Method, system and equipment for calculating short-circuit impact current of network-forming converter and medium

Abstract

The invention relates to the technical field of control and protection of a new energy power system, in particular to a short-circuit impact current calculation method, system and device for a network-forming converter and a medium, and the method comprises the steps: building a complete electromagnetic transient model of the network-forming converter, the electromagnetic transient model comprising a voltage loop, a current loop and an equivalent circuit of an LC filter; reducing the order of the electromagnetic transient model by adopting a dominant pole theory to obtain a second-order reduced-order model which retains the interaction characteristics of the control parameters and the passive device; deriving a d / q-axis current response analytic formula when the voltage of the power grid changes suddenly based on Laplacian transformation, separating transient current of d-axis and q-axis components, and calculating peak current and attenuation index of fault inrush current; and analyzing the quantitative relation of the proportional gain and the integral gain of the voltage loop to the attenuation index, and optimally configuring the proportional gain and the integral gain to suppress the inrush current oscillation, thereby solving the problem that the traditional method cannot quantitatively analyze the influence of the control parameters, and remarkably improving the transient stability of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy power system control and protection technology, and particularly relates to a grid-forming converter short-circuit impulse current calculation method, system, device and medium. BACKGROUND

[0002] At present, the power system is in a critical period of transformation to a high proportion of renewable energy and power electronic equipment. With the rapid development of new energy power generation technologies such as wind power and photovoltaic power and micro-grid systems, non-synchronous power sources dominated by power electronic devices are gradually replacing the dominant position of traditional synchronous generators. This structural change has significantly changed the transient response characteristics of the power system. The system inertia support capability continues to decline, and the overall weakening trend of the power grid is highlighted, forming a low-inertia weak grid operation pattern centered on power electronic devices. Under this background, grid-forming converters, due to their controllable output voltage, have higher flexibility in fault ride-through characteristics and are increasingly widely used in power systems, but they also pose new control challenges.

[0003] When a fault occurs in the power grid and the voltage drops suddenly, the voltage loop, current loop and LC filter of the grid-forming converter are mutually coupled, making the system model high-order and complex. Direct analysis using a high-order linear model is not easy to reveal the influence of control parameters on the dynamic of fault inrush. Existing technologies usually rely on numerical simulation or full-order model design, which makes it difficult to provide intuitive quantitative basis for control parameter tuning.

[0004] The information disclosed in this BACKGROUND section is only intended to enhance the understanding of the general background of the application and is not intended to be taken as an acknowledgement or any form of suggestion that this information forms prior art that is publicly known. SUMMARY

[0005] The present application provides a grid-forming converter short-circuit impulse current calculation method, system, device and medium, thereby effectively solving the problems in the background art.

[0006] In order to achieve the above purpose, the technical solution adopted by the present application is as follows: a grid-forming converter short-circuit impulse current calculation method, comprising the following steps:

[0007] Establishing a complete electromagnetic transient model of the grid-forming converter, the electromagnetic transient model including the equivalent circuit of the voltage loop, the current loop and the LC filter;

[0008] Using the dominant pole theory to reduce the order of the electromagnetic transient model to obtain a second-order reduced-order model that retains the interaction characteristics of the control parameters and the passive devices;

[0009] The d / q axis current response analytical formula is derived based on Laplace transform when grid voltage is suddenly changed, and the transient current of d-axis and q-axis components are separated to calculate the peak current and decay index of fault inrush current.

[0010] Further, the dominant pole theory is used to reduce the order of the electromagnetic transient model, including the following steps:

[0011] The current loop, voltage integral gain and line impedance are combined into equivalent impedance, and the non-dominant poles are discarded;

[0012] The system transfer function is simplified to a second-order model with real poles;

[0013] The coupling relationship between the voltage loop proportional coefficient, integral coefficient and circuit parameters is retained.

[0014] Further, the current loop, voltage integral gain and line impedance are combined into equivalent impedance, and the non-dominant poles are discarded, including:

[0015]

[0016] In the formula, Z leq is the simplification of equivalent impedance, s is the Laplace complex frequency domain variable, L f is the filter side inductance, L g is the grid side filter inductance, K pc is the current loop proportional gain, K iv is the current loop integral gain, a is the equivalent impedance pole position, and N is the equivalent impedance gain coefficient.

[0017] Further, the system transfer function is simplified to a second-order model with real poles, including:

[0018] The dynamic characteristics of PCC voltage under grid voltage disturbance are described:

[0019]

[0020] In the formula, G EU (s) is the transfer function from grid voltage disturbance to PCC voltage, Z leq is the simplification of equivalent impedance, s is the Laplace complex frequency domain variable, L f is the filter side inductance, L g is the grid side filter inductance, K pc is the current loop proportional gain, K iv is the current loop integral gain, a is the equivalent impedance pole position, and N is the equivalent impedance gain coefficient, C f is the filter capacitance.

[0021] The denominator is decomposed into two real poles:

[0022]

[0023] where b 1， b2 is two real poles;

[0024] Considering that the damping ratio is much greater than 1:

[0025]

[0026] Discarding the non-dominant pole b1, the transfer function of the output current and voltage under grid voltage disturbance is as follows:

[0027]

[0028] where

[0029] where M is the amplitude gain constant, i gd (s) represents the Laplace transform of the d-axis current component injected into the grid by the converter in the synchronous rotating coordinate system.

[0030] Further, the derivation of the analytical expression of the d / q-axis current response when the grid voltage suddenly changes based on the Laplace transform comprises the following steps:

[0031] Based on the second-order reduced-order model, considering the grid impedance coupling effect, the transfer function corresponding to the d / q-axis current response is determined;

[0032] The dominant pole in the transfer function characteristic equation is extracted by pole decomposition;

[0033] The time-domain expression is calculated by using the jump response analysis to obtain the analytical expression of the current response.

[0034] Further, the determination of the transfer function corresponding to the d / q-axis current response comprises:

[0035] Due to the symmetry of the structure, the transfer function corresponding to the q-axis current response is the same as that of the d-axis current:

[0036]

[0037] where u dref (s) and u qref (s) are the Laplace transforms of the d-axis and q-axis voltage reference signals output by the voltage loop in the synchronous rotating coordinate system; i gd (s) represents the Laplace transform of the d-axis current component injected into the grid by the converter in the synchronous rotating coordinate system; i gq (s) represents the Laplace transform of the q-axis current component injected into the grid by the converter in the synchronous rotating coordinate system; e sd and e sqis the d-axis and q-axis grid voltage disturbance; s is the Laplace complex frequency variable, L g is the grid-side filter inductance, b 1,2 is the two real poles; M is the magnitude gain constant, and ω is the grid angular frequency.

[0038] Further, the extracting the dominant poles in the characteristic equation of the transfer function by pole decomposition comprises:

[0039] The characteristic equation of the transfer function has two pairs of conjugate poles x1, x2 and x3, x4, and their analytical expressions are as follows:

[0040]

[0041] Since the poles x1, x2 are ten times higher than the poles x3, x4, and the zero point -b2 is also obviously greater than -(b2-M), it is discarded:

[0042]

[0043] In the formula, G Eig_direct (s) describes the intrinsic through component of the d-axis current under the d-axis voltage step excitation; G Eig_cross (s) describes the intrinsic cross component of the d-axis current under the q-axis voltage step excitation.

[0044] Further, the calculating the time-domain expression by using the transition response analysis to obtain the current response analytical expression comprises:

[0045] The occurrence of a grid fault is equivalent to a step change in the grid voltage, and the unit step function is:

[0046] i gd (s) = G Elg_direct (s)[U0-(E d0 -E df ε(s))]+G Elg_cross (s)[0-(E q0 -E qf ε(s))];

[0047] In the formula, i gd is the d-axis grid current, G Elg_direct is the intrinsic through component of the d-axis current under the d-axis voltage step excitation, U0 is the steady-state component of the d-axis voltage reference value, E d0 , E q0 are the steady-state components of the d / q-axis grid voltage, E df , E qf are the fault components of the d / q-axis grid voltage, ε(s) is the step disturbance function of the grid fault, and G Elg_cross is the intrinsic cross component of the d-axis current under the q-axis voltage step excitation.

[0048] The time-domain response is:

[0049]

[0050] wherein:

[0051]

[0052] The component i generated by the q-axis grid voltage variation gdq The calculation is:

[0053]

[0054] In the formula, the decay index Reflects the oscillation decay rate of the fault impact current, and is only related to the control and circuit parameters.

[0055] Further, it also includes dynamically adjusting the overcurrent protection threshold:

[0056] Setting a reference protection threshold;

[0057] Generating an adjustment coefficient according to the decay index calculated in real time;

[0058] Generating a dynamic threshold according to the adjustment coefficient;

[0059] Triggering protection when the measured current exceeds the dynamic threshold and the duration exceeds a set value.

[0060] Further, after calculating the decay index, it also includes:

[0061] Analyzing the quantitative relationship of the voltage loop proportional gain and the integral gain to the decay index, and optimizing the configuration of the proportional gain and the integral gain to suppress the inrush oscillation.

[0062] The present application also includes a short-circuit impact current calculation system for a grid-forming converter, which uses the method as described above, and the system includes:

[0063] A modeling unit for establishing a complete electromagnetic transient model of the grid-forming converter, wherein the electromagnetic transient model includes the equivalent circuit of the voltage loop, the current loop and the LC filter;

[0064] A reduction unit for performing reduction processing on the electromagnetic transient model by using the dominant pole theory to obtain a second-order reduced model that retains the interaction characteristics of the control parameters and the passive devices;

[0065] A decay index calculation unit for deriving an analytical expression of the d / q-axis current response when the grid voltage suddenly changes based on Laplace transform, and separating the transient current of the d-axis and q-axis components to calculate the peak current and the decay index of the fault inrush current.

[0066] The application also comprises a computer device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the method as described above when executing the computer program.

[0067] The application also comprises a storage medium, which stores a computer program, wherein the computer program is executable on a processor to implement the method as described above.

[0068] The application has the beneficial effect that: by adopting the dominant pole theory to perform order reduction on the electromagnetic transient model, a second-order reduced model is obtained, which retains the interaction characteristics of the control parameters and the passive device; the problem that the traditional system model is high-order and complex, and it is not easy to reveal the influence law of the control parameters on the fault inrush current dynamics when directly using a high-order linear model for analysis is solved; based on Laplace transform, the d / q axis current response analytical expression when the grid voltage suddenly changes is derived, and the transient currents of the d-axis and q-axis components are separated to calculate the peak current and decay index of the fault inrush current; the quantitative relationship between the voltage loop proportional gain and integral gain and the decay index is analyzed, and the proportional gain and integral gain are optimized to suppress the inrush current oscillation; quantitative basis is provided for the control optimization and protection setting of the grid-connected converter, which is applicable to new energy station, microgrid and other scenes, solves the problem that the traditional method cannot quantitatively analyze the influence of the control parameters, and significantly improves the transient stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0069] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments described in the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0070] Figure 1 The flowchart of the method in embodiment 1;

[0071] Figure 2 The structural schematic diagram of the system in embodiment 1;

[0072] Figure 3 The flowchart of the method in embodiment 2;

[0073] Figure 4 The control block diagram of the grid-connected converter in embodiment 2;

[0074] Figure 5 The equivalent circuit diagram of the d-axis cascade control;

[0075] Figure 6 The structural schematic diagram of the computer device of the present application. DETAILED DESCRIPTION

[0076] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application.

[0077] Embodiment 1:

[0078] As shown in the formula (1), a network-structured converter short-circuit impulse current calculation method comprises the following steps: Figure 1 A complete electromagnetic transient model of the network-structured converter is established, and the electromagnetic transient model comprises an equivalent circuit of a voltage loop, a current loop and an LC filter;

[0079] The electromagnetic transient model is reduced by using a dominant pole theory to obtain a second-order reduced model that retains the interaction characteristics of control parameters and passive devices;

[0080] Based on Laplace transform, an analytical expression of d / q axis current response when the grid voltage suddenly changes is derived, and the transient currents of d-axis and q-axis components are separated to calculate the peak current and decay index of the fault inrush current.

[0081] In the embodiment, the electromagnetic transient model is reduced by using the dominant pole theory, comprising the following steps:

[0082] The current loop, voltage integral gain and line impedance are combined into an equivalent impedance, and non-dominant poles are discarded;

[0083] The system transfer function is simplified into a second-order model with real poles;

[0084] The coupling relationship between the voltage loop proportional coefficient, integral coefficient and circuit parameters is retained.

[0085] The current loop, voltage integral gain and line impedance are combined into an equivalent impedance, and non-dominant poles are discarded, comprising:

[0086]

[0087]

[0088] In the formula, Z leq is the simplified equivalent impedance, s is a Laplace complex frequency domain variable, L f is a filter-side inductance, L g is a grid-side filter inductance, K pc is a current loop proportional gain, K iv is a current loop integral gain, a is an equivalent impedance pole position, and N is an equivalent impedance gain coefficient.

[0089] The system transfer function is simplified into a second-order model with real poles, comprising: ​

[0090] The PCC voltage dynamic characteristics under grid voltage disturbance are described as:

[0091]

[0092] where G EU (s) is the transfer function from grid voltage disturbance to PCC voltage, Z leq is the simplified equivalent impedance, s is the Laplace complex frequency variable, L f is the filter side inductance, L g is the grid side filter inductance, K pc is the current loop proportional gain, K iv is the current loop integral gain, a is the equivalent impedance pole position, N is the equivalent impedance gain coefficient, C f is the filter capacitance;

[0093] The denominator is decomposed into two real poles:

[0094]

[0095] where b 1,2 are the two real poles;

[0096] Considering that the damping ratio is much larger than 1:

[0097]

[0098] Discarding the non-dominant pole b1, the transfer function of output current and voltage under grid voltage disturbance is as follows:

[0099]

[0100] where

[0101] where M is the amplitude gain constant, i gd (s) represents the Laplace transform of the d-axis current component injected into the grid by the converter in the synchronous rotating coordinate system.

[0102] Based on the Laplace transform, the analytical expression of the d / q-axis current response when the grid voltage suddenly changes is derived, including the following steps:

[0103] Based on the second-order reduced-order model, considering the grid impedance coupling effect, the transfer function corresponding to the d / q-axis current response is determined;

[0104] The dominant pole in the characteristic equation of the transfer function is extracted by pole decomposition;

[0105] The time-domain expression is calculated by using the transition response analysis, and the analytical expression of the current response is obtained.

[0106] The determining of the transfer function corresponding to the d / q-axis current response comprises:

[0107] Due to the symmetry of the structure, the transfer function corresponding to the q-axis current response is the same as that of the d-axis current:

[0108]

[0109] In the formula, u dref (s) and u qref (s) are the Laplace transforms of the d-axis and q-axis voltage reference signals output by the voltage loop in the synchronous rotating coordinate system; i gd (s) represents the Laplace transform of the d-axis current component injected into the power grid by the converter in the synchronous rotating coordinate system; i gq (s) represents the Laplace transform of the q-axis current component injected into the power grid by the converter in the synchronous rotating coordinate system; e sd and e sq are the d-axis and q-axis power grid voltage disturbances; s is a Laplace complex frequency variable, L g is the power grid side filter inductance, b 1,2 are two real poles; M is an amplitude gain constant, and ω is the power grid angular frequency.

[0110] In the embodiment, the dominant poles in the characteristic equation of the transfer function are extracted by pole decomposition, comprising:

[0111] The characteristic equation of the transfer function has two pairs of conjugate poles x1, x2 and x3, x4, and their analytical expressions are as follows:

[0112]

[0113] Since the poles x1, x2 are ten times higher than the poles x3, x4, and the zero point -b2 is also obviously greater than -(b2-M), they are discarded:

[0114]

[0115] In the formula, G Eig_direct (s) describes the intrinsic direct-through component of the d-axis current under the d-axis voltage step excitation; G Eig_cross (s) describes the intrinsic cross component of the d-axis current under the q-axis voltage step excitation.

[0116] As a preferred embodiment of the above embodiment, the time-domain expression is calculated by using the step response analysis to obtain the current response analytical expression, comprising:

[0117] The occurrence of the power grid fault is equivalent to a step change in the power grid voltage, and the unit step function is:

[0118] i gd (s) = G Elg_direct(s)[U0-(E d0 -E df ε(s))]+G Elg_cross (s)[0-(E q0 -E qf ε(s))];

[0119] In the formula, i gd G represents the d-axis grid current. Elg_direct U0 is the intrinsic direct-current component of the d-axis current under d-axis voltage step excitation, and E is the steady-state component of the d-axis voltage reference value. d0 E q0 E represents the steady-state component of the grid voltage along the d / q axes. df E qf Let G be the d / q axis grid voltage fault component, ε(s) be the step disturbance function of the grid fault, and G be the voltage component of the grid fault. Elg_cross This represents the intrinsic crossover component of the d-axis current under q-axis voltage step excitation.

[0120] The time-domain response is:

[0121]

[0122] in:

[0123]

[0124] The component i generated by the q-axis grid voltage change gdq The calculation is as follows:

[0125]

[0126] In the formula, the attenuation exponent The oscillation decay rate, which reflects the fault inrush current, is only related to control and circuit parameters.

[0127] This also includes dynamically adjusting the overcurrent protection threshold:

[0128] Set the baseline protection threshold;

[0129] An adjustment factor is generated based on the real-time calculated attenuation index;

[0130] A dynamic threshold is generated based on the adjustment coefficient;

[0131] Protection is triggered when the measured current exceeds the dynamic threshold and the duration exceeds the set value.

[0132] After calculating the attenuation exponent, the method further includes:

[0133] The quantitative relationship between the voltage loop proportional gain and integral gain and the attenuation exponent is analyzed, and the proportional gain and integral gain are optimized to suppress inrush current oscillation.

[0134] As Figure 2 shown, the embodiment also includes a network configuration type converter short circuit impulse current calculation system, using the method as described above, the system includes:

[0135] a modeling unit for establishing a complete electromagnetic transient model of the network configuration type converter, the electromagnetic transient model including an equivalent circuit of a voltage loop, a current loop and an LC filter;

[0136] a reduction unit for performing reduction processing on the electromagnetic transient model using dominant pole theory to obtain a second-order reduced model that retains control parameters and passive device interaction characteristics;

[0137] an attenuation index calculation unit for deriving an analytical expression of d / q axis current response when the grid voltage suddenly changes based on Laplace transform, and separating transient currents of d-axis and q-axis components to calculate peak current and attenuation index of the fault inrush current.

[0138] Embodiment 2:

[0139] As Figure 3 shown, the embodiment includes a network configuration type converter short circuit impulse current calculation method, including the following steps:

[0140] S1, when a short circuit fault occurs in the grid, the PCC point voltage amplitude and phase change in a step, causing the fault inrush current of the network configuration type converter. The control block diagram of the network configuration type converter is as shown in Figure 4 , the traditional high-order model is difficult to analyze the quantitative relationship between the control parameters and the fault impulse current, and the present application reduces the original system to a second-order model through dominant pole theory, retaining the interaction characteristics of the voltage loop, the current loop and the LC filter, as shown in Figure 5 . The current loop, the voltage integral gain and the line impedance are inductive and are combined as Zleq. Due to the fast dynamic characteristics of the current loop, a high gain Kpc is introduced, s = -Kpc / Lf is a non-dominant pole of Zleq, so it can be discarded. Therefore, Zleq is further simplified as follows:

[0141]

[0142] wherein:

[0143]

[0144] Thus, the PCC voltage dynamic characteristics under grid voltage disturbance can be described as:

[0145]

[0146] Then, the denominator is decomposed into two real pole points:

[0147]

[0148] Since the damping ratio is much larger than 1:

[0149]

[0150] Therefore, the non-dominant pole b1 is discarded, and the transfer function of the output current and voltage under grid voltage disturbance is as follows:

[0151]

[0152] where

[0153] S2, since there is a phase difference between the grid voltage and the PCC voltage, the amplitude drop of the grid voltage Es at the time of fault occurrence will cause the changes of esd and esq in the electromagnetic transient dq coordinate system model. Therefore, based on the reduced-order electromagnetic transient model in (5), considering the grid impedance coupling effect, the d-axis current response under the excitation of d-axis and q-axis voltages is derived as follows, due to the symmetry of the structure, the transfer function corresponding to the q-axis current response is the same as that of the d-axis current.

[0154]

[0155] The characteristic equation of equation (6) has two pairs of conjugate poles x1, x2 and x3, x4, and their analytical expressions are as follows:

[0156]

[0157] Since the poles x1, x2 are ten times higher than the poles x3, x4, and the zero point -b2 is also significantly greater than -(b2-M), they can also be discarded:

[0158]

[0159] The occurrence of grid fault is equivalent to a step change in grid voltage. Write the d-axis response into equation (8), and the unit step function is:

[0160] i gd (s) =G Elg_direct (s)[U0-(E d0 -E df ε(s))] +G Elg_cross (s)[0-(E q0 -E qf ε(s))] (9)

[0161] In the formula, i gd is the d-axis grid current, G Elg_direct is the intrinsic direct component of the d-axis current under the excitation of the d-axis voltage step, U0 is the steady-state component of the d-axis voltage reference value, Ed0 , E q0 is the d / q-axis grid voltage steady-state component, E df , E qf is the d / q-axis grid voltage fault component, and ε(s) is a step disturbance function of the grid fault, G Elg_cross is the intrinsic cross component of the d-axis current under the step excitation of the q-axis voltage;

[0162] The time-domain response can be analytically calculated by equation (8) and equation (9).

[0163]

[0164] wherein:

[0165]

[0166] Similarly, the component igdq generated by the change of the q-axis grid voltage is calculated as:

[0167]

[0168] wherein

[0169]

[0170] In the equation, the damping index reflects the oscillation damping rate of the fault impact current, and is only related to the control and circuit parameters. With the increase of Kpv and the reasonable configuration of Kiv, ξω n is significantly improved, which means that the damping effect of the fault impact current is enhanced.

[0171] By reasonably configuring the voltage controller parameters of the grid-connected type converter, the fault impact current of the converter can be effectively suppressed, and in the case of the same grid fault condition, the suppression speed of the fault impact current will be faster, thereby reducing the oscillation impact on the converter. The traditional fixed threshold protection has the problem of false triggering, and when the voltage deep drops but the fault impact current decays quickly, unnecessary protection actions may be triggered due to temporary over-limit. The method can dynamically adjust the protection threshold based on the real-time calculated damping index.

[0172] Please refer to Figure 6 The computer device provided by the embodiment of the application is shown in the structure schematic diagram. The computer device 400 provided by the embodiment of the application comprises a processor 410 and a memory 420, the memory 420 stores a computer program executable by the processor 410, and the computer program is executed by the processor 410 to execute the method as above.

[0173] The embodiment of the present application further provides a storage medium 430, wherein the storage medium 430 stores a computer program, and the computer program is executed by the processor 410 to perform the method described above.

[0174] The storage medium 430 can be implemented by any type of volatile or nonvolatile storage devices or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk or optical disk.

[0175] In the description of the present application, the terms "first", "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. The meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0176] In the present application, unless otherwise specifically defined and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0177] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any suitable manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples, without contradiction.

[0178] Any process or method descriptions or descriptions of the flow diagrams in the specification can be understood as representing code modules, segments, or portions of code which include one or more executable instructions for performing specific logic functions or steps in the process, and the various embodiments of the application include additional or different modules, segments, or portions of code when implemented in software or firmware in combination with the process described. The various embodiments of the application can be implemented in a computer program product tangibly embodied in a machine-readable storage medium (e.g., magnetic disk, optical disk, memory, etc.) including one or more code modules or portions of code.

[0179] The logic and / or steps represented in the flow diagrams or otherwise described herein, for example, can be embodied in computer-readable instructions, modules, or portions of code, which can be executed by one or more processing units, cores, or processors of one or more computing devices or systems. The various embodiments of the application include additional or different modules, segments, or portions of code when implemented in software or firmware in combination with the process described. The various embodiments of the application can be implemented in a computer program product tangibly embodied in a machine-readable storage medium (e.g., magnetic disk, optical disk, memory, etc.) including one or more code modules or portions of code.

[0180] It should be understood that portions of the present application can be implemented with hardware, software, firmware or a combination thereof. In the above embodiments, a plurality of steps or methods can be implemented with software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any of the following technologies, known in the art, or their combinations can be used: discrete logic circuitry having logic gates for implementing logic functions on data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), etc.

[0181] Those skilled in the art of the present technology can understand that all or part of the steps carried out by the above-mentioned embodiments can be completed by a program instructing the relevant hardware, and the program can be stored in a computer readable storage medium. When the program is executed, it includes one of the steps of the method embodiment or a combination thereof.

[0182] The storage medium mentioned above can be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. A method for calculating short-circuit impulse current of a grid-forming converter, characterized in that, The method comprises the following steps: establishing a complete electromagnetic transient model of the network-forming converter, the electromagnetic transient model comprising a voltage loop, a current loop and an equivalent circuit of an LC filter; performing order reduction on the electromagnetic transient model by using a dominant pole theory to obtain a second-order reduced model that retains the interaction between control parameters and passive devices; on this basis, deriving an analytical expression of d / q-axis current response when a grid voltage suddenly changes based on Laplace transform, and separating transient currents of d-axis and q-axis components to calculate a peak current and a decay index of a fault inrush current.

2. The network configuration type converter short-circuit impulse current calculation method according to claim 1, characterized by, The order reduction on the electromagnetic transient model by using the dominant pole theory comprises the following steps: merging the current loop, voltage integral gain and line impedance into an equivalent impedance, and discarding non-dominant poles; simplifying a system transfer function into a second-order model with real poles; retaining the coupling relationship between voltage loop proportional coefficient, integral coefficient and circuit parameters.

3. The network configuration type converter short-circuit impulse current calculation method according to claim 2, characterized by, The merging of the current loop, voltage integral gain and line impedance into an equivalent impedance, and discarding non-dominant poles comprises: where Z leq is the simplified equivalent impedance, s is the Laplace complex frequency variable, L f is the filter-side inductance, L g is the grid-side filter inductance, K pc is the current loop proportional gain, K iv is the current loop integral gain, a is the equivalent impedance pole position, and N is the equivalent impedance gain coefficient.

4. The network configuration type converter short-circuit impulse current calculation method according to claim 3, characterized by, The simplifying of the system transfer function into a second-order model with real poles comprises: describing dynamic characteristics of PCC voltage under grid voltage disturbance: where u d (s) is the Laplace transform of the d-axis voltage component of the PCC point, e sd (s) is the Laplace transform of the voltage on the d-axis of the grid; K pv is the voltage loop proportional gain, G EU (s) is the transfer function of the grid voltage disturbance to the PCC voltage, C f is the filter capacitance; decomposing a denominator into two real poles: wherein b 1， b2is two real poles; considering that a damping ratio is much greater than 1: discarding non-dominant poles b1, and the transfer function of output current and voltage under grid voltage disturbance is as follows: wherein where M is the magnitude gain constant, i gd (s) represents the Laplace transform of the d-axis current component injected by the converter into the power grid in the synchronous rotating coordinate system.

5. The network configuration type converter short-circuit impulse current calculation method according to claim 1, characterized by, The deriving of the analytical expression of d / q-axis current response when a grid voltage suddenly changes based on Laplace transform comprises the following steps: determining a transfer function corresponding to the d / q-axis current response based on the second-order reduced model and considering grid impedance coupling effects; extracting dominant poles in a characteristic equation of the transfer function by pole decomposition; calculating a time-domain expression based on the dominant poles by using a step response analysis to obtain the analytical expression of the current response.

6. The network configuration type converter short-circuit impulse current calculation method according to claim 5, characterized by, The determination of the transfer function corresponding to the d / q-axis current response comprises: due to symmetry of a structure, the transfer function corresponding to the q-axis current response is the same as that of the d-axis current: where u dref (s) and u qref (s) are the Laplace transforms of the d and q axis voltage reference signals output by the voltage loop in the synchronous rotating reference frame; i gd (s) represents the Laplace transform of the d axis current component injected into the grid by the converter in the synchronous rotating reference frame; i gq (s) represents the Laplace transform of the q axis current component injected into the grid by the converter in the synchronous rotating reference frame; e sd and e sq are the d and q axis grid voltage disturbances; s is the Laplace complex frequency variable, L g is the grid side filter inductance, b 1， b2are two real poles; M is the magnitude gain constant, and ω is the grid angular frequency.

7. The network configuration type converter short-circuit impulse current calculation method according to claim 6, characterized by, The extraction of the dominant poles in the characteristic equation of the transfer function by pole decomposition comprises: the characteristic equation of the transfer function has two pairs of conjugate poles x1, x2 and x3, x4, and their analytical expressions are as follows: since the poles x1, x2 are ten times higher than the poles x3, x4, and the zero point -b2 is also obviously greater than -(b2-M), the zero point -b2 is discarded: where G Eig_direct (s) describes the intrinsic direct axis component of d-axis current under d-axis voltage step excitation; G Eig_cross (s) describes the intrinsic cross-axis component of d-axis current under q-axis voltage step excitation.

8. The network configuration type converter short-circuit impulse current calculation method according to claim 7, characterized by, The calculation of the time-domain expression based on the step response analysis to obtain the analytical expression of the current response comprises: the occurrence of a grid fault is equivalent to a step change of grid voltage, and a unit step function is as follows: i gd (s) = G Elg_direct (s) [U0- (E d0 - E df (s) ] + G Elg_cross (s) [0- (E q0 - E qf (s) ] ; where i gd is the d-axis grid current, G Elg_direct is the intrinsic direct component of the d-axis current under d-axis voltage step excitation, U0is the steady-state component of the d-axis voltage reference, E d0 , E q0 is the steady-state component of the d / q-axis grid voltage, E df , E qf is the fault component of the d / q-axis grid voltage, ε(s) is the step disturbance function of the grid fault, G Elg_cross is the intrinsic cross component of the d-axis current under q-axis voltage step excitation; a time-domain response is as follows: wherein: q-axis grid voltage variation generated component i gdq is calculated as: where the decay exponent The rate of oscillation decay reflecting the fault current is only dependent on control and circuit parameters.

9. The network configuration type converter short-circuit impulse current calculation method according to claim 1, characterized by, The method further comprises the following steps: setting a reference protection threshold; generating an adjustment coefficient according to the decay index calculated in real time; generating a dynamic threshold according to the adjustment coefficient; triggering protection when a measured current exceeds the dynamic threshold and a duration exceeds a set value.

10. The network configuration type converter short-circuit impulse current calculation method according to claim 1, characterized by, After the decay index is calculated, the method further comprises the following steps: analyzing a quantitative relationship between voltage loop proportional gain and integral gain and the decay index, and optimizing configuration of the proportional gain and the integral gain to suppress inrush oscillation.

11. A network configuration type converter short circuit impulse current calculation system characterized by comprising: The system comprises the method according to any one of claims 1 to 10. A modeling unit is configured to establish a complete electromagnetic transient model of the grid-forming converter, which includes equivalent circuits of a voltage loop, a current loop and an LC filter; A reduced-order unit is configured to perform a reduced-order processing on the electromagnetic transient model by using a dominant pole theory to obtain a second-order reduced-order model that retains control parameters and passive device interaction characteristics; An attenuation index calculation unit is configured to derive an analytical expression of d / q-axis current responses when a grid voltage suddenly changes based on a Laplace transform, separate transient currents of d-axis and q-axis components, and calculate a peak current and an attenuation index of a fault inrush current.

12. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the computer program to implement the method in any one of claims 1-10.

13. A storage medium having stored thereon a computer program, characterized in that The computer program is executed by the processor to implement the method in any one of claims 1-10. The computer program is executed by the processor to implement the method in any one of claims 1-10.

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