Method and system for monitoring safety state of node voltage of power distribution network based on holomorphic embedding method

Abstract

The application belongs to power system operation regulation technology, and particularly relates to a distribution network node voltage safety state monitoring method and system based on a full pure embedding method, which first constructs a distribution network voltage visual safety domain, solves a node voltage index trajectory through a physical full pure embedding method, considers changes in the distribution network network topology, proposes a voltage index trajectory fast solving method considering the N-1+1 operation mode of the distribution network, and realizes online visual monitoring of the node voltage safety state. The method has high visualization, and the voltage index trajectory fast solving method used by the method does not need to perform new power flow calculation under the network topology again when the network topology changes, so that the calculation time is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of power system operation and control technology, and specifically relates to a method and system for monitoring the voltage safety status of distribution network nodes based on the fully embedded method. Background Technology

[0002] With the rapid growth of electricity demand, the contradiction between electricity supply and demand persists. Coupled with the fluctuating output characteristics of distributed generation, unreasonable power flow distribution in the distribution network occurs frequently, leading to increasingly prominent system voltage exceedance and stability issues. Existing node voltage status monitoring methods can be broadly classified into three categories: methods based on network topology characteristics, methods based on grid operation characteristics, and data-driven methods.

[0003] Among these methods, weak link identification based on network topology characteristics mainly utilizes complex network theory, combining the characteristics of the power grid topology to construct a series of weakness indicators, such as node degree, clustering coefficient, and degree centrality, to assess the weakness of power grid nodes and thus monitor their security status. However, this type of method ignores the physical operating characteristics of the power system and the influence of system load conditions, resulting in significant limitations. Furthermore, the parameters and weights of the assessment indicators are difficult to accurately obtain in actual power systems.

[0004] Methods based on power grid operating characteristics analyze the key electrical quantity characteristics of the power grid through power flow calculations, study the power flow distribution law and voltage stability of the system, and identify weak nodes in the power grid. However, these methods rely on power flow calculations and are limited by the calculation speed and convergence of the power flow calculation methods themselves. Furthermore, both types of methods require linear approximation of the current operating point of the system, which deviates to a certain extent from the actual system operating conditions, and they rarely consider the N-1 fault of the distribution network.

[0005] Data-driven approaches replace traditional mechanistic modeling of power grids with data analysis, primarily employing methods such as stochastic matrix theory and artificial intelligence. These methods overcome the difficulty of physical modeling in traditional analysis methods by not relying on model mechanisms, but they also lead to poor interpretability of the results. Furthermore, data from actual distribution network fault scenarios is difficult to obtain; current research mostly uses simulation to acquire data and train models. Therefore, the accuracy of these methods in identifying and predicting weak points in actual power systems under different operating conditions remains to be verified.

[0006] Most current power distribution automation systems use conventional power flow calculation methods to obtain key electrical quantities at nodes and then monitor the system's operating status. However, these methods are only effective for the current load status and network topology, and the monitoring results are presented in the form of data reports, resulting in poor visualization.

[0007] In summary, existing methods are insufficient for achieving online visual monitoring of node status under N-1 fault conditions in distribution networks. Summary of the Invention

[0008] To address the problems existing in the background technology, this invention proposes an online monitoring method and system for the voltage safety status of distribution network nodes based on the fully embedded method.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: an online monitoring method for the voltage safety status of distribution network nodes based on a fully embedded method, comprising:

[0010] Construct a voltage visualization security domain for the power distribution network;

[0011] Solving for node voltage index trajectories;

[0012] Solving the node voltage index trajectory of distribution network topology changes;

[0013] Conduct online monitoring of the safety status of node voltage.

[0014] In the above-mentioned online monitoring method for the voltage safety status of distribution network nodes based on the fully embedded method, the online monitoring method specifically includes:

[0015] Step 1: For a power distribution system with one slack node and N load or generator nodes, decouple the power distribution system by constructing virtual branches between each node and the slack node, thus decoupling the power distribution system into multiple two-node systems with virtual branches; based on the solvability conditions of the two-node power flow equations, obtain the parabolic voltage stability boundary of the power distribution network; construct the voltage safety domain of the power distribution network according to the upper and lower voltage limits of the power distribution network; divide the voltage safety domain of the power distribution network according to the high voltage solution and the low voltage solution, and construct the visualized voltage safety domain of the power distribution network.

[0016] Step 2: Based on the physical fully embedded method, perform power flow calculation of the distribution network and obtain the power series of the node voltages; construct the physical fully embedded form of the node voltage index, obtain the analytical expression of the node voltage index based on the power series of the node voltages, and solve the node voltage index trajectory.

[0017] Step 3: Based on the N-1+1 safety criterion of the distribution network, for the network topology formed by power transfer through tie lines after line faults, solve the node voltage index under the initial load state and under different network topology conditions, calculate and save the dynamic offset of the voltage index before and after the topology change; when the topology change occurs, combine the current load state and the saved dynamic offset of the voltage index, and solve the real-time voltage index trajectory by superimposing the dynamic offset of the voltage index.

[0018] Step 4: Combining the distribution network voltage visualization safety domain and node voltage index trajectory, observe the relative position of the node voltage index trajectory and the voltage safety boundary when the system load continues to grow, and realize online monitoring of the node voltage safety status; by pre-calculating and saving the dynamic offset of the node voltage index before and after the distribution network topology change, monitor the voltage safety status of each node in real time under the current operation mode of the distribution network and under the N-1+1 operation mode.

[0019] In the above-mentioned online monitoring method for the voltage safety status of distribution network nodes based on the fully embedded method, the specific implementation of step 1 includes:

[0020] The power flow equations for a two-node system with a virtual branch are as follows:

[0021]

[0022] In the formula, U i Let U be the voltage at node i. sw To balance the node voltage, Z i For virtual branch impedance, S i Let be the complex power of node i, and * represent the conjugate complex number;

[0023] Introducing normalized voltage G i =U i / U sw Then equation (1) is:

[0024]

[0025] In the formula, σ i It is determined by the virtual branch impedance Z i Node complex power S i and the balancing node voltage U sw The integrated complex node voltage index is defined as follows:

[0026]

[0027] G in equation (2) i With σ i Expanding the real and imaginary parts, we get the following equation:

[0028]

[0029] Solving equation (4) simultaneously yields the following formula:

[0030]

[0031] G iR If we consider them as variables, then equation (5) is a quadratic equation. We can determine whether there is a solution based on the discriminant of the quadratic equation.

[0032]

[0033] When the judgment Δ≥0, G can be obtained by the quadratic formula. iR The explicit analytical solution, combined with the G obtained from equation (4) iI G can be obtained i :

[0034]

[0035] In the formula, σ iR and σ iI These are the voltage index σ i The real and imaginary parts; Equation (7) corresponds to a set of voltage solutions for node i: upper branch and lower branch. The upper voltage branch is selected as the voltage steady-state solution of the actual system.

[0036] From equation (6), we know that the discriminant forms a parabolic voltage stability boundary in the σ complex plane;

[0037] Based on the upper and lower voltage limits, a voltage safety domain for the distribution network is constructed.

[0038] Assuming the phase angle of the system's slack node voltage is 0, according to and|U sw |=U sw Equation (4) is:

[0039]

[0040] Squaring the two equations in equation (8) and adding them together, the node voltage index σ i The real and imaginary parts form the equation of a circle:

[0041]

[0042] The expressions for the center and radius are given by:

[0043]

[0044] Substituting equation (9) into equation (6), there is only one set of common points, which is the circle tangent to the parabola;

[0045] In equation (9), the voltage amplitude |U at different nodes i | Corresponding to different inscribed circles, let the node voltage amplitude corresponding to a certain inscribed circle in the σ complex plane be X, if and only if σ i If it lies on the circle, then |U i |=X;

[0046] Introduce upper and lower limit constraints on distribution network voltage, U L ≤|U i |≤U HThen, the inscribed circles corresponding to countless voltage values ​​within the voltage upper and lower limit range form a region;

[0047] Based on the division of the voltage safety domain in the power system using the voltage branch in equation (7) as the actual operating solution, the square of the high-voltage solution amplitude |G is obtained from equation (7). i,high | 2 for:

[0048]

[0049] If the voltage feasible solution is within the upper and lower voltage limits, then |G| is satisfied. i,high | 2 ≤|G H | 2 ,|G H |=|U H | / U sw Then we have:

[0050]

[0051] Expanding equation (12) into the following equation:

[0052]

[0053] Equation (13) shows that the node voltage index σ i It cannot be located inside the inscribed circle corresponding to the upper voltage limit.

[0054] In the above-mentioned online monitoring method for the voltage safety status of distribution network nodes based on the fully embedded method, the specific implementation of step 2 includes:

[0055] In an N-node power distribution system, Slack, PQ, and PV represent the sets of slack nodes, load nodes, and generator nodes, respectively, to construct a physically fully embedded AC power flow model under constant power load conditions:

[0056]

[0057]

[0058]

[0059] Solving the analytical expression for node voltages involves: solving for the first term coefficient of the power series of the unknown quantity; and solving for the coefficients of each order of the power series using a recursive method.

[0060] Embedding equation (2) into the form of equation (17):

[0061]

[0062] Based on the analytical expression of the node voltage in power series form, and then deriving the node voltage index σ according to equation (17) i (s);

[0063] Assuming the equilibrium node has an amplitude of 1 and a phase angle of 0, then G i (s)=U i (s) / U sw =U i (s), in the form of a power series U i (s) and σ i Substituting (s) into equation (17), we get equation (18):

[0064]

[0065] Rearranging equation (18) makes the coefficients of the same order s on both sides of the equation equal, thus obtaining σ. i (s) and U i The relationship between the coefficients of the power series of (s) is given by equation (19);

[0066]

[0067] Obtain the node voltage index σ i The analytical expression for (s) is:

[0068]

[0069] In the above-mentioned online monitoring method for the voltage safety status of distribution network nodes based on the fully embedded method, the specific implementation of step 3 includes:

[0070] Using the system load scaling factor 's' as the offset scaling factor, the dynamic offset of the node voltage index is calculated as follows:

[0071] D i,jl,s =s×[(σ iR -σ iR,jl )+j(σ iI -σ iI,jl )],i∈PQ∪PV (42)

[0072] In the formula, D i,jl,s σ represents the offset of the node i voltage index in the complex plane when the system load is scaled by a factor of s, line j is disconnected due to a fault, and tie line l is closed; iR and σ iI Let σ be the real and imaginary parts of the node voltage index of node i under the initial load condition of the system. iR,jl and σ iI,jl These represent the real and imaginary parts of the node voltage index of node i under the initial load state of the system when line j is open due to a fault and tie line l is closed.

[0073] A system for an online monitoring method of distribution network node voltage security status using a fully embedded method includes a distribution network voltage visualization security domain construction module, a distribution network fully embedded power flow solution module, and a node voltage index trajectory solution module.

[0074] The voltage visualization security domain construction module for distribution networks is used to construct a voltage visualization security domain that considers the solvability conditions of power flow equations and the upper and lower limits of node voltages.

[0075] The distribution network fully embedded power flow solution module is used to perform power flow calculations in distribution networks based on the physical fully embedded method and to obtain the power series of node voltages.

[0076] The node voltage index trajectory solving module is used to solve the node voltage index trajectory under the N-1+1 operation mode of the distribution network based on the proposed fast trajectory solving method.

[0077] An electronic device includes a computer-readable storage medium storing computer-executable instructions; and one or more processors coupled to the computer-readable storage medium and configured to execute the computer-executable instructions, such that the device performs an online monitoring method for the voltage safety status of distribution network nodes based on a fully embedded approach.

[0078] A readable storage medium storing computer-executable instructions, which, when executed by a processor, configure the processor to perform an online monitoring method for the voltage safety status of distribution network nodes based on a fully embedded approach.

[0079] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention takes into account the actual operating characteristics of the distribution network, constructs a voltage visualization security domain for the distribution network, and uses the fully pure embedding method to solve the node voltage index trajectory, thereby realizing online visualization monitoring of the node voltage status.

[0080] This invention considers the N-1+1 operation mode of the distribution network and proposes a fast solution method for the node voltage index trajectory. It realizes the monitoring of node voltage status taking into account network topology changes, and eliminates the need to recalculate the power series of node voltage index after topology changes, which greatly shortens the calculation time. Attached Figure Description

[0081] Figure 1 This is a flowchart of the online monitoring method for node voltage safety status according to an embodiment of the present invention;

[0082] Figure 2 This is a schematic diagram of the decoupling of the power distribution system according to an embodiment of the present invention;

[0083] Figure 3 This is a schematic diagram of the power distribution network voltage visualization security domain according to an embodiment of the present invention;

[0084] Figure 4 This is a trajectory diagram of the node voltage index obtained in the IEEE-33 node system according to an embodiment of the present invention;

[0085] Figure 5 This is a schematic diagram of the node voltage index trajectory considering changes in the distribution network topology in an embodiment of the present invention;

[0086] Figure 6 This is a dynamic offset diagram of node voltage indices when the system load increases uniformly according to an embodiment of the present invention.

[0087] Figure 7 This is a schematic diagram illustrating the application of online monitoring of node voltage safety status in an embodiment of the present invention. Detailed Implementation

[0088] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0089] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0090] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0091] This embodiment proposes an online monitoring method and system for node voltage safety status based on a fully embedded method to monitor node voltage safety status online and predict node voltage exceedance events in future operating environments, taking into account the N-1+1 operation mode of the distribution network. This embodiment constructs a visualized safety domain for distribution network voltage, solves the node voltage index trajectory using a physical fully embedded method, and proposes a fast solution method for voltage index trajectory considering changes in the distribution network topology under the N-1+1 operation mode, achieving online visualized monitoring of node voltage safety status. The monitoring method based on the visualized safety domain and node voltage index trajectory offers high visualization, and the fast solution method for voltage index trajectory eliminates the need for power flow calculations under the new network topology when the network topology changes, significantly reducing computation time.

[0092] This embodiment is achieved through the following technical solution: an online monitoring method for the voltage safety status of distribution network nodes based on a fully embedded method, characterized by the following steps:

[0093] S1: Based on the idea of ​​decoupling the power distribution system, considering the solvability conditions of the two-node power flow equations and the upper and lower limits of the voltage of the distribution network nodes, a visual safety domain for the voltage of the distribution network is constructed.

[0094] The process of constructing the voltage visualization security domain for the distribution network is as follows:

[0095] For a power distribution system with one slack node and N load / generator nodes, the concept of power distribution system decoupling is used to construct virtual branches between each node and the slack node, thus decoupling the power distribution system into multiple two-node systems with virtual branches. According to Ohm's law, the power flow equations for a two-node system with virtual branches are as follows:

[0096]

[0097] In the formula, U i Let U be the voltage at node i. sw To balance the node voltage, Z i For virtual branch impedance, S i Let be the complex power of node i, and let * denote the conjugate complex number.

[0098] Next, a normalized voltage G is introduced. i =U i / U sw Then equation (1) can be rearranged into the following form:

[0099]

[0100] In the formula, σ i It is determined by the virtual branch impedance Z i Node complex power S i and the balancing node voltage U sw The integrated complex node voltage index is defined as follows:

[0101]

[0102] For equation (2), G can be... i With σ i Expanding the real and imaginary parts, we obtain equation (4).

[0103]

[0104] Next, in equation (4), G iI Substituting into the above equation, we obtain equation (5):

[0105]

[0106] Then, G iR If we consider it as a variable, then equation (5) can be rearranged into a quadratic equation. We can determine whether there is a solution based on the discriminant of the quadratic equation, as shown in equation (6).

[0107]

[0108] When the condition Δ≥0, G can be obtained using the quadratic formula. iR The explicit analytical solution, combined with equation (2.4), yields G. iI G can be obtained i :

[0109]

[0110] In the formula, σ iR and σ iI These are the voltage index σ i The real and imaginary parts. It is worth noting that equation (7) corresponds to a set of voltage solutions for node i: "upper branch solution" and "lower branch solution". Usually, the voltage "upper branch solution" (high voltage solution) is selected as the voltage steady-state solution of the actual system.

[0111] Observing equation (6), it can be seen that the discriminant forms a parabolic voltage stability boundary in the σ complex plane. For the distribution network, in addition to focusing on whether the voltage is stable (whether there is a feasible solution), it is also necessary to focus on the problem of voltage exceeding the limit. Therefore, considering the upper and lower voltage limit constraints, the voltage safety domain of the distribution network is further derived and constructed.

[0112] Assuming the system reference (balance node) voltage phase angle is 0, according to and|U sw |=U sw Equation (4) can be rearranged into the following form:

[0113]

[0114] Next, square the two equations in equation (8) and add them together. Based on this, it is easy to observe that the node voltage index σ is... i The real and imaginary parts of form a circular equation, as shown in equation (9).

[0115]

[0116] The expressions for the center and radius of the circle are shown in equation (10). Meanwhile, substituting the circle equation shown in equation (9) into the parabola equation represented by equation (6), it is easy to see that the two have only one common point, that is, the circle is inscribed in the parabola.

[0117]

[0118] In the circular equation represented by equation (9), the voltage amplitudes |U at different nodes i | Corresponding to different inscribed circles, that is, assuming that the node voltage amplitude corresponding to a certain inscribed circle in the σ complex plane is X, then if and only if σ i It can only be represented if it is located exactly on the circle. i|=X. Therefore, upper and lower limits of distribution network voltage are introduced, i.e., U L ≤|U i |≤U H Then, the inscribed circles corresponding to countless voltage values ​​within the upper and lower voltage limits can form a region.

[0119] In addition, considering that in actual power systems, only the voltage "upper branch solution" (i.e., high voltage solution) in equation (7) is usually used as the actual operating solution, and the "lower branch solution" (i.e. low voltage solution) deviates too much from the rated value, causing the system to be unable to operate stably, the voltage safety domain is further divided.

[0120] First, from equation (7), we can obtain the square of the high-voltage solution amplitude |G i,high | 2 As shown in equation (11).

[0121]

[0122] After considering the upper and lower voltage limits, to ensure that the voltage feasible solution (i.e., the high-voltage solution) is within the upper and lower voltage limits, at least |G| must be satisfied. i,high | 2 ≤|G H | 2 (|G H |=|U H | / U sw ), i.e., equation (12).

[0123]

[0124] Next, expanding equation (12), we observe the expanded inequality and find that it can be rearranged into the following form:

[0125]

[0126] Equation (13) shows that the node voltage index σ i Since it cannot be inside the inscribed circle corresponding to the voltage upper limit, the final construction of the power distribution network voltage visualization security domain is completed.

[0127] S2: Based on a physically-based fully embedded power flow model, power flow calculations are performed on the distribution network. The power series of node voltage indices is derived, and the trajectories of node voltage indices are solved. The solution process is as follows:

[0128] Taking an N-node power distribution system as an example, let Slack, PQ, and PV represent the sets of slack nodes, load nodes, and generator nodes, respectively, and only consider constant power loads to construct a physically fully embedded AC power flow model:

[0129]

[0130]

[0131]

[0132] The solution process of the model consists of two steps: 1) solving for the first term coefficient of the power series of the unknown quantity, which is the initial solution with physical meaning; 2) using a recursive method to solve for the coefficients of each order of the power series, thereby completing the solution of the analytical expression of the node voltage.

[0133] Embed Equation (2) into the form of Equation (17).

[0134]

[0135] Based on the analytical expression of the node voltage in power series form, and then deriving the node voltage index σ according to equation (17) i (s).

[0136] Assuming the equilibrium node has an amplitude of 1 and a phase angle of 0, then G i (s)=U i (s) / U sw =U i (s), in the form of a power series U i (s) and σ i Substituting (s) into equation (17), we obtain equation (18):

[0137]

[0138] By rearranging equation (18) and ensuring that the coefficients of the same order s on both sides of the equation are equal, σ can be derived. i (s) and U i The relationship between the coefficients of the power series of (s) is shown in equation (19):

[0139]

[0140] Finally, the node voltage index σ is obtained. i The analytical expression for (s) is:

[0141]

[0142] The required node voltage index σ i The analytical expression of (s) has physical meaning when s takes different values, that is, as s changes, the voltage index trajectory under the corresponding load change state can be solved.

[0143] S3: Considering the changes in the distribution network topology, a fast solution method for the node voltage index trajectory considering the N-1+1 operation mode of the distribution network is proposed; details are as follows:

[0144] Based on the N-1+1 safety criterion of the distribution network, this paper solves the node voltage index under the initial load state and different network topologies for a series of new network topologies formed by power transfer through tie lines after line faults. The offset of the voltage index before and after the topology change is calculated and saved.

[0145] As the system load continues to increase, the system voltage stability will gradually decrease, corresponding to the node voltage index σ after the topology change. i The offset will also increase further. Taking the system load scaling factor 's' as the offset scaling factor, the dynamic offset of the node voltage index is calculated as follows:

[0146] D i,jl,s =s×[(σ iR -σ iR,jl )+j(σ iI -σ iI,jl )],i∈PQ∪PV(63)

[0147] In the formula, D i,jl,s σ represents the offset of the node i voltage index in the complex plane when the system load is scaled by a factor of s, line j is disconnected due to a fault, and tie line l is closed; iR and σ iI Let σ be the real and imaginary parts of the node voltage index of node i under the initial load condition of the system. iR,jl and σ iI,jl These represent the real and imaginary parts of the node voltage index of node i under the initial load state of the system when line j is open due to a fault and tie line l is closed.

[0148] In practical applications, the voltage index offsets under different network topologies are calculated and saved in advance. When a topology change occurs, there is no need to solve the node voltage index trajectory after the topology change. It is only necessary to combine the current load status with the pre-saved voltage index offsets and quickly solve the real-time voltage index trajectory by superimposing the dynamic voltage index offsets.

[0149] S4: By combining the distribution network voltage visualization safety domain with the node voltage index trajectory, online monitoring of node voltage safety status and visualization prediction of voltage over-limit events in the expected operating environment can be achieved.

[0150] The process for online monitoring of node voltage safety status is as follows:

[0151] By combining the distribution network voltage visualization safety domain and node voltage index trajectory, the relative position of the node voltage index trajectory and the voltage safety boundary can be observed when the system load continues to grow, thereby enabling online monitoring of the node voltage safety status.

[0152] By pre-calculating and saving the node voltage index offsets before and after the distribution network topology change, the voltage safety status of each node under the current operation mode and the N-1+1 operation mode of the distribution network can be monitored in real time.

[0153] This embodiment also proposes a system for an online monitoring method of distribution network node voltage security status based on the fully embedded method, including a distribution network voltage visualization security domain construction module, a distribution network fully embedded power flow solution module, and a node voltage index trajectory solution module.

[0154] The voltage visualization security domain construction module for distribution networks is used to construct a voltage visualization security domain that considers the solvability conditions of power flow equations and the upper and lower limits of node voltages. The solvability conditions of power flow equations form a unified parabolic boundary, and the upper and lower limits of node voltages need to be set according to the specific system.

[0155] The distribution network fully embedded power flow solution module is used to calculate the power series of node voltages by performing distribution network power flow calculations based on the physical fully embedded method. Its data input format is the same as that of conventional power flow calculation.

[0156] The node voltage trajectory solving module is used to solve the node voltage trajectory under the N-1+1 operation mode of the distribution network based on the proposed fast trajectory solving method. It requires calling the node voltage power series obtained from the fully embedded power flow solving module of the distribution network. The obtained node voltage trajectory is visualized in the distribution network voltage visualization security domain construction module, ultimately realizing online monitoring of the node voltage security status.

[0157] An electronic device includes a computer-readable storage medium storing computer-executable instructions; and one or more processors coupled to the computer-readable storage medium and configured to execute the computer-executable instructions, such that the device performs an online monitoring method for the voltage safety status of distribution network nodes based on a fully embedded approach.

[0158] A readable storage medium storing computer-executable instructions, which, when executed by a processor, configure the processor to perform an online monitoring method for the voltage safety status of distribution network nodes based on a fully embedded approach.

[0159] Example 1

[0160] The simulation was implemented using the MATPOWER 4.1 toolbox in MATLAB R2020b, with the IEEE-33 node system as the simulation example.

[0161] like Figure 1The flowchart shown is a method for online monitoring of node voltage security status, including the construction of a distribution network voltage visualization security domain, the solution of node voltage index trajectories, the rapid solution of voltage index trajectories considering topology changes, and online monitoring of node voltage status.

[0162] like Figure 2 The diagram shown is a schematic of the decoupling of the power distribution system.

[0163] like Figure 3 The diagram shown is a schematic of the voltage visualization security domain of the distribution network.

[0164] like Figure 4 The figure shown is a trajectory diagram of the node voltage index of the IEEE-33 node system.

[0165] like Figure 5 The figure shows a schematic diagram of the node voltage index trajectory considering changes in the distribution network topology.

[0166] like Figure 6 The figure shown is a dynamic offset diagram of node voltage indices when the system load increases uniformly.

[0167] like Figure 7 The diagram shown is a schematic of an online monitoring application for node voltage safety status.

[0168] The online monitoring method for the voltage safety status of distribution network nodes based on the fully embedded method includes the following steps:

[0169] 1) Construct a voltage visualization security domain for the distribution network.

[0170] For a power distribution system with one slack node and N load / generator nodes, the concept of power distribution system decoupling is used to construct virtual branches between each node and the slack node. This decouples the power distribution system into multiple two-node systems with virtual branches, as shown in the following example. Figure 2 As shown.

[0171] By combining the solvability conditions of the two-node power flow equations with the upper and lower limits of distribution network voltage constraints, a visualized safety domain for distribution network voltage is derived and constructed, as follows: Figure 3 As shown.

[0172] 2) Solving for the node voltage index trajectory.

[0173] Based on a physically-based fully embedded power flow model, power flow calculations are performed on the distribution network. The power series of node voltage indices are further derived from the obtained power series of node voltages, and the node voltage index trajectories are solved. Taking the IEEE-33 node system as an example, the node voltage index trajectories obtained using the proposed method are as follows: Figure 4 As shown.

[0174] 3) Fast solution for voltage index trajectories considering topology changes.

[0175] Based on the N-1+1 safety criterion of distribution networks, this paper addresses a series of new network topologies formed after a line fault via tie lines. It solves for node voltage indices under initial load conditions and different network topologies, calculates and saves the offsets of voltage indices before and after the topology change, as follows: Figure 5 As shown.

[0176] When the system load changes, the saved dynamic offset of the voltage index can be superimposed on the voltage index trajectory of the desired node to achieve rapid solution of the node voltage index trajectory. Taking the IEEE-33 node system as an example, assuming that branch 28-29 experiences a fault and disconnection, and the tie line 25-29 is closed according to the load transfer scheme to transfer the load, the voltage index trajectory of node 18 obtained by the proposed method is as follows: Figure 6 As shown.

[0177] 4) Online monitoring of node voltage safety status.

[0178] By combining the visualized voltage safety domain and node voltage index trajectories of the distribution network, the relative positions of node voltage index trajectories and voltage safety boundaries are observed when the system load continues to increase, thereby enabling online monitoring of node voltage safety status. By pre-calculating and saving the node voltage index offsets before and after distribution network topology changes, the voltage safety status of each node is monitored in real time under the current operating mode and under the N-1+1 operating mode of the distribution network. Specifically, as follows... Figure 7 As shown.

[0179] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. An on-line monitoring method for voltage security state of nodes in a power distribution network based on holomorphic embedding method, characterized in that, include: Construct a voltage visualization security domain for the power distribution network; Solving for node voltage index trajectories; Solving the node voltage index trajectory of distribution network topology changes; Conduct online monitoring of node voltage safety status; The online monitoring method specifically includes: Step 1: For a power distribution system with one slack node and N load or generator nodes, decouple the power distribution system by constructing virtual branches between each node and the slack node, thus decoupling the power distribution system into multiple two-node systems with virtual branches; based on the solvability conditions of the two-node power flow equations, obtain the parabolic voltage stability boundary of the power distribution network; construct the voltage safety domain of the power distribution network according to the upper and lower voltage limits of the power distribution network; divide the voltage safety domain of the power distribution network according to the high voltage solution and the low voltage solution, and construct the visualized voltage safety domain of the power distribution network. Step 2: Based on the physical fully embedded method, perform power flow calculation of the distribution network and obtain the power series of the node voltages; construct the physical fully embedded form of the node voltage index, obtain the analytical expression of the node voltage index based on the power series of the node voltages, and solve the node voltage index trajectory. Step 3: Based on the N-1+1 safety criterion of the distribution network, for the network topology formed by power transfer through tie lines after line faults, solve the node voltage index under the initial load state and under different network topology conditions, calculate and save the dynamic offset of the voltage index before and after the topology change; when the topology change occurs, combine the current load state and the saved dynamic offset of the voltage index, and solve the real-time voltage index trajectory by superimposing the dynamic offset of the voltage index. System load scaling factor s As an offset scaling factor, the node voltage index dynamic offset is calculated as follows: (21) In the formula, D i,jl,s Scaling the system load s Times, Line j Fault disconnection, communication line l When the node is closed i Voltage index at σ Offset within the complex plane; σ iR and σ iI They are nodes i The real and imaginary parts of the node voltage index under the initial load condition of the system. σ iR,jl and σ iI,jl The lines are respectively j Fault disconnection, communication line l When the node is closed i The real and imaginary parts of the node voltage index under the initial load condition of the system, where PQ represents the set of load nodes and PV represents the set of generator nodes; Step 4: Combining the distribution network voltage visualization safety domain and node voltage index trajectory, observe the relative position of the node voltage index trajectory and the voltage safety boundary when the system load continues to grow, and realize online monitoring of the node voltage safety status; by pre-calculating and saving the dynamic offset of the node voltage index before and after the distribution network topology change, monitor the voltage safety status of each node in real time under the current operation mode of the distribution network and under the N-1+1 operation mode.

2. The on-line monitoring method for voltage security state of nodes in power distribution network based on holomorphic embedding method according to claim 1, characterized in that, The specific implementation of step 1 includes: The power flow equations for a two-node system with a virtual branch are as follows: (1) In the formula, U i For nodes i voltage, U sw To balance node voltage, Z i For virtual branch impedance, S i For nodes i The complex power, * represents the conjugate complex number; Introducing the normalized voltage G i = U i / U sw then equation (1) is: (2) In the formula, σ i It is determined by the virtual branch impedance Z i Node complex power S i and balancing node voltage U sw The integrated complex node voltage index is defined as follows: (3) The real and imaginary parts of the expression G i and σ i are expanded to give the following: (4) Solving the equations simultaneously (4), we obtain the following formula: (5) The G iR If considered as a variable, equation (5) is a quadratic equation, and according to the discriminant of the quadratic equation, it is determined whether there is a solution. (6) When judging formula Δ≥0, the explicit analytical solution of G iR is obtained by the root formula, combined with formula (4) to solve G iI G i :​ (7) In the formula, σ iR and σ iI Voltage indicators σ i The real and imaginary parts; Equation (7) corresponds to the nodes i A set of voltage solutions: upper branch and lower branch. The upper voltage branch is selected as the voltage steady-state solution of the actual system. From (6), the discriminant is σ a parabolic voltage stability boundary is formed in the complex plane; Based on the upper and lower voltage limits, a voltage safety domain for the distribution network is constructed. Assuming the phase angle of the system's slack node voltage is 0, according to U 2 i R+ U 2 i I=| U i | 2 and | U sw |= U sw Equation (4) is: (8) The real and imaginary parts of the node voltage index σ i form a circle equation: (9) The expressions for the center and radius are given by: (10) Substituting equation (9) into equation (6), there is only one set of common points, which is the circle tangent to the parabola; In formula (9), the voltage amplitude of different nodes U i |Corresponding to different inscribed circles, let σ The voltage amplitude of a certain inscribed circle in the complex plane is X If and only if σ i Located on the circle, then U i |= X ; introducing upper and lower voltage limits for the distribution network, U L ≤| U i |≤ U H then the infinitely many voltage values within the upper and lower voltage limits interval correspond to a region of inscribed circles; According to the voltage safety domain divided by the voltage upper branch solution of formula (7) as the actual operation solution in the power system, the square of the amplitude of the high voltage solution is obtained from formula (7) G i,high | 2 is: (11) If the voltage feasible solution is within the upper and lower voltage limits, then it satisfies | G i,high | 2 ≤| G H | 2 , | G H |=| U H | / U sw Then we have: (12) Expanding equation (12) into the following equation: (13) Equation (13) shows that the node voltage indicator σ i Cannot be inside the circle inscribed by the upper voltage limit.

3. The on-line monitoring method for voltage security state of distribution network nodes based on holomorphic embedding method according to claim 1, characterized in that, The specific implementation of step 2 includes: N Slack, PQ and PV are used to represent the set of slack, load and generator nodes in the node power distribution system, and the physical holomorphic embedding alternating current power flow model is constructed under the condition of constant power load: (14) (15) (16) Solving the analytical expression for node voltages involves: solving for the first term coefficient of the power series of the unknown quantity; and solving for the coefficients of each order of the power series using a recursive method. Embedding equation (2) into the form of equation (17): (17) Based on the power series form of the node voltage analytical expression, the node voltage index is derived according to equation (17) σ i ( s ) Assuming the equilibrium node has an amplitude of 1 and a phase angle of 0, then G i ( s )= U i ( s ) / U sw = U i ( s ), in the form of power series U i ( s )and σ i ( s Substituting into equation (17), we obtain equation (18): (18) Simplifying equation (18) makes both sides of the equation... s The coefficients of the same order are all equal in a one-to-one correspondence, thus obtaining σ i ( s )and U i ( s The relationship between the coefficients of the power series of ) is given by equation (19). (19) obtaining a node voltage indicator σ i s The analytical expression for the node voltage indicator​ (20)。 4. A system for implementing the on-line monitoring method of the voltage security state of nodes in a power distribution network based on the holomorphic embedding method according to any one of claims 1 to 3, characterized in that, This includes a distribution network voltage visualization security domain construction module, a distribution network fully embedded power flow solution module, and a node voltage index trajectory solution module; The voltage visualization security domain construction module for distribution networks is used to construct a voltage visualization security domain that considers the solvability conditions of power flow equations and the upper and lower limits of node voltages. The distribution network fully embedded power flow solution module is used to perform power flow calculations in distribution networks based on the physical fully embedded method and to obtain the power series of node voltages. The node voltage index trajectory solving module is configured to quickly solve the node voltage index trajectory of the power distribution network based on the trajectory quick solving method N -1+1 operation mode.

5. An electronic device, comprising: A computer-readable storage medium storing computer-executable instructions; and one or more processors coupled to the computer-readable storage medium and configured to execute the computer-executable instructions to cause the device to perform the method according to any one of claims 1-3.

6. A readable storage medium characterized by, The system stores computer-executable instructions that, when executed by a processor, configure the processor to perform the method according to any one of claims 1-3.

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