A control method for improving short-circuit ratio adaptability of a network-forming type converter

Abstract

The application discloses a control method for improving wide short-circuit ratio adaptability of a grid-connected type converter, belongs to the technical field of grid-connected inverters, and solves the problem of how to improve the wide short-circuit ratio adaptability of the grid-connected type converter; a state space model of a grid-connected type converter grid-connected system is established, an unstable mode causing the grid-connected type converter to oscillate and lose stability under a strong power grid is identified, and a full-state feedback gain matrix is calculated; through participation factor analysis, dominant state variables corresponding to the unstable mode are determined; the dominant state variables are taken as partial feedback quantities, a partial state feedback gain matrix is designed, the feedback gain matrix is superimposed on a reference value at a power outer loop input end of the grid-connected type converter, additional damping control is formed, and system poles are reconfigured, so that the stability of the grid-connected type converter under the strong power grid is effectively improved, the grid-connected type converter can stably operate in a wide short-circuit ratio range from a weak power grid to a strong power grid, and grid-connected adaptability is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of inverter grid connection technology and relates to a control method for improving the wide short-circuit ratio adaptability of grid-connected converters. Background Technology

[0002] With the deepening of the "dual carbon" goals and the continuous increase in the penetration rate of new energy sources, power electronic equipment is playing an increasingly crucial role in new power systems. The continuous development of "dual high" power systems can easily lead to the formation of local weak grid environments, resulting in a decrease in the grid short-circuit ratio (SCR). At present, most mainstream new energy converters adopt grid-following control based on phase-locked loop synchronization. When connected to the grid, they exhibit current source characteristics and have the advantage of rapid power response. However, they are prone to stability challenges in weak grids with low short-circuit ratios.

[0003] In contrast, grid-connected converters employ power self-synchronization control and exhibit voltage source characteristics when connected to the grid. They can simulate the operating mechanism of synchronous generators, providing necessary inertia and damping support to the grid, enhancing the system's frequency and voltage regulation capabilities, and demonstrating superior stability in weak grid environments. Existing technologies, such as the invention patent with publication number CN121192781A, disclose a method for optimizing and adjusting the parameters of grid-connected power sources to improve strong grid stability. This method involves performing stability analysis on the grid-connected power source system to obtain the dominant characteristic roots and key parameters requiring optimization. Then, a damping ratio optimization problem based on an exponential weight allocation strategy is established, and the optimal control parameters for the grid-connected power source are obtained using a particle swarm optimization algorithm, significantly improving the strong grid stability of the grid-connected power source.

[0004] However, although grid-connected converters exhibit strong stability in weak power grids, they may face insufficient stability margins in strong power grids with high short-circuit ratios, potentially inducing subsynchronous oscillations and threatening the safety and stability of the power system. Virtual impedance strategies, as an effective means to improve the adaptability of grid-connected converters in strong power grids, enhance system damping by reshaping their output impedance, thereby improving their stability to some extent. However, introducing virtual impedance is equivalent to adding a series inductor in the output circuit, which not only increases system energy loss but also complicates the control strategy, exacerbating the risk of instability caused by dynamic interactions between control loops. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to improve the wide short-circuit ratio adaptability of grid-type converters.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0007] A control method for improving the wide short-circuit ratio adaptability of grid-type converters includes the following steps: Step 1: Establish the state-space model of the grid-connected system of the grid-connected converter; Step 2: Based on the state-space model, identify the instability modes that cause the grid-type converter to oscillate and become unstable under strong power grid conditions, and calculate the full-state feedback gain matrix. By participating in factor analysis, the dominant state variables corresponding to the instability modes are determined; The dominant state variable is used as a partial feedback quantity. A partial state feedback gain matrix is ​​designed and superimposed onto the reference value at the power outer loop input of the grid-type converter to form additional damping control and reconfigure the system poles.

[0008] Furthermore, the state-space model described in step 1 is a small-signal model, represented using the following logic:

[0009] in, For system state variables, The system state matrix, For the input vector, For input variables, For the input matrix, This indicates a small perturbation.

[0010] Furthermore, in step 2, based on the state-space model, the identification of the instability modes that cause the grid-connected converter to oscillate and become unstable under strong power grid conditions, and the calculation of the full-state feedback gain matrix, are specifically as follows: To find the eigenvalues ​​of the system state matrix A, if there exists a pair of conjugate complex roots... The eigenvalue is located in the right half-plane of the complex plane. The corresponding mode is taken as the unstable mode; The eigenvalues ​​are analyzed using the pole placement method. Perform corrections and solve for the desired poles. ; Using the original system state matrix A, input matrix B, and all desired poles as inputs, the full-state feedback gain matrix K is solved using mathematical tools.

[0011] Furthermore, the solution for the desired poles Specifically: First, set the expected extreme point as The damping ratio ζ is set as the optimal damping ratio, and the natural oscillation frequency is... and They have the same natural oscillation frequency; According to the second-order system relation and Calculate the real part of the desired pole. and the virtual part ,Sure .

[0012] Furthermore, the optimal damping ratio is specifically 0.707.

[0013] Furthermore, the dominant state variable corresponding to the instability mode determined through participation factor analysis in step 2 is specifically as follows: Define participation factors Let represent the degree of participation of the i-th state variable in the k-th mode, and let the right eigenvector corresponding to the k-th eigenvalue be . The left eigenvector is The participation factor is calculated using the following logic. :

[0014] in, , These are the i-th elements in the right and left eigenvectors, respectively; Calculate the instability mode for each state variable The participation factors are selected, and state variables with participation factors greater than a preset threshold are selected as dominant state variables.

[0015] Furthermore, the step 2, which uses the dominant state variable as a partial feedback quantity, specifically designs the partial state feedback gain matrix as follows: Set the columns corresponding to all state variables other than the dominant state variable to zero, reduce the dimensionality of the full-state feedback gain matrix K to form a partial-state feedback gain matrix Kn, and define the feedback input control quantity. The small signal model is adjusted to .

[0016] The present invention also provides a grid-connected inverter, which is connected to the grid based on the above-mentioned control method for improving the wide short-circuit ratio adaptability of grid-connected inverters.

[0017] The advantages of this invention are: This invention establishes a state-space model of a grid-connected converter system and, based on this model, obtains the modes that cause oscillations and instability of the grid-connected converter under strong power grid conditions. It then uses participation factor analysis to obtain the dominant state variables of these oscillation modes and superimposes them onto the active power input as partial feedback components via a feedback gain matrix. This achieves an additional damping effect, effectively improving the stability of the grid-connected converter under strong power grid conditions. This enables the converter to operate stably across a wide short-circuit ratio range from weak to strong power grids, enhancing its grid adaptability.

[0018] This invention fundamentally reconfigures the system's unstable poles by shifting them from the left half-plane to the right half-plane through pole placement, eliminating the root cause of oscillations. Simultaneously, this invention only feeds back the dominant state variables with high participation, avoiding the complexity of sampling and feeding back every state variable required by full-state feedback. Instead, it only feeds back the state variables with the greatest impact on the oscillation mode, selected based on the participation factor method, reducing the implementation difficulty and cost of the control system. Furthermore, this invention only enhances damping for specific unstable modes, with minimal impact on other modes, ensuring the original dynamic performance of the system. Attached Figure Description

[0019] Figure 1 This is a topology diagram of the grid-connected system of the grid-type converter according to Embodiment 1 of the present invention; Figure 2 This is a control block diagram of the additional damping enhancement strategy in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram illustrating the change in eigenvalues ​​before and after adding an additional damping control strategy when SCR=10, according to Embodiment 1 of the present invention. Figure 4 This is a waveform diagram showing the step change of active power before and after adding an additional damping control strategy when SCR=10 in Embodiment 1 of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments: Example 1 According to state-space theory, the instability of a grid-connected converter under strong power grid conditions manifests as the appearance of right-half-plane eigenvalues. Therefore, if the system poles can be reconfigured through effective control strategies to shift the right-half-plane eigenvalues ​​back to the left-half-plane, the risk of oscillation instability of the grid-connected converter under strong power grid conditions can be fundamentally eliminated, thereby improving the wide short-circuit ratio adaptability of the grid-connected converter.

[0022] like Figure 1 , Figure 2 As shown, specifically, this invention discloses a control method for improving the wide short-circuit ratio adaptability of grid-type converters, comprising the following steps: Step 1: Establish the state-space model of the grid-connected system of the grid-connected converter.

[0023] like Figure 1 As shown, the main circuit of the grid-connected converter system in this embodiment includes a DC-side voltage, a three-phase inverter bridge, an LC filter, and a grid inductor. L g The main circuit adopts a three-phase full-bridge inverter topology, and is connected to an infinite power grid after passing through an LC filter and equivalent line impedance; the LC filter consists of a filter inductor. L f Filter capacitor C f and with C f series damping resistors R d Composition. In the main circuit, e abc This is the internal potential of the VSG, which is also the output voltage of the three-phase inverter bridge; v oabc VSG port voltage; i labc This refers to the bridge-side current, which flows through the bridge-side inductor. L f The current; i oabc This refers to the grid-side current, which is the current injected into the power grid.

[0024] Furthermore, the grid-connected system employs Virtual Synchronous Generator (VSG) control. The VSG control loop includes a power outer loop and a voltage-current inner loop, with a virtual impedance loop between them. The power outer loop comprises an active-frequency (P-f) control loop and a reactive-voltage (Q-V) control loop, used to simulate the rotor motion equation and reactive-voltage droop characteristics of a synchronous generator, as well as the amplitude and phase of the output port voltage reference signal. The voltage-current inner loop tracks this reference signal through a PI regulator, generating a PWM drive signal to control the inverter switching. The VSG control loop participates in grid frequency and voltage regulation by simulating the characteristics of a synchronous generator. The virtual impedance loop reshapes the output impedance, improves the damping of the grid-connected system, and enhances the stability of the grid-connected converter under strong grid conditions to a certain extent.

[0025] In this embodiment, the grid-type converter employs virtual synchronous generator (VSG) control. A power outer loop is constructed based on the rotor oscillation and excitation control equations of the synchronous generator, dominating the regulation of active power-frequency and reactive power-voltage. Simultaneously, a built-in voltage-current inner loop enhances the system's dynamic performance. The mathematical model of the VSG control loop is represented by the following logic:

[0026] in, The derivative of the VSG output angular frequency; ω 0、 ω These are the reference and actual values ​​of the VSG output angular frequency, respectively. J and D p These are the virtual inertia and damping coefficient of the VSG active-frequency control loop, respectively. P ref , Q ref and P e , Q e These are the reference and actual values ​​for the active and reactive power outputs of the grid-type converter, respectively. E The reference voltage amplitude is output for the VSG reactive-voltage control loop. E The differential; K u and K These are the droop coefficient and integral coefficient of the reactive-voltage control loop, respectively. V n and V rms These are the reference and actual values ​​of the output voltage of the grid-type converter, respectively. X ud , X uq The state variables introduced into the voltage loop of the grid-type converter are respectively d , q Axial components, and They are respectively X ud , X uq The differential; X id , X iq The state variables introduced into the current loop of the grid-type converter are respectively d , q Axial components, and They are respectively X id , X iq The differential; i ld , i lq These are the bridge-side currents of the grid-type converter. d , q Axial components; u od , u oqThese are the output voltages of the grid-type converter. d , q Axial components; K pv , K iv These are the proportional and integral coefficients of the voltage loop, respectively; C f For filtering capacitors in a grid-type converter.

[0027] In this embodiment, switching delay and losses are ignored. It is assumed that the controller output reference voltage is the converter internal potential. The mathematical model of the grid-type converter filter line and connection line is expressed by the following logic:

[0028] in, L f , C f , L g These represent the filter inductance, filter capacitor, and grid inductance of a grid-connected converter, respectively; u d and u q These are the internal potentials of the grid-type converter. d , q Axial component; u gd and u gq These are the grid voltages. d , q Axial components; u od , u oq These are the output voltages of the grid-type converter. d , q Axial components; and These are the output currents. dq Axial components, and They are respectively and The differential; and These are the bridge-side currents. d , q Axial components, and They are respectively and The differential.

[0029] Furthermore, during small-signal modeling and calculation, the rotating coordinate system of the grid-type converter is used as the common coordinate system to establish the phase angle difference between the grid voltage and the synchronous rotating coordinate system of the grid-type converter. The mathematical model is represented by the following logical expression:

[0030] in, ω g Let ω be the angular frequency of the grid voltage. In this embodiment, under small disturbances, it can be considered as... ω g It is a constant value; ω This represents the actual value of the VSG output angular frequency; Phase angle difference The differential.

[0031] By reorganizing the above mathematical model and linearizing it at the steady-state operating point, we obtain the small-signal model of the hybrid grid-connected system:

[0032] in, In the formula This indicates a small perturbation. For system state variables, The system state matrix, For the input vector, For input variables, Let be the input matrix, where .

[0033] In this embodiment, There are dominant state variables in the converter. Depending on the actual operating conditions and parameters, the converter may correspond to different dominant state variables when operating in grid-connected mode. In subsequent steps, the state variables of the dominant instability mode are selected by participating in factor analysis, and precise damping is achieved through partial state feedback.

[0034] Step 2: Based on the state-space model, identify the instability modes that cause grid-connected converters to oscillate and become unstable under strong power grid conditions; By participating in factor analysis, the dominant state variables of the instability mode are identified; The dominant state variable is used as a partial feedback quantity and superimposed onto the power control loop reference value of the grid-type converter through the feedback gain matrix to form additional damping control, thereby reconfiguring the system poles.

[0035] In this embodiment, the eigenvalues ​​of the system state matrix A in the complex plane determine the stability of the system. The eigenvalues ​​of the grid-type converter in the right half-plane under a strong power grid (such as a grid short-circuit ratio SCR=10) can be obtained by eigenvalue calculation. The corresponding mode is taken as the unstable mode. At this time, the grid-type converter will experience subsynchronous oscillation instability.

[0036] In this embodiment, to improve system damping and enhance the wide short-circuit ratio adaptability of the grid-type converter, this embodiment proposes the following... Figure 2The damping enhancement strategy based on partial state feedback calculated from the participation factor is shown below, with the following specific steps: Step 2.1, solve for the eigenvalues ​​of the system state matrix A: For an m×m system state matrix A, its eigenvalues ​​λ satisfy... A set of eigenvalues ​​is calculated under a strong power grid with a preset short-circuit ratio. If a pair of conjugate complex roots exists... Located in the right half-plane (real part) of the complex plane >0), where a is a positive integer and a <m, , They are the real part and the imaginary part, respectively. The value is an imaginary unit. In this case, the mode corresponding to the characteristic value is regarded as the unstable mode, which is considered to be the dominant mode that causes the grid-type converter to become unstable under strong power grid conditions.

[0037] like Figure 3 As shown, this embodiment takes a grid short-circuit ratio (SCR) of 10 as an example to illustrate the process, and obtains a pair of conjugate complex roots. Located on the right half of the complex plane (not on the vertical imaginary axis), the unstable mode of the dominant oscillation is obtained. .

[0038] Step 2.2, Design the desired pole: To eliminate the unstable modes caused by this eigenvalue, the pole placement method is used for correction, specifically: First, let's define the desired closed-loop pole as... Its damping ratio ζ is set to the optimal damping ratio, while maintaining the natural oscillation frequency. Consistent with the original mode, that is, with They have the same natural oscillation frequency.

[0039] Next, according to the second-order system relation... and The real part of the desired pole can be calculated. and the virtual part Thus determine .

[0040] In a preferred embodiment, the optimal damping ratio is specifically 0.707.

[0041] Step 2.3, calculate the full-state feedback gain matrix K: Based on existing linear system theory, for the system If a state feedback control law is introduced Then there exists a closed-loop system state matrix. .

[0042] In this embodiment, the original system state matrix A, input matrix B, and all desired poles are used as inputs. The "place" function in mathematical tools such as MATLAB is used to perform pole placement, solving for the corresponding m×m full-state feedback gain matrix K, and verifying the stability of the closed-loop system. The desired poles include the desired poles. And other original poles.

[0043] Step 2.4: Design the partial state feedback gain matrix Kn by participating in factor analysis of the dominant state variables: To reduce control complexity, this embodiment selects state variables with significant impact on the dominant oscillation mode for feedback matrix calculation, feeding back only the state variables with the greatest influence on the dominant oscillation mode, greatly simplifying the actual control difficulty. The state feedback gain matrix Kn corresponding to the selected state variables is calculated, and the resulting damping compensation is superimposed on the power input to improve converter stability under strong grid conditions, constituting a novel damping compensation strategy. Unlike traditional parameter optimization design, the method provided in this embodiment does not require changing the system's own parameters, and the system can maintain sufficient damping under various adverse operating conditions and parameter conditions. Furthermore, the compensation structure is simpler and more applicable in engineering.

[0044] Step 2.4.1, Define Participation Factors , representing the degree of participation of the i-th state variable in the k-th mode, participation factor. The calculation is based on the system's left and right eigenvectors; specifically, the right eigenvector corresponding to the k-th eigenvalue is... The left eigenvector is The participation factor is calculated using the following logic. :

[0045] in, , These are the i-th elements in the right and left eigenvectors, respectively, and the participation factor. The larger the value, the stronger the correlation between the state variable and the k-th mode.

[0046] In this embodiment, the right eigenvector is used to describe the relative amplitude and phase relationship between each state variable when the system oscillates alone in the k-th mode; while the left eigenvector is used to measure the degree of influence of each state variable on the k-th mode.

[0047] Step 2.4.2, calculate the instability mode for each state variable. The participation factors are selected, and state variables with participation factors greater than a preset threshold are selected as dominant state variables.

[0048] Step 2.4.3: Set the columns corresponding to the remaining state variables to zero, and perform dimensionality reduction on the full-state feedback gain matrix K to form a partial-state feedback gain matrix Kn.

[0049] Step 2.4.4, define the feedback input control quantity. As an additional quantity serving as the reference values ​​for active and reactive power in the outer power loop, the closed-loop system state matrix After damping enhancement, it was adjusted to The small signal model is adjusted to:

[0050] like Figure 2 As shown, the superimposed small-signal model is equivalent to adding a damping compensator at the power input end compared to the original model, thus solving the problem of insufficient damping in grid-connected converters under strong power grids. In this embodiment, wide short-circuit ratio adaptability refers to the grid-connected converter having good stability under both strong and weak power grids. The inherent characteristics of the grid-connected converter determine its inherent good adaptability to weak power grids; therefore, the introduction of the damping compensator increases the grid-connected converter's adaptability to strong power grids, which is equivalent to increasing wide short-circuit ratio adaptability.

[0051] In this embodiment, the state-space model defined in step 1 is used as an example for illustration: First, according to step 1, we know Thirteen state variables were preset, and the relationship between all 13 state variables and the instability mode was calculated. The participation factors, where a is a positive integer and a < 13, are shown in Table 1 below: Table 1. Calculation results of participation factors of all state variables with respect to the unstable mode.

[0052] Next, with a preset threshold of 0.1, state variables with participation factor values ​​greater than 0.1 (i.e., 10%) are selected. These state variables are considered to have a key impact on the system's instability modes, and are then used to construct a partial feedback state vector. , These correspond to columns 1, 2, and 13 of the full-state feedback matrix K, respectively.

[0053] Then, the columns corresponding to the selected state variables in the full-state feedback matrix K are retained (columns 1, 2, and 13 in this example), and the columns corresponding to the state variables are all set to zero, thus obtaining a 13×3 partial state feedback gain matrix Kn.

[0054] Finally, the feedback input control quantity is... As an additional quantity serving as the reference value for active and reactive power in the outer power loop, and as the compensation input of the damping compensator, it enables direct adjustment of the power input to enhance the system's damping.

[0055] The above example is only one implementation of this embodiment. In other grid-connected converter systems, different partial feedback matrices Kn are obtained through step 2, corresponding to different dominant oscillation modes and dominant state variables.

[0056] To verify the effectiveness of the control strategy proposed in this embodiment, a system was built in the Matlab / Simulink environment as follows. Figure 1 The detailed time-domain simulation model shown has the grid short-circuit ratio set to SCR=10. For example... Figure 3 As shown, the eigenvalues ​​of the dominant oscillation mode λ 8,9 Initially located in the right half-plane, the grid-type converter will experience oscillation and instability; adding Figure 2 After the additional damping control strategy shown, λ 8,9 The circuit moved to the left half-plane with a damping ratio of 0.707 and a distance from the imaginary axis, while the other modal eigenvalues ​​remained basically unchanged. This indicates that the additional damping control strategy effectively improved the negative damping oscillation mode of the grid-type converter under strong power grid conditions and enhanced the wide short-circuit ratio adaptability of the grid-type converter.

[0057] Figure 4 By comparing the waveforms of active power step changes before and after adding the additional damping control strategy when the grid short-circuit ratio (SCR) is 10, it can be seen that without the additional damping control strategy, the grid-connected converter has insufficient stability margin under strong grid conditions due to the lack of damping, resulting in subsynchronous oscillation instability. However, after adding the additional damping control strategy, the oscillation characteristics completely disappear, and the grid-connected converter can quickly stabilize according to the new power command after a given power step disturbance. The stability of the grid-connected converter under strong grid conditions is improved, verifying the reliability of the control strategy proposed in this paper. The above simulation results fully demonstrate that the control strategy proposed in this invention can effectively improve the wide short-circuit ratio adaptability of the grid-connected converter and significantly improve the grid-connected power quality.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for improving the wide short-circuit ratio adaptability of a grid-type converter, characterized in that, Includes the following steps: Step 1: Establish the state-space model of the grid-connected system of the grid-connected converter; Step 2: Based on the state-space model, identify the instability modes that cause the grid-type converter to oscillate and become unstable under strong power grid conditions, and calculate the full-state feedback gain matrix. By participating in factor analysis, the dominant state variables corresponding to the instability modes are determined; The dominant state variable is used as a partial feedback quantity. A partial state feedback gain matrix is ​​designed and superimposed onto the reference value at the power outer loop input of the grid-type converter to form additional damping control and reconfigure the system poles.

2. The control method for improving the wide short-circuit ratio adaptability of a grid-type converter according to claim 1, characterized in that, The state-space model described in step 1 is a small-signal model, represented using the following logic: in, For system state variables, The system state matrix, For the input vector, For input variables, For the input matrix, This indicates a small perturbation.

3. The control method for improving the wide short-circuit ratio adaptability of a grid-type converter according to claim 2, characterized in that, Step 2, based on the state-space model, identifies the instability modes that cause grid-connected converters to oscillate and become unstable under strong power grid conditions, and calculates the full-state feedback gain matrix as follows: To find the eigenvalues ​​of the system state matrix A, if there exists a pair of conjugate complex roots... The eigenvalue is located in the right half-plane of the complex plane. The corresponding mode is taken as the unstable mode; The eigenvalues ​​are analyzed using the pole placement method. Perform corrections and solve for the desired poles. ; Using the original system state matrix A, input matrix B, and all desired poles as inputs, the full-state feedback gain matrix K is solved using mathematical tools.

4. The control method for improving the wide short-circuit ratio adaptability of a grid-type converter according to claim 3, characterized in that, The solution to the desired pole Specifically: First, set the expected extreme point as The damping ratio ζ is set as the optimal damping ratio, and the natural oscillation frequency is... and They have the same natural oscillation frequency; According to the second-order system relation and Calculate the real part of the desired pole. and the virtual part ,Sure .

5. The control method for improving the wide short-circuit ratio adaptability of a grid-type converter according to claim 4, characterized in that, The optimal damping ratio is specifically 0.

707.

6. The control method for improving the wide short-circuit ratio adaptability of a grid-type converter according to claim 3, characterized in that, The dominant state variable for determining the instability mode through participation factor analysis, as described in step 2, is as follows: Define participation factors Let represent the degree of participation of the i-th state variable in the k-th mode, and let the right eigenvector corresponding to the k-th eigenvalue be . The left eigenvector is The participation factor is calculated using the following logic. : in, , These are the i-th elements in the right and left eigenvectors, respectively; Calculate the instability mode for each state variable The participation factors are selected, and state variables with participation factors greater than a preset threshold are selected as dominant state variables.

7. The control method for improving the wide short-circuit ratio adaptability of a grid-type converter according to claim 6, characterized in that, Step 2, which uses the dominant state variable as a partial feedback quantity, specifically designs the partial state feedback gain matrix as follows: Set the columns corresponding to all state variables other than the dominant state variable to zero, reduce the dimensionality of the full-state feedback gain matrix K to form a partial-state feedback gain matrix Kn, and define the feedback input control quantity. The small signal model is adjusted to .

8. A grid-connected inverter, characterized in that, The grid connection is carried out based on the control method for improving the wide short-circuit ratio adaptability of the grid-connected converter according to any one of claims 1-7.

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