteria. If any one of these criteria is not met, it can be determined that the system stability margin does not meet the preset requirements.

[0031] When the system stability margin does not meet the preset requirements and multiple first DC lines exist, it is necessary to further determine the correlation between each first DC line and the system stability margin. This allows for the selection of first DC lines with a higher correlation to the system stability margin. The correlation with the system stability margin refers to the contribution of each first DC line to the safety and stability of the sending-end power grid; a higher correlation indicates a greater impact on the safe and stable operation of the sending-end power grid. By considering the correlation between each first DC line and the system stability margin, as well as the regulation attributes of the corresponding power source, a target DC line is selected from among the first DC lines.

[0032] Among them, the target DC is the DC that has a significant impact on the safe and stable operation of the sending-end grid, and whose corresponding supporting power source has a relatively small regulation capability. Off-grid access for this target DC can ensure the stable operation of the sending-end grid without affecting the power reception of the receiving-end grid. If multiple target DCs exist, it is necessary to further screen the target DCs that have a significant impact on safe and stable operation and whose corresponding supporting power source has a relatively small regulation capability. If only one target DC exists, it can be directly controlled to be off-grid, and the corresponding DC transmission system can be switched to islanded operation mode.

[0033] This embodiment comprehensively evaluates and controls DC off-grid operation by considering the off-grid readiness status and multiple criteria affecting the safe and stable operation of the sending-end power grid. While ensuring the safe and stable operation of the sending-end power grid, it does not affect the power reception of the receiving-end power grid, achieving a good balance between carrying capacity and system resilience.

[0034] In another embodiment of the detachable and combinable DC operation mode control method provided by the present invention, step 330 specifically includes: Step 331: Based on the correlation between each first DC and the stability margin of the system, sort the stability impact contribution of each first DC to obtain a first sorting result; Step 332: Based on the regulation attributes of the matching power supply corresponding to each first DC, sort the regulation capabilities of each first DC to obtain a second sorting result; Step 333: Based on the comparison results of the first sorting result and the second sorting result, select the target DC from each of the first DCs.

[0035] Specifically, the criteria for determining whether the stability margin of the aforementioned system meets the preset requirements mainly include: short-circuit current criterion: based on the calculation and analysis of the short-circuit current of the sending-end grid, the short-circuit current of the sending-end main grid will exceed the switching capacity or the set threshold; safety and stability criterion: based on time-domain simulation calculation and analysis, when DC is connected to the sending-end main grid, the system frequency exceeds the limit system setting value after a fault, or there is insufficient system stability margin such as voltage and power angle, or the risk of stability failure; unplanned risk avoidance criterion: when a sudden fault occurs in the sending-end grid, based on time-domain simulation calculation and analysis, the DC is actively converted to islanded mode to reduce the complexity of the main grid operation and improve the overall system resilience; broadband oscillation criterion: based on time-domain simulation calculation and eigenvalue analysis, the interaction of multiple power electronic devices in the sending-end grid is analyzed to identify potential oscillation risks, key oscillation frequencies, and dominant oscillation modes. When the stability margin of broadband oscillation in the sending-end grid does not meet the requirements, a conversion operation can be performed to ensure that the stability margin of broadband oscillation in both the main grid and the islanded system meets the requirements after DC is disconnected from the grid, and there is no risk of dominant oscillation mode.

[0036] When the system stability margin does not meet the preset requirements and there are multiple first DC lines in an off-grid ready state, the stability impact contribution of each first DC line is ranked from largest to smallest based on its correlation with the system stability margin, resulting in a first ranking result. Specifically, for short-circuit current issues, the ranking of DC lines based on short-circuit current contribution from highest to lowest can be calculated; for voltage or power angle stability issues, the ranking of DC lines based on the correlation of key instability paths from highest to lowest can be calculated; for frequency issues affecting the entire grid, the DC line belonging to the supporting power source with the weakest regulation capability can be prioritized as the off-grid DC line, and the DC lines corresponding to the supporting power source's collection station can be ranked from lowest to highest regulation capability; for broadband oscillation issues, the ranking of DC lines based on their ability to reduce broadband oscillation risk from highest to lowest yields the final ranking result.

[0037] While obtaining the first ranking result, the regulation capability of the matching power supply corresponding to each first DC is ranked from low to high to obtain the second ranking result. The first ranking result and the second ranking result are compared, and the first DC that ranks higher in both ranking results is selected as the target DC from all the first DCs.

[0038] This embodiment comprehensively assesses multiple off-grid DC transmission lines by considering the system stability margin correlation and the regulation capability of the corresponding power source. It accurately identifies the target DC transmission line that has a significant impact on the safe and stable operation of the sending-end grid and whose corresponding power source has a relatively small regulation capability. Off-grid access to this target DC transmission line ensures stable operation of the sending-end grid without affecting the power reception of the receiving-end grid, achieving a good balance between system carrying capacity and system resilience.

[0039] In another embodiment of the detachable and combinable DC operation mode control method provided by the present invention, step 300 specifically further includes: Step 350: Obtain the power demand of the receiving-end power grid; the receiving-end power grid is asynchronously connected to the sending-end power grid; Step 360: When there are multiple target DCs, simulate and update the system stability margin of the sending-end power grid and the operating status of the sending-end main grid after each target DC is disconnected from the grid. Step 370: Select off-grid DC from each of the target DC; the system stability margin updated after the off-grid DC is removed from the grid meets the preset requirements, and the operating status updated by the sending-end main grid meets the power receiving requirements; Step 380: Control the off-grid DC to go off-grid, and switch the DC transmission system corresponding to the off-grid DC to islanded operation mode.

[0040] Specifically, the DC operation mode control method that can be switched on and off provided by the present invention also considers the influence of the power demand of the receiving end grid when controlling the DC switching on and off. That is, the switching on and off of the DC does not affect the power demand of the receiving end grid. The receiving end grid and the sending end grid are asynchronously connected. The asynchronous connection is understood as follows: the sending end grid and the receiving end grid are not interconnected in AC. The sending end rectifies the AC power into DC power through a rectifier station and transmits it to the receiving end through DC lines. The receiving end inverts the DC power into AC power through an inverter station. The frequency and phase of the AC grids at both ends are asynchronous.

[0041] When multiple target DCs exist, the impact of each target DC on the power demand of the receiving-end grid can be further assessed. Specifically, the system stability margin of the sending-end grid and the operating status of the sending-end main grid after each target DC is disconnected from the grid are simulated and updated. The target DC whose updated system stability margin meets the preset requirements and whose updated operating status of the sending-end main grid meets the power demand is designated as the off-grid DC. The off-grid DC is then controlled to disconnect from the grid, and the DC transmission system corresponding to the off-grid DC is switched to islanded operation mode.

[0042] This embodiment uses off-grid control to influence the power demand of the receiving-end grid, and further filters out multiple potential target DC lines to accurately achieve a balance between system carrying capacity and system resilience.

[0043] In another embodiment of the detachable and combinable DC operation mode control method provided by the present invention, step 400 specifically includes: Step 410: When the system stability margin meets the preset requirements and there are multiple second DCs, determine the degree of influence of each island corresponding to the second DC on the system stability margin. Step 420: Based on the degree of influence of each second DC and the regulation attributes of the matching power supply of each second DC, select the network DC from each second DC; Step 430: Switch the DC transmission system corresponding to the networked DC to network operation mode.

[0044] Specifically, when there are multiple second DC lines that meet the preset stability margin requirements and are in a grid-ready state, the impact of each second DC line's corresponding island on the system stability margin is further assessed. The criteria mainly include short-circuit current criteria, safety and stability criteria, and broadband oscillation criteria. The short-circuit current criterion is based on grid short-circuit current calculation and analysis, ensuring that the short-circuit current of the sending-end main grid is within the switch breaking capacity or a set threshold. The safety and stability criterion is based on time-domain simulation calculation and analysis, ensuring that when DC lines are connected to the sending-end main grid, the system frequency, voltage, and power angle remain stable after a fault, indicating that the sending-end main grid has the capacity to handle DC lines. The broadband oscillation criterion is based on time-domain simulation calculation and eigenvalue analysis, analyzing the dynamic interaction between the sending-end grid and the sending-end main grid, identifying potential oscillation risks, key oscillation frequencies, and dominant oscillation modes, ensuring that the stability margin of broadband oscillations after DC grid connection meets the requirements and that there is no risk of a dominant oscillation mode.

[0045] Based on the impact of each secondary DC transmission line on the system stability margin and the regulation capability of the corresponding power supply for each secondary DC transmission line, a grid-connected DC transmission line is selected from the secondary DC transmission lines. Among them, the grid-connected DC transmission line has a stronger regulation capability and a lower impact on the system stability margin. The DC transmission system corresponding to this grid-connected DC transmission line is then switched to grid-connected operation mode.

[0046] This embodiment comprehensively evaluates and controls DC grid connection by considering multiple criteria, including grid-connected readiness status and factors affecting system stability margin. This achieves a good balance between carrying capacity and system resilience, ensuring the safe and stable operation of the sending-end grid without affecting the receiving-end grid's power reception.

[0047] The following describes the detachable and combinable DC operation mode control system provided by the present invention. The detachable and combinable DC operation mode control system described below can be referred to in correspondence with the detachable and combinable DC operation mode control method described above.

[0048] Please refer to Figure 3 The present invention also provides a DC operating mode control system that can be switched on and off, comprising: The system stability margin determination module 301 is used to determine the system stability margin of the sending-end power grid based on the operating data of the sending-end power grid; the sending-end power grid includes the sending-end main grid and multiple DC transmission systems; each DC transmission system includes multiple supporting power sources and a DC transmission body; each DC transmission body is connected to the sending-end main grid; The first DC determination module 302 is used to determine the first DC in the off-grid ready state among the DC bodies based on the exchange power between each DC body and the sending end main grid. The grid-connected switching module 303 is used to control the first DC to disconnect from the grid and switch the DC transmission system corresponding to the first DC to islanded operation mode based on the system stability margin and the adjustment attributes of the supporting power supply. The separation-to-connection module 304 is used to control the second DC grid connection in the grid-ready state based on the system stability margin and the adjustment attributes of the supporting power supply, and to switch the DC transmission system corresponding to the second DC to the grid-connected operation mode.

[0049] Optionally, the closing / disclosing module includes: The first DC off-grid control unit is used to control the first DC off-grid and switch the DC transmission system corresponding to the first DC to islanded operation mode when the system stability margin does not meet the preset requirements and there is only one first DC. The correlation degree determination unit is used to determine the correlation degree between each of the first DC and the system stability margin when the system stability margin does not meet the preset requirements and there are multiple first DCs. The target DC filtering unit is used to filter out target DCs from each of the first DCs based on the correlation between each of the first DCs and the stability margin of the system, as well as the adjustment attributes of the matching power supply corresponding to each of the first DCs. The target DC off-grid control unit is used to control the target DC to go off-grid when there is only one target DC, and to switch the DC transmission system corresponding to the target DC to islanded operation mode.

[0050] Optionally, the target DC screening unit includes: The first sorting unit is used to sort the stability impact contribution of each first DC based on the correlation degree between each first DC and the stability margin of the system, and obtain the first sorting result. The second sorting unit is used to sort the regulation capabilities of each first DC power supply based on the regulation attributes of the corresponding power supply of each first DC power supply, and obtain a second sorting result. The sorting comparison unit is used to select the target DC from each of the first DCs based on the comparison result of the first sorting result and the second sorting result.

[0051] Optionally, the closing / disclosing module further includes: A power demand acquisition unit is used to acquire the power demand of the receiving-end power grid; the receiving-end power grid is asynchronously connected to the sending-end power grid; The simulation update unit is used to simulate and update the system stability margin of the sending-end power grid and the operating status of the sending-end main grid after each of the target DCs is disconnected from the grid when there are multiple target DCs. Off-grid DC screening unit is used to screen off-grid DC from each of the target DC; the system stability margin updated after the off-grid DC is disconnected from the grid meets the preset requirements, and the operating status of the main grid at the sending end meets the power receiving requirements. Off-grid DC control unit is used to control the off-grid DC to switch the DC transmission system corresponding to the off-grid DC to islanded operation mode.

[0052] Optionally, the disengagement / engagement module includes: The influence degree determination unit is used to determine the influence degree of each island corresponding to the second DC on the system stability margin when the system stability margin meets the preset requirements and there are multiple second DCs. A networked DC filtering unit is used to filter out networked DCs from each of the second DCs based on the degree of influence of each of the second DCs and the adjustment attributes of the power supply corresponding to each of the second DCs; The networked DC control unit is used to switch the DC transmission system corresponding to the networked DC to network operation mode.

[0053] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method of controlling a disengageable and engageable direct current operation mode, characterized by, include: Based on the operating data of the sending-end power grid, the system stability margin of the sending-end power grid is determined; the sending-end power grid includes the sending-end main grid and multiple DC transmission systems; each DC transmission system includes multiple supporting power sources and a DC main body; each DC main body is connected to the sending-end main grid; Based on the exchange power between each DC body and the sending-end main grid, determine the first DC body in the off-grid ready state among each DC body; Based on the system stability margin and the regulation properties of the supporting power supply, the first DC power is controlled to be disconnected from the grid, and the DC transmission system corresponding to the first DC power is switched to islanded operation mode. Based on the system stability margin and the regulation attributes of the supporting power supply, the second DC power transmission system, which is in the grid-ready state, is controlled to switch to grid-connected operation mode.

2. The convertible DC operation mode control method of claim 1, wherein, The step of controlling the first DC power transmission system to switch to islanded operation mode based on the system stability margin and the regulation attributes of the supporting power supply includes: If the system stability margin does not meet the preset requirements and there is only one first DC, the first DC is controlled to disconnect from the grid, and the DC transmission system corresponding to the first DC is switched to islanded operation mode. When the system stability margin does not meet the preset requirements and there are multiple first DCs, determine the correlation degree between each first DC and the system stability margin; Based on the correlation between each of the first DC and the stability margin of the system, and the regulation attributes of the power supply corresponding to each of the first DC, a target DC is selected from each of the first DCs; If only one target DC exists, the target DC is controlled to be disconnected from the grid, and the DC transmission system corresponding to the target DC is switched to islanded operation mode.

3. The convertible DC operating mode control method of claim 2, wherein, The selection of target DC from the first DC based on the correlation between each first DC and the system stability margin, and the regulation attributes of the corresponding power supply for each first DC, includes: Based on the correlation between each of the first DC and the stability margin of the system, the stability impact contribution of each of the first DC is ranked to obtain a first ranking result; Based on the regulation attributes of the matching power supply corresponding to each first DC, the regulation capabilities of each first DC are sorted to obtain a second sorting result. Based on the comparison between the first sorting result and the second sorting result, the target DC is selected from each of the first DCs.

4. The method of claim 2, wherein the DC operation mode control method is characterized by, The step of selecting a target DC from the first DCs based on the correlation between each first DC and the system stability margin, and the adjustment attributes of the corresponding power supply for each first DC, includes: Obtain the power demand of the receiving-end power grid; the receiving-end power grid is asynchronously connected to the sending-end power grid; When there are multiple target DCs, the system stability margin of the sending-end power grid and the operating status of the sending-end main grid are simulated and updated after each target DC is disconnected from the grid. Off-grid DC is selected from the target DC; the system stability margin updated after the off-grid DC is disconnected from the grid meets the preset requirements, and the operating status of the sending-end main grid updated meets the power receiving requirements; Control the off-grid DC to go off-grid, and switch the DC transmission system corresponding to the off-grid DC to islanded operation mode.

5. The convertible DC operating mode control method of claim 1, wherein, The step of controlling the grid connection of the second DC power transmission system, which is in a grid-ready state, based on the system stability margin and the regulation attributes of the supporting power supply, and switching the DC transmission system corresponding to the second DC power transmission system to grid-connected operation mode includes: When the system stability margin meets the preset requirements and there are multiple second DCs, determine the degree of influence of each island corresponding to the second DC on the system stability margin; Based on the degree of influence of each second DC and the regulation attributes of the power supply corresponding to each second DC, the networked DC is selected from each second DC; The DC transmission system corresponding to the aforementioned DC network will be switched to network operation mode.

6. A disengageable and engageable direct current operation mode control system characterized by comprising: include: The system stability margin determination module is used to determine the system stability margin of the sending-end power grid based on the operating data of the sending-end power grid; the sending-end power grid includes the sending-end main grid and multiple DC transmission systems; each DC transmission system includes multiple supporting power sources and a DC transmission body; each DC transmission body is connected to the sending-end main grid; The first DC determination module is used to determine the first DC in the off-grid ready state among the DC bodies based on the exchange power between each DC body and the sending-end main grid. The grid-connected module is used to control the first DC to disconnect from the grid and switch the DC transmission system corresponding to the first DC to islanded operation mode based on the system stability margin and the regulation attributes of the supporting power supply. The separation-to-connection module is used to control the second DC grid connection in the grid-ready state based on the system stability margin and the regulation attributes of the supporting power supply, and to switch the DC transmission system corresponding to the second DC to the grid-connected operation mode.

7. The convertible DC operating mode control system of claim 6, wherein, The merge-to-disconnect module includes: The first DC off-grid control unit is used to control the first DC off-grid and switch the DC transmission system corresponding to the first DC to islanded operation mode when the system stability margin does not meet the preset requirements and there is only one first DC. The correlation degree determination unit is used to determine the correlation degree between each of the first DC and the system stability margin when the system stability margin does not meet the preset requirements and there are multiple first DCs. The target DC filtering unit is used to filter out target DCs from each of the first DCs based on the correlation between each of the first DCs and the stability margin of the system, as well as the adjustment attributes of the matching power supply corresponding to each of the first DCs. The target DC off-grid control unit is used to control the target DC to go off-grid when there is only one target DC, and to switch the DC transmission system corresponding to the target DC to islanded operation mode.

8. The convertible DC operating mode control system of claim 7, wherein, The target DC screening unit includes: The first sorting unit is used to sort the stability impact contribution of each first DC based on the correlation degree between each first DC and the stability margin of the system, and obtain the first sorting result. The second sorting unit is used to sort the regulation capabilities of each first DC power supply based on the regulation attributes of the corresponding power supply of each first DC power supply, and obtain a second sorting result. The sorting comparison unit is used to select the target DC from each of the first DCs based on the comparison result of the first sorting result and the second sorting result.

9. The convertible DC operating mode control system of claim 7, wherein, The closing / disclosing module also includes: A power demand acquisition unit is used to acquire the power demand of the receiving-end power grid; the receiving-end power grid is asynchronously connected to the sending-end power grid; The simulation update unit is used to simulate and update the system stability margin of the sending-end power grid and the operating status of the sending-end main grid after each of the target DCs is disconnected from the grid when there are multiple target DCs. Off-grid DC screening unit is used to screen off-grid DC from each of the target DC; the system stability margin updated after the off-grid DC is disconnected from the grid meets the preset requirements, and the operating status of the main grid at the sending end meets the power receiving requirements. Off-grid DC control unit is used to control the off-grid DC to switch the DC transmission system corresponding to the off-grid DC to islanded operation mode.

10. The convertible DC operating mode control system of claim 6, wherein, The clutch / engagement module includes: The influence degree determination unit is used to determine the influence degree of each island corresponding to the second DC on the system stability margin when the system stability margin meets the preset requirements and there are multiple second DCs. A networked DC filtering unit is used to filter out networked DCs from each of the second DCs based on the degree of influence of each of the second DCs and the adjustment attributes of the power supply corresponding to each of the second DCs; The networked DC control unit is used to switch the DC transmission system corresponding to the networked DC to network operation mode.

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