A control method and system for a multi - flexible DC feeding power grid

Abstract

The present invention relates to the technical field of power system transient stability, and discloses a control method and system for a multi-flexible DC fed power grid. The control strategy constructed by the present invention can perform coordinated control when the multi-level converter is in the low voltage ride-through mode due to an AC short-circuit fault, and effectively improve the transient power angle stability of the multi-machine system; it solves the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible DC fed power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of power system transient stability, and particularly to a control method and system for a multi - flexible DC fed power grid. Background Art

[0002] With the low - carbon transformation of global energy, new energy represented by wind power and photovoltaic power has been vigorously developed. Modular multilevel converter based high - voltage direct current (MMC - HVDC) has the characteristics of strong controllability, fast response speed, and decoupled active and reactive power output. Its application in scenarios such as far - sea wind power and long - distance power transmission from large - scale new energy bases is becoming increasingly common, and a pattern of multi - flexible DC feeding into the load center is gradually formed.

[0003] In a multi - flexible DC fed power grid, due to different distributions of flexible DC, their impacts on system stability are also different. How to coordinately control the multi - flexible DC fed power grid to improve the stability of the multi - machine system in the multi - flexible DC fed power grid is a problem worthy of discussion. Therefore, there is an urgent need for a control scheme for the multi - flexible DC fed power grid to solve the problems existing in the prior art. Summary of the Invention

[0004] The present invention provides a control method and system for a multi - flexible DC fed power grid, which solves the technical problem of how to improve the transient power - angle stability of the multi - machine system in the multi - flexible DC fed power grid.

[0005] A control method for a multi - flexible DC fed power grid provided in the first aspect of the present invention includes:

[0006] Responding to a control request instruction for the multi - flexible DC fed power grid, and obtaining the grid operation data of the multi - flexible DC fed power grid;

[0007] Constructing a numerical simulation model of the multi - flexible DC fed power grid, and performing a short - circuit fault simulation on the numerical simulation model to obtain active power data;

[0008] Constructing the motion equation of the multi - flexible DC fed power grid, and using the active power data and the grid operation data to solve, so as to obtain the critical penetration rate of each multi - level converter in the multi - flexible DC;

[0009] When a short - circuit fault occurs in the multi - flexible DC fed power grid, the control strategies of each multi - level converter are matched in a strategy library by using the critical penetration rate and the grid operation data, where the control strategy is used to perform active current control on the multi - level converter;

[0010] Send the control strategies of the matched multi-level converters to each of the multi-level converters for execution.

[0011] Optionally, building a numerical simulation model of the multi-flexible DC-fed power grid, and performing a short-circuit fault simulation on the numerical simulation model to obtain active power data, including:

[0012] Build a numerical simulation model of the multi-flexible DC-fed power grid;

[0013] Select a control section of the numerical simulation model;

[0014] Input operating control parameters for simulating an AC short-circuit fault at the control section of the numerical simulation model, and perform a time-domain simulation on the numerical simulation model to output the active power data of the multi-level converter;

[0015] Wherein, the control section includes a transmission channel between the sending end and the receiving end formed by the connecting lines of the preset electrical intervals in the multi-flexible DC-fed power grid.

[0016] Optionally, the control strategy is any one of the following three control strategies;

[0017] A1. Adopt a constant active power control mode and keep the absolute value of the first active current less than the active current threshold; the constant active power control mode is that the synchronous generator in the multi-flexible DC-fed power grid outputs a constant active power;

[0018] The first active current is the operating active current of the multi-flexible DC-fed power grid in the constant active power control mode;

[0019] A2. Control the multi-level converter with a second active current, where the second active current is the ratio of the first active current to a preset current coefficient;

[0020] A3. Control the multi-level converter with a preset third active current.

[0021] Optionally, the matching of the control strategies of each multi-level converter by using the critical penetration rate and the grid operation data in the strategy library includes:

[0022] When the critical penetration rate and the grid operation data of the multi-level converter at the sending end meet the preset first regulation condition, then match the control strategy A3 as the control strategy of the multi-level converter;

[0023] When the critical penetration rate and the grid operation data of the multi-level converter at the receiving end meet the preset first regulation condition, then match the control strategy A1 as the control strategy of the multi-level converter;

[0024] When the critical penetration rate of the multi-level converter at the sending end and the grid operation data satisfy the preset second regulation condition, the matching control strategy A2 is used as the control strategy of the multi-level converter;

[0025] When the critical penetration rate of the multi-level converter at the receiving end and the grid operation data satisfy the preset second regulation condition, the matching control strategy A2 is used as the control strategy of the multi-level converter.

[0026] Optionally, the grid operation data includes the converter penetration rate;

[0027] The specific preset first regulation condition is that the critical penetration rate is greater than a preset first threshold, or the critical penetration rate is less than the preset first threshold and the converter penetration rate is greater than a preset second threshold and the converter penetration rate is less than the critical penetration rate;

[0028] The specific preset second regulation condition is that the critical penetration rate is less than the preset first threshold, and the converter penetration rate is greater than the critical penetration rate and the converter penetration rate is less than the preset first threshold.

[0029] A control system for a multi-flexible DC feeding grid provided in the second aspect of the present invention includes:

[0030] A response module, configured to respond to a control request command for a multi-flexible DC feeding grid and obtain the grid operation data of the multi-flexible DC feeding grid;

[0031] A simulation module, configured to construct a numerical simulation model of the multi-flexible DC feeding grid and perform a short-circuit fault simulation on the numerical simulation model to obtain active power data;

[0032] A solution module, configured to construct a motion equation of the multi-flexible DC feeding grid and use the active power data and the grid operation data for solution to obtain the critical penetration rates of the multi-level converters in the multi-flexible DC;

[0033] A strategy module, configured to, when a short-circuit fault occurs in the multi-flexible DC feeding grid, match the control strategies of the multi-level converters from a strategy library by using the critical penetration rates and the grid operation data, where the control strategies are used to perform active current control on the multi-level converters;

[0034] A control module, configured to send the matched control strategies of the multi-level converters to each of the multi-level converters for execution.

[0035] Optionally, the simulation module includes:

[0036] A model construction sub-module for constructing a numerical simulation model of the multi-flexible DC-fed power grid;

[0037] A section selection sub-module for selecting a control section of the numerical simulation model;

[0038] A time-domain simulation sub-module for inputting operating control parameters for simulating an AC short-circuit fault on the control section of the numerical simulation model, performing a time-domain simulation on the numerical simulation model, and outputting the active power data of the multi-level converter;

[0039] Wherein, the control section includes a power transmission channel between the sending end and the receiving end formed by the connecting lines in a preset electrical interval within the multi-flexible DC-fed power grid.

[0040] An electronic device provided in the third aspect of the present invention includes a memory and a processor. When a computer program stored in the memory is executed by the processor, the processor executes the steps of the control method of the multi-flexible DC-fed power grid as described in any one of the above.

[0041] A computer-readable storage medium provided in the fourth aspect of the present invention has a computer program stored thereon. When the computer program is executed, it implements the control method of the multi-flexible DC-fed power grid as described in any one of the above.

[0042] A computer program product provided in the fifth aspect of the present invention includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer executes the control method of the multi-flexible DC-fed power grid as described in any one of the above.

[0043] It can be seen from the above technical solutions that the present invention has the following advantages:

[0044] The present invention provides a control method and system for a multi-flexible DC-fed power grid, including responding to a control request instruction for the multi-flexible DC-fed power grid, obtaining the grid operation data of the multi-flexible DC-fed power grid; constructing a numerical simulation model of the multi-flexible DC-fed power grid, performing a short-circuit fault simulation on the numerical simulation model, and obtaining active power data; constructing a motion equation of the multi-flexible DC-fed power grid, and using the active power data and the grid operation data to solve, obtaining the critical penetration rate of each multi-level converter in the multi-flexible DC; when a short-circuit fault occurs in the multi-flexible DC-fed power grid, the control strategies of each multi-level converter are matched in the strategy library by using the critical penetration rate and the grid operation data, wherein the control strategy is used to perform active current control on the multi-level converter; the matched control strategies of each multi-level converter are sent to each multi-level converter for execution.

[0045] The control strategy constructed by the present invention can perform coordinated control when the multi-level converter is in the low-voltage ride-through mode due to an AC short-circuit fault, and effectively improve the transient power angle stability of the multi-machine system; it solves the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible DC-fed power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 It is a flowchart of the steps of a control method for a multi-flexible DC-fed power grid provided in Embodiment 1 of the present invention;

[0048] Figure 2 It is a flowchart of the steps of a control method for a multi-flexible DC-fed power grid provided in Embodiment 2 of the present invention;

[0049] Figure 3 It is a two-machine group and two-region system diagram of a multi-flexible DC-fed power grid provided in Embodiment 2 of the present invention;

[0050] Figure 4 It is a structural block diagram of a control system for a multi-flexible DC-fed power grid provided in Embodiment 3 of the present invention;

[0051] Figure 5 It is a structural block diagram of a computer device provided in Embodiment 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] The embodiments of the present invention provide a control method and system for a multi-flexible DC-fed power grid, which are used to solve the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible DC-fed power grid.

[0053] In order to make the objectives, features, and advantages of the present invention more obvious and understandable, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0054] Regarding the transient stability analysis and control of power systems with converters, existing literature has proposed building models containing doubly-fed induction generators (DFIGs) and synchronous machines, and simulating and comparing the power angle stability of synchronous machines when DFIGs adopt constant power factor control and constant voltage control respectively. Existing literature has also proposed that it is found that wind turbines can improve the transient power angle stability by increasing the reactive power injection of the system. Existing literature has also proposed to control the active and reactive currents of the converter by measuring the frequency of the critical synchronous machine, which is essentially to improve the system stability by increasing the electromagnetic power of the critical synchronous machine. However, these control strategies are designed or analyzed based on simulation rules and lack the support of mathematical theories. Existing literature has proposed a wind power active current reference controller based on the transient stability mechanism of a single-machine infinite bus system to improve the system stability, but there is no theoretical proof of the applicability of this control strategy in multi-machine systems. In addition, current research on improving the transient stability of the system mostly focuses on new energy, lacking relevant research on MMC-HVDC.

[0055] In summary, this application proposes a control method for a multi-flexible DC fed power grid by establishing a flexible DC control strategy for improving the power angle stability of a multi-machine system in a multi-flexible DC fed power grid. This control strategy can improve the transient power angle stability of the multi-machine system in the multi-flexible DC fed power grid under different fault scenarios and different MMC-HVDC penetration rates without affecting the transient reactive power support ability of MMC-HVDC.

[0056] It should be noted that a multi-machine system refers to a system composed of multiple synchronous generator groups.

[0057] Please refer to Figure 1 , Figure 1 which is the flowchart of the steps of a control method for a multi-flexible DC fed power grid provided in Embodiment 1 of the present invention.

[0058] A control method for a multi-flexible DC fed power grid provided by the present invention includes:

[0059] Step 101, in response to a control request instruction for the multi-flexible DC fed power grid, obtain the grid operation data of the multi-flexible DC fed power grid.

[0060] A multi-flexible DC fed power grid refers to a power grid system that uses multiple high-voltage direct current (HVDC) transmission terminals in a power system and uses a modular multi-level converter (MMC) as its core component.

[0061] The control request instruction refers to a flexible DC coordination control request instruction for the multi-flexible DC fed power grid, so that the transient power angle stability of the multi-machine system in the controlled multi-flexible DC fed power grid is significantly improved.

[0062] Grid operation data refers to the equivalent power angle difference, equivalent electromagnetic power, total inertia of synchronous generators, total number of synchronous generators, and converter penetration rate of modular multilevel converters in a multi-machine system of a multi-flexible DC fed power grid. Among them, the total inertia of synchronous generators is the total inertia of synchronous generators when the multi-level converter is not connected in the sending area of the multi-flexible DC fed power grid, and the total number of synchronous generators includes the total number of synchronous generators when the multi-level converter is not connected in the sending area of the multi-flexible DC fed power grid and the total number of synchronous generators when the multi-level converter is not connected in the receiving area of the multi-flexible DC fed power grid.

[0063] In an embodiment of the present invention, in response to a received flexible DC coordinated control request instruction for a multi-flexible DC fed power grid, grid operation data of the multi-flexible DC fed power grid is acquired.

[0064] Step 102: Construct a numerical simulation model of a multi-flexible DC fed power grid, and perform a short-circuit fault simulation on the numerical simulation model to obtain active power data.

[0065] The numerical simulation model refers to a numerical simulation model of a multi-flexible DC fed power grid, which is a simulation model used to imitate the operation process of a multi-flexible DC fed power grid and is used to predict fault simulation data when the multi-flexible DC fed power grid is under an AC short-circuit fault.

[0066] In an embodiment of the present invention, a numerical simulation model of a multi-flexible DC fed power grid is constructed, and a short-circuit fault simulation is performed on the numerical simulation model to obtain active power data.

[0067] Step 103: Construct a motion equation of a multi-flexible DC fed power grid, and solve it by using the active power data and the grid operation data to obtain the critical penetration rate of each multi-level converter in the multi-flexible DC.

[0068] The motion equation refers to the motion equation of a multi-machine system in a multi-flexible DC fed power grid during a fault, which is used to characterize the dynamic characteristics of a synchronous generator group.

[0069] The critical penetration rate refers to the critical penetration rate of a multi-level converter in a multi-flexible DC fed power grid.

[0070] In an embodiment of the present invention, a motion equation for characterizing the dynamic characteristics of a synchronous generator group of a multi-flexible DC fed power grid is constructed, and the motion equation is solved by using the active power data and the grid operation data to obtain the critical penetration rate of the multi-level converter in the multi-flexible DC.

[0071] Step 104: When a short - circuit fault occurs in the multi - flexible DC - fed power grid, the control strategies of each multilevel converter are matched in the strategy library by using the critical penetration rate and the grid operation data, where the control strategy is used to control the active current of the multilevel converter.

[0072] In the embodiment of the present invention, when a short - circuit fault occurs in the multi - flexible DC - fed power grid, the control strategies of each multilevel converter in the multi - flexible DC - fed power grid are matched according to the critical penetration rate and the grid operation data.

[0073] Step 105: Send the matched control strategies of each multilevel converter to each multilevel converter for execution.

[0074] In the embodiment of the present invention, the control strategies of each multilevel converter in the multi - flexible DC - fed power grid are matched according to the critical penetration rate and the grid operation data, and the multilevel converter is controlled according to the matching result.

[0075] In the present invention, in response to a control request command for the multi - flexible DC - fed power grid, the grid operation data of the multi - flexible DC - fed power grid is obtained; a numerical simulation model of the multi - flexible DC - fed power grid is constructed, and a short - circuit fault simulation is performed on the numerical simulation model to obtain active power data; a motion equation of the multi - flexible DC - fed power grid is constructed, and the critical penetration rate of each multilevel converter in the multi - flexible DC is obtained by solving using the active power data and the grid operation data; when a short - circuit fault occurs in the multi - flexible DC - fed power grid, the control strategies of each multilevel converter are matched in the strategy library by using the critical penetration rate and the grid operation data, where the control strategy is used to control the active current of the multilevel converter; the matched control strategies of each multilevel converter are sent to each multilevel converter for execution; the control strategy constructed by the present invention can perform coordinated control when the multilevel converter is in the low - voltage ride - through mode due to an AC short - circuit fault, and effectively improve the transient power - angle stability of the multi - machine system; the technical problem of how to improve the transient power - angle stability of the multi - machine system in the multi - flexible DC - fed power grid is solved.

[0076] Please refer to Figure 2 , Figure 2 which is the step - flow chart of a control method for a multi - flexible DC - fed power grid provided in the second embodiment of the present invention.

[0077] A control method for a multi - flexible DC - fed power grid provided by the present invention includes:

[0078] Step 201: In response to a control request command for the multi - flexible DC - fed power grid, obtain the grid operation data of the multi - flexible DC - fed power grid.

[0079] In the embodiment of the present invention, the specific implementation process of step 201 is similar to that of step 101, and will not be elaborated here.

[0080] Step 202: Construct a numerical simulation model of a multi - flexible DC - fed power grid, and conduct a short - circuit fault simulation on the numerical simulation model to obtain active power data.

[0081] Furthermore, the active power data includes the average active power of the sending - end multi - level converter during the fault, the average active power of a single receiving - end multi - level converter during the fault, and the average active power of the load.

[0082] Furthermore, step 202 may include the following sub - steps:

[0083] S11: Construct a numerical simulation model of a multi - flexible DC - fed power grid.

[0084] S12: Select the control section of the numerical simulation model, where the control section includes the transmission channel between the sending - end and the receiving - end formed by the tie - lines in a preset electrical interval within the multi - flexible DC - fed power grid.

[0085] S13: Input the operation control parameters for simulating an AC short - circuit fault on the control section of the numerical simulation model, and conduct a time - domain simulation on the numerical simulation model to output the active power data of the multi - level converter.

[0086] The operation control parameters include, but are not limited to, the topological structure, the operation state, and system parameters. The topological structure includes the connection methods and parameters of power system components such as synchronous generators, transformers, transmission lines, and loads; the operation state includes the system operation conditions before the fault, such as the initial power output of the generator, the power demand of the load, the bus voltage level, etc., and the system parameters include the electrical parameters of various devices, such as resistance, inductance, capacitance values, as well as the inertia constant of the generator, and the parameters of the governor and excitation system.

[0087] In the embodiment of the present invention, a numerical simulation model of a multi - flexible DC - fed power grid is constructed. The long - distance transmission channel formed by the tie - lines in the electrical interval is selected as the weak node of the numerical simulation model. An AC short - circuit fault is set at the weak node of the numerical simulation model near the forward machine group. A time - domain simulation is performed to output the active power data. The average active power of the sending - end and a single receiving - end multi - level converter during the fault are recorded, which are and respectively, and are used as the output of the numerical simulation model. The average active power of the receiving - end load is recorded and used as the output of the numerical simulation model. That is, the active power data includes the average active power of the sending - end and a single receiving - end multi - level converter during the fault and the average active power of the receiving - end load.

[0088] Step 203: Construct the motion equation of the multi - flexible DC - fed power grid.

[0089] The extended equal - area criterion refers to a method for analyzing and evaluating the transient stability of power systems. It is developed based on the traditional equal - area criterion and extends it to a multi - machine system with multiple flexible DC feeding into the power grid. By decoupling the multi - machine system into multiple single - machine infinite - bus systems, each single - machine system represents a generator in the original system, and virtual motion analysis is carried out for each decoupled single - machine system.

[0090] In the embodiment of the present invention, according to the extended equal - area criterion, the motion equation of the multi - machine system during a fault is specifically as follows:

[0091]

[0092] In the formula, represents the equivalent power - angle difference of the multi - machine system, represents the equivalent electromagnetic power, represents the average active power of a single multi - level converter at the sending end, represents the total number of synchronous generators when no multi - level converter is connected in the sending - end area of the power grid with multiple flexible DC feeding, represents the converter penetration rate of the multi - level converter, represents the average active power of a single multi - level converter at the receiving end, represents the average active power of the receiving - end load, represents the total number of synchronous generators when no multi - level converter is connected in the receiving - end area of the power grid with multiple flexible DC feeding, represents the total inertia of synchronous generators when no multi - level converter is connected in the sending - end area of the power grid with multiple flexible DC feeding;

[0093] Step 204: Use the active - power data and power - grid operation data for solution to obtain the critical penetration rate of each multi - level converter in the multiple flexible DC.

[0094] In the embodiment of the present invention, by setting the differential term of the motion equation to 0 and substituting the power - grid operation data and the active - power data of the numerical simulation model, the numerical value of the critical penetration rate can be calculated. .

[0095] It is worth mentioning that when a short - circuit fault occurs in the power grid with multiple flexible DC feeding, the calculated numerical value of the critical penetration rate will be used as the control signal of the MMC - HVDC. According to the control signal, the optimal combination scheme of the low - voltage ride - through control strategy for each MMC - HVDC in the whole system is determined, and the specific steps are as follows:

[0096] Step 205: When a short-circuit fault occurs in a multi-flexible DC-fed power grid, use the critical penetration rate and grid operation data to match the control strategies of each multi-level converter in the strategy library, where the control strategies are used to perform active current control on the multi-level converter.

[0097] Further, step 205 may include the following sub-steps:

[0098] S21: When a short-circuit fault occurs in a multi-flexible DC-fed power grid, obtain the per-unit value of the voltage of the multi-level converter.

[0099] S22: Calculate the reactive current of the multi-level converter using the per-unit value of the voltage.

[0100] The reactive current refers to the reactive current when the voltage at the connection point of the multi-level converter is lower than the set threshold when an AC short-circuit fault occurs in the multi-flexible DC-fed power grid, and the multi-level converter will enter the low-voltage ride-through mode.

[0101] In a specific implementation, to facilitate the implementation of the method, the above process can be converted into a form of formula encapsulation. Among them, the calculation method of the reactive current can be as follows:

[0102]

[0103] In the formula, represents the reactive current, represents the per-unit value of the voltage at the connection point of the multi-level converter;

[0104] S23: Obtain the maximum value of the current of the multi-level converter, and calculate the active current threshold of the first active control strategy using the maximum value of the current and the reactive current.

[0105] In a specific implementation, to facilitate the implementation of the method, the above process can be converted into a form of formula encapsulation. Among them, the calculation method of the active current threshold can be as follows:

[0106]

[0107] In the formula, represents the active current threshold, represents the maximum value of the current;

[0108] In the embodiment of the present invention, by calculating the active current threshold of the first active control strategy, it is used to formulate the critical threshold for coordinating the control of the active current in the first active control strategy.

[0109] S24. A1 adopts a constant active power control mode and keeps the absolute value of the first active current less than the active current threshold. The constant active power control mode means that the synchronous generator in the multi - flexible DC - fed power grid outputs a constant active power. The first active current is the operating active current of the multi - flexible DC - fed power grid under the constant active power control mode.

[0110] The constant active power control mode refers to a power system control strategy that requires the synchronous generator to output a constant active power.

[0111] In the embodiment of the present invention, a control strategy A1 is constructed. That is, when the control strategy A1 is adopted, in the constant active power control mode, the first active current of the multi - level converter can be determined, and the absolute value of the first active current is kept less than the active current threshold.

[0112] S25. A2 controls the multi - level converter by using the second active current, and the second active current is the ratio of the first active current to the preset current coefficient.

[0113] In the embodiment of the present invention, a control strategy A2 is constructed. That is, when the control strategy A2 is adopted, the first active current in the control strategy A1 is divided by the preset current coefficient. The preset current coefficient is preferably 2 to obtain the second active current, and the multi - level converter is controlled according to the second active current.

[0114] S26. A3 controls the multi - level converter by using the preset third active current.

[0115] In the embodiment of the present invention, a control strategy A3 is constructed. That is, when the control strategy A3 is adopted, the multi - level converter is controlled by using the preset third active current. The preset third active current is preferably 0, that is, the active current control of the current multi - level converter is set to 0.

[0116] S27. Match the control strategies of each multi - level converter in the strategy library by using the critical penetration rate and the power grid operation data.

[0117] Further, S27 may include the following sub - steps:

[0118] It should be noted that according to the critical penetration rate and the converter penetration rate to determine the optimal combination scheme of the low - voltage ride - through control strategies of each multi - level converter in the multi - flexible DC - fed power grid.

[0119] S271. When the critical penetration rate of the sending - end multi - level converter and the power grid operation data meet the preset first regulation condition, then match the control strategy A3 as the control strategy of the multi - level converter.

[0120] S272. When the critical penetration rate of the receiving - end multi - level converter and the grid operation data meet the preset first regulation condition, then the matching control strategy A1 is used as the control strategy of the multi - level converter.

[0121] S273. When the critical penetration rate of the sending - end multi - level converter and the grid operation data meet the preset second regulation condition, then the matching control strategy A2 is used as the control strategy of the multi - level converter.

[0122] S274. When the critical penetration rate of the receiving - end multi - level converter and the grid operation data meet the preset second regulation condition, then the matching control strategy A2 is used as the control strategy of the multi - level converter.

[0123] Further, the grid operation data includes the converter penetration rate.

[0124] The preset first regulation condition is specifically that the critical penetration rate is greater than the preset first threshold, or the critical penetration rate is less than the preset first threshold and the converter penetration rate is greater than the preset second threshold and the converter penetration rate is less than the critical penetration rate.

[0125] The preset second regulation condition is specifically that the critical penetration rate is less than the preset first threshold, and the converter penetration rate is greater than the critical penetration rate and the converter penetration rate is less than the preset first threshold.

[0126] In the embodiment of the present invention, when , or, and , the optimal control strategy is: the multi - level converter in the sending - end area is controlled by the control strategy A3, and the multi - level converter in the receiving - end area is controlled by the control strategy A1.

[0127] It should be noted that through the power - angle difference motion equation in step 203, it can be analyzed that after k or k0 satisfies such conditions, the power - angle swings of the sending - end area and the receiving - end area are forward swings, the sending - end synchronous machines are leading machine groups while the receiving - end synchronous machines are lagging machine groups, using A3 at the sending - end can increase the electromagnetic power of the sending - end synchronous machines so as to reduce the unbalanced power of the sending - end synchronous machines, and using A1 at the receiving - end can increase the unbalanced power of the receiving - end synchronous machines. Thus, the power - angle difference between the sending - end and receiving - end synchronous machines can be reduced.

[0128] In the embodiment of the present invention, when and , the optimal control strategy is: the multi - level converters in both the sending - end area and the receiving - end area are controlled by the control strategy A2.

[0129] It should be noted that through the power angle difference motion equation in step 203, it can be analyzed that after k or k0 satisfies such conditions, the power angle swings of the sending end area and the receiving end area are reverse swings, the sending end synchronous machines are the lagging machine group and the receiving end synchronous machines are the leading machine group. If both sides of the synchronous machines adopt the A2 strategy, then according to the power angle difference motion equation, it can be known that the amplitude of the reverse swing will become smaller, thus reducing the power angle difference between the sending end and the receiving end.

[0130] Step 206: Send the control strategies of the matched multi-level converters to each multi-level converter for execution.

[0131] In the embodiment of the present invention, the control strategies of the matched multi-level converters are sent to each multi-level converter for execution.

[0132] For the convenience of understanding, the following provides an application example:

[0133] Please refer to Figure 3 , which is the system diagram of a two-machine group and two-region system with multiple flexible DC feeding into the grid;

[0134] Obtain the grid operation data of the multiple flexible DC feeding into the grid. Among them, the converter penetration rate in the grid operation data is 16.3%, and the fault location is Figure 3 the Y side of the YB circuit No. 1. A three-phase short-circuit fault occurs at 0.5 s and lasts for 0.2 s. The circuit breakers at both ends of the fault line trip at 0.7 s; the total number of synchronous generators in the sending end area of the multiple flexible DC feeding into the grid when no multi-level converter is connected = 6, and the total number of synchronous generators in the receiving end area of the multiple flexible DC feeding into the grid when no multi-level converter is connected = 6;

[0135] Conduct a short-circuit fault simulation on the numerical simulation model of the multiple flexible DC feeding into the grid to obtain the active power data; the active power data includes the average active power of a single multi-level converter at the sending end and the receiving end, which are and respectively, and are used as the output of the numerical simulation model, and record the average active power of the receiving end load;

[0136] Construct the motion equation of the multiple flexible DC feeding into the grid, and substitute , , , , , and calculate the critical penetration rate to be 44.8%.

[0137] When a short - circuit fault occurs in a multi - flexible DC feeding power grid, determine the reactive current of the multi - level converter, and construct a control strategy for the multi - level converter based on the reactive current; among them, the control strategy includes a first active power control strategy, a second active power control strategy, and a third active power control strategy;

[0138] Therefore, when , the multi - level converters in the sending - end area adopt the third active power control strategy, while the multi - level converters in the receiving - end area adopt the first active power control strategy. When , the multi - level converters in both the sending - end area and the receiving - end area adopt the second active power control strategy.

[0139] The following are verification examples:

[0140] To verify the effectiveness of the proposed control strategy, are taken as 16.3%, 32.7%, 49%, 65.4%, 81.7% respectively, and the fault location is Figure 3 on the Y - side or B - side of the YB Line 1, and a three - phase short - circuit fault occurs at 0.5 s and lasts for 0.2 s. The circuit breakers at both ends of the fault line trip at 0.7 s, and the active power data are shown in Tables 1 and 2.

[0141] Table 1. Power - angle and active - power data of different control strategies under Y - side fault

[0142]

[0143] Table 2. Power - angle and active - power data of different control strategies under B - side fault

[0144]

[0145] The traditional control strategy in the table means that the multi - level converters at both the sending - end and the receiving - end adopt the first active power control strategy. The in the table is a characterization index of the transient power - angle stability of the system, the larger it is, the worse the transient power - angle stability of the system. When the equivalent power - angle of the system swings forward during the fault, the in the table refers to the maximum value of the first swing of the equivalent power - angle after the fault. When the equivalent power - angle of the system swings backward during the fault, the in the table refers to the maximum value of the first positive swing of the equivalent power - angle after the fault. The forward swing of the equivalent power - angle during the fault means that the rotor speed of the sending - end synchronous generator group is greater than that of the receiving - end synchronous generator group during the fault.

[0146] From Tables 1 and 2, in different fault scenarios and under different converter penetration rates of the multi - level converter, the control strategy of the multi - level converter of the present invention can improve the transient power - angle stability of the multi - machine system.

[0147] In summary, the control strategy of the present invention can improve the transient power angle stability of a multi-machine system under different fault scenarios and different converter penetration rates of multi-level converters, and this control strategy does not affect the transient reactive power support ability of multi-level converters.

[0148] In the present invention, in response to a control request command for a multi-VSC (voltage source converter) fed power grid, grid operation data of the multi-VSC fed power grid is obtained; a numerical simulation model of the multi-VSC fed power grid is constructed, and a short-circuit fault simulation is performed on the numerical simulation model to obtain active power data; a motion equation of the multi-VSC fed power grid is constructed, and the critical penetration rate of each multi-level converter in the multi-VSC is obtained by solving using the active power data and the grid operation data; when a short-circuit fault occurs in the multi-VSC fed power grid, the control strategy of each multi-level converter is matched in a strategy library using the critical penetration rate and the grid operation data, where the control strategy is used to perform active current control on the multi-level converter; the matched control strategies of each multi-level converter are sent to each multi-level converter for execution; the control strategy constructed by the present invention can perform coordinated control when the multi-level converter is in the low voltage ride-through mode due to an AC short-circuit fault, and effectively improve the transient power angle stability of the multi-machine system; the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-VSC fed power grid is solved.

[0149] Please refer to Figure 4 , Figure 4 which is a structural block diagram of a control system for a multi-VSC fed power grid provided in Embodiment 3 of the present invention.

[0150] A control system for a multi-VSC fed power grid provided by the present invention includes:

[0151] A response module 301, configured to obtain grid operation data of the multi-VSC fed power grid in response to a control request command for the multi-VSC fed power grid;

[0152] A simulation module 302, configured to construct a numerical simulation model of the multi-VSC fed power grid and perform a short-circuit fault simulation on the numerical simulation model to obtain active power data;

[0153] A solution module 303, configured to construct a motion equation of the multi-VSC fed power grid and solve using the active power data and the grid operation data to obtain the critical penetration rate of each multi-level converter in the multi-VSC;

[0154] A strategy module 304, configured to, when a short-circuit fault occurs in the multi-VSC fed power grid, match the control strategy of each multi-level converter in a strategy library using the critical penetration rate and the grid operation data, where the control strategy is used to perform active current control on the multi-level converter;

[0155] The control module 305 is configured to send the control strategies of the matched multi-level converters to each multi-level converter for execution.

[0156] Furthermore, the simulation module 302 includes:

[0157] A model construction sub-module for constructing a numerical simulation model of a multi-flexible DC fed power grid;

[0158] A section selection sub-module for selecting a control section of the numerical simulation model;

[0159] A time-domain simulation sub-module for inputting operating control parameters for simulating an AC short-circuit fault at the control section of the numerical simulation model, performing a time-domain simulation on the numerical simulation model, and outputting the active power data of the multi-level converter;

[0160] Wherein, the control section includes a transmission channel between the sending end and the receiving end formed by the connecting lines of the preset electrical intervals in the multi-flexible DC fed power grid.

[0161] Furthermore, the control strategy is any one of the following three control strategies;

[0162] A1. Adopt a constant active power control mode and keep the absolute value of the first active current less than the active current threshold; the constant active power control mode is that the synchronous generator in the multi-flexible DC fed power grid outputs a constant active power;

[0163] The first active current is the operating active current of the multi-flexible DC fed power grid in the constant active power control mode;

[0164] A2. Control the multi-level converter with a second active current, where the second active current is the ratio of the first active current to a preset current coefficient;

[0165] A3. Control the multi-level converter with a preset third active current.

[0166] Furthermore, the policy module 304 includes:

[0167] A first matching sub-module for matching the control strategy A3 as the control strategy of the multi-level converter when the critical penetration rate of the sending-end multi-level converter and the grid operation data meet the preset first regulation condition;

[0168] A second matching sub-module for matching the control strategy A1 as the control strategy of the multi-level converter when the critical penetration rate of the receiving-end multi-level converter and the grid operation data meet the preset first regulation condition;

[0169] A second matching sub-module, configured to match control strategy A2 as the control strategy of the multi-level converter when the critical penetration rate of the sending-end multi-level converter and the grid operation data meet a preset second regulation condition;

[0170] A second matching sub-module, configured to match control strategy A2 as the control strategy of the multi-level converter when the critical penetration rate of the receiving-end multi-level converter and the grid operation data meet a preset second regulation condition.

[0171] Further, the grid operation data includes the converter penetration rate;

[0172] The preset first regulation condition is specifically that the critical penetration rate is greater than a preset first threshold, or the critical penetration rate is less than the preset first threshold and the converter penetration rate is greater than a preset second threshold and the converter penetration rate is less than the critical penetration rate;

[0173] The preset second regulation condition is specifically that the critical penetration rate is less than the preset first threshold, and the converter penetration rate is greater than the critical penetration rate and the converter penetration rate is less than the preset first threshold.

[0174] In the present invention, in response to a control request command for a multi-flexible DC-fed power grid, grid operation data of the multi-flexible DC-fed power grid is acquired; a numerical simulation model of the multi-flexible DC-fed power grid is constructed, and a short-circuit fault simulation is performed on the numerical simulation model to obtain active power data; a motion equation of the multi-flexible DC-fed power grid is constructed, and the active power data and the grid operation data are used for solution to obtain the critical penetration rate of each multi-level converter in the multi-flexible DC; when a short-circuit fault occurs in the multi-flexible DC-fed power grid, the critical penetration rate and the grid operation data are used to match the control strategy of each multi-level converter in the strategy library, where the control strategy is used to perform active current control on the multi-level converter; the matched control strategies of each multi-level converter are sent to each multi-level converter for execution; the control strategy constructed by the present invention can perform coordinated control when the multi-level converter is in the low-voltage ride-through mode due to an AC short-circuit fault, and effectively improve the transient power angle stability of the multi-machine system; the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible DC-fed power grid is solved.

[0175] Please refer to Figure 5 , Figure 5 which is a structural block diagram of a computer device provided in Embodiment 4 of the present invention.

[0176] An electronic device according to an embodiment of the present invention, the electronic device includes: a memory 401 and a processor 402, and a computer program is stored in the memory 402; when the computer program is executed by the processor 402, the processor 402 is caused to execute the control method of the multi-flexible DC-fed power grid according to any one of the above embodiments.

[0177] The memory 401 can be an electronic memory such as a flash memory, an EEPROM (Electrically Erasable Programmable Read-Only Memory), an EPROM, a hard disk, or a ROM. The memory 401 has a storage space 403 for program code 413 for executing any of the method steps in the above-described method. For example, the storage space 403 for the program code may include respective program codes 413 for implementing the various steps in the above method. These program codes can be read from or written into one or more computer program products. These computer program products include program code carriers such as hard disks, compact discs (CDs), memory cards, or floppy disks. The program code can be compressed in a suitable form, for example. When these codes are run by a computing processing device, they cause the computing processing device to execute each of the steps in the method described above. These program codes can be read from or written into one or more computer program products. These computer program products include program code carriers such as hard disks, compact discs (CDs), memory cards, or floppy disks. The program code can be compressed in a suitable form, for example. When these codes are run by a computing processing device, they cause the computing processing device to execute each of the steps in the control method of the multi-flexible DC-fed power grid described above.

[0178] Embodiment 5 of the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the control method of the multi-flexible DC-fed power grid in any of the above embodiments.

[0179] Embodiment 6 of the present invention further provides a computer program product. The computer program product includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, they cause the computer to execute the control method of the multi-flexible DC-fed power grid in any of the above embodiments.

[0180] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments, and will not be described in detail herein.

[0181] In several embodiments provided by this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of units is only a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections between each other can be through some interfaces, and the indirect couplings or communication connections of devices or units can be in electrical, mechanical, or other forms.

[0182] The units described as separate components may or may not be physically separated. The components shown as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0183] In addition, each functional unit in various embodiments of the present invention can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0184] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods in various embodiments of the present invention. The foregoing storage medium includes: USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical disks and other various media that can store program codes.

[0185] The above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of various embodiments of the present invention.

Claims

1. A control method for a multi - flexible DC feeding power grid, characterized in that Including: Responding to a control request instruction for a multi - flexible DC - fed power grid, and obtaining the grid operation data of the multi - flexible DC - fed power grid; Constructing a numerical simulation model of the multi - flexible DC - fed power grid, and performing short - circuit fault simulation on the numerical simulation model to obtain active power data; Constructing the motion equation of the multi - flexible DC - fed power grid, and using the active power data and the grid operation data to solve for the critical penetration rate of each multi - level converter in the multi - flexible DC; When a short - circuit fault occurs in the multi - flexible DC - fed power grid, then using the critical penetration rate and the grid operation data to match the control strategy of each multi - level converter in the strategy library, where the control strategy is used to perform active current control on the multi - level converter; Issuing the control strategies of each multi - level converter that are matched to each multi - level converter for execution; The control strategy is any one of the following three control strategies; A1. Adopting a constant active power control mode and keeping the absolute value of the first active current less than the active current threshold; the constant active power control mode is that the synchronous generator in the multi - flexible DC - fed power grid outputs a constant active power; The first active current is the operating active current of the multi - flexible DC - fed power grid in the constant active power control mode; A2. Controlling the multi - level converter with a second active current, where the second active current is the ratio of the first active current to a preset current coefficient; A3. Controlling the multi - level converter with a preset third active current; The matching of the control strategies of each multi - level converter in the strategy library by using the critical penetration rate and the grid operation data includes: When the critical penetration rate and the grid operation data of the multi - level converter at the sending end satisfy a preset first regulation condition, then matching the control strategy A3 as the control strategy of the multi - level converter; When the critical penetration rate and the grid operation data of the multi - level converter at the receiving end satisfy a preset first regulation condition, then matching the control strategy A1 as the control strategy of the multi - level converter; When the critical penetration rate and the grid operation data of the multi - level converter at the sending end satisfy a preset second regulation condition, then matching the control strategy A2 as the control strategy of the multi - level converter; When the critical penetration rate and the grid operation data of the multi - level converter at the receiving end satisfy a preset second regulation condition, then matching the control strategy A2 as the control strategy of the multi - level converter; The grid operation data includes converter penetration rate; The preset first regulation condition is specifically that the critical penetration rate is greater than a preset first threshold, or the critical penetration rate is less than the preset first threshold and the converter penetration rate is greater than a preset second threshold and the converter penetration rate is less than the critical penetration rate; The preset second regulation condition is specifically that the critical penetration rate is less than the preset first threshold, and the converter penetration rate is greater than the critical penetration rate and the converter penetration rate is less than the preset first threshold.

2. The control method of the multi - flexible DC feeding power grid according to claim 1, wherein, Construct the numerical simulation model of the multi - flexible DC - fed power grid, and perform short - circuit fault simulation on the numerical simulation model to obtain active power data, including: Construct the numerical simulation model of the multi - flexible DC - fed power grid; Select the control section of the numerical simulation model; Input the operation control parameters for simulating AC short - circuit faults at the control section of the numerical simulation model, and perform time - domain simulation on the numerical simulation model to output the active power data of the multi - level converter; Among them, the control section includes the transmission channel between the sending end and the receiving end formed by the tie lines in the preset electrical interval within the multi - flexible DC - fed power grid.

3. A control system for a multi - flexible DC feeding power grid, characterized in that, Including: A response module, which is used to respond to the control request command for the multi - flexible DC - fed power grid and obtain the grid operation data of the multi - flexible DC - fed power grid; A simulation module, which is used to construct the numerical simulation model of the multi - flexible DC - fed power grid and perform short - circuit fault simulation on the numerical simulation model to obtain active power data; A solution module, which is used to construct the motion equation of the multi - flexible DC - fed power grid and solve it by using the active power data and the grid operation data to obtain the critical penetration rate of each multi - level converter in the multi - flexible DC; A strategy module, which is used to match the control strategies of each multi - level converter in the strategy library by using the critical penetration rate and the grid operation data when a short - circuit fault occurs in the multi - flexible DC - fed power grid, where the control strategy is used to perform active current control on the multi - level converter; A control module, which is used to send the matched control strategies of each multi - level converter to each multi - level converter for execution; The control strategy is any one of the following three control strategies; A1. Adopt the constant active power control mode and keep the absolute value of the first active current less than the active current threshold; the constant active power control mode means that the synchronous generator in the multi - flexible DC - fed power grid outputs a constant active power; The first active current is the operating active current of the multi - flexible DC - fed power grid in the constant active power control mode; A2. Control the multi - level converter by using the second active current, where the second active current is the ratio of the first active current to the preset current coefficient; A3. Control the multi - level converter by using the preset third active current; The strategy module includes: The first matching sub - module, which is used to match the control strategy A3 as the control strategy of the multi - level converter when the critical penetration rate and the grid operation data of the multi - level converter at the sending end meet the preset first regulation condition; The second matching sub - module, which is used to match the control strategy A1 as the control strategy of the multi - level converter when the critical penetration rate and the grid operation data of the multi - level converter at the receiving end meet the preset first regulation condition; The third matching sub - module, which is used to match the control strategy A2 as the control strategy of the multi - level converter when the critical penetration rate and the grid operation data of the multi - level converter at the sending end meet the preset second regulation condition; The fourth matching sub-module is configured to, when the critical penetration rate of the multi-level converter at the receiving end and the grid operation data satisfy a preset second regulation condition, match control strategy A2 as the control strategy of the multi-level converter; The grid operation data includes the converter penetration rate; The specific preset first regulation condition is that the critical penetration rate is greater than a preset first threshold, or the critical penetration rate is less than the preset first threshold and the converter penetration rate is greater than a preset second threshold and the converter penetration rate is less than the critical penetration rate; The specific preset second regulation condition is that the critical penetration rate is less than the preset first threshold, and the converter penetration rate is greater than the critical penetration rate and the converter penetration rate is less than the preset first threshold.

4. The control system of the multi - flexible DC feeding power grid according to claim 3, characterized in that, The simulation module includes: A model construction sub-module for constructing a numerical simulation model of the multi-flexible DC fed power grid; A section selection sub-module for selecting a control section of the numerical simulation model; A time-domain simulation sub-module for inputting operation control parameters for simulating an AC short-circuit fault on the control section of the numerical simulation model, performing a time-domain simulation on the numerical simulation model, and outputting the active power data of the multi-level converter; Wherein, the control section includes a transmission channel between the sending end and the receiving end formed by the tie lines in a preset electrical interval within the multi-flexible DC fed power grid.

5. An electronic device, characterized in that, It includes a memory and a processor. When the computer program stored in the memory is executed by the processor, the processor executes the steps of the control method for the multi-flexible DC fed power grid according to any one of claims 1-2.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed, it implements the control method for the multi-flexible DC fed power grid according to any one of claims 1-2.

7. A computer program product, characterized in that, The computer program product includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer executes the control method for the multi-flexible DC fed power grid according to any one of claims 1-2.

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