Control method and system for multi-flexible direct-current feed-in power grid

Abstract

The invention relates to the technical field of transient stability of a power system, and discloses a control method and system for a multi-flexible direct-current feed-in power grid. Coordinated control can be carried out through a constructed control strategy when a multi-level converter is in a low-voltage ride-through mode due to an alternating-current short-circuit fault; the transient power angle stability of the multi-machine system is effectively improved; the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible direct-current feed-in power grid is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of transient stability of power systems, and in particular to a control method and system for multiple flexible direct current feed-in power grids. Background Art

[0002] With the global energy transition to low-carbon, new energy represented by wind power and photovoltaics has been vigorously developed. Modular multilevel converter based high voltage direct current (MMC-HVDC) has the characteristics of strong controllability, fast response speed and active and reactive decoupled output. Its application in offshore wind power, long-distance power transmission of large-scale new energy bases and other scenarios is becoming increasingly common, and load centers are gradually forming a pattern of multiple flexible DC feeds.

[0003] In a multi-flexible DC feed-in grid, the distribution of flexible DC is different, and its impact on system stability is also different. How to coordinate and control the multi-flexible DC feed-in grid to improve the stability of the multi-machine system in the multi-flexible DC feed-in grid is a problem worth exploring. Therefore, a control scheme for a multi-flexible DC feed-in grid is urgently needed to solve the problems existing in the existing technology. Summary of the invention

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

[0005] A first aspect of the present invention provides a control method for multiple flexible direct current feed-in power grids, comprising:

[0006] In response to a control request instruction for a multiple flexible DC feed-in power grid, obtaining power grid operation data of the multiple flexible DC feed-in power grid;

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

[0008] Constructing a motion equation of the multi-flexible direct current fed into a power grid, and solving it using the active power data and the power grid operation data to obtain a critical permeability of each multi-level converter in the multi-flexible direct current;

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

[0010] The matched control strategies of each multilevel converter are sent to each of the multilevel converters for execution.

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

[0012] Constructing a numerical simulation model of the multi-flexible direct current feed-in power grid;

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

[0014] Inputting operation control parameters for simulating AC short circuit faults on the control section of the numerical simulation model, performing time domain simulation on the numerical simulation model, and outputting active power data of the multilevel converter;

[0015] The control section includes a power transmission channel between a sending end and a receiving end formed by a connecting line of a preset electrical section in the multi-flexible DC feed-in power grid.

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

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

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

[0019] A2. Controlling the multilevel converter by using a second active current, where the second active current is a ratio of the first active current to a preset current coefficient;

[0020] A3. Using a preset third active current to control the multilevel converter.

[0021] Optionally, the using the critical permeability and the grid operation data to match the control strategy of each multilevel converter in a strategy library includes:

[0022] When the critical permeability of the multilevel converter at the sending end and the grid operation data meet a preset first regulation condition, the control strategy A3 is matched as the control strategy of the multilevel converter;

[0023] When the critical permeability of the multilevel converter at the receiving end and the grid operation data meet a preset first regulation condition, the control strategy A1 is matched as the control strategy of the multilevel converter;

[0024] When the critical permeability of the multilevel converter at the sending end and the grid operation data meet the preset second regulation condition, the control strategy A2 is matched as the control strategy of the multilevel converter;

[0025] When the critical permeability of the multilevel converter at the receiving end and the grid operation data meet a preset second regulation condition, the control strategy A2 is matched as the control strategy of the multilevel converter.

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

[0027] The preset first control condition is specifically that the critical permeability is greater than the preset first threshold, or the critical permeability is less than the preset first threshold and the converter permeability is greater than the preset second threshold and the converter permeability is less than the critical permeability;

[0028] The preset second control condition is specifically that the critical permeability is less than the preset first threshold, the converter permeability is greater than the critical permeability, and the converter permeability is less than the preset first threshold.

[0029] A second aspect of the present invention provides a control system for multiple flexible direct current feed-in power grids, comprising:

[0030] A response module, used for responding to a control request instruction for a multi-flexible DC feed-in power grid, and acquiring power grid operation data of the multi-flexible DC feed-in power grid;

[0031] A simulation module, used for constructing a numerical simulation model of the multi-flexible direct current feed-in power grid, and performing short-circuit fault simulation on the numerical simulation model to obtain active power data;

[0032] A solution module, used for constructing the motion equation of the multi-flexible direct current fed into the power grid, and solving it by using the active power data and the power grid operation data to obtain the critical permeability of each multi-level converter in the multi-flexible direct current;

[0033] A strategy module, used for matching the control strategy of each multilevel converter in the strategy library by using the critical permeability and the grid operation data when a short circuit fault occurs in the multi-level flexible DC feed-in grid, wherein the control strategy is used to perform active current control on the multilevel converter;

[0034] The control module is used to send the matched control strategies of each multilevel converter to each of the multilevel converters for execution.

[0035] Optionally, the simulation module includes:

[0036] A model building submodule, used for building a numerical simulation model of the multi-flexible DC feed-in power grid;

[0037] A section selection submodule, used for selecting a control section of the numerical simulation model;

[0038] A time domain simulation submodule, used for inputting operation control parameters for simulating AC short circuit faults on the control section of the numerical simulation model, performing time domain simulation on the numerical simulation model, and outputting active power data of the multilevel converter;

[0039] The control section includes a power transmission channel between a sending end and a receiving end formed by a connecting line of a preset electrical section in the multi-flexible DC feed-in power grid.

[0040] A third aspect of the present invention provides an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the control method for multiple flexible direct current feed-into a power grid as described in any one of the above items.

[0041] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed, the control method for multiple flexible direct current feed-in grids as described in any one of the above items is implemented.

[0042] A fifth aspect of the present invention provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions, wherein when the program instructions are executed by a computer, the computer executes the control method for a multi-flexible DC feed-in power grid as described in any one of the above items.

[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 feed-in power grid, comprising: responding to a control request instruction for the multi-flexible DC feed-in power grid, obtaining power grid operation data of the multi-flexible DC feed-in power grid; constructing a numerical simulation model of the multi-flexible DC feed-in power grid, and performing short-circuit fault simulation on the numerical simulation model to obtain active power data; constructing a motion equation of the multi-flexible DC feed-in power grid, and solving it using active power data and power grid operation data to obtain a critical permeability of each multi-level converter in the multi-flexible DC; when a short-circuit fault occurs in the multi-flexible DC feed-in power grid, matching a control strategy of each multi-level converter in a strategy library using the critical permeability and power grid operation data, wherein the control strategy is used to perform active current control on the multi-level converter; and sending the matched control strategy of each multi-level converter 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 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 a multi-flexible DC feed-in power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] Figure 1 A flowchart of a method for controlling multiple flexible direct current feed-in grids provided in the first embodiment of the present invention;

[0048] Figure 2 A flowchart of a method for controlling multiple flexible direct current feed-in grids provided in Embodiment 2 of the present invention;

[0049] Figure 3 A two-machine group and two-area system diagram of a multi-flexible DC feed-in power grid provided in the second embodiment of the present invention;

[0050] Figure 4 A structural block diagram of a control system for multiple flexible direct current feed-into power grids provided in Embodiment 3 of the present invention;

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

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

[0053] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] Regarding the transient stability analysis and control of power systems containing converters, existing literature proposes to build a model containing a double-fed induction generator (DFIG) and a synchronous machine, and simulates and compares the power angle stability of the synchronous machine under constant power factor control and constant voltage control of the DFIG. Existing literature also proposes that wind turbines can improve the transient power angle stability by increasing the reactive power injection of the system. Existing literature also proposes to achieve active and reactive current control of the converter by measuring the frequency of the critical synchronous machine, which is essentially to improve the stability of the system 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 theory. Existing literature proposes a wind power active current reference controller based on the transient stability mechanism of a single-machine infinite system to improve the stability of the system, but there is no theoretical proof of the applicability of this control strategy in a multi-machine system. In addition, current research on improving system transient stability is mostly focused on new energy, and there is a lack of relevant research on MMC-HVDC.

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

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

[0057] See also Figure 1 , Figure 1 A flowchart of the steps of a control method for multiple flexible direct current feed-into a power grid provided in Embodiment 1 of the present invention.

[0058] The present invention provides a control method for multiple flexible direct current feed-in power grids, comprising:

[0059] Step 101 : Responding to a control request instruction for a multi-flexible DC feed-in power grid, obtaining power grid operation data of the multi-flexible DC feed-in power grid.

[0060] A multi-flexible DC feed-in grid refers to a grid system that uses multiple high-voltage DC (HVDC) transmission terminals in the power system and modular multilevel converters (MMCs) as its core components.

[0061] The control request instruction refers to a flexible DC coordinated control request instruction for a multi-flexible DC feed-in power grid, which significantly improves the transient power angle stability of the multi-machine system in the multi-flexible DC feed-in power grid after control.

[0062] The 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 of multi-machine systems in the multi-flexible DC feed-in grid, among which, the total inertia of synchronous generators is the total inertia of synchronous generators when the sending-end area of ​​the multi-flexible DC feed-in grid is not connected to the multi-level converter, and the total number of synchronous generators includes the total number of synchronous generators when the sending-end area of ​​the multi-flexible DC feed-in grid is not connected to the multi-level converter and the total number of synchronous generators when the receiving-end area of ​​the multi-flexible DC feed-in grid is not connected to the multi-level converter.

[0063] In an embodiment of the present invention, in response to a received flexible DC coordinated control request instruction for multiple flexible DC feeding grids, grid operation data of the multiple flexible DC feeding grids are acquired.

[0064] Step 102: construct a numerical simulation model of a multi-flexible direct current feed-in power grid, and perform 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 feeding grid, which is a simulation model used to simulate the operation process of the multi-flexible DC feeding grid and is used to predict fault simulation data of the multi-flexible DC feeding grid under an AC short circuit fault.

[0066] In an embodiment of the present invention, a numerical simulation model of a multi-flexible direct current feed-in 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 the motion equation of the multi-flexible DC feed-in power grid, and solve it using the active power data and the power grid operation data to obtain the critical penetration rate of each multilevel converter in the multi-flexible DC.

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

[0069] Critical penetration rate refers to the critical penetration rate of multi-level converters in the multi-flexible DC feed-in grid.

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

[0071] Step 104: When a short circuit fault occurs in the multi-level flexible DC feed-in grid, a control strategy for each multilevel converter is matched in a strategy library by using the critical permeability and grid operation data, wherein the control strategy is used to perform active current control on the multilevel converter.

[0072] In an embodiment of the present invention, when a short circuit fault occurs in a multi-flexible DC feeding grid, a control strategy of each multilevel converter in the multi-flexible DC feeding grid is matched according to the critical permeability and 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 strategy of each multilevel converter in the multi-flexible DC feed-in power grid is matched according to the critical permeability and the power 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 instruction for a multi-flexible DC feed-in power grid, grid operation data of the multi-flexible DC feed-in power grid is obtained; a numerical simulation model of the multi-flexible DC feed-in 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 feed-in power grid is constructed, and the active power data and grid operation data are used to solve the equation to obtain the critical permeability of each multi-level converter in the multi-flexible DC; when a short-circuit fault occurs in the multi-flexible DC feed-in power grid, the critical permeability and grid operation data are used to match the control strategy of each multi-level converter in the strategy library, wherein the control strategy is used to perform active current control on the multi-level converter; the control strategy of each matched multi-level converter is sent to each multi-level converter for execution; the present invention can coordinate control when the multi-level converter is in a low voltage ride-through mode due to an AC short-circuit fault through the constructed control strategy, and effectively improve the transient power angle stability of the multi-machine system; and solves the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible DC feed-in power grid.

[0076] See also Figure 2 , Figure 2 A flowchart of the steps of a control method for multiple flexible direct current feeds into a power grid provided in Embodiment 2 of the present invention.

[0077] The present invention provides a control method for multiple flexible direct current feed-in power grids, comprising:

[0078] Step 201 : Responding to a control request instruction for a multi-flexible DC feed-in power grid, obtaining power grid operation data of the multi-flexible DC feed-in power grid.

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

[0080] Step 202: construct a numerical simulation model of a multi-flexible DC feed-in power grid, and perform 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 multilevel converter during the fault period, the average active power of a single multilevel converter at the receiving-end during the fault period, and the average active power of the load.

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

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

[0084] S12. Select a control section of the numerical simulation model, wherein the control section includes a transmission channel between a sending end and a receiving end formed by interconnection lines of a preset electrical section in a multi-flexible DC feed-in power grid.

[0085] S13. Inputting operation control parameters for simulating AC short circuit faults on the control section of the numerical simulation model, performing time domain simulation on the numerical simulation model, and outputting active power data of the multilevel converter.

[0086] Operation control parameters include but are not limited to topology, operating status and system parameters. The topology includes the connection method and parameters of power system components such as synchronous generators, transformers, transmission lines, and loads; the operating status includes the system operating conditions before the fault occurs, such as the initial power output of the generator, the power demand of the load, the bus voltage level, etc. The system parameters include the electrical parameters of various equipment, such as resistance, inductance, capacitance values, as well as the inertia constant of the generator, the parameters of the speed regulator and excitation system, etc.

[0087] In the embodiment of the present invention, a numerical simulation model of a multi-flexible DC feed-in power grid is constructed, a long-distance transmission channel formed by the tie lines of the electrical section is selected as a weak node of the numerical simulation model, an AC short-circuit fault close to the forward group is set on the weak node of the numerical simulation model, a time domain simulation is performed, active power data is output, and the average active power of a single multilevel converter at the sending end and the receiving end during the fault period is recorded, which are respectively and , and as the output of the numerical simulation model, record the average active power of the receiving load And it is used as the output of the numerical simulation model. That is, the active power data includes the average active power of a single multilevel converter at the sending end and the receiving end during the fault period and the average active power of the receiving end load.

[0088] Step 203: construct the motion equations of the multi-flexible DC feed-in power grid.

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

[0090] In the embodiment of the present invention, according to the extended equal area law, the motion equation of the multi-machine system during the fault period 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 multilevel converter at the sending end, It indicates the total number of synchronous generators in the sending end area of ​​the multi-flexible DC feed-in power grid when the multi-level converter is not connected. represents the converter penetration of the multilevel converter, represents the average active power of a single multilevel converter at the receiving end, Represents the average active power of the receiving load, It indicates the total number of synchronous generators in the multi-flexible DC feed-in grid when the receiving area is not connected to the multi-level converter. It represents the total inertia of synchronous generators when the sending end area of ​​the multi-flexible DC feed-in power grid is not connected to the multi-level converter;

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

[0094] In the embodiment of the present invention, the differential term of the motion equation is set to 0, and the grid operation data and the active power data of the numerical simulation model are substituted to calculate the value of the critical permeability: .

[0095] It is worth mentioning that when a short circuit occurs in the multi-flexible DC feed-in grid, the critical permeability value is calculated The control signal of MMC-HVDC is used to determine the optimal combination of low voltage ride-through control strategies for each MMC-HVDC in the whole system according to the control signal. The specific steps are as follows:

[0096] Step 205: When a short circuit fault occurs in the multi-level flexible DC feed-in grid, a control strategy for each multilevel converter is matched in a strategy library by using the critical permeability and grid operation data, wherein the control strategy is used to perform active current control on the multilevel converter.

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

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

[0099] S22. Calculate the reactive current of the multilevel converter using the voltage per unit value.

[0100] Reactive current refers to the reactive current when an AC short circuit occurs in the multi-level flexible DC feed-in grid, causing the voltage at the multi-level converter connection point to be lower than the set threshold and the multi-level converter will enter the low voltage ride-through mode.

[0101] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the reactive current can be calculated as follows:

[0102]

[0103] In the formula, Represents reactive current, Indicates the voltage per unit value of the multilevel converter grid connection point;

[0104] S23: Acquire the maximum current of the multilevel converter, and use the maximum current and the reactive current to calculate the active current threshold of the first active control strategy.

[0105] In a specific implementation, in order to facilitate the implementation of the method, the above process can be converted into a formula encapsulation form, wherein the active current threshold value can be calculated as follows:

[0106]

[0107] In the formula, Indicates the active current threshold, Indicates the maximum current;

[0108] In the embodiment of the present invention, the active current threshold of the first active power control strategy is calculated to formulate a critical threshold for coordinated control of the active current in the first active power control strategy.

[0109] S24 and A1 adopt a fixed active power control mode and keep the absolute value of the first active current less than the active current threshold; the fixed active power control mode is that the synchronous generators in the multi-flexible DC feed-in power grid output a constant active power; the first active current is the operating active current of the multi-flexible DC feed-in power grid in the fixed 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 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, a fixed active power control mode is adopted to determine the first active current of the multilevel converter, and keep the absolute value of the first active current smaller than the active current threshold.

[0112] S25, A2 uses the second active current to control the multilevel converter, and the second active current is the ratio of the first active current to the preset current coefficient.

[0113] In an 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 a preset current coefficient, which is preferably 2, to obtain a second active current, and the multilevel converter is controlled according to the second active current.

[0114] S26 and A3 use the preset third active current to control the multilevel converter.

[0115] In the embodiment of the present invention, a control strategy A3 is constructed. That is, when the control strategy A3 is adopted, a preset third active current is used to control the multilevel converter. The preset third active current is preferably 0, that is, the active current of the current multilevel converter is controlled to be 0.

[0116] S27. Matching the control strategy of each multilevel converter in the strategy library by using the critical penetration rate and the grid operation data.

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

[0118] It should be noted that according to the critical permeability and converter penetration To determine the optimal combination of low voltage ride-through control strategies for multi-level converters in multi-flexible DC feed-in grids.

[0119] S271. When the critical permeability of the sending-end multilevel converter and the grid operation data meet a preset first regulation condition, the control strategy A3 is matched as the control strategy of the multilevel converter.

[0120] S272: When the critical permeability of the receiving-end multilevel converter and the grid operation data meet a preset first regulation condition, the control strategy A1 is matched as the control strategy of the multilevel converter.

[0121] S273: When the critical permeability of the sending-end multilevel converter and the grid operation data meet the preset second regulation condition, the control strategy A2 is matched as the control strategy of the multilevel converter.

[0122] S274: When the critical permeability of the receiving-end multilevel converter and the grid operation data meet the preset second regulation condition, the control strategy A2 is matched as the control strategy of the multilevel converter.

[0123] Furthermore, the grid operation data include converter penetration;

[0124] The preset first control condition is specifically that the critical permeability is greater than the preset first threshold, or the critical permeability is less than the preset first threshold and the converter permeability is greater than the preset second threshold and the converter permeability is less than the critical permeability;

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

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

[0127] It should be noted that, through the power angle difference motion equation of step 203, it can be analyzed that: after k or k0 meets such conditions, the power angle swing in the sending end area and the receiving end area is a positive swing, the sending end synchronous machine is an advanced group and the receiving end synchronous machine is a lagging group, and the sending end adopts A3 to increase the electromagnetic power of the sending end synchronous machine so as to reduce the unbalanced power of the sending end synchronous machine, and the receiving end adopts A1 to increase the unbalanced power of the receiving end synchronous machine, so the power angle difference between the sending end and the receiving end synchronous machine can be reduced.

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

[0129] It should be noted that, through the power angle difference motion equation of step 203, it can be analyzed that: after k or k0 meets such conditions, the power angle swings in the sending end area and the receiving end area are reverse swings, the sending end synchronous machine is a lagging group and the receiving end synchronous machine is an advanced group, and the synchronous machines on both sides adopt the A2 strategy. According to the power angle difference motion equation, it can be known that the amplitude of the reverse swing will become smaller, thereby reducing the power angle difference between the sending and receiving ends.

[0130] Step 206: Send the matched control strategies of each multilevel converter to each multilevel converter for execution.

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

[0132] For ease of understanding, an application example is provided below:

[0133] See also Figure 3 , is a two-group two-area system diagram of multiple flexible DC feed-in power grids;

[0134] Obtain grid operation data of multiple flexible DC feed-in grids, where the converter penetration rate in the grid operation data is is 16.3%, and the fault location is Figure 3 On the Y side of the YB line, a three-phase short circuit fault occurred at 0.5s and lasted for 0.2s. At 0.7s, the circuit breakers at both ends of the fault line tripped. The total number of synchronous generators in the multi-flexible DC feed-in grid when the sending end area is not connected to the multi-level converter in the grid operation data =6, the total number of synchronous generators when the receiving area in the multi-flexible DC feed-in grid is not connected to the multilevel converter =6;

[0135] The short-circuit fault simulation is carried out on the numerical simulation model of the multi-flexible DC feed-in power grid to obtain the active power data; the active power data includes the average active power of a single multilevel converter at the sending end and the receiving end, which are respectively and , and as the output of the numerical simulation model, record the average active power of the receiving load ;

[0136] Construct the motion equations of multiple flexible DC feed-in grids and substitute , , , , , calculate the critical permeability It is 44.8%.

[0137] When a short circuit fault occurs in the multi-level flexible DC feed-in power grid, the reactive current of the multi-level converter is determined, and a control strategy of the multi-level converter is constructed based on the reactive current; wherein 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 multilevel converter in the sending end area adopts the third active power control strategy, while the multilevel converter in the receiving end area adopts the first active power control strategy. , the multilevel converters in both the sending and receiving areas adopt the second active power control strategy.

[0139] The following is a verification example:

[0140] In order to verify the effectiveness of the proposed control strategy, Take 16.3%, 32.7%, 49%, 65.4%, and 81.7% respectively, and the fault location is Figure 3 On the Y side or B side of the YB line, a three-phase short circuit fault occurred at 0.5s and lasted for 0.2s. At 0.7s, the circuit breakers at both ends of the faulty line tripped. 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 fault on side B

[0144]

[0145] The traditional control strategy in the table refers to the multilevel converters at both the sending and receiving ends adopting the first active power control strategy. It is an indicator of the transient power angle stability of the system. The larger the value, the worse the transient power angle stability of the system. When the system equivalent power angle swings positively during the fault period, the value in the table Refers to the maximum value of the first swing of the equivalent power angle after the fault. When the system equivalent power angle swings in the opposite direction during the fault, It refers to the maximum value of the first positive swing of the equivalent power angle after the fault. The positive swing of the equivalent power angle during the fault means that the rotor swing speed of the synchronous generator group at the sending end is greater than the rotor swing speed of the synchronous generator group at the receiving end during the fault.

[0146] From Table 1 and Table 2, it can be seen that under different fault scenarios and different converter penetration rates of the multilevel converters, the multilevel converter control strategy 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 the multi-machine system under different fault scenarios and different converter penetration rates of the multilevel converters, and the control strategy does not affect the transient reactive power support capability of the multilevel converter.

[0148] In the present invention, in response to a control request instruction for a multi-flexible DC feed-in power grid, grid operation data of the multi-flexible DC feed-in power grid is obtained; a numerical simulation model of the multi-flexible DC feed-in 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 feed-in power grid is constructed, and the active power data and grid operation data are used to solve the equation to obtain the critical permeability of each multi-level converter in the multi-flexible DC; when a short-circuit fault occurs in the multi-flexible DC feed-in power grid, the critical permeability and grid operation data are used to match the control strategy of each multi-level converter in the strategy library, wherein the control strategy is used to perform active current control on the multi-level converter; the control strategy of each matched multi-level converter is sent to each multi-level converter for execution; the present invention can coordinate control when the multi-level converter is in a low voltage ride-through mode due to an AC short-circuit fault through the constructed control strategy, and effectively improve the transient power angle stability of the multi-machine system; and solves the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible DC feed-in power grid.

[0149] See also Figure 4 , Figure 4 This is a structural block diagram of a control system for multiple flexible direct current feed-into a power grid provided in Embodiment 3 of the present invention.

[0150] The present invention provides a control system for a multi-flexible direct current feed-in power grid, comprising:

[0151] A response module 301 is used to respond to a control request instruction for a multiple flexible DC feed-in power grid and obtain power grid operation data of the multiple flexible DC feed-in power grid;

[0152] The simulation module 302 is used to construct a numerical simulation model of a multi-flexible DC feed-in power grid, and perform short-circuit fault simulation on the numerical simulation model to obtain active power data;

[0153] A solution module 303 is used to construct a motion equation of a multi-flexible DC feed-in power grid, and solve it using active power data and power grid operation data to obtain a critical permeability of each multilevel converter in the multi-flexible DC;

[0154] A strategy module 304 is used to match the control strategy of each multilevel converter in the strategy library by using the critical permeability and the grid operation data when a short circuit fault occurs in the multi-level flexible DC feed-in grid, wherein the control strategy is used to perform active current control on the multilevel converter;

[0155] The control module 305 is used to send the matched control strategies of each multilevel converter to each multilevel converter for execution.

[0156] Further, the simulation module 302 includes:

[0157] A model building submodule is used to build a numerical simulation model of a multi-flexible DC feed-in power grid;

[0158] The section selection submodule is used to select the control section of the numerical simulation model;

[0159] A time domain simulation submodule is used to input operation control parameters for simulating AC short circuit faults on the control section of the numerical simulation model, perform time domain simulation on the numerical simulation model, and output active power data of the multilevel converter;

[0160] The control section includes a transmission channel between a sending end and a receiving end formed by interconnection lines of preset electrical sections in a multi-flexible DC feed-in power grid.

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

[0162] A1. A fixed active power control mode is adopted and the absolute value of the first active current is kept smaller than the active current threshold value; the fixed active power control mode is that the synchronous generators in the multi-flexible DC feed-in power grid output a constant active power;

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

[0164] A2. Controlling the multilevel converter using a second active current, where the second active current is a ratio of the first active current to a preset current coefficient;

[0165] A3. Use the preset third active current to control the multilevel converter.

[0166] Furthermore, the policy module 304 includes:

[0167] A first matching submodule, configured to match control strategy A3 as the control strategy of the multilevel converter when the critical permeability of the sending-end multilevel converter and the grid operation data meet a preset first regulation condition;

[0168] A second matching submodule, configured to match the control strategy A1 as the control strategy of the multilevel converter when the critical permeability of the receiving-end multilevel converter and the grid operation data meet a preset first regulation condition;

[0169] A second matching submodule, configured to match control strategy A2 as the control strategy of the multilevel converter when the critical permeability of the sending-end multilevel converter and the grid operation data meet a preset second regulation condition;

[0170] The second matching submodule is used to match the control strategy A2 as the control strategy of the multilevel converter when the critical permeability of the receiving-end multilevel converter and the grid operation data meet the preset second regulation condition.

[0171] Furthermore, the grid operation data include converter penetration;

[0172] The preset first control condition is specifically that the critical permeability is greater than the preset first threshold, or the critical permeability is less than the preset first threshold and the converter permeability is greater than the preset second threshold and the converter permeability is less than the critical permeability;

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

[0174] In the present invention, in response to a control request instruction for a multi-flexible DC feed-in power grid, grid operation data of the multi-flexible DC feed-in power grid is obtained; a numerical simulation model of the multi-flexible DC feed-in 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 feed-in power grid is constructed, and the active power data and grid operation data are used to solve the equation to obtain the critical permeability of each multi-level converter in the multi-flexible DC; when a short-circuit fault occurs in the multi-flexible DC feed-in power grid, the critical permeability and grid operation data are used to match the control strategy of each multi-level converter in the strategy library, wherein the control strategy is used to perform active current control on the multi-level converter; the control strategy of each matched multi-level converter is sent to each multi-level converter for execution; the present invention can coordinate control when the multi-level converter is in a low voltage ride-through mode due to an AC short-circuit fault through the constructed control strategy, and effectively improve the transient power angle stability of the multi-machine system; and solves the technical problem of how to improve the transient power angle stability of the multi-machine system in the multi-flexible DC feed-in power grid.

[0175] See also Figure 5 , Figure 5 This 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 includes: a memory 401 and a processor 402, wherein the memory 402 stores a computer program; when the computer program is executed by the processor 402, the processor 402 executes a control method for multiple flexible direct current feed-in grids as in any of the above embodiments.

[0177] The memory 401 may 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 a program code 413 for executing any method step in the above method. For example, the storage space 403 for the program code may include individual program codes 413 for implementing the various steps in the above method, respectively. These program codes may be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards or floppy disks. The program code may be compressed, for example, in an appropriate form. When these codes are run by a computing and processing device, the computing and processing device performs the various steps in the method described above. These program codes may be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards or floppy disks. The program code may be compressed, for example, in an appropriate form. When these codes are executed by a computing and processing device, the computing and processing device is caused to execute each step of the control method for multiple flexible DC feed-in power grids 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, the control method for multiple flexible direct current feed-in grids as in any of the above embodiments is implemented.

[0179] Embodiment 6 of the present invention further provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions, wherein when the program instructions are executed by a computer, the computer executes a control method for a multi-flexible DC feed-in power grid as 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 aforementioned method embodiments and will not be repeated here.

[0181] In the several embodiments provided in the present 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 only schematic. For example, the division of units is only a logical function division. There may be other division methods in actual implementation. 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 mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

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

[0183] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may 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 the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0185] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for multiple flexible direct current feed-in power grids, characterized in that: include: In response to a control request instruction for a multiple flexible DC feed-in power grid, obtaining power grid operation data of the multiple flexible DC feed-in power grid; Constructing a numerical simulation model of the multi-flexible direct current feed-in power grid, and performing short-circuit fault simulation on the numerical simulation model to obtain active power data; Constructing a motion equation of the multi-flexible direct current fed into a power grid, and solving it using the active power data and the power grid operation data to obtain a critical permeability of each multi-level converter in the multi-flexible direct current; When a short circuit fault occurs in the multi-level flexible DC feed-in power grid, a control strategy of each multilevel converter is matched in a strategy library by using the critical permeability and the power grid operation data, wherein the control strategy is used to perform active current control on the multilevel converter; The matched control strategies of each multilevel converter are sent to each of the multilevel converters for execution.

2. The control method for multiple flexible DC feed-in power grids according to claim 1, characterized in that: The constructing of the numerical simulation model of the multi-flexible DC feed-in power grid and performing short-circuit fault simulation on the numerical simulation model to obtain active power data includes: Constructing a numerical simulation model of the multi-flexible direct current feed-in power grid; selecting a control section of the numerical simulation model; Inputting operation control parameters for simulating AC short circuit faults on the control section of the numerical simulation model, performing time domain simulation on the numerical simulation model, and outputting active power data of the multilevel converter; The control section includes a power transmission channel between a sending end and a receiving end formed by a connecting line of a preset electrical section in the multi-flexible DC feed-in power grid.

3. The control method for multiple flexible DC feed-in power grids according to claim 1, characterized in that: The control strategy is any one of the following three control strategies; A1. Adopting a fixed active power control mode and keeping the absolute value of the first active current smaller than the active current threshold; The fixed active power control mode is that the synchronous generator in the multi-flexible DC feed-in power grid outputs a constant active power; The first active current is the operating active current of the multi-flexible DC feed-in power grid in the fixed active power control mode; A2. Controlling the multilevel converter by using a second active current, where the second active current is a ratio of the first active current to a preset current coefficient; A3. Using a preset third active current to control the multilevel converter.

4. The control method for multiple flexible DC feed-in power grids according to claim 3 is characterized in that: The using the critical permeability and the grid operation data to match the control strategy of each multilevel converter in the strategy library includes: When the critical permeability of the multilevel converter at the sending end and the grid operation data meet a preset first regulation condition, the control strategy A3 is matched as the control strategy of the multilevel converter; When the critical permeability of the multilevel converter at the receiving end and the grid operation data meet a preset first regulation condition, the control strategy A1 is matched as the control strategy of the multilevel converter; When the critical permeability of the multilevel converter at the sending end and the grid operation data meet the preset second regulation condition, the control strategy A2 is matched as the control strategy of the multilevel converter; When the critical permeability of the multilevel converter at the receiving end and the grid operation data meet a preset second regulation condition, the control strategy A2 is matched as the control strategy of the multilevel converter.

5. The control method for multiple flexible DC feed-in power grids according to claim 4, characterized in that: The grid operation data includes converter penetration rate; The preset first control condition is specifically that the critical permeability is greater than the preset first threshold, or the critical permeability is less than the preset first threshold and the converter permeability is greater than the preset second threshold and the converter permeability is less than the critical permeability; The preset second control condition is specifically that the critical permeability is less than the preset first threshold, the converter permeability is greater than the critical permeability, and the converter permeability is less than the preset first threshold.

6. A control system for multiple flexible DC feed-in power grids, characterized in that: include: A response module, used for responding to a control request instruction for a multi-flexible DC feed-in power grid, and acquiring power grid operation data of the multi-flexible DC feed-in power grid; A simulation module, used for constructing a numerical simulation model of the multi-flexible direct current feed-in power grid, and performing short-circuit fault simulation on the numerical simulation model to obtain active power data; A solution module, used for constructing the motion equation of the multi-flexible direct current fed into the power grid, and solving it by using the active power data and the power grid operation data to obtain the critical permeability of each multi-level converter in the multi-flexible direct current; A strategy module, used for matching the control strategy of each multilevel converter in the strategy library by using the critical permeability and the grid operation data when a short circuit fault occurs in the multi-level flexible DC feed-in grid, wherein the control strategy is used to perform active current control on the multilevel converter; The control module is used to send the matched control strategies of each multilevel converter to each of the multilevel converters for execution.

7. The control system of multiple flexible DC feed-in power grids according to claim 6, characterized in that: The simulation module comprises: A model building submodule, used for building a numerical simulation model of the multi-flexible DC feed-in power grid; A section selection submodule, used for selecting a control section of the numerical simulation model; A time domain simulation submodule, used for inputting operation control parameters for simulating AC short circuit faults on the control section of the numerical simulation model, performing time domain simulation on the numerical simulation model, and outputting active power data of the multilevel converter; The control section includes a power transmission channel between a sending end and a receiving end formed by a connecting line of a preset electrical section in the multi-flexible DC feed-in power grid.

8. An electronic device, characterized in that: It comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the control method for multiple flexible direct current feed-in grids as described in any one of claims 1 to 5.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the control method for multiple flexible direct current feed-in grids as described in any one of claims 1 to 5 is implemented.

10. A computer program product, characterized in that The computer program product comprises a computer program stored on a non-transitory computer-readable storage medium, wherein the computer program comprises program instructions, wherein when the program instructions are executed by a computer, the computer executes the control method for a multi-flexible DC feed-in power grid as described in any one of claims 1 to 5.

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