Switching system small signal safety domain determination method and device

Abstract

The application provides a switching system small signal safety domain determination method and device, the switching system small signal safety domain determination method comprises the following steps: based on the grid-following control model in the grid-connected converter switching system, the grid-forming control model in the grid-connected converter switching system and the full-order small signal state space model, determining the full-order small signal state space equation corresponding to each subsystem; based on the grid strength, determining the target full-order small signal state space equation corresponding to the target subsystem from the full-order small signal state space equation corresponding to each subsystem; and based on the system state matrix in the target full-order small signal state space equation, determining the small signal safety domain of the grid-connected converter switching system. Through the full-order small signal state space equation containing the grid-following type and the grid-forming type control system, the application can reflect the influence of multiple parameters on the small disturbance stability of the system, thereby improving the accuracy of the small signal safety domain of the switching system and further improving the stability of the control system.

Description

Technical Field

[0001] This invention relates to the field of stable control technology for grid-connected converters in new energy sources, and in particular to a method and apparatus for determining the small-signal safety domain of a switching system. Background Technology

[0002] Due to their different synchronization control strategies, grid-connected and grid-connected converters exhibit complementary stability characteristics when integrated into power grids of varying strengths: grid-connected converters rely on phase-locked loops to track the voltage phase at the grid connection point, exhibiting better stability in strong grids but prone to oscillation and instability when integrated into weak grids; grid-connected converters employ power synchronization control strategies, autonomously constructing their internal potential amplitude and phase, resulting in better stability in weak grids but poorer stability when integrated into strong grids. Therefore, grid-connected and grid-connected converters complement each other's advantages and work collaboratively in large-scale renewable energy grid-connected systems.

[0003] Currently, the main control strategies for grid-connected / grid-connected hybrid modes include switching hybrid mode control, which uses grid-connected control under strong grid conditions and grid-connected control under weak grid conditions. However, existing switching hybrid modes, such as the D-segmentation method, consider a limited number of parameters and state variables. Furthermore, the state variables and system parameters differ between grid-connected and grid-connected control modes, and their stability under small disturbances also varies. Therefore, the limited parameters and state variables fail to accurately characterize the safety domain of the control system parameters, leading to the problem of control system instability. Summary of the Invention

[0004] This invention provides a method and apparatus for determining the small-signal safety domain of a switching system. It addresses the shortcomings of existing switching hybrid modes, such as the D-segmentation method, which considers limited parameters and state variables. Furthermore, the state variables and system parameters differ under both grid-following and grid-connected control modes, leading to variations in small-disturbance stability. Consequently, the limited parameters and state variables fail to accurately characterize the safety domain of the control system parameters, causing instability. This invention reflects the influence of multiple parameters on the system's small-disturbance stability, thereby improving the accuracy of the small-signal safety domain of the switching system and further enhancing the stability of the control system.

[0005] This invention provides a method for determining the small-signal security domain of a switching system, comprising the following steps: Based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system, the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system are determined. Based on the power grid strength, the target full-order small-signal state space equation corresponding to the target subsystem is determined from the full-order small-signal state space equation corresponding to each of the subsystems. Based on the system state matrix in the target full-order small-signal state-space equation, the small-signal safety region of the grid-connected converter switching system is determined. The small-signal safety region is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

[0006] According to a method for determining the small-signal safety domain of a switching system provided by the present invention, the subsystem includes a grid-following subsystem and a grid-building subsystem. The full-order small-signal state-space equation includes a first full-order small-signal state-space equation and a second full-order small-signal state-space equation. The method for determining the full-order small-signal state-space equation corresponding to each subsystem in the grid-connected converter switching system based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system includes: determining the first full-order small-signal state-space equation corresponding to the grid-following subsystem based on the phase-locked loop mathematical model, the power-current dual-closed-loop mathematical model, and the full-order small-signal state-space model in the grid-following control model; and determining the second full-order small-signal state-space equation corresponding to the grid-building subsystem based on the active phase angle control mathematical model, the reactive voltage control mathematical model, the voltage-current dual-closed-loop control mathematical model, and the full-order small-signal state-space model in the grid-building control model.

[0007] According to a method for determining the small-signal safety domain of a switching system provided by the present invention, the step of determining the target full-order small-signal state space equation corresponding to the target subsystem from the full-order small-signal state space equations corresponding to each of the subsystems based on the grid strength includes: determining the target subsystem based on the grid strength and the subsystems currently connected to the grid-connected converter switching system; and determining the target full-order small-signal state space equation from the full-order small-signal state space equations corresponding to each of the subsystems based on the target subsystem.

[0008] According to a method for determining the small-signal security domain of a switching system provided by the present invention, the step of switching the currently connected subsystem of the grid-connected converter switching system based on the grid strength to obtain the target subsystem includes: when the grid strength is less than or equal to a first strength threshold and the currently connected subsystem is a grid-connected subsystem, switching the subsystem connected to the grid-connected converter switching system from the grid-connected subsystem to the grid-connected subsystem to obtain the target subsystem; when the grid strength is greater than or equal to a second strength threshold and the currently connected subsystem is a grid-connected subsystem, switching the subsystem connected to the grid-connected converter switching system from the grid-connected subsystem to the grid-connected subsystem to obtain the target subsystem; and when the grid strength is greater than the first strength threshold and less than the second strength threshold, determining the currently connected subsystem as the target subsystem.

[0009] According to a method for determining the small-signal safety domain of a switching system provided by the present invention, the step of determining the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation includes: determining small-signal safety domain rules and safety domain boundary rules; and determining the small-signal safety domain of the grid-connected converter switching system based on the signal safety domain rules, the safety domain boundary rules, and the system state matrix.

[0010] According to a method for determining the small-signal safety domain of a switching system provided by the present invention, the step of determining the small-signal safety domain of the grid-connected converter switching system based on the signal safety domain rules, the safety domain boundary rules, and the system state matrix includes: determining the eigenvalues ​​corresponding to the system state matrix; determining the sub-safety domains of the target full-order small-signal state space equation based on the signal safety domain rules, the safety domain boundary rules, and the eigenvalues; and determining the small-signal safety domain of the grid-connected converter switching system based on each of the sub-safety domains.

[0011] According to a method for determining the small-signal safety domain of a switching system provided by the present invention, the step of determining the sub-safety domain of the target full-order small-signal state-space equation based on the signal safety domain rules, the safety domain boundary rules, and the eigenvalues ​​includes: determining the initial stable operating point of the grid-connected converter switching system based on the signal safety domain rules, the safety domain boundary rules, and the eigenvalues; performing a search based on multiple orthogonal directions of the initial stable operating point to obtain multiple boundary points corresponding to the initial stable operating point; and determining the sub-safety domain of the target full-order small-signal state-space equation based on the multiple boundary points.

[0012] According to the present invention, a method for determining the small-signal safe domain of a switching system is provided, wherein the sub-safe domain of the target full-order small-signal state-space equation is determined based on the plurality of boundary points, and adjacent boundary points among the plurality of boundary points are sequentially connected to obtain a first hyperplane set; and the sub-safe domain of the target full-order small-signal state-space equation is determined based on the first hyperplane set.

[0013] According to a method for determining the small-signal safe region of a switching system provided by the present invention, the step of determining the sub-safe region of the target full-order small-signal state-space equation based on the first set of hyperplanes includes: optimizing the boundary points in the first set of hyperplanes based on the geometric center points of each hyperplane and the normals of each hyperplane to obtain a second set of hyperplanes; and continuously optimizing the boundary points in the second set of hyperplanes when the volume corresponding to the multidimensional hyperplanes in the second set of hyperplanes is greater than the tolerance, until the volume corresponding to the multidimensional hyperplanes in the optimized set of hyperplanes is less than or equal to the tolerance, thereby obtaining the sub-safe region of the target full-order small-signal state-space equation.

[0014] According to a method for determining the small-signal safety domain of a switching system provided by the present invention, after determining the small-signal safety domain of the grid-connected converter switching system, the method further includes: verifying the small-signal safety domain of the grid-connected converter switching system based on state-space theory calculation to obtain a first verification result; verifying the small-signal safety domain of the grid-connected converter switching system based on electromagnetic transient simulation to obtain a second verification result; and determining the accuracy of the small-signal safety domain of the grid-connected converter switching system based on a comparison between the first verification result and the second verification result.

[0015] The present invention also provides a device for determining the small-signal security domain of a switching system, comprising the following modules: The first determining module is used to determine the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system. The second determining module is used to determine the target full-order small-signal state-space equation corresponding to the target subsystem from the full-order small-signal state-space equations corresponding to each of the subsystems, based on the power grid strength. The third determining module is used to determine the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation. The small-signal safety domain is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

[0016] According to the present invention, a small-signal safety domain determination device for a switching system is provided. The subsystem includes a network tracking subsystem and a network construction subsystem. The full-order small-signal state-space equation includes a first full-order small-signal state-space equation and a second full-order small-signal state-space equation. The first determination module includes a network tracking determination unit and a network construction determination unit. The network tracking determination unit is used to determine the first full-order small-signal state-space equation corresponding to the network tracking subsystem based on the phase-locked loop mathematical model, the power-current dual-closed-loop mathematical model, and the full-order small-signal state-space model in the network tracking control model. The network construction determination unit is used to determine the second full-order small-signal state-space equation corresponding to the network construction subsystem based on the active phase angle control mathematical model, the reactive voltage control mathematical model, the voltage-current dual-closed-loop control mathematical model, and the full-order small-signal state-space model in the network construction control model.

[0017] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the small-signal security domain determination method for switching systems as described above.

[0018] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for determining the small-signal security domain of a switching system as described above.

[0019] The present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the small-signal security domain determination method for switching systems as described above.

[0020] The present invention provides a method and apparatus for determining the small-signal safety domain of a switching system. Based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system, the method determines the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system. Based on the grid strength, the method determines the target full-order small-signal state-space equation for the target subsystem from the full-order small-signal state-space equations corresponding to each subsystem. Based on the system state matrix in the target full-order small-signal state-space equation, the method determines the small-signal safety domain of the grid-connected converter switching system. The small-signal safety domain characterizes the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances. Thus, by including the full-order small-signal state-space equations of both grid-following and grid-building control systems, the method can reflect the influence of multiple parameters on the system's small-disturbance stability, thereby improving the accuracy of the small-signal safety domain of the switching system and further enhancing the stability of the control system. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the grid-connected system of the grid-connected / grid-connected converter provided by the present invention.

[0023] Figure 2 This is a schematic diagram of the response frequencies of each control loop of the converter provided by the present invention.

[0024] Figure 3 This is a flowchart illustrating the method for determining the small-signal security domain of a switching system provided by the present invention.

[0025] Figure 4 This is a schematic diagram of the switching system security domain provided by the present invention.

[0026] Figure 5A This is a schematic diagram of the safety domain of the control parameters of the phase-locked loop provided by the present invention under different power grid strengths.

[0027] Figure 5B This is a schematic diagram of the safety domain of the control parameters of the power outer loop under different power grid intensities provided by the present invention.

[0028] Figure 5C This is a schematic diagram of the safety domain of control parameters for the inner loop of the circuit provided by the present invention under different power grid strengths.

[0029] Figure 6A This is a schematic diagram of the safe operating parameter range of the short-circuit ratio-reactance-resistance ratio provided by the present invention under different current inner loop proportional coefficients.

[0030] Figure 6B This is a schematic diagram of the safe domain of operating parameters for active-reactive power with different current inner loop ratio coefficients provided by the present invention.

[0031] Figure 7A This is a schematic diagram of the safety domain of the control parameters for the voltage outer loop provided by the present invention under different power grid strengths.

[0032] Figure 7B This is a schematic diagram of the safety domain of the control parameters for the inner current loop provided by the present invention under different power grid intensities.

[0033] Figure 8 This is a schematic diagram of the safe domain of the short-circuit ratio-reactance-resistance ratio operating parameters with different current inner loop proportional coefficients provided by the present invention.

[0034] Figure 9AThis is a schematic diagram comparing the theory and simulation of the network control subsystem provided by this invention.

[0035] Figure 9B This is a schematic diagram comparing the theory and simulation of the network control subsystem provided by this invention.

[0036] Figure 10 This is a schematic diagram of the electromagnetic transient simulation results of the instantaneous active power output of the parameter points provided by this invention under steady state and small disturbance.

[0037] Figure 11 This is a schematic diagram of the structure of the small-signal security domain determination device for the switching system provided by the present invention.

[0038] Figure 12 This is a schematic diagram of the structure of the electronic device provided by the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] The power system is rapidly evolving into a new type of power system with a high proportion of renewable energy integration and a high proportion of power electronic equipment applications. The high integration of power electronic equipment dominated by new energy sources has improved the flexibility and economy of the power grid, but it has also profoundly changed the dynamic characteristics of the power system. The system uncertainty and complexity have increased, and problems such as power angle instability, frequency instability, voltage instability, and broadband oscillations are constantly emerging.

[0041] Due to the different synchronization control strategies, the stability characteristics of grid-connected / network-connected converters are complementary when connected to power grids of different strengths. Grid-connected / network-connected converter equipment complements each other in large-scale new energy grid-connected systems and works in synergy with grid connection.

[0042] However, existing switching hybrid modes, such as the D-segmentation method, consider a limited number of parameters and state variables. In the context of networked or grid-connected control modes, the state variables and system parameters are different, and the stability under small disturbances also varies. Therefore, the limited parameters and state variables lack an accurate characterization of the safety domain of the control system parameters, which leads to the problem of instability in the control system.

[0043] Based on the aforementioned problems, this invention proposes a method for determining the small-signal safety domain of a switching system. By using the full-order small-signal state-space equations of both mesh-type and network-type control systems, the method can reflect the influence of multiple parameters on the stability of the system under small disturbances, thereby improving the accuracy of the small-signal safety domain of the switching system and further enhancing the stability of the control system.

[0044] The following is combined Figures 1 to 10 The present invention describes a method for determining the small-signal security domain of a switching system. The subject executing this method can be an electronic device or a device for determining the small-signal security domain of a switching system installed in the electronic device. The device for determining the small-signal security domain of a switching system can be implemented by software, hardware, or a combination of both.

[0045] Figure 1 This is a schematic diagram of the grid-connected / grid-connected converter system provided by the present invention, as shown in the figure. Figure 1 As shown, the system includes an input source 101, a DC bus 102, an inverter 103, a chopper control 104, a pulse width modulation (PWM) unit 105, a first conversion unit 106, a first current inner loop 107, a power outer loop 108, a phase-locked loop 109, a second current inner loop 110, a voltage outer loop 111, a virtual synchronization control loop 112, a filter resistor 113, a filter inductor 114, a filter capacitor 115, a switch 116, a grid disconnection control 117, a ride-through control 118, a connection resistor 119, a connection inductor 120, a three-phase AC grid 121, and a first conversion unit 122. Grid-connected converters have the same electrical components. The input source, including the DC side of equipment such as wind turbines, photovoltaics, energy storage, and static var generators, is inverted by the inverter to the AC grid side and connected to the grid through filter impedances and connection impedances. The following mathematical models are based on... Figure 1 Let's take an example to illustrate.

[0046] The mathematical model of the AC side filter impedance of the grid-connected converter in the dq rotating coordinate system is shown in formula (1): (1) in, The electric angular velocity of the converter. , , These are the filter resistor, filter inductor, and filter capacitor, respectively. , These are the d-axis and q-axis components of the AC side voltage of the converter, respectively. , These are the d-axis and q-axis components of the AC side current of the converter, respectively. , These are the d-axis and q-axis components of the converter grid connection point voltage, respectively. , These are the d-axis and q-axis components of the converter grid-connected current, respectively.

[0047] The mathematical model of the converter grid connection impedance in the dq rotating coordinate system is shown in formula (2): (2) in, The magnitude of the grid voltage vector. The angle by which the d-axis leads the grid voltage vector. , These are the projections of the grid voltage vector onto the d and q axes, respectively. , These are the equivalent connection resistance and connection inductance of the circuit, respectively.

[0048] Depend on Figure 1 It is known that grid-connected and grid-connected converters use the same coordinate transformation, power calculation and modulation links, and can add high / low voltage ride-through control modules and grid disconnection control modules according to the needs of the scenario. However, the two differ in synchronization methods and dual closed-loop control.

[0049] Grid-connected converters typically use Park transformation to convert three-phase AC signals to a two-phase rotating coordinate system dq, which facilitates vector control of the three-phase voltage and current signals, as shown in formula (3): (3) in, Let be the angle between the a-axis of the three-phase stationary coordinate system abc and the d-axis of the two-phase rotating coordinate system dq.

[0050] The power calculation formula for grid-connected converters in a per-unit system is as follows: Formula (4): (4) in, , These represent the active power and reactive power output by the converter, respectively.

[0051] The modulation stage uses Park inverse transform to obtain reference values ​​for the d-axis and q-axis components of the converter grid connection point voltage. , The three-phase reference values ​​(abc) are converted back to control the AC-side controlled voltage source.

[0052] Figure 2 This is a schematic diagram of the response frequencies of each control loop of the converter provided by the present invention, as shown below. Figure 2 As shown. The horizontal axis represents the response frequency in Hertz (Hz), and the vertical axis represents the control loop, which includes the power loop, voltage loop, phase-locked loop, current loop, and switching frequency. It can be seen that the modulation loop has a large bandwidth and a response frequency much higher than other control loops. Therefore, it can be assumed that the AC side voltage of the converter rapidly tracks its modulation reference value, i.e. , .

[0053] It should be noted that the method for determining the small-signal security domain of a switching system provided by this invention can be applied to... Figure 1 Provided grid-connected / network-connected converter systems.

[0054] Figure 3 This is a flowchart illustrating the method for determining the small-signal security domain in a switching system provided by the present invention, as shown below. Figure 3 As shown, the method includes the following: Step 301: Based on the grid-following control model, the grid-connected control model, and the full-order small-signal state-space model in the grid-connected converter switching system, determine the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system.

[0055] Here, the grid control model equates the converter to a controlled current source, while the network control model equates the converter to a controlled voltage source.

[0056] Here, the full-order small-signal state-space model refers to incorporating all time-varying quantities in the network / structure into the state equations. The full-order small-signal state-space model is used to transform complex converter systems into linear mathematical models, enabling precise assessment of system stability, oscillations, and controller regulation.

[0057] The expression for the full-order small-signal state-space model is as follows: (5) (5) in, Indicates a small perturbation. The rate of change of the state variable deviation For system state variables, Input variables to the system, The system state matrix, The input matrix is ​​used for the system.

[0058] It should be noted that the subsystem includes the following subsystems: the following subsystem and the following subsystem. The system state matrix and the system input matrix in the full-order small-signal state-space equations of the following subsystem and the following subsystem are different.

[0059] Furthermore, the subsystem includes a grid-connecting subsystem and a grid-building subsystem. The full-order small-signal state-space equation includes a first full-order small-signal state-space equation and a second full-order small-signal state-space equation. The determination of the full-order small-signal state-space equation corresponding to each subsystem in the grid-connected converter switching system based on the grid-connecting control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system includes: determining the first full-order small-signal state-space equation corresponding to the grid-connecting subsystem based on the phase-locked loop mathematical model, the power-current dual-closed-loop mathematical model, and the full-order small-signal state-space model in the grid-connecting control model; and determining the second full-order small-signal state-space equation corresponding to the grid-building subsystem based on the active phase angle control mathematical model, the reactive voltage control mathematical model, the voltage-current dual-closed-loop control mathematical model, and the full-order small-signal state-space model in the grid-building control model.

[0060] Combination Figure 1 In the grid-connected system of the grid-connected converter, the phase-locked loop (PLL) is controlled by the stator voltage orientation vector. The d-axis of the dq rotating coordinate system is aligned with the voltage vector at the grid connection point, and its q-axis component is kept at 0. The PLL tracks the voltage phase at the grid connection point of the converter. The mathematical model of the PLL is as follows (6): (6) in, For the integral state variable, For the grid synchronization angular velocity, , These are the proportional gain and integral time constant of the phase-locked loop, respectively.

[0061] Here, the power-current dual-loop mathematical model consists of a power outer loop and a current inner loop. The power outer loop of the grid-connected converter is a constant power control, inputting the power deviation into a PI controller to track the active and reactive power setpoints, and outputting reference values ​​for the d- and q-axis components of the AC current of the converter. The current inner loop tracks the current reference value given by the power outer loop and outputs reference values ​​for the d- and q-axis components of the converter's grid-connected voltage. Due to the presence of a filter, there are cross-terms in the current inner loop. The power-current dual-loop mathematical model is given by the following formula (7): (7) in, , , , For the integral state variable, , These are the active power and reactive power reference values ​​set for the converter, respectively. , These are the reference values ​​for the d-axis and q-axis components of the AC side current of the converter, respectively. , These are the proportional gain and integral time constant of the power outer loop, respectively. , These are the proportional coefficient and integral time constant of the inner current loop, respectively.

[0062] The grid-connected control model mainly includes power synchronization (taking Virtual Synchronous Generator (VSG) as an example), voltage outer loop, and current inner loop. Virtual Synchronous Generator simulates the electromechanical characteristics of a traditional synchronous generator, enabling the grid-connected converter to actively participate in grid frequency and voltage regulation and inertia support. Its core is to introduce virtual inertia, damping, and droop characteristics, allowing the converter to exhibit dynamic behavior similar to a synchronous generator within the grid.

[0063] The mathematical model for active phase angle control is shown in the following formula (8): (8) in, This is the virtual power angle (the phase angle difference between the converter's grid connection point voltage and the grid voltage). This is the virtual damping coefficient. For virtual rotational inertia, This is an additional primary frequency modulation coefficient.

[0064] The mathematical model for reactive voltage control is shown in formula (9): (9) in, For the integral state variable, To add a primary voltage regulation coefficient, This is the reactive power weighting coefficient. This is the reference value for the d-axis component of the converter grid connection point voltage. This is a reference value for voltage amplitude. , These are the proportional coefficient and integral time constant of the VSG reactive-voltage control link, respectively.

[0065] The voltage-current dual closed-loop control mathematical model consists of an outer voltage loop and an inner current loop. The outer voltage loop of the grid-connected converter inputs the voltage deviation to the PI controller to track the voltage amplitude reference given by the virtual synchronous control, and outputs reference values ​​for the d- and q-axis components of the AC current of the converter. The inner current loop tracks the current reference value given by the outer voltage loop and outputs reference values ​​for the d- and q-axis components of the converter's grid-connected voltage. Due to the presence of a filter, there are cross-terms in both the outer voltage loop and the inner current loop. The voltage-current dual closed-loop control mathematical model is given by the following formula (10): (10) in, This is the reference value for the q-axis component of the converter grid connection point voltage. , These are the proportional gain and integral time constant of the outer voltage loop, respectively. , These are the proportional coefficient and integral time constant of the inner current loop, respectively.

[0066] For example, by rearranging the power and current dual-loop mathematical models in the phase-locked loop mathematical model and the grid control model into a full-order small-signal state-space model, the first full-order small-signal state-space equation corresponding to the grid subsystem is obtained. The first full-order small-signal state-space equation is a 12th-order state-space model, in which the system state variables... System input variables System state matrix ,in , , , They are represented as follows: System input matrix It is expressed as follows: The second full-order small-signal state-space equation corresponding to the network subsystem is a 13th-order state-space model, in which the system state variables are... System input variables System state matrix ,in, , , , They are represented as follows: System input matrix It is expressed as follows: In this embodiment of the invention, the full-order small-signal state-space equation of the grid subsystem is established using the phase-locked loop mathematical model and the power-current dual-closed-loop mathematical model in the grid-connected control model; the full-order small-signal state-space equation of the grid subsystem is established using the active phase angle control mathematical model, the reactive voltage control mathematical model, and the voltage-current dual-closed-loop control mathematical model in the grid-connected control model. This can reflect the influence of multiple parameters on the stability of the system under small disturbances, thereby improving the accuracy of the small-signal safety domain of the switching system and further improving the stability of the control system.

[0067] Step 302: Based on the power grid strength, determine the target full-order small-signal state-space equation corresponding to the target subsystem from the full-order small-signal state-space equations corresponding to each of the subsystems.

[0068] Here, grid strength can be the short circuit ratio (SCR).

[0069] Here, the target subsystem can be either a network subsystem or a network construction subsystem.

[0070] For example, when the grid strength meets the first threshold, the grid subsystem can be used as the target subsystem; when the grid strength meets the second threshold, the grid construction subsystem can be used as the target subsystem.

[0071] Furthermore, determining the target full-order small-signal state space equation corresponding to the target subsystem from the full-order small-signal state space equations corresponding to each of the subsystems based on grid strength includes: determining the target subsystem based on the grid strength and the subsystems currently connected to the grid-connected converter switching system; and determining the target full-order small-signal state space equation from the full-order small-signal state space equations corresponding to each of the subsystems based on the target subsystem.

[0072] It should be noted that the target full-order small-signal state-space equations are different for different target subsystems.

[0073] It should be noted that the target subsystem may be the switched subsystem or the currently connected subsystem. When the grid strength meets a certain threshold, it is determined whether a subsystem switch is needed, based on the currently connected subsystem. If a switch is needed, the switched subsystem becomes the target subsystem; otherwise, the currently connected subsystem becomes the target subsystem.

[0074] In this embodiment of the invention, appropriate subsystems are switched in a timely manner according to the power grid strength to improve system stability.

[0075] Further, the step of switching the currently connected subsystem of the grid-connected converter switching system based on the grid strength to obtain the target subsystem includes: when the grid strength is less than or equal to a first strength threshold and the currently connected subsystem is a grid-connected subsystem, switching the subsystem connected to the grid-connected converter switching system from the grid-connected subsystem to the grid-connected subsystem to obtain the target subsystem; when the grid strength is greater than or equal to a second strength threshold and the currently connected subsystem is a grid-connected subsystem, switching the subsystem connected to the grid-connected converter switching system from the grid-connected subsystem to the grid-connected subsystem to obtain the target subsystem; and when the grid strength is greater than the first strength threshold and less than the second strength threshold, determining the currently connected subsystem as the target subsystem.

[0076] Here, the first intensity threshold and the second intensity threshold can be any suitable value, for example, the first intensity threshold is 3.0 and the second intensity threshold is 10.0.

[0077] For example, when the grid strength is less than or equal to 3.0, it is considered a weak grid. To maintain system stability, a grid-building subsystem is required. If the currently connected subsystem is a grid-following subsystem, it is switched to the grid-building subsystem; otherwise, the current connection remains unchanged. When the grid strength is greater than or equal to 10.0, it is considered a strong grid. To maintain system stability, a grid-following subsystem is required. If the currently connected subsystem is a grid-following subsystem, it is maintained; otherwise, the grid-building subsystem is switched to the grid-following subsystem. When the grid strength is greater than 3.0 and less than 10.0 (neither a weak nor a strong grid), the currently connected subsystem can be maintained.

[0078] Step 303: Based on the system state matrix in the target full-order small-signal state-space equation, determine the small-signal safety domain of the grid-connected converter switching system.

[0079] The small-signal safety domain is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

[0080] Here, the small-signal safety region is the set of all operating points in the parameter space that can maintain small-signal stability, and the boundary of the safety region is formed by the operating points corresponding to when the system is in a critical stable state.

[0081] It should be noted that a power system can be mathematically modeled as a set of parameterized differential-algebraic equations. By performing small-signal linearization on the state-space equations, the system's eigenvalues ​​can be obtained, and the small-signal stability of the system can be evaluated accordingly.

[0082] According to Lyapunov's indirect method, when the state matrix... When the real parts of all eigenvalues ​​are negative, the system at its stable operating point The system is asymptotically stable in the vicinity, at which point it exhibits small perturbation stability.

[0083] In this embodiment of the invention, a grid-connected converter switching law is introduced to establish a switching system model under grid-connected / grid-connected switching control.

[0084] Furthermore, determining the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation includes: determining the small-signal safety domain rules and the safety domain boundary rules; and determining the small-signal safety domain of the grid-connected converter switching system based on the signal safety domain rules, the safety domain boundary rules, and the system state matrix.

[0085] Here, the small-signal safe domain rule is used to characterize that the real parts of all eigenvalues ​​of the system state matrix are negative, i.e., the expression is as follows: (11) (11) in, Indicates a security domain. Represents the system parameter vector of, Represents the eigenvalue vector. , Indicates by Composition l Hyperspace .

[0086] Furthermore, the safety domain boundary rule is used to characterize that the real parts of all eigenvalues ​​of the system state matrix are negative and infinitely close to 0, and its expression is as follows: (12) (12) in, Indicates the boundary of the security domain. This represents the boundary tolerance, which is greater than 0. It is used to characterize that the rightmost eigenvalue of the system is located near the imaginary axis, that is, the system is in a critically stable state.

[0087] Here, the small signal security domain includes the security domain corresponding to the network subsystem and the security domain corresponding to the network construction subsystem.

[0088] In this embodiment of the invention, the sub-safety domain of each subsystem is determined based on the defined small-signal safety domain, safety domain boundary, and characteristic value of the network / network control switching system parameters, thereby improving the accuracy of the small-signal safety domain and the stability of the system.

[0089] Furthermore, determining the small-signal security domain of the grid-connected converter switching system based on the signal security domain rules, the security domain boundary rules, and the system state matrix includes: determining the eigenvalues ​​corresponding to the system state matrix; determining the sub-security domains of the target full-order small-signal state space equation based on the signal security domain rules, the security domain boundary rules, and the eigenvalues; and determining the small-signal security domain of the grid-connected converter switching system based on each of the sub-security domains.

[0090] It should be noted that when a subsystem switches, the state-space equations of the system will change accordingly, resulting in a reconstruction of the shape of the security domain. For a switched system, its overall security domain can be represented by the union of the security domains of each subsystem.

[0091] For example, if the eigenvalues ​​of the system state matrix corresponding to a running point are all less than 0, then the running point is taken as the running point in the safe domain. The safe domain of the subsystem can be determined by traversing the eigenvalues ​​of the system state matrix corresponding to multiple running points, or by fitting the boundary of the small-signal safe domain in the parameter space.

[0092] Figure 4 This is a schematic diagram of the switching system security domain provided by the present invention, as shown below. Figure 4 Show, Figure 4 The 1 in the text represents the first subsystem. Figure 4 The "2" in the diagram represents the second subsystem. In a switching system containing two subsystems and two parameters, there are three typical interaction modes between the subsystem security domains. The first is... Figure 4 In the diagram on the left, the security domain of one subsystem may be completely contained within the security domain of another subsystem. This indicates that the applied switching control does not improve system stability. In this case, the system will preferentially operate on the second subsystem to obtain a greater stability margin. The second scenario is... Figure 4 The middle diagram shows an intersection between the two subsystems; the third type is... Figure 4 In the diagram on the right, the two subsystems do not intersect. When there is no mutual inclusion relationship between the security domains of the two subsystems, their union will expand the overall security domain of the system.

[0093] In this embodiment of the invention, by introducing a reasonable switching mechanism, the safety domain of the power system can be effectively expanded, thereby improving its small-signal stability.

[0094] Furthermore, determining the sub-safety domain of the target full-order small-signal state-space equation based on the signal safety domain rules, the safety domain boundary rules, and the eigenvalues ​​includes: determining the initial stable operating point of the grid-connected converter switching system based on the signal safety domain rules, the safety domain boundary rules, and the eigenvalues; performing a search based on multiple orthogonal directions of the initial stable operating point to obtain multiple boundary points corresponding to the initial stable operating point; and determining the sub-safety domain of the target full-order small-signal state-space equation based on the multiple boundary points.

[0095] Here, the signal security domain rules and security domain boundary rules can be predefined and input into the calculator. The calculator determines the security domain based on the signal security domain rules, security domain boundary rules, and eigenvalues.

[0096] Here, the initial stable operating point refers to the operating point where all eigenvalues ​​corresponding to the system's characteristic matrix are less than 0. In other words, an operating point with eigenvalues ​​less than 0 is randomly selected as the initial stable operating point.

[0097] Here, the search direction can include the positive and negative directions of each orthogonal direction. The number of orthogonal directions can be the dimension of the parameter space. For example, if the parameter space is n-dimensional, then the orthogonal directions are n-dimensional.

[0098] Here, the number of boundary points can be twice the parameter dimension.

[0099] In this embodiment of the invention, the influence of system parameters on the safety domain is explored based on the parameter safety domain characterization of hyperplane fitting. This can reflect the influence of multiple parameters on the stability of the system under small disturbances, thereby improving the accuracy of the small-signal safety domain of the switching system and further improving the stability of the control system.

[0100] Furthermore, determining the sub-safety region of the target full-order small-signal state-space equation based on the plurality of boundary points includes: sequentially connecting adjacent boundary points among the plurality of boundary points to obtain a first hyperplane set; and determining the sub-safety region of the target full-order small-signal state-space equation based on the first hyperplane set.

[0101] For example, select an initial stable operating point and define n mutually orthogonal directions; search along the positive and negative directions of each direction to identify the corresponding 2n boundary points (critical stable points); then... n Connecting n adjacent boundary points in a combination of orthogonal directions constructs an initial linear approximation of the boundary of the small-signal safe region, which is an (n-1)-dimensional hyperplane set; then, based on the hyperplane set, the sub-safe region is determined.

[0102] In this embodiment of the invention, the influence of system parameters on the safety domain is explored based on the parameter safety domain characterization of hyperplane fitting. This can reflect the influence of multiple parameters on the stability of the system under small disturbances, thereby improving the accuracy of the small-signal safety domain of the switching system and further improving the stability of the control system.

[0103] Furthermore, determining the sub-safety region of the target full-order small-signal state-space equation based on the first hyperplane set includes: optimizing the boundary points in the first hyperplane set based on the geometric center points of each hyperplane and the normals of each hyperplane to obtain a second hyperplane set; and continuously optimizing the boundary points in the second hyperplane set until the volume corresponding to the multidimensional hyperplane in the optimized hyperplane set is less than or equal to the tolerance, thereby obtaining the sub-safety region of the target full-order small-signal state-space equation.

[0104] Here, tolerance is used to characterize the difference between the volume corresponding to the hyperplane and the nominal volume of the model.

[0105] For example, starting from the geometric center point of each hyperplane, the boundary fitting is optimized by locating more precise boundary points along the normal direction of each hyperplane; for each newly added boundary point, the n-dimensional volume enclosed by the point and its n neighboring boundary points is calculated: if the newly added volume is greater than the tolerance, the newly added boundary point is retained and further optimization is performed; if no new boundary points are retained, the final set of fitted boundary points and the analytical expression of the approximate boundary (hyperplane set) are output.

[0106] In this embodiment of the invention, the influence of system parameters on the safety domain is explored based on the parameter safety domain characterization of hyperplane fitting. This can reflect the influence of multiple parameters on the stability of the system under small disturbances, thereby improving the accuracy of the small-signal safety domain of the switching system and further improving the stability of the control system.

[0107] The following section explains the safety domain of control parameters and the safety domain of operating parameters for the converter-grid / network control subsystem. In this subsystem, grid strength is an operating parameter, and the current inner loop proportional coefficient is a system control parameter.

[0108] Figure 5A The diagram illustrates the safety domain of the control parameters of the phase-locked loop provided by this invention under different power grid strengths, as shown below. Figure 5A As shown, the horizontal axis representing the grid strength indicates the proportional gain of the PI controller in the phase-locked loop. The vertical axis represents the phase-locked loop (PLL), and the vertical axis represents the integral gain of the PI controller in the PLL loop. The light blue area represents the safe zone with a short-circuit ratio (SCR) of 4, and the light olive green area represents the safe zone with a short-circuit ratio (SCR) of 2.

[0109] Figure 5B This is a schematic diagram of the safety domain of the control parameters of the power outer loop under different grid strengths provided by the present invention, as shown below. Figure 5B As shown, the horizontal axis represents the proportional gain of the PI controller in the outer power loop. The vertical axis represents the integral gain of the PI controller in the outer power loop. The light blue area represents the safe zone with a short-circuit ratio (SCR) of 4, and the light olive green area represents the safe zone with a short-circuit ratio (SCR) of 2.

[0110] Figure 5C This is a schematic diagram of the safety domain of the control parameters of the inner loop of the circuit provided by the present invention under different power grid strengths, as shown in the figure. Figure 5C As shown, the horizontal axis represents the proportional gain of the PI controller in the inner loop of the circuit. The vertical axis represents the integral gain of the PI controller in the inner loop of the circuit. The light blue area represents the safe zone with a short-circuit ratio (SCR) of 4, and the light olive green area represents the safe zone with a short-circuit ratio (SCR) of 2.

[0111] from Figure 5A , 5B In 5C, it can be seen that under the same grid strength, the safety domain of the PI parameter decreases in the order of current inner loop, phase-locked loop, and power outer loop; when the grid strength weakens, the safety domain of the control parameters of the converter and grid control subsystem decreases significantly, and the shape of the safety domain of the same parameter group is basically the same.

[0112] Figure 6A This is a schematic diagram illustrating the safe domain of operating parameters for the short-circuit ratio-reactance-resistance ratio under different current inner loop proportional coefficients provided by the present invention, as shown below. Figure 6A As shown, the horizontal axis represents the short-circuit ratio (SCR), and the vertical axis represents the reactance-resistance ratio. X / R, The blue area represents the current inner loop proportionality coefficient, i.e. The small-signal safety domain is 1.0, and light olive green represents the current inner loop proportionality coefficient. It is a small-signal security domain of 3.0.

[0113] Figure 6B This is a schematic diagram of the safe domain of operating parameters for active-reactive power with different current inner loop ratio coefficients, as provided by the present invention. Figure 6B As shown, the horizontal axis represents active power, the vertical axis represents reactive power, and the blue area represents the inner loop current proportionality coefficient. The small-signal safety domain is 1.0, and light olive green represents the current inner loop proportionality coefficient. It is a small-signal security domain of 3.0.

[0114] As shown in 6A and 6B, when the short-circuit ratio and reactance resistance corresponding to the operating point of the grid control subsystem are small, the system is unstable under small disturbances; the active power output capacity of this subsystem is greater than the reactive power output capacity; when the current inner loop proportional coefficient increases, the safety domain of the system operating parameters decreases.

[0115] Figure 7A This is a schematic diagram of the safety domain of the control parameters for the voltage outer loop under different power grid strengths provided by the present invention, as shown below. Figure 7A As shown, the horizontal axis represents the proportional gain of the PI controller in the outer voltage loop. The vertical axis represents the integral gain of the PI controller in the inner loop of the circuit. The light blue area represents the safe zone with a short-circuit ratio (SCR) of 4, and the light olive green area represents the safe zone with a short-circuit ratio (SCR) of 2.

[0116] Figure 7B This is a schematic diagram of the safety domain of the control parameters for the inner current loop under different power grid strengths provided by the present invention, as shown below. Figure 7B As shown, the horizontal axis represents the proportional gain of the PI controller in the inner current loop. The vertical axis represents the integral gain of the PI controller in the inner current loop. The light blue area represents the safe zone with a short-circuit ratio (SCR) of 4, and the light olive green area represents the safe zone with a short-circuit ratio (SCR) of 2.

[0117] As shown in 7A and 7B, under the same grid strength, the safety domain of the PI parameter of the voltage outer loop is larger than that of the current inner loop. When the grid strength weakens, the safety domain of the control parameters of the converter grid control subsystem increases, and the shape of the safety domain of the same parameter group is basically the same. The safety domain of the grid control parameters can be extended to a very large PI parameter value, which is significantly larger than the safety domain of the grid control parameters.

[0118] Figure 8 This is a schematic diagram of the safe domain of the short-circuit ratio-reactance-resistance ratio operating parameters under different current inner loop proportional coefficients provided by the present invention, as shown below. Figure 8 As shown, the horizontal axis represents the short-circuit ratio (SCR), and the vertical axis represents the reactance-resistance ratio. X / R, The blue area represents the current inner loop proportionality coefficient, i.e. The small-signal safety domain is 10.0, and the light olive green color represents the current inner loop proportionality coefficient. The small-signal safety domain is 3.0. When the short-circuit ratio and reactance resistance corresponding to the operating point of the network control subsystem are relatively large or extremely small, the system becomes unstable under small disturbances; when the current inner loop proportional coefficient decreases, the system operating parameter safety domain decreases; compared to... Figure 6A The safety domain of network control operation parameters can be extended to a very large range of parameter values, which is significantly larger than the safety domain of network control operation parameters.

[0119] Furthermore, after determining the small-signal safety domain of the grid-connected converter switching system, the method further includes: verifying the small-signal safety domain of the grid-connected converter switching system based on state-space theory calculations to obtain a first verification result; verifying the small-signal safety domain of the grid-connected converter switching system based on electromagnetic transient simulations to obtain a second verification result; and determining the accuracy of the small-signal safety domain of the grid-connected converter switching system based on a comparison between the first verification result and the second verification result.

[0120] Here, the state-space theoretical calculation can be performed in Matlab, and the electromagnetic transient simulation can be performed on the CloudPSS platform. When the first verification result and the second verification result are consistent, it indicates that the small-signal safety domain of the grid-connected converter switching system is accurate; when the first verification result and the second verification result are inconsistent, it indicates that the small-signal safety domain of the grid-connected converter switching system is not safe.

[0121] In this embodiment of the invention, theoretical calculations and electromagnetic transient simulation examples of the following / forming network switching system are constructed to verify the accuracy of the switching system model and the security domain characterization method.

[0122] For example, the accuracy of the proposed grid-connected / grid-connected converter switching system model is verified by comparing the state-space theoretical calculations in Matlab with the time-domain electromagnetic transient simulation results on the CloudPSS platform. Based on a single-unit infinite bus system of the grid-connected converter, after the system reaches steady state, a small disturbance is applied at 0.05s, and the following settings are configured... and .

[0123] Figure 9A This is a schematic diagram comparing the theory and simulation of the network control subsystem provided by this invention, as shown in the figure. Figure 9A As shown, the horizontal axis represents time, in seconds (s), and the vertical axes are respectively... , , , , , , , The solid blue line represents the calculation verification result, and the dashed red line represents the simulation result.

[0124] Figure 9B This is a schematic diagram comparing the theory and simulation of the network control subsystem provided by this invention, as shown below. Figure 9B As shown, the horizontal axis represents time, in seconds (s), and the vertical axes are respectively... , , , , , , , The solid blue line represents the calculation verification result, and the dashed red line represents the simulation result.

[0125] Depend on Figure 9A , 9B It can be seen that the small-signal response of the grid-connected / grid-structured control subsystem obtained by state-space theory calculation and electromagnetic transient simulation exhibits excellent consistency, and the root mean square error of all electrical quantity indicators is lower than that of the grid-connected / grid-structured control subsystem. These results validate the correctness of the proposed converter-to-grid / together-grid control switching system model. Furthermore, under the same small disturbance conditions, the transient response speed of the grid-connected subsystem is faster than that of the together-grid subsystem, while their steady-state values ​​are essentially the same.

[0126] Figure 10 This is a schematic diagram of the electromagnetic transient simulation results of the instantaneous active power output of the parameter points provided by this invention under steady state and small disturbances, as shown in the figure. Figure 10 As shown, with Figure 5C Taking SCR=4.0 as an example, four parameter points are selected: (1.0, 2500) inside the boundary, (3.0, 2500) near the boundary, (3.17, 2500) on the boundary, and (4.0, 2500) outside the boundary. The horizontal axis represents time in seconds (S), and the vertical axis represents active power in Pu (Pu). The green dashed line represents the point outside the boundary. The simulation results are shown in Figure 4, with the red solid line representing points on the boundary. The simulation results are shown in section 3.17, with the orange solid line indicating the points near the boundary. The simulation results are for version 3.0; the purple solid lines represent points inside the boundary. The simulation results are for version 1.0. Figure 10 It can be seen that the system is unstable at the parameter point (4.0, 2500) outside the safety domain boundary, with the instantaneous active power output exhibiting divergent oscillations; the system is critically stable at the parameter point (3.17, 2500) above the safety domain boundary, with the instantaneous active power output exhibiting constant-amplitude oscillations; the system is stable at the parameter points (3.0, 2500) and (1.0, 2500) inside the safety domain boundary, with the instantaneous active power output oscillations converging after a small disturbance, and the convergence speed at the points inside the boundary being faster than that near the boundary. These results verify the accuracy of the parameterized small-signal safety domain.

[0127] The following describes the handover system small-signal security domain determination device provided by the present invention. The handover system small-signal security domain determination device described below can be referred to in correspondence with the handover system small-signal security domain determination method described above.

[0128] Figure 11 This is a schematic diagram of the structure of the small-signal security domain determination device for the switching system provided by the present invention, as shown below. Figure 11As shown, the small-signal security domain determination device 1100 for switching systems includes the following: The first determining module 1110 is used to determine the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system. The second determining module 1120 is used to determine the target full-order small-signal state-space equation corresponding to the target subsystem from the full-order small-signal state-space equations corresponding to each of the subsystems based on the power grid strength. The third determining module 1130 is used to determine the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation. The small-signal safety domain is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

[0129] In this embodiment of the invention, the subsystem includes a network tracking subsystem and a network construction subsystem. The full-order small-signal state-space equation includes a first full-order small-signal state-space equation and a second full-order small-signal state-space equation. The first determining module includes a network tracking determining unit and a network construction determining unit, wherein: the network tracking determining unit is used to determine the first full-order small-signal state-space equation corresponding to the network tracking subsystem based on the phase-locked loop mathematical model, the power-current dual-closed-loop mathematical model, and the full-order small-signal state-space model in the network tracking control model; the network construction determining unit is used to determine the second full-order small-signal state-space equation corresponding to the network construction subsystem based on the active phase angle control mathematical model, the reactive voltage control mathematical model, the voltage-current dual-closed-loop control mathematical model, and the full-order small-signal state-space model in the network construction control model.

[0130] In this embodiment of the invention, the second determining module is specifically used to: determine a target subsystem based on the power grid strength and the subsystem currently connected to the grid-connected converter switching system; and determine the target full-order small-signal state-space equation from the full-order small-signal state-space equations corresponding to each subsystem based on the target subsystem.

[0131] In this embodiment of the invention, the second determining module is further specifically configured to: when the grid strength is less than or equal to a first strength threshold and the currently connected subsystem is a grid-connected subsystem, switch the subsystem connected to the grid-connected converter switching system from the grid-connected subsystem to the grid-building subsystem to obtain the target subsystem; when the grid strength is greater than or equal to a second strength threshold and the currently connected subsystem is a grid-building subsystem, switch the subsystem connected to the grid-connected converter switching system from the grid-building subsystem to the grid-connected subsystem to obtain the target subsystem; and when the grid strength is greater than the first strength threshold and less than the second strength threshold, determine the currently connected subsystem as the target subsystem.

[0132] In this embodiment of the invention, the third determining module is further specifically used for: determining the small-signal security domain rule and the security domain boundary rule; and determining the small-signal security domain of the grid-connected converter switching system based on the signal security domain rule, the security domain boundary rule, and the system state matrix.

[0133] In this embodiment of the invention, the third determining module is further specifically used for: determining the eigenvalues ​​corresponding to the system state matrix; determining the sub-safety domains of the target full-order small-signal state space equation based on the signal safety domain rules, the safety domain boundary rules, and the eigenvalues; and determining the small-signal safety domains of the grid-connected converter switching system based on each of the sub-safety domains.

[0134] In this embodiment of the invention, the third determining module is further specifically used for: determining the initial stable operating point of the grid-connected converter switching system based on the signal security domain rules, the security domain boundary rules, and the feature values; searching based on multiple orthogonal directions of the initial stable operating point to obtain multiple boundary points corresponding to the initial stable operating point; and determining the sub-security domain of the target full-order small-signal state-space equation based on the multiple boundary points.

[0135] In this embodiment of the invention, the third determining module is further specifically used for: sequentially connecting adjacent boundary points among the plurality of boundary points to obtain a first hyperplane set; and determining the sub-safety region of the target full-order small-signal state-space equation based on the first hyperplane set.

[0136] In this embodiment of the invention, the third determining module is further specifically used for: optimizing the boundary points in the first hyperplane set based on the geometric center points of each hyperplane in the first hyperplane set and the normals of each hyperplane to obtain a second hyperplane set; and continuously optimizing the boundary points in the second hyperplane set when the volume corresponding to the multidimensional hyperplane in the second hyperplane set is greater than the tolerance, until the volume corresponding to the multidimensional hyperplane in the optimized hyperplane set is less than or equal to the tolerance, thereby obtaining the sub-safety region of the target full-order small-signal state-space equation.

[0137] In this embodiment of the invention, the switching system small-signal safety domain determination device further includes a first verification module, used for: verifying the small-signal safety domain of the grid-connected converter switching system based on state-space theory calculation to obtain a first verification result; verifying the small-signal safety domain of the grid-connected converter switching system based on electromagnetic transient simulation to obtain a second verification result; and determining the accuracy of the small-signal safety domain of the grid-connected converter switching system based on the comparison result of the first verification result and the second verification result.

[0138] Figure 12 This is a schematic diagram of the structure of the electronic device provided by the present invention, such as... Figure 12 As shown, the electronic device may include: a processor 1210, a communications interface 1220, a memory 1230, and a communication bus 1240, wherein the processor 1210, the communications interface 1220, and the memory 1230 communicate with each other through the communication bus 1240. Processor 1210 can call logic instructions in memory 1230 to execute a method for determining the small-signal safety domain of a switching system. This method includes: determining the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system based on the grid-following control model, the grid-connected converter switching system's network control model, and the full-order small-signal state-space model; determining the target full-order small-signal state-space equation corresponding to the target subsystem from the full-order small-signal state-space equations corresponding to each subsystem based on grid strength; and determining the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation. The small-signal safety domain is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

[0139] Furthermore, the logical instructions in the aforementioned memory 1230 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, essentially, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0140] On the other hand, the present invention also provides a computer program product, which includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the method for determining the small-signal safety domain of the switching system provided by the above methods. The method includes: determining the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system; determining the target full-order small-signal state-space equation corresponding to the target subsystem from the full-order small-signal state-space equations corresponding to each subsystem based on the grid strength; and determining the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation. The small-signal safety domain is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

[0141] In another aspect, the present invention also provides a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements a method for determining the small-signal safety domain of a switching system provided by the methods described above. This method includes: determining the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system based on a grid-following control model, a grid-building control model, and a full-order small-signal state-space model in the grid-connected converter switching system; determining the target full-order small-signal state-space equation corresponding to a target subsystem from the full-order small-signal state-space equations corresponding to each subsystem based on grid strength; and determining the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation, wherein the small-signal safety domain characterizes the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

[0142] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0143] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the small-signal security domain of a switching system, characterized in that, include: Based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system, the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system are determined. Based on the power grid strength, the target full-order small-signal state space equation corresponding to the target subsystem is determined from the full-order small-signal state space equation corresponding to each of the subsystems. Based on the system state matrix in the target full-order small-signal state-space equation, the small-signal safety region of the grid-connected converter switching system is determined. The small-signal safety region is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

2. The method for determining the small-signal security domain of a switching system according to claim 1, characterized in that, The subsystem includes a grid-following subsystem and a grid-building subsystem. The full-order small-signal state-space equations include a first full-order small-signal state-space equation and a second full-order small-signal state-space equation. The determination of the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system, based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system, includes: Based on the phase-locked loop mathematical model, the power and current dual closed-loop mathematical model, and the full-order small-signal state-space model in the grid-following control model, the first full-order small-signal state-space equation corresponding to the grid-following subsystem is determined. Based on the active phase angle control mathematical model, reactive voltage control mathematical model, voltage and current dual closed-loop control mathematical model and the full-order small-signal state-space model in the network control model, the second full-order small-signal state-space equation corresponding to the network subsystem is determined.

3. The method for determining the small-signal security domain of a switching system according to claim 1, characterized in that, The step of determining the target full-order small-signal state-space equation for the target subsystem from the full-order small-signal state-space equations corresponding to each of the subsystems based on grid strength includes: Based on the power grid strength and the subsystems currently connected to the grid-connected converter switching system, the target subsystem is determined; Based on the target subsystem, the target full-order small-signal state-space equation is determined from the full-order small-signal state-space equations corresponding to each subsystem.

4. The method for determining the small-signal security domain of a switching system according to claim 3, characterized in that, The step of switching the currently connected subsystems of the grid-connected converter switching system based on the grid strength to obtain the target subsystem includes: When the grid strength is less than or equal to the first strength threshold and the currently connected subsystem is a grid-connected subsystem, the subsystem connected to the grid-connected converter switching system is switched from the grid-connected subsystem to the grid-connected subsystem to obtain the target subsystem; When the grid strength is greater than or equal to the second strength threshold and the currently connected subsystem is a grid-building subsystem, the subsystem connected to the grid-connected converter switching system is switched from the grid-building subsystem to the grid-connected subsystem to obtain the target subsystem; If the power grid strength is greater than the first strength threshold and less than the second strength threshold, the currently connected subsystem is identified as the target subsystem.

5. The method for determining the small-signal security domain of a switching system according to any one of claims 1 to 4, characterized in that, The determination of the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation includes: Determine the small-signal security domain rules and security domain boundary rules; Based on the signal security domain rules, the security domain boundary rules, and the system state matrix, the small signal security domain of the grid-connected converter switching system is determined.

6. The method for determining the small-signal security domain of a switching system according to claim 5, characterized in that, The determination of the small-signal security domain of the grid-connected converter switching system based on the signal security domain rules, the security domain boundary rules, and the system state matrix includes: Determine the eigenvalues ​​corresponding to the system state matrix; Based on the signal security domain rules, the security domain boundary rules, and the eigenvalues, the sub-security domains of the target full-order small-signal state space equation are determined. Based on each of the sub-security domains, the small-signal security domain of the grid-connected converter switching system is determined.

7. The method for determining the small-signal security domain of a switching system according to claim 6, characterized in that, The step of determining the sub-safety region of the target full-order small-signal state-space equation based on the signal safety region rule, the safety region boundary rule, and the eigenvalue includes: Based on the signal security domain rules, the security domain boundary rules, and the feature values, the initial stable operating point of the grid-connected converter switching system is determined; Searching based on multiple orthogonal directions of the initial stable operating point yields multiple boundary points corresponding to the initial stable operating point. Based on the multiple boundary points, the sub-safety region of the target full-order small-signal state-space equation is determined.

8. The method for determining the small-signal security domain of a switching system according to claim 7, characterized in that, The determination of the sub-safety region of the target full-order small-signal state-space equation based on the multiple boundary points includes: By sequentially connecting adjacent boundary points among the plurality of boundary points, a first hyperplane set is obtained; Based on the first set of hyperplanes, the sub-safe regions of the target full-order small-signal state-space equation are determined.

9. The method for determining the small-signal security domain of a switching system according to claim 8, characterized in that, The step of determining the sub-safety region of the target full-order small-signal state-space equation based on the first hyperplane set includes: Based on the geometric center points of each hyperplane in the first hyperplane set and the normals of each hyperplane, the boundary points in the first hyperplane set are optimized to obtain the second hyperplane set; If the volume corresponding to the multidimensional hyperplane in the second hyperplane set is greater than the tolerance, the boundary points in the second hyperplane set are continuously optimized until the volume corresponding to the multidimensional hyperplane in the optimized hyperplane set is less than or equal to the tolerance, thus obtaining the sub-safety region of the target full-order small-signal state space equation.

10. The method for determining the small-signal security domain of a switching system according to any one of claims 1 to 4, characterized in that, After determining the small-signal safety domain of the grid-connected converter switching system, the method further includes: Based on state-space theory calculations, the small-signal security domain of the grid-connected converter switching system is verified, and the first verification result is obtained. Based on electromagnetic transient simulation, the small-signal safety domain of the grid-connected converter switching system is verified, and a second verification result is obtained. Based on the comparison between the first verification result and the second verification result, the accuracy of the small-signal safety domain of the grid-connected converter switching system is determined.

11. A device for determining the small-signal security domain of a switching system, characterized in that, include: The first determining module is used to determine the full-order small-signal state-space equations corresponding to each subsystem in the grid-connected converter switching system based on the grid-following control model, the grid-building control model, and the full-order small-signal state-space model in the grid-connected converter switching system. The second determining module is used to determine the target full-order small-signal state-space equation corresponding to the target subsystem from the full-order small-signal state-space equations corresponding to each of the subsystems, based on the power grid strength. The third determining module is used to determine the small-signal safety domain of the grid-connected converter switching system based on the system state matrix in the target full-order small-signal state-space equation. The small-signal safety domain is used to characterize the parameter region in which the grid-connected converter switching system can return to stability when subjected to small-signal disturbances.

12. The small-signal security domain determination device for a switching system according to claim 11, characterized in that, The subsystem includes a network tracking subsystem and a network construction subsystem. The full-order small-signal state space equation includes a first full-order small-signal state space equation and a second full-order small-signal state space equation. The first determining module includes a network tracking determining unit and a network construction determining unit, wherein: The grid-following determination unit is used to determine the first full-order small-signal state-space equation corresponding to the grid-following subsystem based on the phase-locked loop mathematical model, the power and current double closed-loop mathematical model in the grid-following control model, and the full-order small-signal state-space model. The network determination unit is used to determine the second full-order small-signal state-space equation corresponding to the network subsystem based on the active phase angle control mathematical model, reactive voltage control mathematical model, voltage and current dual closed-loop control mathematical model and the full-order small-signal state-space model in the network control model.

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