Power distribution network electric energy substitution bearing capacity evaluation method and system based on power grid weak link and electric energy quality, and readable storage medium

Abstract

The invention discloses a power distribution network electric energy substitution bearing capacity assessment method and system based on a power grid weak link and electric energy quality and a readable storage medium, and relates to the field of electric energy substitution bearing capacity assessment. Then, according to the electric energy substitution classification condition, representative electric energy substitution equipment in each industry is selected for harmonic modeling analysis; based on the harmonic model analysis result, evaluating the electric energy substitution access quantity under the harmonic distortion rate constraint condition; and finally, evaluating the bearing capacity of the power distribution network to the electric energy replacement equipment by establishing a power distribution network electric energy replacement bearing capacity evaluation model considering the electric energy quality. According to the method, various safety constraint indexes of a power grid structure and a power distribution system are comprehensively considered, economic benefits are considered, the upper limit of the electric energy substitution capacity which can be accepted by the power distribution network is scientifically determined on the premise of safe, reliable and economic operation of the power distribution network, and support is provided for ordered access and healthy development of electric energy substitution.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy substitution carrying capacity assessment, and more specifically to a method, system and readable storage medium for assessing electric energy substitution carrying capacity of a distribution network based on weak links of the power grid and power quality. Background Art

[0002] At present, electric energy substitution, as an important measure to achieve the dual carbon goals, plays an important role in accelerating the transformation of energy structure and reducing carbon emissions. However, with the access of electric energy substitution equipment in different fields such as industry, construction, and transportation to the distribution network, a large number of electric energy substitution equipment are connected to the power grid, causing a surge in the load of the power grid and an increase in the load rate of power facilities; the power electronic components contained in the electric energy substitution will introduce a large number of harmonics into the power grid, causing the harmonic distortion rate of the power grid to increase. With the rapid development of electric energy substitution, the access of a large number of electric energy substitution equipment may exceed the capacity limit of the power grid, posing severe challenges to the stable operation of the power grid. Among them, the disorderly access of a large number of electric energy substitution equipment not only aggravates the problems of harmonic pollution and voltage deviation in the power grid, but also greatly increases the load-bearing pressure of the power grid at this stage, affecting the safe operation of the power grid.

[0003] Therefore, how to reasonably evaluate the carrying capacity of the distribution network under electric energy substitution access is an urgent problem that technical personnel in this field need to solve. Summary of the invention

[0004] In view of this, the present invention provides a method, system and readable storage medium for evaluating the electric energy substitution carrying capacity of a distribution network based on weak links in the power grid and power quality, so as to solve the problems existing in the background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] On the one hand, a method for evaluating the power substitution carrying capacity of a distribution network based on weak links of the power grid and power quality is provided, including:

[0007] Based on risk utility theory and complex network theory, the grid status weakness assessment index and grid structure weakness assessment index are established respectively;

[0008] The two evaluation indicators are combined by using the least squares support vector machine to obtain the comprehensive evaluation index for identifying the weak links in the distribution network. The weak links in the distribution network are identified by the comprehensive evaluation index.

[0009] Select electric energy replacement equipment from different industries, build an electric energy replacement harmonic simulation model based on the composition and working principle of the electric energy replacement equipment, analyze the harmonics generated by various equipment, and obtain analysis results;

[0010] Through the analysis results of the electric energy substitution harmonic model, the harmonic frequency generated by the electric energy substitution equipment during operation is determined; the electric energy substitution equipment is connected to the weak nodes obtained by the weak link identification of the distribution network, and the harmonic distortion rate of the weak node and other nodes is determined by the harmonic power flow algorithm according to the obtained harmonic frequency. The harmonic distortion rate is used as a constraint condition, combined with the results of the weak link identification of the distribution network, to evaluate the access amount of electric energy substitution considering the harmonics and weak links of the power grid;

[0011] Calculate the economic benefits of electric energy substitution for the distribution network, and determine the nodes where the electric energy substitution equipment is connected based on the obtained economic benefits and the similarity coefficient between the electric energy substitution and the existing net load;

[0012] According to the regulation capability of the electric energy substitution load curve, the electric energy substitution load curve is adjusted; the result of the load curve regulation is obtained; based on the result of the load curve regulation, the electric energy substitution access quantity, and the nodes to which the electric energy substitution equipment is connected, an electric energy substitution carrying capacity assessment model for the distribution network is established, which includes flow constraints, node voltage constraints, equipment capacity constraints, energy storage constraints, electric energy substitution capacity constraints, and minimum electric energy substitution access capacity constraints, to assess the carrying capacity of the distribution network for the electric energy substitution equipment.

[0013] Optionally, the distribution network status weak link assessment indicators include node voltage exceeding limit and line flow exceeding limit; the structural weak link assessment indicators include node degree, line degree, node injection power, and line betweenness.

[0014] Optionally, the constraints determined by the harmonic distortion rate are:

[0015]

[0016] In the formula, S ES U is the amount of electricity replacement equipment connected; N is the rated voltage; μ k It is the content rate limit of each harmonic output by the electric energy replacement equipment; k These are the harmonic currents allowed to be connected to the power grid as specified in the national standard.

[0017] Optionally, the specific process of evaluating the amount of alternative access to electric energy considering grid harmonics and weak links is as follows, combined with the results of weak link identification in the distribution network:

[0018] a. Analyze the harmonic characteristics of electric energy replacement equipment;

[0019] b. Identify the weak links in the distribution network;

[0020] c. Use harmonic power flow calculation to solve the harmonic distortion rate when the electric energy replacement equipment is connected to the power grid;

[0021] d. When the harmonic distortion rate is less than 4%, output the electric energy replacement access amount; when the harmonic distortion rate is greater than or equal to 4%, reduce the access amount of electric energy replacement equipment and return to step c for calculation until the harmonic distortion rate meets the conditions and the evaluation ends.

[0022] Optionally, the distribution network power substitution carrying capacity assessment model is:

[0023] The maximum carrying capacity of the distribution network for electric energy substitution is taken as the objective function:

[0024] maxN=μ 1 N hp +μ 2 N evp +μ 3 N eaf ;

[0025] Where N hp is the number of air source heat pumps connected, N evp is the number of electric vehicle charging piles connected, N eaf is the number of electric furnaces connected; μ 1 , μ 2 , μ 3 are the weight coefficients of the three types of electric energy replacement equipment.

[0026] Optionally, the constraint condition can be expressed as:

[0027] Power flow constraints:

[0028]

[0029] Where i, j are node numbers; v i , v j are the voltages of nodes i and j respectively; P jk , Q jk are respectively the active power and reactive power at the head end of branch jk; P ij , Q ij are respectively the active power and reactive power at the head end of branch ij; r ij +x ij is the impedance of branch ij; I ij is the square of the current in branch ij; k:j→k is the set of child nodes with node j as the parent node; P j , Q j Inject net active and reactive power into the node;

[0030] Node voltage constraints:

[0031] V min ≤V i ≤V max ;

[0032] Where V min and V max They are the voltage lower limit and upper limit respectively;

[0033] Equipment capacity constraints:

[0034]

[0035] In the formula, S ij is the transmission capacity of line ij, is the maximum transmission capacity of line ij;

[0036] Energy storage constraints include energy storage charging and discharging state constraints and energy storage charging and discharging power constraints;

[0037] Energy storage charging and discharging state constraints:

[0038]

[0039] Energy storage charging and discharging power constraints:

[0040]

[0041] where y ch and dis Respectively represent the charging state and the discharging state; P ch,max ,P dis,max are the maximum power of energy storage charging and discharging respectively; in addition, the remaining capacity constraint of energy storage must be met:

[0042]

[0043] E min With E max are the maximum capacity limit and the minimum capacity limit of energy storage respectively; η ch With η dis are the energy storage charging efficiency and discharging efficiency respectively;

[0044] Considering the power replacement capacity constraints of harmonic indicators:

[0045] P ES,i,t ≤P ES,i,t,THDmax ;

[0046] Among them, P ES,i,t,THDmax The upper limit of the amount of node power replacement equipment connected to consider power quality factors;

[0047] The minimum access capacity constraint for electric energy substitution means that the access capacity of each type of electric energy substitution shall not be less than its economically optimal access capacity;

[0048]

[0049] Where N hp,N evp ,N eaf They are the number of air source heat pumps, electric vehicle charging piles, and electric furnaces connected; They are the unit access capacities of air source heat pumps, electric vehicle charging piles, and electric furnaces; They are the economically optimal access capacities for air source heat pumps, electric vehicle charging piles, and electric furnaces.

[0050] On the other hand, a distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality is provided, including:

[0051] The evaluation index establishment module establishes the evaluation index of power grid status weakness and the evaluation index of power grid structure weakness based on risk utility theory and complex network theory respectively;

[0052] The weak link identification module of the distribution network uses the least squares support vector machine to combine the two evaluation indicators to obtain the comprehensive evaluation index for the identification of the weak link of the distribution network, and identifies the weak link of the distribution network through the comprehensive evaluation index;

[0053] The harmonic analysis module selects electric energy replacement equipment from different industries, builds an electric energy replacement harmonic simulation model based on the composition and working principle of the electric energy replacement equipment, analyzes the harmonics generated by various equipment, and obtains analysis results;

[0054] The electric energy substitution access quantity assessment module determines the harmonic frequency generated by the electric energy substitution equipment during operation through the analysis results of the electric energy substitution harmonic model; connects the electric energy substitution equipment to the weak nodes obtained by the weak link identification of the distribution network, and uses the harmonic power flow algorithm to determine the harmonic distortion rate of the weak nodes and other nodes according to the obtained harmonic frequency. With the harmonic distortion rate as a constraint condition, combined with the results of the weak link identification of the distribution network, an assessment is performed to obtain the electric energy substitution access quantity that takes into account the harmonics and weak links of the power grid;

[0055] The node determination module for connecting the electric energy substitution equipment calculates the economic benefits brought by the electric energy substitution to the distribution network, and determines the node for connecting the electric energy substitution equipment according to the obtained economic benefits and the similarity coefficient between the electric energy substitution and the existing net load;

[0056] The distribution network electric energy substitution carrying capacity assessment module adjusts the electric energy substitution load curve according to the adjustment capability of the electric energy substitution load curve to obtain the result of the load curve adjustment; based on the result of the load curve adjustment, the electric energy substitution access quantity, and the nodes to which the electric energy substitution equipment is connected, by establishing a distribution network electric energy substitution carrying capacity assessment model containing flow constraints, node voltage constraints, equipment capacity constraints, energy storage constraints, electric energy substitution capacity constraints, and minimum electric energy substitution access capacity constraints, the distribution network is assessed for the carrying capacity of the electric energy substitution equipment to be assessed.

[0057] Optionally, the distribution network status weak link assessment indicators include node voltage exceeding limit and line flow exceeding limit; the structural weak link assessment indicators include node degree, line degree, node injection power, and line betweenness.

[0058] Optionally, the constraints determined by the harmonic distortion rate are:

[0059]

[0060] In the formula, S ES U is the amount of electricity replacement equipment connected; N is the rated voltage; μ k It is the content rate limit of each harmonic output by the electric energy replacement equipment; k These are the harmonic currents allowed to be connected to the power grid as specified in the national standard.

[0061] Optionally, the specific process of evaluating the amount of alternative access to electric energy considering grid harmonics and weak links is as follows, combined with the results of weak link identification in the distribution network:

[0062] a. Analyze the harmonic characteristics of electric energy replacement equipment;

[0063] b. Identify the weak links in the distribution network;

[0064] c. Use harmonic power flow calculation to solve the harmonic distortion rate when the electric energy replacement equipment is connected to the power grid;

[0065] d. When the harmonic distortion rate is less than 4%, output the electric energy replacement access amount; when the harmonic distortion rate is greater than or equal to 4%, reduce the access amount of electric energy replacement equipment and return to step c for calculation until the harmonic distortion rate meets the conditions and the evaluation ends.

[0066] Optionally, the distribution network power substitution carrying capacity assessment model is:

[0067] The maximum carrying capacity of the distribution network for electric energy substitution is taken as the objective function:

[0068] maxN=μ 1 N hp +μ 2 N evp +μ 3 N eaf ;

[0069] Where N hp is the number of air source heat pumps connected, N evp is the number of electric vehicle charging piles connected, N eaf is the number of electric furnaces connected; μ 1 , μ 2 , μ 3 are the weight coefficients of the three types of electric energy replacement equipment.

[0070] Optionally, the constraint condition can be expressed as:

[0071] Power flow constraints:

[0072]

[0073] Where i, j are node numbers; v i , v j are the voltages of nodes i and j respectively; P jk , Q jk are respectively the active power and reactive power at the head end of branch jk; P ij , Q ij are respectively the active power and reactive power at the head end of branch ij; r ij +x ij is the impedance of branch ij; I ij is the square of the current in branch ij; k:j→k is the set of child nodes with node j as the parent node; P j , Q j Inject net active and reactive power into the node;

[0074] Node voltage constraints:

[0075] V min ≤V i ≤V max ;

[0076] Where V min and V max They are the voltage lower limit and upper limit respectively;

[0077] Equipment capacity constraints:

[0078]

[0079] In the formula, S ij is the transmission capacity of line ij, is the maximum transmission capacity of line ij;

[0080] Energy storage constraints include energy storage charging and discharging state constraints and energy storage charging and discharging power constraints;

[0081] Energy storage charging and discharging state constraints:

[0082]

[0083] Energy storage charging and discharging power constraints:

[0084]

[0085] where y ch and disRespectively represent the charging state and the discharging state; P ch,max ,P dis,max are the maximum power of energy storage charging and discharging respectively; in addition, the remaining capacity constraint of energy storage must be met:

[0086]

[0087] E min With E max are the maximum capacity limit and the minimum capacity limit of energy storage respectively; η ch With η dis are the energy storage charging efficiency and discharging efficiency respectively;

[0088] Considering the power replacement capacity constraints of harmonic indicators:

[0089] P ES,i,t ≤P ES,i,t,THDmax ;

[0090] Among them, P ES,i,t,THDmax The upper limit of the amount of node power replacement equipment connected to consider power quality factors;

[0091] The minimum access capacity constraint for electric energy substitution means that the access capacity of each type of electric energy substitution shall not be less than its economically optimal access capacity;

[0092]

[0093] Where N hp ,N evp ,N eaf They are the number of air source heat pumps, electric vehicle charging piles, and electric furnaces connected; They are the unit access capacities of air source heat pumps, electric vehicle charging piles, and electric furnaces; They are the economically optimal access capacities for air source heat pumps, electric vehicle charging piles, and electric furnaces.

[0094] A computer-readable storage medium stores instructions, which, when executed by a processor, implement the steps of a method for evaluating the electric energy substitution carrying capacity of a distribution network based on weak links in the power grid and the quality of electric energy.

[0095] Through the above technical solutions, it can be known that compared with the prior art, the present invention discloses a method, system and readable storage medium for evaluating the electric energy substitution capacity of distribution networks based on weak links in power grids and power quality. First, the weak links in the power grid are identified according to the evaluation indicators of weak links in the distribution network; then, according to the classification of electric energy substitution, representative electric energy substitution equipment in various industries is selected for harmonic modeling analysis; based on the results of the harmonic model analysis, the amount of electric energy substitution access under the constraints of the harmonic distortion rate is determined; finally, by establishing an electric energy substitution capacity evaluation model for county distribution networks that takes into account power quality, the distribution network's carrying capacity for electric energy substitution equipment is evaluated. The present invention comprehensively considers various safety constraint indicators of the power grid structure and the distribution system, takes into account economic benefits, and scientifically determines the upper limit of the electric energy substitution capacity that can be accepted on the premise of ensuring the safe, reliable and economical operation of the distribution network, providing support for the orderly access and healthy development of electric energy substitution. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0097] Figure 1 A flow chart for evaluating the electric energy substitution carrying capacity provided by the present invention;

[0098] Figure 2 The air source heat pump simulation model provided by the present invention;

[0099] Figure 3 The working current of the air source heat pump provided by the present invention;

[0100] Figure 4 The spectrum of each harmonic content of the air source heat pump provided by the present invention;

[0101] Figure 5 The electric furnace simulation model (a) provided by the present invention;

[0102] Figure 6 The electric furnace simulation model (b) provided by the present invention;

[0103] Figure 7 The working current of the electric furnace provided by the present invention;

[0104] Figure 8 The spectrum of each harmonic content of the working current of the electric furnace provided by the present invention;

[0105] Fig. 9 The structure diagram of the single-phase uncontrolled rectifier charging pile provided by the present invention;

[0106] Fig.10 The equivalent model of the single-phase uncontrolled rectifier charging pile provided by the present invention;

[0107] Fig.11 The electric vehicle charging pile simulation model provided by the present invention;

[0108] Fig.12 The working current of the electric vehicle charging pile provided by the present invention;

[0109] Fig.13 The spectrum of each harmonic content of the working current of the electric vehicle charging pile provided by the present invention;

[0110] Fig.14 A flow chart for evaluating the amount of alternative access to electric energy taking into account harmonics and weak links in the power grid provided by the present invention;

[0111] Fig.15 Each node DLMP of the distribution network provided by the present invention;

[0112] Fig.16 The IEEE33 node distribution network model provided by the present invention;

[0113] Fig.17 The electric energy replacement carrying capacity provided by the present invention. DETAILED DESCRIPTION

[0114] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0115] The embodiment of the present invention discloses a method for evaluating the power substitution carrying capacity of a distribution network based on weak links of the power grid and power quality, such as Figure 1 As shown, including:

[0116] Based on risk utility theory and complex network theory, the grid status weakness assessment index and grid structure weakness assessment index are established respectively;

[0117] The two evaluation indicators are combined by using the least squares support vector machine to obtain the comprehensive evaluation index for identifying the weak links in the distribution network. The weak links in the distribution network are identified by the comprehensive evaluation index.

[0118] Select electric energy replacement equipment from different industries, build an electric energy replacement harmonic simulation model based on the composition and working principle of the electric energy replacement equipment, analyze the harmonics generated by various equipment, and obtain analysis results;

[0119] Through the analysis results of the electric energy substitution harmonic model, the harmonic frequency generated by the electric energy substitution equipment during operation is determined; the electric energy substitution equipment is connected to the weak nodes obtained by the weak link identification of the distribution network, and the harmonic distortion rate of the weak node and other nodes is determined by the harmonic power flow algorithm according to the obtained harmonic frequency. The harmonic distortion rate is used as a constraint condition, combined with the results of the weak link identification of the distribution network, to evaluate the access amount of electric energy substitution considering the harmonics and weak links of the power grid;

[0120] Calculate the economic benefits of electric energy substitution for the distribution network, and determine the nodes where the electric energy substitution equipment is connected based on the obtained economic benefits and the similarity coefficient between the electric energy substitution and the existing net load;

[0121] According to the regulation capability of the electric energy substitution load curve, the electric energy substitution load curve is adjusted to obtain the result of the load curve regulation; based on the result of the load curve regulation, the electric energy substitution access quantity, and the nodes to which the electric energy substitution equipment is connected, an electric energy substitution carrying capacity assessment model for the distribution network is established, which includes flow constraints, node voltage constraints, equipment capacity constraints, energy storage constraints, electric energy substitution capacity constraints, and minimum electric energy substitution access capacity constraints, to assess the carrying capacity of the distribution network for the electric energy substitution equipment to be assessed.

[0122] In a specific embodiment, the weak link evaluation indicators of the distribution network state include node voltage exceeding the limit and line flow exceeding the limit; the weak link evaluation indicators of the structure include node degree, line degree, node injection power, and line betweenness. Specifically:

[0123] (1) Grid status weakness assessment indicators

[0124] 1) Node voltage exceeds limit

[0125] According to relevant standards, the allowable voltage deviation of a 10kV distribution network is ±10% of the rated voltage, and within this range, the voltage is considered to be within the limit. The greater the voltage exceeds this range and the greater the voltage fluctuation, the greater the severity of the voltage over-limit risk. To this end, the present invention uses the node voltage over-limit risk as one of the weak grid status assessment indicators, and expresses it through a risk preference utility function, and the calculation formula is as shown in formula (1) and formula (2):

[0126]

[0127] Where: S ev (w i ) represents the voltage over-limit risk of the ith node, U i represents the voltage per unit value of node i; w i Represents the voltage deviation value of node i.

[0128] According to the voltage over-limit risk calculation results, the system node overvoltage risk value is defined, and the calculation formula is as follows:

[0129]

[0130] Among them, Pr(U i ) represents the probability of voltage exceeding the limit at the i-th node.

[0131] 2) Line flow exceeds the limit

[0132] When electric energy replacement equipment is centrally connected, the load on some lines may increase, causing overload problems on the lines. When the line flow is within the specified range, the line will not exceed the limit. When the line flow exceeds the allowable range, the equipment on the branch will be overloaded, increasing the probability of power outages and affecting the stable operation of the power grid. Therefore, the present invention selects line flow exceeding the limit as another indicator for weak grid status assessment. 80% of the rated load rate of the line is used as the critical value. The calculation formula for line flow exceeding the limit is as follows:

[0133]

[0134] Among them, w Lu It represents the difference between the actual load value and the critical value after the line u exceeds the limit, |L u | represents the ratio of the actual transmission power of branch u to the power limit of branch u. 0 is 0.8, S ev (w Lu ) represents the severity of the line flow exceeding the limit of the u-th branch.

[0135] According to the calculation results of the line power flow over-limit severity, the system line overload risk value Risk (L) is defined, and the calculation formula is as follows:

[0136]

[0137] In the formula, Pr(L i ) represents the probability of exceeding the limit on the i-th branch.

[0138] (2) Grid structure weakness assessment indicators

[0139] 1) Node degree

[0140] The present invention introduces the idea of ​​fusion cohesion into the node degree, taking into account both the number of edges connected to the node and the influence of all nodes connected to the node. N,i The calculation formula is:

[0141]

[0142] Where Dj , D i are the number of branches connected to node j and node i respectively; M is the set of all nodes connected to node i; is the average degree of nodes in the network.

[0143] 2) Line degree

[0144] The line degree is used to describe the number of nodes connected by each edge. For a line, the higher the degree of the nodes connected at both ends, the more important the nodes connected by the line are, and the more important the line is. Considering that the line length is also one of the factors affecting the importance of the line, the concept of line length is incorporated, and the line degree definition is:

[0145]

[0146] Where: D N,i,1 and D N,i,2 are the node degrees of the first and last nodes connected to line u; Z u is the reactance value of line u.

[0147] 3) Node injection power

[0148] In order to reflect the importance of nodes in power transmission and allocation, the concept of node injection power is introduced. p,i for:

[0149]

[0150] Where P i is the injected power of node i, S b This is the system baseline capacity.

[0151] 4) Line Betweenness

[0152] Line Betweenness B L,u The expression is:

[0153]

[0154] Where P ij is the active power of line ij, I ij is the current flowing through line ij. The line betweenness index can fully reflect the importance of line u. The larger its value is, the more important the line is.

[0155] (3) Identification of weak links in distribution networks

[0156] The calculation results of the grid state weakness index and the structural weakness index are used as the basis for completing the identification of the weak links in the distribution network. Subsequently, the two evaluation indicators are combined through the least squares support vector machine to obtain the comprehensive evaluation index for the identification of the weak links in the distribution network, and the weak links in the distribution network are identified through this index.

[0157] In a specific embodiment, the specific process of harmonic model analysis of electric energy replacement equipment is as follows:

[0158] A large number of electric energy replacement devices are introduced into the power grid, which increases the harmonic content of the power grid and affects the safety of the power grid. Therefore, it is particularly important to analyze the harmonic characteristics of electric energy replacement devices. This paper selects typical electric energy replacement devices in the three fields of construction, industry, and transportation, and builds a simulation model through Matlab / Simulink to perform harmonic characteristic analysis.

[0159] (1) Analysis of warm harmonic characteristics of air source heat pumps

[0160] The variable frequency air source heat pump is a heating device that converts clean electrical energy into thermal energy. The heat pump uses electrical energy to do work, converting low-level thermal energy in nature into high-level thermal energy for people to use. Its working principle follows the "Carnot cycle" and mainly includes a compressor, a throttling structure, an evaporator, and a condenser. Figure 2 The simulation model of the air source heat pump is shown in the figure. The simulation model is mainly composed of power supply, power supply line, rectifier module, PWM control module and variable frequency compressor. In the simulation model, the same variable frequency air source heat pump is connected to the three-phase power supply line. The following research content takes the A phase line and the variable frequency air source heat pump carried by the line as the research object. Under ideal working conditions, the working current is as follows Figure 3 As shown: The variable frequency air source heat pump will have a large starting current at the beginning of startup. After running for a period of time, harmonics will be injected into the power grid. The current after 0.5s of normal operation is analyzed, and the frequency spectrum of each harmonic content of the variable frequency air source heat pump current is obtained as shown in Figure 4 shown.

[0161] The specific values ​​of each harmonic content in the harmonic content spectrum of the variable frequency air source heat pump are shown in Table 1.

[0162] Table 1 Statistics of harmonic contents of variable frequency air source heat pump

[0163]

[0164] According to the data in Table 1, the variable frequency air source heat pump will introduce a large number of harmonics into the power grid during operation, with a high proportion of odd-order harmonics, especially the 3rd, 5th, and 7th harmonics, which account for 2.86%, 4.83%, and 2.23% respectively. The content of each harmonic decreases with the increase of the harmonic order.

[0165] (2) Analysis of harmonic characteristics of industrial electric furnaces

[0166] As an important smelting equipment in the steel industry, electric furnaces mainly use electric energy to smelt steel. The electric furnace steelmaking process is mainly divided into three stages: melting period, oxidation period, and reduction period. The smelting principle is: during the steel smelting process, an arc is generated between the electrode and the charge, and the electric energy is converted into heat in the process of the arc to smelt the steel. The three stages of electric furnace smelting are accompanied by a large amount of impact current and short-circuit current, which will cause the current in the power grid to be distorted, and then generate a large amount of harmonic current. The electric furnace simulation model is as follows: Figure 5 and Figure 6 shown.

[0167] The electric furnace simulation model mainly includes power supply and electric furnace module, among which the electric furnace module realizes the hyperbolic model of the electric furnace through the function module. The relevant formula of the function module is as follows:

[0168]

[0169] V at (t) = V at0 [1+m·sin(ω f t)] (11)

[0170] Where V at is the arc length threshold voltage, i is the phase current, C is the arc power, D is the arc current, V at0 is the reference voltage when the arc does not exist, m is the modulation index, ω f is the flicker frequency. The working current obtained after running the electric furnace simulation model obtained through the above content is as follows Figure 7 The current after 0.5s of operation is analyzed, and the spectrum of each harmonic content of the electric furnace current is obtained as shown in Figure 8 shown.

[0171] The specific values ​​of the harmonic content in the harmonic content spectrum of the electric furnace working current are shown in Table 2.

[0172] Table 2 Statistics of harmonic contents of variable frequency air source heat pump

[0173]

[0174] The three stages of electric furnace smelting are accompanied by a large amount of impact current and short-circuit current, which distorts the current in the power grid and generates a large amount of harmonic current. From the simulation results, it can be seen that the harmonic current injected by the electric furnace into the power grid is mainly odd harmonics, among which the third harmonic accounts for the highest proportion, which is 16.52%; followed by the fifth and ninth harmonics, which are 3.80% and 0.72% respectively.

[0175] (3) Analysis of harmonic characteristics of electric vehicle charging piles

[0176] At present, electric vehicle charging piles mainly use DC fast charging technology. The charging principle of this technology is realized through a single-phase bridge uncontrolled rectifier charging device, which consists of a rectifier circuit, a power converter and a filter circuit. Its structure is generally as follows Fig. 9 As shown. The charging pile uses a bridge uncontrolled rectifier circuit to convert single-phase AC power into DC power, and then inputs it into a high-frequency DC / DC power converter through a filter circuit. After DC / DC conversion and filtering again, the current I 1 Converted into the charging current I required by the user 0 .

[0177] Since the charging process of the power battery usually lasts for a long time, we can assume that the charging pile always outputs constant DC power within several power frequency cycles. In other words, the output voltage U 0 and output current I 0 can be regarded as a constant. Based on this simplified assumption, we can regard the DC / DC power converter as being in a constant power state, that is, the input voltage U B With input current I 1 Therefore, in a shorter time, we can use a nonlinear resistor R c To replace the equivalent input impedance of the power conversion circuit. In summary, the equivalent model of the charging pile can be simplified as follows Fig.10 shown.

[0178] According to the above content, the simulation model of electric vehicle charging pile is as follows Fig.11 As shown, the working current during the simulation is shown in 12. Fig.13 Spectrum of harmonic contents of the working current of an electric vehicle charging pile.

[0179] Table 3 shows the specific values ​​of each harmonic content in the harmonic content spectrum of the working current of the electric vehicle charging pile. The data shows that the charging pile will introduce a large number of harmonics into the power grid during the working process, with the 5th harmonic being the most serious, and the 7th, 11th, 13th and 17th harmonics also accounting for a high proportion.

[0180] Table 3 Statistics of harmonic contents of electric vehicle charging piles

[0181]

[0182] In a specific embodiment, the evaluation of the amount of alternative access to electric energy considering grid harmonics and weak links is as follows:

[0183] During the operation of the electric energy replacement equipment, a large amount of harmonics will be injected into the power grid. When a node is connected to the electric energy replacement equipment, the harmonics injected into the power grid will affect the harmonic distortion rate of the adjacent nodes, and affect the operation of the electrical equipment at the adjacent nodes, thereby affecting the power grid's acceptance of the electric energy replacement equipment. Starting from the perspective of the harmonic distortion rate of the power grid, the present invention uses harmonic flow calculation to solve the harmonic current and power of each branch and the harmonic voltage distribution of each node when the electric energy replacement equipment is connected to the power grid. At the same time, combined with the results obtained by identifying the weak links in the distribution network, the electric energy replacement access amount is evaluated according to the electric energy replacement access amount evaluation process considering the harmonics and weak links of the power grid.

[0184] (1) Harmonic power flow algorithm

[0185] Based on the above fundamental power flow solution results, the harmonic power flow algorithm based on harmonic decoupling is as follows:

[0186] 1) The harmonic current vector injected into the grid by nonlinear loads and shunt capacitors is expressed as follows:

[0187]

[0188] In the formula, h is the harmonic order, k is the number of iterations; I (h) is the hth harmonic current vector, Ih (h) The hth current injected into the grid by the nonlinear load; is the hth current absorbed by the parallel capacitor from the grid.

[0189] 2) In order to determine whether a certain harmonic current flows through a branch, a harmonic current coefficient matrix is ​​defined between nodes i and j: Coefficient Matrix The definition is as follows:

[0190]

[0191] In the formula, is the harmonic current coefficient matrix generated by nonlinear load, is the harmonic coefficient matrix absorbed by the parallel capacitor between busbars i and j.

[0192] 3) The branch harmonic current generated by the node-injected harmonic current can be calculated using formula (14):

[0193]

[0194] 4) The road voltage caused by the system harmonic current will be calculated using formula (15):

[0195]

[0196] In the formula, Represents the hth harmonic impedance of branch ij.

[0197] 5) Based on the branch voltage drop calculation results, the node voltage is calculated by the harmonic current using the forward method. The calculation formula is shown in formula (16):

[0198] [V (h),k ]=[HA (h),k ][I (h),k ] (16)

[0199] Where HA (h) It is the relationship matrix between node voltage and system harmonic current.

[0200] 6) The node voltage at the parallel capacitor can be calculated by formula (17):

[0201]

[0202] Since the voltage of the parallel capacitor can be Calculation is performed, therefore, the above formula can be transformed into formula (18), and by simplification, the matrices [HAss] and [HAsh] can be obtained.

[0203]

[0204] 7) Calculate the HLF matrix using equations (19) and (20).

[0205]

[0206] HLF=[HAss]+[Zs] (20)

[0207] Where Zs represents the load harmonic impedance caused by the parallel capacitor.

[0208] 8) Calculate each order of harmonic voltage:

[0209] [V (h),k+1 ]=[V (h),0 ]+[V (h),k ] (twenty one)

[0210] 9) Calculate the iteration error

[0211] |V i (h),k+1 -V i (h),k |≤ε for i=1…N (22)

[0212] Based on the harmonic flow calculation results and the national standard "Power Quality Public Grid Harmonics" (GT / T14549-1993), the present invention uses the injected current when the power replacement equipment is connected to generate the maximum harmonic output to determine its access capacity. Therefore, the constraints determined by the harmonic current are:

[0213]

[0214] In the formula, S ES U is the amount of electricity replacement equipment connected; N is the rated voltage; μ k It is the content rate limit of each harmonic output by the electric energy replacement equipment; k These are the harmonic currents allowed to be connected to the power grid as specified in the national standard.

[0215] According to the national standard "Power Quality Public Grid Harmonics" (GT / T14549-1993), the permissible harmonic voltage content and total harmonic content of voltage in different voltage level systems are different. In order to ensure the effectiveness of the harmonic voltage content constraint, when the power replacement equipment is connected, the harmonic distortion rate of the grid node is 4% to evaluate its access capacity. Combined with the identification results of the weak links in the distribution network, the specific evaluation process is as follows: Fig.14 As shown in the figure, combined with the results of weak link identification of the distribution network, the specific process of evaluating the alternative access amount of electric energy considering grid harmonics and weak links is as follows:

[0216] a. Analyze the harmonic characteristics of electric energy replacement equipment;

[0217] b. Identify the weak links in the distribution network;

[0218] c. Use harmonic power flow calculation to solve the harmonic distortion rate when the electric energy replacement equipment is connected to the power grid;

[0219] d. When the harmonic distortion rate is less than 4%, output the electric energy replacement access amount; when the harmonic distortion rate is greater than or equal to 4%, reduce the access amount of electric energy replacement equipment and return to step c for calculation until the harmonic distortion rate meets the conditions and the evaluation ends.

[0220] In a specific embodiment, the power distribution network power substitution carrying capacity assessment considering power quality

[0221] Due to the relatively backward supporting facilities of the distribution network, the disorderly access of the load of large-scale electricity substitution projects has increased the load-bearing pressure of the distribution network, affecting the safe operation of the power grid. Therefore, a reasonable assessment of the distribution network's carrying capacity for electricity substitution loads is of great significance to ensuring the stable operation of the power grid and promoting the development of electricity substitution. To this end, the present invention determines the nodes suitable for the access of electricity substitution equipment by analyzing the economic benefits brought by electricity substitution to the distribution network, combining the similarity coefficient between electricity substitution and the existing net load. On this basis, a distribution network electricity substitution carrying capacity assessment model that takes into account the quality of electricity is established, and at the same time, the regulation ability of the electricity substitution load is considered to evaluate the access carrying capacity of the electricity substitution equipment.

[0222] The benefit analysis process of electric energy substitution is as follows: The benefit analysis of electric energy substitution in this invention is based on the perspective of terminal energy users, assuming that terminal energy consumers will follow the principle of economy when making energy consumption choices, that is, pursue utility maximization. For electric energy substitution loads, its benefit analysis model includes electric energy substitution investment cost, operating cost and electric energy substitution income:

[0223] The investment cost calculation formula is as follows:

[0224] C 1,p =λ inv,p S ES,p ;

[0225] In the formula, λ inv,p represents the unit capacity investment cost of the electric energy substitution type p, S ES,p represents the electric energy replacement capacity installed on the distribution network;

[0226] The calculation formula of operation and maintenance cost of electric energy substitution is as follows:

[0227]

[0228] In the formula, λ o represents the unit capacity operation and maintenance cost; q is the energy replacement operating life, and r is the discount rate;

[0229] Electricity substitution benefits:

[0230] The benefits of electric energy substitution are calculated through the utility function. The calculation formulas of the utility function and net benefit function of electric energy substitution are as follows:

[0231]

[0232] π ES,i,p =U ES,i,p (P ES,i,p )-λ i P ES,i,p ;

[0233] Where PES,i,p is the type p electric energy replacement power connected to node i; α and ω are the coefficients of the utility function of the electric energy replacement device, and the values ​​are different for different types of electric energy replacement; λ i is the electricity price at node i; in order to reflect the difference in electricity costs between nodes, Fig.15 The node marginal price (DLMP) shown is the electricity price rather than the electricity sales price.

[0234] Based on the above conditions, the economic benefits of electric energy substitution access to each node are calculated, and the economically optimal access amount of electric energy substitution is determined through the economic benefits; the access capacity of electric energy substitution type p calculated based on economic efficiency is as follows:

[0235]

[0236] In a specific embodiment, the analysis process of the similarity coefficient between electric energy substitution and existing net load is as follows:

[0237] The newly added equipment for electric energy substitution should be as dissimilar as possible to the original load curve. According to the matching degree between the electric energy substitution equipment and the existing net load, the nodes are selected as the access points for electric energy substitution according to the dissimilar degree. For this purpose, the similarity coefficient based on time series similarity is introduced as the matching degree index between the newly added electric energy substitution equipment and the original net load data. The calculation formula is as follows:

[0238]

[0239] D w =λD E +δD S ;

[0240] Among them, D E is the Euclidean distance, D s is the cosine similarity, P NL (t) is the net load data at time t, W(t) is the electric energy replacement load value at time t, W max is the maximum load value; λ and δ are the Euclidean distance weight and cosine similarity weight, respectively, both are taken as 0.5; D w is the similarity coefficient between the electric energy replacement and the existing net load. The larger the source-load similarity coefficient, the smaller the similarity between the electric energy replacement equipment and the existing net load. The node with a larger similarity coefficient is selected as the access point for the electric energy replacement. Fig.16 The IEEE33 node shown is the electric energy replacement calculated by the model and the similarity coefficient of the existing net load is shown in Table 4.

[0241] Table 4 Similarity coefficient between electricity substitution and existing net load

[0242]

[0243] In a specific embodiment, the distribution network power substitution carrying capacity evaluation model is:

[0244] The maximum carrying capacity of the distribution network for electric energy substitution is taken as the objective function:

[0245] maxN=μ 1 N hp +μ 2 N evp +μ 3 N eaf ;

[0246] Where N hp is the number of air source heat pumps connected, N evp is the number of electric vehicle charging piles connected, N eaf is the number of electric furnaces connected; μ 1 , μ 2 , μ 3 are the weight coefficients of the three types of electric energy replacement equipment.

[0247] In a specific embodiment, the constraint condition is expressed in the following form:

[0248] Power flow constraints:

[0249]

[0250] Where i, j are node numbers; V i , V j are the voltages of nodes i and j respectively; P jk , Q jk are respectively the active power and reactive power at the head end of branch jk; P ij , Q ij are respectively the active power and reactive power at the head end of branch ij; r ij ,x ij are the resistance and reactance of branch ij respectively; I ij is the square of the current in branch ij; k:j→k is the set of child nodes with node j as the parent node; P j , Q j Inject net active and reactive power into the node;

[0251] Node voltage constraints:

[0252] V min ≤V i ≤V max ;

[0253] Where V min and V max They are the voltage lower limit and upper limit respectively;

[0254] Equipment capacity constraints:

[0255]

[0256] In the formula, S ij is the transmission capacity of line ij, is the maximum transmission capacity of line ij;

[0257] Energy storage constraints include energy storage charging and discharging state constraints and energy storage charging and discharging power constraints;

[0258] Energy storage charging and discharging state constraints:

[0259]

[0260] Energy storage charging and discharging power constraints:

[0261]

[0262] where y ch and dis Respectively represent the charging state and the discharging state; P ch,max ,P dis,max are the maximum power of energy storage charging and discharging respectively; in addition, the remaining capacity constraint of energy storage must be met:

[0263]

[0264] E min With E max are the maximum capacity limit and the minimum capacity limit of energy storage respectively; η ch With η dis are the energy storage charging efficiency and discharging efficiency respectively; E 0 is the initial capacity of energy storage.

[0265] Considering the power replacement capacity constraints of harmonic indicators:

[0266] P ES,i,t ≤P ES,i,t,THDmax ;

[0267] Among them, P ES,i,t,THDmax The upper limit of the amount of node power replacement equipment connected to consider power quality factors;

[0268] Based on the harmonic analysis of power substitution, the harmonic distortion rate of each node after the node is connected to the power substitution grid is calculated through the harmonic power flow algorithm; according to the relevant standards of the national standard "Harmonics of Public Power Grid for Power Quality", the specified limit of the total voltage harmonic distortion rate is used as the judgment standard, and the power substitution access amount of the node is reduced until all nodes meet the power quality requirements, and the upper limit P of the access amount of power substitution equipment of the node considering the power quality factor is obtained. ES,i,t,THDmax The electric energy replacement capacity obtained by the above model is as follows: Fig.17 shown.

[0269] The minimum access capacity constraint for electric energy substitution means that the access capacity of each type of electric energy substitution shall not be less than its economically optimal access capacity;

[0270]

[0271] Where N hp ,N evp ,N eaf They are the number of air source heat pumps, electric vehicle charging piles, and electric furnaces connected; They are the unit access capacities of air source heat pumps, electric vehicle charging piles, and electric furnaces; They are the economically optimal access capacities for air source heat pumps, electric vehicle charging piles, and electric furnaces.

[0272] A distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality, comprising:

[0273] The evaluation index establishment module establishes the evaluation index of power grid status weakness and the evaluation index of power grid structure weakness based on risk utility theory and complex network theory respectively;

[0274] The weak link identification module of the distribution network uses the least squares support vector machine to combine the two evaluation indicators to obtain the comprehensive evaluation index for the identification of the weak link of the distribution network, and identifies the weak link of the distribution network through the comprehensive evaluation index;

[0275] The harmonic analysis module selects electric energy replacement equipment from different industries, builds an electric energy replacement harmonic simulation model based on the composition and working principle of the electric energy replacement equipment, analyzes the harmonics generated by various equipment, and obtains analysis results;

[0276] The electric energy substitution access quantity assessment module determines the harmonic frequency generated by the electric energy substitution equipment during operation through the analysis results of the electric energy substitution harmonic model; connects the electric energy substitution equipment to the weak nodes obtained by the weak link identification of the distribution network, and uses the harmonic power flow algorithm to determine the harmonic distortion rate of the weak nodes and other nodes according to the obtained harmonic frequency. With the harmonic distortion rate as a constraint condition, combined with the results of the weak link identification of the distribution network, an assessment is performed to obtain the electric energy substitution access quantity that takes into account the harmonics and weak links of the power grid;

[0277] The node determination module for connecting the electric energy substitution equipment calculates the economic benefits brought by the electric energy substitution to the distribution network, and determines the node for connecting the electric energy substitution equipment according to the obtained economic benefits and the similarity coefficient between the electric energy substitution and the existing net load;

[0278] The distribution network electric energy substitution carrying capacity assessment module adjusts the electric energy substitution load curve according to the adjustment capability of the electric energy substitution load curve to obtain the result of the load curve adjustment; based on the result of the load curve adjustment, the electric energy substitution access quantity, and the nodes to which the electric energy substitution equipment is connected, the distribution network electric energy substitution carrying capacity assessment model containing flow constraints, node voltage constraints, equipment capacity constraints, energy storage constraints, electric energy substitution capacity constraints, and minimum electric energy substitution access capacity constraints is established to assess the distribution network electric energy substitution carrying capacity.

[0279] A computer-readable storage medium stores instructions, which, when executed by a processor, implement the steps of a method for evaluating the electric energy substitution carrying capacity of a distribution network based on weak links in the power grid and the quality of electric energy.

[0280] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0281] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating the power substitution carrying capacity of a distribution network based on weak links in the power grid and power quality, characterized in that: include: Based on risk utility theory and complex network theory, the grid status weakness assessment index and grid structure weakness assessment index are established respectively; The two evaluation indicators are combined by using the least squares support vector machine to obtain the comprehensive evaluation index for identifying the weak links in the distribution network. The weak links in the distribution network are identified by the comprehensive evaluation index. Select electric energy replacement equipment from different industries, build an electric energy replacement harmonic simulation model based on the composition and working principle of the electric energy replacement equipment, analyze the harmonics generated by various equipment, and obtain analysis results; Through the analysis results of the electric energy replacement harmonic model, determine the number of harmonics generated by the electric energy replacement equipment during operation; Connect the electric energy replacement equipment to the weak nodes identified by the weak links of the distribution network. According to the harmonic order obtained, the harmonic distortion rate of the weak nodes and other nodes is determined by using the harmonic power flow algorithm. The harmonic distortion rate is used as a constraint condition. Combined with the results of the weak link identification of the distribution network, an evaluation is performed to obtain the amount of electric energy replacement access that takes into account the harmonics and weak links of the power grid. Calculate the economic benefits of electric energy substitution for the distribution network, and determine the nodes where the electric energy substitution equipment is connected based on the obtained economic benefits and the similarity coefficient between the electric energy substitution and the existing net load; According to the adjustment capability of the electric energy replacement load curve, the electric energy replacement load curve is adjusted; Obtain the result of load curve adjustment; Based on the results of load curve adjustment, the amount of electric energy substitution access, and the nodes to which electric energy substitution equipment is connected, a distribution network electric energy substitution carrying capacity assessment model is established, which includes flow constraints, node voltage constraints, equipment capacity constraints, energy storage constraints, electric energy substitution capacity constraints, and minimum electric energy substitution access capacity constraints, to assess the distribution network's carrying capacity for the electric energy substitution equipment to be assessed.

2. According to claim 1, a method for evaluating the power substitution carrying capacity of a distribution network based on weak links in the power grid and power quality, characterized in that: The evaluation indicators of weak links in the distribution network status include node voltage exceeding the limit and line power flow exceeding the limit; the evaluation indicators of weak links in the structure include node degree, line degree, node injection power and line betweenness.

3. According to claim 1, a method for evaluating the power substitution carrying capacity of a distribution network based on weak links in the power grid and power quality, characterized in that: The constraints determined by the harmonic distortion rate are: In the formula, S ES U is the amount of electricity replacement equipment connected; N is the rated voltage; μ k It is the content rate limit of each harmonic output by the electric energy replacement equipment; k These are the harmonic currents allowed to be connected to the power grid as specified in the national standard.

4. The method for evaluating the power substitution carrying capacity of a distribution network based on weak links in the power grid and power quality according to claim 1 is characterized in that: Combined with the results of weak link identification of the distribution network, the specific process of evaluating the alternative access amount of electric energy considering grid harmonics and weak links is as follows: a. Analyze the harmonic characteristics of electric energy replacement equipment; b. Identify the weak links in the distribution network; c. Use harmonic power flow calculation to solve the harmonic distortion rate when the electric energy replacement equipment is connected to the power grid; d. When the harmonic distortion rate is less than 4%, output the electric energy replacement access amount; when the harmonic distortion rate is greater than or equal to 4%, reduce the access amount of electric energy replacement equipment and return to step c for calculation until the harmonic distortion rate meets the conditions and the evaluation ends.

5. The method for evaluating the power substitution carrying capacity of a distribution network based on weak links in the power grid and power quality according to claim 1 is characterized in that: The distribution network electric energy substitution carrying capacity assessment model is: The maximum carrying capacity of the distribution network for electric energy substitution is taken as the objective function: maxN=μ1N hp +μ2N evp +μ3N eaf ; Where N hp is the number of air source heat pumps connected, N evp is the number of electric vehicle charging piles connected, N eaf is the number of electric furnaces connected; μ1, μ2, μ3 are the weight coefficients of the three types of electric energy replacement equipment.

6. The method for evaluating the power substitution carrying capacity of a distribution network based on weak links in the power grid and power quality according to claim 1 is characterized in that: The constraints are expressed in the following form: Power flow constraints: Where i, j are node numbers; v i , v j are the voltages of nodes i and j respectively; P jk , Q jk are respectively the active power and reactive power at the head end of branch jk; P ij , Q ij are respectively the active power and reactive power at the head end of branch ij; r ij +x ij is the impedance of branch ij; I ij is the square of the current in branch ij; k:j→k is the set of child nodes with node j as the parent node; P j , Q j Inject net active and reactive power into the node; Node voltage constraints: In min ≤V i ≤V max ; Where V min and V max They are the voltage lower limit and upper limit respectively; Equipment capacity constraints: In the formula, S ij is the transmission capacity of line ij, is the maximum transmission capacity of line ij; Energy storage constraints include energy storage charging and discharging state constraints and energy storage charging and discharging power constraints; Energy storage charging and discharging state constraints: Energy storage charging and discharging power constraints: where y ch and dis Respectively represent the charging state and the discharging state; P ch,max ,P dis,max are the maximum power of energy storage charging and discharging respectively; in addition, the remaining capacity constraint of energy storage must be met: E min With E max are the maximum capacity limit and the minimum capacity limit of energy storage respectively; η ch With η dis are the energy storage charging efficiency and discharging efficiency respectively; Considering the power replacement capacity constraints of harmonic indicators: P ES,i,t ≤P ES,i,t,THDmax ; Among them, P ES,i,t,THDmax The upper limit of the amount of node power replacement equipment connected to consider power quality factors; The minimum access capacity constraint for electric energy substitution means that the access capacity of each type of electric energy substitution shall not be less than its economically optimal access capacity; Where N hp ,N evp ,N eaf They are the number of air source heat pumps, electric vehicle charging piles, and electric furnaces connected; They are the unit access capacities of air source heat pumps, electric vehicle charging piles, and electric furnaces; They are the economically optimal access capacities for air source heat pumps, electric vehicle charging piles, and electric furnaces.

7. A distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality, characterized in that: A method for evaluating the electric energy substitution carrying capacity of a distribution network based on weak links of a power grid and power quality as described in any one of claims 1 to 6 is applied, and the system comprises: The evaluation index establishment module establishes the evaluation index of power grid status weakness and the evaluation index of power grid structure weakness based on risk utility theory and complex network theory respectively; The weak link identification module of the distribution network uses the least squares support vector machine to combine the two evaluation indicators to obtain the comprehensive evaluation index for the identification of the weak link of the distribution network, and identifies the weak link of the distribution network through the comprehensive evaluation index; The harmonic analysis module selects electric energy replacement equipment from different industries, builds an electric energy replacement harmonic simulation model based on the composition and working principle of the electric energy replacement equipment, analyzes the harmonics generated by various equipment, and obtains analysis results; The electric energy substitution access quantity assessment module determines the harmonic frequency generated by the electric energy substitution equipment during operation through the analysis results of the electric energy substitution harmonic model; connects the electric energy substitution equipment to the weak nodes obtained by the weak link identification of the distribution network, and uses the harmonic power flow algorithm to determine the harmonic distortion rate of the weak nodes and other nodes according to the obtained harmonic frequency. With the harmonic distortion rate as a constraint condition, combined with the results of the weak link identification of the distribution network, an assessment is performed to obtain the electric energy substitution access quantity that takes into account the harmonics and weak links of the power grid; The node determination module for connecting the electric energy substitution equipment calculates the economic benefits brought by the electric energy substitution to the distribution network, and determines the node for connecting the electric energy substitution equipment according to the obtained economic benefits and the similarity coefficient between the electric energy substitution and the existing net load; The distribution network electric energy substitution carrying capacity assessment module adjusts the electric energy substitution load curve according to the adjustment capability of the electric energy substitution load curve; obtains the result of the load curve adjustment; based on the result of the load curve adjustment, the electric energy substitution access quantity, and the nodes to which the electric energy substitution equipment is connected, by establishing a distribution network electric energy substitution carrying capacity assessment model containing flow constraints, node voltage constraints, equipment capacity constraints, energy storage constraints, electric energy substitution capacity constraints, and minimum electric energy substitution access capacity constraints, the distribution network is assessed for the carrying capacity of the electric energy substitution equipment to be assessed.

8. A distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality according to claim 7, characterized in that: The evaluation indicators of weak links in the distribution network status include node voltage exceeding the limit and line power flow exceeding the limit; the evaluation indicators of weak links in the structure include node degree, line degree, node injection power and line betweenness.

9. A distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality according to claim 7, characterized in that: The constraints determined by the harmonic distortion rate are: In the formula, S ES U is the amount of electricity replacement equipment connected; N is the rated voltage; μ k It is the content rate limit of each harmonic output by the electric energy replacement equipment; k These are the harmonic currents allowed to be connected to the power grid as specified in the national standard.

10. A distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality according to claim 7, characterized in that: Combined with the results of weak link identification of the distribution network, the specific process of evaluating the alternative access amount of electric energy considering grid harmonics and weak links is as follows: a. Analyze the harmonic characteristics of electric energy replacement equipment; b. Identify the weak links in the distribution network; c. Use harmonic power flow calculation to solve the harmonic distortion rate when the electric energy replacement equipment is connected to the power grid; d. When the harmonic distortion rate is less than 4%, output the electric energy replacement access amount; when the harmonic distortion rate is greater than or equal to 4%, reduce the access amount of electric energy replacement equipment and return to step c for calculation until the harmonic distortion rate meets the conditions and the evaluation ends.

11. A distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality according to claim 7, characterized in that: The distribution network electric energy substitution carrying capacity assessment model is: The maximum carrying capacity of the distribution network for electric energy substitution is taken as the objective function: maxN=μ1N hp +μ2N evp +μ3N eaf ; Where N hp is the number of air source heat pumps connected, N evp is the number of electric vehicle charging piles connected, N eaf is the number of electric furnaces connected; μ1, μ2, μ3 are the weight coefficients of the three types of electric energy replacement equipment.

12. A distribution network power substitution carrying capacity assessment system based on power grid weak links and power quality according to claim 7, characterized in that: The constraints are expressed in the following form: Power flow constraints: Where i, j are node numbers; v i , v j are the voltages of nodes i and j respectively; P jk , Q jk are respectively the active power and reactive power at the head end of branch jk; P ij , Q ij are respectively the active power and reactive power at the head end of branch ij; r ij +x ij is the impedance of branch ij; I ij is the square of the current in branch ij; k:j→k is the set of child nodes with node j as the parent node; P j , Q j Inject net active and reactive power into the node; Node voltage constraints: In min ≤V i ≤V max ; Where V min and V max They are the voltage lower limit and upper limit respectively; Equipment capacity constraints: In the formula, S ij is the transmission capacity of line ij, is the maximum transmission capacity of line ij; Energy storage constraints include energy storage charging and discharging state constraints and energy storage charging and discharging power constraints; Energy storage charging and discharging state constraints: Energy storage charging and discharging power constraints: where y ch and dis Respectively represent the charging state and the discharging state; P ch,max ,P dis,max are the maximum power of energy storage charging and discharging respectively; in addition, the remaining capacity constraint of energy storage must be met: E min With E max are the maximum capacity limit and the minimum capacity limit of energy storage respectively; η ch With η dis are the energy storage charging efficiency and discharging efficiency respectively; Considering the power replacement capacity constraints of harmonic indicators: P ES,i,t ≤P ES,i,t,THDmax ; Among them, P ES,i,t,THDmax The upper limit of the amount of node power replacement equipment connected to consider power quality factors; The minimum access capacity constraint for electric energy substitution means that the access capacity of each type of electric energy substitution shall not be less than its economically optimal access capacity; Where N hp ,N evp ,N eaf They are the number of air source heat pumps, electric vehicle charging piles, and electric furnaces connected; They are the unit access capacities of air source heat pumps, electric vehicle charging piles, and electric furnaces; They are the economically optimal access capacities for air source heat pumps, electric vehicle charging piles, and electric furnaces.

13. A computer-readable storage medium having instructions stored thereon, characterized in that: When the instructions are executed by a processor, the steps of any one of the methods described in claims 1 to 6 are implemented.

Images