Modeling method and related device for multi-construction-network converter grid-connected system

Abstract

The invention belongs to the technical field of new energy grid connection, and discloses a modeling method and a related device for a grid-connected system of a multi-constructed-network converter, and the method comprises the steps: decomposing the system into two key sub-modules, namely a constructed-network converter module and a network module, and carrying out the precise description of each module through employing a state space model, thereby achieving the modeling of a multi-constructed-network converter grid-connected system. And then a virtual grounding resistor is introduced at an interconnection node of the multi-network-construction-type converter grid-connected system, and the small signal state space model of the network-construction-type converter module and the small signal state space model of the network module are integrated, so that a small signal state space model of the multi-network-construction-type converter grid-connected system is obtained. According to the modular modeling mode, the flexibility and expandability of the model are remarkably improved, the model can easily adapt to grid-connected systems of different scales and configurations, the complexity of system modeling is greatly reduced, and the modeling time and cost are effectively saved. In addition, a clear theoretical framework is provided for system stability analysis, and efficient and stable operation of the grid-connected system can be achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy grid connection, and relates to a multi-grid-forming converter grid-connected system modeling method and related devices. BACKGROUND

[0002] With the promotion of energy transformation and the continuous development of renewable energy generation technology, the proportion of renewable energy such as wind energy and solar energy in the power system is increasing. New energy connected through power electronic devices such as converters gradually becomes the main power source in the power grid. In the current power system, the grid-connected converters of photovoltaic, wind power and energy storage devices basically all adopt Grid-Following (GFL) control, which realizes synchronization by phase-locked loop tracking of grid voltage. However, the interaction between GFL converter and weak grid may cause system instability, thereby hindering the growth of the proportion of renewable energy in the power grid. In recent years, the concept of Grid-Forming (GFM) control has been proposed in the academic field and is considered an effective measure to improve the stability of renewable energy integration into weak grids. GFM control generates a reference phase of voltage by adjusting the power exchange with the grid, thereby realizing synchronization with the grid.

[0003] Grid-forming control technology has been developed and applied in uninterruptible power supply, independent power supply system and other scenarios for decades, and has given birth to a variety of control methods. Among them, the most common are droop control and virtual synchronous control technology. At the same time, due to the existence of various control methods, the modeling of multi-grid-forming converter grid-connected system faces many challenges, mainly manifested in that the modeling process of multi-grid-forming converter grid-connected system is complex, the generality and expansibility of the established model are not high, and the model cannot adapt to different grid topologies and grid-forming control methods. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a multi-grid-forming converter grid-connected system modeling method and related devices.

[0005] To achieve the above purpose, the following technical solutions are adopted in the present application:

[0006] According to a first aspect of the present invention, a method for modeling a multi-grid-type converter grid-connected system is provided, comprising: establishing a small-signal state-space model of each grid-type converter, a small-signal state-space model of each line, and a small-signal state-space model of a grid equivalent power supply in the multi-grid-type converter grid-connected system; converting the small-signal state-space model of each grid-type converter into a common reference coordinate system and arranging them in sequence to obtain a small-signal state-space model of the grid-type converter module; converting the small-signal state-space model of each line and the small-signal state-space model of the grid equivalent power supply into a common reference coordinate system and arranging them in sequence to obtain a small-signal state-space model of the network module; and introducing a virtual grounding resistance at the interconnected nodes of the multi-grid-type converter grid-connected system, integrating the small-signal state-space model of the grid-type converter module and the small-signal state-space model of the network module, to obtain a small-signal state-space model of the multi-grid-type converter grid-connected system.

[0007] Optionally, the common reference coordinate system is a rotating coordinate system determined by the grid voltage.

[0008] Optionally, when converting the small signal state space model of each grid-type converter to a common reference coordinate system and converting the small signal state space model of each line and the small signal state space model of the grid equivalent power supply to a common reference coordinate system, a coordinate system conversion equation L is used for conversion:

[0009] L:x DQ =T(δ)x dq

[0010]

[0011] Among them, x DQ is a variable in the common reference coordinate system; x dq is the variable in the current non-public reference coordinate system; δ is the phase angle difference between the public reference coordinate system and the current non-public reference coordinate system.

[0012] Optionally, when establishing the small signal state space model of each grid-type converter in the multi-grid-type converter grid-connected system, for different grid-type control methods of the grid-type converter, the small signal state space model of the grid-type converter is established by correspondingly establishing the small signal state space model of the power outer loop of the grid-type converter.

[0013] Optionally, the converting the small signal state space models of each meshed converter into a common reference coordinate system and arranging them in sequence to obtain the small signal state space model of the meshed converter module includes: converting the small signal state space models of each meshed converter into a common reference coordinate system, obtaining converted small signal state space models of each meshed converter, and arranging them in sequence to obtain the small signal state space model of the meshed converter module; wherein the converted small signal state space model of each meshed converter is:

[0014]

[0015] Δx invx =[Δx px Δψ dqx Δλ dqx Δi ldqx Δu odqx Δi odqx ] T

[0016] Where Δx invx is the state variable of the grid-type converter No. x; is Δx invx The differential form of Δω x The frequency variable generated by the network control link of the network converter No. x; Δu cDQx is the grid-side voltage of the grid-type converter No. x in the common reference coordinate system; Δi oDQx is the output current variable of the x-type grid-type converter in the common reference coordinate system; A inv is the state matrix of the grid-type converter No. x; B invx is the input matrix of the grid-type converter No. x; C invωx is the frequency output matrix of the grid-type converter No. x; C invcx is the current output matrix of the grid-type converter No. x; Δx px is the state variable of the grid-type converter control loop of x; Δψ dqx is the state variable of the voltage loop of the grid-type converter No. x in its own reference coordinate system; Δλ dqx is the state variable of the current loop of the grid-type converter No. x in its own reference coordinate system; Δi ldqx is the bridge arm current of the grid-type converter No. x in its own reference coordinate system; Δu odqx is the output voltage of the grid-type converter No. x in its own reference coordinate system; Δi odqx is the output current of the grid-type converter No. x in its own reference coordinate system.

[0017] The small signal state space model of the grid-type converter module is:

[0018]

[0019] Where Δx inv1、2...n are the state variables of the grid-type converters No. 1 to n; is Δx inv1、2...n The differential form of Δu cDQ1、2...n is the grid-side voltage of grid-type converters No. 1 to n in the common reference coordinate system; Δi oDQ1、2…n is the output current variable of the grid-type converters No. 1 to n in the common reference coordinate system; A inv1、2…n B is the state matrix of grid-type converters 1 to n; inv1、2…n is the input matrix of grid-type converters from 1 to n; C inv1、2…n A is the current output matrix of the meshed converters from 1 to n; inv B is the state matrix of the grid-type converter module; inv is the input matrix of the grid-type converter module; C invc It is the output matrix of the meshed converter module.

[0020] Optionally, the converting the small signal state space model of each line and the small signal state space model of the grid equivalent power supply into a common reference coordinate system and arranging them in sequence to obtain the small signal state space model of the network module includes: converting the small signal state space model of each line and the small signal state space model of the grid equivalent power supply into a common reference coordinate system, obtaining the converted small signal state space model of each line and the converted small signal state space model of the grid equivalent power supply, and arranging them in sequence to obtain the small signal state space model of the network module; wherein the converted small signal state space model of each line is:

[0021]

[0022] Among them, Δi lDQj is the current variable flowing through line j in the common reference coordinate system; is Δi lDQj The differential form of Δu cDQ,j and Δu cDQ,j+1 are the voltage variables of nodes j and j+1 in the common reference coordinate system; A lj is the state matrix of line j; B lj is the input matrix of line j.

[0023] The conversion small signal state space model of the grid equivalent power supply is:

[0024]

[0025] Among them, Δi gDQ is the grid current variable in the public reference coordinate system; is ΔigDQ the differential form of Δu cDQ1 is the voltage variable of the No.1 node in the common reference coordinate system; A g is the state matrix of the power grid; B g is the input matrix of the power grid.

[0026] The small-signal state space model of the network module is:

[0027]

[0028] wherein, Δi lDQ，1、2…(n-1) is the current variable flowing through the No.1 to No.n-1 lines in the common reference coordinate system; is the differential form of Δi lDQ，1、2…(n-1) the differential form of Δu cDQ,1、2…n is the voltage variable of the No.1 to No.n nodes in the common reference coordinate system; A l1、2…(n-1) is the state matrix corresponding to the No.1 to No.n-1 lines; B l1、2…(n-1) is the input matrix corresponding to the No.1 to No.n-1 lines; A l is the state matrix of the network module; B l is the input matrix of the network module.

[0029] Optionally, the small-signal state space model of the multi-constructed grid type converter grid-connected system is obtained by introducing the virtual grounding resistance at the interconnection node of the multi-constructed grid type converter grid-connected system, integrating the small-signal state space model of the constructed grid type converter module and the small-signal state space model of the network module, which comprises that after introducing the virtual grounding resistance at the interconnection node of the multi-constructed grid type converter grid-connected system, the expression of each node voltage is:

[0030]

[0031] wherein, r v is the resistance value of the virtual resistance; A r is the inverter connection matrix; B r is the network connection matrix.

[0032] Based on the expression of each node voltage, the small-signal state space model of the multi-constructed grid type converter grid-connected system is obtained by integrating the small-signal state space model of the constructed grid type converter module and the small-signal state space model of the network module:

[0033]

[0034] wherein, Δx s is the overall state variable of the multi-constructed grid type converter grid-connected system; is the differential form of Δx s ; A s is the system state matrix.

[0035] According to a second aspect of the present invention, a modeling system for a multi-grid-type converter grid-connected system is provided, comprising: a stand-alone model establishment module for establishing a small-signal state-space model of each grid-type converter, a small-signal state-space model of each line, and a small-signal state-space model of a grid equivalent power supply in the multi-grid-type converter grid-connected system; a converter model establishment module for converting the small-signal state-space model of each grid-type converter into a common reference coordinate system and arranging them in sequence to obtain a small-signal state-space model of the grid-type converter module; a network model establishment module for converting the small-signal state-space model of each line and the small-signal state-space model of the grid equivalent power supply into a common reference coordinate system and arranging them in sequence to obtain a small-signal state-space model of the network module; and an integration module for introducing a virtual grounding resistance at the interconnected nodes of the multi-grid-type converter grid-connected system, integrating the small-signal state-space model of the grid-type converter module and the small-signal state-space model of the network module, and obtaining a small-signal state-space model of the multi-grid-type converter grid-connected system.

[0036] According to a third aspect of the present invention, a computer device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned multi-grid converter grid-connected system modeling method when executing the computer program.

[0037] According to a fourth aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the above-mentioned multi-grid converter grid-connected system modeling method are implemented.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The modeling method of the multi-grid-type converter grid-connected system of the present invention successfully realizes the simplified modeling and analysis of complex power electronic systems by decomposing the grid-connected system into two key sub-modules: the grid-type converter module and the network module, and using the state space model to accurately describe each module. This modular modeling approach not only significantly improves the flexibility and scalability of the model, allowing the model to easily adapt to grid-connected systems of different scales and configurations, but also greatly reduces the complexity of system modeling, effectively saving modeling time and costs. In addition, the method provides a clear theoretical framework for system stability analysis, lays a solid foundation for control strategy design, and helps to achieve efficient and stable operation of the grid-connected system. It is particularly suitable for complex power electronic systems containing multiple grid-connected converters, and provides strong technical support for the optimized design and efficient operation of the grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1This is a flow chart of a method for modeling a multi-grid converter grid-connected system according to an embodiment of the present invention.

[0041] Figure 2 Schematic diagram of the structure of a multi-grid converter grid-connected system according to an embodiment of the present invention.

[0042] Figure 3 Schematic diagram of the model structure of the grid-type converter module according to an embodiment of the present invention.

[0043] Figure 4 Schematic diagram of the model structure of the network module according to an embodiment of the present invention.

[0044] Figure 5 Schematic diagram of a common reference coordinate system for a multi-grid converter grid-connected system according to an embodiment of the present invention.

[0045] Figure 6 This is a schematic diagram of the integration relationship and model structure of the multi-grid converter grid-connected system after the virtual grounding resistance is introduced in an embodiment of the present invention.

[0046] Figure 7 1 is a system characteristic value trajectory diagram under different virtual inertias according to an embodiment of the present invention.

[0047] Figure 8 1 is a diagram of system characteristic value trajectories under different active power droop coefficients according to an embodiment of the present invention.

[0048] Figure 9 This is a diagram showing the simulation results of a three-machine hybrid network system under different virtual inertias according to an embodiment of the present invention.

[0049] Figure 10 This is a diagram showing the simulation results of a three-machine hybrid grid system under different active power droop coefficients according to an embodiment of the present invention.

[0050] Figure 11 This is a system structure block diagram of a modeling system for a multi-grid converter grid-connected system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0052] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0053] The present invention is described in further detail below with reference to the accompanying drawings:

[0054] See also Figure 1 In one embodiment of the present invention, a method for modeling a multi-grid-type converter grid-connected system is provided, which can address the poor adaptability and insufficient scalability of prior art modeling of multi-grid-type converter grid-connected systems. Through modular design, the modeling method of the present invention effectively simplifies the modeling process for multi-grid-type converter grid-connected systems, improves the model's versatility and flexibility, and adapts to different power grid topologies and grid control methods.

[0055] Specifically, the multi-grid converter grid-connected system modeling method of the present invention includes the following steps:

[0056] S1: Establish the small signal state space model of each grid-type converter in the multi-grid-type converter grid-connected system, the small signal state space model of each line, and the small signal state space model of the grid equivalent power supply.

[0057] S2: The small signal state space models of each meshed converter are converted to a common reference coordinate system and arranged in sequence to obtain the small signal state space model of the meshed converter module.

[0058] S3: The small signal state space model of each line and the small signal state space model of the grid equivalent power supply are converted into a common reference coordinate system and arranged in sequence to obtain the small signal state space model of the network module.

[0059] S4: By introducing virtual grounding resistance at the interconnection nodes of the multi-grid converter grid-connected system, the small signal state space model of the grid converter module and the small signal state space model of the network module are integrated to obtain the small signal state space model of the multi-grid converter grid-connected system.

[0060] The modeling method of the multi-grid-type converter grid-connected system of the present invention successfully realizes the simplified modeling and analysis of complex power electronic systems by decomposing the grid-connected system into two key sub-modules: the grid-type converter module and the network module, and using the state space model to accurately describe each module. This modular modeling approach not only significantly improves the flexibility and scalability of the model, allowing the model to easily adapt to grid-connected systems of different scales and configurations, but also greatly reduces the complexity of system modeling, effectively saving modeling time and costs. In addition, the method provides a clear theoretical framework for system stability analysis, lays a solid foundation for control strategy design, and helps to achieve efficient and stable operation of the grid-connected system. It is particularly suitable for complex power electronic systems containing multiple grid-connected converters, and provides strong technical support for the optimized design and efficient operation of the grid-connected system.

[0061] Explanatory, see Figure 2 , shows a common multi-grid converter grid-connected system structure, where GFM1~GFMn are grid converters 1 to n, grid represents the power grid, U dc,1-n is the DC side voltage of the converter, i o,1-n ,i l,1-(n-1) and i g is the converter output current, the current flowing through the line and into the grid, Z g and E are the equivalent impedance and voltage of the grid, Z l,1-(n-1) is the line impedance.

[0062] Among the various control methods for grid-based control technologies, the most common are droop control and virtual synchronous generator (VSG) control. Droop control simulates the primary frequency and voltage regulation of synchronous generators based on the active power-frequency and reactive power-voltage curves to control the converter voltage frequency and amplitude. It features a simple control structure, rapid response, and the ability to quickly reach a stable state after a disturbance. However, it lacks the inertia element and the ability to support frequency rate of change. Its active power-frequency and reactive power-voltage equations are:

[0063]

[0064] Among them, ω n 、U n 、P set and Q set are the given values ​​of inverter rated frequency, rated voltage amplitude, active power and reactive power, respectively, m p and n q They are the active power droop coefficient and the reactive power droop coefficient respectively.

[0065] In droop control, the system automatically adjusts generator power output based on load changes to maintain system stability. As shown in the above expression, when the system frequency decreases, the generator increases its output power; conversely, when the frequency increases, the generator decreases its output power. This allows each generator to autonomously adjust its output based on system demand, eliminating reliance on communications and improving system reliability and flexibility.

[0066] Virtual synchronous control is based on the synchronous generator rotor motion equation and can simulate the inertia and damping characteristics of the synchronous generator to cope with frequency fluctuations. Its control equation is:

[0067]

[0068] Among them, J is the virtual moment of inertia, K is the reactive integral coefficient; D p is the active power droop coefficient, D q is the reactive droop coefficient; ω n is the rated frequency; U o and U n are the output voltage amplitude and rated voltage amplitude of the converter, ω and E * are the frequency and voltage amplitude of VSG.

[0069] In VSG control, the controller simulates the rotor motion and electromagnetic transient characteristics of a synchronous generator. When system frequency fluctuates, virtual synchronous control, like a traditional synchronous generator, uses rotor inertia and damping to smooth power fluctuations, providing inertia support and helping the system maintain frequency stability. This control method not only improves the system's frequency regulation capabilities but also enables better response to load changes or disturbances, enhancing grid stability.

[0070] State-space models, which describe the system's dynamic behavior through differential and algebraic equations, clearly reflect the interaction between the grid-type converter's internal state variables (such as voltage, current, and power) and control variables (such as power command values ​​and DC-side voltage command values), providing a mathematical foundation for stability analysis, parameter optimization, and control strategy design. Furthermore, state-space models can be combined with parameter uncertainty analysis to clarify the relationship between parameters and the system, improving the model's robustness under complex operating conditions.

[0071] For illustrative purposes, the modeling method for a multi-grid-type converter grid-connected system of the present invention first divides the multi-grid-type converter grid-connected system into a grid-type converter module and a network module. The state matrix, input, and output variables corresponding to each component are derived separately. Through the relationship between the input and output variables of each module and the operations between the corresponding matrices, the modules are integrated into a whole, thereby establishing a state space model of the entire multi-grid-type converter grid-connected system. Figure 3 and 4respectively show the model structure of the grid-connected converter module and the network module.

[0072] In a possible implementation, the common reference coordinate system is a rotating coordinate system determined by the grid voltage.

[0073] Explanatorily, for the small-signal state space model of each grid-connected converter, the small-signal state space model of each grid-connected converter is generally established in its own reference coordinate system, and it is necessary to transform the small-signal state space model of each grid-connected converter into the same common reference coordinate system for the convenience of analysis. Under small disturbance, the grid voltage frequency can be considered constant. Meanwhile, in order to simplify the model derivation process, the rotating coordinate system determined by the grid voltage is selected as the common reference coordinate system. Referring to Figure 5 , a common reference coordinate system diagram of a multi-grid-connected converter grid-connected system is shown, Figure 5 In the formula, ω0 is the angular frequency of the common reference coordinate system, ω is the frequency of another rotating coordinate system, and δ is the phase angle difference between the two coordinate systems.

[0074] In a possible implementation, when the small-signal state space model of each grid-connected converter is transformed into the common reference coordinate system and the small-signal state space model of each line and the small-signal state space model of the grid equivalent source are transformed into the common reference coordinate system, the coordinate system conversion equation L is used for conversion:

[0075] L: x DQ = T(δ) x dq

[0076]

[0077] In the formula, x DQ is a variable in the common reference coordinate system; x dq is a variable in the current non-common reference coordinate system; and δ is the phase angle difference between the common reference coordinate system and the current non-common reference coordinate system.

[0078] In a possible implementation, when the small-signal state space model of each grid-connected converter in the multi-grid-connected converter grid-connected system is established, for different grid-connected control methods of the grid-connected converter, the small-signal state space model of the grid-connected converter is established by corresponding establishment of the small-signal state space model of the power outer loop of the grid-connected converter.

[0079] Exemplarily, the phase angle difference between the reference coordinate system generated by the power outer loop of the grid-connected converter and the common reference coordinate system can be represented as:

[0080] δ = ∫(ω-ω0)dt

[0081] By linearizing the control equation of the power outer loop of the grid-type converter and the above equation, we can obtain the small signal state space model of the power outer loop of the grid-type converter, as shown in the following equation:

[0082]

[0083] In addition, the output variables of the common grid-type control methods, such as droop control, virtual synchronous control, and matching control, are frequency ω and voltage amplitude E, so their linearized output equations can be written as:

[0084]

[0085] Where Δx p is the state variable of the network control loop, which is composed of Δδ and the state variable introduced by the power outer loop. is Δx p Differential form of Δω, ΔE * The frequency and voltage amplitude variables generated by the network control link, Δi odq , Δi odq and Δi odq are the bridge arm current, output voltage and output current variables in their own reference coordinate system, A p 、B p 、C pω 、C pu 、D pω and D pu The coefficient matrix corresponding to the network control.

[0086] For different grid-type control methods, it is only necessary to model the power outer loop of the grid-type converter and replace different coefficient matrices A p 、B p 、C pw 、C pu 、D pw and D pu , we can get the small signal state space model of the grid-type converter corresponding to different grid-type control methods.

[0087] In a possible embodiment, the small signal state space model of each meshed converter is converted to a common reference coordinate system and then arranged in sequence to obtain the small signal state space model of the meshed converter module, including: converting the small signal state space model of each meshed converter to a common reference coordinate system, obtaining the converted small signal state space model of each meshed converter and arranging them in sequence to obtain the small signal state space model of the meshed converter module.

[0088] Explanatory, by integrating the small signal state space models of the power outer loop and the voltage and current inner loop, and transforming them through the coordinate system transformation equation, the conversion small signal state space model of a single grid-type converter can be obtained, specifically:

[0089]

[0090] Δx invx =[Δx px Δψ dqx Δλ dqx Δi ldqx Δu odqx Δi odqx ] T

[0091] Where Δx invx is the state variable of the grid-type converter No. x; is Δx invx The differential form of Δω x The frequency variable generated by the network control link of the network converter No. x; Δu cDQx is the grid-side voltage of the grid-type converter No. x in the common reference coordinate system; Δi oDQx is the output current variable of the x-type grid-type converter in the common reference coordinate system; A inv is the state matrix of the grid-type converter No. x; B invx is the input matrix of the grid-type converter No. x; C invωx is the frequency output matrix of the grid-type converter No. x; C invcx is the current output matrix of the grid-type converter No. x; Δx px is the state variable of the grid-type converter control loop of x; Δψ dqx is the state variable of the voltage loop of the grid-type converter No. x in its own reference coordinate system; Δλ dqx is the state variable of the current loop of the grid-type converter No. x in its own reference coordinate system; Δi ldqx is the bridge arm current of the grid-type converter No. x in its own reference coordinate system; Δu odqx is the output voltage of the grid-type converter No. x in its own reference coordinate system; Δi odqx is the output current of the grid-type converter No. x in its own reference coordinate system.

[0092] There are n grid-connected converters in the multi-grid-connected converter system. The small signal state space models of each grid-connected converter are arranged in sequence, and the small signal state space model of the grid-connected converter module is obtained as follows:

[0093]

[0094]

[0095] Where Δx inv1、2…n are the state variables of the grid-type converters No. 1 to n; is Δx inv1、2…n The differential form of Δu cDQ1、2…n is the grid-side voltage of grid-type converters No. 1 to n in the common reference coordinate system; Δi oDQ1、2…n is the output current variable of the grid-type converters No. 1 to n in the common reference coordinate system; A inv1、2…n B is the state matrix of grid-type converters 1 to n; inv1、2…n is the input matrix of grid-type converters from 1 to n; C inv1、2…n A is the current output matrix of the meshed converters from 1 to n; inv B is the state matrix of the grid-type converter module; inv is the input matrix of the grid-type converter module; C invc It is the output matrix of the meshed converter module.

[0096] In one possible implementation, the small signal state space model of each line and the small signal state space model of the grid equivalent power supply are converted into a common reference coordinate system and then arranged in sequence to obtain the small signal state space model of the network module, including: converting the small signal state space model of each line and the small signal state space model of the grid equivalent power supply into a common reference coordinate system, obtaining the converted small signal state space model of each line and the converted small signal state space model of the grid equivalent power supply, and arranging them in sequence to obtain the small signal state space model of the network module.

[0097] Explanatory, for the jth line, assume that the current direction is from node j+1 to node j. Then i ljDQ The algebraic differential equation that satisfies the following formula:

[0098]

[0099] By linearizing the above equation, the small signal state space model of the j-th line can be obtained as follows:

[0100]

[0101] Among them, Δi lDQj is the current variable flowing through line j in the common reference coordinate system; is Δi lDQj The differential form of Δu cDQ,j and Δu cDQ,j+1 are the voltage variables of nodes j and j+1 in the common reference coordinate system; A lj is the state matrix of line j; B ljis the input matrix of line j.

[0102] Similarly, the current flowing into the grid satisfies the following equation:

[0103]

[0104] By linearizing the above equation, the conversion small signal state space model of the grid equivalent power supply can be obtained as follows:

[0105]

[0106] Among them, Δi gDQ is the grid current variable in the public reference coordinate system; is Δi gDQ The differential form of Δu cDQ1 is the voltage variable of node 1 in the common reference coordinate system; A g is the state matrix of the power grid; B g is the input matrix of the power grid.

[0107] For a multi-grid-type converter grid-connected system with n grid-type converters, there are n-1 lines. The small signal state space models of each line and the grid equivalent power supply are arranged in sequence to form the small signal state space model of the network module. The small signal state space model of the network module is:

[0108]

[0109] Among them, Δi lDQ，1、2…(n-1) is the current variable flowing through lines 1 to n-1 in the common reference coordinate system; is Δi lDQ，1、2…(n-1) The differential form of Δu cDQ,1、2…n is the voltage variable of nodes 1 to n in the common reference coordinate system; A l1、2…(n-1) is the state matrix corresponding to lines 1 to n-1; B l1、2…(n-1) is the input matrix corresponding to lines 1 to n-1; A l is the state matrix of the network module; B l is the input matrix of the network module.

[0110] In one possible implementation, the method of introducing a virtual grounding resistor at the interconnection node of the multi-grid converter grid-connected system and integrating the small signal state space model of the grid-connected converter module and the small signal state space model of the network module to obtain the small signal state space model of the multi-grid converter grid-connected system includes: after the virtual grounding resistor is introduced at the interconnection node of the multi-grid converter grid-connected system, the expression of each node voltage is:

[0111]

[0112] Among them, r v is the resistance of the virtual resistor; A r B is the inverter connection matrix; r is the network connection matrix.

[0113] Based on the expression of each node voltage, the small signal state space model of the grid-connected converter module and the small signal state space model of the network module are integrated to obtain the small signal state space model of the multi-grid-connected converter grid-connected system:

[0114]

[0115] Where Δx s is the overall state variable of the multi-grid converter grid-connected system; Δx s The differential form of A s is the system state matrix.

[0116] Explanatory note: From the small-signal state-space models of the grid-connected converter module and the network module above, it can be seen that the voltage at each node in the grid-connected system is a common input variable. To eliminate this input variable, a virtual ground resistor is added at the interconnecting nodes of the grid-connected system. If the virtual ground resistor is sufficiently large, its impact can be ignored.

[0117] For multi-grid converter grid-connected systems, a virtual grounding resistor r is introduced. v After that, the expression of each node voltage can be expressed as:

[0118]

[0119] After linearization, the expressions of the voltages of the above nodes can be obtained.

[0120] See also Figure 6 , the integration relationship and model structure of the multi-grid converter grid-connected system after the introduction of virtual grounding resistance are shown. Based on this, the integration of the small signal state space model of the grid-connected converter module and the small signal state space model of the network module is realized, and the small signal state space model of the multi-grid converter grid-connected system is obtained.

[0121] In another embodiment of the present invention, the implementation process and results of the modeling method for a multi-grid-type converter grid-connected system of the present invention are described using a three-machine hybrid grid system as an example. The first and second grid-type converters are droop-controlled converters, and the third grid-type converter is a virtual synchronous machine. The converter rated parameters and circuit component parameters are shown in Table 1.

[0122] Table 1

[0123] parameter value <![CDATA[额定容量S n / kVA]]> 5000 <![CDATA[额定交流线电压U n / V]]> 690 <![CDATA[直流母线额定电压U dc / V]]> 1300 <![CDATA[交流电网频率f g / Hz]]> 50 <![CDATA[滤波电感L f / mH]]> 0.04 <![CDATA[滤波电容C f / mF]]> 1.2 <![CDATA[有功下垂系数m p ]]> 1.26×10-6 reactive droop coefficient n p ]]> 1.47×10-5 <![CDATA[惯量系数J n / kg·m 2 ]]> 500 Voltage integral coefficient K 2000 <![CDATA[电压环k vp ,k vi ]]> 1，3.5 <![CDATA[电流环k ip ,k ii ]]> 2，35 System short circuit ratio SCR 5

[0124] Substituting the parameters of the three-machine hybrid grid system into the small signal state space model of the multi-grid converter grid-connected system, its state space model can be obtained as shown in the following formula:

[0125]

[0126] Where Δx hys is all the state variables corresponding to the system, with a total of 37 dimensions, namely Δx hysys =[Δδ1, Δψ dq1 , Δλ dq1 , Δi ldq1 , Δu odq1 , Δi odq1 , Δδ2, Δψ dq2 , Δλ dq2 , Δi ldq2 , Δu odq2 , Δi odq2 , Δδ3, Δω3, ΔE * 3, Δψ dq3 , Δλ dq3 , Δi ldq3 , Δu odq3 , Δi odq3 , Δi gDQ ], A hys is the system characteristic matrix.

[0127] Based on the state-space model established above, the system stability characteristics it provides are analyzed and compared with simulation results to verify the correctness of the model established by the multi-grid converter grid-connected system modeling method of the present invention. The eigenvalues ​​of the characteristic matrix of the three-machine hybrid grid system are calculated, and the results are shown in Table 2.

[0128] Table 2

[0129]

[0130]

[0131] Set the parameters of the two grid-type converters according to Table 1, and only change the virtual inertia J of VSG from 0.1J to n Increased to 2J n , calculate the characteristic root loci of the VSG / Droop hybrid system respectively, and the results are as follows Figure 7 As shown. Figure 7 It can be seen that the eigenvalues ​​of No. 13, 14 and No. 21 to 26 of the hybrid system change little, while the eigenvalues ​​of No. 17 to 18 move to the right, the damping ratio becomes smaller, and the system stability becomes worse.

[0132] Only change the active power droop coefficient, mp By 2m pn Reduced to 0.5m pn , the results are as follows Figure 8 As shown. Figure 8 It can be seen that reducing m p When , the eigenvalues ​​8, 9, 13, 14, 19 and 20 of the system all move to the negative half plane, the damping ratio increases, the system stability improves, and the system response time shortens.

[0133] When the simulation is set to t = 4s, the grid frequency drops by 0.1Hz. Figure 9 and Figure 10 The dynamic response of the hybrid grid system under different virtual inertia and different active power droop coefficients is given. Figure 9 It can be found that as the inertia increases, the power input to the grid and the response speed of the system frequency slow down, and the overshoot increases. Figure 10 It can be found that as the droop coefficient decreases, the system power and frequency response speed becomes faster. The above simulation results are consistent with the analysis results of the model, effectively verifying the correctness of the small signal state space model of the multi-grid converter grid-connected system established by this multi-grid converter grid-connected system modeling method.

[0134] The following are device embodiments of the present invention, which can be used to perform the method embodiments of the present invention. For details not disclosed in the device embodiments, please refer to the method embodiments of the present invention.

[0135] See also Figure 11 In another embodiment of the present invention, a multi-grid type converter grid-connected system modeling system is provided, which can be used to implement the above-mentioned multi-grid type converter grid-connected system modeling method. Specifically, the multi-grid type converter grid-connected system modeling system includes a stand-alone model building module, a converter model building module, a network model building module and an integration module.

[0136] Among them, the single-machine model establishment module is used to establish the small signal state space model of each grid-type converter, the small signal state space model of each line and the small signal state space model of the grid equivalent power supply in the multi-grid-type converter grid-connected system; the converter model establishment module is used to convert the small signal state space model of each grid-type converter into a common reference coordinate system and arrange them in sequence to obtain the small signal state space model of the grid-type converter module; the network model establishment module is used to convert the small signal state space model of each line and the small signal state space model of the grid equivalent power supply into a common reference coordinate system and arrange them in sequence to obtain the small signal state space model of the network module; the integration module is used to integrate the small signal state space model of the grid-type converter module and the small signal state space model of the network module by introducing a virtual grounding resistance at the interconnection node of the multi-grid-type converter grid-connected system to obtain the small signal state space model of the multi-grid-type converter grid-connected system.

[0137] All relevant contents of each step involved in the embodiment of the aforementioned multi-grid converter grid-connected system modeling method can be referred to the functional description of the functional modules corresponding to the multi-grid converter grid-connected system modeling system in the embodiment of the present invention, and will not be repeated here.

[0138] The module division in the embodiments of the present invention is illustrative and represents only one logical functional division. In actual implementation, other division methods may be used. Furthermore, the functional modules in various embodiments of the present invention may be integrated into a single processor, exist physically as separate modules, or two or more modules may be integrated into a single module. The integrated modules may be implemented in either hardware or software functional modules.

[0139] In another embodiment of the present invention, a computer device is provided, comprising a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the multi-grid type converter grid-connected system modeling method.

[0140] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory). The computer-readable storage medium is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium herein may include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides storage space, which stores the terminal's operating system. In addition, the storage space also stores one or more instructions suitable for being loaded and executed by a processor. These instructions may be one or more computer programs (including program code). It should be noted that the computer-readable storage medium herein may be a high-speed RAM memory or a non-volatile memory, such as at least one disk storage device. The processor may load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the multi-grid-type converter grid-connected system modeling method described in the above embodiment.

[0141] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0142] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0143] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0144] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0145] 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 it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A modeling method for a multi-grid converter grid-connected system, characterized in that: include: Establish the small signal state space model of each grid-type converter in the multi-grid-type converter grid-connected system, the small signal state space model of each line, and the small signal state space model of the grid equivalent power supply; The small signal state space models of each meshed converter are converted to a common reference coordinate system and arranged in sequence to obtain the small signal state space model of the meshed converter module; The small signal state space model of each line and the small signal state space model of the grid equivalent power supply are converted into a common reference coordinate system and arranged in sequence to obtain the small signal state space model of the network module; By introducing virtual grounding resistance at the interconnection nodes of the multi-grid converter grid-connected system and integrating the small signal state space model of the grid-connected converter module and the small signal state space model of the network module, the small signal state space model of the multi-grid converter grid-connected system is obtained.

2. The multi-grid converter grid-connected system modeling method according to claim 1, characterized in that: The common reference coordinate system is a rotating coordinate system determined by the grid voltage.

3. The multi-grid converter grid-connected system modeling method according to claim 1, characterized in that: When converting the small signal state space model of each grid-type converter to a common reference coordinate system and converting the small signal state space model of each line and the small signal state space model of the grid equivalent power supply to a common reference coordinate system, the coordinate system conversion equation L is used for conversion: L:x DQ =T(δ)x dq Among them, x DQ is a variable in the common reference coordinate system; x dq is the variable in the current non-public reference coordinate system; δ is the phase angle difference between the public reference coordinate system and the current non-public reference coordinate system.

4. The multi-grid converter grid-connected system modeling method according to claim 1, characterized in that: When establishing the small signal state space model of each grid-type converter in the multi-grid-type converter grid-connected system, for different grid-type control methods of the grid-type converter, the small signal state space model of the grid-type converter is established by correspondingly establishing the small signal state space model of the power outer loop of the grid-type converter.

5. The multi-grid converter grid-connected system modeling method according to claim 1, characterized in that: The small signal state space models of the meshed converter modules are converted into a common reference coordinate system and arranged in sequence to obtain the small signal state space models of the meshed converter modules. The small signal state space models of the meshed converter modules are: The small signal state space model of each meshed converter is converted to a common reference coordinate system to obtain the converted small signal state space model of each meshed converter and arrange them in order to obtain the small signal state space model of the meshed converter module; wherein, the converted small signal state space model of each meshed converter is: Δx invx =[Δx px Dp dqx Dl dqx Yes ldqx Thu odqx Yes odqx ] T Where Δx invx is the state variable of the grid-type converter No. x; is Δx invx The differential form of Δω x The frequency variable generated by the network control link of the network converter No. x; Δu cDQx is the grid-side voltage of the grid-type converter No. x in the common reference coordinate system; Δi oDQx is the output current variable of the x-type grid-type converter in the common reference coordinate system; A inv is the state matrix of the grid-type converter No. x; B invx is the input matrix of the grid-type converter No. x; C invωx is the frequency output matrix of the grid-type converter No. x; C invcx is the current output matrix of the grid-type converter No. x; Δx px is the state variable of the grid-type converter control loop of x; Δψ dqx is the state variable of the voltage loop of the grid-type converter No. x in its own reference coordinate system; Δλ dqx is the state variable of the current loop of the grid-type converter No. x in its own reference coordinate system; Δi ldqx is the bridge arm current of the grid-type converter No. x in its own reference coordinate system; Δu odqx is the output voltage of the grid-type converter No. x in its own reference coordinate system; Δi odqx is the output current of the grid-type converter No. x in its own reference coordinate system; The small signal state space model of the grid-type converter module is: Where Δx inv1、2…n are the state variables of the grid-type converters No. 1 to n; is Δx inv1、2...n The differential form of Δu cDQ1、2...n is the grid-side voltage of grid-type converters No. 1 to n in the common reference coordinate system; Δi oDQ1、2…n is the output current variable of the grid-type converters No. 1 to n in the common reference coordinate system; A inv1、2...n B is the state matrix of grid-type converters 1 to n; inv1、2...n is the input matrix of grid-type converters from 1 to n; C inv1、2...n A is the current output matrix of the meshed converters from 1 to n; inv B is the state matrix of the grid-type converter module; inv is the input matrix of the grid-type converter module; C invc It is the output matrix of the meshed converter module.

6. The multi-grid converter grid-connected system modeling method according to claim 5, characterized in that: The small signal state space model of each line and the small signal state space model of the grid equivalent power supply are converted into a common reference coordinate system and arranged in sequence to obtain the small signal state space model of the network module, which includes: The small signal state space model of each line and the small signal state space model of the grid equivalent power supply are converted into a common reference coordinate system, and the converted small signal state space model of each line and the converted small signal state space model of the grid equivalent power supply are obtained and arranged in sequence to obtain the small signal state space model of the network module; Among them, the conversion small signal state space model of each line is: Among them, Δi lDQj is the current variable flowing through line j in the common reference coordinate system; is Δi lDQj The differential form of Δu cDQ,j and Δu cDQ,j+1 are the voltage variables of nodes j and j+1 in the common reference coordinate system; A lj is the state matrix of line j; B lj is the input matrix of line j; The conversion small signal state space model of the grid equivalent power supply is: Among them, Δi gDQ is the grid current variable in the public reference coordinate system; is Δi gDQ The differential form of Δu cDQ1 is the voltage variable of node 1 in the common reference coordinate system; A g is the state matrix of the power grid; B g is the input matrix of the power grid; The small signal state space model of the network module is: Among them, Δi lDQ，1、2...(n - 1) is the current variable flowing through lines 1 to n-1 in the common reference coordinate system; is Δi lDQ，1、2...(n-1) The differential form of Δu cDQ,1、2...n is the voltage variable of nodes 1 to n in the common reference coordinate system; A l1、2...(n-1) is the state matrix corresponding to lines 1 to n-1; B l1、2...(n-1) is the input matrix corresponding to lines 1 to n-1; A l is the state matrix of the network module; B l is the input matrix of the network module.

7. The multi-grid converter grid-connected system modeling method according to claim 6, characterized in that: The small signal state space model of the multi-grid converter grid-connected system is obtained by introducing a virtual grounding resistor at the interconnection node of the multi-grid converter grid-connected system and integrating the small signal state space model of the grid-connected converter module and the small signal state space model of the network module. The small signal state space model includes: After introducing virtual grounding resistance at the interconnection nodes of the multi-grid converter grid-connected system, the voltage expression of each node is: Among them, r v is the resistance of the virtual resistor; A r B is the inverter connection matrix; r is the network connection matrix; Based on the expression of each node voltage, the small signal state space model of the grid-connected converter module and the small signal state space model of the network module are integrated to obtain the small signal state space model of the multi-grid-connected converter grid-connected system: Where Δx s is the overall state variable of the multi-grid converter grid-connected system; is Δx s The differential form of A s is the system state matrix.

8. A multi-grid converter grid-connected system modeling system, characterized in that: include: A single-machine model building module is used to build the small-signal state-space model of each grid-type converter in a multi-grid-type converter grid-connected system, the small-signal state-space model of each line, and the small-signal state-space model of the grid equivalent power supply; A converter model building module is used to convert the small signal state space model of each meshed converter into a common reference coordinate system and arrange them in sequence to obtain the small signal state space model of the meshed converter module; A network model building module is used to convert the small signal state space model of each line and the small signal state space model of the grid equivalent power supply into a common reference coordinate system and arrange them in sequence to obtain the small signal state space model of the network module; The integration module is used to integrate the small signal state space model of the grid-connected converter module and the small signal state space model of the network module by introducing a virtual grounding resistance at the interconnection node of the multi-grid-connected converter system, so as to obtain the small signal state space model of the multi-grid-connected converter system.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the multi-grid converter grid-connected system modeling method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the multi-grid converter grid-connected system modeling method according to any one of claims 1 to 7 are implemented.

Images