Impedance response calculation method for three-phase alternating current system model of flexible direct current battery swap station

Abstract

The invention discloses an impedance response calculation method for a three-phase alternating current system model of a flexible direct current battery swap station, and relates to the technical field of power system analysis and control. The method comprises the following steps: taking a three-phase alternating current system model of the flexible direct current battery swap station as a directed graph, obtaining tree branches and connecting branches of the directed graph, and determining a branch admittance matrix of the system model according to the tree branches and the connecting branches; performing cut set selection on the directed graph, determining a cut set matrix of the system model, and determining a cut set voltage column vector of the system model according to an input power supply column vector, a branch admittance matrix and the cut set matrix of the system model; according to the relation between the cut-set voltage and the branch voltage and the cut-set voltage column vector of the system model, the voltage and the current on the input end branch of each phase of the system model are determined, and therefore the input impedance response of each phase of the system model is determined. According to the method, the calculation efficiency of the impedance response of the three-phase alternating current system model of the flexible direct current battery swap station can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system analysis and control, and particularly relates to a method for calculating impedance response of a three-phase AC system model of a flexible DC substation. Background Art

[0002] With the rapid development of power electronics technology, flexible DC transmission technology has shown great potential in fields such as long-distance power transmission, grid connection of offshore wind power, and interconnection of urban power grids. Traditional AC transmission systems have many limitations in long-distance, large-capacity power transmission and stability, while flexible DC transmission technology has gradually become an important part of modern power systems due to its excellent control flexibility and good power transmission performance.

[0003] Among them, to ensure the reliable and efficient operation of a flexible DC substation, it is extremely necessary to analyze the impedance response of the three-phase AC system model of the flexible DC substation. However, in the prior art, the efficiency of calculating the impedance response of the three-phase AC system model of the flexible DC substation is relatively low. Summary of the Invention

[0004] Based on this, in view of the above technical problems, it is necessary to provide a method for calculating impedance response of a three-phase AC system model of a flexible DC substation, which can improve the calculation efficiency of the impedance response of the three-phase AC system model of the flexible DC substation.

[0005] The present invention adopts the following technical solutions:

[0006] The present invention provides a method for calculating impedance response of a three-phase AC system model of a flexible DC substation, including:

[0007] Regarding the three-phase AC system model of the flexible DC substation as a directed graph, obtaining the tree branches and link branches of the directed graph, and determining the branch admittance matrix of the system model according to the tree branches and link branches;

[0008] Performing cut-set selection on the directed graph to determine the cut-set matrix of the system model, and determining the cut-set voltage column vector of the system model according to the input power source column vector, branch admittance matrix, and cut-set matrix of the system model;

[0009] Determining the voltage and current on each phase input terminal branch of the system model according to the relationship between the cut-set voltage and the branch voltage, and the cut-set voltage column vector of the system model;

[0010] Determining the input impedance response of each phase of the system model according to the voltage and current on each phase input terminal branch of the system model.

[0011] Optionally, determining the branch admittance matrix of the system model according to the tree branches and link branches includes:

[0012] Determine the tree-branch admittance matrix according to the admittance of each tree branch;

[0013] Determine the link-branch admittance matrix according to the admittance of each link branch;

[0014] Determine the branch admittance matrix according to the tree-branch admittance matrix and the link-branch admittance matrix; the branch admittance matrix Y is:

[0015]

[0016] where Y tr and Y l are the tree-branch admittance matrix and the link-branch admittance matrix respectively.

[0017] Optionally, perform cut-set selection on the directed graph to determine the cut-set matrix of the system model, including:

[0018] Cut the tree branches in the directed graph to obtain the fundamental cut-sets;

[0019] Determine the cut-set matrix according to the relationship between each branch in the directed graph and the fundamental cut-sets.

[0020] Optionally, determine the cut-set voltage column vector of the system model according to the input power source column vector, the branch admittance matrix and the cut-set matrix of the system model, including:

[0021] Determine the cut-set voltage equation according to Kirchhoff's voltage law and Kirchhoff's current law;

[0022] Simplify the cut-set voltage equation according to the type of the input power source of the system model, the relationship between the branch admittance matrix and the cut-set matrix and the cut-set admittance matrix to obtain the simplified cut-set voltage equation;

[0023] Determine the cut-set voltage column vector of the system model based on the simplified cut-set voltage equation, the input power source column vector, the branch admittance matrix and the cut-set matrix of the system model.

[0024] Optionally, the cut-set voltage equation is QYQ T U t =QYU s -QI s ;

[0025] where Q is the cut-set matrix, Q T is the inverse of Q, Y is the branch admittance matrix, U t is the cut-set voltage column vector, U s is the input voltage source column vector, and I s is the input current source column vector;

[0026] The relationship between the branch admittance matrix, the cut-set matrix, and the cut-set admittance matrix is: Y t = QYQ T ;

[0027] where Y t is the cut-set admittance matrix;

[0028] If the input power source type of the system model is a voltage source, the simplified cut-set voltage equation is: Y t U t = QYU s ;

[0029] If the input power source type of the system model is a current source, the simplified cut-set voltage equation is: Y t U t = -QI s .

[0030] Optionally, the input power source type of the system model is a voltage source; the input power source column vector is the input voltage source column vector; based on the simplified cut-set voltage equation, the input power source column vector of the system model, the branch admittance matrix, and the cut-set matrix, determine the cut-set voltage column vector of the system model, including:

[0031] Determine the cut-set admittance matrix according to the branch admittance matrix and the cut-set matrix;

[0032] Substitute the input voltage source column vector, the cut-set admittance matrix, the branch admittance matrix, and the cut-set matrix of the system model into the simplified cut-set voltage equation to obtain the cut-set voltage column vector.

[0033] Optionally, according to the relationship between the cut-set voltage, the cut-set matrix, and the branch voltage, and the cut-set voltage column vector and the cut-set matrix of the system model, determine the voltage and current on each phase input terminal branch of the system model, including:

[0034] Substitute the cut-set voltage column vector and the cut-set matrix of the system model into the relationship between the cut-set voltage, the cut-set matrix, and the branch voltage to obtain the branch voltage vector of the system model; the relationship between the cut-set voltage, the cut-set matrix, and the branch voltage is: U = Q T U t ;

[0035] Obtain the voltage on each phase input terminal branch of the system model from the input voltage source column vector, and obtain the voltage of the branch where each phase is located from the branch voltage vector;

[0036] Determine the current on each phase input terminal branch respectively according to the voltage on each phase input terminal branch, the voltage of the branch where each phase is located, and the branch admittance of each phase.

[0037] Optionally, the calculation formulas for the current on each phase input terminal branch are respectively:

[0038]

[0039] Among them, I1, I2, and I3 are the currents on the input branches of the A-phase, B-phase, and C-phase of the system model respectively, U1, U2, and U3 are the voltages on the branches where the A-phase, B-phase, and C-phase of the system model are located respectively, U A 、U B and U C are the voltages on the input branches of the A-phase, B-phase, and C-phase of the system model respectively, r A 、r B and r C are the admittances on the input branches of the A-phase, B-phase, and C-phase of the system model respectively.

[0040] The present invention provides an impedance response calculation device for a three-phase AC system model of a flexible DC substation, including:

[0041] A first determination module, configured to regard the three-phase AC system model of the flexible DC substation as a directed graph, obtain the tree branches and link branches of the directed graph, and determine the branch admittance matrix of the system model according to the tree branches and link branches;

[0042] A second determination module, configured to perform cut-set selection on the directed graph, determine the cut-set matrix of the system model, and determine the cut-set voltage column vector of the system model according to the input power supply column vector, branch admittance matrix, and cut-set matrix of the system model;

[0043] A third determination module, configured to determine the voltage and current on the input branch of each phase of the system model according to the relationship between the cut-set voltage and the branch voltage, and the cut-set voltage column vector of the system model;

[0044] A fourth determination module, configured to determine the input impedance response of each phase of the system model according to the voltage and current on the input branch of each phase of the system model.

[0045] The present invention provides a computer-readable storage medium, where the storage medium stores a computer program, and when the computer program is executed by a processor, the above-mentioned impedance response calculation method for a three-phase AC system model of a flexible DC substation is implemented.

[0046] The present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the above-mentioned impedance response calculation method for a three-phase AC system model of a flexible DC substation is implemented.

[0047] The above-mentioned at least one technical solution adopted by the present invention can achieve the following beneficial effects:

[0048] Take the three-phase AC system model of the flexible DC substation as a directed graph, obtain the tree branches and link branches of the directed graph, and determine the branch admittance matrix of the system model according to the tree branches and link branches; perform cut-set selection on the directed graph to determine the cut-set matrix of the system model. By selecting the basic cut-sets, the voltage vector of the required branches can be quickly solved, avoiding the need to solve the voltage and current vectors of each branch in the entire system using traditional methods, thereby efficiently solving the impedance response of the system model and improving the efficiency of calculating the impedance response of the system model. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0050] Figure 1 It is a schematic flow chart of a method for calculating the impedance response of a three-phase AC system model for a flexible DC substation provided by the present invention;

[0051] Figure 2 It is a structural diagram of a three-phase AC system model of a converter station including a three-phase power supply provided by the present invention;

[0052] Figure 3 It is a schematic diagram of a directed graph, selection of tree branches, and selection of cut-sets of a system model provided by the present invention;

[0053] Figure 4 It is a schematic diagram of a device for calculating the impedance response of a three-phase AC system model for a flexible DC substation provided by the present invention;

[0054] Figure 5 It is a schematic diagram of a computer device for implementing a method for calculating the impedance response of a three-phase AC system model for a flexible DC substation provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0056] The execution subject of the method in the present invention can be a server set up in a service platform, or a device such as a desktop computer or a laptop computer that can execute the solution of the present invention.

[0057] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0058] Figure 1 The following is a schematic flowchart of a method for calculating the impedance response of a three-phase AC system model of a flexible DC substation in the present invention, which specifically includes the following steps:

[0059] S101, taking the three-phase AC system model of the flexible DC substation as a directed graph, obtaining the tree branches and link branches of the directed graph, and determining the branch admittance matrix of the system model according to the tree branches and link branches.

[0060] The structure of the three-phase AC system model of the flexible DC substation is as Figure 2 shown. This system model includes a three-phase voltage filter, a three-phase transformer, and a three-phase reactor. This system model can be regarded as a directed graph. The branch direction is specified, and the tree branches and link branches of this directed graph are selected.

[0061] The equivalent directed graph of the system model is as Figure 3 shown. Figure 3 In, the direction of the arrow of each branch represents the direction of the branch (the flow direction of the branch current). This directed graph has 13 nodes and 48 branches. Figure 3 In, the red branches are the tree branches, and the rest of the branches are link branches.

[0062] Optionally, determining the branch admittance matrix of the system model according to the tree branches and link branches includes: determining the tree branch admittance matrix according to the admittance of each tree branch; determining the link branch admittance matrix according to the admittance of each link branch; determining the branch admittance matrix according to the tree branch admittance matrix and the link branch admittance matrix; the branch admittance matrix Y is:

[0063]

[0064] Wherein, Y tr and Y l are the tree branch admittance matrix and the link branch admittance matrix respectively.

[0065] The form of the tree branch admittance is:

[0066] Y tr = diag[r A y2 y3 y4 y5 y6 y7 y8 y9 y10 y11 y12] (2)

[0067] Wherein, r A , y2, y3, y4, y5, y6, y7, y8, y9, y10, y11, y12 are the admittances of the tree branches in the directed graph respectively.

[0068] The form of the link - branch admittance matrix is as follows:

[0069]

[0070] Among them, each element in Y l is the admittance of the link - branch in the directed graph respectively.

[0071] S102: Conduct cut - set selection for the directed graph to determine the cut - set matrix of the system model, and determine the cut - set voltage column vector of the system model according to the input power - supply column vector, branch - admittance matrix and cut - set matrix of the system model.

[0072] Since the three - phase AC system of the flexible DC substation is complex, often including a three - phase filtering system, a three - phase transformer system and a three - phase reactor system, the cut - set voltage method is an effective network analysis method. By only selecting appropriate basic cut - sets, the voltage of the branch cut by the cut - set can be directly solved, and then the voltage vector of the required branch can be quickly solved, so as to efficiently solve the impedance response of the system.

[0073] Optionally, conducting cut - set selection for the directed graph to determine the cut - set matrix of the system model includes: cutting the tree - branch in the directed graph to obtain the basic cut - set; determining the cut - set matrix according to the relationship between each branch in the directed graph and the basic cut - set.

[0074] Specifically, for cut - set selection, please continue to refer to Figure 3 , the selected cut - sets and their directions are represented by blue solid lines and arrows. Since each selected cut - set cuts a tree - branch respectively, the whole cut - set is the basic cut - set, and the number is 12. At this time, the cut - set matrix is a 12×48 - order matrix, denoted as Q. The rows of the cut - set matrix correspond to the cut - sets, and the columns correspond to the branches. Then the incidence relationship between the cut - set and the branch can be represented by any of its elements q ij When q ij = 1, it means that branch j belongs to cut - set i and the direction of branch j is the same as that of cut - set i; when q ij = - 1, it still means that branch j belongs to cut - set i, but the direction of branch j is opposite to that of cut - set i; when q ij = 0, it still means that branch j does not belong to cut - set i. According to this rule, the cut - set matrix Q can be written.

[0075] The specific form of the cut - set matrix Q is as follows: Among them, 1 t is the cut - set matrix of the tree, which is a 12 - order identity matrix, and Q l is the cut - set matrix of the branch, with a dimension of 12×36.

[0076]

[0077] In one embodiment, according to the input power supply column vector, branch admittance matrix, and cut-set matrix of the system model, determining the cut-set voltage column vector of the system model includes: determining the cut-set voltage equation according to Kirchhoff's voltage law and Kirchhoff's current law; simplifying the cut-set voltage equation according to the relationship between the input power supply type of the system model, the branch admittance matrix, and the cut-set matrix and the cut-set admittance matrix to obtain a simplified cut-set voltage equation; and determining the cut-set voltage column vector of the system model based on the simplified cut-set voltage equation, the input power supply column vector, the branch admittance matrix, and the cut-set matrix of the system model.

[0078] Kirchhoff's voltage law and Kirchhoff's current law are as follows:

[0079]

[0080] where I is the branch current, U t is the cut-set voltage column vector, and U s is the input voltage source column vector.

[0081] U s = [U A 0 0…0 U B U C 1×48 (6)

[0082] where U A , U B , and U C are the phase voltages of phases A, B, and C of the three-phase system, respectively.

[0083] Further, the cut-set voltage equation is derived as:

[0084] QYQ T U t = QYU s - QI s (7)

[0085] where Q is the cut-set matrix, Q T is the inverse of Q, Y is the branch admittance matrix, U t is the cut-set voltage column vector, U s is the input voltage source column vector, and I s is the input current source column vector.

[0086] The relationship between the branch admittance matrix, the cut-set matrix, and the cut-set admittance matrix is:

[0087] Y t = QYQ T (8)

[0088] where Y t is the cut-set admittance matrix.

[0089] The input power supply type of the system model is a voltage source, and the input current source is 0. Then, the simplified equation of the cut-set voltage is as follows:

[0090] Y t U t = QYU s (9)

[0091] According to formula (9), the cut-set voltage column vector U t .

[0092] Specifically, if the input power supply type of the system model is a voltage source; the input power supply column vector is the input voltage source column vector; based on the simplified equation of the cut-set voltage, the input power supply column vector of the system model, the branch admittance matrix, and the cut-set matrix, determine the cut-set voltage column vector of the system model, including: determining the cut-set admittance matrix according to the branch admittance matrix and the cut-set matrix (formula (8)); substituting the input voltage source column vector, the cut-set admittance matrix, the branch admittance matrix, and the cut-set matrix of the system model into the simplified equation of the cut-set voltage (formula (9)) to obtain the cut-set voltage column vector.

[0093] S103. According to the relationship between the cut-set voltage, the cut-set matrix, and the branch voltage, as well as the cut-set voltage column vector and the cut-set matrix of the system model, determine the voltage and current on each phase input terminal branch of the system model.

[0094] Since the calculation formula of the impedance response is:

[0095]

[0096] where Z(ω) is the impedance response, U 入端 is the input terminal voltage, and I 入端 is the input terminal current.

[0097] Then, in the case where the input power supply type of the system model is a voltage source, according to the relationship between the cut-set voltage, the cut-set matrix, and the branch voltage, as well as the cut-set voltage column vector and the cut-set matrix of the system model, determine the voltage and current on each phase input terminal branch of the system model, including: substituting the cut-set voltage column vector and the cut-set matrix of the system model into the relationship formula between the cut-set voltage, the cut-set matrix, and the branch voltage to obtain the branch voltage vector of the system model; the relationship formula between the cut-set voltage, the cut-set matrix, and the branch voltage is: U = Q T U t ; obtain the voltage on each phase input terminal branch of the system model from the input voltage source column vector, and obtain the voltage of the branch where each phase is located from the branch voltage vector; determine the current on each phase input terminal branch according to the voltage on each phase input terminal branch, the voltage of the branch where each phase is located, and the branch admittance of each phase.

[0098] Specifically, according to the relationship between the cut-set voltage, the cut-set matrix, and the branch voltage, Figure 3 the branch where the A-phase input terminal in t (i.e., the 1st branch as a tree branch) is only cut by cut-set ①, so directly take U t (1,1) as the voltage U1 of the branch where the A-phase is located in the branch voltage vector, that is, U1 = U U A is the voltage on the branch of the A-phase input terminal, and r A is the branch admittance of the A-phase; the B-phase input terminal is cut by cut-sets ①②③, and the voltage U2 of the branch where the B-phase is located in the branch voltage vector is U t (1,1)+U t (2,1)-U t (3,1). At this time, the current of the B-phase input terminal U B is the voltage on the branch of the B-phase input terminal, and r B is the branch admittance of the B-phase; the C-phase input terminal is cut by cut-sets ①②④, and the voltage U3 of the branch where the C-phase is located in the branch voltage vector is U t (1,1)+U t (2,1)-U t (4,1). At this time, the current of the C-phase input terminal U C is the voltage on the branch of the C-phase input terminal, and r C is the branch admittance of the C-phase.

[0099] S104. Determine the input impedance response of each phase of the system model according to the voltage and current on the branch of each phase input terminal of the system model.

[0100] For the entire three-phase AC system, the input impedance response Z A (ω) of the A-phase of the system model is:

[0101]

[0102] Similarly for the B and C phases, they are respectively:

[0103]

[0104] Among them, Z B (ω) and Z C (ω) are the input impedance responses of the B-phase and C-phase respectively.

[0105] The present invention uses the cut-set voltage method to solve the system model. First, the system model is regarded as a directed graph, and then the tree branches and link branches of this graph are selected. According to the definition of the basic cut-set and the given branch current directions, appropriate basic cut-sets are selected, and then the basic cut-set matrix of the system model is determined. According to Kirchhoff's voltage law, a cut-set voltage equation is established, and further its nodal admittance matrix is obtained, and the cut-set voltage vector is calculated. According to the relationship between the cut-set voltage and the branch voltage, the voltage and current on the input branch of each phase of the system are obtained, and then the input impedance response of each phase of the system is calculated. The present invention can be used to guide system design and evaluate the dynamic response characteristics of the system at different frequencies. The method of the present invention can provide important reference and guidance for the impedance response analysis of the three-phase AC system model of a flexible DC substation.

[0106] Based on Figure 1 the impedance response calculation method for the three-phase AC system model of a flexible DC substation shown in

[0107] When applying the impedance response calculation method for the three-phase AC system model of a flexible DC substation provided by the present invention, it is not necessary to execute according to Figure 1 the order of the steps shown. The specific execution order of each step can be determined according to needs, and the present invention does not limit this.

[0108] The above is the impedance response calculation method for the three-phase AC system model of a flexible DC substation provided by one or more embodiments of the present invention. Based on the same idea, the present invention also provides a corresponding impedance response calculation device for the three-phase AC system model of a flexible DC substation, as Figure 4 shown.

[0109] Figure 4 The schematic diagram of an impedance response calculation device for the three-phase AC system model of a flexible DC substation provided by the present invention. The device 400 includes:

[0110] A first determination module 401, configured to regard the three-phase AC system model of a flexible DC substation as a directed graph, obtain the tree branches and link branches of the directed graph, and determine the branch admittance matrix of the system model according to the tree branches and link branches;

[0111] A second determination module 402, configured to perform cut-set selection on the directed graph, determine the cut-set matrix of the system model, and determine the cut-set voltage column vector of the system model according to the input power source column vector, branch admittance matrix, and cut-set matrix of the system model;

[0112] A third determination module 403, configured to determine the voltage and current on the input branch of each phase of the system model according to the relationship between the cut-set voltage and the branch voltage, and the cut-set voltage column vector of the system model;

[0113] The fourth determination module 404 is configured to determine the input impedance response of each phase of the system model according to the voltage and current on the branch of the input end of each phase of the system model.

[0114] For the specific limitations of the impedance response calculation device for the three-phase AC system model of the flexible DC substation, reference can be made to the limitations of the impedance response calculation method for the three-phase AC system model of the flexible DC substation described above, which will not be elaborated here. Each module in the above impedance response calculation device for the three-phase AC system model of the flexible DC substation can be implemented in whole or in part by software, hardware, and their combination. The above modules can be embedded in the processor in the computer device in hardware form or be independent of it, or can be stored in the memory in the computer device in software form, so as to facilitate the processor to call and execute the operations corresponding to the above modules.

[0115] The present invention also provides a computer-readable storage medium, which stores a computer program that can be used to execute the above Figure 1 provided impedance response calculation method for the three-phase AC system model of the flexible DC substation.

[0116] The present invention also provides Figure 5 the structural schematic diagram of the computer device shown in, as Figure 5 shown, at the hardware level, the computer device includes a processor, an internal bus, a network interface, a memory, and a non-volatile memory. Of course, other hardware required for other services may also be included. The processor reads the corresponding computer program from the non-volatile memory into the memory and then runs it to implement the above Figure 1 provided impedance response calculation method for the three-phase AC system model of the flexible DC substation.

[0117] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium used in the various embodiments provided by the present invention can include at least one of non-volatile and volatile memories. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0118] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope recorded by the present invention.

Claims

1. A method for calculating impedance response of a three-phase AC system model for a flexible DC power exchange station, characterized in that: include: The three-phase AC system model of the flexible DC power exchange station is taken as a directed graph, and the tree branches and the connecting branches of the directed graph are obtained, and the branch admittance matrix of the system model is determined according to the tree branches and the connecting branches; Performing cut set selection on the directed graph to determine a cut set matrix of the system model, and determining a cut set voltage column vector of the system model according to an input power column vector of the system model, the branch admittance matrix and the cut set matrix; Determine the voltage and current on each phase input branch of the system model according to the relationship between the cut set voltage, the cut set matrix and the branch voltage, and the cut set voltage column vector and the cut set matrix of the system model; The input impedance response of each phase of the system model is determined according to the voltage and current on the input terminal branch of each phase of the system model.

2. The method according to claim 1, characterized in that The step of determining a branch admittance matrix of the system model according to the tree branches and the connected branches comprises: According to the admittance of each branch of the tree, determine the admittance matrix of the branch of the tree; According to the admittance of each connected branch, determine the connected branch admittance matrix; The branch admittance matrix is ​​determined according to the tree branch admittance matrix and the connected branch admittance matrix; the branch admittance matrix Y is: Among them, Y tr and Y l They are the tree branch admittance matrix and the connected branch admittance matrix respectively.

3. The method according to claim 1, characterized in that The step of performing cut set selection on the directed graph to determine a cut set matrix of the system model includes: Cutting the tree branches in the directed graph to obtain a basic cut set; The cut set matrix is ​​determined according to the relationship between each branch in the directed graph and the basic cut set.

4. The method according to claim 1, characterized in that Determining the cut set voltage column vector of the system model according to the input power column vector of the system model, the branch admittance matrix and the cut set matrix includes: According to Kirchhoff's voltage law and Kirchhoff's current law, the cut set voltage equation is determined; According to the input power type of the system model and the relationship between the branch admittance matrix and the cut set matrix and the cut set admittance matrix, the cut set voltage equation is simplified to obtain a simplified cut set voltage equation; The cut set voltage column vector of the system model is determined based on the cut set voltage simplified equation, the input power column vector of the system model, the branch admittance matrix and the cut set matrix.

5. The method according to claim 4, characterized in that The cut set voltage equation is QYQ T U t =QYU s -QI s ; Among them, Q is the cut set matrix, Q T is the inverse of Q, Y is the branch admittance matrix, U t is the cut set voltage column vector, U s is the input voltage source column vector, I s is the column vector of input current source; The relationship between the branch admittance matrix and the cut set matrix and the cut set admittance matrix is: t =QYQ T ; Among them, Y t is the cut set admittance matrix; The input power type of the system model is a voltage source, so the simplified equation of the cut set voltage is: t U t =QYU s ; The input power type of the system model is a current source, so the simplified equation of the cut-set voltage is: t U t =-QI s .

6. The method according to claim 5, characterized in that The input power type of the system model is a voltage source; the input power column vector is an input voltage source column vector; and determining the cut set voltage column vector of the system model based on the cut set voltage simplified equation, the input power column vector of the system model, the branch admittance matrix and the cut set matrix comprises: Determine a cut set admittance matrix according to the branch admittance matrix and the cut set matrix; The input voltage source column vector of the system model, the cut set admittance matrix, the branch admittance matrix and the cut set matrix are substituted into the cut set voltage simplified equation to obtain the cut set voltage column vector.

7. The method according to claim 6, characterized in that Determining the voltage and current on each phase input branch of the system model according to the relationship between the cut set voltage, the cut set matrix and the branch voltage, and the cut set voltage column vector and the cut set matrix of the system model, comprises: Substitute the cut set voltage column vector and the cut set matrix of the system model into the relationship between the cut set voltage, the cut set matrix and the branch voltage to obtain the branch voltage vector of the system model; the relationship between the cut set voltage, the cut set matrix and the branch voltage is: U = Q T U t ; Obtaining the voltage on each phase input terminal branch of the system model from the input voltage source column vector, and obtaining the voltage of each phase branch from the branch voltage vector; The current on the branch at the input end of each phase is determined according to the voltage on the branch at the input end of each phase, the voltage of the branch where each phase is located and the branch admittance of each phase.

8. The method according to claim 7, characterized in that The calculation formulas for the current on each phase input branch are: Among them, I1, I2 and I3 are the currents on the input branches of phase A, phase B and phase C of the system model respectively, U1, U2 and U3 are the voltages on the branches where phase A, phase B and phase C of the system model are located respectively, and U A , U B and U C are the voltages on the input branches of phase A, phase B and phase C of the system model, r A 、r B and r C They are the admittances on the input branches of phase A, phase B and phase C of the system model respectively.

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