Method, system, device and medium for operating control of flexible direct current power transmission system

Abstract

The application discloses a kind of flexible direct current transmission system operation control method, system, equipment and medium, belong to power system control technical field, the method is: when the operation state of the district power grid is off-grid state, disconnect the electrical connection between the first station and the second station in the district power grid, obtain all the first subnetwork corresponding to the first station;The short-circuit capacity of the first subnetwork and the operation capacity of the flexible direct current transmission system are calculated to obtain a ratio;When the ratio is greater than the threshold value, control the flexible direct current transmission system to operate according to the voltage signal and the frequency signal of the main network;Otherwise, control the flexible direct current transmission system to operate according to the preset voltage and the preset frequency, until it is restored to the networking state, control the flexible direct current transmission system to operate according to the voltage signal and the frequency signal, therefore, by implementing the present application, the power supply reliability of important load and system operation stability can be improved.

Description

Technical Field

[0001] This invention relates to the field of power system control technology, and in particular to an operation control method, system, equipment and medium for a flexible DC transmission system. Background Technology

[0002] With the continuous growth of urban load, interconnecting regional power grids with the main grid through flexible DC transmission systems has become an important way to improve power supply capacity. In actual operation, regional power grids may be disconnected from the main grid due to faults or dispatching needs, and the operation and control mode of the flexible DC transmission system directly affects the voltage and frequency stability of the regional power grid.

[0003] Currently, a common operation and control method for flexible DC transmission systems is that when the regional power grid is disconnected from the main grid, the flexible DC transmission system adopts a constant AC voltage and constant frequency control mode, using preset voltage amplitude and frequency values ​​as control targets. It does not rely on the synchronization signal of the main grid and independently provides voltage and frequency to the regional power grid until the regional power grid is reconnected to the main grid.

[0004] However, in the event of a power grid failure in a region, to ensure the stable operation of critical load areas such as hospitals, these areas are typically isolated from other areas, forming an independently operating subgrid. In this isolated scenario, the flexible DC transmission system and the subgrid's internal power supply operate simultaneously as voltage sources, which can easily lead to control system instability issues such as control conflicts and power oscillations, resulting in poor control performance. Summary of the Invention

[0005] This invention provides an operation control method, system, equipment, and medium for a flexible DC transmission system, which can solve the problem of how to avoid control conflicts and power oscillations caused by the flexible DC transmission system and the power sources inside the subgrid operating simultaneously as voltage sources after the important load area is isolated, and achieve coordinated and stable control.

[0006] This invention provides an operation control method for a flexible DC transmission system, comprising: The power grid operation status of the area is obtained, wherein the power grid operation status includes outage operation status and network connection operation status; When the power grid is in the outage operation state, the electrical connection between the first station and the second station in the area power grid is disconnected to obtain the first sub-network corresponding to all the first stations. The first station is the station with the target load, and the second station is the other station in the area power grid besides the first station. Obtain the short-circuit capacity of the first subnet and the operating capacity of the flexible DC transmission system used to connect the regional power grid and the main grid, and calculate the ratio between the short-circuit capacity and the operating capacity; When the ratio is greater than a preset threshold, the flexible DC transmission system is controlled to operate according to the voltage and frequency signals of the main grid; when the ratio is less than or equal to the preset threshold, the flexible DC transmission system is controlled to operate according to a preset voltage and a preset frequency until the grid operation state is restored to the interconnected operation state, at which point the flexible DC transmission system is controlled to operate according to the voltage and frequency signals.

[0007] This invention establishes an intelligent operation control system for flexible DC transmission systems through a complete process of grid status perception, active disconnection control, subgrid strength assessment, and dual-mode adaptive switching. It achieves accurate assessment of subgrid capabilities and dynamic optimization selection of flexible DC control modes under grid outage scenarios, significantly improving the voltage and frequency stability, power supply reliability, and fault recovery capability of the regional power grid in islanded operation, and ensuring continuous and safe power supply to critical loads.

[0008] Furthermore, prior to disconnecting the electrical connection between the first and second stations in the regional power grid, the method further includes: Obtain load and power data for each station within the power grid area; Calculate the power balance index for each of the stations based on the load data and the power data, and determine the stations whose power balance index is greater than a preset balance threshold as candidate stations. The first site is obtained by identifying the site with the target load among the candidate sites.

[0009] This complete process, including site supply and demand data collection, balance index calculation, threshold screening, and critical load identification, establishes a site intelligent selection mechanism for proactive load shedding. It enables site capacity assessment based on real-time balance status and priority protection for critical loads, significantly improving the scientific nature, relevance, and reliability of power supply to important loads in the power grid shedding strategy.

[0010] Furthermore, the acquisition of the power grid operating status of the area specifically includes: Obtain the equipment operating status of the interconnection equipment between the regional power grid and the main grid, and obtain the first electrical quantity corresponding to the regional power grid and the second electrical quantity corresponding to the main grid; If the device is in an off state and the difference between the first electrical quantity and the second electrical quantity is greater than a preset deviation threshold, then the power grid is in an off-grid state; otherwise, it is in a network-connected state.

[0011] This complete process, which involves monitoring the status of interconnecting equipment, collecting electrical quantities from both sides, and fusing dual criteria, establishes a precise identification mechanism for the power grid's operating status. It enables a comprehensive judgment of the differences between physical connection status and electrical status, significantly improving the accuracy, reliability, and timeliness of detecting power outages and providing a reliable decision-making basis for the selection of subsequent control strategies.

[0012] Furthermore, the control of the flexible DC transmission system to operate according to a preset voltage and a preset frequency specifically includes: The flexible DC transmission system is controlled to output at the preset voltage and preset frequency as target values, and the actual voltage and actual frequency output by the flexible DC transmission system are obtained. If the actual voltage is not equal to the preset voltage, the reactive power of the flexible DC transmission system is adjusted according to the voltage difference between the actual voltage and the preset voltage so that the flexible DC transmission system operates according to the preset voltage. If the actual frequency is not equal to the preset frequency, the active power of the flexible DC transmission system is adjusted according to the frequency parameters between the actual frequency and the preset frequency, so that the flexible DC transmission system operates according to the preset frequency.

[0013] By establishing a complete process of target value setting, actual output feedback, voltage reactive closed-loop control, and frequency active closed-loop control, a refined voltage and frequency control mechanism for flexible DC transmission systems in grid-connected mode was established. This achieved high-precision matching between the output electrical quantities and the preset targets, significantly improving the stability, control accuracy, and power supply quality of the subgrid voltage and frequency under islanded grid operation.

[0014] Furthermore, adjusting the active power of the flexible DC transmission system based on the frequency parameters between the actual frequency and the preset frequency specifically involves: Obtain at least one frequency parameter from the following: the frequency deviation value between the actual frequency and the preset frequency, the frequency change rate of the actual frequency, and the frequency change acceleration of the actual frequency. The first active power adjustment amount is determined based on the frequency deviation value and the preset adjustment coefficient, wherein the first active power adjustment amount is used to realize the primary frequency regulation function. Alternatively, a second active power adjustment amount can be determined based on the frequency change rate and a preset virtual inertia coefficient, wherein the second active power adjustment amount is used to realize the inertia response function. Alternatively, a third active power adjustment amount may be determined based on the frequency change acceleration and a preset frequency acceleration control coefficient, wherein the third active power adjustment amount is used to implement the frequency change rate control function. The active power of the flexible DC transmission system is adjusted according to at least one of the first active power adjustment amount, the second active power adjustment amount, and the third active power adjustment amount.

[0015] By employing multi-functional collaboration of frequency multi-parameter sensing, primary frequency regulation, virtual inertia, and frequency change rate control, a comprehensive active frequency support system for flexible DC transmission systems has been established. This system enables all-round control of frequency steady-state deviation, dynamic changes, and trends, significantly improving the stability, anti-disturbance capability, and dynamic response performance of subgrid frequencies under islanded operation, thus giving flexible DC transmission systems frequency support capabilities similar to synchronous machines.

[0016] Furthermore, disconnecting the electrical connection between the first and second stations in the power grid area specifically involves: Obtain load forecast data and power supply forecast data for each station within the power grid area; Based on the load forecast data and the power supply forecast data, predict the power balance status of the regional power grid within a preset time period. When the power balance is unbalanced, disconnect the electrical connection between the first station and the second station.

[0017] This complete process of predictive data collection, balance state prediction, and preventive disconnection control establishes a proactive disconnection decision-making mechanism for future operating conditions, realizing a shift from a passive response to a proactive prevention control mode. It significantly improves the predictability, timeliness, and power supply reliability of power grid disconnection control, ensuring that effective safeguards are implemented before imbalances are predicted.

[0018] Furthermore, disconnecting the electrical connection between the first and second stations in the power grid area specifically involves: Determine the fault type corresponding to the network outage operation state, the fault type including main transformer fault and line fault; When the fault type is a main transformer fault, for each first station, disconnect the electrical connection between the first station and all second stations; When the fault type is a line fault, the faulty line corresponding to the line fault is determined, the second station connected to the faulty line is taken as the target station, and the electrical connection between the first station and the target station is disconnected.

[0019] By employing differentiated strategies such as fault type identification, comprehensive regional isolation of main transformer faults, and selective isolation of line faults, a refined regional isolation mechanism for different fault types has been established. This achieves precise matching between the fault impact range and the isolation range, significantly improving the pertinence, flexibility, and economy of power grid isolation control, and minimizing the power supply impact range caused by faults while ensuring power supply safety.

[0020] Another embodiment of the present invention provides an operation control system for a flexible DC transmission system, comprising: The module consists of an acquisition module, a network sub-module, a calculation module, and a control module. The acquisition module is used to acquire the power grid operation status of the area power grid, wherein the power grid operation status includes the out-of-grid operation status and the connected-grid operation status; The sub-network module is used to disconnect the electrical connection between the first station and the second station in the area power grid when the power grid is in the out-of-network operation state, so as to obtain the first sub-network corresponding to all the first stations. The first station is the station with the target load, and the second station is the other station in the area power grid except for the first station. The calculation module is used to obtain the short-circuit capacity of the first subgrid and the operating capacity of the flexible DC transmission system used to connect the regional power grid and the main grid, and to calculate the ratio between the short-circuit capacity and the operating capacity. The control module is used to control the flexible DC transmission system to operate according to the voltage and frequency signals of the main grid when the ratio is greater than a preset threshold; and to control the flexible DC transmission system to operate according to a preset voltage and preset frequency when the ratio is less than or equal to the preset threshold, until the grid operation state is restored to the interconnected operation state, and then control the flexible DC transmission system to operate according to the voltage and frequency signals.

[0021] Another embodiment of the present invention provides a terminal device, including: a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, it implements the steps of the operation control method of the flexible DC transmission system of the present invention.

[0022] Another embodiment of the present invention provides a computer-readable storage medium, comprising: a stored computer program, wherein when the computer program is executed, the device on which the computer-readable storage medium is located executes the steps of the operation control method of the flexible DC transmission system of the present invention. Attached Figure Description

[0023] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1This is a flowchart illustrating an operation control method for a flexible DC transmission system provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of a subnet splitting operation provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the operation and control system of a flexible DC transmission system provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Unless otherwise defined, 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; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0027] 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. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0028] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0029] 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: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0030] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0031] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0032] See Figure 1 To address the problem in existing technologies of how to avoid control conflicts and power oscillations caused by the simultaneous operation of flexible DC transmission systems and subgrid power sources as voltage sources after isolation of critical load areas, and to achieve coordinated and stable control, an embodiment of the present invention provides an operation control method for a flexible DC transmission system, comprising: Step S101: Obtain the power grid operation status of the area's power grid, wherein the power grid operation status includes disconnected operation status and connected operation status.

[0033] In this step, the operating status of the interconnecting transformers or interconnecting lines between the regional power grid and the main grid is monitored in real time by the safety control devices configured in the power grid. Specifically, the open / closed position of the interconnecting switch and the protection trip signal of the interconnecting switch are ORed, and the result of the OR logic is used to determine whether the regional power grid has entered a grid disconnection state.

[0034] As an example of an embodiment of the present invention, the acquisition of the power grid operation status of the regional power grid specifically includes: Obtain the equipment operating status of the interconnection equipment between the regional power grid and the main grid, and obtain the first electrical quantity corresponding to the regional power grid and the second electrical quantity corresponding to the main grid; If the device is in an off state and the difference between the first electrical quantity and the second electrical quantity is greater than a preset deviation threshold, then the power grid is in an off-grid state; otherwise, it is in a network-connected state.

[0035] The interconnection equipment includes a main transformer and interconnection lines. The main transformer is the largest and highest voltage transformer in the substation, used to convert electrical energy between different voltage levels. For example, when the main transformer connects the main grid (500kV) and the regional power grid (220kV), it is used to step down the voltage of the main grid before sending it to the regional power grid.

[0036] In this embodiment, the operating status of the interconnection equipment between the regional power grid and the main grid is monitored in real time by a safety and stability control device configured in the power grid. The interconnection equipment includes interconnection transformers or interconnection lines. When the switching position signal of the interconnection transformer is "open position" or the protection trip signal of the interconnection line is "triggered", the "OR logic" result is true, and the equipment operating status is determined to be disconnected; otherwise, the equipment operating status is determined to be closed. The safety and stability control device obtains the first electrical quantity (mainly voltage) on the regional power grid side and the second electrical quantity (mainly voltage) on the main grid side, and calculates the voltage difference between the first electrical quantity and the second electrical quantity. When the following two conditions are met simultaneously, the power grid operating status is determined to be disconnected: the equipment operating status is disconnected (i.e., the switching position signal is open position, or the protection trip signal has been triggered); the voltage difference between the first electrical quantity and the second electrical quantity is greater than a preset deviation threshold. The preset deviation threshold is preset according to the electrical quantity fluctuation range during normal power grid operation. The electrical quantity difference serves as an auxiliary anti-misjudgment criterion to prevent misjudgments caused by signal malfunctions. If any of the above conditions are not met, the power grid is determined to be in a grid-connected operation state.

[0037] Step S102: When the power grid is in the out-of-grid operation state, disconnect the electrical connection between the first station and the second station in the area power grid to obtain the first sub-network corresponding to all the first stations. The first station is the station with the target load, and the second station is the other station in the area power grid besides the first station.

[0038] In this step, if the regional power grid is disconnected from the main grid, it enters an isolated grid state. Considering the large load and limited local 220kV power supply within the urban isolated grid, and the presence of many critical loads, there is a significant power balance issue when passively entering the isolated grid. To ensure stable operation of the isolated grid, it is necessary to split the subgrid, disconnecting the electrical connection between the important load areas within the isolated grid and the 220kV subgrids of the regional power grid. Based on the operating status of the main transformer or connecting line between the regional power grid and the main grid detected in step 101, the safety and stability control device is activated to disconnect the connecting switches between the subgrid and other 220kV subgrids in the isolated grid. The subgrids involved are designed according to preset areas, mainly considering subgrids containing critical loads, and the critical areas are electrically isolated from other areas by disconnecting the line switches.

[0039] Step S103: Obtain the short-circuit capacity of the first subgrid and the operating capacity of the flexible DC transmission system used to connect the regional power grid and the main grid, and calculate the ratio between the short-circuit capacity and the operating capacity.

[0040] In this step, the short-circuit ratio of the islanded network short-circuit capacity and the flexible DC operation capacity is evaluated. The calculation formula is expressed as follows: ; Where SCR is the short-circuit ratio. For short-circuit capacity in an isolated network, This refers to the capacity for flexible DC operation.

[0041] Step S104: When the ratio is greater than a preset threshold, control the flexible DC transmission system to operate according to the voltage and frequency signals of the main grid; when the ratio is less than or equal to the preset threshold, control the flexible DC transmission system to operate according to a preset voltage and a preset frequency until the grid operation state is restored to the interconnected operation state, then control the flexible DC transmission system to operate according to the voltage and frequency signals.

[0042] In this embodiment, the calculated short-circuit ratio is compared with a preset threshold, preferably 2. If the short-circuit ratio is greater than the preset threshold, it indicates that the first subgrid provides strong support to the flexible DC transmission system. The flexible DC transmission system maintains a grid-following operation control mode, that is, it operates according to the voltage and frequency signals of the main grid, acting as a system fast frequency control unit to provide transient reactive power support. When the short-circuit ratio is not greater than the threshold, it indicates that the first subgrid provides insufficient support to the flexible DC transmission system. To ensure the operational stability of the flexible DC transmission system itself and to provide steady-state voltage support to the first subgrid, the control mode of the flexible DC transmission system is switched from the grid-following operation control mode to the grid-building operation control mode, that is, it operates according to a preset voltage and preset frequency, providing steady-state voltage support to the power grid system.

[0043] As an example of an embodiment of the present invention, before disconnecting the electrical connection between the first and second stations in the regional power grid, the method further includes: Obtain load and power data for each station within the power grid area; Calculate the power balance index for each of the stations based on the load data and the power data, and determine the stations whose power balance index is greater than a preset balance threshold as candidate stations. The first site is obtained by identifying the site with the target load among the candidate sites.

[0044] In this embodiment, load and power data of each station within the regional power grid are acquired in real time through a Supervisory Control and Data Acquisition (SCADA) system or an Energy Management System (EMS). Load data includes active load, reactive load, and load importance level for each station; power data includes the capacity of generator units connected to each station, the output of distributed power sources, and the capacity of energy storage devices. Based on the load and power data of each station, a power balance index is calculated for each station. The power balance index characterizes the station's internal power supply capacity to support the load. Specifically, it can be calculated as follows: the ratio of the total power supply capacity to the total load capacity within the station, i.e., power balance index = total power supply capacity / total load capacity; or, considering both power supply reliability and load importance, a weighted summation method can be used to calculate the power balance index. The calculated power balance index is compared with a preset balance threshold, which is pre-set according to power grid operation requirements (e.g., a value of 1 indicates that the power supply capacity and load capacity are basically balanced). Stations with a power balance index greater than the preset balance threshold are identified as candidate stations, indicating that these stations possess a certain self-balancing capability and are suitable as core stations of independently operating subnetworks. Within the candidate sites, further identification is needed to determine if target loads exist. Target loads refer to critical loads, including but not limited to hospitals, high-tech enterprises, government agencies, data centers, and other users with high power supply reliability requirements. This identification can be achieved through the following methods: querying load classification tags in the power grid dispatch system to identify users marked as "critical loads"; filtering loads based on their importance level, identifying loads with a preset importance level as target loads. If a target load exists among the candidate sites, that site is designated as the first site; if no target load exists among the candidate sites, a site with a higher power balance index can be selected as the first site based on actual needs, or the scope of candidate sites can be further expanded for further filtering. The first site identified through the above methods will be isolated to form the first subgrid during network outage operation, with the flexible DC transmission system providing voltage and frequency support to ensure stable power supply to critical loads.

[0045] As an example of an embodiment of the present invention, controlling the flexible DC transmission system to operate according to a preset voltage and a preset frequency specifically includes: The flexible DC transmission system is controlled to output at the preset voltage and preset frequency as target values, and the actual voltage and actual frequency output by the flexible DC transmission system are obtained. If the actual voltage is not equal to the preset voltage, the reactive power of the flexible DC transmission system is adjusted according to the voltage difference between the actual voltage and the preset voltage so that the flexible DC transmission system operates according to the preset voltage. If the actual frequency is not equal to the preset frequency, the active power of the flexible DC transmission system is adjusted according to the frequency parameters between the actual frequency and the preset frequency, so that the flexible DC transmission system operates according to the preset frequency.

[0046] In this embodiment, when the flexible DC transmission system switches to the grid-type operation control mode, the control system will preset the voltage U. ref (e.g., rated voltage 10kV) and preset frequency f ref Using a rated frequency of 50Hz as the control target, the flexible DC transmission system is modulated to ensure that the voltage and frequency of the regional power grid are constructed according to this target value. Simultaneously, voltage transformers and frequency measuring devices located on the AC side of the flexible DC transmission system are used to collect the actual voltage U output by the converter in real time. act and actual frequency f act The actual voltage U act With preset voltage U ref Compare the values, calculate the voltage difference, and express it as ΔU=U ref -U act .

[0047] If the voltage difference ΔU is not zero (i.e., the actual voltage is not equal to the preset voltage), the reactive power of the flexible DC transmission system is adjusted based on the voltage difference. Specifically, the voltage difference is input to the voltage controller (usually a proportional-integral (PI) controller), and the voltage controller outputs a reactive power adjustment amount ΔQ, which is calculated using the formula ΔQ=K. p_U ×ΔU+K i_U ×∫ΔUdt, where K p_U K is the proportional coefficient of the voltage controller. i_U This is the integral coefficient. The reactive power adjustment ΔQ is added to the reactive power command value Q. ref In the middle, the updated reactive power command value is Q. ref_new =Q ref +ΔQ. The converter of the flexible DC transmission system adjusts the trigger pulse of the converter valve according to the updated reactive power command value through the inner loop current control and modulation link, thereby changing the reactive power output and making the actual voltage approach the preset voltage.

[0048] The actual frequency f ref With preset frequency f ref Compare and calculate the frequency difference Δf=f ref -f refIf the frequency difference Δf is not zero (i.e., the actual frequency is not equal to the preset frequency), the active power of the flexible DC transmission system is adjusted according to the frequency parameters. The frequency parameters include at least one of the following: frequency deviation, frequency change rate, and frequency change acceleration. Specifically, the active power adjustment amount can be determined in the following ways: (1) Primary frequency modulation method: based on the frequency deviation value Δf and the preset droop coefficient K droop Calculate the active power regulation.

[0049] (2) Inertia response mode: based on the frequency change rate df / dt and the preset virtual inertia coefficient K inertia Calculate the active power regulation.

[0050] (3) Frequency change rate control method: based on the frequency change acceleration d²f / dt² and the preset frequency acceleration control coefficient K acc Calculate the active power regulation.

[0051] The above-mentioned one or more active power regulation quantities are superimposed to obtain the total active power regulation quantity, which is then added to the active power command value to obtain the updated active power command value. Based on the updated active power command value, the converter of the flexible DC transmission system adjusts the trigger pulse of the converter valve through inner loop current control and modulation, thereby changing the active power output and thus making the actual frequency approach the preset frequency.

[0052] As an example of an embodiment of the present invention, adjusting the active power of the flexible DC transmission system based on the frequency parameter between the actual frequency and the preset frequency specifically involves: Obtain at least one frequency parameter from the following: the frequency deviation value between the actual frequency and the preset frequency, the frequency change rate of the actual frequency, and the frequency change acceleration of the actual frequency. The first active power adjustment amount is determined based on the frequency deviation value and the preset adjustment coefficient, wherein the first active power adjustment amount is used to realize the primary frequency regulation function. Alternatively, a second active power adjustment amount can be determined based on the frequency change rate and a preset virtual inertia coefficient, wherein the second active power adjustment amount is used to realize the inertia response function. Alternatively, a third active power adjustment amount may be determined based on the frequency change acceleration and a preset frequency acceleration control coefficient, wherein the third active power adjustment amount is used to implement the frequency change rate control function. The active power of the flexible DC transmission system is adjusted according to at least one of the first active power adjustment amount, the second active power adjustment amount, and the third active power adjustment amount.

[0053] In this embodiment, the actual frequency of the system access point is detected in real time by the phase-locked loop (PLL) of the flexible DC transmission system. The actual frequency is compared with the preset frequency (rated frequency, such as 50Hz) to obtain at least one of the following frequency parameters: frequency deviation value Δf, i.e., the actual frequency f. actual With preset frequency f nominal The difference is expressed as Δf = f actual -f nominal The rate of change of frequency, df / dt, is calculated by differentiating the actual frequency and reflects the rate of frequency change over time; the acceleration of frequency change, d²f / dt², is calculated by differentiating the rate of change of frequency and reflects the speed of frequency change. Based on the obtained frequency parameters, the active power regulation is determined using at least one of the following methods: based on the frequency deviation value Δf and the preset droop coefficient K. droop Calculate the first active power regulation, expressed by the formula ΔP1 = -K. droop ×Δf, where the adjustment coefficient K droop The settings are pre-set based on unit capacity and grid requirements. The negative sign indicates that the active power adjustment direction is opposite to the frequency deviation direction; that is, active power output increases when the frequency decreases and decreases when the frequency increases. This is based on the frequency change rate df / dt and the preset virtual inertia coefficient K. inertia Calculate the second active power regulation, expressed by the formula ΔP2 = -K. inertia ×(df / dt), where the virtual inertia coefficient K inertia This is used to simulate the rotor inertia characteristics of a synchronous generator. The negative sign indicates that the direction of active power regulation is opposite to the direction of the frequency change rate; that is, when the frequency decreases, the active power output is increased to slow down the rate of frequency decrease. This is based on the frequency change acceleration d²f / dt² and the preset frequency acceleration control coefficient K. acc The third active power regulation is calculated using the formula ΔP3 = -K. acc ×(d²f / dt²), where K is the frequency acceleration control coefficient. acc This is used to achieve an anticipatory response to frequency change trends. The negative sign indicates that the direction of active power regulation is opposite to the direction of frequency change acceleration. The total active power regulation ΔP is obtained by superimposing at least one of the calculated first, second, and third active power regulation values. total The total active power regulation is added to the active power command value P of the flexible DC transmission system. ref In the middle, it is represented as P ref =P0+ΔP total Where P0 is the active power command value during steady-state operation. Based on the updated active power command value, the converter of the flexible DC transmission system adjusts the trigger pulses of the converter valves through inner-loop current control and modulation, thereby achieving rapid regulation of active power.

[0054] As an example of an embodiment of the present invention, disconnecting the electrical connection between the first station and the second station in the regional power grid specifically means: Obtain load forecast data and power supply forecast data for each station within the power grid area; Based on the load forecast data and the power supply forecast data, predict the power balance status of the regional power grid within a preset time period. When the power balance is unbalanced, disconnect the electrical connection between the first station and the second station.

[0055] In this embodiment, load forecasting data and power generation forecasting data for each station within the regional power grid are acquired through a power grid dispatch automation system (SCADA system) or an energy management system (EMS). Specifically: Load forecasting data can be obtained by using time series analysis, neural network forecasting, and other methods based on historical load data, meteorological data, and date type (weekday, holiday, etc.) to predict the active and reactive load trends of each station within a preset time period (e.g., the next 24 hours, the next 1 hour, etc.). Power generation forecasting data is obtained by acquiring the planned output of generator units connected to each station, the predicted output of new energy sources (wind power, photovoltaic), and the charging and discharging plans of energy storage devices. For new energy sources, output forecasting can be combined with meteorological forecasting data (wind speed, solar intensity); for conventional sources, their output arrangements are obtained according to the dispatching plan.

[0056] Based on the acquired load and power forecast data, the power balance index for each station within a preset time period is calculated. The calculated power balance index is compared with a preset balance threshold (e.g., 1.0): if the power balance index ≥ the preset balance threshold, the predicted power balance is balanced, indicating that the power output within the station can meet the load demand; if the power balance index < the preset balance threshold, the predicted power balance is unbalanced, indicating that the power output within the station is insufficient to meet the load demand. When the predicted power balance is unbalanced, it indicates that maintaining the electrical connection between the first and second stations within the preset time period may result in the power supply within the first station being unable to support the total load of the first and second stations, thus affecting the stable power supply to critical loads. In this case, the safety and stability control device or the station protection control device performs a disconnection operation, disconnecting the interconnection switch between the first and second stations, electrically isolating the first station from other areas, forming an independently operating first sub-network. After disconnecting the electrical connection, the first sub-network only includes the first station with critical loads, and the flexible DC transmission system provides voltage and frequency support to ensure the stable power supply to critical loads. Meanwhile, the second station and other areas can adopt other operating modes (such as load reduction, activation of backup power, etc.) to maintain operation and avoid large-scale power outages caused by power imbalance. If the predicted power balance is balanced, the electrical connection between the first and second stations can be maintained according to the actual situation, or disconnected according to other operating conditions.

[0057] As an example of an embodiment of the present invention, disconnecting the electrical connection between the first station and the second station in the regional power grid specifically means: Determine the fault type corresponding to the network outage operation state, the fault type including main transformer fault and line fault; When the fault type is a main transformer fault, for each first station, disconnect the electrical connection between the first station and all second stations; When the fault type is a line fault, the faulty line corresponding to the line fault is determined, the second station connected to the faulty line is taken as the target station, and the electrical connection between the first station and the target station is disconnected.

[0058] Among them, a main transformer fault is defined as a situation where the main transformer connecting the regional power grid and the main grid trips due to protection, both switches on both sides of the main transformer are in the open position, and the electrical quantities (voltage and current) of the main transformer disappear. A line fault is defined as a situation where the connecting line between the regional power grid and the main grid trips due to protection, both switches on both sides of the line are in the open position, and the electrical quantities (voltage and current) of the line disappear.

[0059] In this embodiment, a safety and stability control device configured in the power grid monitors the operating status of the interconnection equipment between the regional power grid and the main grid in real time. When a regional power grid is detected to be in a state of network outage, the cause of the outage is further analyzed to determine the fault type. When the fault type is a main transformer fault, it indicates that the connection between the regional power grid and the main grid is completely disconnected, and the main transformer fault usually has a large impact range, which may cause multiple stations to lose the main grid power supply support. At this time, in order to ensure the stable operation of the important load area, it is necessary to isolate the first station with important loads from all second stations. Specifically, the safety and stability control device obtains a pre-determined list of first stations (stations with important loads such as hospitals and high-tech enterprises); for each first station, it identifies the interconnection lines and their corresponding interconnection switches between the first station and each second station; the safety and stability control device issues a trip command to disconnect the interconnection switches between the first station and all second stations, completely isolating the first station and the second station electrically; after isolation, each first station forms an independent first sub-network, which is provided with voltage and frequency support by the flexible DC transmission system alone.

[0060] When the fault type is a line fault, it indicates that the connection between the regional power grid and the main grid is only broken through a specific line, and the impact range is relatively small. In this case, it is only necessary to disconnect the electrical connection between the first and second stations related to the faulty line. Specifically, the safety and stability control device determines the faulty line based on protection action information and switch change information; analyzes the topological connection relationship of the faulty line to determine the second station directly connected to the faulty line, which is taken as the target station; identifies the first station that has an electrical connection with the target station; the safety and stability control device issues a trip command to disconnect the interconnection switch between the first station and the target station, isolating only the affected part; after isolation, other first stations unrelated to the faulty line can continue to maintain their connection with the corresponding second station, or decide whether further isolation is needed based on the actual situation.

[0061] by Figure 2 For example, the specific application process of the operation control method provided by this invention is as follows: First, detect the operating status of the tie switches QF1-1 and QF1-2 between the regional power grid and the main grid to determine whether the regional power grid has passively entered an isolated state; when the regional power grid has entered an isolated state, the safety and stability control device operates to disconnect the tie switches QF2-1 and QF2-2 between the first sub-grid (including important load areas) within the isolated grid and other 220kV substations of regional power grid A. Figure 3The gray dashed line in the diagram represents the split subgrid cutting line, used to electrically isolate important load areas from other areas; the frequency control of the isolated grid is achieved through the flexible DC transmission system, and the main transformer and lines of the faulty grid in the area are restored by emergency repair, or the isolated grid is restored to synchronous operation with the main grid by synchronizing with the grid outside the area through the 220kV line. After the isolated grid is connected to the grid, the control mode of the flexible DC transmission system is switched to the grid-following operation control mode.

[0062] like Figure 3 As shown, based on the above-mentioned method embodiments, an embodiment of the present invention provides an operation control system 300 for a flexible DC transmission system, including: an acquisition module 301, a sub-network module 302, a calculation module 303, and a control module 304; The acquisition module 301 is used to acquire the power grid operation status of the area power grid, wherein the power grid operation status includes a disconnection operation status and a connection operation status. The sub-network module 302 is used to disconnect the electrical connection between the first station and the second station in the area power grid when the power grid is in the out-of-network operation state, and obtain the first sub-network corresponding to all the first stations, wherein the first station is the station with the target load, and the second station is the other station in the area power grid besides the first station. The calculation module 303 is used to obtain the short-circuit capacity of the first sub-network and the operating capacity of the flexible DC transmission system for connecting the regional power grid and the main grid, and to calculate the ratio between the short-circuit capacity and the operating capacity. The control module 304 is used to control the flexible DC transmission system to operate according to the voltage and frequency signals of the main grid when the ratio is greater than a preset threshold; and to control the flexible DC transmission system to operate according to a preset voltage and preset frequency when the ratio is less than or equal to the preset threshold, until the grid operation state is restored to the network operation state, and then control the flexible DC transmission system to operate according to the voltage and frequency signals.

[0063] It is understood that the above system embodiments correspond to the method embodiments of the present invention, and can implement the operation control method of the flexible DC transmission system provided by any of the above method embodiments of the present invention.

[0064] It should be noted that the system embodiments described above are merely illustrative, and some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the system embodiments provided by this invention, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.

[0065] For ease of description and brevity, the system embodiments of the present invention include all the implementation methods described in the above embodiments of the operation control method for flexible DC transmission systems, and will not be repeated here.

[0066] Based on the above embodiments of the operation control method for flexible DC transmission systems, another embodiment of the present invention provides a terminal device, which includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the operation control method for flexible DC transmission systems according to any embodiment of the present invention.

[0067] For example, in this embodiment, the computer program can be divided into one or more modules, which are stored in the memory and executed by the processor to complete the present invention. The one or more modules may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in the terminal device.

[0068] The terminal device may be a desktop computer, laptop, handheld computer, or cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0069] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor. The processor is the control center of the terminal device, connecting all parts of the terminal device via various interfaces and lines.

[0070] Based on the above-described method embodiments, another embodiment of the present invention provides a computer-readable storage medium including a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to execute the operation control method of the flexible DC transmission system described in any of the above-described method embodiments of the present invention.

[0071] Based on the above-described method embodiments, this invention also provides a computer program / program product, which is stored in a storage medium and executed by at least one processor to implement the various processes of any of the above-described method embodiments, and can achieve the same technical effect. To avoid repetition, it will not be described again here.

[0072] The modules / units integrated in the device / terminal equipment, if implemented as software functional units and sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0073] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method of operating control of a flexible direct current power transmission system, characterized by, include: The power grid operation status of the area is obtained, wherein the power grid operation status includes outage operation status and network connection operation status; When the power grid is in the outage operation state, the electrical connection between the first station and the second station in the area power grid is disconnected to obtain the first sub-network corresponding to all the first stations. The first station is the station with the target load, and the second station is the other station in the area power grid besides the first station. Obtain the short-circuit capacity of the first subnet and the operating capacity of the flexible DC transmission system used to connect the regional power grid and the main grid, and calculate the ratio between the short-circuit capacity and the operating capacity; When the ratio is greater than a preset threshold, the flexible DC transmission system is controlled to operate according to the voltage and frequency signals of the main grid; when the ratio is less than or equal to the preset threshold, the flexible DC transmission system is controlled to operate according to a preset voltage and a preset frequency until the grid operation state is restored to the interconnected operation state, at which point the flexible DC transmission system is controlled to operate according to the voltage and frequency signals.

2. The operation control method of a flexible direct-current power transmission system according to Claim 1, characterized by, Before disconnecting the electrical connection between the first and second stations in the power grid area, the method further includes: Obtain load and power data for each station within the power grid area; Calculate the power balance index for each of the stations based on the load data and the power data, and determine the stations whose power balance index is greater than a preset balance threshold as candidate stations. The first site is obtained by identifying the site with the target load among the candidate sites.

3. The operation control method of a flexible DC power transmission system according to Claim 1, wherein The acquisition of the power grid operation status of the area specifically involves: Obtain the equipment operating status of the interconnection equipment between the regional power grid and the main grid, and obtain the first electrical quantity corresponding to the regional power grid and the second electrical quantity corresponding to the main grid; If the device is in an off state and the difference between the first electrical quantity and the second electrical quantity is greater than a preset deviation threshold, then the power grid is in an off-grid state; otherwise, it is in a network-connected state.

4. The operation control method of a flexible direct-current power transmission system according to Claim 1, characterized by, The control of the flexible DC transmission system to operate according to a preset voltage and a preset frequency specifically includes: The flexible DC transmission system is controlled to output at the preset voltage and preset frequency as target values, and the actual voltage and actual frequency output by the flexible DC transmission system are obtained. If the actual voltage is not equal to the preset voltage, the reactive power of the flexible DC transmission system is adjusted according to the voltage difference between the actual voltage and the preset voltage so that the flexible DC transmission system operates according to the preset voltage. If the actual frequency is not equal to the preset frequency, the active power of the flexible DC transmission system is adjusted according to the frequency parameters between the actual frequency and the preset frequency, so that the flexible DC transmission system operates according to the preset frequency.

5. The operation control method of a flexible direct-current power transmission system according to Claim 4, characterized by, The adjustment of the active power of the flexible DC transmission system based on the frequency parameter between the actual frequency and the preset frequency specifically involves: Acquire at least one frequency parameter among the frequency deviation value between the actual frequency and the preset frequency, the frequency change rate of the actual frequency, and the frequency change acceleration of the actual frequency; The first active power adjustment amount is determined based on the frequency deviation value and the preset adjustment coefficient, wherein the first active power adjustment amount is used to realize the primary frequency regulation function. Alternatively, a second active power adjustment amount can be determined based on the frequency change rate and a preset virtual inertia coefficient, wherein the second active power adjustment amount is used to realize the inertia response function. Alternatively, a third active power adjustment amount may be determined based on the frequency change acceleration and a preset frequency acceleration control coefficient, wherein the third active power adjustment amount is used to implement the frequency change rate control function. The active power of the flexible DC transmission system is adjusted according to at least one of the first active power adjustment amount, the second active power adjustment amount, and the third active power adjustment amount.

6. The operation control method of a flexible direct-current power transmission system according to Claim 1, wherein The disconnection of the electrical connection between the first and second stations in the power grid area specifically includes: Obtain load forecast data and power supply forecast data for each station within the power grid area; Based on the load forecast data and the power supply forecast data, predict the power balance status of the regional power grid within a preset time period. When the power balance is unbalanced, disconnect the electrical connection between the first station and the second station.

7. The operation control method of a flexible direct-current power transmission system according to Claim 1, wherein The disconnection of the electrical connection between the first and second stations in the power grid area specifically includes: Determine the fault type corresponding to the network outage operation state, the fault type including main transformer fault and line fault; When the fault type is a main transformer fault, for each first station, disconnect the electrical connection between the first station and all second stations; When the fault type is a line fault, the faulty line corresponding to the line fault is determined, the second station connected to the faulty line is taken as the target station, and the electrical connection between the first station and the target station is disconnected.

8. An operating control system for a flexible DC power transmission system, characterized in that include: The module consists of an acquisition module, a network sub-module, a calculation module, and a control module. The acquisition module is used to acquire the power grid operation status of the area power grid, wherein the power grid operation status includes the out-of-grid operation status and the connected-grid operation status; The sub-network module is used to disconnect the electrical connection between the first station and the second station in the area power grid when the power grid is in the out-of-network operation state, so as to obtain the first sub-network corresponding to all the first stations. The first station is the station with the target load, and the second station is the other station in the area power grid except for the first station. The calculation module is used to obtain the short-circuit capacity of the first subgrid and the operating capacity of the flexible DC transmission system used to connect the regional power grid and the main grid, and to calculate the ratio between the short-circuit capacity and the operating capacity. The control module is used to control the flexible DC transmission system to operate according to the voltage and frequency signals of the main grid when the ratio is greater than a preset threshold; and to control the flexible DC transmission system to operate according to a preset voltage and preset frequency when the ratio is less than or equal to the preset threshold, until the grid operation state is restored to the interconnected operation state, and then control the flexible DC transmission system to operate according to the voltage and frequency signals.

9. A terminal device, comprising: The system includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, it implements the operation control method for the flexible DC transmission system as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, include: A stored computer program, wherein, when the computer program is executed, it controls the device containing the computer-readable storage medium to perform the operation control method for the flexible DC transmission system as described in any one of claims 1-7.

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