Method, system and equipment for adjusting fusion coefficient in converter network following-network construction fusion control, and medium

Abstract

The invention provides a method, a system and equipment for adjusting a fusion coefficient in converter network following-network construction fusion control, and a medium. The method comprises the steps of calculating a target fusion coefficient according to a grid-connected point short-circuit ratio; when the deviation between the current fusion coefficient and the target fusion coefficient exceeds the maximum deviation range, entering an adjustment process of the fusion coefficient in converter following network-constructing network fusion control; dynamically updating the current fusion coefficient every predetermined duration, wherein the step of dynamically updating the current fusion coefficient comprises the following steps: acquiring the sampling quantity of a main circuit formed by the flexible DC converter and a power grid connected with the flexible DC converter every predetermined duration; determining a current fusion coefficient change rate according to the sampling amount and the current fusion coefficient and based on a time-varying relationship between the fusion coefficient change rate and the grid-connected point current change rate; integrating the current fusion coefficient change rate to obtain an updated fusion coefficient; and performing network following-network construction fusion control on the converter based on the updated fusion coefficient until the deviation is within the maximum deviation range.

Description

Technical Field

[0001] This application relates to the field of converter control strategy technology, and in particular to a method, system, device and medium for adjusting the fusion coefficient in converter and grid-network fusion control. Background Technology

[0002] In recent years, an increasing number of large-scale renewable energy generation projects have been transmitted to the outside world via flexible DC (Voltage Source Converter - High Voltage Direct Current, VSC-HVDC). Currently, flexible DC converters widely adopt the grid-following (GFL) control strategy and rely on phase-locked loops (PLLs) to maintain synchronization with the grid. GFL technology is mature, has a fast power response speed, and is suitable for scenarios with strong grids. However, with the increase in the proportion of renewable energy generation, the short circuit ratio (SCR) at the grid connection point decreases, and the grid strength weakens, the applicability of PLLs faces significant challenges and may cause converter power oscillations or even instability. To improve the stable operation capability under weak grid conditions, researchers have proposed a grid-forming (GFM) control strategy. Through a power synchronization loop (PSL), the converter autonomously constructs its voltage and frequency, exhibiting voltage source characteristics and possessing a certain degree of active support capability. However, GFM also suffers from problems such as slow power response and difficulty in coordinating multiple units in parallel; furthermore, under strong grid conditions, GFM mode also carries the risk of oscillation and instability. Given that GFL is more suitable for strong grids and GFM is more suitable for weak grids, and both adopt similar "power loop + current loop" control structures, the industry has proposed using grid-connected and grid-structured integrated control for flexible DC converters to improve their adaptability to different grid intensities.

[0003] In this type of fusion control, the synchronization angle and current reference values ​​generated by the GFL and GFM branches often differ significantly. When the fusion coefficient changes abruptly, it causes a synchronous change in the synchronization angle and current reference, leading to severe fluctuations in the converter current and even triggering overcurrent protection, threatening equipment safety. For example, when a large-scale disconnection of renewable energy sources occurs near the flexible DC converter station, causing a sudden drop in SCR, the change in the fusion coefficient approaches a step, and the converter's control mode is approximately switched instantaneously from GFL to GFM, posing a significant safety and stability risk. Therefore, although the transient process of fusion coefficient adjustment is short, it is crucial to ensure a smooth transition of the converter and avoid significant current spikes. Summary of the Invention

[0004] The purpose of this application is to provide a method, system, device and medium for adjusting the fusion coefficient in converter and grid-to-grid fusion control, which can solve at least one of the technical problems mentioned in the prior art.

[0005] One aspect of this application provides a method for adjusting the fusion coefficient in converter-grid-network integration control. The adjustment method includes: obtaining the grid connection point short-circuit ratio; calculating a target fusion coefficient according to the grid connection point short-circuit ratio and grid-network-network adaptive integration control rules; when the deviation between the current fusion coefficient and the target fusion coefficient exceeds a maximum deviation range, entering an adjustment process for the fusion coefficient in converter-grid-network integration control; during the adjustment process, dynamically updating the current fusion coefficient every predetermined time interval, including: obtaining a sample quantity of the main circuit consisting of the flexible DC converter and the grid connected to the flexible DC converter every predetermined time interval; determining the current fusion coefficient change rate based on the sample quantity and the current fusion coefficient, and based on a pre-established time-varying relationship between the fusion coefficient change rate and the grid connection point current change rate; integrating the current fusion coefficient change rate to obtain an updated fusion coefficient; and performing grid-network-network integration control on the converter based on the updated fusion coefficient until the deviation between the current fusion coefficient and the target fusion coefficient is within the maximum deviation range.

[0006] Furthermore, the time-varying relationship between the rate of change of the fusion coefficient and the rate of change of the grid connection point current includes a linear time-varying state equation with the first derivative of the grid connection point current amplitude as the state variable, the rate of change of the fusion coefficient as the input variable, and the second derivative of the grid connection point current amplitude as the output variable.

[0007] Furthermore, the expression for the linear time-varying state equation is: , in, , in, , in, The second derivative of the current amplitude at the grid connection point; The current amplitude at the grid connection point; The fusion coefficient; The rate of change of the fusion coefficient; The difference in synchronization angle; The synchronization angle of the power grid; This is from the perspective of synchronization after the integration of the network and the network structure; The synchronous angular velocity of the power grid; The angular velocity is the synchronization velocity after the network is integrated with the network structure; the superscript in the formula above... sThis indicates that the coordinate system used in the expression is based on the synchronization angle of the power grid. of; superscript h This means that the coordinate system used in the expression is based on the merged synchronization angle. Based on; , The corresponding synchronization angles are based on the power grid. The d-axis and q-axis voltages of the AC output port of the converter in the coordinate system; , They respectively adopted the synchronization angle after fusion The d-axis and q-axis voltages of the AC output port of the converter in a coordinate system with as the reference. To adopt a grid-based synchronization angle The grid voltage in the coordinate system; , The corresponding synchronization angles are based on the power grid. The converter's d-axis and q-axis currents in the coordinate system; , They respectively adopted the synchronization angle after fusion The converter's d-axis and q-axis currents in a coordinate system with d as the reference. This represents the equivalent inductance from the AC output port of the converter to the power grid, where The equivalent connection inductance of the converter, The equivalent inductance of the line; , These are the proportional and integral coefficients of the current inner-loop PI controller, respectively. and These are the synchronization angles generated by the network tracking and network construction controls, respectively. and These are the synchronous angular velocities generated by the net-following and net-building controls, respectively. and These are the d-axis current reference values ​​for wire mesh and wire mesh control, respectively. and These are the reference values ​​for the q-axis currents of the wire mesh and the wire mesh control, respectively. and These are the d-axis and q-axis current reference values ​​after the fusion of the ground network and the structural network, respectively.

[0008] Furthermore, the second derivative of the grid connection point current amplitude is obtained by: obtaining the first derivative of the grid connection point current amplitude based on the sampling amount; and obtaining the second derivative of the grid connection point current amplitude by PI control based on the error between the first derivative of the grid connection point current amplitude and the reference value of the first derivative of the grid connection point current amplitude.

[0009] Furthermore, the expression for the first derivative of the grid connection point current amplitude is: , in, It is the first derivative of the current amplitude at the grid connection point.

[0010] Another aspect of this application provides a computer device. The computer device includes a memory, a processor, and a computer program stored in the memory, the processor executing the computer program to implement the steps of the method for adjusting the convergence coefficient in converter-grid convergence control as described above.

[0011] Another aspect of this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method for adjusting the fusion coefficient in converter-grid fusion control as described above.

[0012] Another aspect of this application provides a system for adjusting the fusion coefficient in the grid-connection fusion control of a converter. The system includes a main circuit, a grid-connection fusion control strategy module, a switching determination module, and a fusion coefficient update module. The main circuit consists of a flexible DC converter and the grid to which the flexible DC converter is connected; the grid-connection fusion control strategy module is connected to the main circuit and is used to calculate the target fusion coefficient according to the grid connection point short-circuit ratio and the grid-connection adaptive fusion control rules, and to perform grid-connection fusion control based on the fusion coefficient, ultimately generating a switching drive signal to control the flexible DC converter; wherein, the system has a steady state and a regulating state, and the switching determination module is used to determine the deviation between the current fusion coefficient and the target fusion coefficient. When the deviation exceeds the maximum deviation range, the switching determination module is used to initiate the switching control. The fusion coefficient update module is used to acquire the sampled quantity of the main circuit at predetermined intervals. Based on the sampled quantity and the current fusion coefficient, and based on the time-varying relationship between the fusion coefficient change rate and the grid connection point current change rate established in advance, the module determines the current fusion coefficient change rate. The module integrates the current fusion coefficient change rate to obtain the updated fusion coefficient, which is then sent to the grid-connection fusion control strategy module. When the deviation is within the maximum deviation range, the switching determination module is used to shut down the fusion coefficient update module, and the adjustment system enters a steady state.

[0013] Furthermore, the time-varying relationship between the rate of change of the fusion coefficient and the rate of change of the grid connection point current includes a linear time-varying state equation with the first derivative of the grid connection point current amplitude as the state variable, the rate of change of the fusion coefficient as the input variable, and the second derivative of the grid connection point current amplitude as the output variable. The fusion coefficient update module includes a sampling quantity acquisition module, a fusion coefficient rate of change acquisition module, a first selection switch, and an integrator. The sampling quantity acquisition module is used to perform variable calculations based on the sampling quantity of the main circuit and the current fusion coefficient at predetermined intervals, and output the first derivative of the grid-connected point current amplitude, the first time-domain variable, and the second time-domain variable; the fusion coefficient change rate acquisition module is used to determine the current fusion coefficient change rate based on the first derivative of the grid-connected point current amplitude, the first time-domain variable, the second time-domain variable, and the current fusion coefficient, and based on the linear time-varying state equation; the fusion coefficient change rate acquisition module is connected to the integrator through the first selection switch; the switching determination module is used to control the first selection switch, wherein, when the adjustment system is in a steady state, the switching determination module controls the first selection switch to a first state, and the input of the integrator is forced to 0; when the adjustment system is in an adjustment state, the switching determination module controls the first selection switch to a second state, and the input of the integrator is connected to the output of the fusion coefficient change rate acquisition module.

[0014] Further, the fusion coefficient change rate acquisition module includes a first subtractor, a second selection switch, a PI controller, and a divider. The first subtractor receives the first derivative of the grid-connected point current amplitude and a reference value of the first derivative of the grid-connected point current amplitude output by the sampling acquisition module. The first subtractor is connected to the PI controller via the second selection switch. The switching determination module controls the second selection switch. When the adjustment system is in a steady state, the switching determination module controls the second selection switch to a first state, and the input of the PI controller is forced to 0. When the adjustment system is in an adjustment state, the switching determination module controls the second selection switch to a second state, and the input of the PI controller is connected to the output of the first subtractor. The second subtractor receives the output of the PI controller and the first time-domain variable output by the sampling acquisition module. The divider divides the output of the second subtractor by the second time-domain variable output by the sampling acquisition module to obtain the current fusion coefficient change rate.

[0015] Furthermore, the formulas for calculating the first time-domain variable, the second time-domain variable, and the first derivative of the grid-connected point current amplitude are as follows: , , in, This is the first time-domain variable; This is the second time-domain variable; The first derivative of the current amplitude at the grid connection point is given by [the first derivative of the first derivative of the second derivative of the third derivative , in, The second derivative of the current amplitude at the grid connection point; This is the first derivative of the current amplitude at the grid connection point; The current amplitude at the grid connection point; The fusion coefficient; The rate of change of the fusion coefficient; The difference in synchronization angle; The synchronization angle of the power grid; This is from the perspective of synchronization after the integration of the network and the network structure; The synchronous angular velocity of the power grid; The angular velocity is the synchronization velocity after the network is integrated with the network structure; the superscript in the formula above... s This indicates that the coordinate system used in the expression is based on the synchronization angle of the power grid. of; superscript h This means that the coordinate system used in the expression is based on the merged synchronization angle. Based on; , The corresponding synchronization angles are based on the power grid. The d-axis and q-axis voltages of the AC output port of the converter in the coordinate system; , They respectively adopted the synchronization angle after fusion The d-axis and q-axis voltages of the AC output port of the converter in a coordinate system with as the reference. To adopt a grid-based synchronization angle The grid voltage in the coordinate system; , The corresponding synchronization angles are based on the power grid. The converter's d-axis and q-axis currents in the coordinate system; , They respectively adopted the synchronization angle after fusion The converter's d-axis and q-axis currents in a coordinate system with d as the reference. This represents the equivalent inductance from the AC output port of the converter to the power grid, where The equivalent connection inductance of the converter, The equivalent inductance of the line; , These are the proportional and integral coefficients of the current inner-loop PI controller, respectively. and These are the synchronization angles generated by the network tracking and network construction controls, respectively. and These are the synchronous angular velocities generated by the net-following and net-building controls, respectively. and These are the d-axis current reference values ​​for wire mesh and wire mesh control, respectively. and These are the reference values ​​for the q-axis currents of the wire mesh and the wire mesh control, respectively. and These are the d-axis and q-axis current reference values ​​after the fusion of the ground network and the structural network, respectively.

[0016] In one or more embodiments of this application, the method, system, device, and medium for adjusting the fusion coefficient in converter-grid-network fusion control can enter an adjustment state when the deviation between the current fusion coefficient and the target fusion coefficient exceeds the maximum deviation range. During the adjustment process, a closed-loop constraint can be implemented on the rate of change of the fusion coefficient, so that the fusion coefficient can transition controllably from the current value to the target fusion coefficient, suppressing transient surges and drops in the amplitude of the grid connection point current, and achieving stable switching between strong and weak grids. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the main circuit and the network-to-network fusion control strategy module according to an embodiment of this application.

[0018] Figure 2 This is a block diagram of the current inner loop control according to an embodiment of this application.

[0019] Figure 3 This is a schematic diagram of the adjustment system for the fusion coefficient in the converter and grid-to-grid fusion control according to an embodiment of this application.

[0020] Figure 4 This is a flowchart illustrating a method for adjusting the fusion coefficient in converter and grid-to-grid fusion control according to an embodiment of this application.

[0021] Figure 5 This is a schematic block diagram of a computer device 500 according to an embodiment of this application.

[0022] Figure 6 This application provides a fusion control method for adjusting the fusion coefficient in an additional fusion coefficient adjustment stage. and its rate of change The curve.

[0023] Figure 7 The current vector magnitude curves of fusion control with additional fusion coefficient adjustment and conventional fusion control according to one embodiment of this application are given.

[0024] Figure 8Additional fusion coefficients are given in one embodiment of this application. The active power curves of the converter under regulated fusion control and conventional fusion control.

[0025] Figure 9 Additional fusion coefficients are given in one embodiment of this application. The reactive power curves of the converter under regulated fusion control and conventional fusion control.

[0026] Figure 10 The fusion control method with additional fusion coefficient adjustment according to another embodiment of this application is given, showing the curves of the fusion coefficient and its rate of change in the fusion coefficient adjustment stage.

[0027] Figure 11 The current vector magnitude curves of fusion control with additional fusion coefficient adjustment and conventional fusion control according to another embodiment of this application are given.

[0028] Figure 12 Curves of converter active power for fusion control with additional fusion coefficient adjustment and conventional fusion control according to another embodiment of this application are provided.

[0029] Figure 13 The converter reactive power curves for fusion control with additional fusion coefficient adjustment and conventional fusion control according to another embodiment of this application are given. Detailed Implementation

[0030] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses consistent with some aspects of this application as detailed in the appended claims.

[0031] This application addresses the integration coefficient of flexible DC converters in grid-to-grid integrated control. When the grid strength changes abruptly, near-step changes are likely to occur, causing the synchronization angle and current reference value in the grid-connected control branch and the grid-building control branch to jump synchronously, thereby affecting the grid connection point current. To address the problem of transient spikes and even overcurrent protection triggering, a method is proposed using the first derivative of the grid-connected current amplitude. For explicit constraints, the second derivative of the grid connection point current amplitude is used. This is a method for adjusting the fusion coefficient of equivalent channel quantity.

[0032] The following detailed description, with reference to the accompanying drawings, outlines the method, system, equipment, and medium for adjusting the fusion coefficient in the converter-grid convergence control of this application. Unless otherwise specified, the features described in the following embodiments and implementations can be combined with each other.

[0033] Figure 1 This document discloses a schematic diagram of the topology of the main circuit 100 according to an embodiment of this application and the network-network fusion control strategy module 200 it employs. (See attached diagram.) Figure 1 As shown, the main circuit 100 consists of a flexible DC converter 110 and the power grid to which the flexible DC converter 110 is connected. The flexible DC converter 110 adopts a modular multilevel converter (MMC).

[0034] The grid-connection and grid-building fusion control strategy module 200 of the flexible DC converter 110 mainly includes a synchronization angle fusion link, a current command fusion link, and a current control inner loop. The grid-connection and grid-building fusion control strategy module 200 includes a power outer loop for grid-connection control and a power outer loop for grid-building control.

[0035] The grid-connection and grid-building integrated control strategy module 200 collects the grid connection point voltage and current. After power calculation by the power calculation module 201, it outputs active power and reactive power. The power outer loops of grid-connection control and grid-building control respectively generate their respective synchronization angle and current reference values. Specifically, in the power outer loop of grid-connection control, the phase-locked loop 211 obtains the synchronization angular velocity of grid-connection control based on the grid connection point voltage. Synchronous angular velocity with network control The synchronization angle for network control is obtained after integrator 212. Active power P and active power reference value P ref The difference between the reactive power Q and the reactive power reference value Q ref The difference is used by PI controllers 213 and 214 to obtain the reference values ​​of the d-axis and q-axis currents for grid control. , In the power outer loop of the grid control system, the active power P and the active power reference value P ref The difference is passed through the active power-frequency (Pf) stage to obtain the synchronous angular velocity for grid control. Reactive power Q and reactive power reference value Q ref The difference is processed through a reactive power-voltage (QU) circuit to obtain the voltage amplitude reference value for grid control; the voltage amplitude reference value for grid control and the synchronization angular velocity for grid control... The d-axis and q-axis current reference values ​​for network control are obtained through a virtual impedance circuit. , Then, the synchronous angular velocity of the network control. The synchronization angle for network control is obtained after integrator 222. The fusion coefficient between network control and network construction control is: Synchronization angle after fusion Used for rotational coordinate transformation, fused current reference value , (That is, the current command output from the outer power loop to the inner current loop) serves as the target value for the converter output current.

[0036] The expression for the synchronization angle fusion stage is: (1) in, The synchronized angle after fusion; and These are the synchronization angles generated by network control and network construction control, respectively. and These are the synchronization angular velocities generated by network tracking control and network construction control, respectively; fusion coefficients The value range is [0, 1].

[0037] The reference values ​​for the d-axis and q-axis currents generated by the current command fusion stage are: (2) Among them, the upper right corner h This means that the coordinate system used in the expression is based on the merged synchronization angle. Based on; and These are the reference values ​​for the d-axis and q-axis currents after fusion; and These are the d-axis and q-axis current reference values ​​generated under GFL control, respectively. and These are the d-axis and q-axis current reference values ​​generated under GFM control, respectively.

[0038] d-axis and q-axis current reference values ​​generated by the current command fusion stage , The d-axis and q-axis voltage reference values ​​are obtained through the inner current loop. , Then, the d-axis and q-axis voltage reference values. , After coordinate transformation from the dq (two-phase rotating) coordinate system to the abc (three-phase stationary) coordinate system and PWM modulation, a switching drive signal is generated to control the flexible DC converter 110 of the main circuit 100.

[0039] Synchronization angle caused by network following and network construction control and They are different; current reference value. and as well as and They are also different. Fusion coefficient The faster the change, the faster the synchronization angle after fusion. and current reference value , The faster the change, the more important it is to maintain the synchronization angle generated by the network and network control. and They are different; current reference value. and , and When there are significant differences, the fusion coefficient Rapid changes in current mean coordinate transformation and significant disturbances in the inner current loop. In this case, although the power command of the outer control loop maintains its original stable state, the flexible DC converter 110 will still enter a transient process of rapid current oscillation.

[0040] The following will detail the rate of change of the fusion coefficient. The mechanism of influence on transient current is investigated, and based on this mechanism, the rate of change of the fusion coefficient is pre-constructed. The time-varying relationship between the current at the grid connection point and the current change rate.

[0041] To study the rate of change of the fusion coefficient To understand the impact of current variations, a mathematical model of the rate of change of current must first be established in the grid synchronous dq coordinate system. When grid losses are neglected, the flexible DC converter 110 operates at the grid phase angle... The grid-connected current in the dq coordinate system with the synchronization angle The dynamic equation can be written as: (3) In the formula of this application, the superscript 's' indicates that the coordinate system is based on the synchronization angle of the power grid. of; , To adopt a grid-based synchronization angle The d-axis and q-axis voltages of the converter's AC output port in the coordinate system. To adopt a grid-based synchronization angle The grid voltage in the coordinate system; , To adopt a grid-based synchronization angle The converter's d-axis and q-axis currents in the coordinate system. , This represents the rate of change of the d-axis and q-axis currents of the converter; The synchronous angular velocity of the power grid. This represents the equivalent inductance from the AC output port of the converter to the power grid, where The equivalent connection inductance of the converter, This is the equivalent inductance of the line.

[0042] In the fused synchronous dq coordinate system, the current dynamic equation of the converter can be written as: (4) In this application's formula, the superscript 'h' indicates that the coordinate system used in the expression is based on the fused synchronization angle. Based on; , To adopt the fused synchronization angle The converter's d-axis and q-axis currents in a coordinate system with d as the reference. , To adopt the fused synchronization angle The d-axis and q-axis voltages of the converter's AC output port in a coordinate system with as the reference. Defined as the synchronous angular velocity after the fusion of the network and the network structure.

[0043] Because the dq coordinate system used in converter control is not the synchronous angle of the power grid. It is not about the synchronization angle after the network and network construction are integrated. Therefore, it is necessary to write out the relationship between physical quantities in two coordinate systems. Let the difference between the two synchronization angles be denoted as... So for vectors ,have: (5) in, P and P -1 These represent the Park transformation and inverse Park transformation matrices, respectively.

[0044] According to formula (5), the formula (3) and use and By substitution, we can obtain: (6) in, , These are the first derivatives of the d-axis and q-axis currents of the converter, respectively.

[0045] Taking the derivative of the above equation, we can further obtain: (7) in, , These are the second derivatives of the d-axis and q-axis currents of the converter, respectively; the rate of change of the synchronization angle difference. From the synchronization angle fusion process, we have: (8) Ignoring drive signal delay and converter non-ideal characteristics, the d-axis and q-axis voltages at the AC ports of the converter are assumed to be... , Equal to the reference values ​​of the d-axis and q-axis voltages at the AC ports of the converter. , Therefore, the rate of change of AC port voltage of the converter can be considered to come from the current command fusion link and the current control inner loop.

[0046] Figure 2 A current inner loop control block diagram of one embodiment of this application is disclosed. For example... Figure 2 As shown, , They respectively adopted the synchronization angle after fusion The voltages along the d-axis and q-axis of the grid connection point in a coordinate system with as the reference. , These are the proportional and integral coefficients of the current inner-loop PI controller 323, respectively. According to... Figure 2 The current inner loop control strategy shown has the following: (9) Considering that the time scale of the power outer loop control is much larger than that of the current inner loop, and the rate of change of the converter grid connection point voltage is also slower, the derivative of formula (9) is: (10) Substituting formula (4) into the above formula, we get: (11) Substituting equations (3), (8), and (11) into equation (7), and rearranging, we obtain the dynamic equation for the rate of change of converter current as follows: (12) in, As can be seen from formula (12), the rate of change of converter current is affected by the rate of change of the fusion coefficient. The fusion coefficient is directly affected by the controller parameters, main circuit parameters, and instantaneous voltage and current values. In different grid-to-grid control strategies, the fusion coefficient... The different ways in which the current changes affect its rate of change are also different. For example, in switching control and without adjusting the rate of change of the fusion coefficient... In controlled fusion control, the instantaneous change rate of the fusion coefficient during SCR variation. As the current approaches infinity, the second derivative of the current also approaches infinity, which in turn causes large transient fluctuations in the current.

[0047] The above analysis shows that the fusion coefficient Adjusting the rate of change in the transient process can directly affect the second derivative of the current, thereby suppressing the transient current. However, the adjustment method varies with different control strategies and operating conditions and is difficult to express analytically. An excessively large rate of change in the fusion coefficient... Excessive scalar coefficients can lead to large current fluctuations and ineffective suppression; conversely, excessively small scalar coefficients may result in prolonged transient processes, affecting system stability. Therefore, this application proposes a fusion coefficient adjustment method based on the time-varying relationship between the fusion coefficient change rate and the grid connection point current change rate. This method adjusts the fusion coefficient change rate... Suppress transient currents.

[0048] When considering overcurrent in a device, the magnitude of the current is usually of greater concern, and its expression is: (13) By taking the second derivative of the above equation and substituting formulas (3) and (12) to eliminate the first and second derivative terms of the d-axis and q-axis currents, the time-varying relationship between the rate of change of the fusion coefficient and the rate of change of the grid connection point current can be obtained.

[0049] Specifically, the time-varying relationship between the rate of change of the fusion coefficient and the rate of change of the grid-connected current is a linear time-varying state equation with the first derivative of the grid-connected current amplitude as the state variable, the rate of change of the fusion coefficient as the input variable, and the second derivative of the grid-connected current amplitude as the output variable, as shown in formula (14). It is the first time-domain variable, used to describe the rate of change of the fusion coefficient. Second derivative with respect to the magnitude of the grid-connected current The equivalent time-varying gain, It is the second time-domain variable, used to represent the rate of change of the fusion coefficient. Irrelevant equivalents.

[0050] (14) in, in, Formula (14) can actually be regarded as the rate of change of current. As a state, the rate of change of the fusion coefficient The input is a linear time-varying state equation. The first time-domain variable... Second time-domain variable Although the forms are relatively complex, they are all calculable. Specifically, the main circuit parameters include, for example, the equivalent inductance from the AC output port of the converter to the power grid. Equivalent connection inductance of the converter Synchronous angular velocity of the power grid The known quantity is the PI parameter of the 323 inner-loop PI controller. , It is a preset, synchronized angular velocity after network integration and network construction. It is caused by the synchronization angle fusion process; the difference in synchronization angle is due to... The voltage and current can be calculated based on the fused reference angle. , , , , This was obtained through actual measurement. Based on this, this application proposes a closed-loop regulator with the current change rate as the state variable, which controls the change rate of the fusion coefficient. Control measures are implemented to suppress transient currents.

[0051] This application provides a system 300 for adjusting the fusion coefficient in converter and grid-to-grid fusion control. Figure 3 A schematic diagram of a converter and grid-to-grid convergence control system 300 according to an embodiment of this application is shown. Figure 3 As shown, the system 300 for adjusting the fusion coefficient in the converter-grid-network fusion control may include a main circuit 100, a grid-network fusion control strategy module 200, a switching determination module 301, and a fusion coefficient update module 302.

[0052] The grid-connection-network integration control strategy module 200 is connected to the main circuit 100. The grid-connection-network integration control strategy module 200 can calculate the target integration coefficient based on the short-circuit ratio (SCR) at the grid connection point. .

[0053] The rule governing the variation of the target fusion coefficient with SCR in this application (i.e., the adaptive fusion control rule between network connection and network construction) is as follows: (15) in, , These are the two threshold values ​​for SCR under weak and strong power grids, respectively.

[0054] Therefore, after knowing the short-circuit ratio (SCR) at the grid connection point, the target fusion coefficient can be obtained according to the above formula (15). .

[0055] The grid-connection and grid-building fusion control strategy module 200 can obtain the fusion coefficient of grid-connection and grid-building fusion control based on the grid connection point voltage and current of the main circuit 100 through the grid-connection control power outer loop and the grid-building control power outer loop. Therefore, based on this fusion coefficient Finally, a switching drive signal is generated to drive and control the flexible DC converter 110.

[0056] The adjustment system 300 of this application has a steady state and an adjustment state, and the switching determination module 301 can be used to determine the current fusion coefficient. Between the fusion coefficients with the target The deviation.

[0057] At the current fusion coefficient Fusion coefficient with target When the deviation between them exceeds the maximum deviation range, the switching judgment module 301 can activate the fusion coefficient update module 302, and the adjustment system 300 enters the adjustment state. The fusion coefficient update module 302 is used to acquire the sampling amount of the main circuit 100 at predetermined intervals, and based on the sampling amount and the current fusion coefficient... Based on the pre-established time-varying relationship between the rate of change of the fusion coefficient and the rate of change of the grid connection point current, the current rate of change of the fusion coefficient is determined. ; rate of change of the current fusion coefficient Integrate to obtain the updated fusion coefficient. The data is then sent to the grid-network fusion control strategy module 200. The grid-network fusion control strategy module 200 synthesizes the grid-connection control and network-building control branches in the synchronization angle fusion stage and the current command fusion stage to obtain the fused synchronization angle and the fused current reference value, which are then sent to the current inner loop.

[0058] At the current fusion coefficient Fusion coefficient with target When the deviation between them is within the maximum deviation range, the switching judgment module 301 can shut down the fusion coefficient update module 302 and adjust the system 300 to enter a steady state.

[0059] In some embodiments, the rate of change of the fusion coefficient The time-varying relationship between the current and the rate of change of the grid connection point current includes the first derivative with respect to the magnitude of the grid connection point current. As a state variable, the rate of change of the fusion coefficient The linear time-varying state equation with the second derivative of the grid connection point current amplitude as the input variable is shown in formula (14) above. The fusion coefficient update module 302 may include a sampling quantity acquisition module 310, a fusion coefficient change rate acquisition module 320, a first selection switch 330, and an integrator 340.

[0060] The sampling acquisition module 310 is used to perform variable calculations based on the sampling amount of the main circuit 100 and the current fusion coefficient at predetermined intervals, and outputs the first derivative of the grid connection point current amplitude and the first time-domain variable. and the second time domain variable First time-domain variable Second time-domain variable The calculation formula is shown above.

[0061] The expression for the first derivative of the current amplitude at the grid connection point is: (16) in, It is the first derivative of the current amplitude at the grid connection point.

[0062] The fusion coefficient change rate acquisition module 320 can obtain the first derivative of the current amplitude at the grid connection point. First time domain variable Second time-domain variable Based on the linear time-varying state equation shown in the above formula (14), the current fusion coefficient change rate is determined; the fusion coefficient change rate acquisition module 320 is connected to the integrator 340 through the first selection switch 330.

[0063] The switching determination module 301 can control the first selection switch 330. When the adjustment system 300 is in a steady state, the switching determination module 301 can control the first selection switch 330 to a first state, and the input of the integrator 340 is forced to 0. When the adjustment system 300 is in an adjustment state, the switching determination module 301 can control the first selection switch 330 to a second state, and the input of the integrator 340 is connected to the output of the fusion coefficient change rate acquisition module 320.

[0064] In some embodiments, the sampling acquisition module 310 is used to perform variable calculations based on the sampling amount of the main circuit 100 at predetermined intervals, and output the first derivative of the current amplitude at the grid connection point. First time domain variable and the second time domain variable The fusion coefficient change rate acquisition module 320 may include a first subtractor 321, a second selection switch 322, a PI controller 323, a second subtractor 324, and a divider 325.

[0065] The first subtractor 321 can receive the first derivative of the grid-connected point current amplitude output by the sampling acquisition module 310. and the reference value of the first derivative of the current amplitude at the grid connection point It also outputs a reference value for the first derivative of the grid connection point current amplitude. First derivative with the magnitude of the grid connection point current Error signals between The first subtractor 321 is connected to the PI controller 323 via the second selection switch 322.

[0066] The switching determination module 301 can control the second selection switch 322. When the regulating system 300 is in a steady state, the switching determination module 301 can control the second selection switch 322 to a first state, forcing the input of the PI controller 323 to 0. When the regulating system 300 is in a regulating state, the switching determination module 301 can control the second selection switch 322 to a second state, connecting the input of the PI controller 323 to the output of the first subtractor 321, and the error signal output by the first subtractor 321... The data is fed into the PI controller 323 to obtain the shaped value. It is used to represent the second derivative of the equivalent grid-connected point current amplitude that the closed loop aims to achieve. Total demand.

[0067] The second subtractor 324 can receive the output of the PI controller 323 and the first time-domain variable output by the sampling acquisition module 310. First, feedforward compensation is performed to obtain the required change rate of the fusion coefficient. The second derivative of the equivalent grid-connected current amplitude borne by the channel need .

[0068] Divider 325 can divide the output of second subtractor 324 by the second time-domain variable output by sample acquisition module 310. Perform dynamic inverse calculation to obtain the current rate of change of the fusion coefficient. .

[0069] At the current fusion coefficient Fusion coefficient with target When the deviation exceeds the maximum deviation range, the adjustment system 300 of this application starts to operate, switching the first selection switch 330 and the second selection switch 322 from the first state to the second state, allowing the subsequently generated deviation signal to enter the integrator 340. The adjustment system 300 of this application enters the adjustment state from the steady state, and performs the calculation of the rate of change of the fusion coefficient and the update process of the fusion coefficient.

[0070] When the current fusion coefficient Fusion coefficient with target When the deviation is within the maximum deviation range, the adjustment system 300 of this application ends the adjustment and resets. The ending action includes: changing the first selection switch 330 and the second selection switch 322 from the second state to the first state, so that the input of the integrator 340 is 0 and the PI controller 323 is cleared to zero. Subsequently, the adjustment system 300 of this application enters steady-state monitoring until the conditions for entering the adjustment state are met again.

[0071] In this application, the converter and grid-to-grid convergence control system 300 adjusts the convergence coefficient at the current convergence coefficient. Fusion coefficient with target When the deviation exceeds the maximum deviation range, it can enter the adjustment state. During the adjustment process, the rate of change of the fusion coefficient can be monitored. Implement closed-loop constraints to make the fusion coefficient From current value to target fusion coefficient Achieve controllable transition and suppress grid connection point current amplitude. The transient surges and drops enable stable switching between strong and weak networks.

[0072] Figure 4 This document presents a flowchart illustrating a method for adjusting the fusion coefficient in converter-grid fusion control according to an embodiment of this application. Figure 4 As shown, a method for adjusting the fusion coefficient in converter and grid-to-grid fusion control according to an embodiment of this application may include steps S1 to S6.

[0073] In step S1, the short-circuit ratio (SCR) at the grid connection point is obtained.

[0074] In step S2, the target fusion coefficient can be calculated based on the grid connection point short-circuit ratio (SCR) according to the grid-connection adaptive fusion control rule. .

[0075] In step S3, the current fusion coefficient is compared with the target fusion coefficient. The magnitude of the deviation between them.

[0076] In step S4, at the current fusion coefficient When the deviation from the target fusion coefficient exceeds the maximum deviation range, the fusion coefficient adjustment process in the converter and grid-network fusion control is initiated. During the adjustment process, the current fusion coefficient is dynamically updated every predetermined time interval.

[0077] In some embodiments, step S4 adjusts the current fusion coefficient every predetermined time interval. Dynamic updates may further include steps S41 to S43.

[0078] In step S41, the sampling amount of the main circuit 100 consisting of the flexible DC converter 110 and the power grid connected to the flexible DC converter 110 is acquired at predetermined intervals.

[0079] In step S42, based on the sampling amount and the current fusion coefficient And based on the pre-established rate of change of the fusion coefficient The time-varying relationship between the current change rate at the grid connection point and the current change rate is used to determine the current rate of change of the fusion coefficient. .

[0080] In some embodiments, the rate of change of the fusion coefficient The time-varying relationship between the current at the grid connection point and the rate of change of the grid connection point current includes: using the first derivative of the current amplitude at the grid connection point as the state variable, and the rate of change of the fusion coefficient as the state variable. As the input variable, the second derivative of the current amplitude at the grid connection point is used. The linear time-varying state equation for the output variable is shown in formula (14) above.

[0081] In step S43, the rate of change of the current fusion coefficient is... Integrate to obtain the updated fusion coefficient. .

[0082] In step S5, the updated fusion coefficients obtained in step S4 can be used as a basis. To perform grid-to-grid integration control on the flexible DC converter 110.

[0083] Repeat steps S3 to S5 above until the current fusion coefficient is reached. Fusion coefficient with target The deviation between them is within the range of the maximum deviation.

[0084] When step S3 determines the current fusion coefficient Fusion coefficient with target When the deviation between the two values ​​is within the maximum deviation range, the process proceeds to step S6. In step S6, the process is in a steady state, and no adjustment of the fusion coefficient is performed.

[0085] In some embodiments, the second derivative of the grid-connected point current amplitude is obtained by: obtaining the first derivative of the grid-connected point current amplitude based on the sampling amount; and obtaining the second derivative based on the first derivative of the grid-connected point current amplitude. Reference value of the first derivative of the grid connection point current amplitude error The second derivative of the grid-connected current amplitude is obtained through PI control. .

[0086] This application also provides a computer device. Figure 5A schematic block diagram of a computer device 500 according to one embodiment of this application is shown. Figure 5 As shown, a computer device 500 according to one embodiment of this application includes a processor 501, an internal bus 502, a network interface 503, a memory 504, and a storage device 505, and may also include other hardware required for services. The processor 501 can read the corresponding computer program from the storage device 505 into the memory device 504 and then run it to implement the steps of the method for adjusting the convergence coefficient in the converter and network-to-network convergence control as described above. Of course, in addition to the software implementation, this application does not exclude other implementation methods, such as logic devices or a combination of hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0087] This application also provides a computer-readable storage medium having a computer program stored thereon. When executed by a processor, the computer program implements the steps of the method for adjusting the fusion coefficient in the converter-grid fusion control as described above.

[0088] The following section will use an engineering project as an example to clearly and completely describe the adjustment system and method of the fusion coefficient in the converter-grid fusion control of this application. The specific example below is based on data from a 500kV / 2100MW flexible DC converter station, where the main parameters are shown in Table 1.

[0089] Table 1 Main Parameters To verify the availability of the adjustment method of this application under the condition of SCR reduction, the SCR was set to decrease from an initial value of 16 to 10, 6 and 1.6 at 0.5s, 1s and 1.5s respectively.

[0090] The method for adjusting the fusion coefficient in converter-grid control proposed in this application, when applied in this example, may include the following steps: Step 1, Target Generation: Based on the short-circuit ratio (SCR) information of the grid connection point provided by the upper-level dispatch center, the target fusion coefficient is calculated according to the adaptive fusion control rule described in formula (17). .

[0091] Step 2, Switching Decision: When the current fusion coefficient is detected... and When the deviation exceeds the maximum deviation range, the adjustment system of this application starts to operate, switching the first selection switch and the second selection switch from the first state to the second state, and the adjustment system of this application enters the adjustment state.

[0092] Step 3, Variable Calculation: Calculate the first time-domain variable based on the sampling amount of the main circuit. Second time-domain variable First derivative with the magnitude of the grid connection point current .

[0093] Step 4, Error Construction and PI Shaping: The first derivative reference value of the grid connection point current amplitude is used... The first derivative of the actual grid connection point current amplitude Subtraction construction error signal The error signal The sample is fed into the PI (pipeline initiation) stage for PI shaping to obtain the shaping volume. .

[0094] Step 5, Feedforward cancellation and dynamic inverse calculation: For First, feedforward compensation is performed to obtain the required change rate of the fusion coefficient. The second derivative of the equivalent grid-connected current amplitude borne by the channel Demand, that is And then Perform dynamic inverse calculation to obtain the rate of change of the fusion coefficient. ,Right now .

[0095] Step 6, Integral Update: The rate of change of the fusion coefficients obtained in Step 5 is then updated. As input to the integrator, the rate of change of the fusion coefficient Perform an integral update to obtain the updated fusion coefficient. .

[0096] Step 7, Merge Execution: Execute the updated fusion coefficients. In the input grid-network fusion control strategy module 200, the grid-network fusion control strategy module 200 synthesizes the grid-connection control and network-network control branches according to formula (1) and formula (2) in the synchronization angle fusion link and the current command fusion link, obtains the fused synchronization angle and current reference value and sends it into the current inner loop, and then performs coordinate transformation and PWM modulation to generate switching drive signals to control the flexible DC converter accordingly.

[0097] Step S8, Adjustment End and Reset: When the current fusion coefficient and When the deviation is within the maximum deviation range, the regulation system of this application ends the regulation, sets the integrator input to 0, and clears the PI controller. Subsequently, the regulation system of this application enters steady-state monitoring until the conditions for entering the regulation state are met again, at which point it returns to step 3.

[0098] Based on the above steps, the fusion coefficient of this application can be obtained. Simulation curves of the fusion control of the adjustment.

[0099] Figure 6 This application presents a fusion control method for adjusting the additional fusion coefficient, where the fusion coefficient is adjusted in the fusion coefficient adjustment stage. and its rate of change The curve. For example... Figure 6 As shown, the fusion coefficient and its rate of change The curves are shown as the solid red line and the dashed blue line in the figure, respectively. It can be seen that the fusion coefficient changes with each SCR variation. There was no jump; instead, the change rate was calculated in real time according to the fusion coefficient. Begin transitioning towards the target value, when the fusion coefficient When the target value is reached, the rate of change of the fusion coefficient It becomes 0. It can also be seen that as the SCR decreases from high to low, the rate of change of the fusion coefficient... The amplitude also decreased overall. As the SCR decreased from 16 to 10, the rate of change of the fusion coefficient... The fusion coefficient is approximately between -4 and -5. The transition from 1 to approximately 0.62; the rate of change of the fusion coefficient as the SCR decreases from 10 to 6. The fusion coefficient is approximately between -2 and -3. The transition from 0.62 to approximately 0.19; the rate of change of the fusion coefficient as the SCR decreased from 6 to 1.6. The fusion coefficient is approximately between -1 and -3. The coefficient transitioned from 0.19 to 0. In other words, as the power grid weakens, the adjustment process of the fusion coefficient becomes smoother, which helps to reduce disturbances to the system.

[0100] To enhance the additional fusion coefficient of this application The effects of the adjusted fusion control method and the conventional fusion control method are compared, and the conventional fusion control method is also simulated.

[0101] The following will provide the additional fusion coefficient of this application when the SCR is reduced. A comparison of simulation curves between the regulated fusion control method and the conventional fusion control method.

[0102] Figure 7 The additional fusion coefficients of this application are given. The current vector magnitude curves of the regulated fusion control and the conventional fusion control. (Example) Figure 7 As shown, the additional fusion coefficient of this application The current vector magnitude curves of the regulated fusion control and the conventional fusion control are shown as the solid red line and dashed blue line in the figure, respectively. It can be seen that the steady-state current of the converter is 3.2 kA. Although the conventional fusion control can maintain the stable operation of the converter, when the SCR decreases from 10 to 6, the valley of the transient current drops to 2.1 kA and the peak surges to 3.9 kA; when the SCR decreases from 6 to 1.6, the valley of the transient current drops to 1.8 kA and the peak surges to 3.75 kA. The fusion coefficient is calculated in this application. After adjustment, the transient current valley values ​​in these two cases are approximately 3.2kA and 2.9kA, respectively, and the peak values ​​are approximately 3.2kA and 3.3kA, respectively.

[0103] Figure 8 The additional fusion coefficients of this application are given. The active power curves of the converter under regulated fusion control and conventional fusion control. Figure 9 The additional fusion coefficients of this application are given. The converter reactive power curves for regulated fusion control and conventional fusion control. For example... Figure 8 and Figure 9 As shown, it can be seen that after the transient current is effectively controlled, the power oscillation of the converter is also effectively suppressed, and the maximum active and reactive power fluctuations are reduced from 1300MW and 190MVar to 200MW and 70MVar, respectively.

[0104] Similarly, to verify the usability of the fusion control method for adjusting the additional fusion coefficient in this application under conditions of increased SCR, the SCR was set to increase from an initial value of 1.6 to 6, 10, and 16 at 0.5s, 1s, and 1.5s, respectively. Using the same steps described above, the fusion coefficient of this application can be obtained. Simulation curves of the fusion control of the adjustment.

[0105] Figure 10 This application presents a fusion control method for adjusting the additional fusion coefficient, where the fusion coefficient is adjusted in the fusion coefficient adjustment stage. and its rate of change The curve. For example... Figure 10 As shown, the fusion coefficient and its rate of change The curves are shown as the solid red line and the dashed blue line in the figure, respectively. It can be seen that as the SCR increases from low to high, the rate of change of the fusion coefficient... The amplitude also increased overall. As the SCR increased from 1.6 to 6, the rate of change of the fusion coefficient... The coefficient is approximately between 1 and 3, resulting in a fusion coefficient of approximately 1. The transition from 0 to approximately 0.19; the rate of change of the fusion coefficient as the SCR increases from 6 to 10. The coefficient is approximately between 2 and 3, resulting in a fusion coefficient of approximately 3. The transition from 0.19 to approximately 0.62; the rate of change of the fusion coefficient when the SCR increases from 10 to 16. The coefficient is approximately between 4 and 5, resulting in a fusion coefficient of approximately 5. The coefficient transitioned from 0.62 to 1. In other words, as the power grid strengthens, the integration coefficient... The adjustment process can become increasingly faster, which is beneficial for maximizing the efficiency of the converter.

[0106] Figure 11 The additional fusion coefficients of this application are given. The current vector magnitude curves of the regulated fusion control and the conventional fusion control. (Example) Figure 11 As shown, the additional fusion coefficient of this application The current vector magnitude curves of the regulated fusion control and the conventional fusion control are shown as the solid red line and dashed blue line in the figure, respectively. It can be seen that with the conventional fusion control, when the SCR is increased from 1.6 to 6, the transient current valley drops to 2.3kA and the peak surges to 4.9kA; when the SCR is increased from 6 to 10, the transient current valley is 3.2kA, but the peak surges to 3.7kA. The fusion coefficient is calculated in this application. After adjustment, the transient current valley values ​​in these two cases are approximately 3kA and 3.2kA, respectively, and the peak values ​​are approximately 3.7kA and 3.55kA, respectively.

[0107] Figure 12 The additional fusion coefficients of this application are given. The active power curves of the converter under regulated fusion control and conventional fusion control. Figure 13 The additional fusion coefficients of this application are given. The converter reactive power curves for regulated fusion control and conventional fusion control. For example... Figure 12 and Figure 13 As shown, the power oscillation of the converter was also effectively suppressed, with the maximum active and reactive power fluctuations reduced from 1100MW and 800MVar to 300MW and 100MVar, respectively.

[0108] The above comparison results fully demonstrate the additional fusion coefficient of this application. The effectiveness of the integrated control mechanism ensures that the transient current and power of the converter are kept within a safe range, greatly reducing the risk of triggering overcurrent protection and thus providing a solid theoretical basis for the construction and operation of related projects.

[0109] The method, system, equipment, and medium for adjusting the fusion coefficient in the converter-grid fusion control of this application enable the fusion coefficient adjustment rate to be adaptively adjusted according to the change of converter current, thereby suppressing the sudden increase and drop of transient current and ensuring the smooth transition of the system between different grid intensities.

[0110] The foregoing has provided a detailed description of the method, system, device, and medium for adjusting the fusion coefficient in converter-grid-grid fusion control according to embodiments of this application. Specific examples have been used to illustrate the method, system, device, and medium for adjusting the fusion coefficient in converter-grid-grid fusion control according to embodiments of this application. The descriptions of the embodiments above are only for helping to understand the core ideas of this application and are not intended to limit this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the spirit and principles of this application, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for adjusting the fusion coefficient in converter-grid fusion control, characterized in that, include: Obtain the short-circuit ratio at the grid connection point; The target fusion coefficient is calculated based on the short-circuit ratio at the grid connection point according to the adaptive fusion control rule of grid connection-network structure. When the deviation between the current fusion coefficient and the target fusion coefficient exceeds the maximum deviation range, the process of adjusting the fusion coefficient in the converter and grid-grid fusion control is initiated. During the adjustment of the fusion coefficient, the current fusion coefficient is dynamically updated every predetermined time interval, including: The sampling data of the main circuit consisting of the flexible DC converter and the power grid connected to the flexible DC converter is acquired at predetermined intervals. Based on the sampling amount and the current fusion coefficient, and based on the time-varying relationship between the pre-established fusion coefficient change rate and the grid connection point current change rate, the current fusion coefficient change rate is determined; Integrating the rate of change of the current fusion coefficient yields the updated fusion coefficient; The converter is subjected to grid-to-grid fusion control based on the updated fusion coefficient until the deviation between the current fusion coefficient and the target fusion coefficient is within the maximum deviation range.

2. The adjustment method as described in claim 1, characterized in that, The time-varying relationship between the rate of change of the fusion coefficient and the rate of change of the grid connection point current includes: A linear time-varying state equation with the first derivative of the current amplitude at the grid connection point as the state variable, the rate of change of the fusion coefficient as the input variable, and the second derivative of the current amplitude at the grid connection point as the output variable.

3. The adjustment method as described in claim 2, characterized in that, The expression for the linear time-varying state equation is: , in, , in, , in, The second derivative of the current amplitude at the grid connection point; The current amplitude at the grid connection point; The fusion coefficient; The rate of change of the fusion coefficient; The difference in synchronization angle; The synchronization angle of the power grid; This is from the perspective of synchronization after the integration of the network and the network structure; The synchronous angular velocity of the power grid; The angular velocity is the synchronization velocity after the network is integrated with the network structure; the superscript in the formula above... s This indicates that the coordinate system used in the expression is based on the synchronization angle of the power grid. of; superscript h This means that the coordinate system used in the expression is based on the merged synchronization angle. Based on; , The corresponding synchronization angles are based on the power grid. The d-axis and q-axis voltages of the AC output port of the converter in the coordinate system; , They respectively adopted the synchronization angle after fusion The d-axis and q-axis voltages of the AC output port of the converter in a coordinate system with as the reference. To adopt a grid-based synchronization angle The grid voltage in the coordinate system; , The corresponding synchronization angles are based on the power grid. The converter's d-axis and q-axis currents in the coordinate system; , They respectively adopted the synchronization angle after fusion The converter's d-axis and q-axis currents in a coordinate system with d as the reference. This represents the equivalent inductance from the AC output port of the converter to the power grid, where The equivalent connection inductance of the converter, The equivalent inductance of the line; , These are the proportional and integral coefficients of the current inner-loop PI controller, respectively. and These are the synchronization angles generated by the network tracking and network construction controls, respectively. and These are the synchronous angular velocities generated by the net-following and net-building controls, respectively. and These are the d-axis current reference values ​​for wire mesh and wire mesh control, respectively. and These are the reference values ​​for the q-axis currents of the wire mesh and the wire mesh control, respectively. and These are the d-axis and q-axis current reference values ​​after the fusion of the ground network and the structural network, respectively.

4. The adjustment method as described in claim 3, characterized in that, The second derivative of the grid connection point current amplitude is obtained as follows: The first derivative of the grid connection point current amplitude is obtained based on the sampling amount; The second derivative of the grid-connected current amplitude is obtained by PI control based on the error between the first derivative of the grid-connected current amplitude and the reference value of the first derivative of the grid-connected current amplitude.

5. The adjustment method as described in claim 4, characterized in that, The expression for the first derivative of the current amplitude at the grid connection point is: , in, It is the first derivative of the current amplitude at the grid connection point.

6. A computer device, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method for adjusting the fusion coefficient in the converter-grid fusion control as described in any one of claims 1 to 5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for adjusting the fusion coefficient in the converter-grid fusion control as described in any one of claims 1 to 5.

8. A system for adjusting the fusion coefficient in converter-grid fusion control, characterized in that, This includes the main circuit, the network-to-network fusion control strategy module, the handover determination module, and the fusion coefficient update module. The main circuit consists of a flexible DC converter and the power grid to which the flexible DC converter is connected; The grid-connection-grid integration control strategy module is connected to the main circuit and is used to calculate the target integration coefficient according to the grid connection point short-circuit ratio and the grid-connection-grid adaptive integration control rules, and to perform grid-connection-grid integration control based on the integration coefficient and finally generate a switch drive signal to control the flexible DC converter. The adjustment system has a steady state and an adjustment state. The switching determination module is used to determine the deviation between the current fusion coefficient and the target fusion coefficient. When the deviation exceeds the maximum deviation range, the switching determination module is used to activate the fusion coefficient update module, and the adjustment system enters the adjustment state. The fusion coefficient update module is used to acquire the sampling amount of the main circuit at predetermined intervals, determine the current fusion coefficient change rate based on the sampling amount and the current fusion coefficient, and based on the time-varying relationship between the fusion coefficient change rate and the grid connection point current change rate established in advance; integrate the current fusion coefficient change rate to obtain the updated fusion coefficient and send it to the grid-connection fusion control strategy module; when the deviation is within the maximum deviation range, the switching determination module is used to shut down the fusion coefficient update module, and the adjustment system enters the steady state.

9. The adjustment system as described in claim 8, characterized in that, The time-varying relationship between the rate of change of the fusion coefficient and the rate of change of the grid-connected current includes a linear time-varying state equation with the first derivative of the grid-connected current amplitude as the state variable, the rate of change of the fusion coefficient as the input variable, and the second derivative of the grid-connected current amplitude as the output variable. The fusion coefficient update module includes a sampling acquisition module, a fusion coefficient change rate acquisition module, a first selection switch, and an integrator. The sampling quantity acquisition module is used to perform variable calculations based on the sampling quantity of the main circuit and the current fusion coefficient at predetermined intervals, and output the first derivative of the current amplitude at the grid connection point, the first time domain variable, and the second time domain variable. The fusion coefficient change rate acquisition module is used to determine the current fusion coefficient change rate based on the first derivative of the grid connection point current amplitude, the first time domain variable, the second time domain variable, and the current fusion coefficient, and based on the linear time-varying state equation. The fusion coefficient change rate acquisition module is connected to the integrator via the first selection switch; The switching determination module is used to control the first selection switch. When the adjustment system is in a steady state, the switching determination module controls the first selection switch to a first state, and the input of the integrator is forced to 0. When the adjustment system is in an adjustment state, the switching determination module controls the first selection switch to a second state, and the input of the integrator is connected to the output of the fusion coefficient change rate acquisition module.

10. The adjustment system as described in claim 9, characterized in that, The fusion coefficient change rate acquisition module includes a first subtractor, a second selection switch, a PI controller, a second subtractor, and a divider, wherein... The first subtractor is used to receive the first derivative of the grid-connected point current amplitude and a reference value of the first derivative of the grid-connected point current amplitude output by the sampling acquisition module; the first subtractor is connected to the PI controller through the second selection switch. The switching determination module is used to control the second selection switch. When the adjustment system is in a steady state, the switching determination module controls the second selection switch to a first state, and the input of the PI controller is forced to 0. When the adjustment system is in an adjustment state, the switching determination module controls the second selection switch to a second state, and the input of the PI controller is connected to the output of the first subtractor. The second subtractor is used to receive the output of the PI controller and the first time-domain variable output by the sampling acquisition module; The divider is used to divide the output of the second subtractor by the second time-domain variable output by the sampling acquisition module to obtain the current rate of change of the fusion coefficient.

11. The regulating system as described in claim 10, characterized in that, The formulas for calculating the first time-domain variable, the second time-domain variable, and the first derivative of the grid-connected point current amplitude are as follows: , , in, This is the first time-domain variable; This is the second time-domain variable; The first derivative of the current amplitude at the grid connection point is given by [the first derivative of the first derivative of the second derivative of the third derivative , in, The second derivative of the current amplitude at the grid connection point; This is the first derivative of the current amplitude at the grid connection point; The current amplitude at the grid connection point; The fusion coefficient; The rate of change of the fusion coefficient; The difference in synchronization angle; The synchronization angle of the power grid; This is from the perspective of synchronization after the integration of the network and the network structure; The synchronous angular velocity of the power grid; The angular velocity is the synchronization velocity after the network is integrated with the network structure; the superscript in the formula above... s This indicates that the coordinate system used in the expression is based on the synchronization angle of the power grid. of; superscript h This means that the coordinate system used in the expression is based on the merged synchronization angle. Based on; , The corresponding synchronization angles are based on the power grid. The d-axis and q-axis voltages of the AC output port of the converter in the coordinate system; , They respectively adopted the synchronization angle after fusion The d-axis and q-axis voltages of the AC output port of the converter in a coordinate system with as the reference. To adopt a grid-based synchronization angle The grid voltage in the coordinate system; , The corresponding synchronization angles are based on the power grid. The converter's d-axis and q-axis currents in the coordinate system; , They respectively adopted the synchronization angle after fusion The converter's d-axis and q-axis currents in a coordinate system with d as the reference. This represents the equivalent inductance from the AC output port of the converter to the power grid, where The equivalent connection inductance of the converter, The equivalent inductance of the line; , These are the proportional and integral coefficients of the current inner-loop PI controller, respectively. and These are the synchronization angles generated by the network tracking and network construction controls, respectively. and These are the synchronous angular velocities generated by the net-following and net-building controls, respectively. and These are the d-axis current reference values ​​for wire mesh and wire mesh control, respectively. and These are the reference values ​​for the q-axis currents of the wire mesh and the wire mesh control, respectively. and These are the d-axis and q-axis current reference values ​​after the fusion of the ground network and the structural network, respectively.

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