Analysis method, and analysis device

Abstract

To practically implement effective value analysis of a power system including a GFM inverter comprising a current limit function.SOLUTION: An analysis device 1 comprises: an effective value analysis section 110 which performs effective value analysis of a power system A including one or more GFM inverters A1 each comprising a current limit function; a contraction method application section 112 for identifying a third algebraic equation AE3 required in a system contraction method to a second algebraic equation AE2 relating to a tidal current and a voltage of the power system A; and an equation decomposition section for identifying a fourth algebraic equation AE4 representing a first algebraic equation AE1, which represents an internal state of the GFM inverter A1, using a first variable representing an operational state of the current limit function by an exclusive logic for each first condition branch which is established when the current limit function is active and each second condition branch which is established when the current limit function is inactive. The effective value analysis section 110 performs the effective value analysis of the power system A using a first differential equation DE1 of dynamic characteristics of the GFM inverter A1, the third algebraic equation AE3 and the fourth algebraic equation AE4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an analysis method and an analysis device. [Background technology]

[0002] In recent years, there has been a demand for improving the flexibility and resilience of power systems. For example, when the voltage source of a distribution substation is lost due to an event such as abnormal weather or a natural disaster, it is required that some or all of the feeders extending from the distribution substation operate autonomously. One of the possible measures is to introduce a grid-forming inverter (GFM inverter) into the power system (see, for example, Patent Document 1). A GFM inverter is a type of power conditioner system (PCS), and is a device equipped with a control function that establishes voltage autonomously and maintains stable operation.

[0003] A distributed energy system that establishes voltage independently of the power grid is called a "microgrid." In addition, when the entire feeder below the distribution substation is independent of the upper power grid, it is also called a "regional microgrid." In the following, we will focus on configurations that include GFM inverters for such power grids.

[0004] In the operation of a power system such as a regional microgrid, it is expected that transient fluctuations in voltage and frequency will become evident, so maintaining the dynamic reliability of the power system, including the GFM inverter, is important. The standard for dynamic reliability here is whether the power flow, frequency, voltage, and stability are within the operational limits, and these conditions are determined by dynamic analysis of the entire power system, including the GFM inverter.

[0005] In general, instantaneous value models (electromagnetic transient models) are used for dynamic analysis of power systems. However, although instantaneous value models are suitable for verifying the performance of a small number of PCSs, they are not suitable for simulating real systems represented by thousands of nodes, or for evaluating the dynamic reliability of power systems in real time.

[0006] On the other hand, in cases where a real-time dynamic reliability evaluation is required for a large-scale power system, RMS models such as the Phasor model and the Transient Stability model have been used. Regarding RMS models, a program called the Y method, developed by the Central Research Institute of the Electric Power Industry, has been put to practical use as a tool for RMS analysis of power transmission systems. However, the Y method is a tool based on the conventional synchronous generator model and load model. In addition, scenario power flow calculation is known as one of the dynamic analysis methods for power distribution systems. However, scenario power flow calculation is classified as a so-called quasi-steady-state analysis that calculates the power flow of the analysis target on a time scale of one second or more, and is not suitable for analysis of frequency and voltage fluctuations and stability that occur on a time scale of one second or less.

[0007] In addition, the GFM inverter has a current limiting function that limits the current when an overcurrent is detected in order to protect the internal components. However, the current limiting operation is likely to cause problems with transient stability when a voltage drop occurs due to an accident in the power system. For example, Non-Patent Documents 1 and 2 show that the current limiting in the GFM inverter has a significant impact on transient stability.

[0008] As mentioned above, there are various technical challenges in the effective value analysis of a power system including a GFM inverter. To address this issue, Non-Patent Document 3 proposes a method of effective value analysis for a GFM inverter that has a current limiting function that limits the current when a ground fault or the like occurs. [Prior art documents]

Chartered Documents

[0009] [Patent Document 1] JP-2023-012086

Non-licensed documents

[0010]

Non-patent document 1

Non-patent document 2

Non-patent document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] One of the factors that hinders the practicality of the effective value analysis method including the logic for simulating the current limiting function of the GFM inverter is the high speed of calculation. Specifically, the logic for simulating the current limiting function of the GFM inverter is mainly implemented by the current control loop. To accurately simulate the current limiting function of the GFM inverter, it is required to process the current control loop at high speed. Therefore, in the normal effective value analysis where the calculation period is generally 1 ms or more, it is difficult to simulate the current limiting function of the GFM inverter.

[0012] Non-Patent Document 3 avoids the problems caused by using the current control loop by using algebraic equations formulated for each conditional branch of the If-then rule instead of using the current control loop as the logic for simulating the current limiting function. However, in this case, it is necessary to solve a so-called combinatorial problem of obtaining a set of algebraic equations that satisfy the complementary conditions of the If-then rule. And it is not easy to solve this combinatorial problem, and Non-Patent Document 3 does not show the solution to an implementable extent.

[0013] An object of the present disclosure is to provide an analysis method and an analysis device that can more practically perform effective value analysis of a power system including a GFM inverter with a current limiting function. [Means for solving the problem]

[0014] An analysis method according to one embodiment of the present disclosure performs an effective value analysis of a power system based on a first differential equation representing dynamic characteristics of one or more GFM inverters having a current limiting function, a first algebraic equation representing an internal state of the one or more GFM inverters, and a second algebraic equation representing a relationship between power flow and voltage in a network of the power system having the one or more GFM inverters, for each of a first conditional branch that is true when the current limiting function is operating and a second conditional branch that is true when the current limiting function is not operating, the method includes: identifying a third algebraic equation obtained by applying a system reduction method to the second algebraic equation; identifying a fourth algebraic equation expressing a decomposed form of the first algebraic equation by using a first variable that represents an operating state of the current limiting function using exclusive logic; and performing an effective value analysis of the power system based on the first differential equation, the third algebraic equation, and the fourth algebraic equation.

[0015] An analysis device according to one embodiment of the present disclosure includes an effective value analysis unit that performs an effective value analysis of a power system having one or more GFM inverters having a current limiting function; a reduction method application unit that identifies a third algebraic equation obtained by applying a system reduction method to a second algebraic equation that represents the relationship between the power flow and voltage in a network of the power system; and an equation decomposition unit that identifies a fourth algebraic equation that expresses the first algebraic equation that represents an internal state of the one or more GFM inverters in a decomposed form by using a first variable that represents the operating state of the current limiting function using exclusive logic, for each of a first conditional branch that is satisfied when the current limiting function is operating and a second conditional branch that is satisfied when the current limiting function is not operating. The effective value analysis unit performs an effective value analysis of the power system based on a first differential equation that represents dynamic characteristics of the one or more GFM inverters, the third algebraic equation, and the fourth algebraic equation. Effect of the Invention

[0016] According to one aspect of the present disclosure, effective value analysis of a power system including a GFM inverter having a current limiting function can be performed more practically. [Brief description of the drawings]

[0017] [Figure 1] 1 is a diagram illustrating an example of an electrical configuration of an analysis device according to an embodiment of the present disclosure, together with a power system to be analyzed. [Diagram 2] 13 is a flowchart showing a calculation process of an effective value analysis. [Diagram 3] FIG. 1 is a diagram showing an electric power system that is a target for effective value analysis by an analysis device. [Figure 4] FIG. 4 is a diagram showing the results of an analysis performed by an effective value analysis of the output current and terminal voltage during a three-phase ground fault in the power system of FIG. 3 when the maximum current at which the current limiter of the GFM inverter operates is set to 1.2 pu. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a preferred embodiment of the present disclosure will be described with reference to the drawings. In the drawings, the dimensions and scale of each part may differ from the actual ones, and some parts may be shown diagrammatically to facilitate understanding. In addition, unless otherwise specified in the following description to the effect that the present disclosure is limited, the scope of the present disclosure is not limited to the embodiments described in the following description. The scope of the present disclosure includes the equivalent scope of the embodiments.

[0019] 1. Embodiment FIG. 1 is a diagram showing an example of the electrical configuration of an analysis device 1 according to this embodiment, together with a power system A to be analyzed. The analysis device 1 is a device that quickly performs an effective value analysis of a power system A that includes one or more GFM inverters A1. As described above, the GFM inverter A1 is a device that has a control function for independently establishing a voltage and maintaining stable operation.

[0020] Such an effective value analysis can be used to evaluate frequency fluctuations and monitor system stability when power system A becomes autonomous after a disaster occurs, etc. It can also be used to design system stability measures and system stabilization controls for power system A.

[0021] As shown in FIG. 1, the analysis device 1 of this embodiment includes a computer equipped with a processing device 10, a storage device 12, an input I / F device 14, and an output I / F device 16, and this computer may be a personal computer, a supercomputer, or the like. The processing device 10 includes at least one processor, such as a central processing unit (CPU). A part of the functions of the processing device 10 may be configured by a circuit such as a field programmable gate array (FPGA). The storage device 12 is a recording medium readable by the processing device 10. The storage device 12 includes, for example, a nonvolatile memory and a volatile memory. The nonvolatile memory is, for example, a read only memory (ROM), an erasable programmable read only memory (EPROM), or an electrically erasable programmable read only memory (EEPROM). The volatile memory is, for example, a random access memory (RAM). The input I / F device 14 is a device including an input interface circuit to which an input device is connected by wire or wirelessly, and receives input of data from the external device and outputs the received data to the processing device 10. The output I / F device 16 is a device including an output interface circuit to which an output device is connected by wire or wirelessly, and outputs various data to the output device under the control of the processing device 10. Typical examples of the input device include a keyboard, a recording medium reader, and another computer. Typical examples of the output device include a display, a printer, a recording medium recorder, and another computer.

[0022] The storage device 12 of the present embodiment stores a program PR for effective value analysis. The analysis device 1 functions as an effective value analysis unit 110, a reduction method application unit 112, and an equation decomposition unit 114 by the processing device 10 executing the program PR.

[0023] Each functional unit will be described in detail below. In the following description, it is assumed that the power system A includes i GFM inverters A1, where i=1, 2, 3, . . . , m, and m is a natural number.

[0024] The effective value analysis unit 110 is a functional unit that performs an effective value analysis of the power system A based on a first differential equation DE1, a first algebraic equation AE1, and a second algebraic equation AE2. The first differential equation DE1, the first algebraic equation AE1, and the second algebraic equation AE2 are equations derived from the effective value analysis method of the above-mentioned Non-Patent Document 3.

[0025] Specifically, the first differential equation DE1 expresses the dynamic characteristic f of the i-th GFM inverter A1 in the power system A. i is a differential equation expressed by the following equation (1A). In this formula (1A), "E i " indicates the internal state of the GFM inverter A1. In this embodiment, the internal state E i Assume the inverter internal voltage as E i ∈C 1 In addition, "C" represents the set of all complex numbers. In addition, in formula (1A), "V i (t)" indicates the terminal voltage of the GFM inverter A1, and "I i (t)" indicates the output current of the GFM inverter A1.

[0026]

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[0027] The first algebraic equation AE1 is an algebraic equation that represents the internal state of the GFM inverter A1 for each of the first condition branch that is true when the current limiting function is operating and the second condition branch that is true when the current limiting function is not operating, and includes the following equations (1B), (1C), and (1D).

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[0031] In the formulas (1B) and (1D), the symbol " - " with "I i (t) is the output current when the current is limited in the GFM inverter A1. i " is a constant representing the coupling impedance of the GFM inverter A1, and Z i ∈C 1 It is.

[0032] The second algebraic equation AE2 is an algebraic equation that represents the relationship between the power flow and voltage in the network of the power system A, and is expressed by the following equation (1E): In this equation (1E), w(t) is a variable other than the GFM inverter A1, and includes, for example, a variable related to the load bus.

[0033]

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[0034] In the above equations, the output current value I during current limiting and E(0) are set appropriately.

[0035] Here, when the if-then rule of the first condition branch in formula (1B) is satisfied, that is, when the current is not limited, E i ’ By eliminating (t), we obtain the following equation (2).

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[0037] In this formula (2), I i (t), and V i(t) is found by solving the algebraic equations (1C), (1D), and (1E).

[0038] On the other hand, if the if-then rule of the second conditional branch in formula (1B) is satisfied, that is, if the current limiting operation is performed, the following formula (3) is determined regardless of formula (1E), and V i (t) is found by solving equation (1E).

[0039]

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[0040] However, the "I i "(t)" is also a state variable of equation (1E). That is, when the effective value analysis unit 110 performs an effective value analysis of the power system A by the conventional method, it is necessary to perform a calculation for simultaneously solving equation (1B) indicating the first conditional branch and the second conditional branch included in the first algebraic equation AE1, equation (1C), equation (1D) included in the first algebraic equation AE1, and equation (1E) included in the second algebraic equation AE2. In general, a calculation using a method for solving a combinatorial problem is required to solve an algebraic equation including the first conditional branch and the second conditional branch, and the calculation requires a large amount of calculation and takes time to solve. In addition, the effective value analysis unit 110 needs to solve a nonlinear equation even when trying one of a plurality of possible combinations, and needs to perform a convergence calculation such as the Newton-Raphson method, for example.

[0041] Therefore, the analysis device 1 of this embodiment calculates such a solution by a stepwise and explicit solution scheme, and further reduces the amount of calculations significantly by introducing a system contraction method for the power system A. For these calculations, the analysis device 1 includes a contraction method application unit 112 and an equation decomposition unit 114.

[0042] More specifically, the reduction method application unit 112 is a functional unit that specifies a third algebraic equation AE3 obtained by applying a system reduction method to the above-mentioned second algebraic equation AE2. For example, the system reduction method shown in Non-Patent Document 4 is used as the system reduction method. Non-Patent Document 4 is "PW Sauer, et al., "Power System Dynamics and Stability 2nd Edition", Wiley IEEE Press, 2018".

[0043] The system reduction method is described in detail. Generally, loads are divided into three types: constant impedance, constant current, and constant power. When a load has a constant current or constant power characteristic, the nodal equations of the system calculation become nonlinear. Therefore, in system calculations, it is often assumed that all loads in the power system A have a constant impedance characteristic. Under this assumption, the load admittance matrix Y L It is now possible to incorporate this as part of the system admittance, and the internal voltage E of the GFM inverter A1, the terminal voltage V, and the voltage V of the load node L The relation between Y and the output current I of the GFM inverter A1 is expressed by the following equation (4). G is the coupling admittance of the GFM inverter A1.

[0044]

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[0045] Then, by solving equation (4), the following equations (5) and (6) are obtained.

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[0048] From these equations (5) and (6), the terminal voltage V and the voltage V at the load node are LBy eliminating, the following equations (7A) and (7B) are obtained.

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[0051] Then, the contraction method application unit 112 specifies a third algebraic equation AE3 obtained by applying the contraction method shown in equation (7A) and equation (7B) to the second algebraic equation AE2. In this embodiment, the third algebraic equation AE3 is shown by the following equation (8). In equation (8), Y red is the contracted admittance, which corresponds to the determinant in parentheses on the right-hand side of equation (7A).

[0052]

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[0053] As shown in equation (8), the third algebraic equation AE3 is linearized like the second algebraic equation AE2, and the matrix size is reduced to only the GFM inverter A1, making the calculation easier.

[0054] The equation decomposition unit 114 specifies a fourth algebraic equation AE4 expressing the first algebraic equation AE1 in a decomposed form by using a first variable that expresses the operating state of the current limiting function in the GFM inverter A1 by exclusive logic. Specifically, the first variable is shown in the following equation (9), and the exclusive logic of the first variable is shown in the following equation (10). Moreover, the fourth algebraic equation AE4 is specified by the following equations (11A) to (11F). In the following equations, "diag(matrix A)" indicates the diagonal matrix of matrix A.

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[0063] Then, the effective value analysis unit 110 performs an effective value analysis of the power system A based on the above-mentioned first differential equation DE1, the third algebraic equation AE3 identified by the reduction method application unit 112, and the fourth algebraic equation AE4 identified by the equation decomposition unit 114.

[0064] In the analysis device 1 of this embodiment, various parameter values ​​required for the effective value analysis are input from the input I / F device 14, and the results of the effective value analysis are output from the output I / F device 16.

[0065] FIG. 2 is a flowchart showing the calculation process of the effective value analysis by the effective value analysis unit 110. As shown in the figure, for a certain time t, the effective value analysis unit 110 solves the above formula (1A), which is the first differential equation DE1, the above formula (8), which is the third algebraic equation AE3, and the above formula (11A), which is part of the fourth algebraic equation AE4, to determine the output current I(t), internal voltage E(t), and terminal voltage V(t) when the GFM inverter A1 is not performing current limiting (step Sa1).

[0066] Next, the effective value analysis unit 110 determines the value of the first variable by determining whether the first conditional branch and the second conditional branch in equations (9) and (10) are true or false based on the result of the output current I(t) obtained in step Sa1 (step Sa2).

[0067] If the result of the determination in step Sa2 is that the first conditional branch of equations (9) and (10) is satisfied in all GFM inverters A1 in power system A, that is, if the current limiting function of all GFM inverters A1 is not operating (step Sa3: Yes), the value of equation (9) indicating the first variable in step Sa2 becomes "1", and the value of equation (10) indicating the exclusive logic of equation (9) becomes "0". In this case, equations (11A) and (11B) become equivalent, and I(t) = I'(t), E(t) = E'(t), and V(t) = V'(t), so the effective value analysis unit 110 omits the calculation of equations (11B) to (11D), which are part of the fourth algebraic equation AE4, and ends the calculation process.

[0068] On the other hand, if the result of the determination in step Sa2 is that the second conditional branch of equations (9) and (10) is satisfied in one or more GFM inverters A1 in the power system A, that is, if the current limiting function is operating in one or more GFM inverters A1 (step Sa3: No), equation (11B) becomes the following equation (12). Therefore, the effective value analysis unit 110 calculates the internal voltage E'(t), output current I'(t), and terminal voltage V'(t) when the current limiting function is operating based on equation (12) and each of equations (11C) to (11E) (step Sa4).

[0069]

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[0070] In the calculation of step Sa4, the internal voltage E'(t) when the current limiting function is operating is calculated step by step from equation (11D). Among equations (11A) to (11E), the only simultaneous equation is equation (11B), which is linear. Therefore, E'(t), I'(t), and V'(t) when the current is limited for a certain time t can be calculated quickly, and a sufficiently practical effective value analysis can be realized. By using the effective value analysis of this embodiment for the operation of the power system A equipped with the GFM inverter A1, the frequency and voltage fluctuations and stability occurring on a time scale of 1 second or less can be grasped.

[0071] Next, an example of the effective value analysis will be described.

[0072] FIG. 3 is a diagram showing power system A that is the subject of effective value analysis. As shown in the figure, the target power system A is a system including nine buses and three generators. In this analysis example, node 1 is a slack bus, node 2 is a synchronous generator SG, and node 3 is a GFM inverter A1. In this analysis example, the size of the original admittance matrix in the system calculation is 9 × 9, while the admittance contraction matrix Y red becomes 3 x 3.

[0073] FIG. 4 shows the results of the above-mentioned effective value analysis of the output current and terminal voltage during a three-phase ground fault in the power system A of FIG. 3 when the maximum current at which the current limiting function of the GFM inverter A1 operates is set to 1.2 pu. In the figure, the period during which the fault occurred is from 1.0 second to 1.08 seconds. During this period, the output current of the slack bus and the synchronous generator SG increases with a voltage drop, while the output current of the GFM inverter A1 is limited to 1.2 pu. Therefore, it can be seen that the operation of the current limiting function of the GFM inverter A1 in the power system A is appropriately analyzed in the above effective value analysis.

[0074] As described above, the analysis device 1 of the present embodiment includes an effective value analysis unit 110 that performs an effective value analysis of the power system A having one or more GFM inverters A1 with a current limiting function, a contraction method application unit 112 that specifies a third algebraic equation AE3 obtained by applying a system contraction method to a second algebraic equation AE2 that represents the relationship between the power flow and voltage of the network of the power system A, and an equation decomposition unit 114 that specifies a fourth algebraic equation AE4 that expresses the first algebraic equation AE1 that represents the internal state of the one or more GFM inverters in a form that is decomposed by using a first variable that represents the operating state of the current limiting function by exclusive logic, for each of a first conditional branch that is satisfied when the current limiting function is operating and a second conditional branch that is satisfied when the current limiting function is not operating. The effective value analysis unit 110 performs an effective value analysis of the power system A based on a first differential equation DE1 that represents the dynamic characteristics of the one or more GFM inverters A1, the third algebraic equation AE3, and the fourth algebraic equation AE4.

[0075] According to this configuration, the first algebraic equation AE1 representing the internal state of the GFM inverter A1 for each of the first condition branch and the second condition branch is expressed by the equation decomposition unit 114 as a fourth algebraic equation AE4 that does not include the first condition branch and the second condition branch. Therefore, the internal state of the GFM inverter A1 can be calculated stepwise and quickly without solving a combinatorial problem of an if-then rule consisting of the first condition branch and the second condition branch, and a sufficiently practical effective value analysis can be realized.

[0076] In the analysis device 1 of this embodiment, the power system A includes one or more synchronous generators SG and one or more GFM inverters A1 as power sources. According to the analysis device 1 of the present embodiment, even if the power system A has one or more synchronous generators SG as power sources in addition to one or more GFM inverters A1, it is possible to perform a sufficiently practical effective value analysis.

[0077] In the analysis device 1 of this embodiment, the third algebraic equation AE3 is calculated by assuming that all loads included in the power system A have constant impedance characteristics, and the internal voltage E, terminal voltage V, and load node voltage V of one or more GFM inverters A1 are expressed as L The relationship between the output current I of one or more GFM inverters A1 and the combined admittance Y G It can be calculated based on the relational expression expressed using

[0078] According to this configuration, the third algebraic equation AE3 is expressed as the linearized second algebraic equation AE2, and the matrix size is reduced to only the GFM inverter A1, making the calculation easier and faster.

[0079] 2. Variations The above-described embodiment can be modified, for example, as follows.

[0080] (Variation 1) In the embodiment exemplified above, analysis device 1 may store in advance in storage device 12 the third algebraic equation AE3 identified by reduction method application unit 112, the fourth algebraic equation AE4 identified by equation decomposition unit 114, and the above-mentioned first differential equation DE1 expressing the dynamic characteristics of one or more GFM inverters A1. Then, when performing the effective value analysis, analysis device 1 may cause the effective value analysis unit 110 to read out the third algebraic equation AE3 and the fourth algebraic equation AE4 from storage device 12 and perform the effective value analysis.

[0081] (Variation 2) The program PR that causes a computer to function as the analysis device 1 may be implemented by distributing it on an appropriate recording medium or through an electric communication line. [Explanation of symbols]

[0082] 1...analysis device, 2B...GFM inverter, 10...processing device, 12...memory device, 110...effective value analysis unit, 112...contraction method application unit, 114...equation decomposition unit, A...power system, A1...GFM inverter, AE1...first algebraic equation, AE2...second algebraic equation, AE3...third algebraic equation, AE4...fourth algebraic equation, DE1...first differential equation, PR...program, SG...synchronous generator.

Claims

1. a first differential equation describing the dynamic characteristics of one or more GFM inverters having current limiting capabilities; a first algebraic equation expressing an internal state of the one or more GFM inverters for each of a first condition branch that is satisfied when the current limiting function is operating and a second condition branch that is satisfied when the current limiting function is not operating; a second algebraic equation expressing power flow and voltage relationships in a power system network having the one or more GFM inverters; In the analysis method for performing an effective value analysis of the power system based on identifying a third algebraic equation obtained by applying a system reduction method to the second algebraic equation; identifying a fourth algebraic equation expressing the first algebraic equation in a decomposed form by using a first variable that expresses an operating state of the current limiting function by exclusive logic; performing an effective value analysis of the power system based on the first differential equation, the third algebraic equation, and the fourth algebraic equation; Analysis methods including:

2. The third algebraic equation is: By assuming that all loads included in the power system have constant impedance characteristics, the relationship between the internal voltage, terminal voltage, and voltage of the load node of the one or more GFM inverters and the output current of the one or more GFM inverters is obtained based on a relational expression expressed using a combined admittance of the one or more GFM inverters. The analysis method according to claim 1 .

3. The power system includes one or more synchronous generators and one or more GFM inverters as power sources. The analysis method according to claim 1 or 2.

4. an effective value analysis unit that performs an effective value analysis of a power system having one or more GFM inverters with a current limiting function; a reduction method application unit that identifies a third algebraic equation obtained by applying a system reduction method to a second algebraic equation that represents a relationship between a power flow and a voltage in the power system network; an equation decomposition unit that identifies a fourth algebraic equation that expresses a first algebraic equation that represents an internal state of the one or more GFM inverters in a decomposed form by using a first variable that represents an operating state of the current limiting function by exclusive logic, for each of a first conditional branch that is established when the current limiting function is operating and a second conditional branch that is established when the current limiting function is not operating; Equipped with The effective value analysis unit performing an effective value analysis of the power system based on a first differential equation representing dynamic characteristics of the one or more GFM inverters, the third algebraic equation, and the fourth algebraic equation; Analysis device.

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