Networking inverter modeling method, system, equipment and medium

Abstract

The invention discloses a modeling method, system, equipment and medium for a network-constructed inverter, and relates to the technical field of operation analysis of a novel power system, and the method comprises the steps: building a small-signal frequency domain model of a voltage and current double closed loop based on a voltage and current loop controller and an inverter main circuit structure in a network-constructed inverter grid-connected system; the method comprises the following steps: establishing a small signal frequency domain model of a power controller on the basis of a power calculation structure and a power controller structure in a network-forming inverter grid-connected system; the method comprises the following steps: establishing a small signal frequency domain model of line impedance based on a line impedance structure in a network-building inverter grid-connected system; the method comprises the following steps of: establishing a small signal frequency domain model of coordinate transformation on the basis of a conversion relation between an inverter control reference coordinate system and a system reference coordinate system in a grid-forming inverter grid-connected system; and finally, combining the models to obtain a network-forming inverter model. According to the method, the dynamic model suitable for the grid-forming type inversion device under the grid-connected working condition is accurately established.

Description

Technical Field

[0001] This invention relates to the field of novel power system operation analysis technology, and in particular to a method, system, equipment and medium for modeling grid-type inverters. Background Technology

[0002] New distribution networks are characterized by a high proportion of distributed generation and power electronic equipment. Against this backdrop, power electronic converters, as interface devices for distributed generation grid connection, will become core equipment in new distribution networks, significantly impacting their stability. Grid-connected inverters, with their frequency and voltage support capabilities, are widely used in distribution networks. Accurate modeling of grid-connected inverters is helpful for analyzing the oscillation mechanisms and stability of distribution networks with a high proportion of distributed generation. Furthermore, in grid-connected systems, the inverter's output power and frequency dynamics are typically of greater concern than voltage and current dynamics.

[0003] However, in existing technologies, grid-connected inverter modeling often employs either detailed modeling or partially simplified modeling. Detailed modeling covers the dynamic characteristics of the entire process, including the main circuit topology, voltage and current dual closed-loop control, and power control. Partially simplified modeling simplifies certain aspects (such as ignoring certain high-frequency dynamics). Both detailed and partially simplified modeling methods have the following main drawbacks: 1) They include too many non-core dynamic details such as voltage and current, making them unsuitable for large-scale operation analysis of distribution networks with a high proportion of distributed power sources; 2) They do not prioritize modeling the core power and frequency dynamics under grid-connected conditions, making it difficult to meet the requirements for power response and frequency support characteristics in distribution network stability analysis; 3) Some simplified models lose key dynamic characteristics, resulting in insufficient accuracy and an inability to accurately describe the power loop closed-loop behavior of grid-connected inverters. Therefore, it is necessary to design a simplified modeling method for grid-connected inverters suitable for operation analysis of distribution networks with a high proportion of distributed power sources. Summary of the Invention

[0004] To address the shortcomings of the prior art mentioned in the background section, this invention provides a method, system, device, and medium for modeling grid-connected inverters, which are used to accurately establish dynamic models of grid-connected inverter devices suitable for grid-connected operating conditions.

[0005] In view of this, the first aspect of the present invention provides a method for modeling a grid-type inverter, the method comprising: Based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system, a small-signal frequency domain model of voltage and current dual closed loop is established. Based on the power calculation structure and power controller structure in the grid-connected inverter system, a small-signal frequency domain model of the power controller is established. Based on the line impedance structure in a grid-connected inverter system, a small-signal frequency domain model of the line impedance is established. Based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in a grid-connected inverter system, a small-signal frequency domain model of coordinate transformation is established. By combining the small-signal frequency domain model of the voltage and current dual closed loop, the small-signal frequency domain model of the power controller, the small-signal frequency domain model of the line impedance, and the small-signal frequency domain model of the coordinate transformation, a grid-type inverter model is obtained.

[0006] Optionally, the establishment of a small-signal frequency domain model with dual closed-loop voltage and current based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system includes: Based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system, the large-signal frequency domain equations of the voltage and current double closed loop in the dq coordinate system are written and then linearized to obtain the small-signal frequency domain model of the voltage and current double closed loop. The expression for the small-signal frequency domain model of the voltage-current dual closed loop is as follows: ; In the formula, , and These represent the voltage loop command value, inverter output current, and small-signal quantities of the output capacitor voltage in the inverter control reference coordinate system, respectively. and These are the transfer functions from the capacitor voltage command value and the inverter output current to the inverter output capacitor voltage, respectively.

[0007] Optionally, the establishment of a small-signal frequency domain model of the power controller based on the power calculation structure and power controller structure in the grid-connected inverter system includes: The power calculation formula in the power calculation structure in the dq coordinate system is linearized by small signal to obtain the transfer function of the power calculation link; Based on the power controller structure, write the large-signal frequency domain equations for power control and perform small-signal linearization to obtain the small-signal model of the power controller for the grid-type inverter. By combining the transfer function of the power calculation stage with the small-signal model of the power controller, the small-signal frequency domain model of the power controller is obtained.

[0008] Optionally, the establishment of a small-signal frequency domain model of the line impedance based on the line impedance structure in the grid-connected inverter system includes: Based on the physical relationship of line impedance, the large-signal frequency domain equation of line impedance is written and then linearized to obtain the small-signal frequency domain model of line impedance. The expression for the small-signal frequency domain model of the line impedance is as follows: ; In the formula, This refers to the small signal quantity of the inverter output capacitor voltage in the inverter control reference coordinate system. This refers to the small signal quantity of the inverter grid connection point voltage in the inverter control reference coordinate system. This is the transfer function of line impedance.

[0009] Optionally, the establishment of a small-signal frequency domain model for coordinate transformation based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in a grid-connected inverter system includes: Based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system, the large-signal frequency domain equation of the coordinate transformation is written and the small-signal linearization is performed to obtain the small-signal frequency domain model of the coordinate transformation. The expression for the small-signal frequency domain model of the coordinate transformation is as follows: ; In the formula, For the Laplace operator, For small signal quantities at the power grid frequency, A small signal quantity for the inverter output frequency. This refers to the small signal quantity of the inverter grid connection point voltage in the system reference coordinate system. and All of these are coordinate transformation transfer functions.

[0010] Optionally, the expression for the grid-type inverter model is: ; In the formula, This is the transfer function of the active power controller. A small semaphore representing the active power command value. and These are the small signal quantities representing the active and reactive power outputs of the inverter, respectively. This is the transfer function from reactive power deviation to the dq-axis voltage command value. A small semaphore representing the reactive power command value. and These are the transfer functions from output current and capacitor voltage to output active power, respectively. and These are the transfer functions from output current and capacitor voltage to output reactive power, respectively.

[0011] Optionally, it also includes: The grid-connected inverter model is transformed by using the output active power and output reactive power of the grid-connected system as output variables to obtain the grid-connected inverter power loop model. The power loop model of the grid-connected inverter is simplified in the first step to obtain the active power related transfer function of the grid-connected inverter. The first simplification process includes: retaining the active power as the output variable and canceling the other intermediate variables. The power loop model of the grid-connected inverter is simplified in a second way to obtain the reactive power related transfer function of the grid-connected inverter. The second simplification process includes: retaining reactive power as the output variable and canceling the other intermediate variables.

[0012] A second aspect of the present invention provides a grid-type inverter modeling system, the system comprising: The first establishment unit is used to establish a small-signal frequency domain model of voltage and current double closed loop based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system. The second establishment unit is used to establish a small-signal frequency domain model of the power controller based on the power calculation structure and power controller structure in the grid-connected inverter system. The third establishment unit is used to establish a small-signal frequency domain model of the line impedance based on the line impedance structure in the grid-connected system of the grid-connected inverter. The fourth unit is used to establish a small-signal frequency domain model of coordinate transformation based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in a grid-connected inverter system. The fifth establishment unit is used to establish the small-signal frequency domain model of the voltage and current dual closed loop, the small-signal frequency domain model of the power controller, the small-signal frequency domain model of the line impedance, and the small-signal frequency domain model of the coordinate transformation to obtain the grid-type inverter model.

[0013] A third aspect of the present invention provides a grid-type inverter modeling device, the device comprising a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the steps of the grid-type inverter modeling method as described in the first aspect above, according to the instructions in the program code.

[0014] A fourth aspect of the present invention provides a computer-readable storage medium for storing program code for executing the grid-type inverter modeling method described in the first aspect above.

[0015] As can be seen from the above technical solutions, the present invention has the following advantages: This invention provides a modeling method for grid-connected inverters. Based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system, a small-signal frequency domain model of the voltage and current dual closed loop is established. Based on the power calculation structure and power controller structure in the grid-connected inverter system, a small-signal frequency domain model of the power controller is established. Based on the line impedance structure in the grid-connected inverter system, a small-signal frequency domain model of the line impedance is established. Based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in the grid-connected inverter system, a small-signal frequency domain model of coordinate transformation is established. By combining the small-signal frequency domain models of the voltage and current dual closed loop, the power controller, the line impedance, and the coordinate transformation, the grid-connected inverter model is obtained. This invention establishes a closed-loop small-signal model of the power loop of a distributed grid-connected inverter for distribution networks using the small-signal analysis method. The model is accurate, scalable, and widely applicable. It can accurately describe the power and frequency dynamics of the grid-connected inverter and provides a precise mathematical model for parameter optimization, damping response, and inertia response of the grid-connected inverter, laying a solid foundation for the large-scale application of distributed grid-connected inverters for distribution networks. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart illustrating a grid-type inverter modeling method provided in an embodiment of the present invention; Figure 2 A schematic diagram of a distributed grid-connected inverter system for distribution networks provided in an embodiment of the present invention; Figure 3 A control block diagram of a distributed grid-type inverter device for distribution networks provided in an embodiment of the present invention; Figure 4 A block diagram of a voltage and current dual closed-loop model in a distributed grid inverter provided in an embodiment of the present invention; Figure 5 A model block diagram of the power controller in a distributed grid inverter provided in an embodiment of the present invention; Figure 6 This is a model block diagram of a distributed grid-type inverter provided in an embodiment of the present invention; Figure 7A power loop model block diagram of a distributed grid-type inverter provided in an embodiment of the present invention; Figure 8 The modeling results and frequency sweep results of the distributed grid-type inverter device provided in the embodiments of the present invention are shown in the figure. Figure 9 This is a schematic diagram of a grid-type inverter modeling system provided in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] Please see Figure 1 The present invention provides a grid-type inverter modeling method, comprising: Step 101: Based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system, establish a small-signal frequency domain model of voltage and current dual closed loop. In one embodiment, step 101 includes: Based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system, the large-signal frequency domain equations of the voltage and current double closed loop in the dq coordinate system are written and then linearized to obtain the small-signal frequency domain model of the voltage and current double closed loop. It should be noted that the voltage and current loop controller in a grid-connected inverter system, such as... Figure 3 As shown, the inverter main circuit structure is as follows: Figure 2 As shown, including as Figure 2 The bridge arm and filter inductor shown L f and filter capacitor C fFirst, based on the voltage and current loop controller and inverter main circuit structure in a grid-connected inverter system, the large-signal frequency domain equations of the voltage and current dual closed loops in the dq coordinate system are written. This involves first using the dq coordinate system to convert the three-phase AC time-varying variables into quasi-DC variables for simplified modeling. Based on the dual closed-loop collaborative control logic where the voltage loop maintains stable output voltage and the current loop quickly tracks commands and limits overcurrent, combined with the inverter main circuit and controller structure and electrical laws, a complete dynamic equation retaining the system's nonlinear characteristics is derived. This equation is then transformed into frequency domain form using a Laplace transform, resulting in the large-signal frequency domain equations. These equations form the basis for subsequent small-signal linearization and system stability analysis. Next, small-signal linearization is performed to obtain the small-signal frequency domain model of the voltage and current dual closed loops. This involves establishing the voltage and current dual closed-loop large-signal frequency domain equations in the dq coordinate system based on the voltage and current loop controller and inverter main circuit. By assuming that the disturbances to the system variables are much smaller than the steady-state values, small-signal linearization is performed, transforming the nonlinear large-signal equations into a linear small-signal frequency domain model. Finally, this is presented in block diagram form (see [link]). Figure 4 , Figure 4 (a) is a block diagram of the small-signal frequency domain model of the power calculation stage, which corresponds to the power calculation transfer function model obtained after performing small-signal linearization on the power calculation formula in the dq coordinate system in step 201. Figure 4 Figure (b) shows the small-signal frequency domain model block diagram of the active power loop (VSG control) and reactive power loop (PI control), corresponding to the transfer function models of the active power controller (VSG) and reactive power controller (PI) listed in step 202. The two combined constitute a complete small-signal frequency domain model of the power controller.

[0020] The expression for the small-signal frequency domain model of the voltage-current dual closed loop is as follows: ; In the formula, , and These represent the voltage loop command value, inverter output current, and small-signal quantities of the output capacitor voltage in the inverter control reference coordinate system, respectively. and These are the transfer functions from the capacitor voltage command value and the inverter output current to the inverter output capacitor voltage, respectively.

[0021] The expression for the transfer function from the capacitor voltage command value and the inverter output current to the inverter output capacitor voltage is as follows: ; In the formula, This is the characteristic formula for a voltage-current dual closed-loop circuit. 2 The identity matrix of 2, and These are the transfer functions for the voltage and current controllers, respectively. The transfer function for PWM modulation. and Let be the transfer functions of the filter inductor and filter capacitor in an LC filter, respectively, and their expressions are as follows: ; In the formula, k pv and k iv These are the proportional and integral coefficients of the voltage controller, respectively. k pc and k ic These are the proportional and integral coefficients of the current controller, respectively. V dc This represents the steady-state value of the DC-side voltage of the inverter. C f , L f and r Lf These are the filter capacitor, filter inductor, and their parasitic resistance, respectively, in Ω. c This represents the steady-state value of the inverter's output frequency. s For the Laplace operator.

[0022] Step 102: Based on the power calculation structure and power controller structure in the grid-connected inverter system, establish a small-signal frequency domain model of the power controller; It should be noted that the power calculation structure can be found in the following document. Figure 3 Power controller such as Figure 3 As shown, that is Figure 3 The blue part.

[0023] In one embodiment, step 102 includes: Step 1021: Perform small-signal linearization on the power calculation formula in the power calculation structure under the dq coordinate system to obtain the transfer function of the power calculation link; It should be noted that by performing small-signal linearization on the power calculation formula in the power calculation structure in the dq coordinate system, the transfer function of the power calculation stage is obtained, and its expression is as follows: ; In the formula, and These are the small signal quantities representing the active and reactive power outputs of the inverter, respectively. and These are the transfer functions from output current and capacitor voltage to output active power, respectively. and Let be the transfer functions from output current and capacitor voltage to output reactive power, respectively, and their expressions are: ; In the formula, , , and These are the steady-state values ​​of the capacitor voltage and the output current d-axis and q-axis components, respectively, in the inverter control coordinate system.

[0024] Step 1022: Write the large-signal frequency domain equations for power control based on the power controller structure and perform small-signal linearization to obtain the small-signal model of the power controller for the grid-type inverter. It should be noted that, based on the structure of the grid-type inverter power controller (containing active VSG control and reactive PI control), the large-signal frequency domain equations of power control with the nonlinear characteristics of the system are first written out. Then, by assuming that the variable disturbance is much smaller than the steady-state value, small-signal linearization is performed to transform the nonlinear equations into a linear small-signal frequency domain model. Finally, a small-signal model that can be used to analyze the dynamic response and stability of the power controller is obtained.

[0025] ; In the formula, , and These are small signal quantities representing the active power command value, the reactive power command value, and the inverter output frequency, respectively. G ωp This is the transfer function of the active power controller. The transfer function from reactive power deviation to the dq-axis voltage command value is expressed as follows: ; In the formula, ω 0 represents the inverter's rated angular frequency. J and D These are the inertia and damping coefficient of the active loop, respectively. k pq and k iq These are the proportional and integral coefficients of the reactive power controller, respectively.

[0026] Step 1023: Combine the transfer function of the power calculation stage with the small-signal model of the power controller to obtain the small-signal frequency domain model of the power controller.

[0027] It should be noted that the transfer function model of the power calculation stage obtained in step 1021 by linearizing the small-signal power calculation formula in the dq coordinate system is integrated with the small-signal power controller model obtained in step 1022 by writing and linearizing the large-signal equation based on the power controller structure to form a complete small-signal frequency domain model of the power controller. This model is presented in block diagram form (please refer to...). Figure 5 The presentation visually demonstrates the transmission relationship between power calculation and various components of the controller.

[0028] Step 103: Based on the line impedance structure in the grid-connected inverter system, establish a small-signal frequency domain model of the line impedance. It should be noted that you should refer to [link / reference]. Figure 2 The line impedance structure specifically refers to the AC side impedance of the distributed grid inverter in the distribution network. L C After the filter, the equivalent impedance of the distribution lines connected to the common junction point via distribution lines is determined by the equivalent line inductance ( L C ) and equivalent line resistance ( R C It consists of two parts.

[0029] In one embodiment, step 103 includes: Based on the physical relationship of line impedance, the large-signal frequency domain equation of line impedance is written and then linearized to obtain the small-signal frequency domain model of line impedance. It should be noted that this is based on the fact that the circuit is equivalent to an inductor. L C With resistance R C The physical relationship of series connection is first described by writing large-signal frequency domain equations to depict the nonlinear dynamics between line voltage and current. Then, assuming that disturbances in the electrical quantities of the line are much smaller than their steady-state values, small-signal linearization is applied to the large-signal equations to eliminate nonlinear terms. Finally, a linear frequency domain model reflecting the impedance transfer characteristics under small-signal disturbances is obtained. This model uses the transfer function G... ZC This indicates that its parameters are directly related to the equivalent line inductance. L C and resistance R C .

[0030] Among them, the small-signal frequency domain model of line impedance: ; In the formula, G is the small signal quantity of the inverter grid connection point voltage in the inverter control reference coordinate system. ZC Let be the transfer function of the line impedance, and its expression is: ; In the formula, L C and R C These are the equivalent line inductance and line resistance, respectively.

[0031] Step 104: Based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in the grid-connected inverter system, establish a small-signal frequency domain model of coordinate transformation; It should be noted that the coordinate transformation relationship between the inverter control reference coordinate system and the system reference coordinate system is based on the power angle δ (the phase difference between the inverter output voltage and the grid voltage). This is used to realize the conversion of electrical quantities (such as grid connection point voltage) between the inverter control side and the grid system side under different reference systems.

[0032] In one embodiment, step 104 includes: Based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system, the large-signal frequency domain equation of the coordinate transformation is written and the small-signal linearization is performed to obtain the small-signal frequency domain model of the coordinate transformation. It should be noted that, firstly, the steady-state values ​​based on the power angle between the inverter control reference coordinate system and the system reference coordinate system should be clearly defined. The coordinate transformation relationship is determined; then, based on this transformation relationship, a large-signal frequency domain equation describing the voltage variable transformation between the two coordinate systems is written (preserving nonlinear characteristics); then, assuming that the electrical disturbances involved in the coordinate system transformation are much smaller than their steady-state values, the large-signal equation is linearized using small-signal methods to eliminate nonlinear terms; finally, the equation is obtained from the transfer function... and The coordinate transformation small-signal frequency domain model represents the steady-state operating point of the inverter grid-connected voltage along the d and q axes and the steady-state value of the power angle in the system reference coordinate system. This model can describe the transformation characteristics of variables between two coordinate systems under small signal perturbation.

[0033] Among them, the small-signal frequency domain model of coordinate transformation: ; In the formula, This refers to the small signal quantity of the inverter grid connection point voltage in the system reference coordinate system. and The coordinate transformation transfer function is expressed as follows: ; In the formula, and These represent the steady-state operating points of the inverter grid-connected voltage along the d and q axes, respectively, in the system reference coordinate system. δ 0 represents the steady-state value of the inverter's power angle.

[0034] Step 105: Combine the small-signal frequency domain models of the voltage and current dual closed loops, the small-signal frequency domain model of the power controller, the small-signal frequency domain model of the line impedance, and the small-signal frequency domain model of the coordinate transformation to obtain the grid-type inverter model.

[0035] It should be noted that the established voltage and current dual-loop small-signal frequency domain models, power controller small-signal frequency domain models, line impedance small-signal frequency domain models, and coordinate transformation small-signal frequency domain models are connected according to the actual signal transmission and physical connection relationships (e.g., the frequency and voltage commands output by the power controller serve as inputs to the voltage and current dual-loop, the output of the voltage and current dual-loop is transmitted to the grid connection point via the line impedance model, and then associated with the system reference coordinate system through the coordinate transformation model, while the power calculation stage feeds back to the power controller to form a closed loop). By integrating the transfer functions and variable relationships of each model, a complete model block diagram of the grid-connected inverter is obtained (see [link to relevant documentation]). Figure 6 The mathematical expression for ) is: ; In the formula, This is the transfer function of the active power controller. A small semaphore representing the active power command value. and These are the small signal quantities representing the active and reactive power outputs of the inverter, respectively. This is the transfer function from reactive power deviation to the dq-axis voltage command value. A small semaphore representing the reactive power command value. and These are the transfer functions from output current and capacitor voltage to output active power, respectively. and These are the transfer functions from output current and capacitor voltage to output reactive power, respectively.

[0036] It should be noted that the grid-connected inverter model obtained in step 105 involves all variable relationships across multiple stages, including voltage and current dual closed loops, power controllers, line impedance, and coordinate transformations, making it quite complex. Subsequent steps 106-108 focus on the more critical power and frequency dynamic characteristics of the grid-connected system: Step 106 uses the output active / reactive power as the core output variable to extract the power loop model, clarifying the key transmission path of power dynamics; Steps 107-108 further eliminate intermediate variables, obtaining the relevant transfer functions for active and reactive power, making the model simpler and allowing direct quantification of the impact of inputs such as active power commands, reactive power commands, grid frequency, and grid voltage on output power. This provides accurate and easy-to-use mathematical tools for parameter optimization, damping response, and inertia response analysis of grid-connected inverters.

[0037] In one embodiment, step 105 is followed by: Step 106: Transform the grid-connected inverter model by using the output active power and output reactive power of the grid-connected system as output variables to obtain the grid-connected inverter power loop model. It should be noted that, based on the grid-connected inverter model block diagram obtained in step 105, with active and reactive power output as the core output variables, the signal transmission paths in the model are reorganized. Links directly related to power dynamics (such as power calculation, power controller, and parts affecting power in coordinate transformation) are retained, and the representations of internal auxiliary links such as voltage and current dual closed loops are merged or simplified. Finally, a grid-connected inverter power loop model is obtained that focuses solely on the dynamic relationship between power input (command value, grid parameters) and output (active / reactive power), as shown below. Figure 7 As shown.

[0038] Step 107: Perform a first simplification process on the power loop model of the grid-type inverter to obtain the active power related transfer function of the grid-type inverter. The first simplification process includes: retaining the active power as the output variable and canceling the other intermediate variables. Understandably, by retaining active power as the output variable and canceling out other intermediate variables, the above model can be simplified to obtain the active power-related transfer function of the grid-connected inverter: ; In the formula, G pP0 , G pQ0 , G pω and G pv Let be the closed-loop transfer function from the active power command value, reactive power command value, grid frequency, and grid voltage to the inverter output active power, respectively. Where: ; Step 108: Perform a second simplification process on the power loop model of the grid-type inverter to obtain the reactive power related transfer function of the grid-type inverter. The second simplification process includes: keeping the reactive power as the output variable and canceling the other intermediate variables.

[0039] Understandably, by retaining reactive power as the output variable and canceling out other intermediate variables, the above model can be simplified to obtain the reactive power-related transfer function of the grid-connected inverter: ; In the formula, G qP0 , G qQ0 , G qω and Gqv Let be the closed-loop transfer function from the active power command value, reactive power command value, grid frequency, and grid voltage to the inverter output reactive power, respectively. Where: ; The following is a description of the simulation examples: This embodiment utilizes MATLAB / Simulink to build a grid-connected inverter. DC power, after passing through the DC bus capacitor, is converted into three-phase AC power by the grid-connected inverter and then fed into the power grid through the line impedance. The electrical parameter settings during the simulation are shown in Table 1. Table 1

[0040] Figure 8 These are the modeling and frequency sweep results of the distributed grid-type inverter of this invention. Figure 8 It can be seen that the frequency sweep results are basically consistent with the modeling results, indicating that the modeling method of the distributed grid-type inverter of the present invention is accurate and effective.

[0041] This invention establishes a closed-loop small-signal model of the power loop of a distributed grid-connected inverter for distribution networks using the small-signal analysis method. The model is accurate, scalable, and widely applicable. It can accurately describe the power and frequency dynamics of the grid-connected inverter and provides a precise mathematical model for parameter optimization, damping response, and inertia response of the grid-connected inverter, laying a solid foundation for the large-scale application of distributed grid-connected inverters for distribution networks.

[0042] The above is a modeling method for a grid-type inverter provided in the embodiments of the present invention. The following is a modeling system for a grid-type inverter provided in the embodiments of the present invention.

[0043] Please see Figure 9 The present invention provides a grid-type inverter modeling system, comprising: The first establishment unit 201 is used to establish a small-signal frequency domain model of voltage and current double closed loop based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system. The second establishment unit 202 is used to establish a small-signal frequency domain model of the power controller based on the power calculation structure and power controller structure in the grid-connected inverter system. The third establishment unit 203 is used to establish a small-signal frequency domain model of the line impedance based on the line impedance structure in the grid-connected system of the grid-connected inverter. The fourth unit 204 is used to establish a small-signal frequency domain model of coordinate transformation based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in the grid-connected inverter system. The fifth unit 205 is used to establish the small-signal frequency domain model of the voltage and current dual closed loop, the small-signal frequency domain model of the power controller, the small-signal frequency domain model of the line impedance, and the small-signal frequency domain model of the coordinate transformation to obtain the grid-type inverter model.

[0044] Furthermore, this embodiment of the invention also provides a grid-type inverter modeling device, the device including a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the steps of the grid-type inverter modeling method as described in the above method embodiments, according to the instructions in the program code.

[0045] Furthermore, this embodiment of the invention also provides a computer-readable storage medium for storing program code, which is used to execute the grid-type inverter modeling method described in the above method embodiments.

[0046] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the system and unit described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0047] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.

[0048] 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 units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0049] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0050] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. 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 of 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.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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. Such 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 modeling a grid-type inverter, characterized in that, include: Based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system, a small-signal frequency domain model of voltage and current dual closed loop is established. Based on the power calculation structure and power controller structure in the grid-connected inverter system, a small-signal frequency domain model of the power controller is established. Based on the line impedance structure in a grid-connected inverter system, a small-signal frequency domain model of the line impedance is established. Based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in a grid-connected inverter system, a small-signal frequency domain model of coordinate transformation is established. By combining the small-signal frequency domain model of the voltage and current dual closed loop, the small-signal frequency domain model of the power controller, the small-signal frequency domain model of the line impedance, and the small-signal frequency domain model of the coordinate transformation, a grid-type inverter model is obtained.

2. The grid-type inverter modeling method according to claim 1, characterized in that, The voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system are used to establish a small-signal frequency domain model with dual closed-loop voltage and current, including: Based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system, the large-signal frequency domain equations of the voltage and current double closed loop in the dq coordinate system are written and then linearized to obtain the small-signal frequency domain model of the voltage and current double closed loop. The expression for the small-signal frequency domain model of the voltage-current dual closed loop is as follows: ； In the formula, , and These represent the voltage loop command value, inverter output current, and small-signal quantities of the output capacitor voltage in the inverter control reference coordinate system, respectively. and These are the transfer functions from the capacitor voltage command value and the inverter output current to the inverter output capacitor voltage, respectively.

3. The grid-type inverter modeling method according to claim 2, characterized in that, The power calculation structure and power controller structure in the grid-connected inverter system are used to establish a small-signal frequency domain model of the power controller, including: The power calculation formula in the power calculation structure in the dq coordinate system is linearized by small signal to obtain the transfer function of the power calculation link; Based on the power controller structure, write the large-signal frequency domain equations for power control and perform small-signal linearization to obtain the small-signal model of the power controller for the grid-type inverter. By combining the transfer function of the power calculation stage with the small-signal model of the power controller, the small-signal frequency domain model of the power controller is obtained.

4. The grid-type inverter modeling method according to claim 3, characterized in that, The small-signal frequency domain model of the line impedance is established based on the line impedance structure in the grid-connected inverter system, including: Based on the physical relationship of line impedance, the large-signal frequency domain equation of line impedance is written and then linearized to obtain the small-signal frequency domain model of line impedance. The expression for the small-signal frequency domain model of the line impedance is as follows: ； In the formula, This refers to the small signal quantity of the inverter output capacitor voltage in the inverter control reference coordinate system. This refers to the small signal quantity of the inverter grid connection point voltage in the inverter control reference coordinate system. This is the transfer function of line impedance.

5. The grid-type inverter modeling method according to claim 4, characterized in that, The transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in the grid-connected inverter system is used to establish a small-signal frequency domain model of coordinate transformation, including: Based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system, the large-signal frequency domain equation of the coordinate transformation is written and the small-signal linearization is performed to obtain the small-signal frequency domain model of the coordinate transformation. The expression for the small-signal frequency domain model of the coordinate transformation is as follows: ； In the formula, For the Laplace operator, For small signal quantities at the power grid frequency, A small signal quantity for the inverter output frequency. This refers to the small signal quantity of the inverter grid connection point voltage in the system reference coordinate system. and All of these are coordinate transformation transfer functions.

6. The grid-type inverter modeling method according to claim 5, characterized in that, The expression for the grid-type inverter model is: ； In the formula, This is the transfer function of the active power controller. A small semaphore representing the active power command value. and These are the small signal quantities representing the active and reactive power outputs of the inverter, respectively. This is the transfer function from reactive power deviation to the dq-axis voltage command value. A small semaphore representing the reactive power command value. and These are the transfer functions from output current and capacitor voltage to output active power, respectively. and These are the transfer functions from output current and capacitor voltage to output reactive power, respectively.

7. The grid-type inverter modeling method according to claim 6, characterized in that, Also includes: The grid-connected inverter model is transformed by using the output active power and output reactive power of the grid-connected system as output variables to obtain the grid-connected inverter power loop model. The power loop model of the grid-connected inverter is simplified in the first step to obtain the active power related transfer function of the grid-connected inverter. The first simplification process includes: retaining the active power as the output variable and canceling the other intermediate variables. The power loop model of the grid-connected inverter is simplified in a second way to obtain the reactive power related transfer function of the grid-connected inverter. The second simplification process includes: retaining reactive power as the output variable and canceling the other intermediate variables.

8. A grid-type inverter modeling system, characterized in that, include: The first establishment unit is used to establish a small-signal frequency domain model of voltage and current double closed loop based on the voltage and current loop controller and inverter main circuit structure in the grid-connected inverter system. The second establishment unit is used to establish a small-signal frequency domain model of the power controller based on the power calculation structure and power controller structure in the grid-connected inverter system. The third establishment unit is used to establish a small-signal frequency domain model of the line impedance based on the line impedance structure in the grid-connected system of the grid-connected inverter. The fourth unit is used to establish a small-signal frequency domain model of coordinate transformation based on the transformation relationship between the inverter control reference coordinate system and the system reference coordinate system in a grid-connected inverter system. The fifth establishment unit is used to establish the small-signal frequency domain model of the voltage and current dual closed loop, the small-signal frequency domain model of the power controller, the small-signal frequency domain model of the line impedance, and the small-signal frequency domain model of the coordinate transformation to obtain the grid-type inverter model.

9. A grid-type inverter modeling device, characterized in that, The device includes a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the grid-type inverter modeling method according to any one of claims 1-7 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used to store program code for executing the grid-type inverter modeling method according to any one of claims 1-7.

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