Short circuit ratio calculation method considering contribution of short circuit current of grid-connected inverter

Abstract

This invention discloses a method for calculating the short-circuit ratio considering the short-circuit current contribution of grid-connected / grid-connected inverters, applicable to new energy grid-connected systems with a mix of grid-connected and grid-connected inverters. This method constructs an equivalent fault model of the grid-connected inverter under short-circuit fault conditions, and combines the Thevenin-Norton equivalent method to perform unified equivalent modeling of the power grid system, grid-connected inverter sites, and grid-connected inverter sites. A corrected short-circuit ratio considering the contribution of multi-source short-circuit currents is derived, and the system support strength of the new energy grid connection point is analyzed based on this corrected short-circuit ratio. This method can more accurately reflect the impact of different types of inverters on system strength in hybrid grid-connected / grid-connected systems, and is applicable to new energy grid connection assessment and related analysis scenarios.

Description

Technical Field

[0001] This invention relates to the field of new energy grid connection analysis and power system stability assessment technology, and in particular to a method for calculating the short-circuit ratio that takes into account the short-circuit current contribution of grid-connected inverters. Background Technology

[0002] As the global energy structure shifts towards a higher proportion of renewable energy, the installed capacity and grid connection rate of new energy power generation, represented by wind power and photovoltaics, continue to increase in the power system. The power system is gradually shifting from a traditional structure dominated by synchronous generators to an operating mode dominated by power electronic inverters. While promoting the clean and low-carbon development of the energy structure, this shift also poses new requirements and challenges to the safe and stable operation of the power system, especially in areas where new energy sources are concentrated, where the system voltage support capacity and stability margin issues are becoming increasingly prominent.

[0003] In the analysis and planning of renewable energy grid connection, the voltage support strength at the grid connection point is generally considered an important factor affecting the system's static voltage stability, small-disturbance stability, and renewable energy absorption capacity. The short-circuit ratio (SCR), as a commonly used indicator reflecting the system strength at the grid connection point, is widely used in renewable energy grid connection assessment, power grid planning and design, and operation analysis. Existing short-circuit ratios and their extended indicators are mostly based on the relationship between the power grid's equivalent short-circuit capacity and the installed capacity of renewable energy, and can reflect the voltage support level at the grid connection point to a certain extent.

[0004] However, existing system strength assessment methods typically assume that renewable energy power plants use grid-connected control during modeling, treating renewable energy inverters as equivalent controlled current sources. Their short-circuit current output capability is constrained by control strategies and current-limiting mechanisms. As the requirements for active support capabilities from renewable energy sources increase, more renewable energy power plants are adopting grid-connected control. Grid-connected inverters exhibit voltage source characteristics similar to synchronous generators during faults, and their short-circuit current contribution capability differs significantly from that of grid-connected inverters. In systems with a mix of grid-connected and grid-connected inverters, continuing to use short-circuit ratio calculation methods that only consider the characteristics of grid-connected inverters can easily lead to deviations in the assessment results of the system's equivalent short-circuit capacity and grid connection point support strength, thus affecting the accuracy of system planning and operational decisions. Summary of the Invention

[0005] To address the problems of existing technologies, embodiments of the present invention provide a method for calculating the short-circuit ratio that takes into account the contribution of short-circuit current in a grid-connected inverter. The technical solution is as follows: On the one hand, a method for calculating the short-circuit ratio that takes into account the short-circuit current contribution of grid-connected / grid-connected inverters is provided, applicable to new energy grid-connected systems with a mix of grid-connected and grid-connected inverters, including the following steps: S1. Construct the fault equivalent model of the grid-type inverter under short-circuit fault conditions, and determine the equivalent impedance of the grid-type inverter based on the grid-type control structure. S2. Based on the equivalent model of the grid-connected inverter, construct an equivalent model of the grid-connected / grid-connected hybrid system, which includes the grid system, the grid-connected inverter station, and the grid-connected inverter station. S3. Based on the Thevenin-Norton equivalent method, the hybrid system of the wire / structure network is modeled equivalently, and the corrected short-circuit ratio considering the contribution of multi-source short-circuit current is derived. S4. Based on the modified short-circuit ratio, analyze the system support strength of the new energy grid connection point.

[0006] Furthermore, in step S1, the grid-type inverter adopts a grid-type control mode, establishes the phase angle and amplitude of the virtual internal potential through power synchronization control, and combines a virtual admittance current limiting structure to make the grid-type inverter exhibit the characteristics of a controlled voltage source under short-circuit fault conditions.

[0007] Furthermore, the equivalent impedance of the grid-type inverter is composed of the equivalent impedance component formed by reactive voltage droop control and the equivalent impedance component corresponding to the virtual admittance current limiting structure. The reactive voltage droop control is used to describe the voltage-reactive power relationship, and the virtual admittance current limiting structure is used to limit the short-circuit current amplitude.

[0008] Furthermore, in step S2, the equivalent model of the grid-connected / connected hybrid system is constructed based on the quasi-steady-state condition of short-circuit fault, wherein the grid-connected inverter station and the grid system are equivalent to the Thevenin model, and the grid-connected inverter station is equivalent to the Norton model of the parallel output impedance of the controlled current source.

[0009] Furthermore, in step S3, the equivalent modeling process includes: disconnecting the new energy power station to be evaluated from the system, while maintaining the original physical connection structure of the remaining online power sources, to form an equivalent network for calculating the corrected short-circuit ratio.

[0010] Furthermore, in the equivalent network, the Thevenin model of the power grid system and the grid-connected inverter station is converted into the Norton model and merged with the Norton model of the grid-connected inverter station at the grid connection point to obtain the equivalent admittance and equivalent current corresponding to the grid connection point, and then the equivalent impedance and equivalent voltage are calculated in reverse.

[0011] Furthermore, the modified short-circuit ratio is used to characterize the system support strength perceived by the new energy grid connection point under the condition of taking into account the short-circuit current contribution of all online grid-connected and grid-connected inverters.

[0012] Furthermore, in step S4, the variation law of the modified short-circuit ratio is analyzed by changing the access ratio of the grid-type inverter in the system, the grid-type control parameters, and the grid-connected line impedance.

[0013] On the other hand, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, is used to implement the short-circuit ratio calculation method.

[0014] On the other hand, an electronic device is provided, including a processor and a memory, wherein the memory stores a computer program, which, when executed by the processor, is used to implement the short-circuit ratio calculation method.

[0015] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: This invention provides a short-circuit ratio calculation method that takes into account the short-circuit current contribution of grid-connected and grid-connected inverters. By simultaneously considering the differentiated short-circuit current contribution characteristics of grid-connected and grid-connected inverters under short-circuit fault conditions during the short-circuit ratio calculation process, it achieves unified modeling and evaluation of the grid connection support strength of hybrid renewable energy systems. Compared with system strength evaluation methods based solely on the assumption of grid-connected inverters, this method can more realistically reflect the actual impact of various renewable energy power plants on the equivalent short-circuit capacity of the system in hybrid systems.

[0016] Furthermore, this invention constructs a fault equivalent model for grid-connected inverters and combines it with the Thevenin-Norton equivalent method to perform unified equivalent modeling of the power grid system, grid-connected inverter sites, and interconnected inverter sites. This allows for the derivation of the corrected short-circuit ratio, taking into account the contribution of multi-source short-circuit currents, within the same computational framework. This calculation process clearly distinguishes the equivalent characteristics of inverters with different control types, making the physical meaning of the short-circuit ratio index clearer in interconnected / grid-connected hybrid systems. It is applicable to renewable energy grid connection analysis scenarios involving multiple sites and multiple access methods.

[0017] Furthermore, based on the modified short-circuit ratio, this invention analyzes the impact of factors such as the access ratio of grid-connected inverters, grid-connected control parameters, and grid-connected line impedance on the system support strength. The consistency and reproducibility of the analysis results are verified through simulation, thus providing an implementable analysis method for new energy grid connection planning, system operation evaluation, and related parameter configuration. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating the method for calculating the short-circuit ratio considering the contribution of short-circuit current from the grid-connected inverter, as described in an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the grid-type inverter control structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the voltage source characteristics of a grid-type inverter according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the equivalent circuit partitioning of a grid-type converter according to an embodiment of the present invention; Figure 5 This is the grid connection system of the entire grid transformation of station B in this embodiment of the invention; Wherein, (a) is the system structure; (b) is the Norton equivalent circuit; and (c) is the Thevenin equivalent circuit. Figure 6 This is a schematic diagram illustrating the effect of different network configuration ratios and control parameters on the short-circuit ratio in an embodiment of the present invention. Among them, (a) represents the impact of reactive power droop factor and network ratio on short-circuit ratio; (b) represents the impact of virtual impedance and network ratio on short-circuit ratio. Figure 7 This is a schematic diagram of the short-circuit current at node 1 of the power station under different network configuration ratios according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the short-circuit current at node 1 of the power station under different reactive power droop coefficients according to an embodiment of the present invention. Figure 9 This is a schematic diagram of the short-circuit current at node 1 of the power station under different virtual impedances according to an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0022] Example 1 This embodiment provides a method for calculating the short-circuit ratio that takes into account the contribution of short-circuit current in a grid-connected inverter, such as... Figure 1 As shown, this method is applicable to new energy grid-connected systems where grid-connected inverters and grid-mounted inverters are mixed, and includes the following steps: Construct a fault equivalent model for a grid-connected inverter and determine the equivalent impedance corresponding to grid-connected control; Based on the Thevenin-Norton equivalent theorem, an equivalent model of the root / structured network hybrid system is performed, and the corrected short-circuit ratio considering the contribution of multi-source short-circuit current is derived. Based on the modified short-circuit ratio, the influence of the grid control parameters and the grid line impedance on the system support strength is analyzed.

[0023] To facilitate the explanation of the technical implementation process of the above method, the following will be combined with... Figure 1 The method flow shown further explains the specific implementation of each step in this embodiment. It should be noted that... Figure 1 The steps shown are not strictly defined in terms of execution order. Without affecting the technical effect of the invention, the execution order of each step can be appropriately adjusted according to the actual application scenario. The following will elaborate on the fault equivalent modeling of the grid-connected inverter, the equivalent modeling of the hybrid system (with / with grid connection), and the calculation process of the corrected short-circuit ratio, following the method flow.

[0024] In this embodiment, a short-circuit ratio calculation method that takes into account the short-circuit current contribution of grid-connected and grid-connected inverters is provided. This method calculates the short-circuit ratio by considering the short-circuit current contribution of grid-connected and grid-connected inverters, thereby achieving an accurate assessment of the strength of the grid-connected and grid-connected hybrid system.

[0025] The network control structure used in this embodiment is as follows: Figure 2 As shown, the power synchronization control loop in the inverter uses VSG control to establish the virtual internal potential phase angle θ and the virtual internal potential amplitude E, where P ref P e These are the active power reference value and the active power output at the grid connection point, respectively; Q ref Q e These represent the reactive power reference value and the reactive power output at the grid connection point, respectively; D and J represent the damping coefficient and moment of inertia, respectively; ω and ω0 represent the system angular velocity and synchronous angular velocity, respectively; U * k q These represent the voltage reference value and the reactive power droop factor, respectively. To maintain the controlled voltage source characteristics of the grid-connected inverter and to consider the limited overcurrent capacity during grid-connected inverter faults, this embodiment uses virtual admittance control to achieve current limiting, where E... dq u pdq These are the virtual internal potential and the dq-axis components of the grid connection point voltage, respectively. v L and Lv represent the virtual resistance and virtual inductance, respectively. In the current loop, i... sdq i*sdq represents the actual and reference values ​​of the inverter output current, and u dqref u*abc are the voltage reference values ​​for the inverter's dq axis and abc axis, respectively.

[0026]

Step S1

[0027] From the perspective of grid-connected characteristics, current-source grid-connected control is currently the mainstream control method, aiming to control the output current to precisely regulate the required grid-connected power. In the grid, a grid-connected inverter is equivalent to a controlled current source in parallel impedance. In contrast, grid-based control directly controls the output voltage, establishing control commands based on amplitude and phase angle references. Depending on the current-limiting type, a grid-based inverter can be equivalent to a controlled current source in parallel impedance or a controlled voltage source in series impedance. In this embodiment, a virtual admittance current-limiting method is used; therefore, the grid-based inverter is equivalent to a controlled voltage source in series impedance in the grid, such as... Figure 3 As shown, where I G For the output current of the grid-connected inverter, Z G Z g These are the equivalent impedance of the grid-connected inverter connected in series and the grid impedance, respectively.

[0028] Based on the virtual admittance control, the inner current loop, and the inverter port short-circuit equations, the virtual admittance loop decoupling control block diagram is as follows: Figure 4 As shown.

[0029] Considering the current tracking speed, the cutoff angular frequency of the inner current loop is usually set to 10 times the synchronous angular frequency. The transient process duration of the inner current loop is much shorter than that of the virtual admittance loop. Therefore, when considering the response of the virtual admittance loop, the current reference value is equal to the actual value, which can be equivalent to a current source.

[0030] Observing the structure of the virtual admittance loop, it is clear that it is completely consistent with the structure of the circuit equation. Therefore, analogous to the input-output relationship of the physical circuit equation, the input and output of the virtual admittance control loop are the voltage-current relationship before and after the virtual admittance. Given a reference voltage, it outputs a reference current. Therefore, considering the response of the virtual admittance loop, its output reference current is equal to the actual current across the physical filter impedance. Thus, it is assumed that the control passes through the filter impedance in the form of current, and the filter impedance is not included in the equivalent impedance. At this time, the equivalent impedance Z between the virtual internal potential and the grid connection point is... G =Z v Numerically, this is represented as the reciprocal of the virtual admittance.

[0031] In such Figure 3 In the equivalent schematic diagram of the grid-type voltage source, the input voltage of the virtual admittance is the virtual internal potential after the reactive voltage loop. Since the reactive voltage loop essentially defines the droop relationship of UQ, and the impedance describes the droop relationship of UI, the reactive droop factor k is used. qThe exhibited equivalent impedance X q The derivation of the relation is briefly as follows: (1) (2) Therefore, when a grid-type inverter is equivalent to a voltage source with series impedance, the voltage reference value U in the reactive voltage loop is... * Defined as the voltage source amplitude, the equivalent impedance will encompass the reactive droop coefficient equivalent impedance in VSG control and the reciprocal of the virtual admittance in the virtual admittance current limiting loop. The equivalent impedance of the structured grid inverter is shown in equation (3).

[0032] (3)

Step S2

[0033] 1) Quasi-steady-state equivalent models for each source The system baseline capacity is S B All parameters have been reduced to per-unit values ​​of a uniform voltage level. During the fault quasi-steady-state phase, the following applies: (1) Power grid system: equivalent to Thevenin circuit, i.e. ideal voltage source Series impedance , where α is the initial phase angle of the power grid.

[0034] (2) Grid-type inverter station: equivalent to Thevenin circuit, i.e., controlled voltage source Its total output impedance is connected in series The preceding text refers to the voltage reference value U in the reactive voltage loop. * Defined as the voltage source amplitude, the output impedance at this point encompasses the reactive droop equivalent impedance, and therefore can be equivalent to an ideal voltage source. Its equivalent impedance in series .

[0035] (3) Grid-connected inverter power stations: New energy power stations using grid-connected control exhibit current source characteristics, and their equivalent impedance can be considered as infinite. Therefore, after filtering the impedance, they are equivalent to a controlled current source. Parallel its output impedance , here This refers to the impedance of the station transformer and the line impedance.

[0036]

Step S3

[0037] 3) Formula for calculating the short-circuit ratio of a hybrid grid system The entire grid structure of substation B in the pure grid-connected inverter power supply system will be modified as follows: Figure 5 (a) The grid-connected system structure, in Section 1), the grid-connected power station is equivalent to an ideal voltage source in series with equivalent impedance using Thevenin's method, and is then equivalent to the grid system using Norton's method. The corresponding system equivalent circuit is as follows: Figure 5 As shown in (b).

[0038] in To construct the Norton equivalent current of the power grid station, To match the output impedance of the network station Level 1 transformer With line impedance The sum of these yields Norton's equivalent admittance: (9) Applying the Thevenin equivalent to the parallel Norton current and Norton impedance yields the following: Figure 5 (c) shows the Thevenin equivalent model, where the equivalent impedance for: (10) The equivalent voltage source is: (11) The SCR'1 of node 1 at this time is calculated according to equation (8), as shown in equation (12): (12) The system strength was analyzed based on equation (12). Referring to the national standard for virtual synchronous machine control, the reactive voltage droop coefficient should be within the range of 0.03-0.08. For the scenario where all substation B is converted to a grid, the following parameters are set: =0.03+j0.3, other parameters remain consistent with those in the appendix, and the reactive voltage droop coefficient k in SCR'1 and VSG control considering different network ratios is plotted according to equations (3) and (12). q The influence curves between them, such as Figure 6 As shown in (a). Let k be... q =0.04, other parameters remain consistent with those in the appendix, and the virtual impedance Z in SCR'1 and VSG control considering different network proportions is plotted according to equations (3) and (12). v The influence curves between them, such as Figure 6 As shown in (b).

[0039] Depend on Figure 6 (a) It can be seen that when the total capacity of power stations A and B remains constant, SCR'1 decreases with the increase of the reactive power droop factor, and the change increases with the increase of the grid ratio. The increase of the reactive power droop factor reduces the contribution of the grid to the short-circuit current, thus reducing the system strength. Figure 6 (b) It can be seen that when the total capacity of station A and station B remains unchanged, SCR'1 decreases as the virtual impedance increases, and the change increases as the proportion of the network increases. The increase in virtual impedance reduces the contribution of the network to the short-circuit current, thus reducing the system strength.

[0040] The resulting modified short-circuit ratio is used to characterize the system support strength perceived at the grid connection point, taking into account the short-circuit current contribution of all online / grid-connected inverters.

[0041]

Step S4

[0042] To verify the effectiveness of the short-circuit ratio calculation method proposed in this invention, which takes into account the contribution of the short-circuit current of the grid inverter, a system was built in Matlab / Simulink. Figure 5(a) shows the electromagnetic transient simulation model of the hybrid system with grid, and the relevant parameters are shown in Tables 1 and 2.

[0043] Table 1 Basic parameters of the grid connection simulation model Table 2 Basic parameters of the grid-connected simulation model (1) The impact of network ratio on system short-circuit current In a hybrid grid-connected system, a three-phase symmetrical short-circuit fault occurs at the grid connection point of substation A at t=2s. If substation B is completely converted to a grid-connected scenario, and the total capacity of substations A and B remains unchanged, with grid-connected capacity ratios of 0%, 20%, 50%, and 80% respectively, the short-circuit current at node 1 of substation A is as follows: Figure 7 As shown Depend on Figure 7 It can be seen that as the proportion of the network increases, the short-circuit current at port 1 of the substation A increases, the contribution of the network short-circuit current increases, the system strength improves, and the change in short-circuit current in some renovation scenarios is smaller than that in all renovation scenarios. Figure 6 The curves change in the same direction.

[0044] (2) The effect of reactive power droop factor on system short-circuit current In a hybrid grid-connected system, a three-phase symmetrical short-circuit fault occurs at the grid connection point of station A at t=2s. Station B is then completely converted to a grid-connected scenario, with the total capacity of stations A and B remaining unchanged, and the grid-connected capacity accounting for 50%. =0.03+j0.3, and the reactive power droop factors are 0.035, 0.055, and 0.075 respectively. The short-circuit current at node 1 of station A is as follows: Figure 8 As shown Depend on Figure 8 It can be seen that as the reactive power droop factor increases, the short-circuit current at port 1 of the power station decreases, the contribution of the grid short-circuit current decreases, the system strength decreases, and the change in short-circuit current in some renovation scenarios is smaller than that in all renovation scenarios. Figure 6 The curves change in a consistent manner.

[0045] (3) The effect of virtual impedance on the system short-circuit current In a hybrid grid-connected system, a three-phase symmetrical short-circuit fault occurs at the grid connection point of station A at t=2s. Station B is then completely converted to a grid-connected scenario, with the total capacity of stations A and B remaining unchanged, and the grid-connected capacity accounting for 50%. q =0.04, and the virtual impedances are 0.1, 0.2, and 0.3 respectively. The short-circuit current at node 1 of station A is as follows: Figure 9 As shown.

[0046] Depend on Figure 9It can be seen that as the virtual impedance increases, the short-circuit current at port 1 of the station A decreases, the contribution of the network short-circuit current decreases, the system strength decreases, and the change in short-circuit current in some modification scenarios is smaller than that in all modification scenarios. Figure 6 The curves change in a consistent manner.

[0047] In summary, this embodiment constructs a fault equivalent model for grid-connected inverters and, combined with the Thevenin-Norton equivalent method, uniformly models the short-circuit current contribution of grid-connected and grid-connected inverters under short-circuit fault conditions, thereby deriving a corrected short-circuit ratio that takes into account the contribution of multi-source short-circuit current. This method can accurately reflect the system support strength perceived by the grid connection point in new energy grid-connected systems with mixed grid-connected and grid-connected inverters. Simulation results verify the applicability and consistency of the method under different grid ratios and control parameters. Therefore, the method described in this embodiment provides an effective technical implementation for system strength analysis and related operational evaluation of mixed grid-connected and grid-connected systems.

[0048] In other embodiments, a computer-readable storage medium is also provided, wherein a computer program is stored therein. When called and executed by a processor, the computer program is used to implement the short-circuit ratio calculation method considering the contribution of short-circuit current from the grid-connected inverter described in the foregoing embodiments.

[0049] Specifically, during execution, the computer program sequentially performs the following operations: constructs an equivalent fault model of the grid-connected inverter under short-circuit fault conditions, and determines the equivalent impedance of the grid-connected inverter based on the grid-connected control structure; on this basis, it constructs an equivalent model of the grid system, the grid-connected inverter power station, and the grid-connected inverter power station; it performs equivalent modeling of the system based on the Thevenin-Norton equivalent method, derives the corrected short-circuit ratio considering the contribution of multi-source short-circuit current; and analyzes the system support strength of the renewable energy grid connection point based on the corrected short-circuit ratio.

[0050] The computer-readable storage medium may be any one of magnetic storage medium, optical storage medium or semiconductor storage medium, and its specific form is not limited.

[0051] In other embodiments, an electronic device is also provided, the electronic device including a processor and a memory, the memory storing a computer program, which, when executed by the processor, is used to implement the short-circuit ratio calculation method considering the contribution of short-circuit current of the grid-connected inverter described in the foregoing embodiments.

[0052] The processor is used to call and execute computer programs stored in the memory to complete operational steps such as equivalent modeling of grid-connected inverter faults, equivalent modeling of hybrid systems connected to / from the grid, calculation of the corrected short-circuit ratio, and system support strength analysis. The memory is used to store program instructions and related data required to implement the above methods.

[0053] In this embodiment, the electronic device may be a server, an industrial control computer, or other computing device with data processing capabilities, and its specific form is not limited.

[0054] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calculating the short-circuit ratio considering the contribution of short-circuit current in a grid-connected inverter, characterized in that, For new energy grid-connected systems that combine grid-connected and grid-mounted inverters, the following steps are included: S1. Construct the fault equivalent model of the grid-type inverter under short-circuit fault conditions, and determine the equivalent impedance of the grid-type inverter based on the grid-type control structure. S2. Based on the equivalent model of the grid-connected inverter, construct an equivalent model of the grid-connected / grid-connected hybrid system, which includes the grid system, the grid-connected inverter station, and the grid-connected inverter station. S3. Based on the Thevenin-Norton equivalent method, the hybrid system of the wire / structure network is modeled equivalently, and the corrected short-circuit ratio considering the contribution of multi-source short-circuit current is derived. S4. Based on the modified short-circuit ratio, analyze the system support strength of the new energy grid connection point.

2. The short-circuit ratio calculation method according to claim 1, characterized in that: In step S1, the grid-type inverter adopts a grid-type control mode, which establishes the phase angle and amplitude of the virtual internal potential through power synchronization control, and combines the virtual admittance current limiting structure to make the grid-type inverter exhibit the characteristics of a controlled voltage source under short-circuit fault conditions.

3. The short-circuit ratio calculation method according to claim 2, characterized in that: The equivalent impedance of the grid-type inverter is composed of the equivalent impedance component formed by reactive voltage droop control and the equivalent impedance component corresponding to the virtual admittance current limiting structure. The reactive voltage droop control is used to describe the voltage-reactive power relationship, and the virtual admittance current limiting structure is used to limit the short-circuit current amplitude.

4. The short-circuit ratio calculation method according to claim 1, characterized in that: In step S2, the equivalent model of the grid-connected / grid-connected hybrid system is constructed based on the quasi-steady-state condition of short-circuit fault. The grid-connected inverter station and the grid system are equivalent to the Thevenin model, and the grid-connected inverter station is equivalent to the Norton model of the parallel output impedance of the controlled current source.

5. The short-circuit ratio calculation method according to claim 1, characterized in that: In step S3, the equivalent modeling process includes: disconnecting the new energy power station to be evaluated from the system, while maintaining the original physical connection structure of the remaining online power sources, to form an equivalent network for calculating the corrected short-circuit ratio.

6. The short-circuit ratio calculation method according to claim 5, characterized in that: In the equivalent network, the Thevenin model of the power grid system and the grid-connected inverter station is converted into the Norton model and merged with the Norton model of the grid-connected inverter station at the grid connection point to obtain the equivalent admittance and equivalent current corresponding to the grid connection point, and then the equivalent impedance and equivalent voltage are calculated.

7. The short-circuit ratio calculation method according to claim 1, characterized in that: The modified short-circuit ratio is used to characterize the system support strength perceived by the new energy grid connection point, taking into account the short-circuit current contribution of all online grid-connected and grid-connected inverters.

8. The short-circuit ratio calculation method according to claim 1, characterized in that: In step S4, the variation law of the modified short-circuit ratio is analyzed by changing the access ratio of the grid-type inverter in the system, the grid-type control parameters, and the grid-connected line impedance.

9. A computer-readable storage medium having a computer program stored thereon, the computer program being executed by a processor to implement the short-circuit ratio calculation method as described in any one of claims 1 to 8.

10. An electronic device comprising a processor and a memory, the memory storing a computer program, which, when executed by the processor, implements the short-circuit ratio calculation method as described in any one of claims 1 to 8.

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