Three-phase unbalance real-time power flow calculation method and system based on main distribution integration

Abstract

The three-phase imbalance real-time power flow calculation method based on main distribution integration comprises: integrated modeling of low-voltage and medium-high voltage networks; obtaining active power and reactive power of each phase at the outlet of the distribution transformer low-voltage side by iterative solution of power balance equation, wherein the voltage at the outlet of the distribution transformer low-voltage side is taken as a boundary condition during the solution; calculating the active power and reactive power of each phase at the high-voltage side of the distribution transformer, which are taken as load injection power of the medium-high voltage network to participate in the power flow calculation of the medium-high voltage network; obtaining the active power, reactive power and voltage value of each node and the branch current value of the medium-high voltage network through iterative calculation of the power flow of the medium-high voltage network; calculating the voltage at the outlet of the distribution transformer low-voltage side according to the voltage of the terminal node of the medium-high voltage network, and if the residual error of the voltage at the outlet of the distribution transformer low-voltage side is less than the set difference threshold, the iterative calculation is stopped, otherwise, the next iteration is carried out. The present application adopts a hierarchical-distributed-coordinated iterative architecture to more accurately calculate the real-time power flow of the high, medium and low voltage networks.

Description

Technical Field

[0001] This invention belongs to the field of power information technology, and more specifically, relates to a method and system for real-time power flow calculation of three-phase imbalance based on the integration of main and distribution systems. Background Technology

[0002] The distribution network's low-voltage network connects to a large number of distributed power sources. These distributed power sources and loads exacerbate the three-phase imbalance. Traditional high-voltage power flow calculations neglect the details of the low-voltage network and distribution transformers, resulting in "blind spots." Existing methods either fail to accurately calculate low-voltage data or cannot calculate the entire system, making operation and maintenance reliant on experience and difficult to trace the root cause of problems.

[0003] High, medium, and low voltage networks possess different network characteristics and measurement acquisition conditions. The parameter structure of low-voltage networks is asymmetrical, while the number of branch lines and nodes in medium-voltage networks is constantly increasing. Existing distribution network monitoring terminals are mainly deployed at the main feeder line outlets and distribution transformers, with limited coverage of branch line monitoring terminals, making it impossible to achieve comprehensive, real-time, and observable distribution network operation status. Furthermore, considering the non-negligible impact of different wiring and grounding methods of distribution transformers and main transformers, as well as different phase shifts, on power flow distribution, it is necessary to perform integrated three-phase unbalanced power flow calculations encompassing high, medium, and low voltage levels.

[0004] In existing technologies, due to the large number of branch lines and nodes in the distribution network, existing distribution network monitoring terminals are mainly deployed at the main feeder outlets and distribution transformers. The coverage of branch line monitoring terminals is limited, making it impossible to achieve comprehensive, real-time, and observable distribution network operation status. The scope of large-scale three-phase unbalanced online real-time power flow calculation and analysis for medium-voltage main and distribution networks is generally limited to power flow fluctuations within the medium and low voltage range of 10kV. With the widespread integration of distributed generation, the backfeeding of distributed generation from low-voltage distribution areas to 10kV feeders, and the backfeeding of 10kV feeder power to the high-voltage side of the main transformer within the substation, are becoming increasingly common. The large-scale three-phase unbalanced online real-time power flow calculation for medium-voltage main and distribution networks can no longer meet the needs of large-scale distributed generation integration. Therefore, it is necessary to perform integrated main and distribution power flow calculation and analysis based on integrated main and distribution calculation modeling. Considering the impact analysis of large-scale distributed generation integration on the power grid, it is essential to achieve integrated main and distribution power flow calculation based on integrated main and distribution modeling to accurately calculate the power flow changes after distributed generation backfeeding. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and system for real-time calculation of three-phase unbalanced power flow based on the integration of primary and secondary systems.

[0006] The present invention adopts the following technical solution.

[0007] The first aspect of this invention proposes a real-time power flow calculation method for three-phase unbalance based on integrated master and distribution systems, comprising: Integrated modeling of low-voltage and medium-high-voltage networks is performed to identify node composition and network parameters, including transformer grounding method, wiring method and phase shift, as well as the voltage of each power supply bus in the high-voltage network. The active and reactive power of each phase at the outlet of the low-voltage side of the distribution transformer are obtained by iteratively solving the power balance equation. The outlet voltage of the low-voltage side of the distribution transformer is used as the boundary condition. If it is the first outer layer iteration, the outlet voltage of the low-voltage side of the distribution transformer is the set initial rated voltage value. Based on the active and reactive power of each phase at the low-voltage side outlet of the distribution transformer, taking into account the grounding method, wiring method and phase shift of the distribution transformer, the active and reactive power of each phase on the high-voltage side of the distribution transformer is calculated and used as the load injection power of the medium- and high-voltage network to participate in the power flow calculation of the medium- and high-voltage network. By performing power balance equations to perform iterative calculations of power flow in medium- and high-voltage networks, the active and reactive power and voltage values ​​of each node in the medium- and high-voltage network, as well as the current values ​​of each branch, are obtained, thus completing one outer-layer iteration. The low-voltage side outlet voltage of the distribution transformer is calculated based on the voltage of the terminal node of the medium- and high-voltage network. The difference between the current calculated low-voltage side outlet voltage and the previous outer layer iteration is calculated. If the difference is less than the set difference threshold, the iterative calculation is stopped, and the active and reactive power of all nodes are output. Otherwise, the low-voltage side outlet voltage of the distribution transformer is updated to the currently calculated value, and the next outer layer iteration is performed. The above steps are repeated starting from obtaining the active and reactive power of each phase of the low-voltage side of the distribution transformer through iteration using the power balance equation.

[0008] Preferably, the low-voltage and medium-high-voltage networks are modeled as a whole, specifically as follows: Integrated modeling includes power source model, load model, branch model, distributed power source model and energy storage model. Topology nodes are identified to construct a main and distribution integrated electrical island. Network parameters are read through the main and distribution integrated electrical island. Network parameters include branch impedance, distribution transformer grounding method, wiring method and phase shift, as well as real-time measurement data. Real-time measurement data includes generator, equivalent power source, distributed power source power, load power, and voltage of each power source bus in the high-voltage network, circuit breaker and disconnector status.

[0009] Preferably, the active and reactive power of each phase at the low-voltage side outlet of the distribution transformer is obtained by iteratively solving the power balance equation, specifically as follows: The power balance equation is solved iteratively using the Newton-Raphson method. The power balance equation is as follows:

[0010] in, , The k-th node The active power imbalance and reactive power imbalance represent the different phases. , The k-th node The active and reactive power injected by the power source of the other phase; , The k-th node The active and reactive power of the loads are represented by their respective phases. , These are the nodal admittance matrices. The matrix corresponding to the k-th node and the m-th node The difference between the two is indicated by the fact that the two phases are distinct. The real part (conductance) and imaginary part (susceptance) of the admittance between phases are represented. , For the m-th node The real and imaginary parts of the phase voltage are represented. , it is These represent phase A, phase B, phase C, and neutral line N, respectively. Based on the active and reactive power of each node at the low-voltage side outlet of the distribution transformer and the low-voltage network topology, the active and reactive power at the low-voltage side outlet of the distribution transformer are obtained.

[0011] Preferably, the low-voltage side outlet voltage of the distribution transformer is the root voltage of the low-voltage side of the distribution transformer. The boundary condition is: the root voltage is obtained based on the calculated phase voltages of all nodes and the low-voltage network topology. The root voltage is a fixed value in each iteration. The fixed value is the set initial rated voltage value or the low-voltage side outlet voltage of the distribution transformer calculated in the previous outer iteration.

[0012] Preferably, if the power source is a distributed power source and is of PQ type, then the corresponding , Substituting the known quantities directly into the power balance equation, if the power source is a distributed source and is PV type, then the corresponding... Given, the corresponding The variable is adjusted through a reactive power iteration loop. Maintain a constant output voltage.

[0013] Preferably, based on the active and reactive power of each phase at the low-voltage side outlet of the distribution transformer, taking into account the transformer grounding method, wiring method, and phase shift, the active and reactive power of each phase on the high-voltage side of the distribution transformer is calculated, specifically as follows: The order admittance matrix is ​​obtained based on the wiring and grounding methods; For each phase, the complex power is obtained based on the active and reactive power at the low-voltage side outlet of each distribution transformer. The complex power is divided by the set ideal low-voltage side phase voltage to calculate the low-voltage side phase current. The low-voltage side phase current is converted into low-voltage side sequence current. The current phase shift matrix and voltage phase shift matrix corresponding to the wiring method and phase shift are obtained. The low-voltage side sequence current is multiplied by the negative current phase shift matrix to obtain the high-voltage side sequence current. The sequence admittance matrix is ​​converted into the distribution transformer impedance value. The high-voltage side sequence current is converted into high-voltage side phase current. The ideal low-voltage side phase voltage is multiplied by the turns ratio and then by the voltage phase shift matrix to obtain the ideal high-voltage sequence voltage. The ideal high-voltage sequence voltage is converted into the ideal high-voltage phase voltage. The actual high-voltage side complex power is calculated based on the high-voltage side phase current, the ideal high-voltage side phase voltage, and the distribution transformer impedance value. The active and reactive power of the high-voltage side are obtained based on the actual high-voltage side complex power.

[0014] Preferably, the complex power on the actual high-voltage side is calculated based on the high-voltage side phase current, the ideal high-voltage side phase voltage, and the transformer impedance value, specifically as follows: The ideal high-voltage side phase voltage and high-voltage side phase current are multiplied to obtain the ideal high-voltage complex power. The transformer impedance value is multiplied by the square of the high-voltage side phase current to obtain the transformer complex power loss. The transformer complex power loss is added to the ideal high-voltage side complex power to obtain the actual high-voltage side complex power of the transformer. Alternatively, the voltage loss of the distribution transformer can be calculated by multiplying the phase current on the high-voltage side and the transformer impedance value. The actual phase voltage on the high-voltage side of the distribution transformer can be obtained by superimposing the ideal phase voltage on the high-voltage side and the voltage loss on the distribution transformer. The actual complex power on the high-voltage side can be calculated by multiplying the actual phase voltage on the high-voltage side and the phase current on the high-voltage side.

[0015] Preferably, iterative calculations of power flow in medium- and high-voltage networks are performed, specifically as follows: If the distributed power source supplying the corresponding branch is of type PQ, then the formula for power flow iteration calculation is:

[0016] If the distributed power source supplying the corresponding branch is of PV type, then the formula for power flow iteration calculation is:

[0017]

[0018] in, The active power injected into node i of the medium- and high-voltage network; The reactive power injected into node i of the medium- and high-voltage network; , These are the real and imaginary parts of the p-phase voltage at node i in the medium- and high-voltage network, respectively. , These are the real and imaginary parts of the m-phase voltage at node j in the medium- and high-voltage network, respectively. When A, B, and C are respectively, they represent phase A, phase B, and phase C. Let i be the active power value of node i in the medium- and high-voltage network. This represents the reactive power output of the generator. The reactive power of the load at node i in the medium- and high-voltage network; Let be the reactive power value of phase p of node i in the medium- and high-voltage network; Let be the real part of the mutual admittance between the p-phase of medium-high voltage network node i and the m-phase of medium-high voltage network node j; Let be the imaginary part of the mutual admittance between the p-phase of medium- and high-voltage network node i and the m-phase of medium- and high-voltage network node j; For a given voltage amplitude, for The correction amount, The voltage of phase p of node i in the medium- and high-voltage network The amplitude is N, where N is the total number of branches.

[0019] Preferably, when modeling a medium- and high-voltage network, for a dual-winding transformer, only one branch model is created during modeling. The branch model sets the phase shift of the primary winding, and the phase shift of the secondary winding is set to 0 by default. For a three-winding main transformer, three branch models are created during modeling, with each winding corresponding to one branch model. In the branch model, the primary winding does not have a phase shift angle set, but only the phase shifts of the secondary and tertiary windings are set. The corresponding phase shift matrix is ​​obtained based on the phase shift matrix. The mutual admittance between the p phase of the medium- and high-voltage network node i and the m phase of the medium- and high-voltage network node j is calculated based on the corresponding phase shift matrix.

[0020] Preferably, the low-voltage side outlet voltage of the distribution transformer is calculated based on the voltage of the terminal node of the medium- and high-voltage network. Specifically, the voltage of the terminal node of the medium- and high-voltage network is the voltage of the high-voltage side bus of the distribution transformer. The low-voltage side outlet voltage of the distribution transformer is calculated based on the active and reactive power of each phase on the high-voltage side of the distribution transformer and the voltage of the high-voltage side bus of the distribution transformer. The high-voltage side power of the transformer is calculated based on the active and reactive power of each phase on the high-voltage side and the high-voltage side bus voltage. The high-voltage side phase current is calculated based on the transformer impedance and the high-voltage side phase current. The voltage loss of the high-voltage winding is calculated based on the voltage loss of the ideal high-voltage side phase voltage. The voltage value of the ideal high-voltage winding is obtained by subtracting the voltage loss from the ideal high-voltage side phase voltage. The voltage value of the ideal high-voltage winding is converted into a sequence component, and the voltage sequence component of the ideal low-voltage winding is calculated. The voltage phase component of the low-voltage winding is obtained based on the calculated voltage sequence component of the ideal low-voltage winding. The voltage phase component of the low-voltage winding is the low-voltage side outlet voltage of the transformer.

[0021] The second aspect of the present invention proposes a real-time three-phase unbalanced power flow calculation system based on the method described in the first aspect of the present invention, comprising a modeling module, a low-voltage network power flow calculation module, a distribution transformer power flow calculation module, a medium- and high-voltage network power flow calculation module, and an outer iteration module, specifically: Modeling module: Used for integrated modeling of low-voltage and medium-high voltage networks, identifying node composition and network parameters, including transformer grounding method, wiring method and phase shift, as well as the voltage of each power supply bus in the high-voltage network; Low-voltage network power flow calculation module: It is used to obtain the active and reactive power of each phase at the outlet of the low-voltage side of the distribution transformer by iteratively solving the power balance equation. The outlet voltage of the low-voltage side of the distribution transformer is used as the boundary condition. If it is the first outer layer iteration, the outlet voltage of the low-voltage side of the distribution transformer is the set initial rated voltage value. Transformer power flow calculation module: Based on the active and reactive power of each phase at the low-voltage side outlet of the transformer, taking into account the transformer grounding method, wiring method and phase shift, the active and reactive power of each phase on the high-voltage side of the transformer is calculated and used as the load injection power of the medium and high voltage network to participate in the power flow calculation of the medium and high voltage network. Medium and high voltage network power flow calculation module: used to perform iterative calculation of power flow in medium and high voltage networks through power balance equations, obtain the active and reactive power and voltage values ​​of each node in the medium and high voltage network as well as the current values ​​of each branch, and complete one outer layer iteration; Outer Iteration Module: This module calculates the low-voltage side outlet voltage of the distribution transformer based on the voltage of the terminal nodes of the medium- and high-voltage network. It calculates the difference between the current calculated low-voltage side outlet voltage and the voltage from the previous outer iteration. If the difference is less than the set threshold, the iteration calculation stops, and the active and reactive power of all nodes is output. Otherwise, the low-voltage side outlet voltage is updated to the currently calculated value, and the next outer iteration is performed. The above steps are repeated starting from obtaining the active and reactive power of each phase on the low-voltage side of the distribution transformer through iteration using the power balance equation.

[0022] A third aspect of the present invention provides an apparatus comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor performing steps using the real-time power flow calculation method for three-phase unbalance based on master-distributor integration described in the first aspect of the present invention.

[0023] The fourth aspect of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, uses the steps of the real-time power flow calculation method for three-phase unbalance based on the integration of primary and secondary systems described in the first aspect of the present invention.

[0024] The beneficial effects of this invention are as follows: Compared with existing technologies, the method of this invention comprehensively considers the different parameter characteristics of different voltage levels in actual power grids, the maintenance status of power grid parameters, and the measurement and acquisition status, and adopts calculation methods suitable for different voltage levels. By comprehensively employing the phase component method and sequence component matching to match the parameter characteristics of each voltage level, the calculation is more accurate. The modular software design facilitates code development and maintenance, and the fault isolation mechanism improves system robustness. The integrated three-phase unbalanced power flow calculation scheme for high, medium, and low voltage systems adopts a hierarchical-distributed-coordinated iterative architecture, which not only solves the key technical bottlenecks in current power system analysis but also provides a core computing engine for the future development of smart grids, possessing significant theoretical and engineering value. Attached Figure Description

[0025] Figure 1 This is a flowchart of the inner and outer layer dual-iteration calculation process; Figure 2 A flowchart for calculating the inner layer's hierarchical partitioning; Figure 3 A flowchart for calculating three-phase imbalance in a distribution transformer; Figure 4 This is a flowchart of time-series power flow calculation; Figure 5 This is a schematic diagram of the test circuit. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0027] like Figure 1 and Figure 2 As shown, Embodiment 1 of the present invention provides a method and system for real-time calculation of three-phase unbalanced power flow based on integrated main and distribution systems, specifically as follows: Step (1): Construct an integrated main and auxiliary calculation model.

[0028] 1.1) Calculation Scope Description In this embodiment, the integrated power flow calculation research object includes: equipment covering the entire power supply range of the high, medium and low voltage distribution network, with a default voltage level range of 220V to 220kV; the power supply area includes the range of 210kV substations to 10kV feeders and all transformer substations under the feeders.

[0029] The integrated main and distribution calculation model adopts an integrated high, medium, and low voltage modeling method. The high-voltage side power supply range of the distribution transformer from the 220kV substation to the 10kV feeder area is treated as an independent calculation unit for electrical island analysis, enabling power flow solutions for the high and medium voltage networks. Using the low-voltage side voltage of the distribution transformer as boundary conditions, the low-voltage network within the low-voltage side power supply range of the distribution transformer is treated as an independent calculation unit to achieve power flow solutions for the low-voltage network. Then, the distribution transformer is calculated independently as the boundary device for both the medium-high voltage and low-voltage networks. Through outer-layer secondary iterative calculations, integrated main and distribution modeling with high, medium, and low voltage is achieved, along with layered-distributed-coordinated inner and outer-layer iterative calculations for the integrated main and distribution system.

[0030] 1.2) Model Data Description The integrated high- and medium-voltage model equipment includes: main grid model data and distribution network model data. The main grid model data is divided into container type and equipment type. Container type includes: voltage level, region, substation, and bay. Equipment type includes generators, main grid transformers, transformer windings, main grid AC segments, AC segment endpoints, main grid busbars, main grid disconnectors, main grid circuit breakers, and main grid capacitive reactors. The medium-voltage equipment in the distribution network model data includes 10kV lines, distribution network switches, distribution network disconnectors, distribution network feeder segments, distribution network transformers, and distribution network loads. Low-voltage equipment includes low-voltage switches, low-voltage feeder segments, low-voltage loads, and low-voltage capacitors. Distributed energy includes photovoltaic power plants, photovoltaic inverters, energy storage, charging piles, etc. The distribution network switches include identification information indicating whether they are automated switches; the distribution network transformers include data on public and private transformers; and the measurement data for distributed photovoltaic grid-connected switches needs to include the measurement direction.

[0031] 1.3) Description of measurement data.

[0032] Based on the integrated main and auxiliary model, the fusion data source for power flow calculation and analysis is obtained, including real-time measurement data of equipment, estimated data based on historical data, and pseudo-measurement data based on measurement data of other systems.

[0033] The measurement data loading includes: real-time phase bus voltage of the substation, current, active and reactive power, and remote signaling status of each phase of the circuit breaker, current, active and reactive power measurements of each phase of the load, active and reactive power measurements of each phase of the distributed power source, real-time measurement data from the automated distribution network switches of the distribution automation system, near-real-time distribution measurement data from the consumer acquisition system, and some real-time data from the integrated terminals accessed by the cloud master station, as well as directional power measurement data from the 10kV photovoltaic grid-connected switch. Among these, for the two sources of measurement data for the distribution transformer, the integrated terminal data will be the primary source, and reasonable data will be selected as the distribution measurement data.

[0034] Calculations should be performed periodically as needed when power system events cause changes in network topology, and when measurement deviations exceed the parameter thresholds used in the previous operation.

[0035] 1.4) Model construction instructions.

[0036] The integrated master-distribution modeling employs a unified data structure and normalizes heterogeneous data, enabling rapid matching of physical devices and efficient data fusion. This gives each type of device self-expressive capabilities, allowing for the rapid and flexible representation of the data perception capabilities of each device object. Integrated master-distribution modeling provides the computational foundation for power flow calculation and analysis, and is a fundamental prerequisite for the correct calculation of data prediction, state estimation, and power flow computation.

[0037] The specific details of the modeling and implementation of the integrated main and auxiliary computing model include: 1) Model the generator as an independent power source, set up an independent calculation unit, model the corresponding power source as an equivalent power source, and take distributed power sources into consideration to establish a corresponding model; 2) The load aggregation on the low-voltage side of the distribution transformer is used as the equivalent load model, and the energy storage and charging piles are used as the load model model; 3) Calculate and verify the rationality of nominal values ​​for parameters of main grid lines, main transformer windings, distribution transformer windings, capacitors, and distribution network feeder segments, and convert them to per-unit values; Parameter rationality verification includes verifying missing parameters and default parameter assignments for equipment (lines, main transformers, distribution transformers, capacitors, reactors, etc.); verifying missing parameters and model of distribution network feeder segments; verifying logical errors in equipment parameters, such as whether the capacity direction and value of capacitors and reactors are consistent, and whether the voltage of the equipment deviates significantly from the rated voltage; and verifying the rationality of equipment parameters according to multiple dimensions such as different equipment types, different voltage levels, and different capacities.

[0038] 4) Topology verification of major equipment such as lines, main transformers, distribution transformers, generators, energy storage, and feeder sections, to check equipment connectivity. Equipment connectivity verification includes: checking for incorrect equipment node numbers and unconnected nodes; checking equipment subordination relationships, such as whether a substation belongs to a specific area or a feeder belongs to a specific substation; and checking equipment hierarchical relationships, such as verifying the relationship between the number of line terminals and lines, and the correspondence between the number of windings and the type of distribution transformer.

[0039] 5) Power grid equipment is modeled in layers according to its region, substation, feeder, and distribution area.

[0040] 1.5) Electrical island analysis.

[0041] 1) Forming computing nodes Network topology analysis obtains the node connection relationships and remote signaling status of power grid equipment components such as main grid AC lines, AC line endpoints, main transformers, distribution transformers, distribution transformer windings, generators, loads, switches, capacitors, distribution network feeder segments, distribution network switches, distribution network disconnectors, distribution network transformers, and distribution network loads. By connecting the physical nodes of each device together through closed switches, a busbar calculation node is formed. AC lines, main transformer windings, distribution transformer windings, and distribution network feeder segments form branches, forming a node branch model.

[0042] 2) Formation of electrical islands Multiple computing nodes are connected by branches using either a breadth-first or depth-first topology search method to form multiple electrical islands; 3) Sorting and Classification of Electrical Islands The nodes are sorted according to their number, and the electrical islands are analyzed to determine if they are live. Live islands with a node count greater than a threshold are selected to complete the multi-island topology analysis of the power grid. An electrical island containing both generators and loads is considered a live island; otherwise, it is considered a dead island. Power flow calculations only include live islands; dead islands are excluded.

[0043] After forming the electrical islands, the nodes are optimized and numbered based on these islands. By adjusting the calculation order of the nodes, the injected elements generated during the elimination process are minimized, thus maintaining the sparsity of the matrix. The use of sparse matrix storage technology reduces memory requirements and significantly shortens the iteration time and improves computation speed by reducing invalid operations during the elimination and back-substitution processes in solving the correction equations.

[0044] Step (2): Calculation of low-pressure three-phase unbalanced power flow 2.1) Low-voltage distribution network topology verification Topology verification mainly includes two parts: first, identifying customers on the same feeder to achieve customer-feeder identification; second, identifying the upstream and downstream relationships of different feeders. Customer-feeder identification is based on clustering algorithms, while upstream and downstream relationships are distinguished by the magnitude of voltage characteristics when load occurs.

[0045] Household-to-line identification and feeder-to-upstream / downstream relationships are based on existing technologies to realize topology verification of low-voltage distribution networks. This provides a model data foundation for topology analysis and power flow calculation in low-voltage distribution networks, ensuring the accuracy of topology data and power flow calculation. Specific methods will not be described in detail here.

[0046] 2.2) Low-voltage power distribution network data model The low-voltage power distribution network adopts a core structure of "layered radiation, three-phase four-wire". Multiple main lines are drawn from the low-voltage side of the distribution transformer. Each main line branches out like a tree trunk, supplying power to numerous users through multi-level branch boxes. Three phase wires (A / B / C, live wires) provide 380V power, and one neutral wire (N, neutral wire) works with any phase wire to provide 220V lighting power.

[0047] Typical characteristics of low-voltage distribution networks include: no line transposition, significant asymmetry in line parameters leading to a non-diagonal sequence impedance matrix, i.e., inter-sequence coupling; random connection of numerous single-phase and two-phase loads, resulting in asymmetry in the amplitude and phase of the three-phase currents and unbalanced three-phase loads; asymmetric inter-phase coupling; and different zero-sequence paths due to grounding methods such as TN-C, TN-S, and TT. Therefore, the sequence component method used for medium- and high-voltage networks cannot be used for parameter calculation; instead, the phase component method (direct three-phase modeling) is employed.

[0048] In a low-voltage three-phase four-wire system, each phase and the neutral line need to be considered. Therefore, each node has four voltages: phase A, phase B, phase C, and the neutral line N. The neutral line is typically grounded at the transformer, so the neutral voltage may not be zero (especially under unbalanced current conditions causing neutral point offset).

[0049] (1) Low-voltage line model For a three-phase four-wire line using a pi-type equivalent circuit, both its series impedance and parallel admittance are 4×4 matrices. For a line connecting node u and node v: its corresponding series impedance matrix Z... series It is a 4×4 matrix, including the mutual impedances between each phase and the neutral line. Typically, the neutral line has a higher impedance and is coupled to each phase. The contribution of the series portion of the line to the nodal admittance matrix is: Z added to the self-admittances of nodes u and v. series -1 Subtract Z from the mutual admittance series -1 The parallel components (capacitance to ground and conductance) are typically added to the node self-admittance.

[0050] Specifically: Series impedance matrix Z series (4×4):

[0051] in, express The difference between the two is indicated by the fact that the two phases are distinct. The series impedance between the phases is represented. , it is These represent phase A, phase B, phase C, and neutral line N, respectively.

[0052] Ground-connected admittance matrix Y shunt :

[0053] in, for The difference between the two is indicated by the fact that the two phases are distinct. The series-to-ground parallel admittance between the phases is represented; The self-admittance matrix is:

[0054] in, , Let be the self-admittance matrix of the u-th and v-th nodes; The mutual admittance matrix is:

[0055] in, , These are the mutual admittance matrices between the u-th node and the v-th node, and between the v-th node and the u-th node, respectively.

[0056] 2.3) Three-phase unbalanced power flow in low-voltage distribution networks For an n-node system, the voltage at each node There are 4 voltage components:

[0057] in, These are the phase A, phase B, and phase C voltages of the k-th node, and the neutral line N-to-ground voltage, respectively.

[0058] Node injection current vector :

[0059] in, The voltages of phase A, phase B, and phase C at the k-th node and the current injected into the neutral line at node N are respectively.

[0060] The node voltages of all nodes form a voltage matrix. The node-injected current vectors of all nodes form the current matrix. The node admittance matrix composed of the self-admittance matrix and the mutual admittance matrix The low-voltage network equation is:

[0061] Low-voltage systems have a large number of single-phase and two-phase loads. The solution for single-phase / two-phase loads is to connect the load to the corresponding phase, leaving the current in other phases zero. The neutral current is the vector sum of the three-phase currents.

[0062] Low-voltage network power flow analysis using the Newton-Raphson method: State variables: Each node has 8 variables (4 real voltage parts and 4 imaginary voltage parts): in, For state variables, , , , They are respectively The real part; , , , They are respectively The imaginary part.

[0063] Power balance equations: For each node k (except the slack node):

[0064] in, , The k-th node The active power imbalance and reactive power imbalance represent the different phases. , The k-th node The active and reactive power injected by the power source of the other phase; , The k-th node The active and reactive power of the loads are represented by their respective phases. , These are the nodal admittance matrices. The matrix corresponding to the k-th node and the m-th node The difference between the two is indicated by the fact that the two phases are distinct. The real part (conductance) and imaginary part (susceptance) of the admittance between phases are represented. , For the m-th node The real and imaginary parts of the phase voltage are represented. Because low-voltage networks have a large number of distributed generation (DG) sources connected, it is necessary to consider the participation of DG sources in power flow calculations. For DG sources, PQ type: they directly participate in current calculations. PV type: a reactive power iteration loop needs to be added to adjust the reactive power sustaining voltage. Therefore, if the DG source connected to node k is of type PQ, then the corresponding... , Substitute the known quantities directly into the above equation. If it is a PV type, the corresponding... It is known, but It becomes a variable to be determined, and is adjusted through a reactive power iteration loop. To maintain a constant voltage.

[0065] The neutral line typically receives no power injection, i.e. , All are 0.

[0066] The Newton-Raphson method is used to perform power flow analysis on low-voltage networks, and output the active and reactive power of each phase at the low-voltage side outlet of the distribution transformer.

[0067] The output voltage of the low-voltage side of the distribution transformer is the root voltage of the low-voltage side of the distribution transformer. The boundary condition is: the root voltage is obtained based on the calculated phase voltages of all nodes and the low-voltage network topology. The root voltage satisfies a fixed value in each iteration. The fixed value is the set initial value or the output voltage of the low-voltage side of the distribution transformer calculated in the previous outer iteration.

[0068] Based on the active and reactive power of each node on the low-voltage side of the distribution transformer and the low-voltage network topology, the active and reactive power of the low-voltage side of the distribution transformer are obtained.

[0069] Step (3): Calculation of three-phase unbalanced power flow in the distribution transformer The calculation of three-phase unbalanced power flow in distribution transformers includes modeling of three-phase unbalance in the transformer area, phase shift analysis of distribution transformers, and an introduction to the calculation methods and procedures for distribution transformers.

[0070] 3.1) Modeling of three-phase imbalance in distribution transformers.

[0071] Modeling calculations considering different wiring and grounding methods for distribution transformers, as well as different phase shifts, are performed. The calculations comprehensively consider different wiring methods and neutral grounding methods on both the high-voltage and low-voltage sides of the distribution transformer. Common wiring methods for distribution transformers include D-Yn11 (Delta-Yne neutral point grounded through a small resistor) and Y-Yn0 (star-star neutral point directly grounded). Different wiring methods affect the phase relationship and voltage transformation between the high-voltage and low-voltage sides, thus affecting power calculations. The neutral grounding method can affect the zero-sequence current path of the system, which is particularly important under three-phase imbalance conditions, as analyzed below.

[0072] (1) Transformer wiring methods include: YY connection: If the neutral point is not grounded, zero-sequence current cannot flow, and the zero-sequence impedance is infinite; if the neutral point is grounded, the neutral point grounding impedance must be considered. In positive-sequence and negative-sequence networks, the transformer impedance is the leakage impedance.

[0073] Y-Δ connection: There is a 30° phase shift in both positive and negative sequence cases. From the y-terminal to the Δ-terminal, the positive sequence voltage lags by 30°, and the negative sequence voltage leads by 30°. Zero-sequence current forms a circulating current at the Δ-terminal, and zero-sequence current at the y-terminal cannot flow into the Δ-terminal.

[0074] Δ-Δ connection: In both positive and negative sequence networks, the transformer's impedance is the leakage impedance. Zero-sequence current forms a circulating current in the windings at both ends; if the winding resistance is neglected, the zero-sequence impedance is zero. In summary, the sequence admittance matrix can be obtained based on the wiring and grounding methods. .

[0075] (2) Phase shift analysis of the distribution transformer Phase shift settings instructions: Different phase shifts include primary voltage leading secondary voltage by 30 degrees and primary voltage lagging secondary voltage by 30 degrees (the lead and lag relationships of voltage and current are opposite).

[0076] For different wiring and different phase shifts, voltage and current have corresponding voltage phase shift matrices and current phase shift matrices.

[0077] (3) Calculation of power of high voltage winding of distribution transformer Calculate the three-phase unbalanced power of the high-voltage winding of the distribution transformer based on the three-phase unbalanced power on the low-voltage side of the distribution transformer.

[0078] Step 1: First, calculate the phase current on the low-voltage side based on the active and reactive power and the phase voltage (rated voltage) on the low-voltage side of each distribution transformer.

[0079]

[0080] Step 2: Use the sequence component conversion formula to convert the low-voltage phase current into the corresponding sequence current.

[0081] Symmetric component transformation matrix for:

[0082] in, For a constant value, , It is an imaginary number.

[0083] The formula for converting phase component current to sequence component current is:

[0084] in, Indicates the low-voltage side-sequence current; This indicates the phase current on the low-voltage side.

[0085] Step 3: Convert the low-voltage side sequence current into the high-voltage side sequence current according to the phase shift and turns ratio, and calculate the transformer impedance value; The phase shift needs to be considered. Specifically, in this embodiment, one of the transformers is a Y-Δ wiring transformer, and there is a 30° phase shift between the Y end and the Δ end.

[0086] Terminal current phase shift matrix K i for: The current phase shift matrix for the wiring phase shift in this embodiment is: for:

[0087] High-voltage side sequence current for: in, The ratio of the variable is the ratio of the variable.

[0088] The ordered admittance matrix is:

[0089] in, , , These are positive-sequence admittance, negative-sequence admittance, and zero-sequence admittance, respectively.

[0090] Convert the sequence admittance matrix into phase component matrices. : The transformer impedance value is:

[0091] Step 4: Convert the high-voltage side sequence current into the high-voltage side phase current.

[0092] Calculate the phase current on the high-voltage side :

[0093] Step 5: Convert the ideal low-voltage side phase voltage into the ideal distribution transformer high-voltage phase voltage according to the transformation ratio and phase shift.

[0094] For a Y-Δ connection, the phase relationship between the phase voltage and the line voltage needs to be represented by matrix transformation. Taking Dyn11 as an example, the three sequence components of the primary voltage phase are all lagging by 30°, so the relationship between the Δ-terminal voltage and the Y-terminal voltage is: Voltage phase shift matrix for:

[0095] Ideal distribution transformer high-voltage side sequence voltage :

[0096] in, For the ratio of the variable, This is the ideal low-voltage side sequence voltage; Find the ideal high-voltage side phase voltage :

[0097] Step 6: Based on the ideal high-voltage side phase voltage and phase current Solving for the complex power of an ideal distribution transformer high voltage .

[0098] The formula is:

[0099] Step 7: Based on the phase current on the high-voltage side and transformer impedance value Calculate the complex power loss of the distribution transformer :

[0100] Step 8: Ideal distribution transformer high-voltage side power The actual high-voltage side complex power of the distribution transformer is obtained by adding the complex power loss of the distribution transformer. :

[0101] The active and reactive power of the actual high-voltage side of the distribution transformer can be obtained by using the actual high-voltage side power of the distribution transformer.

[0102] Alternatively, another calculation method can be used: Step 6: Calculate the voltage loss of the distribution transformer by multiplying the phase current on the high-voltage side and the transformer impedance value.

[0103] Step 7: The actual high-voltage phase voltage of the distribution transformer is obtained by superimposing the ideal high-voltage phase voltage onto the distribution transformer voltage loss.

[0104] Step 8: Calculate the actual high-voltage side complex power by multiplying the actual high-voltage side phase voltage and high-voltage side phase current. Then, obtain the actual high-voltage side active power and reactive power of the distribution transformer through the actual high-voltage side complex power.

[0105] Step (4): Calculation of unbalanced three-phase power flow under high and medium pressure 4.1) Circuit Modeling Medium and high voltage lines are three-phase lines without a neutral conductor. The line parameter matrix is ​​a 3×3 matrix. For medium voltage lines, the phase impedance matrix can be directly used. For high voltage lines, the conductor arrangement is symmetrical, and the line parameter structure is completely symmetrical, so sequence components can be used in the calculation.

[0106] Therefore, for medium- and high-voltage networks, the series impedance matrix is:

[0107] in, for The difference between the two is indicated by the fact that the two phases are distinct. The series impedance between the phases is represented. , it is These represent phase A, phase B, and phase C, respectively.

[0108] Ground-connected admittance matrix Y shunt :

[0109] in, for The difference between the two is indicated by the fact that the two phases are distinct. The series-to-ground parallel admittance between the phases is represented.

[0110] 4.2) Transformer Modeling The phase shift degree is set according to the main transformer wiring method: For a two-winding transformer, only one branch model is created during modeling, and the phase shift of the primary winding is set in this branch model. That is, the secondary winding phase shift is set to 0 by default, while the primary winding phase shift is set. The primary winding leads the secondary winding in positive sequence. Degree, negative order lags behind the second side The degree is set, and the corresponding phase shift matrix is ​​obtained based on the phase shift. For example, when the pointer is 1, the primary side leads the secondary side by 30° in positive sequence, and the branch phase shift is set as follows during calculation: When the pointer is at 11, the primary side lags the secondary side by 30° in positive sequence. The branch phase shift is set as follows during calculation: The phase shift matrix from node i to node j of the branch. And the phase shift matrix from node j of branch to node i of branch. for:

[0111] For a three-winding main transformer, during modeling, three branch models are created, with one branch model corresponding to each winding. In the branch models, the primary winding's phase shift angle is not set; only the phase shifts of the secondary and tertiary windings are set. That is, the primary phase shift is set to 0 by default, and only the phase shifts of the secondary and tertiary windings are set. For example, in the transformer wiring configuration YNd11, the primary side lags the secondary side by 30 degrees, and the secondary side leads the primary side by 30 degrees. During calculation, the secondary winding is set to 30 degrees, and the primary winding's phase shift angle is not set, while the secondary winding's phase shift angle is set to 30 degrees.

[0112] Considering the transformation ratio and phase shift, calculate the elements of the principal variable order component admittance matrix and then transform them into phase components: in, , These are the three-order self-admittance matrices of nodes i and j in the medium- and high-voltage network, respectively. , These are the three-order mutual admittance matrices from node i to node j and from node j to node i in the medium-high voltage network, respectively. This is the ordered admittance matrix of the corresponding network; , These are the transformer ratios of nodes i and j in the medium- and high-voltage network, respectively. , These are the three-phase self-admittance matrices of nodes i and j in the medium- and high-voltage network, respectively. , These are the three mutual admittance matrices from node i to node j and from node j to node i in the medium-high voltage network, respectively. , Let i and j be the rated voltages of nodes i and j in the branch, respectively. , These are the reference voltages for nodes i and j of the branch, respectively.

[0113] 4.3) Computational Model Construction and Solution Solving large-scale power systems, especially radially operating medium- and low-voltage distribution networks, generally involves large-scale problems with good sparsity. Using rectangular coordinates, the mathematical model for solving the injected power can be described as a quadratic function, which can be abstractly described as:

[0114] Here, the quadratic function value of node i in phase p (phase A, B, or C) of the medium-high voltage network may represent a power or current-related quantity. Let be the voltage state vector of node i and node j in the medium-high voltage network, containing real and imaginary components; It is a constant matrix. When the matrix is ​​composed of real conductances of three-phase mutual admittances (or three-phase self-admittances if i and j are equal), To inject active power; When the matrix is ​​composed of imaginary susceptances of the three mutual admittances (or three-phase self-admittances if i and j are equal), it is a matrix composed of imaginary susceptances. Let N be the reactive power injection power, and N be the total number of nodes i.

[0115] Considering three-phase branches with identical coupling, the admittance matrix parameters are expressed in rectangular coordinates. The formulas for the current and power of each phase branch are derived as follows: The three-phase voltages (in rectangular coordinates) of nodes i and j in the medium- and high-voltage network are:

[0116] in, , , These are the three-phase voltages A, B, and C of node i in the medium- and high-voltage network, respectively. , , These are the real parts of the three-phase voltages A, B, and C of node i in the medium- and high-voltage network, respectively. , , These are the imaginary parts of the three-phase voltages A, B, and C of node i in the medium- and high-voltage network, respectively. , , These are the three-phase voltages A, B, and C of node j in the medium- and high-voltage network, respectively. , , These are the real parts of the three-phase voltages A, B, and C at node j in the medium- and high-voltage network, respectively. , , Let A, B, and C be the imaginary parts of the three-phase voltages at node j in the medium-high voltage network. The three-phase admittance matrix (including self-admittance and mutual admittance) (in rectangular coordinates) is:

[0117] in, , , These are the self-admittances of phases A, B, and C and phase p (A, B, or C) of node i in the medium- and high-voltage network, respectively. , , These are the real parts of the self-admittance of phases A, B, C and p of node i in the medium-high voltage network, respectively. , , These are the imaginary parts of the self-admittance of phases A, B, C and p of node i in the medium-high voltage network, respectively. , , These are the mutual admittances of phases A, B, and C of medium- and high-voltage network node i and phase p (A, B, or C) of medium- and high-voltage network node j, respectively. , , These are the real parts of the mutual admittances between phases A, B, and C of medium- and high-voltage network node i and phase p (A, B, or C) of medium- and high-voltage network node j, respectively. , , These are the imaginary parts of the mutual admittance between phases A, B, and C of medium- and high-voltage network node i and phase p (A, B, or C) of medium- and high-voltage network node j, respectively. The formulas for the branch currents (injecting current from node i in the medium-high voltage network to the branch) are as follows:

[0118]

[0119]

[0120] in, , , These are the currents of the A, B, or C phase branches, respectively.

[0121] The formulas for the real and imaginary parts of the current in each phase of the branch can be derived from the above formulas as follows:

[0122] in, , , These are the real parts of the currents in the A, B, or C phase branches, respectively. , , These are the imaginary parts of the currents in the A, B, or C phase branches, respectively.

[0123] The power of each phase of the branch is calculated based on the real and imaginary parts of the current in each phase:

[0124] in, , These represent the active and reactive power values ​​of each phase flowing from node i to node j in the medium- and high-voltage network. These represent the active and reactive power values ​​of each phase flowing from node j to node i in the medium- and high-voltage network. , These are the active and reactive power values ​​of nodes i and j in the medium- and high-voltage network, respectively. For PV-connected branches, the active power injected into node i of the medium- and high-voltage network is... and reactive power injection for:

[0125] in, This represents the active power output of the generator. The active power of the load at node i in the medium- and high-voltage network; Let i be the active power value of node i in the medium- and high-voltage network. This represents the reactive power output of the generator. The reactive power of the load at node i in the medium- and high-voltage network; Let be the reactive power value of phase p of node i in the medium- and high-voltage network; Let be the real part of the mutual admittance between the p-phase of medium- and high-voltage network node i and the m-phase of medium- and high-voltage network node j (i.e., the conductance between the p-phase of medium- and high-voltage network node i and the m-phase of medium- and high-voltage network node j). It is the imaginary part of the mutual admittance between phase p of medium- and high-voltage network node i and phase m of medium- and high-voltage network node j (i.e., the susceptance between phase p of medium- and high-voltage network node i and phase m of medium- and high-voltage network node j); m is also the phase index, m=A, B, C means phases A, B, and C.

[0126] The real and imaginary parts of the three-phase voltages A, B, and C of the branch are used as state vectors and solved using the Newton-Raphson method. When calculating the Jacobian matrix, the calculation of partial derivatives for node power can be greatly simplified by merging like terms in the sparse matrix. Therefore, since it is necessary to access specified elements of the sparse matrix or sparse vector multiple times based on row and column numbers to merge like terms, a mapping table is used. Both sparse matrices and sparse vectors can be described using second-order mapping tables.

[0127] When solving the corrected equation, it is only necessary to traverse and access the elements of the sparse matrix or vector. Therefore, the sparse matrix is ​​described by a triple array of <row number, column number, value>, and the sparse vector is described by a binary array of <row number, value>, in order to save memory space and improve traversal access efficiency.

[0128] The Jacobian matrix is:

[0129] in, , These are the real and imaginary vectors of the voltage correction for nodes other than node i in the medium- and high-voltage network.

[0130] For PV-connected nodes, active power injection The equations are the same as those for PV connection, except that the equation for reactive power injection is replaced by the voltage equation:

[0131] in, For a given voltage amplitude, for The correction amount, for The amplitude.

[0132] Step (5): Outer Iteration Loop The low-voltage outlet voltage of the distribution transformer is calculated based on the voltages of each node in the medium- and high-voltage network. Specifically: The voltage at the end node of the medium- and high-voltage network is the voltage of the high-voltage bus of the distribution transformer. The low-voltage outlet voltage of the distribution transformer is calculated based on the active and reactive power of each phase on the high-voltage side of the distribution transformer and the voltage of the high-voltage bus of the distribution transformer.

[0133] Step 1: Calculate the phase current on the high-voltage side of the transformer based on the power on the high-voltage side of the transformer and the bus voltage on the high-voltage side of the transformer.

[0134]

[0135] in, This refers to the voltage of the high-voltage side busbar of the distribution transformer.

[0136] Step 2: Calculate the voltage loss of the high-voltage winding of the distribution transformer based on the transformer impedance and the phase current on the high-voltage side. .

[0137]

[0138] Step 3: Calculate the voltage value of the ideal transformer high-voltage winding. .

[0139]

[0140] Step 4: Calculate the voltage sequence components of the ideal distribution transformer high-voltage winding. .

[0141]

[0142] Step 5: Calculate the voltage sequence components of the low-voltage winding of the ideal distribution transformer. .

[0143]

[0144] Step 6: Calculate the voltage phase components of the low-voltage winding of the distribution transformer. (i.e., low-voltage output voltage).

[0145]

[0146] Calculate the difference between the current low-voltage side outlet voltage of the distribution transformer and the low-voltage side outlet voltage of the distribution transformer in the previous outer layer iteration. If it is the first outer layer iteration, the low-voltage side outlet voltage of the distribution transformer in the previous outer layer iteration is the set initial value. If the difference is less than the set difference threshold, stop the outer layer iteration calculation and output all active and reactive power. Otherwise, proceed to the next outer layer iteration and update the low-voltage side outlet voltage of the distribution transformer to the currently calculated value. Repeat the above steps starting from obtaining the active and reactive power of each phase of the low-voltage side of the distribution transformer through iteration using the power balance equation.

[0147] It should be noted that the above-mentioned integrated main and distribution large-scale three-phase unbalanced online real-time power flow calculation process is divided into static power flow calculation and dynamic power flow calculation.

[0148] (1) Static power flow calculation Static power flow calculation considers the power flow changes under the superimposed operating state model at a certain moment. Based on the topology of the power grid under a specified operating state, substation bus voltage, and operating power of load equipment, it calculates node voltage, branch current, and power distribution, and statistically analyzes equipment with node voltage exceeding limits and equipment with branch current overload, providing dynamic power flow data support and safety verification services for other business needs.

[0149] The integrated main and distribution large-scale three-phase unbalanced online real-time power flow calculation is used to perform power flow calculation based on the estimated real-time power flow operating status, taking into account changes in operating mode, load power adjustment and distributed power output adjustment, thereby realizing the integrated main and distribution large-scale three-phase unbalanced online real-time power flow calculation.

[0150] (2) Time-series power flow calculation Time-series power flow calculation responds to hypothetical scenarios consisting of time-varying load and distributed generation output changes superimposed with system events. It analyzes dynamic load change data and dynamic power flow changes under dynamic event hypothetical scenarios, providing a dynamic power flow response. The calculation process is as follows: Figure 4 As shown.

[0151] The implementation process involves first initializing the cross-sectional data, overlaying operational state simulations and event simulations to generate a dynamic simulation model and data, and then performing power flow calculations in a time sequence at relatively short time intervals to complete the online real-time power flow calculation and analysis of large-scale three-phase imbalance between main and distribution systems over a future period. Finally, the simulation calculation results and power flow verification results are given to assess the system security over a long time scale and check for continuous or intermittent over-limits (voltage, line power flow), which can be used to guide the safe and stable operation of the power grid and the execution of strategies.

[0152] The operation status simulation allows for scaling loads, specifying loads individually, modifying bus voltages, and changing device status and parameter values; it also considers distributed resource adjustments and energy storage charging and discharging status adjustments; and it can specify the grid operation mode. The equivalent data obtained based on the simulation data will replace the real-time data and / or saved data required in the application's operating environment.

[0153] Event simulation considers event operations under different application scenarios such as main and distribution equipment commissioning and shutdown, load transfer, load adjustment, tap changer adjustment, and equipment failure at a specified time.

[0154] Power flow calculations consider both distribution network parameter imbalance and three-phase load imbalance. Three-phase unbalanced power flow calculations are used to analyze the phase imbalance of the three-phase circuits. The formula is the average phase current minus the minimum phase current, then divided by the average current. The voltage imbalance of the three-phase busbars is calculated using the formula: maximum voltage minus average voltage, then divided by the average voltage.

[0155] This embodiment can perform three-phase unbalanced power flow calculations online in real time within the dispatching system, analyze the theoretical total loss and loss ratio under the current network operating mode, and statistically analyze the phase imbalance and three-phase voltage imbalance of the three-phase circuits in real time. Based on a selected initial cross-section, it can perform various simulation operations such as mode adjustment, load power and generation power adjustment, and equipment parameter adjustment under real-time, research, and simulation modes, considering multiple scenarios and applications. It provides power flow distribution changes and power flow calculation results after the simulation operations, performs equipment safety constraint alarm statistics, and conducts overload and reverse overload assessments, as well as voltage limit exceedance assessments.

[0156] This embodiment addresses, for example... Figure 5 The test line is subjected to power flow calculation, and the power flow calculation results are compared with the ETAP calculation results. The error between the power flow calculation results and the ETAP calculation results is analyzed to determine the accuracy of the power flow calculation.

[0157] (1) Calculation of three-phase imbalance of distribution transformer This paper analyzes the impact of unbalanced three-phase load power on the medium-voltage distribution network, considering the low-voltage side of the distribution transformer. It requires calculating the unbalanced three-phase power flow under different transformer wiring and neutral grounding methods, and analyzing the error between the ETAP calculation results and the power flow calculation results. Distribution transformer DT2 is used as an example for illustration.

[0158] 1) Distribution transformer wiring method Dyn11 The calculation results are shown in Table 1: Table 1 Comparison of Transformer Calculation Results

[0159] 2) Transformer wiring method Dyn1 The calculation results are shown in Table 2: Table 2 Comparison of Transformer Calculation Results

[0160] (2) Calculation of three-phase imbalance in medium and high voltage networks The power flow error comparison on medium and high voltage network lines can be directly reflected in the power flow error of the main transformer. Therefore, for the sake of simplicity, this paper only compares the changes in the three-phase power flow distribution on the high voltage side of the main transformer under different wiring methods, and compares the error analysis with the ETAP calculation results.

[0161] 1) Main transformer wiring method YNd11 The calculation results are shown in Table 3: Table 3 Comparison of Calculation Results for High Voltage Side of Main Transformer

[0162] 2) Main transformer wiring method YNd1 The calculation results are shown in Table 4: Table 4 Comparison of Calculation Results for the High Voltage Side of the Main Transformer

[0163] As can be seen above, the integrated three-phase unbalanced power flow calculation scheme of high, medium and low voltage in this embodiment adopts a hierarchical-distributed-coordinated iterative architecture, and the calculated power flow calculation results have small errors. It not only solves the key technical bottlenecks in the current power system analysis, but also provides a core computing engine for the future development of smart grids.

[0164] Embodiment 2 of the present invention proposes a real-time three-phase unbalanced power flow calculation system based on the method described in the first aspect of the present invention, comprising a modeling module, a low-voltage network power flow calculation module, a distribution transformer power flow calculation module, a medium- and high-voltage network power flow calculation module, and an outer iteration module, specifically: Modeling module: Used for integrated modeling of low-voltage and medium-high voltage networks, identifying node composition and network parameters, including transformer grounding method, wiring method and phase shift, as well as the voltage of each power supply bus in the high-voltage network; Low-voltage network power flow calculation module: It is used to obtain the active and reactive power of each phase at the outlet of the low-voltage side of the distribution transformer by iteratively solving the power balance equation. The outlet voltage of the low-voltage side of the distribution transformer is used as the boundary condition. If it is the first outer layer iteration, the outlet voltage of the low-voltage side of the distribution transformer is the set initial rated voltage value. Transformer power flow calculation module: Based on the active and reactive power of each phase at the low-voltage side outlet of the transformer, taking into account the transformer grounding method, wiring method and phase shift, the active and reactive power of each phase on the high-voltage side of the transformer is calculated and used as the load injection power of the medium and high voltage network to participate in the power flow calculation of the medium and high voltage network. Medium and high voltage network power flow calculation module: used to perform iterative calculation of power flow in medium and high voltage networks through power balance equations, obtain the active and reactive power and voltage values ​​of each node in the medium and high voltage network as well as the current values ​​of each branch, and complete one outer layer iteration; Outer Iteration Module: This module calculates the low-voltage side outlet voltage of the distribution transformer based on the voltage of the terminal nodes of the medium- and high-voltage network. It calculates the difference between the current calculated low-voltage side outlet voltage and the voltage from the previous outer iteration. If the difference is less than the set threshold, the iteration calculation stops, and the active and reactive power of all nodes is output. Otherwise, the low-voltage side outlet voltage is updated to the currently calculated value, and the next outer iteration is performed. The above steps are repeated starting from obtaining the active and reactive power of each phase on the low-voltage side of the distribution transformer through iteration using the power balance equation.

[0165] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0166] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0167] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0168] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0169] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A real-time power flow calculation method for three-phase unbalance based on integrated master and distribution systems, characterized in that, include: Integrated modeling of low-voltage and medium-high-voltage networks is performed to identify node composition and network parameters, including transformer grounding method, wiring method and phase shift, as well as the voltage of each power supply bus in the high-voltage network. The active and reactive power of each phase at the low-voltage side outlet of the distribution transformer is obtained by iteratively solving the power balance equation. The low-voltage side outlet voltage of the distribution transformer is used as the boundary condition during the solution. If it is the first outer layer iteration, the low-voltage side outlet voltage of the distribution transformer is the set initial rated voltage value. Based on the active and reactive power of each phase at the low-voltage side outlet of the distribution transformer, taking into account the grounding method, wiring method and phase shift of the distribution transformer, the active and reactive power of each phase on the high-voltage side of the distribution transformer is calculated and used as the load injection power of the medium- and high-voltage network to participate in the power flow calculation of the medium- and high-voltage network. By performing power balance equations to perform iterative calculations of power flow in medium- and high-voltage networks, the active and reactive power and voltage values ​​of each node in the medium- and high-voltage network, as well as the current values ​​of each branch, are obtained, thus completing one outer-layer iteration. The low-voltage side outlet voltage of the distribution transformer is calculated based on the voltage of the terminal node of the medium- and high-voltage network. The difference between the current calculated low-voltage side outlet voltage and the previous outer layer iteration is calculated. If the difference is less than the set difference threshold, the iterative calculation is stopped, and the active and reactive power of all nodes are output. Otherwise, the low-voltage side outlet voltage of the distribution transformer is updated to the currently calculated value, and the next outer layer iteration is performed. The above steps are repeated starting from obtaining the active and reactive power of each phase of the low-voltage side of the distribution transformer through iteration using the power balance equation.

2. The method for real-time power flow calculation of three-phase imbalance based on integrated main and distribution systems according to claim 1, characterized in that: Integrated modeling of low-voltage and medium-voltage networks is performed, specifically as follows: Integrated modeling includes power source model, load model, branch model, distributed power source model and energy storage model. Topology nodes are identified to construct a main and distribution integrated electrical island. Network parameters are read through the main and distribution integrated electrical island. Network parameters include branch impedance, distribution transformer grounding method, wiring method and phase shift, as well as real-time measurement data. Real-time measurement data includes generator, equivalent power source, distributed power source power, load power, and voltage of each power source bus in the high-voltage network, circuit breaker and disconnector status.

3. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 1, characterized in that: The active and reactive power of each phase at the low-voltage side outlet of the distribution transformer are obtained by iteratively solving the power balance equation. Specifically: The power balance equation is solved iteratively using the Newton-Raphson method. The power balance equation is as follows: in, , The k-th node The active power imbalance and reactive power imbalance represent the different phases. , The k-th node The active and reactive power injected by the power source of the other phase; , The k-th node The active and reactive power of the loads are represented by their respective phases. , These are the nodal admittance matrices. The matrix corresponding to the k-th node and the m-th node The difference between the two is indicated by the fact that the two phases are distinct. The real part (conductance) and imaginary part (susceptance) of the admittance between phases are represented. , For the m-th node The real and imaginary parts of the phase voltage are represented. , it is These represent phase A, phase B, phase C, and neutral line N, respectively. Based on the active and reactive power of each node at the low-voltage side outlet of the distribution transformer and the low-voltage network topology, the active and reactive power at the low-voltage side outlet of the distribution transformer are obtained.

4. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 3, characterized in that: The output voltage of the low-voltage side of the distribution transformer is the root voltage of the low-voltage side of the distribution transformer. The boundary condition is: the root voltage is obtained based on the calculated phase voltages of all nodes and the low-voltage network topology. The root voltage is a fixed value in each iteration. The fixed value is the set initial rated voltage value or the output voltage of the low-voltage side of the distribution transformer calculated in the previous outer iteration.

5. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 3, characterized in that: If the power source is a distributed power source and is of type PQ, then the corresponding , Substituting the known quantities directly into the power balance equation, if the power source is a distributed source and is PV type, then the corresponding... Given, the corresponding The variable is adjusted through a reactive power iteration loop. Maintain a constant output voltage.

6. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 3, characterized in that: Based on the active and reactive power of each phase at the low-voltage side outlet of the distribution transformer, taking into account the transformer grounding method, wiring method, and phase shift, the active and reactive power of each phase on the high-voltage side of the distribution transformer are calculated as follows: The order admittance matrix is ​​obtained based on the wiring and grounding methods; For each phase, the complex power is obtained based on the active and reactive power at the low-voltage side outlet of each distribution transformer. The complex power is divided by the set ideal low-voltage side phase voltage to calculate the low-voltage side phase current. The low-voltage side phase current is converted into low-voltage side sequence current. The current phase shift matrix and voltage phase shift matrix corresponding to the wiring method and phase shift are obtained. The low-voltage side sequence current is multiplied by the negative current phase shift matrix to obtain the high-voltage side sequence current. The sequence admittance matrix is ​​converted into the distribution transformer impedance value. The high-voltage side sequence current is converted into high-voltage side phase current. The ideal low-voltage side phase voltage is multiplied by the turns ratio and then by the voltage phase shift matrix to obtain the ideal high-voltage sequence voltage. The ideal high-voltage sequence voltage is converted into the ideal high-voltage phase voltage. The actual high-voltage side complex power is calculated based on the high-voltage side phase current, the ideal high-voltage side phase voltage, and the distribution transformer impedance value. The active and reactive power of the high-voltage side are obtained based on the actual high-voltage side complex power.

7. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 6, characterized in that: The actual complex power on the high-voltage side is calculated based on the high-voltage side phase current, the ideal high-voltage side phase voltage, and the transformer impedance value. Specifically: The ideal high-voltage side phase voltage and high-voltage side phase current are multiplied to obtain the ideal high-voltage complex power. The transformer impedance value is multiplied by the square of the high-voltage side phase current to obtain the transformer complex power loss. The transformer complex power loss is added to the ideal high-voltage side complex power to obtain the actual high-voltage side complex power of the transformer. Alternatively, the voltage loss of the distribution transformer can be calculated by multiplying the phase current on the high-voltage side and the transformer impedance value. The actual phase voltage on the high-voltage side of the distribution transformer can be obtained by superimposing the ideal phase voltage on the high-voltage side and the voltage loss on the distribution transformer. The actual complex power on the high-voltage side can be calculated by multiplying the actual phase voltage on the high-voltage side and the phase current on the high-voltage side.

8. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 2, characterized in that: Perform iterative calculations of power flow in medium- and high-voltage networks, specifically as follows: If the distributed power source supplying the corresponding branch is of type PQ, then the formula for power flow iteration calculation is: If the distributed power source supplying the corresponding branch is of PV type, then the formula for power flow iteration calculation is: in, The active power injected into node i of the medium- and high-voltage network; The reactive power injected into node i of the medium- and high-voltage network; , These are the real and imaginary parts of the p-phase voltage at node i in the medium- and high-voltage network, respectively. , These are the real and imaginary parts of the m-phase voltage at node j in the medium- and high-voltage network, respectively. When A, B, and C are respectively, they represent phase A, phase B, and phase C. Let i be the active power value of node i in the medium- and high-voltage network. This represents the reactive power output of the generator. The reactive power of the load at node i in the medium- and high-voltage network; Let be the reactive power value of phase p of node i in the medium- and high-voltage network; Let be the real part of the mutual admittance between the p-phase of medium-high voltage network node i and the m-phase of medium-high voltage network node j; Let be the imaginary part of the mutual admittance between the p-phase of medium- and high-voltage network node i and the m-phase of medium- and high-voltage network node j; For a given voltage amplitude, for The correction amount, The voltage of phase p of node i in the medium- and high-voltage network The amplitude is N, where N is the total number of branches.

9. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 8, characterized in that: When modeling medium- and high-voltage networks, for double-winding transformers, only one branch model is created. In the branch model, the phase shift of the primary winding is set, and the phase shift of the secondary winding is 0 by default. For a three-winding main transformer, three branch models are created during modeling, with each winding corresponding to one branch model. In the branch model, the primary winding does not have a phase shift angle set, but only the phase shifts of the secondary and tertiary windings are set. The corresponding phase shift matrix is ​​obtained based on the phase shift matrix. The mutual admittance between the p phase of the medium- and high-voltage network node i and the m phase of the medium- and high-voltage network node j is calculated based on the corresponding phase shift matrix.

10. The method for calculating real-time three-phase unbalanced power flow based on integrated main and distribution systems according to claim 1, characterized in that: The low-voltage side outlet voltage of the distribution transformer is calculated based on the voltage at the terminal node of the medium- and high-voltage network. Specifically, the voltage at the terminal node of the medium- and high-voltage network is the voltage of the high-voltage side bus of the distribution transformer. The low-voltage side outlet voltage of the distribution transformer is calculated based on the active and reactive power of each phase on the high-voltage side and the voltage of the high-voltage side bus of the distribution transformer. The high-voltage side power of the transformer is calculated based on the active and reactive power of each phase on the high-voltage side and the high-voltage side bus voltage. The high-voltage side phase current is calculated based on the transformer impedance and the high-voltage side phase current. The voltage loss of the high-voltage winding is calculated based on the voltage loss of the ideal high-voltage side phase voltage. The voltage value of the ideal high-voltage winding is obtained by subtracting the voltage loss from the ideal high-voltage side phase voltage. The voltage value of the ideal high-voltage winding is converted into a sequence component, and the voltage sequence component of the ideal low-voltage winding is calculated. The voltage phase component of the low-voltage winding is obtained based on the calculated voltage sequence component of the ideal low-voltage winding. The voltage phase component of the low-voltage winding is the low-voltage side outlet voltage of the transformer.

11. A real-time three-phase unbalanced power flow calculation system based on the method of any one of claims 1-10, comprising a modeling module, a low-voltage network power flow calculation module, a distribution transformer power flow calculation module, a medium- and high-voltage network power flow calculation module, and an outer iteration module, characterized in that: Modeling module: Used for integrated modeling of low-voltage and medium-high voltage networks, identifying node composition and network parameters, including transformer grounding method, wiring method and phase shift, as well as the voltage of each power supply bus in the high-voltage network; Low-voltage network power flow calculation module: It is used to obtain the active and reactive power of each phase at the outlet of the low-voltage side of the distribution transformer by iteratively solving the power balance equation. The outlet voltage of the low-voltage side of the distribution transformer is used as the boundary condition. If it is the first outer layer iteration, the outlet voltage of the low-voltage side of the distribution transformer is the set initial rated voltage value. Transformer power flow calculation module: Based on the active and reactive power of each phase at the low-voltage side outlet of the transformer, taking into account the transformer grounding method, wiring method and phase shift, the active and reactive power of each phase on the high-voltage side of the transformer is calculated and used as the load injection power of the medium and high voltage network to participate in the power flow calculation of the medium and high voltage network. Medium and high voltage network power flow calculation module: used to perform iterative calculation of power flow in medium and high voltage networks through power balance equations, obtain the active and reactive power and voltage values ​​of each node in the medium and high voltage network as well as the current values ​​of each branch, and complete one outer layer iteration; Outer Iteration Module: This module calculates the low-voltage side outlet voltage of the distribution transformer based on the voltage of the terminal nodes of the medium- and high-voltage network. It calculates the difference between the current calculated low-voltage side outlet voltage and the voltage from the previous outer iteration. If the difference is less than the set threshold, the iteration calculation stops, and the active and reactive power of all nodes is output. Otherwise, the low-voltage side outlet voltage is updated to the currently calculated value, and the next outer iteration is performed. The above steps are repeated starting from obtaining the active and reactive power of each phase on the low-voltage side of the distribution transformer through iteration using the power balance equation.

12. An apparatus comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor performing steps of the real-time power flow calculation method based on the master-slave integrated three-phase unbalance method according to any one of claims 1 to 9.

13. A computer-readable storage medium storing a computer program that, when executed by a processor, uses the steps of the three-phase unbalanced real-time power flow calculation method based on the master-distributor integration as described in any one of claims 1 to 9.

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