System and method for controlling steady-state power decoupling of grid-forming inverter

Abstract

The present invention relates to a system and a method for controlling steady-state power decoupling of a grid-forming inverter and, more specifically, to a system and a method for controlling steady-state power decoupling of a grid-forming inverter, which estimate an optimal virtual impedance value and a transient virtual resistance value at which steady-state power decoupling control can be achieved during operation of the grid-forming inverter, and control so that output reactive power fluctuations due to active power command fluctuations of the grid-forming inverter do not occur.

Description

Steady-state power decoupling control system and method for grid-forming inverter

[0001] The present invention relates to a steady-state power decoupling control system and method for a grid-forming inverter, and more specifically, to a steady-state power decoupling control system and method for a grid-forming inverter that estimates an optimal virtual impedance value and a transient virtual resistance value capable of achieving steady-state power decoupling control during grid-forming inverter operation, thereby controlling so that no fluctuation in output reactive power occurs due to fluctuation in active power command of the grid-forming inverter.

[0002] With the recent increase in the proportion of distributed energy resources based on power converters, grid-forming inverters (GFMI) are receiving significant attention to improve the stability of power systems. Unlike conventional grid-following inverters (GFLI) that synchronize with the grid through phase-locked loop technology, GFMI synchronizes based on the power balance principle and provides reference voltage and frequency, similar to an uninterruptible power supply. Additionally, GFMI can support voltage and frequency and enables both standalone and grid-connected operation, contributing to the flexible operation of microgrids (MGs).

[0003] However, unlike GFLI, GFMI causes unintended coupling in the power control loop, making the design of GFMI control parameters difficult and significantly degrading stability, power transfer capabilities, and dynamic performance. The lower the X / R ratio of the grid impedance (i.e., for medium and low voltage microgrids), the more pronounced the power coupling problem becomes. Therefore, there is a need for a system to address these issues in low-voltage microgrids.

[0004] The present invention was created out of the above-mentioned necessity, and the objective of the present invention is to provide a steady-state power decoupling control system and method for a grid-forming inverter that estimates an optimal virtual impedance value and a transient virtual resistance value capable of achieving steady-state power decoupling control during grid-forming inverter operation, thereby controlling so that no fluctuation in output reactive power occurs due to fluctuation in the active power command of the grid-forming inverter.

[0005] A steady-state power decoupling control system for a grid-forming inverter according to an embodiment of the present invention, for achieving the above-mentioned purpose, comprises: a grid-forming inverter operable to form a reference voltage and frequency and provide inertia and damping; and an optimal virtual impedance value ( ) and transient virtual resistance values( It is characterized by including a gridforming inverter controller that estimates ) and controls steady-state power decoupling of the gridforming inverter.

[0006] In addition, the gridforming inverter is characterized by including a virtual impedance, a voltage controller, and a current controller as internal control loops, and including an active power controller and a reactive power controller as external control loops.

[0007] In addition, the dq-axis output voltage command, which is the input of the above voltage controller, is characterized by being as shown in the following mathematical formula.

[0008]

[0009] Here, is a transient virtual resistance, the first-order high-pass filtering term ensures system attenuation, and the last parenthetical term on the right is a voltage compensation term consisting of a virtual impedance used for power decoupling.

[0010] In addition, the active power controller performs frequency support through virtual inertia and Pf droop control, and the reactive power controller performs voltage support through QV droop control.

[0011] In addition, the gridforming inverter controller, through a pre-learned grid impedance estimation algorithm, the grid resistance of the power system ( ) and system inductance( A power system estimation unit that estimates ); and the system resistance estimated by the power system estimation unit ( ) and system inductance( A short-circuit ratio calculation unit that calculates the short-circuit ratio (SCR) as shown in the following mathematical formula through ); ​​the above-mentioned system resistance ( ), system inductance( A control value estimation unit that estimates an optimal virtual impedance value and a transient virtual resistance value through ) and a short-circuit ratio (SCR); and an optimal virtual impedance value estimated by the control value estimation unit ( ) and transient virtual resistance values( It is characterized by including a grid forming inverter control unit that controls the grid forming inverter according to the above.

[0012]

[0013] In addition, the control value estimation unit obtains the optimal virtual impedance value (through the following mathematical formula) ) and transient virtual resistance values( It is characterized by estimating ).

[0014]

[0015] In addition, the gridforming inverter control unit checks for a change in grid impedance through the following mathematical formula, and when the grid impedance changes, the short-circuit ratio calculation unit and the control value estimation unit calculate the short-circuit ratio and the optimal virtual impedance value ( ) and transient virtual resistance values( It is characterized by controlling the re-execution of the estimation.

[0016]

[0017] A steady-state power decoupling control method for a grid-forming inverter according to an embodiment of the present invention comprises: a step A in which the grid-forming inverter operates to form a reference voltage and frequency and provide inertia and damping; and a grid-forming inverter controller having an optimal virtual impedance value ( ) and transient virtual resistance values( It is characterized by including step B, which estimates ) and controls the steady-state power decoupling of the grid forming inverter.

[0018] In addition, the gridforming inverter is characterized by including a virtual impedance, a voltage controller, and a current controller as internal control loops, and including an active power controller and a reactive power controller as external control loops.

[0019] In addition, the dq-axis output voltage command, which is the input of the above voltage controller, is characterized by being as shown in the following mathematical formula.

[0020]

[0021] Here, is a transient virtual resistance, which ensures system attenuation along with the first-order high-pass filtering term, and the last parenthetical term on the right is a voltage compensation term consisting of a virtual impedance used for power decoupling.

[0022] In addition, the active power controller performs frequency support through virtual inertia and Pf droop control, and the reactive power controller performs voltage support through QV droop control.

[0023] In addition, the above-mentioned Step B comprises the power system estimation unit using a pre-learned system impedance estimation algorithm to determine the system resistance of the power system ( ) and system inductance( A step of estimating ); the short-circuit ratio calculation unit estimates the system resistance ( ) and system inductance( A step of calculating the short-circuit ratio (SCR) as shown in the following mathematical formula through ); ​​a control value estimation unit the system resistance ( ), system inductance( Optimal virtual impedance value ( ) and transient virtual resistance values( A step of estimating ); and a gridforming inverter control unit estimating the optimal virtual impedance value ( ) and transient virtual resistance values( It is characterized by including a step of controlling the grid-forming inverter according to ).

[0024]

[0025] In addition, the control value estimation unit obtains the optimal virtual impedance value (through the following mathematical formula) ) and transient virtual resistance values( It is characterized by estimating ).

[0026]

[0027] In addition, the gridforming inverter control unit checks for a change in grid impedance through the following mathematical formula, and when the grid impedance changes, the short-circuit ratio calculation unit and the control value estimation unit calculate the short-circuit ratio and the optimal virtual impedance value ( ) and transient virtual resistance values( It is characterized by controlling the re-execution of the estimation.

[0028]

[0029] The steady-state power decoupling control system and method of a grid-forming inverter according to the present invention has the effect of controlling so that output reactive power fluctuations do not occur due to active power command fluctuations of the grid-forming inverter by estimating optimal virtual impedance values ​​and transient virtual resistance values ​​capable of achieving steady-state power decoupling control during grid-forming inverter operation.

[0030] The problems solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0031] FIG. 1 is a block diagram of a control system according to an embodiment of the present invention.

[0032] FIG. 2 is a circuit diagram of a grid-forming inverter according to an embodiment of the present invention.

[0033] FIG. 3 is a circuit diagram of a virtual impedance according to an embodiment of the present invention.

[0034] FIG. 4 is a block diagram of a grid forming inverter controller according to an embodiment of the present invention.

[0035] FIG. 5 is a flowchart of a steady-state power decoupling control method of a gridforming inverter according to an embodiment of the present invention.

[0036] FIG. 6 is a detailed flowchart of a steady-state power decoupling control method of a gridforming inverter according to an embodiment of the present invention.

[0037] FIG. 7 is an example diagram of hardware for validating the effectiveness of a control system according to an embodiment of the present invention.

[0038] FIG. 8 is an example diagram of validity verification of a control system according to an embodiment of the present invention.

[0039] FIG. 9 is an example diagram of validity verification of a control system according to an embodiment of the present invention.

[0040] FIG. 10 is an example of validity verification of a control system according to an embodiment of the present invention.

[0041] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete, and to ensure that the spirit of the present invention is sufficiently conveyed to those skilled in the art.

[0042]

[0043] In describing the present invention, terms such as first, second, etc. may be used to describe various components, but the components may not be limited by the terms. The terms are intended solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be named the second component, and similarly, the second component may be named the first component.

[0044]

[0045] When it is mentioned that a component is connected to or coupled with another component, it can be understood that it may be directly connected to or coupled with that other component, or that there may be other components in between.

[0046]

[0047] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions may include plural expressions unless the context clearly indicates otherwise.

[0048]

[0049] In this specification, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0050] Hereinafter, specific technical details to be implemented in the present invention will be described in detail with reference to the attached drawings.

[0051]

[0052] FIG. 1 is a block diagram of a control system according to an embodiment of the present invention. As shown in FIG. 1, the steady-state power decoupling control system of a grid-forming inverter according to the present invention may include a grid-forming inverter (100) and a grid-forming inverter controller (200).

[0053]

[0054] The grid-forming inverter (100) above is a device that independently generates power in a power grid and can perform a role similar to a generator. By operating in a voltage source control method rather than a conventional current source control method, it can mitigate voltage and frequency instability in the power grid. In addition, since the grid-forming inverter (100) can generate and apply voltage and phase on its own, it has the advantage of increasing grid stability by providing an inertia effect to power grids with reduced robustness as the proportion of new and renewable energy increases in a carbon-neutral environment where synchronous generators have become scarce.

[0055]

[0056] Therefore, the gridforming inverter (100) acts as an energy buffer for the variability of renewable energy, and thus can have an operating strategy to increase the acceptance and efficiency of renewable energy and increase the stability of the power grid, so it can be expected to play an important role in future power grids with a high proportion of new and renewable energy.

[0057]

[0058] However, such gridforming inverters (100) have a problem in that unintended coupling occurs in the power control loop, making it difficult to design control parameters and significantly degrading stability, power transfer function, and dynamic performance, and the power coupling problem becomes more pronounced as the X / R ratio of the grid impedance is lower (i.e., in the case of medium and low voltage microgrids).

[0059]

[0060] To solve this, the gridforming inverter (100) according to the present invention may include a virtual impedance (110), a voltage controller (120), and a current controller (130) as internal loop control, and an active power controller (140) and a reactive power controller (150) as external loop control, as shown in FIG. 2. FIG. 2 is a circuit diagram of a gridforming inverter according to an embodiment of the present invention.

[0061]

[0062] Here, the dq-axis output voltage command, which is the input of the voltage controller (120), is equal to the following mathematical formula 1.

[0063]

[0064] Here, is a transient virtual resistance, which ensures system attenuation along with the first-order high-pass filtering term, and the last parenthetical term on the right is a voltage compensation term consisting of a virtual impedance used for power decoupling.

[0065]

[0066] That is, it means that the virtual impedance (110) includes both a transient virtual resistance and a virtual impedance, and the configuration of the virtual impedance (110) is as shown in FIG. 3. FIG. 3 is a circuit diagram of a virtual impedance according to an embodiment of the present invention. As shown in FIG. 3, the virtual impedance (110) includes both a transient virtual resistance (TVR) and a virtual impedance (VI), the transient virtual resistance is composed of a high-pass filter, a virtual resistance, and an output current, and the virtual impedance is composed of a virtual resistance, a reactance, and an output current.

[0067]

[0068] The power oscillation problem of the grid-forming inverter (100) can be resolved through the above-mentioned transient virtual resistance, and at this time, it has high-pass characteristics so as not to affect steady-state conditions. In addition, the coupling between P and Q can be relieved through the above-mentioned virtual impedance, so steady-state decoupling control of the grid-forming inverter (100) is possible.

[0069]

[0070] The active power controller (140) performs frequency support through virtual inertia and Pf droop control, and the reactive power controller (150) performs voltage support through QV droop control.

[0071]

[0072] The above gridforming inverter controller (200) has an optimal virtual impedance value ( ) and transient virtual resistance values( The grid forming inverter (100) is configured to control steady-state power decoupling by estimating the grid forming inverter (100), and as shown in FIG. 4, it may include a power system estimation unit (210), a short-circuit ratio calculation unit (220), a control value estimation unit (230), and a grid forming inverter control unit (240). FIG. 4 is a block diagram of a grid forming inverter controller according to an embodiment of the present invention.

[0073]

[0074] The above power system estimation unit (210) uses a pre-learned system impedance estimation algorithm to determine the system resistance of the power system ( ) and system inductance( The above algorithm may be an artificial intelligence algorithm learned through learning data collected from various types of power systems, as a configuration for estimating ).

[0075]

[0076] The above short-circuit ratio calculation unit (220) is the system resistance estimated by the power system estimation unit (210). ) and system inductance( It is a configuration that calculates the short-circuit ratio (SCR) through ). The short-circuit ratio refers to the ratio of the short-circuit current to the rated current.

[0077]

[0078] The above control value estimation unit (230) is the system resistance ( ), system inductance( Optimal virtual impedance value ( ) and transient virtual resistance values( The configuration estimates the optimal virtual impedance value and transient virtual resistance value through a mathematical formula calculated through a series of processes.

[0079]

[0080] The above gridforming inverter control unit (240) has the optimal virtual impedance value (estimated by the control value estimation unit (230)) ) and transient virtual resistance values( The grid forming inverter (100) is controlled according to the configuration, and overall control of the grid forming inverter (100) and the grid forming inverter controller (200) is possible.

[0081] Hereinafter, a steady-state decoupling control method of a grid-forming inverter through a control system according to the present invention configured as described above will be explained in detail with reference to FIGS. 5 and 6.

[0082]

[0083] FIG. 5 is a flowchart of a steady-state power decoupling control method for a grid-forming inverter according to an embodiment of the present invention. As shown in FIG. 5, the steady-state decoupling control method for a grid-forming inverter through a control system according to the present invention includes a step (S100) in which the grid-forming inverter (100) is connected to a power grid and operates to provide inertia, and a step (S200) in which a grid-forming inverter controller (200) estimates an optimal virtual impedance value and a transient virtual resistance value when the grid-forming inverter (100) is operating, thereby controlling the grid-forming inverter (100) for steady-state power decoupling.

[0084]

[0085] The above step (S200) is described in more detail as shown in FIG. 6. FIG. 6 is a detailed flowchart of a steady-state power decoupling control method of a gridforming inverter according to an embodiment of the present invention. As shown in FIG. 6, in the above step (S200), first, the power system estimation unit (210) uses a pre-learned system impedance estimation algorithm to determine the system resistance of the power system ( ) and system inductance( It includes a step (S210) of estimating ) In the step (S210), the system impedance estimation algorithm preferably estimates the system resistance ( through iterative learning and relearning using sufficient learning data). ) and system inductance( Values ​​such as accuracy, precision, and recall for estimation may indicate that the algorithm is at a reliable level.

[0086]

[0087] Next, in the above step (S200), the short-circuit ratio calculation unit (220) calculates the system resistance (estimated by the power system estimation unit (210) ) and system inductance( It includes a step (S220) of calculating the short-circuit ratio through ). In the above step (S220), the short-circuit ratio calculation unit (220) calculates the short-circuit ratio (SCR) through the following mathematical formula 2. The short-circuit ratio refers to the ratio of the short-circuit current to the rated current.

[0088]

[0089] Next, in the above step (S200), the control value estimation unit (230) has a system resistance ( ), system inductance( Optimal virtual impedance value ( ) and transient virtual resistance values( It includes a step (S230) of estimating ). In the step (S230), the control value estimation unit (230) obtains the optimal virtual impedance value ( ) and transient virtual resistance values( Estimates )

[0090]

[0091] Meanwhile, mathematical formula 3 as described above is an ideal power decoupling condition under the assumption that the gridforming inverter (100) is three-phase balanced ( Output voltage change calculated according to ) ) and output current change( By reflecting ) in the active power calculated at the steady-state operating point under ideal power decoupling conditions, the following mathematical formula 4 is derived, and by reflecting the output current, output voltage, and power angle at the steady-state operating point under ideal power decoupling conditions in the derived mathematical formula 4, the optimal virtual impedance value can be calculated.

[0092]

[0093] Next, in the above step (S200), the gridforming inverter control unit (240) determines the optimal virtual impedance value (estimated by the control value estimation unit (230) ) and transient virtual resistance values( It includes a step (S240) of controlling the grid forming inverter (100) according to ). In the step (S240), the grid forming inverter control unit (240) checks for a change in grid impedance through the following mathematical formula 5, and when the grid impedance changes, the short-circuit ratio calculation unit (230) and the control value estimation unit (240) calculate the short-circuit ratio and the optimal virtual impedance value ( ) and transient virtual resistance values( ) Controls the re-execution of the estimation.

[0094]

[0095]

[0096] Accordingly, the steady-state power decoupling control system of the grid-forming inverter according to the present invention enables steady-state power decoupling control of the grid-forming inverter (100) when the grid-forming inverter (100) is in operation or when the grid impedance is changed.

[0097]

[0098] Meanwhile, by configuring the hardware as shown in FIG. 7, a test can be performed to verify the validity of the steady-state power decoupling control system of the grid-forming inverter according to the present invention as described above. FIG. 7 is an example diagram of hardware for verifying the validity of a control system according to an embodiment of the present invention. As shown in FIG. 7, the control algorithm was implemented through a 32-bit floating-point digital signal processor (TMS320F28069M), and the hardware was virtually implemented through the real-time simulator HIL606. The parameters applied for the validity verification are as shown in Tables 1 and 2 below.

[0099]

[0100]

[0101] The optimal virtual impedance values ​​in Case 1 and Case 2 are, respectively and It is the same as.

[0102]

[0103] FIG. 8 is an example diagram 1 of the validity verification of a control system according to an embodiment of the present invention. When the parameters are the same as in Case 1 It can be confirmed that steady-state power decoupling control is achieved in FIG. 8b, which applies the power decoupling control strategy according to the present invention while α changes from 0 to 0.5 pu, unlike FIG. 8a, which does not apply the strategy. In addition, when the parameter is the same as in Case 2 It can be seen that steady-state power decoupling control is achieved in FIG. 8d, which applies the power decoupling control strategy according to the present invention while changing from 0 to 0.5 pu, unlike FIG. 8c, which does not apply the strategy.

[0104]

[0105] FIG. 9 is an example diagram 2 of the validation of a control system according to an embodiment of the present invention. As shown in FIG. 9, when the parameters are the same as in Case 1 When the power decoupling control strategy according to the present invention is applied while ga changes from 0 to 1 pu, Regardless of the value, the optimal virtual impedance value =- and = Maintain the relationship.

[0106]

[0107] FIG. 10 is an example diagram 3 of the validation of a control system according to an embodiment of the present invention. As shown in FIG. 10, when the parameters are the same as in Case 2 It can be confirmed that the power decoupling control strategy according to the present invention is applied while changing from 0 to 1 pu, and that FIG. 10b, which considers transient virtual resistance, is more stable than FIG. 10a, which applies the power decoupling control strategy according to the present invention but does not consider transient virtual resistance.

[0108]

[0109] Accordingly, the steady-state power decoupling control system of a grid-forming inverter according to the present invention can estimate the optimal virtual impedance value and transient virtual resistance value during grid-forming inverter operation to control the grid-forming inverter in steady-state power decoupling, thereby accurately following the active power command in accordance with the power dispatch instructions of the grid operator and minimizing the impact on the reactive power side, and has the effect of solving the overcurrent problem by improving the dynamic power response.

[0110]

[0111] Meanwhile, although preferred embodiments illustrating the technical concept of the present invention have been described and illustrated above, the present invention is not limited to the configuration and operation as illustrated and described, and those skilled in the art will understand that numerous changes and modifications are possible to the present invention without departing from the scope of the technical concept. Accordingly, all such appropriate changes, modifications, and equivalents should be deemed to fall within the scope of the present invention. Accordingly, the true scope of technical protection of the present invention should be determined by the technical concept of the appended claims.

[0112] The present invention can be used as a core control technology required for inverter manufacturing.

Claims

1. A grid-forming inverter operable to form a reference voltage and frequency and provide inertia and damping; and The optimal virtual impedance value when the above gridforming inverter is in operation ( ) and transient virtual resistance values( A gridforming inverter controller that estimates ) and controls steady-state power decoupling of the gridforming inverter; A steady-state power decoupling control system for a gridforming inverter characterized by including 2. In Paragraph 1, The above gridforming inverter is, A steady-state power decoupling control system for a grid-forming inverter, characterized in that the grid-forming inverter includes a virtual impedance, a voltage controller, and a current controller as internal control loops, and includes an active power controller and a reactive power controller as external control loops.

3. In Paragraph 2, A steady-state power decoupling control system for a grid-forming inverter, characterized in that the dq-axis output voltage command, which is the input of the above voltage controller, is the same as the following mathematical formula. Here, is a transient virtual resistance, which ensures system attenuation along with the first-order high-pass filtering term, and the last parenthetical term on the right is a voltage compensation term consisting of a virtual impedance used for power decoupling.

4. In Paragraph 2, The above active power controller is, It performs frequency support through virtual inertia and Pf droop control, and The above reactive power controller is, A steady-state power decoupling control system for a gridforming inverter characterized by performing voltage support through QV droop control.

5. In Paragraph 1, The above gridforming inverter controller is, The power system's grid resistance ( ) and system inductance( Power system estimation unit estimating ); The system resistance estimated by the above power system estimation unit ( ) and system inductance( Mathematical formula through ) A short-circuit ratio calculation unit that calculates the short-circuit ratio (SCR) using [the method]; The above system resistance ( ), system inductance( A control value estimation unit that estimates optimal virtual impedance values ​​and transient virtual resistance values ​​through ) and short-circuit ratio (SCR); and The optimal virtual impedance value estimated by the above control value estimation unit ( ) and transient virtual resistance values( A grid forming inverter control unit that controls the grid forming inverter according to ); A steady-state power decoupling control system for a gridforming inverter characterized by including 6. In Paragraph 5, The above control value estimation unit is, mathematical formula Through this, the optimal virtual impedance value ( ) and transient virtual resistance values( A steady-state power decoupling control system for a gridforming inverter characterized by estimating ).

7. In Paragraph 5, The above gridforming inverter control unit is, mathematical formula Through this, the change in system impedance is checked, and when the system impedance changes, the short-circuit ratio calculation unit and the control value estimation unit calculate the short-circuit ratio and the optimal virtual impedance value ( ) and transient virtual resistance values( A steady-state power decoupling control system for a gridforming inverter characterized by controlling the re-execution of estimation.

8. Stage A in which the gridforming inverter operates to form a reference voltage and frequency and to provide inertia and damping; and The gridforming inverter controller has the optimal virtual impedance value when the gridforming inverter is operating ( ) and transient virtual resistance values( Step B, which estimates ) and controls the gridforming inverter for steady-state power decoupling; A steady-state power decoupling control method for a gridforming inverter characterized by including 9. In Paragraph 8, A steady-state power decoupling control method for a grid-forming inverter, characterized in that the grid-forming inverter includes a virtual impedance, a voltage controller, and a current controller as internal control loops, and includes an active power controller and a reactive power controller as external control loops.

10. In Paragraph 9, A steady-state power decoupling control method for a grid-forming inverter, characterized in that the dq-axis output voltage command, which is the input of the above voltage controller, is the same as the following mathematical formula. Here, is a transient virtual resistance, which ensures system attenuation along with the first-order high-pass filtering term, and the last parenthetical term on the right is a voltage compensation term consisting of a virtual impedance used for power decoupling.

11. In Paragraph 9, The above active power controller is, It performs frequency support through virtual inertia and Pf droop control, and The above reactive power controller is, A steady-state power decoupling control method for a gridforming inverter characterized by performing voltage support through QV droop control.

12. In Paragraph 8, The above Step B is, The power system estimation unit uses a pre-learned system impedance estimation algorithm to estimate the power system's system resistance ( ) and system inductance( Step of estimating ); The short-circuit ratio calculation unit estimates the system resistance (the power system estimation unit above) ) and system inductance( Mathematical formula through ) Step of calculating the short-circuit ratio (SCR) using; The control value estimation unit is the above system resistance ( ), system inductance( Optimal virtual impedance value ( ) and transient virtual resistance values( Step of estimating ); and The gridforming inverter control unit estimates the optimal virtual impedance value ( ) and transient virtual resistance values( A step of controlling the gridforming inverter according to ); A steady-state power decoupling control method for a gridforming inverter characterized by including 13. In Paragraph 12, The above control value estimation unit is, mathematical formula Through this, the optimal virtual impedance value ( ) and transient virtual resistance values( A steady-state power decoupling control method for a gridforming inverter characterized by estimating ).

14. In Paragraph 12, The above gridforming inverter control unit is, mathematical formula Through this, the change in system impedance is checked, and when the system impedance changes, the short-circuit ratio calculation unit and the control value estimation unit calculate the short-circuit ratio and the optimal virtual impedance value ( ) and transient virtual resistance values( A steady-state power decoupling control method for a gridforming inverter characterized by controlling the re-execution of estimation.

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