Self-adaptive virtual impedance stability control method and system for grid-connected inverter

Abstract

The invention provides a grid-connected inverter adaptive virtual impedance stability control method and system, and the method comprises the steps: obtaining a grid-connected point voltage amplitude, an inverter side current amplitude and a power angle, and obtaining a power grid impedance amplitude through calculation according to the voltage amplitude, the inverter side current amplitude and the power angle; when the calculated power grid impedance amplitude value is stable for the first time, recording the calculated numerical value as a power grid impedance initial amplitude value and storing the power grid impedance initial amplitude value, and obtaining a difference value of the impedance amplitude value according to the difference between the power grid impedance initial amplitude value and the calculated power grid impedance amplitude value; judging whether the impedance amplitude difference meets a limiting condition or not, if the condition is met, outputting the difference value of the impedance amplitude, and otherwise, outputting and setting the difference value as a set value; according to the output, control parameters of a virtual impedance link of a voltage and current double-closed-loop control preceding stage are set, virtual impedance is adjusted in real time, overshoot in the transient process of SCR switching is reduced, and power oscillation of the system is restrained.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy grid-connected power generation, and particularly relates to an adaptive virtual impedance stable control method and system for a grid-connected inverter. Background Art

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] With the wide application of new energy power generation, its randomness and volatility have brought challenges to the stable operation of the power grid. The virtual synchronous generator technology (VSG, Virtual Synchronous Generator) provides a new idea for solving this problem by simulating the operating characteristics of synchronous generators, which can effectively improve the acceptance capacity of the power grid for new energy, thus ensuring the stable operation of the system and being conducive to the large-scale grid connection of new energy. Therefore, the virtual synchronous generator technology has received more attention.

[0004] When an inverter controlled by VSG is connected to the grid for operation, processes such as line switching may occur, which may cause changes in the grid strength (SCR, Short Circuit Ratio), resulting in large fluctuations in the output power and current of the inverter during the transient process of switching, causing system oscillation and endangering the safe and stable operation of the system.

[0005] Currently, most research focuses on the stability of the inverter under a wide range of SCRs. For new energy systems controlled by VSG, special attention is paid to the problem that they can operate stably under weak grid conditions but are prone to instability under strong grid conditions. However, there is less research on the system stability during the transient process of SCR switching.

[0006] Therefore, in the context of changing SCR, VSG should have strong anti-interference ability to ensure that the system has sufficient robustness to suppress the oscillation of the system during the transient process of grid strength change and improve the stability of the system. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes an adaptive virtual impedance stable control method and system for a grid-connected inverter, which adaptively adjusts the virtual impedance value of the control loop according to the online calculation of the grid impedance amplitude, realizes the suppression of power and current oscillation during the transient process when SCR changes, simultaneously speeds up the response speed, shortens the transient time, improves the safety performance of the equipment, and can realize the stable operation of the system under a wide range of SCRs.

[0008] According to some embodiments, the present invention adopts the following technical solutions:

[0009] An adaptive virtual impedance stabilization control method for a grid-connected inverter, comprising the following steps:

[0010] Obtain the grid connection point voltage amplitude, the inverter side current amplitude and the power angle, and calculate the grid impedance amplitude therefrom;

[0011] When the calculated grid impedance amplitude reaches stability for the first time, record the calculated value as the initial grid impedance amplitude and save it. After the initial grid impedance amplitude is calculated, the above stability judgment process is no longer carried out, and the output hold is set to zero before the initial grid impedance amplitude is calculated;

[0012] Subtract the initial grid impedance amplitude from the calculated grid impedance amplitude to obtain the difference in impedance amplitude;

[0013] Judge whether the impedance amplitude difference meets the limiting conditions. If the conditions are met, output the difference in impedance amplitude; otherwise, output is set to a set value;

[0014] Set the control parameters of the virtual impedance link in the front stage of the voltage-current double closed-loop control according to the output.

[0015] As an alternative implementation, the process of obtaining the grid connection point voltage amplitude, the inverter side current amplitude and the power angle includes obtaining the grid connection point voltage, the inverter side current and the angular frequency difference output by the active control loop, and obtaining the dq-axis components of the grid connection point voltage and the inverter side current through dq transformation;

[0016] Calculate the active power, reactive power, grid connection point voltage amplitude and current amplitude output by the grid-connected inverter according to the dq-axis components of the grid connection point voltage and the inverter side current, and obtain the power angle by integrating the angular frequency difference.

[0017] As a further step, the process of calculating the active power P e and reactive power Q e includes:

[0018]

[0019] Calculate the grid voltage amplitude U m and the inverter side current amplitude i m as:

[0020]

[0021] where V Cd and V Cq respectively represent the d-axis component and q-axis component of the grid connection point voltage, and i sd and i sq respectively represent the d-axis component and q-axis component of the inverter side current;

[0022] The calculation method of the power angle δ is as follows:

[0023] δ = ∫(ω m - ω n )

[0024] ω m - ω n is the angular frequency difference output by the active power control loop.

[0025] As an alternative implementation, the process of calculating the amplitude of the grid impedance includes:

[0026] After simplified calculation, the amplitude of the line impedance Z is:

[0027]

[0028] where δ is the power angle, U m is the amplitude of the grid connection point voltage, and i m is the amplitude of the inverter side current.

[0029] As an alternative implementation, the process of recording the calculated value as the initial amplitude of the grid impedance and saving it includes judging whether the amplitude of the line impedance Z can be stabilized within ±ΔZ * of a certain predetermined value within a set time period. If the above conditions are met, record the corresponding Z as the amplitude of the line impedance Z under the initial operating conditions 0 , and when recording the amplitude of the line impedance Z 0 , terminate the judgment process of whether Z is stable.

[0030] As an alternative implementation, the process of judging whether the difference in impedance amplitude meets the limit conditions. If the conditions are met, output the difference in the impedance amplitude; otherwise, the process of setting it to a set value includes: setting an impedance threshold Z th , comparing the absolute value |ΔZ| of the difference ΔZ in the amplitude of the grid impedance obtained by calculation with Z th . Once the condition |ΔZ| > Z th is met, start outputting ΔZ, and no longer perform the comparison of |ΔZ| > Z th . Otherwise, output zero.

[0031] As an alternative implementation, the process of setting the control parameters of the virtual impedance link in the front stage of the voltage and current double closed-loop control according to the output includes: multiplying the output by the corresponding feedback coefficients respectively, and then adding the initial virtual resistance and virtual reactance of the control loop. The obtained result is used as the control parameters of the virtual impedance link in the front stage of the voltage and current double closed-loop control.

[0032] As an alternative implementation, when the line impedance of the system reaches a stable state again, the system operates the above steps under the new steady-state conditions.

[0033] An adaptive virtual impedance stabilization control system for a grid-connected inverter, comprising:

[0034] A grid impedance amplitude calculation module, configured to obtain the grid-connected point voltage amplitude, the inverter-side current amplitude, and the power angle, and calculate the grid impedance amplitude according to these;

[0035] A stability judgment module, configured to, when the calculated grid impedance amplitude reaches stability for the first time, record the calculated value as the initial grid impedance amplitude and save it, and the above-mentioned stability judgment process will no longer be carried out after the initial grid impedance amplitude is calculated, and the output remains zero before the initial grid impedance amplitude is calculated;

[0036] A difference calculation module, configured to calculate the difference between the initial grid impedance amplitude and the calculated grid impedance amplitude to obtain the difference in impedance amplitude;

[0037] An adaptive virtual impedance module, configured to judge whether the impedance amplitude difference meets the limit conditions. If it meets the conditions, output the difference in impedance amplitude, otherwise output a set value; according to the output, set the control parameters of the virtual impedance link in the front stage of the voltage-current double closed-loop control.

[0038] An electronic device, comprising a memory, a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the steps in the above method are completed.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] The present invention innovatively proposes an adaptive virtual impedance stabilization control method for a grid-connected inverter under the change of grid strength. When the SCR fluctuates, according to the online calculated grid impedance amplitude, the virtual impedance is adjusted in real time to reduce the overshoot in the transient process of SCR switching, suppress the power oscillation of the system, and ensure the stability of the inverter. The main circuit data required for calculating the grid impedance amplitude is also the data that needs to be sampled for VSG control, and no additional sampling equipment needs to be added, which can effectively reduce costs. At the same time, the proposed control method can also accelerate the response speed of the system, so that the system quickly enters a stable state.

[0041] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following specifically gives preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0043] Figure 1 This is the main circuit diagram of the grid-connected system of this embodiment;

[0044] Figure 2 This is the control block diagram of the virtual synchronous generator of this embodiment;

[0045] Figure 3 This is the introduced adaptive virtual impedance control block diagram of this embodiment;

[0046] Figure 4 This is the equivalent circuit diagram of the latter stage of the inverter of the grid-connected system of this embodiment;

[0047] Figure 5 This is the flow chart of the introduced adaptive virtual impedance control of this embodiment;

[0048] Figure 6 Under the condition that the grid strength changes, it is the waveform diagrams of the active power, voltage and current output by the corresponding inverter using the traditional virtual synchronous generator control;

[0049] Figure 7 Under the condition that the grid strength changes, it is the waveform diagrams of the active power, voltage and current output by the corresponding inverter using the improved virtual synchronous generator control of this embodiment. Specific implementation mode

[0050] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0051] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further descriptions of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0052] It should be noted that the terms used herein are only for describing specific implementation modes and are not intended to limit the exemplary implementation modes according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0053] In the case of no conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0054] Embodiment 1

[0055] Taking Figure 1 the grid-connected operation condition of a three-phase grid-connected inverter shown as an example, from left to right, it includes a DC power supply V dc, a three-phase full-bridge inverter circuit composed of six IGBT switching tubes, a filter inductor L s and a resistor R s , a filter capacitor C f , a grid-side inductor L g and a resistor R g and an AC grid V gabc . The output angular velocity of the VSG is denoted as ω m , and the rated angular velocity of the grid is denoted as ω n . Generally, the grid resistance is much smaller than the grid reactance, and the grid resistance can be ignored during analysis.

[0056] Figure 2 is the control block diagram of the virtual synchronous generator. It mainly includes parts such as main circuit sampling, power loop, voltage-current double closed loop, and SVPWM module.

[0057] The power loop includes an active power loop and a reactive power loop. The voltage amplitude reference signal E output by the reactive power loop dref and the output current i on the inverter side sabc , the capacitor voltage V cabc after Park transformation of i sdq , V cdq , together serve as the input signals of the virtual impedance link and the voltage-current double closed loop control link to obtain the reference signals of the dq-axis voltages of the inverter, and then through Park inverse transformation and SVPWM link, the three-phase modulation waves are finally obtained.

[0058] In the figure, the control equation of the VSG is:

[0059]

[0060] Among them, P ref represents the reference value of the active power, ω m and ω n represent the actual angular frequency and the rated angular frequency respectively, J represents the moment of inertia, D p represents the damping coefficient, θ represents the reference phase, Q ref represents the reference value of the reactive power, K represents the inertia coefficient of the reactive power loop, D q represents the voltage droop coefficient of the reactive power loop, E dref represents the internal electromotive force of the virtual synchronous generator.

[0061] As Figure 5 shown, the adaptive virtual impedance control method provided by this embodiment includes the following steps:

[0062] S1: Collect the grid-connected voltage, the current on the inverter side, and the angular frequency difference ω output by the active control loop m -ω n, the dq-axis components of the grid connection point voltage and the inverter-side current are obtained through dq transformation;

[0063] S2: Calculate the active power P e , reactive power Q e output by the grid-connected inverter and the grid connection point voltage amplitude U m , current amplitude i m according to the angular frequency difference, and obtain the power angle δ through integration;

[0064] S3: According to the grid connection point voltage amplitude U m , the inverter-side current amplitude i m and the power angle δ obtained by integrating the output angular frequency difference of the active power loop, calculate the grid impedance amplitude Z in real time;

[0065] S4: When the calculated grid impedance amplitude first reaches stability, record the calculated value as Z 0 that is, the initial amplitude of the grid impedance and save it. When Z 0 is calculated, the above stability judgment process will no longer be carried out. Before Z 0 is calculated, the output remains zero;

[0066] S5: Take the difference between Z 0 and the real-time calculated grid impedance amplitude Z to obtain the difference ΔZ of the impedance amplitude = Z 0 - Z;

[0067] S6: As Figure 3 shown, judge whether the impedance amplitude difference meets the limit conditions. If the conditions are met, the adaptive virtual impedance control module outputs ΔZ, otherwise the output is set to 0, and the above judgment process will no longer be carried out after startup;

[0068] S7: According to the output of the adaptive virtual impedance control module, multiply by the feedback coefficient respectively and then add the initial virtual resistance R v0 of the control loop, virtual reactance X v0 to obtain the control parameters of the virtual impedance link in the front stage of the voltage-current double closed-loop control.

[0069] As described below, in actual control, the online calculation of the grid impedance is simplified a lot, reducing the calculation amount, but it will bring certain errors. Therefore, a feedback coefficient is added in S7 for correction, and at the same time, the control effect of the system is improved.

[0070] When the line impedance of the system reaches a stable state again, the system operates under the new steady-state conditions.

[0071] In S2, specifically, it includes the following steps:

[0072] Calculate the active power \(P\) output by the grid-connected inverter through the following formula e and the reactive power \(Q\) e :

[0073]

[0074] Calculate the grid voltage amplitude \(U\) through the following formula m and the inverter-side current amplitude \(i\) m :

[0075]

[0076] where \(V\) Cd and \(V\) Cq represent the d-axis component and q-axis component of the grid connection point voltage respectively, and \(i\) sd and \(i\) sq represent the d-axis component and q-axis component of the inverter-side current respectively.

[0077] The calculation method of the power angle \(\delta\) is as follows:

[0078] \(\delta=\int(\omega\) m -\omega\) n )(4)

[0079] Obtain the grid connection point voltage reference signal through the following formula:

[0080]

[0081] \(R\) v and \(X\) v represent the virtual resistance and virtual reactance respectively, which are obtained by the adaptive virtual impedance control link. Under the initial conditions, the values of \(R\) V and \(X\) v are \(R\) v0 , \(X\) v0 . \(V\) Cdref and \(V\) Cqref represent the d-axis and q-axis reference signals of the grid connection point voltage respectively.

[0082] Obtain the voltage command of the inverter through the following formula:

[0083]

[0084] where \(i\) sdref and \(i\) sqref represent the given values of the inverter-side current on the d-axis and q-axis respectively, \(e\) dref and \(e\) qref represent the d-axis component and q-axis component of the inverter voltage command respectively, \(k\) pu and \(k\) iu represent the voltage loop proportional coefficient and integral coefficient respectively, \(k\) pi and \(k\)ii respectively represent the proportional coefficient and integral coefficient of the current loop, and L s represents the inductor on the inverter side, and C f represents the filter capacitor.

[0085] The calculation method of the grid impedance amplitude in S3 is as follows:

[0086] Since the VSG operates under the grid-connected operation condition, it can be considered that the grid voltage remains unchanged, and its amplitude is U gm = 311V. In fact, there is a slight difference between the inverter-side current and the PCC point output current. In this paper, for the sake of simplifying the calculation and reducing unnecessary sampling equipment, the power angle δ calculated in S2 is used as the phase angle difference between the PCC point voltage and the three-phase grid voltage, and i m is used as the amplitude of the PCC point output current. At the same time, according to the obtained grid connection point voltage amplitude U m , the line impedance amplitude is calculated online, and the specific calculation method is as follows:

[0087] As Figure 4 shown, it can be seen that the line impedance amplitude can be calculated according to the following formula:

[0088]

[0089] where θ 1 is the phase angle of the inverter output current (with the grid voltage phase as the reference).

[0090] Since the power angle δ is very small and U m ≈U gm , the line impedance amplitude calculation formula can be simplified as follows:

[0091]

[0092] In S4, the solution method of Z 0 is as follows:

[0093] Set the time value Δt and the impedance value ΔZ * , and according to the impedance amplitude Z calculated in S3, judge whether Z can be stabilized within ±ΔZ * of a specific value within the time period of Δt. If the above conditions are met, record the corresponding Z as the line impedance amplitude Z 0 under the initial operating conditions. When the line impedance amplitude Z 0 is recorded, terminate the judgment program of whether Z is stable.

[0094] In S6, it specifically includes the following steps:

[0095] Given the impedance threshold Z th according to the actual situation., the absolute value |ΔZ| of the difference ΔZ in the amplitude of the grid impedance obtained by calculation in S5 and Z th are compared. Once the condition |ΔZ| > Z is satisfied th then ΔZ is output, and the comparison of |ΔZ| > Z is no longer performed afterwards th Otherwise, the output is set to zero.

[0096] In S7, after obtaining the output ΔZ of the adaptive virtual impedance control link according to the above steps, the virtual resistance and virtual reactance values of the virtual impedance unit in the control loop are calculated according to the following formula:

[0097]

[0098] where K 1 and K 2 are the feedback coefficients of the adaptive virtual impedance control module corresponding to the virtual resistance and virtual reactance.

[0099] Specifically, the calculation formula of the grid strength SCR is as follows:

[0100]

[0101] where S ac is the system short-circuit capacity, U n is the rated AC voltage, P n is the rated power. Under rated conditions, the system rated capacity S n = P n , Z is the line impedance. Since the line resistance is much smaller than the line reactance, Z can be considered equal to the line reactance in the analysis.

[0102] The grid-connected operation conditions of the three-phase grid-connected inverter under the control method of this embodiment are simulated. It is generally considered that the SCR is 6 - 10 or less for a weak grid and 20 - 25 or more for a strong grid. Since the inverter controlled by VSG often operates under weak grid conditions, the single-phase grid inductance L g of the grid-connected inverter controlled by VSG is set to 20 mH under the initial operating conditions. According to formula (10), the corresponding grid strength SCR is 2.3.

[0103] At the 1st s, 2nd s, 3rd s, 4th s, 5th s, 6th s, and 7th s respectively, the grid inductance is switched to 15 mH, 10 mH, 5 mH, 2 mH, 7.5 mH, 15 mH, and 20 mH, and the corresponding grid strength SCRs become 3.1, 4.6, 9.2, 23, 6.1, 3.1, and 2.3 respectively, so as to simulate the switching process of the grid strength under different conditions.

[0104] By comparing with the traditional virtual synchronous generator control method (such as Figure 6as shown) and the control effect after the virtual synchronous generator control of the present invention (such as Figure 7 As can be seen from the control effects shown in Figure 7 and after the virtual synchronous generator control of the present invention (as shown), both control methods can make the system maintain stable operation after a certain adjustment when the SCR switch occurs. However, adopting this embodiment can reduce the oscillation of active power and current during the transient process of sudden change in grid strength, reduce overshoot, accelerate the transient process, help the system to quickly adjust, and the system can track the given value and maintain stable operation after adjustment, improving the robustness and safety of the system.

[0105] Embodiment 2

[0106] A grid-connected inverter adaptive virtual impedance stable control system, comprising:

[0107] A grid impedance amplitude calculation module, configured to obtain the grid-connected point voltage amplitude, the inverter-side current amplitude and the power angle, and calculate the grid impedance amplitude according to them;

[0108] A stability judgment module, configured to record the calculated value as the initial grid impedance amplitude and save it when the calculated grid impedance amplitude reaches stability for the first time. After the initial grid impedance amplitude is calculated, the above-mentioned stability judgment process is no longer carried out, and the output is kept zero before the initial grid impedance amplitude is calculated;

[0109] A difference calculation module, configured to calculate the difference between the initial grid impedance amplitude and the calculated grid impedance amplitude to obtain the difference in impedance amplitude;

[0110] An adaptive virtual impedance module, configured to judge whether the impedance amplitude difference meets the limiting conditions. If the conditions are met, output the difference in impedance amplitude, otherwise output a set value; according to the output, set the control parameters of the virtual impedance link in the front stage of the voltage-current double closed-loop control.

[0111] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art without creative work within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A grid-connected inverter adaptive virtual impedance stabilization control method, characterized in that: The following steps are involved: Obtain the voltage amplitude at the grid connection point, the current amplitude at the inverter side and the power angle, and calculate the grid impedance amplitude based on them; When the calculated grid impedance amplitude reaches stability for the first time, the calculated value is recorded as the initial grid impedance amplitude and saved. After the initial grid impedance amplitude is calculated, the above stability judgment process is no longer performed. Before the initial grid impedance amplitude is calculated, the output remains zero. The difference between the initial grid impedance amplitude and the calculated grid impedance amplitude is subtracted to obtain the impedance amplitude difference; Determine whether the impedance amplitude difference meets the limiting condition, if so, output the impedance amplitude difference, otherwise the output is set to the set value; According to the output, control parameters of the virtual impedance link of the front stage of the voltage and current double closed-loop control are set.

2. The method for adaptive virtual impedance stabilization control of a grid-connected inverter according to claim 1, characterized in that: The process of obtaining the grid-connected point voltage amplitude, the inverter-side current amplitude and the power angle includes obtaining the grid-connected point voltage, the inverter-side current and the angular frequency difference of the active control loop output, and obtaining the dq axis components of the grid-connected point voltage and the inverter-side current through dq transformation; The active power, reactive power output by the grid-connected inverter, as well as the grid-connected point voltage amplitude and current amplitude are calculated according to the dq-axis components of the grid-connected point voltage and the inverter-side current, and the power angle is obtained by integrating the angular frequency difference.

3. The method for adaptive virtual impedance stabilization control of a grid-connected inverter according to claim 2, characterized in that: Calculate the active power P output by the grid-connected inverter e and reactive power Q e The process includes: Calculate the grid voltage amplitude U m And the inverter side current amplitude i m for: Among them, V Cd and V Cq They represent the d-axis component and q-axis component of the grid-connected point voltage respectively, i sd and i sq They represent the d-axis component and q-axis component of the inverter-side current respectively; The calculation method of power angle δ is: δ=∫(ω m -oh n ) ω m -ω n is the angular frequency difference of the active control loop output.

4. The method for adaptive virtual impedance stabilization control of a grid-connected inverter according to claim 1, characterized in that: The process of calculating the grid impedance amplitude includes: After simplified calculation, the line impedance amplitude Z is: Among them, δ is the power angle, U m is the voltage amplitude at the grid connection point and i m is the current amplitude on the inverter side.

5. A grid-connected inverter adaptive virtual impedance stabilization control method as claimed in claim 1 or 4, characterized in that: The process of recording the calculated value as the initial amplitude of the grid impedance and saving it includes determining whether the line impedance amplitude Z can be stabilized within a predetermined value ±ΔZ within a set time period. * Within the range, if the above conditions are met, the corresponding Z is recorded as the line impedance amplitude Z0 under the initial operating conditions. After the line impedance amplitude Z0 is recorded, the process of determining whether Z is stable is terminated.

6. The method for adaptive virtual impedance stabilization control of a grid-connected inverter according to claim 1, characterized in that: The process of judging whether the impedance amplitude difference satisfies the limiting condition, and if so, outputting the impedance amplitude difference, or otherwise setting the output to the set value includes: setting the impedance threshold Z th , the absolute value of the difference in grid impedance amplitude ΔZ obtained by calculation |ΔZ| and Z th Compare, once the condition |ΔZ|>Z is met th Then the output ΔZ is started, and there will be no more |ΔZ|>Z th Compare, otherwise the output is set to zero.

7. The method for adaptive virtual impedance stabilization control of a grid-connected inverter according to claim 1, characterized in that: According to the output, the process of setting the control parameters of the virtual impedance link of the front stage of the voltage and current dual closed-loop control includes: multiplying the output by the corresponding feedback coefficient, and then adding it to the initial virtual resistance and virtual reactance of the control loop, and the obtained result is used as the control parameter of the virtual impedance link of the front stage of the voltage and current dual closed-loop control.

8. The method for adaptive virtual impedance stabilization control of a grid-connected inverter according to claim 1, characterized in that: When the line impedance of the system reaches a steady state again, the system runs the above steps under the new steady-state condition.

9. An adaptive virtual impedance stability control system for a grid-connected inverter, characterized in that: include: The grid impedance amplitude calculation module is configured to obtain the grid connection point voltage amplitude, the inverter side current amplitude and the power angle, and calculate the grid impedance amplitude based on the obtained voltage amplitude, the inverter side current amplitude and the power angle; The stability judgment module is configured to record and save the calculated value as the initial amplitude of the grid impedance when the calculated grid impedance amplitude reaches stability for the first time, and the above stability judgment process is no longer performed after the initial amplitude of the grid impedance is calculated, and the output remains zero before the initial amplitude of the grid impedance is calculated; The difference calculation module is configured to obtain a difference in impedance amplitude by performing a difference between the initial amplitude of the grid impedance and the calculated grid impedance amplitude; The adaptive virtual impedance module is configured to determine whether the impedance amplitude difference meets the specified conditions. If the conditions are met, the impedance amplitude difference is output, otherwise the output is set to a set value; according to the output, the control parameters of the virtual impedance link of the front stage of the voltage and current dual closed-loop control are set.

10. An electronic device, characterized in that: The method comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the steps in the method according to any one of claims 1 to 8 are completed.

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