Converter networking control method with low-frequency impedance remodeling function

Abstract

The invention relates to the technical field of power electronic converters, in particular to a converter networking control method with a low-frequency impedance remodeling function. Comprising a network construction control module, a virtual impedance control module, a first coordinate transformation module, a second coordinate transformation module, a third coordinate transformation module, a current control module, a voltage filtering module, a low-frequency impedance remodeling module and a coordinate inverse transformation module. According to the method, low-frequency-band positive impedance is achieved, the stability of the power electronic converter in a weak power grid environment is improved, meanwhile, the modular design is easily integrated into an existing converter system, the oscillation risk caused by fundamental frequency negative impedance is thoroughly eliminated, broadband compatibility is achieved, the 0-200 Hz harmonic range is covered, and the performance is optimized through an adjustable remolding coefficient kz.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronic converters, in particular to a converter grid-forming control method with low-frequency impedance reshaping function. BACKGROUND

[0002] In the new power system, grid-forming converters are the key equipment to maintain grid voltage stability and support system dynamic response, and their impedance characteristics directly determine the safety and stability of interaction with the grid.

[0003] Conventional grid-forming converters exhibit a significant negative real part of impedance at low frequencies (usually below 50Hz). This negative impedance characteristic forms an energy amplification mechanism: when there is a small disturbance in the grid (such as new energy unit power fluctuation, load sudden change, etc.), the negative impedance will continuously absorb system energy and feedback to the grid, causing the disturbance amplitude to rise continuously, easily inducing subsynchronous oscillation (SSO) or wideband oscillation. In the scenario of high penetration of new energy, such oscillations can quickly spread through the grid topology, causing large-scale de-connection of new energy units such as wind farms and photovoltaic power stations, and even causing irreversible stress damage to key equipment such as transformers and circuit breakers due to overvoltage and overcurrent, ultimately leading to regional grid instability accidents.

[0004] Although conventional grid-forming converters maintain positive impedance at frequencies above 50Hz, the safety hazards caused by their low-frequency negative impedance have become a major obstacle to the development of new power systems. Existing solutions rely heavily on hardware superposition (such as adding damping resistors, filters, etc.), which not only increases the size and cost of the equipment, but also sacrifices the dynamic response speed and compensation accuracy of the converter, making it difficult to meet the complex demands of multi-condition power grids.

[0005] Therefore, there is an urgent engineering need and great application value to develop a new grid-forming control method that can fundamentally reshape the impedance characteristics of grid-forming converters. SUMMARY

[0006] The present application provides a converter grid-forming control method with low-frequency impedance reshaping function, which aims to solve the problem of negative impedance near the fundamental frequency when the converter uses conventional grid-forming control, and ensure that the converter exhibits positive impedance in the full frequency range of 0-200Hz, eliminating the risk of operating oscillation of grid-forming converters.

[0007] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0008] A converter grid-forming control method with low-frequency impedance reshaping function, comprising a grid-forming control module, a virtual impedance control module, a first coordinate transformation module, a second coordinate transformation module, a third coordinate transformation module, a current control module, a voltage filter module, a low-frequency impedance reshaping module, and a coordinate inverse transformation module.

[0009] The outputs of the grid control module are the grid control AC internal potential E and the grid control angle θ. The grid control AC internal potential E, the grid control angle θ, and the three-phase AC voltage U of the power grid are also specified. gabc The input is fed into the virtual impedance control module, and the virtual impedance output is used to control the current reference quantity I. gabcref Grid control current reference quantity I gabcref Input to the third coordinate transformation module;

[0010] The inputs to the first coordinate transformation module are the grid control angle θ and the three-phase AC current I flowing into the grid. gabc The output is the d-axis and q-axis current feedback I in a synchronously rotating coordinate system. gdfbk I gqfbk The output of the first coordinate transformation module is input to the current control module and the low-frequency impedance reshaping module.

[0011] The inputs to the second coordinate transformation module are the grid control angle θ and the three-phase AC voltage U of the power grid. gabc The output is the first d-axis and q-axis voltage feedback quantity U. gdfbk1 U gqfbk1 The output of the second coordinate transformation module is then input to the voltage filtering module.

[0012] The inputs to the third coordinate transformation module are the network control angle θ and the network control current reference value I. gabcref The output quantities are the d-axis and q-axis current reference quantities I. gdref I gqref The output of the third coordinate transformation module is then input to the current control module.

[0013] The current control module outputs the first d-axis and q-axis voltage control quantity U. d1 U q1 The output of the voltage filter module provides feedback on the second d-axis and q-axis voltages, U. gdfbk2 U gqfbk2 Summing the corresponding values ​​generates the second d-axis and q-axis voltage control quantity U. d2 U q2 The input is sent to the low-frequency impedance reshaping module;

[0014] The low-frequency impedance reshaping module outputs the third d-axis and q-axis voltage control quantity U. d3 U q3 The inputs to the coordinate inverse transformation module are the network control angle θ and the third d-axis and q-axis voltage control quantities U. d3 U q3 The inverse transformation outputs the converter modulation signal U in the three-phase stationary coordinate system. vabc .

[0015] Furthermore, the specific process of the virtual impedance control module includes: multiplying the internal AC potential E of the grid control by the three-phase cosine signal generated by the grid control angle θ to obtain the grid control electromotive force Eabc; and multiplying the grid control electromotive force Eabc by the grid voltage U. gabc Perform the difference calculation and input the difference value into the virtual reactance L. v and virtual resistance R v The inertial elements that make up the network generate the reference quantity I for the control current. gabcref .

[0016] Furthermore, the specific process of the current control module includes: d-axis current reference quantity I gdref With feedback quantity I gdfbk The difference is input to the d-axis PI controller and then subtracted from the q-axis current feedback I. gqfbk The product of the voltage control quantity U and the impedance ωL of the series reactor yields the first d-axis voltage control quantity U. d1 q-axis current reference quantity I gqref With feedback quantity I gqfbk The difference is input to the q-axis PI controller, and then the d-axis current feedback I is added. gdfbk The product of ωL and ωL yields the first q-axis voltage control quantity U. q1 .

[0017] Furthermore, the specific process of the voltage filtering module includes: the voltage filtering module processes the first d-axis and q-axis voltage feedback quantities through a first-order inertial filter with a time constant T, and outputs the second d-axis and q-axis voltage feedback quantity U. gdfbk2 U gqfbk2 .

[0018] Furthermore, the low-frequency impedance reshaping module outputs a third d-axis and q-axis voltage control quantity U. d3 U q3 Specifically, this includes: the second d-axis voltage control quantity U d2 Subtract q-axis current feedback I gqfbk With impedance reshaping coefficient k z The product of these two factors generates the third d-axis voltage control quantity U. d3 Second q-axis voltage control quantity U q2 Add d-axis current feedback I gdfbk With the impedance reshaping coefficient k z The product of these two factors generates the third q-axis voltage control quantity U. q3 .

[0019] Furthermore, the impedance reshaping coefficient k z This is an adjustable parameter, with a value of 2ωL, which can be adjusted by k. z Optimize the low-frequency impedance characteristics of the converter to ensure that the converter presents positive impedance in the 0-200Hz low-frequency range.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1) Completely solve the problem of negative impedance near the base frequency and achieve full positive impedance in the low frequency band: This invention reshapes the impedance characteristics of conventional grid SVG near the base frequency through a low frequency impedance reshaping module, ensuring that the entire low frequency band from 0 to 200 Hz presents positive impedance, eliminating the risk of system oscillation, and significantly improving the stability of the converter in a weak grid environment.

[0022] 2) Modular design simplifies implementation and integration: This invention decomposes complex control into nine standardized modules, such as coordinate transformation and impedance reshaping modules, using conventional components, which are easy to deploy in existing power electronic converter systems;

[0023] 3) Wideband compatibility and reduced risk: The full-band positive impedance characteristic not only covers the fundamental frequency but also extends to the 200Hz harmonic range, making it compatible with different power grid conditions. At the same time, the adjustability of the low-frequency impedance reshaping coefficient kz provides flexibility to optimize performance and eliminates the risk of unreasonable converter operating parameters. Attached Figure Description

[0024] Figure 1 This is a block diagram of the method described in this invention.

[0025] Figure 2 This is a schematic diagram of the virtual impedance control module described in this invention.

[0026] Figure 3 This is a schematic diagram of the current control module described in this invention.

[0027] Figure 4 This is a schematic diagram of the voltage filtering module described in this invention.

[0028] Figure 5 This is a schematic diagram of the low-frequency impedance reshaping module described in this invention.

[0029] Figure 6 This is a schematic diagram of the impedance amplitude of the conventional mesh-type SVG described in this invention.

[0030] Figure 7 This is a schematic diagram of the impedance phase of the conventional mesh-type SVG described in this invention.

[0031] Figure 8 This is the impedance amplitude diagram of the mesh-type SVG with low-frequency impedance reshaping as described in this invention.

[0032] Figure 9 This is the impedance phase diagram of the mesh-type SVG with low-frequency impedance reshaping described in this invention. Detailed Implementation

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0034] See Figure 1 This is a block diagram of the method described in this invention. This invention provides a converter grid control method with low-frequency impedance reshaping function, comprising a grid control module, a virtual impedance control module, a first coordinate transformation module, a second coordinate transformation module, a third coordinate transformation module, a current control module, a voltage filtering module, a low-frequency impedance reshaping module, and a coordinate inverse transformation module; the connection relationships of each module are as follows:

[0035] The outputs of the network control module are: the internal AC potential E of the network control and the network control angle θ. The internal AC potential E of the network control is input to the virtual impedance control module, and the network control current is obtained through the virtual impedance. The network control angle θ is input to the first, second, and third coordinate transformation modules and the inverse coordinate transformation module to provide the angle required for coordinate transformation.

[0036] The virtual impedance control module receives the grid control AC internal potential E and the three-phase AC voltage U of the power grid as inputs. gabc Its output is the reference value I for the grid control current. gabcref It is connected to the input of the third coordinate transformation module; see Figure 2 The grid control internal electromotive force E is multiplied by the three-phase cosine signal generated by the grid control angle θ to obtain the grid control electromotive force Eabc. The grid control electromotive force E is then multiplied by the grid voltage U. gabc Perform the difference calculation and input the difference value into the virtual reactance L. v and virtual resistance R v The inertial elements that make up the network generate the reference quantity I for the control current. gabcref .

[0037] The first coordinate transformation module uses the grid control angle θ to transform the three-phase AC current I flowing into the power grid. gabc Converted to d-axis and q-axis current feedback I in a synchronous rotating coordinate system gdfbk I gqfbk And feed back the d-axis and q-axis current values ​​I. gdfbk I gqfbk The output is sent to the current control module and the low-frequency impedance reshaping module. The coordinate transformation is a transformation from three-phase stationary coordinates to a synchronous rotating coordinate system, which is a conventional coordinate transformation method in the field of converter control.

[0038] The second coordinate transformation module uses the grid control angle θ to transform the three-phase AC voltage U of the power grid. gabc Converted to first d- and q-axis voltage feedback quantity U gdfbk1 U gqfbk1 It is then output to the voltage filtering module.

[0039] The third coordinate transformation module uses the network control angle θ to transform the network control current reference quantity I. gabcref Convert to d-axis and q-axis current reference quantity I gdref I gqref And output to the current control module.

[0040] The current control module compares the d-axis and q-axis current reference values ​​I. gdref I gqref With feedback quantity I gdfbk I gqfbk The first d-axis and q-axis voltage control quantity U is generated through the current control module. d1 U q1 This module implements closed-loop regulation of current error: see Figure 3 d-axis current reference quantity I gdref With feedback quantity I gdfbk The difference is input to the d-axis PI controller and then subtracted from the q-axis current feedback I. gqfbk The product of the voltage control quantity U and the impedance ωL of the series reactor yields the first d-axis voltage control quantity U. d1 q-axis current reference quantity I gqref With feedback quantity I gqfbk The difference is input to the q-axis PI controller, and then the d-axis current feedback I is added. gdfbk The product of ωL and ωL yields the first q-axis voltage control quantity U. q1 Series reactors are standard components of the bridge arm of the converter.

[0041] Voltage filtering module, see Figure 4 The first d-axis and q-axis voltage feedback quantity U gdfbk1 U gqfbk1 After passing through a first-order inertial filter with a time constant T of 0.02s, the second d-axis and q-axis voltage feedback quantity U is output. gdfbk2 U gqfbk2 Second d-axis and q-axis voltage feedback quantity U gdfbk2 U gqfbk2 With the first d-axis and q-axis voltage control quantity U d1 U q1 Summing generates the second d-axis and q-axis voltage control quantity U. d2 U q2 The input is sent to the low-frequency impedance reshaping module.

[0042] The low-frequency impedance reshaping module controls the second d-axis and q-axis voltage U. d2 U q2 Feedback quantities I of d-axis and q-axis currents gdfbk I gqfbk Reorganization: See Figure 5 The second d-axis voltage control quantity U d2 Subtract q-axis current feedback I gqfbkWith impedance reshaping coefficient k z The product of these two factors generates the third d-axis voltage control quantity U. d3 Second q-axis voltage control quantity U q2 Add d-axis current feedback I gdfbk With the impedance reshaping coefficient k z The product of these two factors generates the third q-axis voltage control quantity U. q3 Output the third d-axis and q-axis voltage control quantity U d3 U q3 Connect the inverse coordinate transformation module.

[0043] The coordinate inverse transformation module uses the network control angle θ to transform the third d-axis and q-axis voltage control quantities U. d3 U q3 Inverse transformation outputs the converter modulation signal U in the three-phase stationary coordinate system. vabc The inverse coordinate transformation is a transformation from a synchronous rotating coordinate system to a three-phase stationary coordinate system, which is a conventional coordinate transformation method in the field of converter control.

[0044] The inputs of the grid control module include the active power and reactive power of the converter, and the outputs include the grid control AC internal potential and the grid control angle.

[0045] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0046] Example 1:

[0047] This invention proposes a converter grid configuration control method with low-frequency impedance reshaping function, comprising: a grid configuration control module, a virtual impedance control module, a first coordinate transformation module, a second coordinate transformation module, a third coordinate transformation module, a current control module, a voltage filtering module, a low-frequency impedance reshaping module, and a coordinate inverse transformation module, such as... Figure 1 As shown, the connection relationships between the modules are as follows:

[0048] The outputs of the network control module are: the internal AC potential E of the network control and the network control angle θ; wherein, the internal AC potential of the network control is input to the virtual impedance control module, and the network control current is obtained through the virtual impedance; the network control angle θ is input to the first, second, and third coordinate transformation modules and the inverse coordinate transformation module to provide the angle required for coordinate transformation.

[0049] Virtual impedance control module, such as Figure 2 As shown, its output is the grid control current reference quantity I. gabcref It is connected to the input of the third coordinate transformation module.

[0050] The first coordinate transformation module uses the grid control angle θ to transform the three-phase AC current I flowing into the power grid. gabc Converted to d-axis and q-axis current feedback I in a synchronous rotating coordinate system gdfbk I gqfbk , and I gdfbk I gqfbk The output is sent to the current control module and the low-frequency impedance reshaping module; the coordinate transformation is a transformation from three-phase stationary coordinates to a synchronous rotating coordinate system, which is a conventional coordinate transformation method in the field of converter control, and its coordinate transformation matrix is:

[0051] (1)

[0052] The second coordinate transformation module uses the grid control angle θ to transform the three-phase AC voltage U of the power grid. gabc Converted to first d- and q-axis voltage feedback quantity U gdfbk1 U gqfbk1 It is then output to the voltage filtering module.

[0053] The third coordinate transformation module uses the network control angle θ to transform the network control current reference quantity I. gabcref Convert to d-axis and q-axis current reference quantity I gdref I gqref And output to the current control module.

[0054] Current control module such as Figure 3 As shown, by comparing the d-axis and q-axis current reference values ​​I... gdref I gqref With feedback quantity I gdfbk I gqfbk The first d-axis and q-axis voltage control quantity U is generated by the current controller. d1 U q1 The current control module implements closed-loop adjustment of the current error: d-axis current reference quantity I. gdref With feedback quantity I gdfbk The difference is input to the d-axis PI controller, and then subtracted from the q-axis current feedback I. gqfbk The product of the series reactor impedance (ωL) and ωLI gqfbk The first d-axis voltage control quantity U is obtained. d1 q-axis current reference quantity I gqref With feedback quantity I gqfbk The difference is input to the q-axis PI controller, and then the d-axis current feedback I is added. gdfbk The product of ωL and ωLI gdfbk The first q-axis voltage control quantity U is obtained. q1 Series reactors are standard components of the converter's bridge arm.

[0055] Voltage filtering module, such as Figure 4As shown, it feeds back the first d-axis and q-axis voltage U. gdfbk1 U gqfbk1 After passing through a first-order inertial filter with a time constant T (typically taken as 0.02s), the second d-axis and q-axis voltage feedback quantity U is output. gdfbk2 U gqfbk2 Second d-axis and q-axis voltage feedback quantity U gdfbk2 U gqfbk2 With the first d-axis and q-axis voltage control quantity U d1 U q1 Summing generates the second d-axis and q-axis voltage control quantity U. d2 U q2 The input is sent to the low-frequency impedance reshaping module; the first-order inertial filtering stage is as follows:

[0056] (2)

[0057] Low-frequency impedance reshaping module such as Figure 5 As shown, it controls the second d-axis and q-axis voltage U. d2 U q2 Feedback quantities I of d-axis and q-axis currents gdfbk I gqfbk Reorganization: Second d-axis voltage control quantity U d2 Subtract q-axis current feedback I gqfbk The impedance reshaping coefficient k is given. z The product of (generally taken as 2ωL) is used to generate the third d-axis voltage control quantity U. d3 Second q-axis voltage control quantity U q2 Add d-axis current feedback I gdfbk With impedance reshaping coefficient k z The product of these two factors generates the third q-axis voltage control quantity U. q3 Output the third d-axis and q-axis voltage control quantity U d3 U q3 Connect the inverse coordinate transformation module.

[0058] The coordinate inverse transformation module uses the network control angle θ to transform the third d-axis and q-axis voltage control quantities U. d3 U q3 Inverse transformation into the converter modulation signal U in the three-phase stationary coordinate system vabc The inverse coordinate transformation is a transformation from a synchronous rotating coordinate system to a three-phase stationary coordinate system, which is a conventional coordinate transformation method in the field of converter control. Its coordinate transformation matrix is:

[0059] (3)

[0060] in, In preparation for changing the angle, here The size is equal to the netting control angle θ;

[0061] The inputs of the grid control module include the active power P and reactive power Q of the converter, and the outputs include the grid control AC internal potential E and the grid control angle θ.

[0062] Virtual impedance control module, such as Figure 2 As shown, its inputs include the grid control AC electromotive force E and the three-phase AC voltage U of the power grid. gabc The output quantity is the reference quantity I for the grid control current. gabcref ; The control electromotive force E and the grid voltage I gabcref Perform the difference calculation and input the difference value into the virtual reactance L. v and virtual resistance R v The inertial elements that make up the network generate the reference current for the control current; the virtual reactance L v and virtual resistance R v The inertial components are:

[0063] (4)

[0064] Example 2:

[0065] The present invention proposes a converter grid control method with low-frequency impedance reshaping function. The method is consistent with the process of Example 1, except that the coordinate transformation module is specifically implemented as follows:

[0066] The calculation process of the first coordinate transformation module is as follows:

[0067] (5)

[0068] in, This is the feedback quantity of the A-phase power grid current; This is the feedback quantity of the B-phase power grid current; This is the C-phase grid current feedback quantity;

[0069] The calculation process of the second coordinate transformation module is as follows:

[0070] (6)

[0071] in, This is the voltage feedback quantity of phase A of the power grid; This is the voltage feedback quantity for phase B of the power grid; This is the voltage feedback quantity for phase C of the power grid;

[0072] The calculation process of the third coordinate transformation module is as follows:

[0073] (7)

[0074] in, Provide the current setpoint for phase A of the power grid; Provide the current setpoint for phase B of the power grid; Provide the current setpoint for phase C of the power grid;

[0075] The calculation process of the inverse coordinate transformation module is as follows:

[0076] (8)

[0077] in, This is the modulation signal for phase A of the converter; This is the modulation signal for phase B of the converter; This is the C-phase modulation signal for the converter.

[0078] Example 3:

[0079] To demonstrate the effectiveness of the aforementioned converter grid control method with low-frequency impedance reshaping, this study takes an SVG (Static Var Generator) power electronic converter with reactive power compensation as an example to explore the impedance characteristics of grid-type SVGs under different control strategies. The method is the same as in Example 1, except that:

[0080] System impedance scanning tests were conducted on conventional meshed SVG and meshed SVG with low-frequency impedance reshaping capability. Impedance spectra of the two meshed SVG types were obtained by continuous frequency sweep analysis within the 0–200 Hz frequency range, as detailed below. Figures 6-7 Impedance diagram of conventional grid-type SVG and Figures 8-9 The impedance diagram of the low-frequency impedance reshaping mesh SVG is shown.

[0081] The impedance characteristics of a conventional mesh-type SVG are as follows: Figures 6-7 As shown in the figure, the trend of the impedance curve clearly shows that this type of SVG exhibits typical resistive-inductive characteristics in the mid-to-high frequency range above 50Hz, with a positive impedance value. This means that within this frequency range, the SVG has a benign suppression effect on the energy feedback of the system and will not cause additional stability risks. However, in the low-frequency range of 20Hz to 50Hz, its impedance characteristics show obvious abnormalities, with a significant negative impedance region. This negative impedance characteristic has potential hazards in the power system: when there are disturbance signals in this frequency band in the system, the negative impedance may lead to an energy amplification effect, causing dynamic interaction instability between the SVG and the power grid, and even inducing system-level oscillations, seriously threatening the safe and stable operation of the power system.

[0082] The impedance characteristics of a mesh-type SVG with low-frequency impedance reshaping function are as follows: Figures 8-9 As shown; through with Figures 6-7A comparative analysis of the impedance curves of conventional grid-type SVG reveals that the low-frequency impedance reshaping technology effectively solves the negative impedance problem in the low-frequency range of 20Hz to 50Hz. Specifically, the impedance value of the SVG remains positive across the entire frequency range of 0-200Hz, exhibiting stable impedance-inductance characteristics in the low-frequency range (20Hz~50Hz), with a smooth impedance curve free from abnormal fluctuations. This full-frequency positive impedance characteristic fundamentally eliminates the energy amplification effect caused by low-frequency negative impedance, avoids the risk of dynamic coupling oscillation between the SVG and the power grid, and significantly improves the operational stability of grid-type SVG in complex power grid environments.

Claims

1. A converter grid control method with low-frequency impedance reshaping function, characterized in that, It includes a network control module, a virtual impedance control module, a first coordinate transformation module, a second coordinate transformation module, a third coordinate transformation module, a current control module, a voltage filtering module, a low-frequency impedance reshaping module, and a coordinate inverse transformation module; The outputs of the grid control module are the grid control AC internal potential E and the grid control angle θ. The grid control AC internal potential E, the grid control angle θ, and the three-phase AC voltage U of the power grid are also specified. gabc The input is fed into the virtual impedance control module, and the virtual impedance output is used to control the current reference quantity I. gabcref Grid control current reference quantity I gabcref Input to the third coordinate transformation module; The inputs to the first coordinate transformation module are the grid control angle θ and the three-phase AC current I flowing into the grid. gabc The output is the d-axis and q-axis current feedback I in a synchronously rotating coordinate system. gdfbk I gqfbk The output of the first coordinate transformation module is input to the current control module and the low-frequency impedance reshaping module. The inputs to the second coordinate transformation module are the grid control angle θ and the three-phase AC voltage U of the power grid. gabc The output is the first d-axis and q-axis voltage feedback quantity U. gdfbk1 U gqfbk1 The output of the second coordinate transformation module is then input to the voltage filtering module. The inputs to the third coordinate transformation module are the network control angle θ and the network control current reference value I. gabcref The output quantities are the d-axis and q-axis current reference quantities I. gdref I gqref The output of the third coordinate transformation module is then input to the current control module. The current control module outputs the first d-axis and q-axis voltage control quantity U. d1 U q1 The output of the voltage filter module provides feedback on the second d-axis and q-axis voltages, U. gdfbk2 U gqfbk2 Summing the corresponding values ​​generates the second d-axis and q-axis voltage control quantity U. d2 U q2 The input is sent to the low-frequency impedance reshaping module; The low-frequency impedance reshaping module outputs the third d-axis and q-axis voltage control quantity U. d3 U q3 The inputs to the coordinate inverse transformation module are the network control angle θ and the third d-axis and q-axis voltage control quantities U. d3 U q3 The inverse transformation outputs the converter modulation signal U in the three-phase stationary coordinate system. vabc .

2. The converter grid control method with low-frequency impedance reshaping function according to claim 1, characterized in that, The specific process of the virtual impedance control module includes: multiplying the internal AC potential E of the grid control by the three-phase cosine signal generated by the grid control angle θ to obtain the grid control electromotive force Eabc; and multiplying the grid control electromotive force Eabc by the grid voltage U. gabc Perform the difference calculation and input the difference value into the virtual reactance L. v and virtual resistance R v The inertial elements that make up the network generate the reference quantity I for the control current. gabcref .

3. The converter grid control method with low-frequency impedance reshaping function according to claim 1, characterized in that, The specific process of the current control module includes: d-axis current reference quantity I gdref With feedback quantity I gdfbk The difference is input to the d-axis PI controller and then subtracted from the q-axis current feedback I. gqfbk The product of the voltage control quantity U and the impedance ωL of the series reactor yields the first d-axis voltage control quantity U. d1 q-axis current reference quantity I gqref With feedback quantity I gqfbk The difference is input to the q-axis PI controller, and then the d-axis current feedback I is added. gdfbk The product of ωL and ωL yields the first q-axis voltage control quantity U. q1 .

4. A converter grid control method with low-frequency impedance reshaping function according to claim 1, characterized in that, The specific process of the voltage filtering module includes: the voltage filtering module processes the first d-axis and q-axis voltage feedback quantities through a first-order inertial filter with a time constant T, and outputs the second d-axis and q-axis voltage feedback quantity U. gdfbk2 U gqfbk2 .

5. A converter grid control method with low-frequency impedance reshaping function according to claim 1, characterized in that, The low-frequency impedance reshaping module outputs the third d-axis and q-axis voltage control quantity U. d3 U q3 Specifically, this includes: the second d-axis voltage control quantity U d2 Subtract q-axis current feedback I gqfbk With impedance reshaping coefficient k z The product of these two values ​​generates the third d-axis voltage control quantity U. d3 Second q-axis voltage control quantity U q2 Add d-axis current feedback I gdfbk With the impedance reshaping coefficient k z The product of these two factors generates the third q-axis voltage control quantity U. q3 .

6. A converter grid control method with low-frequency impedance reshaping function according to claim 5, characterized in that, The impedance reshaping coefficient k z This is an adjustable parameter, with a value of 2ωL, which can be adjusted by k. z Optimize the low-frequency impedance characteristics of the converter to ensure that the converter presents positive impedance in the 0-200Hz low-frequency range.

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