Source-containing power distribution network short-circuit current calculation method, system, equipment and medium

Abstract

The invention discloses an active power distribution network short-circuit current calculation method, system and device and a medium, and relates to the technical field of power plant intelligent fault management, and the method comprises the steps: building an inverter grid-connected model according to a distributed power supply grid-connected topological structure; performing two different transformations on the model to obtain a model under a dq coordinate system, and realizing different control modes by controlling dq-axis positive and negative sequence current output by an inverter; and constructing a composite sequence network diagram when the power distribution network has a fault, determining a fault point short-circuit current and inverter grid-connected point voltage expression and an inverter grid-connected point voltage expression, and solving a short-circuit current value of the fault point. According to the method for calculating the short-circuit current of the source-containing power distribution network, the inverter grid-connected mathematical model is established, Clark conversion and Park conversion are carried out, the dynamic response and short-circuit current characteristics of an inversion type distributed power supply can be simulated more accurately, and the defect that the dynamic characteristics of the distributed power supply are ignored in a traditional calculation method is overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent fault management of power plants, and in particular to a method, system, equipment and medium for calculating short-circuit current of a power distribution network containing a source. Background Art

[0002] In modern power systems, distribution networks, as a key link in power transmission, undertake the important task of transmitting power from substations to end users. With the rapid development of renewable energy, more and more inverter-type distributed power sources (such as photovoltaic power generation and wind power generation) are connected to distribution networks, which not only improves the sustainability of power supply, but also brings new challenges. Especially in the case of short-circuit faults, the short-circuit current characteristics of the distribution network have changed significantly. Accurate calculation of short-circuit current is crucial to the safety and economy of the power system.

[0003] At present, the short-circuit current calculation of many distribution networks containing distributed generation relies on traditional iterative calculation methods, which usually ignore the dynamic characteristics of distributed generation, especially the transient response after a fault occurs. The physical modeling-based method can simulate the dynamic response and short-circuit current characteristics of inverter-type distributed generation more deeply. The physical model can comprehensively consider the control strategy of the inverter, the grid-connected conditions, and various nonlinear characteristics of the power grid. Combining physical modeling with data-driven methods can effectively improve the accuracy of short-circuit current calculation and perform precise analysis for different working conditions. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is: the existing short-circuit current calculation method ignores the dynamic response of the inverter, has low calculation accuracy, and neglects the nonlinear characteristics of the power grid, and how to combine physical modeling with data-driven methods to improve calculation accuracy.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: a method for calculating the short-circuit current of a source distribution network, comprising constructing an inverter grid-connected model according to a distributed power grid-connected topology structure; performing two different transformations on the model to obtain a model in a dq coordinate system, and realizing different control modes by controlling the dq axis positive and negative sequence currents output by the inverter; constructing a composite sequence network diagram when a distribution network fails, determining the short-circuit current at the fault point and the inverter grid-connected point voltage expression and the inverter grid-connected point voltage expression, and solving the short-circuit current value at the fault point.

[0007] As a preferred solution of the method for calculating short-circuit current of a source-containing distribution network described in the present invention, wherein: the distributed power supply grid-connected topology structure includes a DC side voltage source, a three-phase bridge inverter, and an LCL filter;

[0008] Photovoltaic power generation is represented by a DC voltage source, which is connected to an inverter, and the inverter is connected to the grid after LCL filtering.

[0009] As a preferred solution of the method for calculating the short-circuit current of the source distribution network of the present invention, the construction of the inverter grid-connected model includes listing the inverter grid-connected mathematical model according to the distributed power grid-connected topology structure, and the model is expressed as:

[0010]

[0011] Among them, u is the inverter AC output voltage, i is the inverter AC output current, e is the grid voltage, R is the equivalent resistance, and L is the filter inductor.

[0012] As a preferred solution of the method for calculating short-circuit current of a source distribution network described in the present invention, wherein: the two different transformations are performed, including performing Clark transformation and Park transformation on the mathematical model in sequence to obtain a mathematical model in a dq coordinate system. First, the Clark transformation matrix transforms the electrical quantity in the ABC three-phase coordinate system into the electrical quantity in the αβ two-phase stationary coordinate system, and then the Park transformation matrix transforms the two-phase electrical quantity in the αβ stationary coordinate system into the electrical quantity in the dq two-phase rotating coordinate system.

[0013] As a preferred solution of the method for calculating short-circuit current of a source distribution network described in the present invention, the control method includes, according to a mathematical model in a dq coordinate system, realizing different control methods by controlling the dq axis positive and negative sequence current output by the inverter, and the control methods include the inverter outputting three-phase symmetrical current, the inverter outputting constant reactive power, and the inverter outputting constant active power.

[0014] As a preferred solution of the method for calculating the short-circuit current of the source distribution network described in the present invention, the method of determining the short-circuit current at the fault point and the voltage expression of the inverter grid-connected point and the voltage expression of the inverter grid-connected point include, according to the symmetrical component method, making a composite sequence network diagram when the distribution network fails, and obtaining the short-circuit current expression at the fault point and the voltage expression of the inverter grid-connected point. In the positive-sequence network, the inverter is equivalent to a current source model controlled by the positive-sequence voltage of the grid-connected point, and outputs the positive-sequence current. In the negative-sequence network, the inverter is equivalent to a current source model controlled by the negative-sequence voltage of the grid-connected point, and outputs the negative-sequence current.

[0015] As a preferred solution of the method for calculating short-circuit current of a power distribution network with a source according to the present invention, the short-circuit current value of a fault point is obtained by:

[0016] According to different control modes, the short-circuit current value of the fault point is solved by simultaneous equations. The simultaneous equations include the expression of the short-circuit current at the fault point, the expression of the positive and negative sequence voltages at the inverter grid-connected point, and the expression of the inverter output dq axis positive sequence current determined by the control mode.

[0017] Another object of the present invention is to provide a short-circuit current calculation system for a source distribution network, which can achieve different control objectives by controlling the dq axis positive and negative sequence currents output by the inverter, thereby providing more effective current support when a short-circuit fault occurs, enhancing the stability and reliability of the power grid in the face of asymmetric faults, and solving the problem that the current power plant fault recommendation technology contains the problem of ignoring the nonlinear characteristics of the power grid.

[0018] As a preferred solution of the source-containing distribution network short-circuit current calculation system of the present invention, it includes: an inverter grid-connected model building module, a control module, and a short-circuit current calculation module;

[0019] The inverter grid-connected model construction module is used to construct a mathematical model of the inverter grid-connected based on the distributed power grid-connected topology, and determine the electrical connection relationship between the DC voltage source, the three-phase bridge inverter, the LCL filter, etc.; the control module is used for coordinate transformation and the generation and adjustment of control strategies, including the Clark transformation module, the Park transformation module and the control and adjustment module. First, the Clark transformation module is used to convert the electric quantity in the three-phase coordinate system into the electric quantity in the αβ stationary coordinate system, and then the Park transformation module is used to convert the electric quantity in the αβ coordinate system into the electric quantity in the dq coordinate system. The control and adjustment module formulates different control strategies by controlling the positive and negative sequence currents of the dq axes; the short-circuit current calculation module is used to determine the fault model and solve the short-circuit current value of the fault point, including the composite sequence network diagram construction module and the solution module. The composite sequence network diagram construction module makes a composite sequence network diagram when the distribution network fails based on the symmetrical component method, and the solution module solves the short-circuit current value of the fault point by simultaneous equations according to different control methods.

[0020] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement a method for calculating short-circuit current of a power distribution network with a source.

[0021] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a method for calculating short-circuit current of a power distribution network containing a source.

[0022] Beneficial effects of the present invention: The short-circuit current calculation method for the source distribution network provided by the present invention can more accurately simulate the dynamic response and short-circuit current characteristics of the inverter-type distributed power source by establishing a mathematical model of the inverter grid-connected and performing Clark transformation and Park transformation. Accurate modeling helps to capture the instantaneous response of the inverter-type distributed power source in the event of a short-circuit fault, overcoming the defect that the traditional calculation method ignores the dynamic characteristics of the distributed power source. At the same time, the method achieves different control objectives by controlling the dq-axis positive and negative sequence current output by the inverter, including the inverter outputting three-phase symmetrical current, constant reactive power and constant active power, thereby providing more effective current support when a short-circuit fault occurs, and enhancing the stability and reliability of the power grid in the face of asymmetric faults. The present invention achieves better results in terms of accuracy, response speed and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0024] Figure 1 This is an overall flow chart of a method for calculating short-circuit current in a source distribution network provided in the first embodiment of the present invention.

[0025] Figure 2 The complex composite sequence network of the method for calculating short-circuit current of the source distribution network provided in the first embodiment of the present invention is converted into a simplified composite sequence network schematic diagram.

[0026] Figure 3 This is a comparison chart of the accuracy of the method for calculating short-circuit current of a source distribution network provided in the second embodiment of the present invention.

[0027] Figure 4 This is a time comparison diagram of the method for calculating short-circuit current of a source distribution network provided in the second embodiment of the present invention.

[0028] Figure 5 This is an overall flow chart of a short-circuit current calculation system for a source distribution network provided in the third embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0030] Example 1, referring to Figure 1 and Figure 2 , which is an embodiment of the present invention, provides a method for calculating the short-circuit current of a source-containing distribution network, including:

[0031] S1: Construct an inverter grid-connected model according to the distributed power grid-connected topology.

[0032] Furthermore, an infrared thermal imager is used to photograph the reactor bushings of different fault types and the reactor bushings without faults for data acquisition.

[0033] The distributed power grid-connected topology includes a DC-side voltage source, a three-phase bridge inverter, and an LCL filter.

[0034] Photovoltaic power generation is represented by a DC voltage source. The DC voltage source is connected to the inverter, and the inverter is connected to the grid after LCL filtering.

[0035] It should be noted that photovoltaic power generation is represented by a DC voltage source and is connected to the inverter. As a typical renewable energy, the output of photovoltaic power generation is essentially DC. By abstracting it as a DC voltage source, the modeling and calculation process can be simplified, facilitating subsequent system analysis and short-circuit current calculation. Representing photovoltaic power generation as a DC voltage source simplifies the system modeling and avoids directly considering the complexity and nonlinear characteristics of photovoltaic modules. The representation of the DC voltage source has high accuracy and calculation efficiency in short-circuit current calculation and power flow analysis. After abstracting photovoltaic power generation as a DC voltage source, it can be more conveniently coupled with the inverter and the grid, facilitating the analysis of the current response of the system under fault conditions, thereby providing an accurate voltage value reference for the control strategy of the inverter and improving the response speed and prediction ability of the system.

[0036] Furthermore, constructing the inverter grid-connected model includes listing the inverter grid-connected mathematical model according to the distributed power grid-connected topology, and the model is expressed as:

[0037]

[0038] where u is the output voltage of the inverter on the AC side, i is the output current of the inverter on the AC side, e is the grid connection point voltage, R is the equivalent resistance, and L is the filter inductance.

[0039] S2: Perform two different transformations on the model to obtain the model in the dq coordinate system, and achieve different control methods by controlling the positive and negative sequence currents of the dq axes of the inverter output.

[0040] Furthermore, two different transformations are performed, including Clark transformation and Park transformation of the mathematical model in sequence to obtain the mathematical model in the dq coordinate system. First, the Clark transformation matrix transforms the electrical quantity in the ABC three-phase coordinate system into the electrical quantity in the αβ two-phase stationary coordinate system, and then the Park transformation matrix transforms the two-phase electrical quantity in the αβ stationary coordinate system into the electrical quantity in the dq two-phase rotating coordinate system.

[0041] Clark transformation matrix, expressed as:

[0042]

[0043] The Park transformation matrix is ​​expressed as:

[0044]

[0045] In a source-based distribution network, the output control strategy of the inverter (such as constant power, constant current, etc.) directly affects the stability and current response of the power grid. Traditional calculation methods often simplify the control characteristics of the inverter and fail to accurately consider the nonlinearity of the power grid and the instantaneous regulation capability of the inverter. However, through Clark transformation and Park transformation, the control strategy of the inverter can be coupled with the dynamic response of the power grid, and its behavior can be accurately described in the dq coordinate system. When faced with complex power systems and multi-source grid connection, current analysis and calculation directly in the three-phase coordinate system will appear very complicated and difficult to handle. Clark transformation and Park transformation convert the originally complex three-phase electricity into simplified two-phase components, making current analysis more intuitive and easy to understand. This conversion not only improves the efficiency of current calculation, but also enables better modeling and simulation of the dynamic interaction between the inverter and the power grid.

[0046] It should be noted that the mathematical model is subjected to Clark transformation and Park transformation in turn to obtain the mathematical model in the dq coordinate system, which is expressed as:

[0047]

[0048] Among them, u d + 、u q + 、u d - 、u q - are the inverter output voltage d q Axis positive and negative sequence components. d + 、i q + 、i d - 、i q- are the inverter output current d q Axis positive and negative sequence components. d + 、e q + 、e d - 、e q - are the grid voltage and q The positive and negative sequence components of the shaft. ω is the angular frequency of the power grid.

[0049] Furthermore, according to the mathematical model in the dq coordinate system, different control modes are achieved by controlling the dq axis positive and negative sequence currents output by the inverter, including the inverter outputting three-phase symmetrical current, the inverter outputting constant reactive power, and the inverter outputting constant active power.

[0050] The inverter output three-phase symmetrical current is expressed as:

[0051]

[0052] The inverter output constant reactive power is expressed as:

[0053]

[0054] The inverter output constant active power is expressed as:

[0055]

[0056] Among them, V + 、V - are the amplitudes of the positive and negative sequence components of the grid voltage, A=(V + ) 2 -(V - ) 2 , B=(V + ) 2 +(V - ) 2 .

[0057] S3: Construct a composite sequence network diagram when the distribution network fails, determine the short-circuit current at the fault point and the voltage expression of the inverter grid-connected point, and solve the short-circuit current value at the fault point.

[0058] Furthermore, based on the symmetrical component method, a composite sequence network diagram is made when the distribution network fails, and the expression of the short-circuit current at the fault point and the voltage expression at the inverter grid-connected point are obtained. In the positive-sequence network, the inverter is equivalent to a current source model controlled by the positive-sequence voltage at the grid-connected point, and outputs a positive-sequence current. In the negative-sequence network, the inverter is equivalent to a current source model controlled by the negative-sequence voltage at the grid-connected point, and outputs a negative-sequence current.

[0059] It should be noted that if Figure 2 As shown in the figure, the composite sequence network diagram for a single-phase ground fault is shown. The short-circuit current at the fault point is I, and the voltage at the inverter grid connection point in the positive sequence network is V + , the output current is I S + , the voltage of the inverter grid connection point in the negative sequence network is V - , the output current is I S - At the same time, according to the boundary conditions of a single-phase grounding fault (the fault phase voltage is 0, and the non-fault phase current is 0), the composite sequence network of the positive and negative zero sequence network is a positive and negative zero sequence series form, such as Figure 2 As shown, Z MF It represents the impedance between busbar M and fault point F. The subscripts 1, 2, and 0 represent positive sequence, negative sequence, and zero sequence networks, respectively. For example, Z DM2 It represents the negative sequence impedance between busbar D and busbar M. Figure 2 By transforming the positive and negative sequence networks shown in the figure into star-delta networks, we can obtain a simplified composite sequence network diagram.

[0060] Under normal conditions: the system power supply (ES) provides the main current to the load in the phase network through the transformer (T1) step-down phase, and the current flows to the load in each branch through the main line (M). The distributed power source converts DC power into AC power through the inverter and transformer and injects it into the grid for use by the load.

[0061] In case of fault: short circuit causes the current at the fault point to increase sharply, and the AC power provided by the power supply and distributed power supply all flows to the short circuit point.

[0062] The current flows in the same way as before simplification. The system power supply provides positive sequence current, and the distributed power supply provides positive and negative sequence currents, all flowing to the short circuit point.

[0063] Simplification is the simplification within the power grid. For the short-circuit point, the injected current is still equivalent and will not change the original structure of the power grid. Therefore, the current at the fault point can still be accurately measured after simplification.

[0064] It should also be noted that the symmetrical component method is a method commonly used to analyze asymmetrical systems (such as power systems under fault conditions). This method greatly simplifies the analysis of asymmetrical systems by decomposing the three-phase unbalanced current or voltage into positive sequence, negative sequence and zero sequence components. In the present invention, the construction of the composite sequence network diagram is to decompose the grid current and voltage under fault conditions into three parts: positive sequence, negative sequence and zero sequence by the symmetrical component method, with special attention paid to the positive sequence and negative sequence parts because they are directly related to the dynamic response when a fault occurs in the distribution network.

[0065] Positive sequence component: represents the current and voltage during normal operation of the power grid.

[0066] Negative sequence component: represents the asymmetric part of current and voltage when an asymmetric fault occurs in the power grid (such as single-phase grounding, two-phase short circuit, etc.).

[0067] Furthermore, the method for solving the short-circuit current value at the fault point includes, according to different control methods, solving the short-circuit current value at the fault point by simultaneous equations, and the simultaneous equations include an expression for the short-circuit current at the fault point, an expression for the positive and negative sequence voltages at the inverter grid-connected point, and an expression for the inverter output dq-axis positive sequence current determined by the control method.

[0068] Example 2, reference Figure 3 and Figure 4 , which is an embodiment of the present invention, provides a method for calculating the short-circuit current of a source distribution network. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0069] First, determine the appropriate distribution network model containing inverter-type distributed power sources, including the types of distributed power sources. This experiment takes the photovoltaic power source access to the ring distribution network as an example. In Simulink, the inverter grid-connected model is constructed according to the distributed power grid-connected topology. Clark transformation and Park transformation are performed to obtain the model in the dq coordinate system. The goal of outputting constant active power is achieved by controlling the dq axis positive and negative sequence current output by the inverter. Secondly, set the fault type required for the simulation (taking single-phase grounding fault as an example), the time when the fault occurs, and the duration of the fault. Finally, the traditional iterative calculation method is implemented through Matlab programming, ignoring the dynamic characteristics of the distributed power source, directly calculating the short-circuit current, and comparing the simulation results with the calculation results of the Matlab program.

[0070] Simulation software conditions: Windows 11 operating system, MATLAB / SimulinkR2022a.

[0071] Simulation parameters: simulation time is 1 second, fault duration is 0.3-0.5 seconds, grounding resistance is 3Ω, line positive sequence impedance is 0.047+j0.063Ω / km, and line zero sequence impedance parameter is 0.141+j0.189Ω / km.

[0072] Reference Figure 4 It can be seen that the method used in the present invention shows a relatively stable and high R 2 This shows that the method of the present invention can maintain high calculation accuracy at different nodes, has low sensitivity to node changes, and has good stability and reliability. 2The value fluctuates greatly and is generally lower than that of the method of the present invention. This means that the prior art has poor stability in calculation accuracy when processing different nodes, performing well on some nodes but poorly on other nodes.

[0073] Reference Figure 5 It can be seen that the calculation time of the method used in the present invention is generally short and the fluctuation is small. This shows that when processing a large number of nodes, the method of the present invention can not only quickly complete the calculation task, but also has good stability in the calculation time, which is particularly important for application scenarios that require fast response. The existing iterative calculation method has a long calculation time and large fluctuations. This may lead to the fact that in practical applications, when processing a large number of nodes, the existing technology not only has low calculation efficiency, but also has difficulty in predicting the completion time of the calculation task, increasing uncertainty.

[0074] Example 3, reference Figure 5 , which is an embodiment of the present invention, provides a short-circuit current calculation system for a source distribution network, including an inverter grid-connected model building module 100, a control module 200, and a short-circuit current calculation module 300.

[0075] The inverter grid-connected model building module 100 is used to build a mathematical model of the inverter grid-connected based on the distributed power grid-connected topology structure, and determine the electrical connection relationship between the DC voltage source, the three-phase bridge inverter, the LCL filter, etc.

[0076] The control module 200 is used for coordinate transformation and generation and adjustment of control strategies, and includes a Clark transformation module 201, a Park transformation module 202 and a control and adjustment module 203. First, the Clark transformation module 201 converts the electric quantity in the three-phase coordinate system into the electric quantity in the αβ stationary coordinate system, and then the Park transformation module 202 converts the electric quantity in the αβ coordinate system into the electric quantity in the dq coordinate system. The control and adjustment module 203 formulates different control strategies by controlling the positive and negative sequence currents of the dq axes.

[0077] The short-circuit current calculation module 300 is used to determine the fault model and solve the short-circuit current value of the fault point, including a composite sequence network diagram construction module 301 and a solution module 302. The composite sequence network diagram construction module 301 makes a composite sequence network diagram when the distribution network fails according to the symmetrical component method, and the solution module 302 solves the short-circuit current value of the fault point by simultaneous equations according to different control methods.

[0078] It should be noted that the inverter grid-connected model building module 100 provides a basic electrical model for the control module 200 and the short-circuit current calculation module 300. These models describe the interaction between the inverter, the filter and the grid through mathematical expressions, and are the core basis for subsequent calculations.

[0079] The control module 200 relies on the mathematical model provided by the inverter grid-connected model building module 100 to perform coordinate transformation and control strategy generation. Clark transformation and Park transformation convert the three-phase current of the inverter into the current in the dq coordinate system, so that the subsequent control and regulation module can accurately adjust the positive and negative sequence currents and realize the regulation of the inverter under different working conditions.

[0080] The composite sequence network diagram construction module and the solution module of the short-circuit current calculation module 300 directly depend on the control strategy output by the control module 200 and the grid-connected model of the inverter. The composite sequence network diagram analyzes the fault condition based on the symmetrical component method, while the solution module solves the short-circuit current through simultaneous equations.

[0081] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0082] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0083] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or processing in another suitable manner as necessary, and then stored in a computer memory.

[0084] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc. It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limited. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for calculating short-circuit current of a power distribution network including a source, characterized in that: include: Construct an inverter grid-connected model based on the distributed power grid-connected topology; The model is transformed twice to obtain the model in the dq coordinate system, and different control methods are realized by controlling the dq axis positive and negative sequence current output by the inverter; Construct a composite sequence network diagram when the distribution network fails, determine the short-circuit current at the fault point and the voltage expression of the inverter grid-connected point, and solve the short-circuit current value at the fault point.

2. The method for calculating short-circuit current of a power distribution network containing a source according to claim 1, characterized in that: The distributed power grid-connected topology structure includes: DC side voltage source, three-phase bridge inverter, LCL filter; Photovoltaic power generation is represented by a DC voltage source, which is connected to an inverter, and the inverter is connected to the grid after LCL filtering.

3. The method for calculating short-circuit current of a power distribution network containing a source according to claim 1 or 2, characterized in that: The construction of the inverter grid-connected model includes: According to the distributed power grid-connected topology, the inverter grid-connected mathematical model is listed, and the model is expressed as: Among them, u is the inverter AC output voltage, i is the inverter AC output current, e is the grid voltage, R is the equivalent resistance, and L is the filter inductor.

4. The method for calculating short-circuit current of a power distribution network containing a source according to claim 3, characterized in that: The two different transformations are performed, including: The mathematical model is subjected to Clark transformation and Park transformation in sequence to obtain the mathematical model in the dq coordinate system. First, the Clark transformation matrix transforms the electrical quantity in the ABC three-phase coordinate system into the electrical quantity in the αβ two-phase stationary coordinate system, and then the Park transformation matrix transforms the two-phase electrical quantity in the αβ stationary coordinate system into the electrical quantity in the dq two-phase rotating coordinate system.

5. The method for calculating short-circuit current of a power distribution network containing a source according to claim 4, characterized in that: The control method includes: According to the mathematical model in the dq coordinate system, different control modes are realized by controlling the dq axis positive and negative sequence current output by the inverter. The control modes include inverter outputting three-phase symmetrical current, inverter outputting constant reactive power and inverter outputting constant active power.

6. The method for calculating short-circuit current of a power distribution network containing a source according to claim 1, characterized in that: The method for determining the short-circuit current at the fault point and the voltage expression at the inverter grid connection point and the voltage expression at the inverter grid connection point includes: According to the symmetrical component method, a composite sequence network diagram is made when the distribution network fails, and the expression of the short-circuit current at the fault point and the voltage expression of the inverter grid-connected point are obtained. In the positive-sequence network, the inverter is equivalent to a current source model controlled by the positive-sequence voltage at the grid-connected point, and outputs positive-sequence current. In the negative-sequence network, the inverter is equivalent to a current source model controlled by the negative-sequence voltage at the grid-connected point, and outputs negative-sequence current.

7. The method for calculating short-circuit current of a power distribution network containing a source according to claim 1, 2, 5 or 6, characterized in that: The short-circuit current value of the fault point is obtained. include, According to different control modes, the short-circuit current value of the fault point is solved by simultaneous equations. The simultaneous equations include the expression of the short-circuit current at the fault point, the expression of the positive and negative sequence voltages at the inverter grid-connected point, and the expression of the inverter output dq axis positive sequence current determined by the control mode.

8. A short-circuit current calculation system for a source distribution network, characterized in that: It comprises an inverter grid-connected model building module (100), a control module (200), and a short-circuit current calculation module (300); The inverter grid-connected model building module (100) is used to build a mathematical model of the inverter grid-connected based on the distributed power grid-connected topology structure, and determine the electrical connection relationship between the DC voltage source, the three-phase bridge inverter, the LCL filter, etc. The control module (200) is used for coordinate transformation and generation and adjustment of control strategies, and comprises a Clark transformation module (201), a Park transformation module (202) and a control adjustment module (203). Firstly, the Clark transformation module (201) transforms the electric quantity in the three-phase coordinate system into the electric quantity in the αβ stationary coordinate system, and then the Park transformation module (202) transforms the electric quantity in the αβ coordinate system into the electric quantity in the dq coordinate system. The control adjustment module (203) formulates different control strategies by controlling the positive and negative sequence currents of the dq axes. The short-circuit current calculation module (300) is used to determine the fault model and solve the short-circuit current value of the fault point, and comprises a composite sequence network diagram construction module (301) and a solution module (302). The composite sequence network diagram construction module (301) makes a composite sequence network diagram when the distribution network fails according to the symmetrical component method, and the solution module (302) solves the short-circuit current value of the fault point by simultaneous equations according to different control modes.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for calculating short-circuit current of a power distribution network with a source according to any one of claims 1 to 7 are implemented.

10. 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 method for calculating short-circuit current of a power distribution network with a source according to any one of claims 1 to 7 are implemented.

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