Network construction type control method and device giving consideration to voltage supporting capability and current limiting requirement

Abstract

The invention belongs to the technical field of power grid control, and provides a network construction type control method and device giving consideration to voltage supporting capacity and current limiting requirements. The network construction type control method considering the voltage supporting capability and the current limiting requirement comprises the following steps: determining equivalent impedance of each control link of the network construction type converter system according to a topological structure of the network construction type converter system; wherein the network construction type converter system is controlled by a virtual synchronous machine; according to the equivalent impedance of each control link, determining a fault current of the network-forming converter system; and determining the virtual impedance of the network construction type converter system according to the magnitude relationship between the fault current and the preset maximum short-circuit current and the current internal potential of the network construction type converter system, and inputting the virtual impedance to the virtual synchronous machine. According to the method provided by the invention, the voltage supporting capability and the current limiting requirement are considered.

Description

Technical Field

[0001] The present application belongs to the field of power grid control technology, and in particular to the technical field related to grid-forming converters, and in particular to a grid-forming control method and device that takes into account both voltage support capability and current limiting requirements. Background Art

[0002] In the prior art, the method for steady-state voltage support for a single-machine system is generally a reactive control strategy, which includes: blocking the reactive regulator during a fault to improve reactive output capacity; improving reactive voltage control based on the third-order model of the synchronous machine to improve the reactive voltage support capacity of the unit; improving the power loop of the VSG control, setting the voltage reference value according to the power angle, and improving the reactive power characteristics during the fault; adopting reactive priority control to provide voltage support for the system by injecting dynamic reactive current. The new power system based on power electronic converters has high flexibility and strong controllability, and voltage support can be achieved by controlling the reactive power output of the converter. However, the research on the voltage support of virtual synchronous generators (VSG) focuses on the improvement of control strategies, and the prior art does not consider the system short-circuit current limitation, that is, the optimal voltage support effect cannot be achieved during system faults. Summary of the invention

[0003] The grid-type control method and device provided by the present invention that take into account both voltage support capability and current limiting requirements are intended to solve the technical pain point of the poor voltage support capability of the grid-type converter system during a fault in the prior art.

[0004] In order to solve the technical problems in the background technology of this application, the present invention provides the following technical solutions:

[0005] In a first aspect, the present invention provides a grid-type control method that takes into account both voltage support capability and current limiting requirements, the method comprising:

[0006] Determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine;

[0007] Determining the fault current of the grid-type converter system according to the equivalent impedance of each control link;

[0008] The virtual impedance of the grid-type converter system is determined according to the magnitude relationship between the fault current and the preset maximum short-circuit current and the current internal potential of the grid-type converter system, and the virtual impedance is input into the virtual synchronous machine.

[0009] In some embodiments of the present application, the control link includes: a reactive voltage control link and a voltage and current dual inner loop control link;

[0010] Determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system includes:

[0011] Determining the equivalent impedance of the reactive voltage control link according to the power transmission model of the virtual synchronous machine;

[0012] The equivalent impedance of the voltage-current dual inner loop control link is determined according to the control structure and circuit equation of the voltage-current dual inner loop control link.

[0013] In some embodiments of the present application, determining the fault current of the grid-connected converter system according to the equivalent impedance of each control link includes:

[0014] Determining the internal potential of the grid-type converter system according to the equivalent impedance of each control link;

[0015] Determining the terminal voltage of the machine when the grid voltage drops according to the internal potential;

[0016] The fault current is determined according to the machine-end voltage and the impedance between the machine-end bus and the fault point.

[0017] In some embodiments of the present application, determining the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and the preset maximum short-circuit current and the current internal potential of the grid-type converter system includes:

[0018] When the fault current is not greater than the maximum short-circuit current, setting the virtual impedance to an initial setting value;

[0019] Otherwise, the virtual impedance is determined according to the current internal potential and the maximum short-circuit current.

[0020] In some embodiments of the present application, determining the virtual impedance according to the current internal potential and the maximum short-circuit current includes:

[0021] Determining a current voltage compensation coefficient of the grid-type converter system according to the current internal potential;

[0022] The virtual impedance is determined according to the current internal potential and the current voltage compensation coefficient.

[0023] In a second aspect, the present invention provides a grid-type control device for taking into account both voltage support capability and current limiting requirements, the device comprising:

[0024] An equivalent impedance determination module, used to determine the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine;

[0025] A fault current determination module, used to determine the fault current of the grid-type converter system according to the equivalent impedance of each control link;

[0026] A virtual impedance determination module is used to determine the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and input the virtual impedance to the virtual synchronous machine.

[0027] In some embodiments of the present application, the control link includes: a reactive voltage control link and a voltage and current dual inner loop control link;

[0028] The equivalent impedance determination module comprises:

[0029] An equivalent impedance determining first unit is used to determine the equivalent impedance of the reactive voltage control link according to the power transmission model of the virtual synchronous machine;

[0030] The second equivalent impedance determination unit is used to determine the equivalent impedance of the voltage and current dual inner loop control link according to the control structure and circuit equation of the voltage and current dual inner loop control link.

[0031] In some embodiments of the present application, the fault current determination module includes:

[0032] An internal potential determination unit, used to determine the internal potential of the grid-type converter system according to the equivalent impedance of each control link;

[0033] A machine-end voltage determination unit, used to determine the machine-end voltage when the grid voltage drops according to the internal potential;

[0034] The fault current determination unit is used to determine the fault current according to the machine-end voltage and the impedance between the machine-end bus and the fault point.

[0035] In some embodiments of the present application, the virtual impedance determination module includes:

[0036] A virtual impedance determining first unit, configured to set the virtual impedance to an initial setting value when the fault current is not greater than the maximum short-circuit current;

[0037] The virtual impedance determining second unit is used to determine the virtual impedance according to the current internal potential and the maximum short-circuit current.

[0038] In some embodiments of the present application, the virtual impedance determining second unit includes:

[0039] A current voltage compensation coefficient determination unit, configured to determine a current voltage compensation coefficient of the grid-type converter system according to the current internal potential;

[0040] The virtual impedance determination subunit is used to determine the virtual impedance according to the current internal potential and the current voltage compensation coefficient.

[0041] In a third aspect, the present invention provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the steps of a grid-forming control method that takes into account both voltage support capability and current limiting requirements.

[0042] In a fourth aspect, the present invention provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the processor implements the steps of a networking control method that takes into account both voltage support capability and current limiting requirements.

[0043] In a fifth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a grid-forming control method that takes into account both voltage support capability and current limiting requirements.

[0044] From the above description, it can be seen that an embodiment of the present invention provides a meshed control method and device that take into account both voltage support capability and current limiting requirements. The corresponding meshed control method that takes into account both voltage support capability and current limiting requirements includes: first, determining the equivalent impedance of each control link of the meshed converter system according to the topological structure of the meshed converter system; wherein the meshed converter system is controlled by a virtual synchronous machine; then, determining the fault current of the meshed converter system according to the equivalent impedance of each control link; finally, determining the virtual impedance of the meshed converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the meshed converter system, and inputting the virtual impedance into the virtual synchronous machine.

[0045] First, the virtual impedance in the present invention can change with the change of the voltage compensation coefficient, and can ensure that the short-circuit current during the fault is always the maximum short-circuit current allowed by the system, and achieve the optimal voltage support effect while meeting the short-circuit current limit. First, based on the voltage source characteristics of the converter, the equivalent impedance of each control link in the steady state is analyzed, and a system equivalent circuit model is established. The output external voltage of each link of the system is characterized based on the equivalent impedance; secondly, based on the equivalent circuit, the short-circuit current characteristics of the system are analyzed, the machine-end voltage expression is derived, and the influencing factors are analyzed; then, considering the voltage support capability and the short-circuit current limit requirements, a virtual impedance and voltage compensation coefficient adaptive control strategy is proposed; finally, the effectiveness of the control method is verified through time domain simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 It is a flow chart of a grid-connected control method that takes into account both voltage support capability and current limiting requirements in an embodiment of the present invention.

[0048] Figure 2 1 is a flow chart of step 100 of a grid-connecting control method that takes into account both voltage support capability and current limiting requirements in an embodiment of the present invention.

[0049] Figure 3 It is a flowchart diagram of step 200 of a grid-connecting control method that takes into account both voltage support capability and current limiting requirements in an embodiment of the present invention.

[0050] Figure 4 It is a flowchart diagram of step 300 of a grid-forming control method that takes into account both voltage support capability and current limiting requirements in an embodiment of the present invention.

[0051] Figure 5 3 is a flow chart of step 302 of a grid-connecting control method that takes into account both voltage support capability and current limiting requirements in an embodiment of the present invention.

[0052] Figure 6 It is a flow chart of a grid-forming control method that takes into account both voltage support capability and current limiting requirements in a specific implementation of the present invention.

[0053] Figure 7 It is a schematic diagram of the topological structure of a grid-connected converter based on VSG control in a specific implementation manner of the present invention.

[0054] Figure 8 It is a schematic diagram of an equivalent circuit of a VSG control system in a specific implementation manner of the present invention.

[0055] Fig. 9 It is a schematic diagram of a voltage loop control structure based on control equations and circuit equations in a specific implementation manner of the present invention.

[0056] Fig.10 It is a simplified schematic diagram of the voltage loop control structure in a specific implementation manner of the present invention.

[0057] Fig.11 It is a simplified schematic diagram of an equivalent circuit of a VSG-based control system in a specific implementation manner of the present invention.

[0058] Fig.12 It is a three-dimensional curve of the terminal voltage, virtual impedance and droop coefficient in a specific implementation manner of the present invention.

[0059] Fig.13 It is a curve of terminal voltage and voltage compensation coefficient in a specific implementation manner of the present invention.

[0060] Fig.14 The figure is a schematic diagram of a virtual impedance and a voltage compensation coefficient adaptive control structure in a specific implementation manner of the present invention.

[0061] Fig.15 It is the terminal voltage waveform of the machine controlled by conventional VSG under three-phase short circuit fault in the specific implementation mode of the present invention.

[0062] Fig.16 The waveform of the machine-end current controlled by conventional VSG under a three-phase short circuit fault in a specific implementation manner of the present invention is shown.

[0063] Fig.17 It is a machine-end voltage waveform that uses virtual impedance and voltage compensation coefficient adaptive control under a three-phase short-circuit fault in a specific implementation manner of the present invention.

[0064] Fig.18 It is a machine-end current waveform that adopts adaptive control of virtual impedance and voltage compensation coefficient under three-phase short circuit fault in a specific implementation manner of the present invention.

[0065] Fig.19 It is a virtual impedance waveform that uses adaptive control of virtual impedance and voltage compensation coefficient under a three-phase short circuit fault in a specific implementation manner of the present invention.

[0066] Fig. 20 It is a block diagram of a grid-type control device that takes into account both voltage support capability and current limiting requirements in an embodiment of the present invention.

[0067] Fig.21is a block diagram of an equivalent impedance determination module 10 in an embodiment of the present invention;

[0068] Fig. 22 is a block diagram of a fault current determination module 20 in an embodiment of the present invention;

[0069] Fig.23 is a block diagram of a virtual impedance determination module 30 in an embodiment of the present invention;

[0070] Fig.24 A block diagram of a second virtual impedance determination unit 30b in an embodiment of the present invention;

[0071] Fig.25 It is a schematic diagram of the structure of an electronic device in an embodiment of the present invention. DETAILED DESCRIPTION

[0072] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0073] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0074] It should be noted that the terms "including" and "having" in the specification and claims of the present application and the above-mentioned drawings and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. In the absence of conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0075] At present, new energy will become an important part of future energy and has great development potential. However, with the rapid development of new energy power generation, the access of large-scale power electronic devices, mainly wind turbines, has changed the structure of the power system. The current power grid is gradually moving away from the large-scale synchronous power grid characteristics under the large inertia and strong voltage support dominated by traditional rotating equipment, and is transitioning to a new power system dominated by the characteristics of power electronic equipment. Under the new architecture, the reactive voltage regulation capability of the converter based on grid-following (GFL) control is limited, and the access of grid-following converters will lead to a decrease in the system voltage support capability. Therefore, it is of great significance to transform the converter from traditional grid-following control to grid-forming (GFM) control to improve the system voltage support capability.

[0076] The key to improving the voltage support of the system by grid-type control is to change the external characteristics of the converter. The external characteristics of the traditional grid-type control are controlled current sources, which have poor voltage support capabilities during faults and are prone to unit disconnection accidents, which is not conducive to the safe and stable operation of the system. The external characteristics of the grid-type converter based on VSG control are controlled voltage sources, which can actively support the system voltage, but because the internal potential is almost constant during faults, a large short-circuit current will be generated.

[0077] The current limiting strategies of grid-type converters can be divided into two categories: one is to change the external characteristics of the converter. During a fault, the grid-type control is switched to the grid-type control based on phase-locked loop synchronization or the current loop is saturated by the current limiter, both of which change the external characteristics of the converter from voltage source characteristics to current source characteristics; the other is based on virtual impedance current limiting. This method does not change the external characteristics of the converter and achieves current limiting by increasing the equivalent impedance of the system. At present, many meaningful studies have been conducted on short-circuit current suppression, but short-circuit current and voltage support affect each other, and there are few studies on control strategies that take into account both short-circuit current and voltage support capabilities.

[0078] Based on this, the embodiment of the present invention provides a specific implementation method of a grid-type control method that takes into account both voltage support capability and current limiting requirements, see Figure 1 , the method comprising:

[0079] Step 100: determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine;

[0080] Step 200: determining the fault current of the grid-connected converter system according to the equivalent impedance of each control link;

[0081] Step 300: Determine the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and input the virtual impedance to the virtual synchronous machine.

[0082] From the above description, it can be seen that an embodiment of the present invention provides a grid-type control method that takes into account both voltage support capability and current limiting requirements, including: first, determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine; then, determining the fault current of the grid-type converter system according to the equivalent impedance of each control link; finally, determining the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and inputting the virtual impedance into the virtual synchronous machine.

[0083] The embodiment of the present invention provides a meshing control method that takes into account both voltage support capability and current limiting requirements. It is a meshing control strategy that takes into account both voltage support capability and current limiting requirements. First, a system equivalent circuit is constructed based on the topological structure of a meshing converter system controlled by a VSG, and the equivalent impedance of each control link is derived; then, based on the equivalent impedance, the influencing factors of VSG voltage support and the output current characteristics of VSG under a short-circuit fault are analyzed; finally, the VSG control strategy is improved by taking into account both voltage support capability and short-circuit current limiting requirements, and a virtual impedance and voltage compensation coefficient adaptive control strategy is proposed.

[0084] The virtual synchronous generator (VSG) control in step 100 realizes voltage and frequency regulation by simulating the operating characteristics of the synchronous generator, has the function of actively supporting the system frequency and voltage, and can effectively improve the inertia level of the new energy unit.

[0085] When step 100 is implemented, the composition of the equivalent impedance of the system can be analyzed for the topological structure of the grid-type converter system based on VSG control, and the equivalent impedance expression of each control link can be derived.

[0086] For step 200, the voltage support capability and output current characteristics of the VSG are analyzed based on the equivalent impedance. Specifically, the influence of the virtual impedance, reactive voltage droop coefficient and voltage compensation coefficient on the terminal voltage and short-circuit current is analyzed based on the equivalent impedance model.

[0087] It is understandable that step 300 improves VSG control by taking into account both voltage support capability and current limiting requirements. Specifically, the virtual impedance value that meets the short-circuit current limiting requirement is calculated based on the current compensation coefficient, and the optimal voltage support state is achieved under the premise that the short-circuit current does not exceed the current limiting requirement.

[0088] In some embodiments of the present application, the control link includes: a reactive voltage control link and a voltage and current dual inner loop control link;

[0089] In some embodiments of the present application, see Figure 2 , step 100 comprises:

[0090] Step 101: determining the equivalent impedance of the reactive voltage control link according to the power transmission model of the virtual synchronous machine;

[0091] Specifically, the equivalent impedance of the reactive voltage control link is solved by the VSG power transmission formula, and the equivalent impedance of the reactive voltage droop control can be expressed as:

[0092] X q =k q U s (1)

[0093] In the formula, k q is the reactive voltage droop coefficient, U s is the terminal voltage.

[0094] Step 102: Determine the equivalent impedance of the voltage-current dual inner loop control link according to the control structure and circuit equation of the voltage-current dual inner loop control link.

[0095] Specifically, the voltage-current dual inner loop equivalent impedance can be solved according to its control structure and circuit equation. Definition C f is the filter capacitance, i sd 、i sq is the dq axis component of the converter terminal current, i gd 、i gq is the dq axis component of the machine-end current. According to Kirchhoff's current law, the three-phase current flowing through the filter capacitor in the dq coordinate system satisfies:

[0096]

[0097] Perform Laplace transform on equation (2):

[0098]

[0099] When the PI regulator is used to design the voltage loop control structure, the control equation of the voltage loop can be expressed as:

[0100]

[0101] Since the response speed of the current inner loop is much higher than that of the voltage outer loop, the current loop can be equivalent to unity gain when designing the voltage loop. According to the circuit equation and control equation of the voltage loop, the voltage and current dual loop control equivalent impedance X dWith filter reactance X f Offset each other.

[0102] In addition, based on the topological structure of the grid-connected converter controlled by VSG, it can be seen that the equivalent impedance between the internal potential and the grid can be divided into the following three parts: the equivalent impedance between the internal potential and the grid is only the equivalent impedance of the reactive voltage link X q , virtual impedance X v and line impedance X g .

[0103] In some embodiments of the present application, see Figure 3 , step 200 comprises:

[0104] Step 201: determining the internal potential of the grid-connected converter system according to the equivalent impedance of each control link;

[0105] Step 202: determining the terminal voltage when the grid voltage drops according to the internal potential;

[0106] Step 203: Determine the fault current according to the machine-end voltage and the impedance between the machine-end bus and the fault point.

[0107] In step 201 to step 203, the potential inside the converter is defined as E. When the grid voltage drops, the voltage at the machine end can be expressed as follows according to the series voltage division principle:

[0108]

[0109] Where U ref is the voltage reference value, k q is the reactive voltage droop coefficient, k v is the voltage compensation coefficient.

[0110] Define X F is the impedance between the machine-end busbar and the fault point. When a three-phase ground short circuit fault occurs at the midpoint of the transmission line, ignoring the system equivalent resistance, the fault current can be expressed as:

[0111]

[0112] According to the expressions of terminal voltage and fault current, the influence of system equivalent impedance on VSG voltage support capacity and fault current is analyzed. Reducing virtual impedance and droop coefficient, or adding voltage compensation control can improve the terminal voltage support capacity, but it will also increase the short-circuit current of the system.

[0113] In some embodiments of the present application, see Figure 4 , step 300 comprises:

[0114] Step 301: When the fault current is not greater than the maximum short-circuit current, the virtual impedance is set to an initial setting value;

[0115] Step 302: Otherwise, determine the virtual impedance according to the current internal potential and the maximum short-circuit current.

[0116] In step 301 and step 302, first, it is detected whether the fault current exceeds the maximum short-circuit current limit. When the fault current is less than the maximum short-circuit current, the virtual impedance is the initial setting value; when it is detected that the fault current is greater than the maximum short-circuit current, the virtual impedance is obtained according to the potential in the system and the maximum short-circuit current at this time, and the pseudo-impedance and voltage compensation coefficient are adaptively controlled. The virtual impedance expression is:

[0117]

[0118] In the formula, I fmax is the maximum short-circuit current, take I fmax =3I N At this time, during the fault period, the short-circuit current is limited to 3 times the rated current, and the short-circuit current does not exceed the limit and can be fully utilized.

[0119] In some embodiments of the present application, see Figure 5 , step 302 comprises:

[0120] Step 3021: determining a current voltage compensation coefficient of the grid-type converter system according to the current internal potential;

[0121] Step 3022: Determine the virtual impedance according to the current internal potential and the current voltage compensation coefficient.

[0122] From the above description, it can be seen that an embodiment of the present invention provides a grid-type control method that takes into account both voltage support capability and current limiting requirements, including: first, determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine; then, determining the fault current of the grid-type converter system according to the equivalent impedance of each control link; finally, determining the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and inputting the virtual impedance into the virtual synchronous machine.

[0123] The beneficial effects of the present invention are as follows: first, the equivalent impedance of each control link in steady state is derived to obtain the equivalent circuit of the grid-type converter based on VSG control; then, by analyzing the influence of the equivalent impedance on the voltage support capability and fault current of the VSG, it is proved that the voltage support capability and the fault current are mutually coupled, and the key to achieving voltage value support is to make full use of the short-circuit current to generate timely and appropriate reactive power; finally, by improving the VSG control strategy, the virtual impedance matching the current voltage compensation coefficient is calculated according to the short-circuit current requirements, that is, the virtual impedance and the voltage compensation coefficient are adaptively controlled to achieve maximum voltage support.

[0124] To further illustrate the solution, the present invention also provides a specific implementation of a grid-type control method that takes into account both voltage support capability and current limiting requirements, see Figure 6 , the method includes the following contents:

[0125] S1: Determine the equivalent impedance of the grid-connected converter system;

[0126] Specifically, first, a grid-connected inverter topology based on VSG control is constructed. The converter power outer loop control uses VSG control to generate virtual voltage amplitude and phase

[26] ; The virtual voltage generates the reference voltage of the inner loop control after passing through the virtual impedance. The virtual impedance is used to simulate the stator resistance and synchronous reactance of the synchronous generator; the inner loop of the converter adopts voltage and current dual loop control, and the voltage reference value is generated through voltage and current dual loop control. The converter in this article adopts the average value model, so the reference voltage does not need to be modulated by PWM and can be directly used as the driving voltage to control the converter. The topology of the grid-connected converter based on VSG control is as follows Figure 7 shown. Figure 7 The variables in the grid-connected converter topology are defined as follows: d is the DC voltage, L f , C f are the filter inductance and capacitance, Z g is the line equivalent impedance, u c is the voltage at the converter terminal, u s is the terminal voltage, i s is the converter terminal current, i g is the machine end current, u g is the grid voltage.

[0127] Next, we construct a grid-connected inverter system based on VSG control and other circuits. Specifically, when constructing the system equivalent circuit based on the converter voltage source characteristics, it is assumed that each control link in the system has reached a steady state. When designing the parameters, in order to make the system inductive, the virtual resistance and line resistance are much smaller than the virtual reactance and line reactance, and they are ignored in subsequent analysis. Figure 7Based on the topological structure of the grid-connected converter controlled by VSG, the equivalent impedance between the internal potential and the grid can be divided into the following five parts: the equivalent impedance of the reactive voltage link X q , virtual impedance X v , voltage and current dual-loop control link equivalent impedance X d 、Filter reactance X f And line impedance X g Based on the equivalent circuit of VSG control system Figure 8 shown.

[0128] For the equivalent impedance of the reactive voltage control link, the equivalent impedance of the reactive voltage control link is solved by the VSG power transmission formula. f As the reference point, the VSG output reactive power satisfies equation (8).

[0129]

[0130] Virtual voltage E f With the grid voltage U g When the power angle between is very small, cosδ can be considered to be 1. In this case, equation (8) can be simplified to:

[0131]

[0132] according to Figure 7 In the reactive voltage loop control structure, when k v =0, the reactive voltage control link is reactive voltage droop control, and the virtual voltage amplitude can be expressed as:

[0133] E f =U ref +k q (Q ref -Q s ) (10)

[0134] Substituting formula (10) into formula (9), we can obtain:

[0135]

[0136] Since the reactive reference value Q ref =0, voltage reference value U ref =1, the potential E=1 in the converter remains almost unchanged, so equation (11) can be rewritten as:

[0137]

[0138] Formula (12) has a similar form to Formula (9), so the denominator of Formula (12) is the equivalent impedance between the internal potential and the grid connection point, so the equivalent impedance of reactive voltage droop control can be expressed as:

[0139] X q =k q U s (13)

[0140] When k v ≠0, the reactive voltage control link is compared with the reactive voltage droop control, and the reference voltage is U ref Change to U ref +ΔU v , which is equivalent to adding voltage compensation in reactive voltage droop control. The reactive power after adding voltage compensation can be obtained:

[0141]

[0142] At this time, after adding voltage compensation, the potential in the system is:

[0143] E=U ref +k v (U ref -U s ) (15)

[0144] The equivalent impedance of the reactive voltage link still satisfies equation (13), that is, X q =k q U s .

[0145] For the equivalent impedance of the voltage and current dual inner loop control link, according to Kirchhoff's current law, Figure 7 The current flowing through the filter capacitor satisfies the following in the dq coordinate system:

[0146]

[0147] When the PI regulator is used to design the voltage loop control structure, the control equation of the voltage loop can be expressed as:

[0148]

[0149] Since the response speed of the current inner loop is much higher than that of the voltage outer loop, when designing the voltage loop, the current loop can be equivalent to unity gain, that is, i sdref =i sd ,i sqref =i sq According to the voltage loop circuit equation (16) and the voltage loop control equation (17), the decoupling control structure of the voltage loop can be obtained as follows: Fig. 9 The feedforward term and dq axis cross coupling term in the voltage loop control structure cancel each other out with the feedforward term and dq axis cross coupling term in the circuit equation. The decoupling control structure of the voltage loop after cancellation is as follows: Fig.10 shown.

[0150] according to Figure 7 Based on the VSG controlled grid-connected converter topology, the voltage loop reference value is the voltage after passing through the virtual impedance, that is, Figure 8 U c The actual value of the filter capacitor voltage is the voltage after the filter impedance, which is equal to the machine end voltage U s . Fig.10 The actual value of the filter capacitor voltage and the given value form negative feedback. By reasonably designing the voltage loop PI parameters, the actual value of the filter capacitor voltage can follow the given value, that is, U c =U s ,so Figure 8 Medium voltage and current dual loop control equivalent impedance X d With filter reactance X f Offset each other.

[0151] In summary, the equivalent impedance between the internal potential and the power grid can be regarded as the equivalent impedance X of the reactive voltage droop link. q , virtual impedance X v and line impedance X g The equivalent circuit of the system is as follows: Fig.11 shown.

[0152] S2: Analyze VSG voltage support capability and output current characteristics based on equivalent impedance.

[0153] First, the factors affecting the voltage support capacity of VSG are analyzed. Based on the system equivalent circuit, when the grid voltage drops, the voltage at the computer end can be calculated according to the series voltage division principle:

[0154]

[0155] Substituting equation (13) into equation (18), we can obtain the terminal voltage without additional voltage compensation when the grid voltage drops:

[0156]

[0157] Substituting equation (15) into equation (18), the terminal voltage after additional voltage compensation when the grid voltage drops can be obtained:

[0158]

[0159] According to formula (19), a three-dimensional curve of terminal voltage, virtual impedance and droop coefficient is drawn as follows: Fig.12 As shown in Figure 2, when the grid voltage amplitude drops, the terminal voltage is related to the virtual impedance and reactive voltage droop coefficient, and decreases with the increase of the virtual impedance and reactive voltage droop coefficient. The terminal voltage and voltage compensation coefficient curve is drawn according to formula (20), as shown in Figure 2 Fig.13When the grid voltage amplitude drops, the terminal voltage is related to the voltage compensation coefficient and increases with the increase of the voltage compensation coefficient.

[0160] Next, determine the VSG output current characteristics under short-circuit fault. When a three-phase ground short-circuit fault occurs at the midpoint of the transmission line, ignoring the system equivalent resistance, the fault current can be expressed as:

[0161]

[0162] According to formula (21), reducing virtual impedance, reducing droop coefficient, and adding voltage compensation control can improve the voltage support capability, but the system also has overcurrent risks. q The variable range is small. When the fault condition is confirmed, X F Therefore, the change of equivalent impedance mainly depends on the virtual impedance, and the virtual impedance can be adjusted according to the current voltage compensation coefficient to meet the system current limiting requirements.

[0163] S3: Improve VSG control by taking into account both voltage support capability and current limiting requirements.

[0164] It is understandable that the key to a good voltage support capability of a grid-connected converter system is to make full use of the short-circuit current and generate timely and appropriate reactive power. In order to balance the voltage support capability and the short-circuit current limitation, two conditions must be met when designing the virtual impedance:

[0165] (1) Ensure that the fault current is always no greater than the maximum short-circuit current to prevent the current from exceeding the limit;

[0166] (2) Make full use of short-circuit current during fault conditions to achieve the best voltage support effect.

[0167] Based on the above conditions, the virtual impedance that meets the requirements can be obtained according to the current internal potential and the maximum short-circuit current. The expression of the virtual impedance is shown in formula (21).

[0168]

[0169] When the fault current is less than the maximum short-circuit current, the virtual impedance is the initial setting value; when the fault current is greater than the maximum short-circuit current, the virtual impedance is calculated based on the system potential and the maximum short-circuit current. Figure 7 The VSG control structure shown in the figure is improved to obtain the adaptive control of virtual impedance and voltage compensation coefficient as shown in Fig.14 shown.

[0170] Feasibility verification: The topology of the simulation example system is as follows Figure 7 As shown, the droop coefficient k q =0.04, virtual reactance X v=0.04pu, filter reactance X f =0.33pu, the transformer impedance is 0.08pu, the line impedance is 0.04pu, Figure 7 The effectiveness of the present invention is verified by taking a three-phase short circuit fault at the midpoint of a 35kV line as an example. In order to highlight the superiority of the method adopted by the invention, simulations of conventional VSG control and virtual impedance and voltage compensation coefficient adaptive control are carried out under fault conditions to observe the changes in the terminal voltage and current and the adaptive virtual impedance.

[0171] Fig.15 , Fig.16 The following are the voltage and current waveforms of the machine end when conventional VSG control is used under three-phase short circuit fault and different virtual impedances and voltage compensation coefficients. Fig.15 It can be seen that the voltage at the generator end is increased during the fault period by reducing the virtual impedance or adding voltage compensation control under conventional VSG control. Fig.16 It can be seen that when the voltage compensation coefficient is 0.5, the virtual impedance X v =0.36pu The current is limited to 3 times the rated current, but when the voltage compensation coefficient decreases, the short-circuit current cannot be fully utilized.

[0172] Fig.17 , Fig.18 , Fig.19 The waveforms of the terminal voltage, current and virtual impedance at different voltage compensation coefficients are shown in the figure below, respectively, when virtual impedance and voltage compensation adaptive control are used under three-phase short-circuit fault. With the virtual impedance and voltage compensation coefficient adaptive control, the virtual impedance can change with the voltage compensation coefficient, and the short-circuit current can always be the maximum short-circuit current allowed by the system during the fault, achieving the optimal voltage support effect while meeting the short-circuit current limit.

[0173] contrast Figures 15 to 19 The simulation results show that the control strategy described in the present invention takes into account the voltage support capability while ensuring that the current does not exceed the limit, and the effectiveness and feasibility of the grid-connected control strategy described in the present invention that takes into account both the voltage support capability and the current limiting requirements.

[0174] From the above description, it can be seen that an embodiment of the present invention provides a grid-type control method that takes into account both voltage support capability and current limiting requirements, including: first, determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine; then, determining the fault current of the grid-type converter system according to the equivalent impedance of each control link; finally, determining the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and inputting the virtual impedance into the virtual synchronous machine.

[0175] In summary, the grid-type control strategy of the present invention that takes into account both voltage support capability and current limiting requirements is fully utilized under the premise that the short-circuit current does not exceed the limit, thereby improving the voltage support capability. Before analyzing the voltage source characteristics of the grid-type converter controlled by VSG, the system equivalent impedance is divided into five parts according to the topological structure of the grid-type converter controlled by VSG, the equivalent impedance of each part is derived and the system equivalent circuit is constructed. Then, based on the system impedance, the influence of virtual impedance, reactive voltage droop coefficient and voltage compensation coefficient on the machine-end voltage is analyzed, and the influence of the influencing factors of voltage support on the short-circuit current is analyzed based on the system equivalent circuit. Finally, considering the requirements of voltage support capability and short-circuit current limitation comprehensively, the VSG control strategy is improved, and adaptive control of virtual impedance and voltage compensation coefficient is proposed. The present invention utilizes the voltage source characteristics of grid-type control to achieve voltage support and effectively suppress short-circuit current.

[0176] Based on the same inventive concept, the embodiments of the present application also provide a meshed control device that takes into account both voltage support capability and current limiting requirements, which can be used to implement the methods described in the above embodiments, such as the following embodiments. Since the principle of solving the problem by the meshed control device that takes into account both voltage support capability and current limiting requirements is similar to that of the meshed control method that takes into account both voltage support capability and current limiting requirements, the implementation of the meshed control device that takes into account both voltage support capability and current limiting requirements can refer to the implementation of the meshed control method that takes into account both voltage support capability and current limiting requirements, and the repeated parts will not be repeated. As used below, the terms "unit" or "module" can be a combination of software and / or hardware that implements predetermined functions. Although the system described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceived.

[0177] The embodiment of the present invention provides a specific implementation method of a network-type control device that takes into account both voltage support capability and current limiting requirements, which can realize a network-type control method that takes into account both voltage support capability and current limiting requirements, see Fig. 20 A grid-type control device that takes into account both voltage support capability and current limiting requirements specifically includes the following contents:

[0178] An equivalent impedance determination module 10 is used to determine the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine;

[0179] A fault current determination module 20, configured to determine the fault current of the grid-connected converter system according to the equivalent impedance of each control link;

[0180] The virtual impedance determination module 30 is used to determine the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and the preset maximum short-circuit current and the current internal potential of the grid-type converter system, and input the virtual impedance to the virtual synchronous machine.

[0181] In some embodiments of the present application, the control link includes: a reactive voltage control link and a voltage and current dual inner loop control link;

[0182] See also Fig.21 , the equivalent impedance determination module 10 comprises:

[0183] The first equivalent impedance determination unit 10a is used to determine the equivalent impedance of the reactive voltage control link according to the power transmission model of the virtual synchronous machine;

[0184] The second equivalent impedance determination unit 10b is used to determine the equivalent impedance of the voltage and current dual inner loop control link according to the control structure and circuit equation of the voltage and current dual inner loop control link.

[0185] In some embodiments of the present application, see Fig. 22 , the fault current determination module 20 includes:

[0186] An internal potential determination unit 20a, configured to determine the internal potential of the grid-type converter system according to the equivalent impedance of each control link;

[0187] A machine-end voltage determination unit 20b, used to determine the machine-end voltage when the grid voltage drops according to the internal potential;

[0188] The fault current determination unit 20c is used to determine the fault current according to the generator-end voltage and the impedance between the generator-end bus and the fault point.

[0189] In some embodiments of the present application, see Fig.23 , the virtual impedance determination module 30 includes:

[0190] A first virtual impedance determination unit 30a, configured to set the virtual impedance to an initial setting value when the fault current is not greater than the maximum short-circuit current;

[0191] The second virtual impedance determination unit 30b is used to determine the virtual impedance according to the current internal potential and the maximum short-circuit current.

[0192] In some embodiments of the present application, see Fig.24 , the virtual impedance determining second unit 30b comprises:

[0193] A current voltage compensation coefficient determining unit 30b1, configured to determine a current voltage compensation coefficient of the grid-type converter system according to the current internal potential;

[0194] The virtual impedance determination subunit 30b2 is used to determine the virtual impedance according to the current internal potential and the current voltage compensation coefficient.

[0195] From the above description, it can be seen that an embodiment of the present invention provides a grid-type control device that takes into account both voltage support capability and current limiting requirements, including: an equivalent impedance determination module, used to determine the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine; a fault current determination module, used to determine the fault current of the grid-type converter system according to the equivalent impedance of each control link; a virtual impedance determination module, used to determine the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and input the virtual impedance to the virtual synchronous machine.

[0196] First, the virtual impedance in the present invention can change with the change of the voltage compensation coefficient, and can ensure that the short-circuit current during the fault is always the maximum short-circuit current allowed by the system, and achieve the optimal voltage support effect while meeting the short-circuit current limit. First, based on the voltage source characteristics of the converter, the equivalent impedance of each control link in the steady state is analyzed, and a system equivalent circuit model is established. The output external voltage of each link of the system is characterized based on the equivalent impedance; secondly, based on the equivalent circuit, the short-circuit current characteristics of the system are analyzed, the machine-end voltage expression is derived, and the influencing factors are analyzed; then, considering the voltage support capability and the short-circuit current limit requirements, a virtual impedance and voltage compensation coefficient adaptive control strategy is proposed; finally, the effectiveness of the control method is verified through time domain simulation.

[0197] The embodiment of the present application also provides a specific implementation of an electronic device that can implement all steps in the network-building control method that takes into account both voltage support capability and current limiting requirements in the above embodiment, see Fig.25 , electronic equipment specifically includes the following:

[0198] Processor (processor) 1201, memory (memory) 1202, communication interface (CommunicationsInterface) 1203 and bus 1204;

[0199] The processor 1201, the memory 1202, and the communication interface 1203 communicate with each other through the bus 1204; the communication interface 1203 is used to realize information transmission between the server device and the client device and other related devices;

[0200] The processor 1201 is used to call the computer program in the memory 1202. When the processor executes the computer program, all steps in the grid-forming control method that takes into account both the voltage support capability and the current limiting requirements in the above embodiment are implemented. For example, when the processor executes the computer program, the following steps are implemented:

[0201] Step 100: determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine;

[0202] Step 200: determining the fault current of the grid-connected converter system according to the equivalent impedance of each control link;

[0203] Step 300: Determine the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and input the virtual impedance to the virtual synchronous machine.

[0204] The embodiments of the present application also provide a computer-readable storage medium capable of implementing all steps of the network-based control method that takes into account both the voltage support capability and the current limiting requirement in the above-mentioned embodiment. The computer-readable storage medium stores a computer program. When the computer program is executed by a processor, all steps of the network-based control method that takes into account both the voltage support capability and the current limiting requirement in the above-mentioned embodiment are implemented. For example, when the processor executes the computer program, the following steps are implemented:

[0205] Step 100: determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine;

[0206] Step 200: determining the fault current of the grid-connected converter system according to the equivalent impedance of each control link;

[0207] Step 300: Determine the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and input the virtual impedance to the virtual synchronous machine.

[0208] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the hardware + program embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0209] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0210] Although the present application provides method operation steps such as embodiments or flow charts, more or fewer operation steps may be included based on conventional or non-creative labor. The order of steps listed in the embodiments is only one way of executing the order of many steps and does not represent the only execution order. When the actual device or client product is executed, it can be executed in the order of the method shown in the embodiments or the drawings or in parallel (for example, in a parallel processor or multi-threaded processing environment).

[0211] For the convenience of description, the above devices are described in various modules according to their functions. Of course, when implementing the embodiments of this specification, the functions of each module can be implemented in the same or more software and / or hardware, or the module implementing the same function can be implemented by a combination of multiple sub-modules or sub-units. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0212] Those skilled in the art also know that, in addition to implementing the controller in a purely computer-readable program code, the controller can be made to implement the same function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, such a controller can be considered as a hardware component, and the devices for implementing various functions included therein can also be considered as structures within the hardware component. Or even, the devices for implementing various functions can be considered as both software modules for implementing the method and structures within the hardware component.

[0213] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0214] The memory may include non-permanent storage in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0215] The present specification embodiments may be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. The present specification embodiments may also be practiced in distributed computing environments where tasks are performed by remote processing devices connected through a communication network. In a distributed computing environment, program modules may be located in local and remote computer storage media, including storage devices.

[0216] Each embodiment in this specification is described in a progressive manner, and the same and similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. In the description of this specification, the description of the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of this specification. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, in the absence of contradiction, a person skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0217] The above is only an example of the embodiment of the present specification and is not intended to limit the embodiment of the present specification. For those skilled in the art, the embodiment of the present specification may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiment of the present specification shall be included in the scope of the claims of the embodiment of the present specification.

Claims

1. A grid-forming control method that takes into account both voltage support capability and current limiting requirements, characterized in that: include: Determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine; Determining the fault current of the grid-type converter system according to the equivalent impedance of each control link; The virtual impedance of the grid-type converter system is determined according to the magnitude relationship between the fault current and the preset maximum short-circuit current and the current internal potential of the grid-type converter system, and the virtual impedance is input into the virtual synchronous machine.

2. The network control method according to claim 1, characterized in that: The control link includes: a reactive voltage control link and a voltage and current double inner loop control link; Determining the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system includes: Determining the equivalent impedance of the reactive voltage control link according to the power transmission model of the virtual synchronous machine; The equivalent impedance of the voltage-current dual inner loop control link is determined according to the control structure and circuit equation of the voltage-current dual inner loop control link.

3. The network control method according to claim 1, characterized in that: Determining the fault current of the grid-type converter system according to the equivalent impedance of each control link includes: Determining the internal potential of the grid-type converter system according to the equivalent impedance of each control link; Determining the terminal voltage of the machine when the grid voltage drops according to the internal potential; The fault current is determined according to the machine-end voltage and the impedance between the machine-end bus and the fault point.

4. The network control method according to claim 1, characterized in that: Determining the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and the preset maximum short-circuit current and the current internal potential of the grid-type converter system includes: When the fault current is not greater than the maximum short-circuit current, setting the virtual impedance to an initial setting value; Otherwise, the virtual impedance is determined according to the current internal potential and the maximum short-circuit current.

5. The network control method according to claim 4, characterized in that: Determining the virtual impedance according to the current internal potential and the maximum short-circuit current includes: Determining a current voltage compensation coefficient of the grid-type converter system according to the current internal potential; The virtual impedance is determined according to the current internal potential and the current voltage compensation coefficient.

6. A grid-type control device that takes into account both voltage support capability and current limiting requirements, characterized in that: include: An equivalent impedance determination module, used to determine the equivalent impedance of each control link of the grid-type converter system according to the topological structure of the grid-type converter system; wherein the grid-type converter system is controlled by a virtual synchronous machine; A fault current determination module, used to determine the fault current of the grid-type converter system according to the equivalent impedance of each control link; A virtual impedance determination module is used to determine the virtual impedance of the grid-type converter system according to the magnitude relationship between the fault current and a preset maximum short-circuit current and the current internal potential of the grid-type converter system, and input the virtual impedance to the virtual synchronous machine.

7. The network-type control device according to claim 6, characterized in that: The control link includes: a reactive voltage control link and a voltage and current double inner loop control link; The equivalent impedance determination module comprises: An equivalent impedance determining first unit is used to determine the equivalent impedance of the reactive voltage control link according to the power transmission model of the virtual synchronous machine; The second equivalent impedance determination unit is used to determine the equivalent impedance of the voltage and current dual inner loop control link according to the control structure and circuit equation of the voltage and current dual inner loop control link.

8. The network control device according to claim 6, characterized in that: The fault current determination module comprises: An internal potential determination unit, used to determine the internal potential of the grid-type converter system according to the equivalent impedance of each control link; A machine-end voltage determination unit, used to determine the machine-end voltage when the grid voltage drops according to the internal potential; The fault current determination unit is used to determine the fault current according to the machine-end voltage and the impedance between the machine-end bus and the fault point.

9. The network-type control device according to claim 6, characterized in that: The virtual impedance determination module comprises: A virtual impedance determining first unit, configured to set the virtual impedance to an initial setting value when the fault current is not greater than the maximum short-circuit current; The virtual impedance determining second unit is used to determine the virtual impedance according to the current internal potential and the maximum short-circuit current.

10. The network control device according to claim 9, characterized in that: The virtual impedance determining second unit comprises: A current voltage compensation coefficient determination unit, configured to determine a current voltage compensation coefficient of the grid-type converter system according to the current internal potential; The virtual impedance determination subunit is used to determine the virtual impedance according to the current internal potential and the current voltage compensation coefficient.

11. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the steps of the grid-forming control method taking into account both voltage support capability and current limiting requirements as described in any one of claims 1 to 5 are implemented.

12. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the grid-connected control method taking into account both voltage support capability and current limiting requirements as described in any one of claims 1 to 5 are implemented.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the grid-forming control method taking into account both voltage support capability and current limiting requirements as described in any one of claims 1 to 5 are implemented.

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