A method and system for calculating voltage stability index based on wide-area measurement

Abstract

The present invention discloses a method and system for calculating a voltage stability index based on wide-area measurement. The method includes: obtaining the branch power flow direction, and determining the head end and the tail end of the branch according to the branch power flow direction; respectively obtaining the head-end voltage amplitude and the tail-end voltage amplitude of the branch based on a preset PMU; calculating the voltage stability index of each branch of the active distribution network system according to the head-end voltage amplitude and the tail-end voltage amplitude; and taking the maximum value of the voltage stability indexes of all branches at the same moment as the voltage stability index of the active distribution network system. Starting from the characteristic that the upper and lower half-branch voltage feasible solutions of the PV curve approach each other continuously during the voltage instability process, by using the node voltage amplitude information measured by the PMU, it is possible to quickly and accurately calculate the voltage stability index of the system online without measuring the line impedance parameters of the active distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of voltage stability analysis of active distribution networks, and particularly relates to a method and system for calculating voltage stability indexes based on wide-area measurement. Background Art

[0002] In recent years, distributed renewable energy represented by solar photovoltaic and wind energy has developed rapidly. The access of renewable energy will affect the magnitude and direction of the power flow in the power system, thus inevitably affecting the voltage stability of the system.

[0003] In view of this, studying the voltage stability and voltage collapse of active distribution networks has important social significance. At present, in order to measure the stable degree of the operation of the power system, many voltage stability indexes have been proposed. Commonly used static voltage stability indexes include voltage stability proximity indexes, local indexes, sensitivity indexes, and load margin indexes. However, these indexes all have the disadvantages of complex calculation and poor linearity. Especially when distributed power sources are connected, the changes in some bus voltage stability indexes are not obvious, and the sensitivity of the bus voltage stability when the load and distributed power sources change cannot be reflected. In addition, to calculate these indexes, the voltage parameters of each node in the system need to be obtained through power flow calculation, which greatly increases the calculation amount and weakens the judging speed of the power system stability.

[0004] With the rapid development of PMU (phasor measurement unit) technology, an on-line voltage stability index based on synchronous vector measurement - a static voltage stability index based on the feasible solution domain of the branch end voltage has come into people's vision. Such indexes can be directly calculated by combining the impedance matrix of the power system, PMU measurement information, generator output, and load parameters. However, these indexes have the following disadvantages:

[0005] 1) Calculating these indexes all requires prior knowledge of the branch impedance parameters of the power system, and in the special case where the branch impedance is 0, some indexes will also fail;

[0006] 2) When the line parameters change with the voltage level of the power system, the calculated voltage stability indexes are inaccurate;

[0007] 3) These indexes all contain the quadratic term of the post-line end voltage, which is extremely disadvantageous to the linearity of the indexes. Summary of the Invention

[0008] The present invention provides a method and system for calculating voltage stability indexes based on wide-area measurement, which are used to solve the technical problems of being unable to accurately calculate the voltage stability indexes of the system online and the poor linearity of the calculated voltage stability indexes.

[0009] In a first aspect, the present invention provides a method for calculating a voltage stability index based on wide-area measurement, including: obtaining the branch power flow direction, and determining the head and end of the branch according to the branch power flow direction; obtaining the head voltage amplitude and the end voltage amplitude of the branch based on a preset PMU respectively; calculating the voltage stability index of each branch of the active distribution network system according to the head voltage amplitude and the end voltage amplitude; and taking the maximum value of the voltage stability indices of all branches at the same moment as the voltage stability index of the active distribution network system.

[0010] In a second aspect, the present invention provides a system for calculating a voltage stability index based on wide-area measurement, including: a judgment module configured to obtain the branch power flow direction and determine the head and end of the branch according to the branch power flow direction; an obtaining module configured to obtain the head voltage amplitude and the end voltage amplitude of the branch based on a preset PMU respectively; a calculation module configured to calculate the voltage stability index of each branch of the active distribution network system according to the head voltage amplitude and the end voltage amplitude; and a selection module configured to take the maximum value of the voltage stability indices of all branches at the same moment as the voltage stability index of the active distribution network system.

[0011] In a third aspect, there is provided an electronic device, which 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, and the instructions are executed by the at least one processor so that the at least one processor can execute the steps of calculating the voltage stability index based on wide-area measurement according to any embodiment of the present invention.

[0012] In a fourth aspect, the present invention further provides a computer-readable storage medium, on which a computer program is stored, and when the program instructions are executed by a processor, the processor is caused to execute the steps of calculating the voltage stability index based on wide-area measurement according to any embodiment of the present invention.

[0013] The method and system for calculating the voltage stability index based on wide-area measurement of the present application start from the characteristic that the upper and lower half-branch voltage feasible solutions of the PV curve approach each other continuously during the voltage instability process, utilize the node voltage amplitude information measured by the PMU, and can quickly and accurately calculate the voltage stability index of the system online without measuring the line impedance parameters of the active distribution network. Moreover, there is no quadratic term of the branch terminal voltage in the derived voltage stability index calculation formula, which greatly enhances the linearity of the index and is conducive to providing accurate voltage stability information to dispatchers. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0015] Figure 1 It is a flowchart of a method for calculating voltage stability index based on wide-area measurement provided by an embodiment of the present invention;

[0016] Figure 2 It is a schematic diagram of the equivalent circuit of a single branch in an active distribution network provided by a specific embodiment of the present invention;

[0017] Figure 3 It is a schematic diagram of the equivalent circuit of a single branch in an active distribution network when ignoring the shunt admittance to the ground provided by a specific embodiment of the present invention;

[0018] Figure 4 It is a schematic diagram of an IEEE 33-node distribution network with distributed power sources provided by a specific embodiment of the present invention;

[0019] Figure 5 It is a PV curve and index curve diagram provided by a specific embodiment of the present invention;

[0020] Figure 6 It is a comparison diagram of different voltage stability indices on branch 27-28 provided by a specific embodiment of the present invention;

[0021] Figure 7 It is a structural block diagram of a system for calculating voltage stability index based on wide-area measurement provided by an embodiment of the present invention;

[0022] Figure 8 It is a schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. Specific embodiments

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. 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.

[0024] Please refer to Figure 1 , which shows a flowchart of a method for calculating voltage stability index based on wide-area measurement of the present application.

[0025] As Figure 1 shown, the method for calculating the voltage stability index based on wide - area measurement specifically includes the steps:

[0026] Step S101: Obtain the branch power flow direction, and determine the head and tail ends of the branch according to the branch power flow direction.

[0027] In this embodiment, according to the installation cost of the PMU and the importance of the bus, one end of a branch may be installed with a PMU while the other end is not. For relatively important branches, in order to achieve fast calculation, both ends may be installed with PMUs.

[0028] In an actual active distribution network, one end of a branch may be connected to multiple branches. Then, under different load levels, a certain bus may be the tail end of another bus or its head end. Based on the true direction of the branch power flow, the head and tail ends of the branch can be determined.

[0029] Step S102: Based on the preset PMUs, obtain the head - end voltage amplitude and tail - end voltage amplitude of the branch respectively.

[0030] In this embodiment, obtain the network topology structure of the current distribution network system, and set the installation positions of the PMUs according to the network topology structure. Among them, the network topology structure includes the total number of branches, the total number of nodes, and the correlation between nodes.

[0031] Specifically, assume that the head - end voltage of a certain branch is the tail - end voltage is the injection power at the head - end of the line is P i +jQ i , the output power at the tail - end is P j +jQ j , the equivalent impedance of the line is Z<θ = R + jX, the equivalent admittance at both ends of the branch is jB / 2, the power injected into the equivalent impedance through the bus is P′ i +jQ′ i , the power flowing from the branch impedance to the j - side of the bus is P′ j +jQ′ j , when the PMU is installed at the tail - end of the branch, it can be known that:

[0032]

[0033]

[0034] In the formula, P′ i is the active power passing through the impedance near the i - side, Q′ i is the reactive power passing through the impedance near the i - side, P i$P$ is the active power of the first - stage node of the injection branch, $Q$ i is the reactive power of the first - stage node of the injection branch, $j$ is the end number of the branch, $U$ i is the voltage amplitude of the first - stage of the branch, $B / 2$ is the equivalent admittance at both ends of the branch, $P'$ j is the active power flowing out of the impedance side near $j$, $Q'$ j is the reactive power flowing out of the impedance side near $j$, $P$ j is the active power of the end - stage node of the outflow branch, $Q$ j is the reactive power of the end - stage node of the outflow branch, $U$ j is the voltage amplitude of the end - stage of the branch;

[0035] When the voltage on the side of bus $j$ is used as the reference vector, i.e., $\delta$ j $ = 0$, the current flowing through the branch can be measured by the PMU and is denoted as We can get:

[0036]

[0037] $\Delta U$ j $=(P'$ j $R + Q'$ j $X) / U$ j ,

[0038] $\delta U$ j $=(P'$ j $X - Q'$ j $R) / U$ j ,

[0039] In the formula, is the voltage vector at the first - stage of the branch, is the voltage vector at the end - stage of the branch, is the current vector flowing from node $i$ to node $j$, $R$ is the branch resistance, $X$ is the branch reactance, $\Delta U$ j is the longitudinal component of the voltage difference between the first - stage and the end - stage of the branch, $\delta U$ j is the transverse component of the voltage difference between the first - stage and the end - stage of the branch;

[0040] The voltage amplitude of the first - stage is:

[0041]

[0042] The difference between the phase angle of the first - stage voltage and the phase angle of the end - stage voltage is:

[0043] $\delta=\arctan(\delta U$ j $ / (U$ j $+\Delta U$ j $))$;

[0044] When the PMU is installed at the first - stage of the branch, the active power loss and the end - stage power of the branch are:

[0045]

[0046] P j = P i - ΔP,

[0047] where ΔP is the active power loss of the branch;

[0048] The magnitude of the terminal voltage is:

[0049]

[0050] ΔU i = (P' i R + Q' i X) / U i ,

[0051] δU i = (P' i X - Q' i R) / U i ,

[0052] The difference between the phase angle of the sending - end voltage and the phase angle of the receiving - end voltage is:

[0053] δ = arctan(δU i / (U i + Δu i ))

[0054] It should be noted that when PMUs are installed at both ends of the branch, the magnitude and phase - angle information at both ends of the branch can be known simultaneously.

[0055] Step S103: Calculate the voltage stability index of each branch in the active distribution network system according to the magnitude of the sending - end voltage and the magnitude of the receiving - end voltage.

[0056] In this embodiment, the equivalent circuit of a single - branch is as Figure 2 shown. Among them, the voltage magnitude and the phase - angle difference can both be derived and calculated according to the measurement information of the above - mentioned PMU; P j , Q j are the active power and reactive power injected into node j respectively; Z = R + jX is the impedance of the branch; is the admittance to ground of the branch; the power injected into the equivalent impedance through the bus is P' i + jQ' i , and the power flowing from the branch impedance to the j - side of the bus is P' j + jQ' j . In the distribution network, due to the low voltage level, the admittance to ground of the branch can be ignored, and the simplified branch circuit model is as Figure 3As shown, where U i <δ i 、U i <δ i are the voltage phasors at the beginning and end of the branch, respectively.

[0057] Specifically, the derivation of the voltage stability index of the branch is as follows:

[0058] From the power flow equation of the branch, we have:

[0059]

[0060] Separating the real part and the imaginary part of Equation (1) gives:

[0061]

[0062]

[0063] where δ = δ i -δ j Combining Equation (2) and Equation (3) gives:

[0064]

[0065] RQ j -XP j =-U i U j s i nδ, (5)

[0066] Combining Equation (4) and Equation (5) and eliminating P j 、Q j respectively gives:

[0067]

[0068]

[0069] Combining Equation (6) and Equation (7) gives:

[0070]

[0071] where Combining Equation (4) and Equation (8) and eliminating δ gives:

[0072]

[0073] Since the voltage value on the PV curve is greater than 0, the solution of Equation (9) is:

[0074]

[0075] Let U j1 、Uj2 They are the upper and lower branch solutions of the PV curve respectively. Then, from Equation (10), we have:

[0076]

[0077] By combining Equations (4), (8), and (11), we get:

[0078]

[0079] Since the phase angle difference between the voltages at the beginning and end of the power system branch is very small, we can assume that δ≈0. Then, cosδ≈1, and Equation (12) can be simplified to:

[0080]

[0081] When the system is gradually approaching the collapse point, U j1 -U j2 gradually approaches zero. When the system is operating stably until it is approaching collapse, we have:

[0082]

[0083] By transforming Equation (14), we obtain the branch voltage stability index:

[0084]

[0085] Step S104: Take the maximum value of the voltage stability indices of all branches at the same moment as the voltage stability index of the active distribution network system.

[0086] In this embodiment, after obtaining the voltage stability indices of each branch, the maximum value of the voltage stability indices in the branch is the voltage stability index of the active distribution network. The voltage stability index of the system is determined by the following formula:

[0087] L det.max = max k∈N L det，k ,

[0088] where N is the set of all branches of the system, and L det，k is the voltage stability index of the k-th branch.

[0089] In summary, the method of this embodiment can achieve the following technical effects:

[0090] 1). The established voltage stability index does not need to calculate the impedance parameters of the line and can be directly obtained according to the PMU measurement data, greatly reducing the error of the voltage stability index caused by the change of the line impedance parameters with the voltage level, and at the same time greatly improving the calculation speed of the voltage stability index;

[0091] 2) The established voltage stability index overcomes the situation where the voltage stability index cannot be effectively calculated when the line impedance is 0 under special circumstances;

[0092] 3) The proposed voltage stability index formula does not contain the quadratic term of the line terminal voltage, greatly improving the linearity of the voltage stability index.

[0093] For Figure 4 the IEEE 33-node active distribution network example in Figure 5 is simulated and analyzed. First, the maximum load growth rate of the system is calculated using the continuation power flow. The load model adopts the constant power load, and it is set that the system load increases with its respective initial power factor as the load growth rate λ increases. The PV curve and index curve diagram in the example provided by the present invention are as shown in

[0094] During the process of growing to system collapse, the voltage stability index of branch 27 - 28 reaches 1 first. At the same time, the voltage stability indexes of the branches adjacent to branch 27 - 28 are all relatively high, because the system collapse starts from the weakest branch and spreads to the adjacent branches. Figure 6 For the comparison results, it can be seen that the errors of L Pj and L Qj are both relatively large. L Pj and L Qj are two voltage stability indexes derived respectively based on whether the voltage equations at the beginning and end nodes of the branch have solutions. The reasons are as follows. First, when the power factor angle at both ends of the line is equal to the line impedance angle, the voltages calculated at the relevant end nodes are on the PV curve, resulting in relatively large calculation errors. Second, the head node is equivalent to an infinite power grid, and the end node has a strong coupling with the head node, which will result in relatively poor linearity and accuracy of the obtained indexes. Secondly, when the resistance of the line is 0 under special circumstances, both indexes are invalid. For the L mn index, L mn is a voltage stability index derived based on the concept of the feasible solution domain of the branch power flow equilibrium point. Its accuracy and linearity are both relatively good. However, when the load is relatively light, its stability index is relatively high, which is not conducive to evaluating the voltage stability under light load conditions. For the L det index, to obtain this voltage stability index, only the voltage amplitude data measured by the PMU is required, without the need for circuit impedance parameters, thus overcoming the drawbacks caused by the resistance being 0 in L Pj and L Qj . Secondly, in the voltage stability index formula, the line terminal voltages are all first-order terms, greatly improving the linearity of the index. The above results show that the L det index has outstanding advantages in both linearity and accuracy.

[0095] Please refer toFigure 7 , which shows the structural block diagram of the voltage stability index calculation system based on wide-area measurement of the present application.

[0096] As shown in Figure 7 , the voltage stability index calculation system 200 includes a judgment module 210, an acquisition module 220, a calculation module 230, and a selection module 240.

[0097] Among them, the judgment module 210 is configured to obtain the branch power flow direction and judge the head and end of the branch according to the branch power flow direction; the acquisition module 220 is configured to respectively obtain the head voltage amplitude and the end voltage amplitude of the branch based on a preset PMU; the calculation module 230 is configured to calculate the voltage stability index of each branch of the active distribution network system according to the head voltage amplitude and the end voltage amplitude; the selection module 240 is configured to take the maximum value of the voltage stability indexes of all branches at the same moment as the voltage stability index of the active distribution network system.

[0098] It should be understood that Figure 7 The various modules recorded in Figure 1 correspond to the respective steps in the method described with reference to Figure 7 . Therefore, the operations and features described above for the method and the corresponding technical effects also apply to

[0099] In some other embodiments, the embodiments of the present invention further provide a computer-readable storage medium, on which a computer program is stored. When the program instructions are executed by a processor, the processor executes the voltage stability index calculation method based on wide-area measurement in any of the above method embodiments;

[0100] As an implementation manner, the computer-readable storage medium of the present invention stores computer-executable instructions, and the computer-executable instructions are set as:

[0101] Obtain the branch power flow direction and judge the head and end of the branch according to the branch power flow direction;

[0102] Respectively obtain the head voltage amplitude and the end voltage amplitude of the branch based on a preset PMU;

[0103] Calculate the voltage stability index of each branch of the active distribution network system according to the head voltage amplitude and the end voltage amplitude;

[0104] Take the maximum value of the voltage stability indexes of all branches at the same moment as the voltage stability index of the active distribution network system.

[0105] A computer-readable storage medium may include a program storage area and a data storage area. Among them, the program storage area may store an operating system and application programs required for at least one function; the data storage area may store data created according to the use of a system for calculating voltage stability indicators based on wide-area measurement, etc. In addition, the computer-readable storage medium may include a high-speed random access memory, and may also include a memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state storage devices. In some embodiments, the computer-readable storage medium may optionally include a memory remotely provided with respect to the processor, and these remote memories may be connected to the system for calculating voltage stability indicators based on wide-area measurement through a network. Examples of the above network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0106] Figure 3 is a schematic structural diagram of an electronic device provided by an embodiment of the present invention, as Figure 3 shown, the device includes: a processor 310 and a memory 320. The electronic device may further include: an input device 330 and an output device 340. The processor 310, the memory 320, the input device 330, and the output device 340 may be connected through a bus or other means, Figure 3 and here, taking the connection through the bus as an example. The memory 320 is the above-mentioned computer-readable storage medium. The processor 310 executes various functional applications and data processing of the server by running non-volatile software programs, instructions, and modules stored in the memory 320, that is, implements the method for calculating voltage stability indicators based on wide-area measurement in the above method embodiments. The input device 330 may receive input digital or character information, and generate key signal inputs related to user settings and function controls of the system for calculating voltage stability indicators based on wide-area measurement. The output device 340 may include display devices such as a display screen.

[0107] The above electronic device may execute the method provided by the embodiment of the present invention, and has corresponding functional modules and beneficial effects for executing the method. For technical details not described in detail in this embodiment, reference may be made to the method provided by the embodiment of the present invention.

[0108] As an implementation manner, the above electronic device is applied to a system for calculating voltage stability indicators based on wide-area measurement and is used for a client, including: 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, and the instructions are executed by the at least one processor to enable the at least one processor to:

[0109] Obtain the branch power flow direction, and judge the head end and the tail end of the branch according to the branch power flow direction;

[0110] Obtain the voltage amplitude at the head end and the voltage amplitude at the end of each branch based on a preset PMU respectively;

[0111] Calculate the voltage stability index of each branch of the active distribution network system according to the voltage amplitude at the head end and the voltage amplitude at the end;

[0112] Take the maximum value of the voltage stability indexes of all branches at the same moment as the voltage stability index of the active distribution network system.

[0113] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the essence of the above technical solution, 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., and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods of each embodiment or some parts of the embodiments.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. A method for calculating voltage stability index based on wide-area measurement, characterized in that, Including: Obtain the branch power flow direction, and determine the head and end of the branch according to the branch power flow direction; Based on a preset PMU, obtain the head voltage amplitude and end voltage amplitude of the branch respectively. Wherein, the obtaining the head voltage amplitude and end voltage amplitude of the branch based on a preset PMU includes: Suppose the voltage at the beginning of a certain branch is , the voltage at the end is , the power injected at the beginning of the line is , the power output at the end is , the equivalent impedance of the line is , the equivalent admittance at both ends of the branch is , the power passing through the equivalent impedance of the bus injection is , from the branch impedance to the bus side power is , when the PMU is installed at the end of the branch, it can be known that: ， ， Wherein, is the active power through the impedance near side, is the reactive power through the impedance near side, is the active power injected into the first node of the branch, is the reactive power injected into the first node of the branch, is the end number of the branch, is the voltage amplitude at the first section of the branch, is the equivalent admittance at both ends of the branch, is the active power flowing out through the impedance near side, is the reactive power flowing out through the impedance near side, is the active power flowing out from the end node of the branch, is the reactive power flowing out from the end node of the branch, is the voltage amplitude at the end of the branch; When taking the voltage on the busbar as the reference vector, that is , the current flowing through the branch can be measured by the PMU, denoted as , and we can obtain: ， ， ， In the formula, is the voltage vector at the beginning of the branch, is the voltage vector at the end of the branch, is from the current vector flowing from node to node is the branch resistance, is the branch reactance, is the longitudinal component of the voltage difference between the beginning and the end of the branch, is the transverse component of the voltage difference between the beginning and the end of the branch; The head section voltage amplitude is: ， The difference between the head voltage phase angle and the end voltage phase angle is: ； Calculate the voltage stability index of each branch of the active distribution network system according to the head voltage amplitude and the end voltage amplitude; Take the maximum value of the voltage stability indexes of all branches at the same moment as the voltage stability index of the active distribution network system.

2. The method for calculating a voltage stability index based on wide-area measurement according to claim 1, wherein Before obtaining the head voltage amplitude and end voltage amplitude of the branch based on a preset PMU respectively, the method further includes: Obtain the network topology structure of the current distribution network system, and set the installation position of the PMU according to the network topology structure.

3. A method for calculating a voltage stability index based on wide-area measurement according to claim 1, characterized in that The obtaining the head voltage amplitude and end voltage amplitude of the branch based on a preset PMU respectively further includes: When the PMU is installed at the head section of the branch, the branch active power loss and end power are: ， ， Wherein, is the active power loss of the branch; The end voltage amplitude is: ， ， ， The difference between the head voltage phase angle and the end voltage phase angle is: 。 4. A method for calculating a voltage stability index based on wide-area measurement according to claim 1, characterized in that, Wherein, The expression for calculating the voltage stability index of each branch of the active distribution network system is: ， Wherein, is the voltage amplitude at the head of the branch, is the voltage amplitude at the end of the branch.

5. A voltage stability index calculation system based on wide-area measurement, characterized in that Including: A judgment module configured to obtain the branch power flow direction and determine the head and end of the branch according to the branch power flow direction; An obtaining module configured to obtain the head voltage amplitude and end voltage amplitude of the branch based on a preset PMU respectively. Wherein, the obtaining the head voltage amplitude and end voltage amplitude of the branch based on a preset PMU includes: Suppose the voltage at the head of a certain branch is , and the voltage at the end is . The injected power at the head of the line is , and the output power at the end is . The equivalent impedance of the line is , and the equivalent admittance at both ends of the branch is . The power injected through the equivalent impedance of the bus is . The power flowing from the branch impedance to the side of the bus is . When the PMU is installed at the end of the branch, it can be known that: ， ， Wherein, is the active power through the impedance on the side, is the reactive power through the impedance on the side, is the active power injected into the first node of the branch, is the reactive power injected into the first node of the branch, is the end number of the branch, is the amplitude of the voltage at the first section of the branch, is the equivalent admittance at both ends of the branch, is the active power flowing out through the impedance on the side, is the reactive power flowing out through the impedance on the side, is the active power flowing out of the end node of the branch, is the reactive power flowing out of the end node of the branch, is the amplitude of the voltage at the end of the branch; When using the voltage on the busbar as the reference vector, that is , the current flowing through the branch can be measured by the PMU, denoted as , and we can obtain: ， ， ， Wherein, is the voltage vector at the head of the branch, is the voltage vector at the end of the branch, is from the current vector flowing from node to node, is the branch resistance, is the branch reactance, is the longitudinal component of the voltage difference between the head and end of the branch, is the transverse component of the voltage difference between the head and end of the branch; The head section voltage amplitude is: ， The difference between the head voltage phase angle and the end voltage phase angle is: ； A calculation module configured to calculate the voltage stability index of each branch of the active distribution network system according to the head voltage amplitude and the end voltage amplitude; A selection module configured to take the maximum value of the voltage stability indexes of all branches at the same moment as the voltage stability index of the active distribution network system.

6. An electronic device, characterized in that, Including: 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, and the instructions are executed by the at least one processor so that the at least one processor can execute the method according to any one of claims 1 to 4.

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

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