Inverter impedance remodeling and network power flow control method based on virtual two ports

Abstract

The invention discloses a virtual two-port-based inverter impedance remodeling and network power flow control method. The virtual two-port-based inverter impedance remodeling and network power flow control method comprises a voltage source type inverter impedance remodeling method and a voltage source type inverter network power flow control method. According to the voltage source inverter impedance remodeling method, system impedance modeling is firstly analyzed, virtual two-port network parameters are designed, then a control signal is calculated and input into an original system, and impedance remodeling is completed; the voltage source type inverter network power flow control method comprises the steps of collecting data, building a line model, calculating power flow control parameters, calculating control signals, inputting the control signals into an original system, and completing power flow control. The invention discloses a virtual two-port-based inverter impedance remodeling and network power flow control method, and aims to solve the problems that parameters of existing virtual impedance control exceed an actual engineering achievable range in a strong negative impedance scene and parameter setting is complicated and stability and robustness are insufficient in an asymmetric impedance scene. According to the technical scheme of impedance remodeling, the problem is effectively solved by processing symmetric and asymmetric systems in a differentiated mode.

Description

Technical Field

[0001] This invention belongs to the field of inverter control technology and relates to a method for inverter impedance reshaping and network power flow control based on virtual two-port inverters. Background Technology

[0002] With the widespread application of voltage source converters (VSCs) in renewable energy grid integration and microgrids, stability issues arising from dynamic interactions are becoming increasingly prominent. The core challenges lie in the negative impedance characteristics and resistance / reactance ratios resulting from various inverter control methods (such as phase-locked loop control). R / X The problem of power decoupling is difficult to achieve in short-circuit scenarios where the ratio cannot be ignored.

[0003] Currently, the main system impedance control technology used in power systems is virtual impedance control technology. This technology achieves system passivity by adding virtual impedance to the original impedance. However, when the system has strong negative impedance characteristics, it is necessary to use extremely large positive virtual impedance to offset the negative impedance, which causes parameters such as virtual resistance and virtual inductance to far exceed the range that can be achieved in actual engineering (such as hardware capacity and cost limitations).

[0004] In actual VSC systems, factors such as phase-locked loop dynamics and non-ideal grid topology can cause impedance to exhibit asymmetrical characteristics. In this case, virtual impedance control needs to achieve passivity through impedance matrix correction, which requires solving complex parameter conditions. These conditions are affected by multivariate coupling, making parameter tuning difficult. Furthermore, when the grid impedance fluctuates, the parameters need to be resolved, resulting in insufficient stability and robustness, and easily triggering dq-axis coupled oscillations.

[0005] For the input impedance of a symmetrical system, if for any All have If the input impedance is passive, then its input impedance is said to be passive; for the input impedance of an asymmetric system, if for any ,matrix It is a positive definite matrix (i.e.) If the input impedance is passive, then its input impedance is said to be passive. For the power transmission of a transmission line, consider a transmission line between a voltage source inverter and the power grid, and assume the inverter-side voltage is... The grid-side voltage is The impedance of the transmission line is The power transmitted on the line is And they have the following relationship:

[0006] in, This represents the active power transmitted through the transmission line. This represents the reactive power transmitted by the transmission line. Indicates the magnitude of the grid-side voltage. This indicates the amplitude of the inverter-side voltage. This represents the phase angle difference between the inverter-side voltage and the grid-side voltage. This indicates the resistance of the transmission line. This represents the reactance of the transmission line.

[0007] In resistive feeders (scenarios where line resistance cannot be ignored), active power ( P ) and reactive power ( Q This can lead to strong coupling—changes in active power can interfere with reactive power regulation, and vice versa, resulting in decreased power distribution accuracy. Negative virtual resistance is achieved by introducing a virtual impedance parameter with characteristics opposite to those of the line resistance. PQ Decoupling allows for independent adjustment of active and reactive power control, improving the stability of local power distribution. However, when dealing with stable systems with strong negative impedance characteristics, unrealistic control parameters (such as excessively high virtual resistance) may be required. Furthermore, when virtual impedance control is tasked with controlling network power flow, its flexibility is insufficient because it can only provide virtual series compensation to the grid.

[0008] In summary, existing technologies suffer from several problems: unrealistic parameters for virtual impedance control in strong negative impedance scenarios; complex parameter tuning and poor robustness under asymmetrical impedance; and insufficient power flow control flexibility due to strong coupling between active and reactive power in resistive feeder scenarios. Summary of the Invention

[0009] The purpose of this invention is to provide an inverter impedance reshaping and network power flow control method based on virtual two-port, which solves the problems in the prior art where virtual impedance control parameters are impractical in strong negative impedance scenarios, parameter tuning is complex and has poor robustness under asymmetrical impedance, and the strong coupling between active and reactive power in resistive feeder scenarios leads to insufficient power flow control flexibility.

[0010] The technical solution adopted in this invention is an inverter impedance reshaping and network power flow control method based on virtual two-port, including a voltage source inverter impedance reshaping method and a voltage source inverter network power flow control method. The impedance reshaping method for voltage source inverters first analyzes and models the system impedance, designs virtual two-port network parameters, and then calculates the control signal input to the original system to complete the impedance reshaping. The power flow control method for voltage source inverter networks involves collecting data to build a line model, calculating power flow control parameters, and then calculating the control signal input to the original system to complete power flow control.

[0011] The invention is further characterized by: Impedance reshaping methods for voltage source inverters include: Step A1: Analyze and model the impedance characteristics of the original system; Step A2: Design the control parameters for the virtual two-port network; Step A3: Calculate the control signal based on the control parameters and input it into the original system to complete impedance reshaping.

[0012] Step A1 includes: Step A1.1: Collect electrical quantity data of the original impedance system; Step A1.2: Construct the original system impedance model based on the system classification; Based on the system input impedance, the original system is divided into symmetric and asymmetric systems. The system input impedance is the ratio of the voltage to the current at the point of common coupling from the grid terminal to the inverter terminal. The input impedance of a symmetrical system is represented by a vector form for voltage. Current and system input impedance The relationship is:

[0013]

[0014] in, Represents the voltage phasor in a symmetrical system. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the current phasor in a symmetrical system. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Indicates the system's input impedance. Indicates input impedance The real part, Indicates input impedance The imaginary part; The input impedance of an asymmetric system is represented by a real-space vector representing voltage. Current The system input impedance is represented in matrix form: , in Represents the voltage real space vector. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the real space vector of current. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Represents the system input impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the q-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current to the q-axis voltage in the impedance matrix.

[0015] Step A2 includes: Step A2.1: Design the structure of the transfer matrix for the two-port network; Step A2.2: Associate the transfer matrix of the two-port network with the Pi-type equivalent circuit; Step A2.3: Design parameters for different scenarios; For the input impedance of a symmetrical system, if its real part Then, a system consisting of finite positive components is used. , and That's sufficient; if the real part of the system input impedance is... Even with finite negative values, the aforementioned control parameters can still meet the requirements of most systems. If not, the following can be calculated: positive , and Values ​​can be used for control, or they can be set to... Virtual two-port control is converted into virtual impedance control by setting... This allows for control; For the input impedance of an asymmetric system, let , , , .

[0016] The relationship between the transfer matrix of the two-port network in step A2.1 and the voltage and current across the two-port network is shown below:

[0017]

[0018]

[0019] , , , , in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the q-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 1 of a two-port network. The q-axis current component represents the complex vector of the current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 2 of the two-port network. This represents the q-axis voltage component of the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 2 of a two-port network. The q-axis current component represents the complex vector of the current at port 2 of a two-port network. The transfer matrix in step A2.2 The relationship between the Pi-type equivalent circuit and is as follows:

[0020]

[0021]

[0022]

[0023] Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis component.

[0024] Step A3 includes: For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as

[0025] Then after control , Before control , The relationship is as follows:

[0026] in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows:

[0027] in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input.

[0028] Power flow control methods for voltage source inverter networks include: Step B1: After collecting transmission line data, construct a transmission line model; Step B2: Calculate power flow control parameters based on the transmission line model; Step B3: Calculate the power flow control signal based on the power flow control parameters and input it into the original system to complete the network power flow control.

[0029] Step B1 includes: Step B1.1: Collect transmission line and voltage parameters; Step B1.2: Construct a transmission line model for virtual two-port network control; The voltage-current-transfer matrix relationship at both ends of the virtual two-port network is shown below:

[0030]

[0031]

[0032] in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. The relationship between the transfer matrix and the Pi-type equivalent circuit of the virtual two-port network is as follows:

[0033] Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. This represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit.

[0034] Step B2 includes: After simplifying the transmission line model controlled by a virtual two-port network, through... Specific expressions and The specific expression derivation shows that: due to and It is known that, through and It can control the voltage amplitude and phase angle by changing and The value is adjusted to control the impedance relationship of the transmission line; The specific expression is:

[0035] in, This represents the equivalent impedance of the transmission line after being controlled by a virtual two-port network. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the equivalent impedance. This represents the virtual part auxiliary variable defined when deriving the equivalent impedance. This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. Represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. The specific expression is:

[0036] in, This represents the target equivalent impedance of a transmission line under virtual two-port network control. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the target equivalent impedance. This represents the virtual sub-variable auxiliary variable defined when deriving the target equivalent impedance. L This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. This represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. This represents the direct-axis component of the impedance of the middle arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the middle bridge arm in a virtual two-port network.

[0037] Step B3 includes: For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as

[0038] Then after control , Before control , The relationship is as follows:

[0039] in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows:

[0040] in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input.

[0041] The beneficial effects of this invention are as follows: Addressing the problems of existing virtual impedance control parameters exceeding practically achievable ranges in strong negative impedance scenarios and complex parameter tuning and insufficient stability and robustness in asymmetrical impedance scenarios, the impedance reshaping technology of this invention effectively solves these problems by differentiating between symmetrical and asymmetrical systems. For symmetrical systems, when the real part of the system input impedance exhibits extremely strong negative characteristics, there is no need to use excessively large positive virtual impedances; impedance reshaping can be achieved simply by configuring the impedances of the left, middle, and right arms of a Pi-type equivalent circuit composed of finite positive components. When the real part of the symmetrical system input impedance is finitely negative, virtual two-port control can be transformed into a simplified virtual impedance control mode, achieving control simply by setting the impedance of the middle arm of the Pi-type equivalent circuit, significantly simplifying the parameter configuration process. For asymmetric systems, there is no need to solve complex parameter conditions affected by multivariable coupling. The parameter tuning can be completed simply by setting the correspondence of specific block elements in the virtual two-port network transfer matrix. Furthermore, there is no need to resolve the parameters when the grid impedance fluctuates, which significantly improves the system's stability and robustness. At the same time, it ensures that the passive requirement of the input impedance can be met after control, regardless of whether the system is symmetric or asymmetric, thus providing a guarantee for the dynamic stability of the system.

[0042] To address the issue of insufficient power flow control flexibility caused by strong coupling between active and reactive power in resistive feeder scenarios, this invention achieves a breakthrough by constructing a virtual two-port network control transmission line model and its equivalent simplified structure. This scheme equates the virtual two-port network to a Pi-type circuit. Through the derivation and analysis of the equivalent impedance of the transmission line, it is clarified that, given the direct-axis and quadrature-axis impedance components of the original transmission line, the amplitude and phase angle of the grid-side voltage can be precisely controlled by adjusting the direct-axis and quadrature-axis impedance components of the Pi-type circuit's arm closest to the grid. Furthermore, by adjusting the direct-axis and quadrature-axis impedance components of the middle arm of the Pi-type circuit, the impedance relationship of the transmission line can be flexibly adjusted, thereby breaking the strong coupling between active and reactive power and enabling independent adjustment of both, thus improving the flexibility of power allocation. Simultaneously, when it is necessary to adjust the grid-side voltage amplitude by a factor or the voltage phase angle incrementally, this scheme can be implemented as long as specific operating conditions are met, significantly improving the flexibility and applicability of network power flow control and enhancing the accuracy of power transmission in transmission lines.

[0043] The technical solution of this invention also possesses significant advantages in engineering practicality, with low computational and implementation costs and a wide range of applicability. In terms of control parameter solving, no complex derivation and iterative calculations are required; only the input impedance of the existing system or the impedance parameters of the transmission line need to be selected accordingly, reducing computational costs and difficulty. In terms of engineering implementation, no large-scale modification of the original voltage source inverter system is required; only the addition of corresponding input feedforward and output feedback channels to the original system is needed to achieve the control function, reducing the difficulty and cost of engineering implementation. Regarding its applicability, this method can not only meet the impedance reshaping requirements of symmetrical and asymmetrical systems but also adapt to the network power flow control requirements of different types of transmission lines. It can be applied to general voltage source inverter systems, and is particularly suitable for renewable energy grid connection and microgrid scenarios, possessing broad practicality and promotional value. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the Pi-type equivalent circuit in the voltage source inverter impedance reshaping method of the present invention; Figure 2 This is a virtual two-port control block diagram of the input impedance of a symmetrical system in the voltage source inverter impedance reshaping method of the present invention; Figure 3 This is a virtual two-port control block diagram of the input impedance of an asymmetric system in the voltage source inverter impedance reshaping method of the present invention; Figure 4 This is a schematic diagram of the transmission line after virtual two-port control in the voltage source inverter network power flow control method of the present invention; Figure 5 This is a schematic diagram of the equivalent structure of the transmission line after virtual two-port control in the voltage source inverter network power flow control method of the present invention; Figure 6 This is a different virtual two-port control under the embodiments of the present invention. under what value? A schematic diagram. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0046] Inverter impedance reshaping and network power flow control methods based on virtual two-port converters include: Impedance reshaping methods for voltage source inverters include: Step A1: Analyze and model the impedance characteristics of the original system; Step A1.1: Collect electrical quantity data of the original impedance system; Step A1.2: Construct the original system impedance model based on the system classification; Based on the system input impedance, the original system is divided into symmetric and asymmetric systems. The system input impedance is the ratio of the voltage to the current at the point of common coupling from the grid terminal to the inverter terminal. The input impedance of a symmetrical system is represented by a vector form for voltage. Current and system input impedance The relationship is:

[0047]

[0048] in, Represents the voltage phasor in a symmetrical system. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the current phasor in a symmetrical system. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Indicates the system's input impedance. Indicates input impedance The real part, Indicates input impedance The imaginary part; The input impedance of an asymmetric system is represented by a real-space vector representing voltage. Current The system input impedance is represented in matrix form: , in Represents the voltage real space vector. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the real space vector of current. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Represents the system input impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the q-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current to the q-axis voltage in the impedance matrix; Step A2: Design the control parameters for the virtual two-port network; Step A2.1: Design the structure of the transfer matrix for the two-port network; The relationship between the transfer matrix of a two-port network and the voltage and current across the two-port network is shown below:

[0049]

[0050]

[0051] , , , , in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the q-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 1 of a two-port network. The q-axis current component represents the complex vector of the current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 2 of the two-port network. This represents the q-axis voltage component of the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 2 of a two-port network. The q-axis current component represents the complex vector of the current at port 2 of a two-port network. Step A2.2: Associate the transfer matrix of the two-port network with the Pi-type equivalent circuit; Transfer matrix The relationship between the Pi-type equivalent circuit and is as follows:

[0052]

[0053]

[0054]

[0055] Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components; Step A2.3: Design parameters for different scenarios; For the input impedance of a symmetrical system, if its real part Then, a system consisting of finite positive components is used. , and That's sufficient; if the real part of the system input impedance is... Even with finite negative values, the aforementioned control parameters can still meet the requirements of most systems. If not, the following can be calculated: positive , and Values ​​can be used for control, or they can be set to... Virtual two-port control is converted into virtual impedance control by setting... This allows for control; For the input impedance of an asymmetric system, let , , , ; Step A3: Calculate the control signal based on the control parameters and input it into the original system to complete impedance reshaping; For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as

[0056] Then after control , Before control , The relationship is as follows:

[0057] in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows:

[0058] in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. Power flow control methods for voltage source inverter networks include: Step B1: After collecting transmission line data, construct a transmission line model; Step B1.1: Collect transmission line and voltage parameters; Step B1.2: Construct a transmission line model for virtual two-port network control; The voltage-current-transfer matrix relationship at both ends of the virtual two-port network is shown below:

[0059]

[0060]

[0061] in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. The relationship between the transfer matrix and the Pi-type equivalent circuit of the virtual two-port network is as follows:

[0062] Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. Represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit; Step B2: Calculate power flow control parameters based on the transmission line model; After simplifying the transmission line model controlled by a virtual two-port network, through... Specific expressions and The specific expression derivation shows that: due to and It is known that, through and It can control the voltage amplitude and phase angle by changing and The value is adjusted to control the impedance relationship of the transmission line; The specific expression is:

[0063] in, This represents the equivalent impedance of the transmission line after being controlled by a virtual two-port network. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the equivalent impedance. This represents the virtual part auxiliary variable defined when deriving the equivalent impedance. This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. This represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. The specific expression is:

[0064] in, This represents the target equivalent impedance of a transmission line under virtual two-port network control. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the target equivalent impedance. This represents the virtual sub-variable auxiliary variable defined when deriving the target equivalent impedance. L This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. This represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. This represents the direct-axis component of the impedance of the middle arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the middle bridge arm in a virtual two-port network. Step B3: Calculate the power flow control signal based on the power flow control parameters and input it into the original system to complete the network power flow control; For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as

[0065] Then after control , Before control , The relationship is as follows:

[0066] in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows:

[0067] in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. This invention proposes impedance reshaping and network power flow control for voltage source inverters based on a virtual two-port network. The virtual two-port network refers to a method similar to virtual impedance control, which effectively adds a two-port network to the system, thereby achieving system impedance reshaping and network power flow control. This method offers more reasonable parameter settings and more flexible control strategies. This invention first requires obtaining a system input impedance or line impedance, and then designs the control based on the actual application scenario. The proposed method is computationally simple and easy to implement, requiring only the addition of corresponding control loops to the original system, effectively solving the impedance reshaping and network power flow control problems in power systems. Furthermore, the calculation of control parameters is simple, requiring only selection based on the existing system input impedance or transmission line impedance; the controller design is concise and easy to implement, requiring only the addition of input feedforward and output feedback channels to the original system; and it has broad applicability, suitable for general voltage source inverter systems.

[0068] In this invention and These are the voltage and current at port 1 (flowing from port 1 to port 2), which also represent the system's initial input and output. and These are the voltage and current at port 2 (flowing from port 1 to port 2), representing the system's input and output after control. For example... Figure 1 As shown, and The impedances of the left and right arms of the Pi-type equivalent circuit are given. Let be the bridge arm impedance of the Pi-type equivalent circuit. For the input impedance of a symmetrical system, if its real part... Then, as long as we use a system composed of finite positive components... , and That's sufficient. If the real part of the system input impedance... Even with finite negative values, the aforementioned control parameters can still meet the requirements of most systems. If not, the following can be calculated: positive , and Values ​​can be used for control, or they can be set to... Virtual two-port control is converted into virtual impedance control by setting... Control can then be achieved. For the input impedance of an asymmetric system, let... , , , .

[0069] Power flow control methods for voltage source inverter networks, such as Figure 4As shown, the transmission line model controlled by the virtual two-port network is equivalent to connecting a Pi-type two-port network at the point of common junction, where... For the impedance of the transmission line, For the bridge arm impedance closest to the inverter side, For the bridge arm impedance closest to the grid side, For the impedance of the middle bridge arm, The voltage at the point of common coupling. This refers to the grid voltage. like Figure 5 As shown, the transmission line model of virtual two-port network control is equivalent to... Figure 5 The form shown, where , When it is necessary to adjust the amplitude and phase angle of the grid-side voltage (to change the amplitude to...) k The sum is increased based on the original phase angle. When ), as long as k and Virtual two-port control can be used when the following relationship is satisfied:

[0070] in, The direct-axis component representing the impedance of a transmission line. The quadrature-axis component represents the impedance of a transmission line. This represents the change in voltage phase angle. k This represents the adjustment coefficient for voltage amplitude; Example 1 This embodiment proposes a method for inverter impedance reshaping and network power flow control based on virtual two-port inverters, including a voltage source inverter impedance reshaping method and a voltage source inverter network power flow control method. The voltage source inverter impedance reshaping method first analyzes the system impedance model, designs virtual two-port network parameters, and then calculates the control signal input to the original system to complete impedance reshaping. The voltage source inverter network power flow control method collects data to build a line model, calculates power flow control parameters, and then calculates the control signal input to the original system to complete power flow control.

[0071] Example 2 This embodiment proposes a method for inverter impedance reshaping and network power flow control based on virtual two-port, including a voltage source inverter impedance reshaping method and a voltage source inverter network power flow control method. Impedance reshaping methods for voltage source inverters include: Step A1: Analyze and model the impedance characteristics of the original system; Step A2: Design the control parameters for the virtual two-port network; Step A3: Calculate the control signal based on the control parameters and input it into the original system to complete impedance reshaping; Power flow control methods for voltage source inverter networks include: Step B1: After collecting transmission line data, construct a transmission line model; Step B2: Calculate power flow control parameters based on the transmission line model; Step B3: Calculate the power flow control signal based on the power flow control parameters and input it into the original system to complete the network power flow control.

[0072] Example 3 This embodiment proposes a method for inverter impedance reshaping and network power flow control based on virtual two-port inverters, including a voltage source inverter impedance reshaping method and a voltage source inverter network power flow control method. The voltage source inverter impedance reshaping method first analyzes the system impedance model, designs virtual two-port network parameters, and then calculates the control signal input to the original system to complete impedance reshaping. The voltage source inverter network power flow control method collects data to build a line model, calculates power flow control parameters, and then calculates the control signal input to the original system to complete power flow control.

[0073] Impedance reshaping methods for voltage source inverters include: Step A1: Analyze and model the impedance characteristics of the original system; Step A1.1: Collect electrical quantity data of the original impedance system; Step A1.2: Construct the original system impedance model based on the system classification; Based on the system input impedance, the original system is divided into symmetric and asymmetric systems. The system input impedance is the ratio of the voltage to the current at the point of common coupling from the grid terminal to the inverter terminal. The input impedance of a symmetrical system is represented by a vector form for voltage. Current and system input impedance The relationship is:

[0074]

[0075] in, Represents the voltage phasor in a symmetrical system. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the current phasor in a symmetrical system. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Indicates the system's input impedance. Indicates input impedance The real part, Indicates input impedance The imaginary part; The input impedance of an asymmetric system is represented by a real-space vector representing voltage. Current The system input impedance is represented in matrix form: , in Represents the voltage real space vector. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the real space vector of current. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Represents the system input impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the q-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current to the q-axis voltage in the impedance matrix; Step A2: Design the control parameters for the virtual two-port network; Step A2.1: Design the structure of the transfer matrix for the two-port network; Step A2.2: Associate the transfer matrix of the two-port network with the Pi-type equivalent circuit; Step A2.3: Design parameters for different scenarios; For the input impedance of a symmetrical system, if its real part Then, a system consisting of finite positive components is used. , and That's sufficient; if the real part of the system input impedance is... Even with finite negative values, the aforementioned control parameters can still meet the requirements of most systems. If not, the following can be calculated: positive , and Values ​​can be used for control, or they can be set to... Virtual two-port control is converted into virtual impedance control by setting... This allows for control; For the input impedance of an asymmetric system, let , , , ; Step A3: Calculate the control signal based on the control parameters and input it into the original system to complete impedance reshaping.

[0076] In this embodiment, the system input impedance is symmetrical. .in , The value is negative. It is known that the input impedance of this system does not satisfy the passive condition. What is the input impedance of the above system? The real part of the original system input impedance Assume the control objective is to make the input impedance of the system passive after control (…). In this example, the system input impedance is symmetrical, therefore the control method for symmetrical cases is used. . and thus obtain =2.25-0.75j, =12-20j, =0.2-0.05j, =2.25-0.75j, E=0.545-0.457j, =-1.143+6.903j, =-0.05+0.036j, =0.545-0.457j; the result is as follows Figure 6 As shown by the curve, in hour The value is basically stable, and for all values ​​less than 0... This control can enable .

[0077] Example 4 This embodiment proposes a method for inverter impedance reshaping and network power flow control based on virtual two-port inverters, including a voltage source inverter impedance reshaping method and a voltage source inverter network power flow control method. The voltage source inverter impedance reshaping method first analyzes the system impedance model, designs virtual two-port network parameters, and then calculates the control signal input to the original system to complete impedance reshaping. The voltage source inverter network power flow control method collects data to build a line model, calculates power flow control parameters, and then calculates the control signal input to the original system to complete power flow control.

[0078] Impedance reshaping methods for voltage source inverters include: Step A1: Analyze and model the impedance characteristics of the original system; Step A2: Design the control parameters for the virtual two-port network; Step A2.1: Design the structure of the transfer matrix for the two-port network; The relationship between the transfer matrix of a two-port network and the voltage and current across the two-port network is shown below:

[0079]

[0080]

[0081] , , , , in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the q-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 1 of a two-port network. The q-axis current component represents the complex vector of the current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 2 of the two-port network. This represents the q-axis voltage component of the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 2 of a two-port network. The q-axis current component represents the complex vector of the current at port 2 of a two-port network. Step A2.2: Associate the transfer matrix of the two-port network with the Pi-type equivalent circuit; Transfer matrix The relationship between the Pi-type equivalent circuit and is as follows:

[0082]

[0083]

[0084]

[0085] Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components; Step A2.3: Design parameters for different scenarios; For the input impedance of a symmetrical system, if its real part Then, a system consisting of finite positive components is used. , and That's sufficient; if the real part of the system input impedance is... Even with finite negative values, the aforementioned control parameters can still meet the requirements of most systems. If not, the following can be calculated: positive , and Values ​​can be used for control, or they can be set to... Virtual two-port control is converted into virtual impedance control by setting... This allows for control; For the input impedance of an asymmetric system, let , , , ; Step A3: Calculate the control signal based on the control parameters and input it into the original system to complete impedance reshaping; For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as

[0086] Then after control , Before control , The relationship is as follows:

[0087] in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows:

[0088] in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input.

[0089] In this embodiment, the system input impedance is asymmetrical. =-200, =60, =40, =-100. It is known that the input impedance of this system does not satisfy the passive condition. What is the input impedance of the above system? The sum of the original system input impedance and its transpose Non-positive definite. Assume the control objective is to make the input impedance of the system passive after control ( In this example, the system input impedance is asymmetrical, therefore the control method for asymmetrical cases is used. , , , The result is as follows: Figure 6 As shown by the straight line. eigenvalues It always satisfies the passive condition.

[0090] Example 5 This embodiment proposes a method for inverter impedance reshaping and network power flow control based on virtual two-port inverters, including a voltage source inverter impedance reshaping method and a voltage source inverter network power flow control method. The voltage source inverter impedance reshaping method first analyzes the system impedance model, designs virtual two-port network parameters, and then calculates the control signal input to the original system to complete impedance reshaping. The voltage source inverter network power flow control method collects data to build a line model, calculates power flow control parameters, and then calculates the control signal input to the original system to complete power flow control.

[0091] Power flow control methods for voltage source inverter networks include: Step B1: After collecting transmission line data, construct a transmission line model; Step B1.1: Collect transmission line and voltage parameters; Step B1.2: Construct a transmission line model for virtual two-port network control; The voltage-current-transfer matrix relationship at both ends of the virtual two-port network is shown below:

[0092]

[0093]

[0094] in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. The relationship between the transfer matrix and the Pi-type equivalent circuit of the virtual two-port network is as follows:

[0095] Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. This represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit.

[0096] Step B2: Calculate power flow control parameters based on the transmission line model; Step B3: Calculate the power flow control signal based on the power flow control parameters and input it into the original system to complete the network power flow control.

[0097] In this embodiment, the system input impedance is symmetrical. .in , The value is negative. It is known that the input impedance of this system does not satisfy the passive condition. What is the input impedance of the above system? ,in =0.5, =0.08, and =390 , Assume the control objective is to... The amplitude drops to around 380, while the phase angle remains essentially unchanged, and this causes the transmission line to... .Pick Therefore, from (5) and (6), we get =1.25+0.25j, =0.1-0.1j, =0.01+5j, =1, E=1.20-0.40j, =-0.16+0.08j, =-1.99-6.02j, =1.40 + 0.80j. After control. , =0.49 + j5.09. At this point... 0.97 =378.3, the phase angle changes to Transmission line impedance ,at this time .

[0098] Example 6 This embodiment proposes a method for inverter impedance reshaping and network power flow control based on virtual two-port inverters, including a voltage source inverter impedance reshaping method and a voltage source inverter network power flow control method. The voltage source inverter impedance reshaping method first analyzes the system impedance model, designs virtual two-port network parameters, and then calculates the control signal input to the original system to complete impedance reshaping. The voltage source inverter network power flow control method collects data to build a line model, calculates power flow control parameters, and then calculates the control signal input to the original system to complete power flow control.

[0099] Power flow control methods for voltage source inverter networks include: Step B1: After collecting transmission line data, construct a transmission line model; Step B2: Calculate power flow control parameters based on the transmission line model; After simplifying the transmission line model controlled by a virtual two-port network, through... Specific expressions and The specific expression derivation shows that: due to and It is known that, through and It can control the voltage amplitude and phase angle by changing and The value is adjusted to control the impedance relationship of the transmission line; The specific expression is:

[0100] in, This represents the equivalent impedance of the transmission line after being controlled by a virtual two-port network. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the equivalent impedance. This represents the virtual part auxiliary variable defined when deriving the equivalent impedance. This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. This represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. The specific expression is:

[0101] in, This represents the target equivalent impedance of a transmission line under virtual two-port network control. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the target equivalent impedance. This represents the virtual sub-variable auxiliary variable defined when deriving the target equivalent impedance. L This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. This represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. This represents the direct-axis component of the impedance of the middle arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the middle bridge arm in a virtual two-port network. Step B3: Calculate the power flow control signal based on the power flow control parameters and input it into the original system to complete the network power flow control; For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as

[0102] Then after control , Before control , The relationship is as follows:

[0103] in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows:

[0104] in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input.

[0105] Figure 1 This is a schematic diagram of the Pi-type equivalent circuit in the impedance reshaping method of the voltage source inverter of the present invention. The diagram shows the core components of the Pi-type equivalent circuit, where Z1(s) is the complex frequency domain impedance of the left arm of the circuit, Z3(s) is the complex frequency domain impedance of the right arm, and Z2(s) is the complex frequency domain impedance of the middle bridge arm. This circuit corresponds to the port characteristics of the two-port network. The voltage v1 and current i1 of port 1 (flowing from port 1 to port 2, representing the original input and output of the system) and the voltage v2 and current i2 of port 2 (flowing in the same direction as port 1, representing the input and output of the system after control) can be reflected by the impedance characteristics through this circuit, providing a basis for the derivation of subsequent control parameters.

[0106] Figure 2 This is a virtual two-port control block diagram of the input impedance of a symmetrical system in the impedance reshaping method for voltage source inverters of this invention. The block diagram includes the signal transmission paths and calculation modules required for symmetrical system control, and can reflect the voltage v and current i of the system before control and the voltage i of the system after control. Current The correlation incorporates elements E and F of the inverse matrix of the virtual two-port network transfer matrix and elements C and D of the transfer matrix blocks. Through signal computation and transmission, control signal calculation is achieved, ultimately ensuring that the input impedance of the controlled symmetrical system meets the passivity requirement (i.e., Re(Z(s)) = Z). n (s)>0, Re(s)>0).

[0107] Figure 3 This is a virtual two-port control block diagram of the input impedance of an asymmetric system in the impedance reshaping method of a voltage source inverter of the present invention. For the asymmetric system design represented by the impedance matrix Z(s), it presents the system voltage vector v and current vector i before control, and the voltage vector voltage after control. Current vector The signal relationships incorporate the block elements A, B, C, and D of the transfer matrix that satisfy the requirements a1=c1≠0, a2=c2≠0, b1=d1≠0, and b2=d2≠0. These elements are used to generate control signals through logical operations, ensuring that the input impedance of the asymmetric system meets the passive requirement after control (i.e.,...). (s)+ (s) It is a positive definite matrix. Re (s)>0).

[0108] Figure 4 This is a schematic diagram of the transmission line after virtual two-port control in the voltage source inverter network power flow control method of the present invention. The diagram shows the transmission line structure connected to the Pi-type two-port network at the point of common coupling. The impedance of the transmission line is marked. The impedances of the three arms of the Pi-type network are Z1 near the inverter side, Z3 near the grid side, and Z2 in the middle. The voltage at the point of common coupling and the grid voltage are also marked, clearly showing the connection relationship of each part.

[0109] Figure 5 This is a schematic diagram of the equivalent structure of the transmission line after virtual two-port control in the voltage source inverter network power flow control method of the present invention. The transmission line model is simplified equivalently in the figure, and the key equivalent impedance Z is marked. eq1 and Z eq2 Z eq1 Z is the parallel impedance of Z3 and Z2, Z eq2 For Z2 and Z eq1 The series impedance, this equivalent structure can be used to derive the series voltage amplitude regulation (coefficient) of the power grid side. k ) and phase angle adjustment (change amount) θ The conditions provide impedance model support for the calculation of power flow control parameters.

Claims

1. A method for inverter impedance reshaping and network power flow control based on virtual two-port inverters, characterized in that, This includes impedance reshaping methods for voltage source inverters and network power flow control methods for voltage source inverters. The impedance reshaping method for voltage source inverters first analyzes the system impedance model, designs virtual two-port network parameters, and then calculates the control signal input to the original system to complete the impedance reshaping. The voltage source inverter network power flow control method acquires data to build a line model, calculates power flow control parameters, and then calculates the control signal input to the original system to complete power flow control.

2. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 1, characterized in that, The impedance reshaping method for voltage source inverters includes: Step A1: Analyze and model the impedance characteristics of the original system; Step A2: Design the control parameters for the virtual two-port network; Step A3: Calculate the control signal based on the control parameters and input it into the original system to complete impedance reshaping.

3. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 2, characterized in that, Step A1 includes: Step A1.1: Collect electrical quantity data of the original impedance system; Step A1.2: Construct the original system impedance model based on the system classification; Based on the system input impedance, the original system is divided into symmetric and asymmetric systems. The system input impedance is the ratio of the voltage to the current at the point of common coupling from the grid terminal to the inverter terminal. The input impedance of a symmetrical system is represented by a vector form for voltage. Current and system input impedance The relationship is: in, Represents the voltage phasor in a symmetrical system. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the current phasor in a symmetrical system. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Indicates the system's input impedance. Indicates input impedance The real part, Indicates input impedance The imaginary part; The input impedance of an asymmetric system is represented by a real-space vector representing voltage. Current The system input impedance is represented in matrix form: ， in Represents the voltage real space vector. This represents the direct-axis voltage component of the voltage in the dq coordinate system. This represents the cross-axis voltage component of the voltage in the dq coordinate system. Represents the real space vector of current. This represents the direct-axis current component in the dq coordinate system. This represents the quadrature-axis current component of the current in the dq coordinate system. Represents the system input impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current with respect to the d-axis voltage in the impedance matrix. This represents the impedance characteristic of the d-axis current with respect to the q-axis voltage in the impedance matrix. This represents the impedance characteristic of the q-axis current to the q-axis voltage in the impedance matrix.

4. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 2, characterized in that, Step A2 includes: Step A2.1: Design the structure of the transfer matrix for the two-port network; Step A2.2: Associate the transfer matrix of the two-port network with the Pi-type equivalent circuit; Step A2.3: Design parameters for different scenarios; For the input impedance of a symmetrical system, if its real part Then, a system consisting of finite positive components is used. , and That's sufficient; if the real part of the system input impedance is... Even with finite negative values, the aforementioned control parameters can still meet the requirements of most systems. If not, the following can be calculated: positive , and Values ​​can be used for control, or they can be set to... Virtual two-port control is converted into virtual impedance control by setting... This allows for control; For the input impedance of an asymmetric system, let , , , .

5. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 4, characterized in that, The relationship between the transfer matrix of the two-port network in step A2.1 and the voltage and current across the two-port network is as follows: ， ， ， ， in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the q-axis voltage component of the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 1 of a two-port network. The q-axis current component represents the complex vector of the current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the d-axis voltage component of the complex voltage vector at port 2 of the two-port network. This represents the q-axis voltage component of the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. This represents the d-axis current component of the complex vector of the current at port 2 of a two-port network. The q-axis current component represents the complex vector of the current at port 2 of a two-port network. The transfer matrix in step A2.2 The relationship between the Pi-type equivalent circuit and is as follows: Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis components, This represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit. express The direct-axis component, express The cross-axis component.

6. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 2, characterized in that, Step A3 includes: For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as Then after control , Before control , The relationship is as follows: in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows: in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input.

7. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 1, characterized in that, The voltage source inverter network power flow control method includes: Step B1: After collecting transmission line data, construct a transmission line model; Step B2: Calculate power flow control parameters based on the transmission line model; Step B3: Calculate the power flow control signal based on the power flow control parameters and input it into the original system to complete the network power flow control.

8. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 7, characterized in that, Step B1 includes: Step B1.1: Collect transmission line and voltage parameters; Step B1.2: Construct a transmission line model for virtual two-port network control; The voltage-current-transfer matrix relationship at both ends of the virtual two-port network is shown below: in, Let represent the transfer matrix of the two-port network; A, B, C, and D represent the block elements of the transfer matrix of the two-port network, respectively. Denotes the real part of A. Denotes the imaginary part of A. Denotes the real part of B. Denotes the imaginary part of B. Denotes the real part of C. Denotes the imaginary part of C. Denotes the real part of D. Represent the imaginary part of D; This represents the complex voltage vector at port 1 of a two-port network. This represents the complex vector of current at port 1 of a two-port network. This represents the complex voltage vector at port 2 of a two-port network. This represents the complex vector of current at port 2 of a two-port network. The relationship between the transfer matrix and the Pi-type equivalent circuit of the virtual two-port network is as follows: Where A, B, C, and D represent the block elements of the transfer matrix of the two-port network. This represents the complex frequency domain impedance of the left arm of the Pi-type equivalent circuit. This represents the complex frequency domain impedance of the middle arm of the Pi-type equivalent circuit. This represents the complex frequency domain impedance of the right arm of the Pi-type equivalent circuit.

9. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 7, characterized in that, Step B2 includes: After simplifying the transmission line model controlled by a virtual two-port network, through... Specific expressions and The specific expression derivation shows that: due to and It is known that, through and It can control the voltage amplitude and phase angle by changing and The value is adjusted to control the impedance relationship of the transmission line; The specific expression is: in, This represents the equivalent impedance of the transmission line after being controlled by a virtual two-port network. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the equivalent impedance. This represents the virtual part auxiliary variable defined when deriving the equivalent impedance. This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. This represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. The specific expression is: in, This represents the target equivalent impedance of a transmission line under virtual two-port network control. This represents the impedance of the original transmission line before it is controlled by a virtual two-port network. This represents the real-part auxiliary variable defined when deriving the target equivalent impedance. This represents the virtual sub-variable auxiliary variable defined when deriving the target equivalent impedance. L This represents the auxiliary variable in the denominator defined when deriving the equivalent impedance. This represents the direct-axis component of the original transmission line impedance. This represents the quadrature-axis component of the original transmission line impedance. This represents the direct-axis component of the impedance of the right arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the right arm in a virtual two-port network. This represents the direct-axis component of the impedance of the middle arm in a virtual two-port network. This represents the quadrature-axis component of the impedance of the middle bridge arm in a virtual two-port network.

10. The inverter impedance reshaping and network power flow control method based on virtual two-port as described in claim 7, characterized in that, Step B3 includes: For the input impedance of a symmetrical system, calculate... inverse matrix , recorded as Then after control , Before control , The relationship is as follows: in, Representation of the transfer matrix The inverse matrix, , , , They represent the inverse matrix respectively. Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input. For the input impedance of an asymmetric system Irreversible, directly derived from the control after , Before control , The relationship is as follows: in, , , , Representing the transfer matrix respectively Block elements, Let v represent the complex vector of current before the control signal input, and let v represent the complex vector of voltage before the control signal input. This represents the complex vector of current after the control signal is input. This represents the complex voltage vector after the control signal is input.

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