A method and apparatus for calculating three-phase unbalanced short-circuit current in distribution networks considering photovoltaic power generation.

Abstract

This invention discloses a method and apparatus for calculating the three-phase asymmetrical short-circuit current in a distribution network considering photovoltaic (PV) power. The method includes: before a fault, using power flow calculations to obtain the node voltage and injected current of each node, including the PV node, during normal operation; equating the power source to a current source and the load to an impedance based on Norton's equivalent; calculating the admittance matrix based on an equivalent circuit model after a three-phase asymmetrical short-circuit fault; and constructing a network equation for the PV short-circuit calculation node impedance suitable for Gaussian iteration; simultaneously establishing nonlinear piecewise expressions for the voltage and current of the renewable energy node; and solving for the current and voltage during a renewable energy fault using an iterative method to obtain the fault short-circuit current. By constructing the admittance matrix and corresponding voltage and current expressions for single-phase-to-ground short circuits and two-phase-to-phase short circuits, and using iterative calculations to derive the final result, the accuracy of the calculation is improved.

Description

Technical Field

[0001] This invention belongs to the field of power system fault analysis technology, and in particular relates to a method and apparatus for calculating three-phase unbalanced short-circuit current in distribution networks considering photovoltaics. Background Technology

[0002] Distributed generation, with its advantages of being environmentally friendly, having high power generation efficiency, and being easy to install, has been widely used in power systems. To address the increasingly severe energy crisis, photovoltaic and wind power have developed most rapidly. When photovoltaic power is extensively integrated into the distribution network, the distribution network transforms from a single-source, few-loop network into a multi-source, multi-loop network, rendering traditional distribution network short-circuit calculation methods inapplicable. Traditional power grid fault analysis methods primarily rely on the symmetrical component method for fault calculation.

[0003] However, there are currently many types of photovoltaic (PV) units, and their structures and connection methods differ significantly from traditional AC synchronous motors, resulting in substantial changes in their short-circuit current characteristics. Traditional short-circuit calculation methods are no longer applicable. When asymmetrical faults occur in the power grid, using the traditional symmetrical component method for calculation will lead to significant deviations between the calculated results and the actual results. Therefore, it is urgent to research a calculation method that can improve the accuracy of asymmetrical short-circuit calculations in distribution networks containing PV systems. Summary of the Invention

[0004] This invention provides a method and apparatus for calculating three-phase unbalanced short-circuit current in distribution networks considering photovoltaics, which is used to solve the technical problem of low accuracy in calculating unbalanced short-circuit current in distribution networks containing photovoltaics.

[0005] In a first aspect, the present invention provides a method for calculating the three-phase unbalanced short-circuit current of a distribution network considering photovoltaics, comprising: Step A: Before a fault, using power flow calculations, the node voltage and injected current of each node, including the photovoltaic node, during normal operation are obtained, wherein the voltage of the i-th node during normal operation is... The current during normal operation is Injection power is Step B: Based on Norton's equivalent, the power supply is equivalent to a current source, and the load is equivalent to an impedance. The admittance matrix is ​​calculated based on the equivalent circuit model after a three-phase asymmetrical short-circuit fault. A photovoltaic short-circuit calculation node impedance network equation suitable for Gaussian iteration is constructed. Specifically, the construction of the photovoltaic short-circuit calculation node impedance network equation includes: when a single-phase ground fault occurs due to an asymmetrical short circuit, phase a is assumed to be the fault phase. The operating modes of phases b and c remain unchanged, and the fault point is considered a newly added node in the network. The impedance simulation method suitable for Gaussian iteration in photovoltaic short-circuit calculation is used to modify the admittance matrix of phase a node to the short-circuit current calculation admittance matrix Y. AFurthermore, an impedance network equation for photovoltaic short-circuit calculation nodes suitable for Gaussian iteration is constructed. When a two-phase short circuit occurs due to an asymmetrical short circuit fault, it is assumed that phases b and c are the faulty phases. At this time, the operating mode of phase a remains unchanged. The connection point between the two phases is regarded as two newly added fault nodes. The impedance simulation method suitable for photovoltaic short-circuit calculation using Gaussian iteration is adopted to modify the admittance matrix of phases b and c into a short-circuit current calculation admittance matrix Y. BC And construct the photovoltaic short-circuit calculation node impedance network equation suitable for Gaussian iteration; Step C: Combine the nonlinear piecewise expressions of the voltage and current of the new energy node, solve the current and voltage when the new energy fails by iterative method, and then obtain the fault short-circuit current.

[0006] Secondly, this invention provides a three-phase unbalanced short-circuit current calculation device for a distribution network considering photovoltaics, comprising: a calculation module configured to calculate, before a fault, the node voltage and injected current of each node, including the photovoltaic node, during normal operation using power flow calculation, wherein the voltage of the i-th node during normal operation is... The current during normal operation is Injection power is The module is configured to equate the power supply to a current source and the load to an impedance based on Norton's equivalent model. It calculates the admittance matrix based on an equivalent circuit model after a three-phase asymmetrical short-circuit fault and constructs the photovoltaic short-circuit calculation node impedance network equations suitable for Gaussian iteration. Specifically, the construction of these equations includes: when a single-phase ground fault occurs due to an asymmetrical short circuit, assuming phase a is the faulty phase, while the operating modes of phases b and c remain unchanged, the fault point is considered a newly added node in the network. The impedance simulation method suitable for Gaussian iteration in photovoltaic short-circuit calculation is used to modify the admittance matrix of phase a node to a short-circuit current calculation admittance matrix Y. A Furthermore, an impedance network equation for photovoltaic short-circuit calculation nodes suitable for Gaussian iteration is constructed. When a two-phase short circuit occurs due to an asymmetrical short circuit fault, it is assumed that phases b and c are the faulty phases. At this time, the operating mode of phase a remains unchanged. The connection point between the two phases is regarded as two newly added fault nodes. The impedance simulation method suitable for photovoltaic short-circuit calculation using Gaussian iteration is adopted to modify the admittance matrix of phases b and c into a short-circuit current calculation admittance matrix Y. BC The system constructs a photovoltaic short-circuit calculation node impedance network equation suitable for Gaussian iteration; the iteration module is configured to simultaneously solve the nonlinear piecewise expressions of the voltage and current of the new energy node, and solve the current and voltage when the new energy fails by iterative method, and then obtain the fault short-circuit current.

[0007] Thirdly, an electronic device is provided, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the steps of the method for calculating the three-phase asymmetrical short-circuit current of a distribution network considering photovoltaics according to any embodiment of the present invention.

[0008] Fourthly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the steps of the method for calculating the three-phase asymmetrical short-circuit current of a distribution network considering photovoltaics according to any embodiment of the present invention.

[0009] This application presents a method and apparatus for calculating the three-phase asymmetrical short-circuit current in photovoltaic distribution networks. By constructing the admittance matrix and corresponding voltage and current expressions for single-phase grounding short circuit and two-phase interphase short circuit respectively, and using iterative calculation to derive the final result, the accuracy of the calculation is improved. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 A flowchart of a method for calculating the three-phase unbalanced short-circuit current of a distribution network considering photovoltaics, provided in an embodiment of the present invention;

[0012] Figure 2 A structural block diagram of a three-phase unbalanced short-circuit current calculation device for a distribution network considering photovoltaics, provided in an embodiment of the present invention;

[0013] Figure 3 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Please see Figure 1The diagram shows a flowchart of a method for calculating the three-phase unbalanced short-circuit current of a distribution network considering photovoltaics, as described in this application.

[0016] like Figure 1 As shown, the specific steps for calculating the three-phase unbalanced short-circuit current of a distribution network considering photovoltaics include:

[0017] Step A: Before the fault, use power flow calculations to obtain the node voltage and injected current of each node, including the photovoltaic node, during normal operation. The voltage of the i-th node during normal operation is... The current during normal operation is Injection power is

[0018] Step B: Equivalent the power source to a current source and the load to an impedance according to Norton's equivalent. Calculate the admittance matrix based on the equivalent circuit model after a three-phase asymmetrical short-circuit fault and construct the photovoltaic short-circuit calculation node impedance network equation suitable for Gaussian iteration.

[0019] In this embodiment, step B1: The node load simulated admittance is calculated using the node injected power and node voltage under normal network conditions, and is expressed as follows:

[0020]

[0021] In the formula, Y Loadi For the load simulation admittance of node i, Inject the power conjugate into node i. The voltage of the i-th node during normal operation. The conjugate of the voltage at node i during normal operation;

[0022] After being converted into load admittance, the current vector injected at the load node

[0023] Step B2: The generator adopts the Norton equivalent model, and the generator's equivalent reactance is X. g Then the equivalent admittance of the generator is:

[0024]

[0025] In the formula, y g This is the equivalent admittance of the generator;

[0026] Step B3: When a single-phase ground fault occurs, the fault point is considered a newly added node in the network, and the single-phase ground fault admittance of the fault point is set to y. f The photovoltaic short-circuit current admittance array Y is obtained by summing the self-admittance of the PQ node with its load analog admittance, the short-circuit fault node with its grounding admittance, and the slack node self-admittance with its generator equivalent reactance. Aexpression:

[0027]

[0028] In the formula, y 11 Let y be the self-admittance of load node 1 in the power flow calculation. nn Let n be the self-admittance of the load node n in the power flow calculation. The self-admittance of photovoltaic node 1 in power flow calculation. Let y be the mutual admittance of photovoltaic node m and load node n in power flow calculation. loadn The load simulation admittance for node n;

[0029] Step B4: When a two-phase-to-phase fault occurs, the fault connection point is considered a newly added line in the network. Simultaneously, two new nodes are set at the beginning and end of the line, and the admittance of the two-phase-to-phase connection point is set to y. f The photovoltaic short-circuit current admittance array Y is obtained by summing the self-admittance of the PQ node with its load analog admittance, the short-circuit fault node with its grounding admittance, and the slack node self-admittance with its generator equivalent reactance. BC expression:

[0030]

[0031] in,

[0032]

[0033]

[0034] In the formula, y bfcf The mutual admittance between newly added nodes is given by a value of -y. f , Y cc =Y bb ;

[0035] Step B5: The power flow calculation before the fault yields the injected current at slack node 1 as follows: Node voltage is The generator uses the Norton equivalent model, and represents a one-phase model as a three-phase model, so that the generator output current of one phase can be calculated. Represented as:

[0036] In the formula, j is the imaginary part symbol, X a This is the equivalent reactance of the generator;

[0037] Assuming the generator output current before and after the short circuit fault The equivalent reactance of the generator remains unchanged. g If it remains unchanged, then the current injected into one phase of the generator at the slack node 1 during a fault can be expressed as:

[0038]

[0039] The relationship between the injected current and the node voltage at the photovoltaic node is as follows:

[0040]

[0041] In the formula, Let be the injection current of the m-th photovoltaic node. Let be the node voltage of the m-th photovoltaic node;

[0042] Step B6: In the case of a single-phase ground fault, the expression for the network equation of the short-circuit calculation node impedance is as follows:

[0043]

[0044] In the formula, Let be a matrix composed of the voltages at each node of phase a. It is a matrix composed of the currents at each node of phase a;

[0045] in,

[0046] In the formula, Let be the node voltage of the first node in phase a. Let be the node voltage at the fault location of phase a. Let be the node voltage of the m-th photovoltaic node in phase a. Let be the node voltage of the nth node in phase a;

[0047] In the case of a two-phase short circuit, the equation for the short-circuit calculation node impedance network is as follows:

[0048]

[0049] in,

[0050] Step C: Combine the nonlinear piecewise expressions for the voltage and current of the new energy node, and solve for the current and voltage when the new energy node fails using the iterative method, and then obtain the fault short-circuit current.

[0051] In this embodiment, step C1: the nonlinear piecewise expression for the new energy current and voltage is:

[0052]

[0053]

[0054] In the formula, Let m be the voltage magnitude of the photovoltaic node. Let m be the phase angle of the voltage at photovoltaic node m after the (k-1)th iteration. Let m be the voltage magnitude of the photovoltaic node after the (k-1)th iteration. Let m be the current mode of the photovoltaic node. Let m be the magnitude of the output current of photovoltaic node m after the k-th iteration. Let pv be the injected current vector of photovoltaic node m. m ∈a, b, c phase;

[0055] Step C2: Assuming the photovoltaic power output remains unchanged, set the short-circuit voltage values ​​of each node obtained after the fault as the initial voltage iteration values ​​for the Gaussian iterative short-circuit current node admittance equation. The voltage iteration formula is as follows:

[0056]

[0057] In the formula, Y represents the voltage value of the i-th node after the (k+1)-th iteration. ij Let be the admittance matrix. Let i be the current value of the j-th node after the k-th iteration, where i is the i-th node, j is the j-th node, and n is the total number of nodes.

[0058] Step C3: Repeat the iterative calculation until the voltage difference between each node on both the front and back sides is calculated. If the value is less than a preset threshold, the node voltage value is obtained after k iterations. Then it can be based on The short-circuit current values ​​of each branch were calculated, where Z is the voltage vector at node j after k iterations. ij Let be the impedance between node i and node j. Let be the injected current vector between node i and node j.

[0059] In summary, the method of this application first calculates the voltage and injected current before the generator node fault using power flow calculation. Then, it uses Norton's equivalent to convert the power source into a current source and the load into an impedance, establishing an equivalent circuit model after a three-phase asymmetrical short-circuit fault and calculating the admittance matrix. Next, it classifies the fault type into single-phase grounding and two-phase inter-fault faults for separate discussion, providing different handling schemes. Then, it provides admittance matrices adapted to each situation for single-phase grounding and two-phase inter-fault faults. Based on the node classification, it provides voltage and current expressions for single-phase grounding and two-phase inter-fault faults for different short-circuit conditions. Finally, it combines the nonlinear piecewise expressions of the voltage and current of the renewable energy node and uses the Gaussian iteration method to solve for the voltage during renewable energy faults, thereby obtaining the fault short-circuit current. This method achieves the calculation of three-phase asymmetrical short-circuit current applicable to multiple inverter-type renewable energy sources connected to the grid, with high calculation accuracy and short computation time, meeting the needs of current power systems.

[0060] Please see Figure 2 The diagram shows a structural block diagram of a three-phase unbalanced short-circuit current calculation device for a distribution network considering photovoltaics, according to this application.

[0061] like Figure 2 As shown, the distribution network three-phase unbalanced short-circuit current calculation device 200 includes a calculation module 210, a construction module 220, and an iteration module 230.

[0062] The calculation module 210 is configured to calculate the node voltage and injected current of each node, including the photovoltaic node, during normal operation before a fault occurs, using power flow calculations. The voltage of the i-th node during normal operation is... The current during normal operation is Injection power is

[0063] Module 220 is configured to equate the power supply to a current source and the load to an impedance based on Norton's equivalent model. It calculates the admittance matrix based on an equivalent circuit model after a three-phase asymmetrical short-circuit fault and constructs a photovoltaic short-circuit calculation node impedance network equation suitable for Gaussian iteration. Specifically, the construction of the photovoltaic short-circuit calculation node impedance network equation includes: when a single-phase ground fault occurs due to an asymmetrical short circuit, assuming phase a is the faulty phase, while the operating modes of phases b and c remain unchanged, the fault point is considered a newly added node in the network. The impedance simulation method suitable for photovoltaic short-circuit calculation using Gaussian iteration is used to modify the admittance matrix of phase a node to a short-circuit current calculation admittance matrix Y. AFurthermore, an impedance network equation for photovoltaic short-circuit calculation nodes suitable for Gaussian iteration is constructed. When a two-phase short circuit occurs due to an asymmetrical short circuit fault, it is assumed that phases b and c are the faulty phases. At this time, the operating mode of phase a remains unchanged. The connection point between the two phases is regarded as two newly added fault nodes. The impedance simulation method suitable for photovoltaic short-circuit calculation using Gaussian iteration is adopted to modify the admittance matrix of phases b and c into a short-circuit current calculation admittance matrix Y. BC The system constructs a photovoltaic short-circuit calculation node impedance network equation suitable for Gaussian iteration; the iteration module 230 is configured to combine the nonlinear piecewise expressions of the voltage and current of the new energy node, and solve the current and voltage when the new energy fails by iterative method, and then obtain the fault short-circuit current.

[0064] It should be understood that Figure 2 The modules and references described in the document Figure 1 The steps described in the text correspond to those in the method described above. Therefore, the operations, features, and corresponding technical effects described above also apply to the method described in the text. Figure 2 The various modules in the document will not be described in detail here.

[0065] In other embodiments, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the method for calculating the three-phase unbalanced short-circuit current of the distribution network in any of the above method embodiments.

[0066] In one embodiment, the computer-readable storage medium of the present invention stores computer-executable instructions, which are configured as follows:

[0067] Before the fault, the node voltage and injected current of each node, including the photovoltaic node, during normal operation were obtained using power flow calculations. The voltage of the i-th node during normal operation was... The current during normal operation is Injection power is

[0068] Based on Norton's equivalent, the power source is equivalent to a current source and the load is equivalent to an impedance. The admittance matrix is ​​calculated based on the equivalent circuit model after a three-phase asymmetrical short circuit fault, and the photovoltaic short circuit calculation node impedance network equation suitable for Gaussian iteration is constructed.

[0069] By combining the nonlinear piecewise expressions of voltage and current at the new energy node, the current and voltage during a new energy fault are solved using an iterative method, and then the fault short-circuit current is obtained.

[0070] Computer-readable storage media may include a stored program area and a stored data area, wherein the stored program area may store an operating system and an application program required for at least one function; the stored data area may store data created based on the use of the distribution network three-phase unbalanced short-circuit current calculation device, etc. Furthermore, the computer-readable storage medium may include high-speed random access memory, and may also include memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the computer-readable storage medium may optionally include memory remotely disposed relative to a processor, and this remote memory may be connected to the distribution network three-phase unbalanced short-circuit current calculation device via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0071] Figure 3 This is a schematic diagram of the structure of the electronic device provided in the embodiment of the present invention, such as... Figure 3 As shown, the device includes a processor 310 and a memory 320. The electronic device may also include an input device 330 and an output device 340. The processor 310, memory 320, input device 330, and output device 340 can be connected via a bus or other means. Figure 3 Taking a bus connection as an example, the memory 320 is the computer-readable storage medium described above. The processor 310 executes various server functions and data processing by running non-volatile software programs, instructions, and modules stored in the memory 320, thereby implementing the distribution network three-phase unbalanced short-circuit current calculation method described in the above embodiment. The input device 330 can receive input digital or character information and generate key signal inputs related to user settings and function control of the distribution network three-phase unbalanced short-circuit current calculation device. The output device 340 may include a display screen or other display device.

[0072] The aforementioned electronic device can execute the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0073] In one implementation, the above-described electronic device is used in a three-phase unbalanced short-circuit current calculation device for a distribution network, serving as a client, and includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to:

[0074] Before the fault, the node voltage and injected current of each node, including the photovoltaic node, during normal operation were obtained using power flow calculations. The voltage of the i-th node during normal operation was... The current during normal operation is Injection power is

[0075] Based on Norton's equivalent, the power source is equivalent to a current source and the load is equivalent to an impedance. The admittance matrix is ​​calculated based on the equivalent circuit model after a three-phase asymmetrical short circuit fault, and the photovoltaic short circuit calculation node impedance network equation suitable for Gaussian iteration is constructed.

[0076] By combining the nonlinear piecewise expressions of voltage and current at the new energy node, the current and voltage during a new energy fault are solved using an iterative method, and then the fault short-circuit current is obtained.

[0077] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating a three-phase asymmetric short-circuit current of a distribution network considering photovoltaics, characterized in that, Comprise: Step A: Before the fault, the node voltage and injection current of each node including the photovoltaic node in normal operation are obtained by using the power flow calculation, wherein the voltage of the ith node in normal operation is , the current in normal operation is , and the injection power is ; Step B: according to the Norton equivalent into a current source, the load is equivalent to impedance, based on the establishment of the equivalent circuit model after the occurrence of three-phase asymmetric short-circuit fault calculation admittance matrix, and construct suitable for Gauss iteration photovoltaic short-circuit calculation node impedance network equation, wherein the construction of photovoltaic short-circuit calculation node impedance network equation specifically includes: When a single-phase ground fault of asymmetric short-circuit fault occurs, assuming that phase a is the fault phase, at this time the operation modes of phases b and c remain unchanged, the fault point is regarded as a newly added node in the network, and the impedance simulation method suitable for photovoltaic short-circuit calculation of Gauss iteration is used to modify the admittance matrix of the a-phase node into a short-circuit current calculation admittance matrix , and a node impedance network equation suitable for photovoltaic short-circuit calculation of Gauss iteration is constructed. When two-phase inter-phase short-circuit occurs in asymmetric short-circuit fault, assuming that phases b and c are fault phases, at this time, the operation mode of phase a remains unchanged, the connection between the two phases is regarded as two newly added fault nodes, the impedance simulation method suitable for Gaussian iteration is used to modify the node admittance matrix of phases b and c into a short-circuit current calculation admittance matrix , and a node impedance network equation suitable for Gaussian iteration is constructed for photovoltaic short-circuit calculation. Step C: simultaneous nonlinear piecewise expression of new energy node voltage and current, the current and voltage of new energy fault are solved by iteration method, and then the fault short-circuit current is calculated, wherein, in step C, the simultaneous nonlinear piecewise expression of new energy node voltage and current, the current and voltage of new energy fault are solved by iteration method, and then the fault short-circuit current is calculated, including: Step C1: the nonlinear piecewise expression of new energy current and voltage is: ， ， wherein is the voltage magnitude of photovoltaic node m, is the phase angle of the voltage of photovoltaic node m after the k-1th iteration, is the voltage magnitude of photovoltaic node m after the k-1th iteration, is the current magnitude of photovoltaic node m, is the magnitude of the output current of photovoltaic node m after the kth iteration, is the injection current vector of photovoltaic node m, ; Step C2: Assuming the output of the photovoltaic power supply is constant, the short-circuit voltage value of each node after the fault is solved, which is set as the initial value of the voltage iteration of the short-circuit current node admittance equation The voltage iteration formula is as follows: ， wherein Vik+1is the voltage value of the ith node after the k+1th iteration, Y is the admittance matrix, Ijkis the current value of the jth node after the kth iteration, is the ith node, is the jth node, and n is the total number of nodes. Step C3: Repeat the iterative calculation until the voltage difference between each node on both sides is reached. If the value is less than a preset threshold, the node voltage value obtained after several iterations is obtained. Therefore, it is possible to base it on The short-circuit current values ​​of each branch were calculated, where for The voltage vector at node j after the next iteration. Let be the impedance between node i and node j. Let be the injected current vector between node i and node j.

2. The method for calculating the three-phase asymmetric short-circuit current of the distribution network considering photovoltaic according to claim 1, characterized in that, In step B, the impedance simulation method for photovoltaic short-circuit calculation suitable for Gauss iteration modifies the a-phase node admittance matrix to a short-circuit current calculation admittance matrix comprising: Step B1: the node load simulation admittance is calculated by using the node injected power and node voltage under normal network state: ， wherein Yi is the admittance of the load at node i, Qi* is the conjugate of the injection power at node i, Vi is the voltage at the i-th node when the system is in normal operation, Vi* is the conjugate of the voltage at node i when the system is in normal operation. Equivalent load admittance, load node injection current vector ; Step B2: The generator is modeled by Norton equivalent, the equivalent reactance of the generator is The equivalent admittance of the generator is then ， In the formula, Y is the equivalent admittance of the generator. Step B3: When in single-phase ground fault, the fault point is considered as a new node in the network, and the single-phase ground admittance of the fault point is set as The PQ node self-admittance in the original admittance matrix is added to the load simulation admittance, the short-circuit fault node is added to its ground admittance, and the balance node self-admittance is added to the equivalent reactance of the generator, to obtain the photovoltaic short-circuit current admittance matrix Expression: ， wherein, is the self-admittance of load node 1 in power flow calculation, is the self-admittance of load node n in power flow calculation, is the self-admittance of PV node 1 in power flow calculation, is the mutual-admittance of PV node m and load node n in power flow calculation, is the load analog admittance of node n.

3. The method for calculating the three-phase asymmetric short-circuit current of the distribution network considering photovoltaic according to claim 2, characterized in that, In step B, the impedance simulation method for photovoltaic short-circuit calculation suitable for Gauss iteration modifies the b, c phase node admittance matrix to a short-circuit current calculation admittance matrix comprising: Step B4: When in two-phase interphase fault, the fault phase connection is considered as a new line added in the network, and two new nodes are set at the beginning and end of the line, and the admittance of the two-phase interphase connection is set as The PQ node self-admittance in the original admittance matrix is added with the load simulation admittance, the short-circuit fault node is added with its ground admittance, and the balance node self-admittance is added with the equivalent reactance of the generator, to obtain the photovoltaic short-circuit current admittance matrix Expression: ， Wherein, wherein is the new mutual admittance between nodes, which has the value , , .

4. The method for calculating the three-phase asymmetric short-circuit current of the distribution network considering photovoltaic according to claim 3, characterized in that, In step B, the construction of photovoltaic short-circuit calculation node impedance network equation suitable for Gauss iteration includes: Step B5: The pre-fault power flow calculation gives the injection current at bus 1 as , the bus voltage as , the generator is modeled using the Norton equivalent and one phase model is represented as three phase model, so that the generator output current in one phase is calculated as: , wherein is the imaginary part symbol, is the generator equivalent reactance; Let the generator output current before and after the short circuit fault be unchanged, the equivalent reactance of the generator unchanged, the current injected by the generator phase at the balance node 1 during the fault can be expressed as: ； That is, the relationship between the injected current and the node voltage at the photovoltaic node is: ， wherein Imis the injection current of the mth photovoltaic node, Vmis the node voltage of the mth photovoltaic node; Step B6: under the condition of single-phase ground fault, the short-circuit calculation node impedance network equation expression is: wherein is a matrix of the individual node voltages of the a phase, is a matrix of the individual node currents of the a phase; wherein , wherein, is the node voltage of the first node of phase a, is the node voltage at the fault of phase a, is the node voltage of the mth photovoltaic node of phase a, is the node voltage of the nth node of phase a; Under the condition of two-phase interphase short-circuit, the short-circuit calculation node impedance network equation expression is: ， wherein .

5. A device for calculating a three-phase asymmetric short-circuit current of a distribution network considering photovoltaics, characterized by Comprise: The computing module is configured to, before the fault, utilize power flow calculation to obtain node voltage and injection current of each node including the photovoltaic node when the nodes are normally operated, wherein the voltage of the i-th node when the nodes are normally operated is , the current when the nodes are normally operated is , and the injection power is ; The construction module is configured to equivalent the power into a current source according to the Norton equivalent, equivalent the load into impedance, calculate the admittance matrix based on the establishment of the equivalent circuit model after the occurrence of three-phase asymmetric short-circuit fault, and construct photovoltaic short-circuit calculation node impedance network equation suitable for Gauss iteration, wherein the construction of photovoltaic short-circuit calculation node impedance network equation specifically includes: When a single-phase ground fault of asymmetric short-circuit fault occurs, assuming that phase a is the fault phase, at this time the operation modes of phases b and c remain unchanged, the fault point is regarded as a newly added node in the network, the node admittance matrix of phase a is modified into a short-circuit current calculation admittance matrix by using the impedance simulation method suitable for photovoltaic short-circuit calculation of Gauss iteration , and a node impedance network equation suitable for photovoltaic short-circuit calculation of Gauss iteration is constructed; when a two-phase interphase short-circuit of asymmetric short-circuit fault occurs, assuming that phases b and c are the fault phases, at this time the operation mode of phase a remains unchanged, the two-phase connection is regarded as two newly added fault nodes, the node admittance matrix of phases b and c is modified into a short-circuit current calculation admittance matrix by using the impedance simulation method suitable for photovoltaic short-circuit calculation of Gauss iteration , and a node impedance network equation suitable for photovoltaic short-circuit calculation of Gauss iteration is constructed; The iteration module is configured to simultaneously solve the nonlinear piecewise expression of new energy node voltage and current, the current and voltage of new energy fault are solved by iteration method, and then the fault short-circuit current is calculated, wherein, in step C, the simultaneous nonlinear piecewise expression of new energy node voltage and current, the current and voltage of new energy fault are solved by iteration method, and then the fault short-circuit current is calculated, including: Step C1: the nonlinear piecewise expression of new energy current and voltage is: ， ， wherein is the voltage magnitude of photovoltaic node m, is the phase angle of the voltage of photovoltaic node m after the k-1th iteration, is the voltage magnitude of photovoltaic node m after the k-1th iteration, is the current magnitude of photovoltaic node m, is the magnitude of the output current of photovoltaic node m after the kth iteration, is the injection current vector of photovoltaic node m, ; Step C2: Assuming the output of the photovoltaic power supply is constant, the short-circuit voltage value of each node after the fault is solved, which is set as the initial value of the voltage iteration of the short-circuit current node admittance equation The voltage iteration formula is as follows: ， wherein Vik+1is the voltage value of the i-th node after the k+1-th iteration, Y is the admittance matrix, Ijkis the current value of the j-th node after the k-th iteration, is the i-th node, is the j-th node, and n is the total number of nodes. Step C3: Repeat the iterative calculation until the voltage difference between each node on both sides is reached. If the value is less than a preset threshold, the node voltage value obtained after several iterations is obtained. Therefore, it is possible to base it on The short-circuit current values ​​of each branch were calculated, where for The voltage vector at node j after the next iteration. Let be the impedance between node i and node j. Let be the injected current vector between node i and node j.

6. An electronic device, comprising: Comprise: At least one processor, and a memory connected with the at least one processor in communication, wherein the memory stores instructions executable by the at least one processor, the instructions are executed by the at least one processor to enable the at least one processor to execute the method of any one of claims 1 to 4.

7. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to realize the method of any one of claims 1 to 4.

Images