Phase-changing switch location planning method and system for three-phase imbalance control in transformer area

Abstract

The present invention discloses a method and system for phase-changing switch site selection planning for three-phase imbalance control in a substation, including: determining decision variables for phase-changing switch site selection planning; constructing a phase-changing switch site selection planning model with the minimum comprehensive cost of the substation as the objective function based on the decision variables; modeling the phase-changing switch site selection planning model as a mixed integer non-convex programming problem, and performing linearization and convex relaxation processing, and realizing the phase-changing switch site selection planning for three-phase imbalance control in the substation by solving the problem. In the site selection of phase-changing switches, the present invention takes the minimum comprehensive cost of the substation as the goal, takes into account the construction cost and operation cost of the phase-changing switch, ensures the economy of control, and simultaneously accurately models the power flow distribution of the substation, improves the accuracy of cost calculation, and ensures the safety of distribution network operation. In addition, the present invention can directly use the solver to solve and obtain the global optimal solution, without the need to write a solution algorithm, and has high calculation efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of power system operation planning, and in particular to a phase-changing switch site selection planning method and system for three-phase imbalance management in a transformer area. Background Art

[0002] As the requirements of distribution network users for power quality continue to increase, the three-phase imbalance problem of distribution networks has become one of the issues that the industry and academia are paying more and more attention to. There are a large number of randomly connected single-phase loads in the low-voltage distribution network. Their uneven distribution in space and inconsistent fluctuations in time are the main reasons for the three-phase imbalance. In traditional governance methods, it is usually considered to install thyristor-controlled reactors, static VAR generators, and static VAR compensators at the outlet of the low-voltage side of the distribution transformer to improve the three-phase imbalance by adjusting the three-phase current and dynamically compensating reactive power. However, the scope of these devices is limited to the outlet of the distribution transformer, and the degree of adjustment is limited, making it difficult to fundamentally solve the three-phase imbalance problem.

[0003] With the development of power electronics technology, low-voltage load phase-changing switches have attracted widespread attention as a new means to effectively manage three-phase imbalance. The principle of this method is to use phase-changing switches to intelligently switch the phases of single-phase users, and balance the three-phase load by switching some users connected to the heavy-load phase to the light-load phase, so as to achieve the purpose of three-phase imbalance management, which has an immediate effect in low-voltage distribution networks with severe three-phase imbalance. Among them, some scholars focus on the hardware or software system design of phase-changing switches, so that they can complete phase change faster and reduce the impact on users. For the phase-changing switches that have been installed and configured in the system, many scholars have conducted extensive discussions on the research of phase-changing switch switching strategies. However, there are relatively few studies on the optimal location method of phase-changing switches. The existing literature considers the power flow distribution of the substation, establishes a phase-changing switch location model with the goal of minimizing the three-phase power imbalance on the low-voltage side of the distribution transformer, and reconstructs the problem into a mixed integer linear programming model, so that the model can be directly solved by commercial solvers. However, this method ignores the investment and operating costs of phase-changing switches, and its economic efficiency cannot be guaranteed. In the existing literature, a site selection model is established with the goal of minimizing the sum of the construction cost of the phase-changing switch and the operating costs of each typical scenario, but the number of operations of the phase-changing switch is not restricted. Since the phase-changing switch is connected in series on the line, its frequent operation will increase the possibility of its failure, thereby affecting the reliability of power supply. In the existing literature, a two-layer optimization model for the site selection of the phase-changing switch is established, in which the upper model optimizes the position of the phase-changing switch and the lower model optimizes the operating cost. However, this model does not take into account the power flow distribution of the distribution network, and the cost calculation accuracy is poor.

[0004] In summary, current research on phase-changing switch site selection methods rarely takes into account the accurate modeling of phase-changing switch investment and operation costs and the power flow distribution analysis of distribution networks. Summary of the invention

[0005] In view of the above existing problems, the present invention is proposed.

[0006] Therefore, the present invention provides a phase-changing switch site selection planning method and system for the management of three-phase imbalance in substations. In the site selection of phase-changing switches, the minimum comprehensive cost of the substation is taken as the goal, the construction cost and operation cost of the phase-changing switch are taken into consideration to ensure the economy of the management, and at the same time, the power flow distribution of the substation is accurately modeled, which improves the accuracy of cost calculation and ensures the safety of distribution network operation.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] In the first aspect, the present invention provides a phase-changing switch site selection planning method for three-phase imbalance control in a substation, comprising: determining decision variables for phase-changing switch site selection planning; constructing a phase-changing switch site selection planning model with the minimum comprehensive cost of the substation as the objective function based on the decision variables; modeling the phase-changing switch site selection planning model as a mixed integer non-convex programming problem, and performing linearization and convex relaxation processing, and realizing the phase-changing switch site selection planning for three-phase imbalance control in the substation by solving the problem.

[0009] As a preferred solution of the phase-changing switch site selection planning method for three-phase unbalance management in the substation area described in the present invention, the decision variables for determining the phase-changing switch site selection planning include:

[0010] Consider treating users connected to the same root node as equivalent, and use equivalent users as candidate locations for phase-changing switch construction. If a root node contains users who cannot install phase-changing switches, this root node cannot be selected as a candidate location for phase-changing switch construction. Based on this, the phase-changing switch location matrix S and the user phase matrix Λ are defined;

[0011] The phase-changing switch location matrix S and the user phase matrix Λ constitute decision variables of the phase-changing switch location planning model, wherein the phase-changing switch location matrix S determines the optimal phase-changing switch installation position, and the user phase matrix Λ determines the optimal phase-changing strategy.

[0012] As a preferred solution of the phase-changing switch site selection and planning method for three-phase unbalance management in the substation described in the present invention, the objective function of the phase-changing switch site selection and planning model is:

[0013] minC=min(C new +C sw +C loss +C unb )

[0014]

[0015] C sw =365c s D s

[0016]

[0017] Among them, C is the comprehensive cost of the area, C new is the phase-changing switch system investment cost, C sw is the switching cost, C loss is the network loss cost of the area, C unb is the penalty cost of three-phase imbalance in the transformer area, c e is the investment cost of the commutation master controller, Ω T It is a collection of various phase-changing switch models. is the installation cost of the ω-type phase-changing switch, is the number of ω-type phase-changing switches installed, w is the service life of the phase-changing switches, r is the cash flow discount rate, c s is the cost of one phase-changing switch action, D s is the sum of the number of operations of all phase-changing switches in the transformer area, c p is the network loss cost coefficient, I l,t is the current flowing through line l at time t, r l is the line resistance, Ω l is the line set, c u is the three-phase unbalance penalty coefficient, γ t is the three-phase imbalance degree exceeding the standard in the substation at time t, and ε is the three-phase imbalance penalty threshold.

[0018] As a preferred solution of the phase-changing switch site selection planning method for three-phase imbalance control in the substation described in the present invention, the constraints of the phase-changing switch site selection planning model include phase-changing switch constraints, user phase constraints, and distribution station area constraints.

[0019] As a preferred solution of the phase-changing switch site selection planning method for three-phase unbalance management in the substation described in the present invention, the phase-changing switch site selection planning model is modeled as a mixed integer non-convex programming problem, and linearization processing includes:

[0020] The linearization processing includes three-phase imbalance linearization processing and phase constraint linearization processing. The three-phase imbalance linearization processing is to replace the real-time three-phase current average value of the denominator in the three-phase imbalance calculation with the three-phase current average value before treatment. The phase constraint linearization processing is to use the big M method to convert the logical constraint equivalent into a linear inequality.

[0021] As a preferred solution of the phase-changing switch site selection planning method for three-phase imbalance management in the substation described in the present invention, the phase-changing switch site selection planning model is modeled as a mixed integer non-convex programming problem, and convex relaxation processing is performed, including:

[0022] Perform variable replacement on the power flow constraints of the distribution station area after phase angle relaxation;

[0023] The transformed equality constraint is relaxed into a second-order cone by using a second-order cone relaxation technique, and rewritten into a standard second-order cone form to obtain a convexly relaxed power flow constraint;

[0024] When there is a situation of disconnected branch circuit, the large M method is introduced to improve the power flow constraint after convex relaxation.

[0025] As a preferred solution of the phase-changing switch site selection planning method for three-phase unbalance management in the substation area described in the present invention, the phase-changing switch site selection planning for three-phase unbalance management in the substation area by solving the problem includes:

[0026] After relaxation, the model is transformed from a mixed integer non-convex programming problem into a mixed integer second-order cone programming problem, which is solved by the CPLEX solver to realize the site selection planning of phase-changing switches for three-phase imbalance control in the substation.

[0027] In a second aspect, the present invention provides a phase-changing switch site selection and planning system for three-phase unbalance management in a transformer area, comprising:

[0028] A decision variable determination module, used to determine the decision variables for the phase-changing switch site selection planning;

[0029] A model building module, used to build a phase-changing switch location planning model with the minimum comprehensive cost of the substation as the objective function based on the decision variables;

[0030] The planning and solving module is used to model the phase-changing switch site selection planning model as a mixed integer non-convex planning problem, and perform linearization and convex relaxation processing, so as to realize the phase-changing switch site selection planning for three-phase imbalance management in the substation area by solving the problem.

[0031] In a third aspect, the present invention provides an electronic device, comprising:

[0032] Memory and processor;

[0033] The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the phase-changing switch site selection planning method for three-phase imbalance control in the substation are realized.

[0034] In a fourth aspect, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the phase-changing switch site selection planning method for three-phase imbalance control in a substation.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a phase-changing switch site selection and planning method and system for the management of three-phase imbalance in substations, which comprehensively considers the investment and operation costs of the phase-changing switches and the power flow distribution in the substation, and can obtain the optimal installation position and the optimal phase-changing strategy of the phase-changing switches. When the number of installed phase-changing switches and the number of operations are small, the three-phase imbalance can be effectively managed while achieving the best economy; the present invention can not only plan the optimal number and location of installation for substations with uncertain number and location of phase-changing switches, but also provide the optimal installation location for substations with determined number of phase-changing switches, and has strong versatility; in addition, the phase-changing switch site selection and planning method proposed in the present invention is a mixed integer second-order cone programming model, which can directly use the solver to obtain the global optimal solution without writing a solution algorithm, and has high computational efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0037] Figure 1 A schematic diagram of the overall process logic of a phase-changing switch site selection and planning method for three-phase imbalance control in a transformer area according to an embodiment of the present invention;

[0038] Figure 2 A schematic diagram of the phase-changing switch configuration results of the phase-changing switch site selection and planning method for three-phase imbalance control in a transformer area according to an embodiment of the present invention;

[0039] Figure 3 A three-phase current curve diagram of each scenario of the phase-changing switch site selection and planning method for three-phase imbalance control in the substation according to an embodiment of the present invention;

[0040] Figure 4 A schematic diagram of the three-phase imbalance degree of a substation in each scenario of a phase-changing switch site planning method for three-phase imbalance management in a substation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0042] Example 1

[0043] Reference Figure 1 This is an embodiment of the present invention. Currently, the research on the site selection of phase-changing switches rarely takes into account the accurate modeling of the investment and operation costs of the phase-changing switches and the power flow distribution analysis of the distribution network. Failure to consider the investment and operation costs of the phase-changing switches will reduce the economic benefits of three-phase imbalance management. Failure to consider the power flow distribution of the distribution network will reduce the accuracy of the calculation of the economic benefits of three-phase imbalance management, and the safety of the distribution network operation cannot be guaranteed. In response to the shortcomings of current research, the present invention proposes a phase-changing switch site selection planning method for three-phase imbalance management in substations. This method takes the minimum comprehensive cost of the substation as the goal in the site selection of the phase-changing switches, takes into account the construction cost and operation cost of the phase-changing switches, ensures the economy of the management, and simultaneously accurately models the power flow distribution of the substation, improves the accuracy of cost calculation, and ensures the safety of the distribution network operation. Figure 1 The specific steps shown include:

[0044] S100: Determine decision variables for commutation switch site planning;

[0045] S200: constructing the objective function and constraint conditions of the commutation switch location planning model based on the decision variables;

[0046] S300: The phase-changing switch location planning model is modeled as a mixed integer non-convex programming problem, and linearized and convexly relaxed. By solving the problem, the phase-changing switch location planning for three-phase imbalance control in the substation is realized.

[0047] It should be noted that the present invention provides a method and system for the site selection and planning of phase-changing switches for the management of three-phase imbalance in substations. The method comprehensively considers the investment and operation costs of the phase-changing switches and the power flow distribution in the substation, and can obtain the optimal installation position and the optimal phase-changing strategy of the phase-changing switches. When the number of installed phase-changing switches and the number of operations are small, the three-phase imbalance can be effectively managed while achieving the best economy. The present invention can not only plan the optimal number and location of phase-changing switches for substations with uncertain number and location of phase-changing switches, but also provide the optimal installation location for substations with determined number of phase-changing switches, and has strong versatility. In addition, the proposed method for site selection and planning of phase-changing switches is a mixed integer second-order cone programming model, which can be directly solved by a solver to obtain the global optimal solution without the need to write a solution algorithm, and has high computational efficiency.

[0048] In the embodiment of the present application, the decision variables for determining the location planning of the commutation switch in the above step S100 include:

[0049] Considering that the distribution station area is radial, in order to reduce the number of phase-changing switches installed and ensure the adjustment accuracy, it is considered to treat the users connected to the same root node equivalently, and use the equivalent users as the alternative locations for the construction of phase-changing switches. Phase-changing switches are installed here to uniformly control the phases of each user. If a root node contains users who cannot install phase-changing switches, this root node cannot be selected as an alternative location for the construction of phase-changing switches. Based on this, the phase-changing switch location matrix S is defined as:

[0050] S=[s1 s2 … s H ]

[0051] Among them, s h = 0 means no phase-changing switch is installed at the root node h, s h =1 means that a phase-changing switch is installed at the root node h, and H is the number of root nodes where phase-changing switches can be installed;

[0052] In order to optimize the action strategy of the phase-changing switch, the user phase matrix Λ is defined;

[0053]

[0054] Among them, N is the number of users in the area, T is the length of the scheduling time series, and A n,t =[α 1,n,t α 2,n,t α 3,n,t ] is a 1x3 vector, α 1,n,t =1 means that at time t, user n is connected to phase A. Similarly, α 2,n,t =1, α 3,n,t =1 means that at time t, user n is connected to phases B and C.

[0055] Furthermore, the phase-changing switch location matrix S and the user phase matrix Λ constitute the decision variables of the phase-changing switch location planning model, where the phase-changing switch location matrix S determines the optimal phase-changing switch installation location, and the user phase matrix Λ determines the optimal phase-changing strategy. The economic management of three-phase imbalance is achieved by optimizing the phase-changing switch location matrix S and the user phase matrix Λ.

[0056] It should be noted that the above step S100 can ensure that the established model is both close to reality and flexible enough to meet the needs of different scenarios by accurately identifying which variables will affect the location selection of the phase-changing switch, such as geographical location, power load distribution characteristics, existing power grid structure, etc. At the same time, the reasonable setting of decision variables helps to simplify complex problems, making the model easier to understand and solve, thereby improving the effectiveness and practicality of the final solution. In addition, the precise definition of decision variables also makes quantitative analysis possible, so that the objective function and constraints constructed based on these variables can more accurately reflect the goal of controlling three-phase imbalance, thereby laying a solid foundation for achieving efficient phase-changing switch site selection planning.

[0057] In the embodiment of the present application, the above step S200 includes the following sub-steps B1-B2;

[0058] In B1: construct the objective function of the commutation switch location planning model;

[0059] In B2: construct the constraints of the commutation switch location planning model;

[0060] In a feasible implementation, the phase-changing switch site selection planning model aims to minimize the comprehensive cost of the substation. On the one hand, it considers maximizing the degree of three-phase imbalance in the substation to achieve effective management of three-phase imbalance. On the other hand, it improves the economic efficiency of management by optimizing the installation location and phase-changing strategy of the phase-changing switch. The objective function is calculated as:

[0061] minC=min(C new +C sw +C loss +C unb )

[0062] Among them, C is the comprehensive cost of the area, C new is the phase-changing switch system investment cost, C sw is the switching cost, C loss is the area network loss cost, C unb Penalty cost for three-phase imbalance in the transformer area;

[0063] Specifically, a phase-changing switch system usually includes a main controller and several phase-changing switches. For a substation, one phase-changing switch system is generally configured. Considering the power of different users, high-power phase-changing switches can be installed for high-power users, and low-power phase-changing switches can be installed for low-power users to improve the utilization rate of phase-changing switches. Considering that the phase-changing switch is a long-term operating equipment, the annual value method is used to calculate its investment cost. Therefore, the investment cost of the phase-changing switch system is expressed as:

[0064]

[0065] Among them, c e is the investment cost of the commutation master controller, Ω T It is a collection of various phase-changing switch models. is the installation cost of the ω-type phase-changing switch, is the number of ω-type phase-changing switches installed, w is the service life of the phase-changing switches, and r is the cash flow discount rate.

[0066] Specifically, switching the user phase through the phase-changing switch will inevitably have an impact on the user. Since the phase-changing switch is connected in series on the line, the frequent operation of the phase-changing switch will significantly increase the impact on the user and reduce the service life of the equipment, thereby generating additional costs. The operation cost of the phase-changing switch is related to the number of switching times, so the operation cost of the phase-changing switch is expressed as:

[0067] C sw =365c s D s

[0068] Among them, c s is the cost of one phase-changing switch action, D s It is the sum of the operation times of all phase-changing switches in the transformer area, and its calculation method is:

[0069]

[0070] Among them, A m,t represents the phase of the commutation switch m at time t, t = 0 represents the initial phase, and M is the total number of commutation switches;

[0071] Specifically, the network loss cost of the substation will increase rapidly as the degree of three-phase imbalance increases. It is related to the square of the current flowing through each line. Therefore, the network loss cost of the substation is expressed as:

[0072]

[0073] Among them, c p is the network loss cost coefficient, I l,t is the current flowing through line l at time t, r l is the line resistance, Ω l A collection of lines.

[0074] Specifically, three-phase load imbalance can also cause protection malfunction, transformer damage, light-load phase voltage high damage to equipment, heavy-load phase voltage low equipment cannot be used, etc. In the power grid assessment, a fine is imposed on the three-phase imbalance that exceeds the limit, so the penalty cost of three-phase imbalance is expressed as:

[0075]

[0076] Among them, c uis the three-phase unbalance penalty coefficient, γ t is the three-phase imbalance degree that exceeds the standard in the substation at time t, ε is the three-phase imbalance penalty threshold, and the three-phase imbalance degree is calculated as follows:

[0077]

[0078] Among them, I t X is the total current of phase X at time t, X∈{A,B,C}.

[0079] In a feasible implementation, the constraints of the phase-changing switch location planning model include phase-changing switch constraints, user phase constraints, and distribution station area constraints;

[0080] Specifically, the phase-changing switch is an actual physical device, and the number of its installations is limited. At the same time, in order to ensure power supply reliability, the current flowing through the phase-changing switch should not be too large. These constraints are expressed as:

[0081]

[0082] Among them, N s is the number of phase-changing switches installed, I h,t is the current flowing through the root node h at time t. In the above formula, the first item limits the phase-changing switch location matrix S to a binary variable matrix, the second item is used to calculate the number of phase-changing switches to be installed, which indicates that the number of phase-changing switches to be installed should be equal to the number of 1s in the phase-changing switch location matrix S, the third item indicates that the number of phase-changing switches to be installed is equal to the sum of the number of phase-changing switches of each model, the fourth item limits the number of phase-changing switches of each model to be installed less than the purchase quantity, the fifth item indicates that the root node where the phase-changing switch is installed should have a current flowing through it less than the rated current of the phase-changing switch, and the sixth item limits the maximum number of phase changes.

[0083] Specifically, the distribution area is generally single-phase users, who can only use electricity in single phase. For users who have installed phase-changing switches, their phase should be consistent with the phase-changing switches. These constraints can be expressed as:

[0084]

[0085] Where n∈Ω h ,Ω h is the set of users connected to the root node h, is the initial phase of user n, A h,tRepresents the phase of the phase-changing switch installed at the root node h at time t; the first term in the above formula limits the user phase matrix Λ to a binary variable matrix, and it also indicates that a single-phase user can only connect to one phase; the second term in the above formula indicates that for the user connected to the root node h, if a phase-changing switch is not installed, its phase should always be equal to the initial phase; if a phase-changing switch is installed, its phase is controlled by the phase-changing switch and should be equal to the phase connected by the phase-changing switch.

[0086] Specifically, the distribution area is a radial distribution network, and there should be no loops. At the same time, the voltage of each node and the power of each branch in the distribution network should be within the allowable range. These constraints can be expressed as:

[0087]

[0088] Among them, z ij is a binary variable representing the disconnection of branch ij, z ij 1 indicates that the branch is connected, 0 indicates that the branch is disconnected, n b and n s Respectively represent the number of nodes and power supply nodes in the area, P ij,t and Q ij,t is the active and reactive power of line ij at time t, S line.max is the upper limit of line transmission capacity, V i,t is the voltage amplitude of node i at time t, V max 、V min is the upper and lower limits of the node voltage, P jk,t , Q jk,t is the active and reactive power flowing from node j to node k via line jk at time t, is the active and reactive power of the load at node j at time t, r ij 、x ij is the resistance and reactance of line ij. The first term in the above formula limits the distribution area to operate in a radial shape; the second term in the above formula indicates that during the governance process, the transmission power of each line should be less than the maximum transmission capacity of the line, and the voltage of each node should be within the allowable range. Since the radial distribution area is taken into account, the branch flow model after phase angle relaxation is selected for the flow calculation, which is expressed by the second term in the above formula.

[0089] It should be noted that the above step S200 converts the abstract decision variables into specific and quantifiable mathematical expressions, thereby providing a clear direction and standard for solving the three-phase imbalance problem, ensuring that the optimization process focuses on key goals such as reducing imbalance, reducing line losses or improving power quality, while setting reasonable constraints to ensure the feasibility and safety of the solution in actual power grid operation. It not only enhances the accuracy and reliability of problem solving, but also makes the comparison between different solutions intuitive and feasible, which ultimately helps to find the optimal phase-changing switch configuration strategy and achieve efficient and economical power system management.

[0090] In the embodiment of the present application, the above step S300 includes the following sub-steps C1-C2;

[0091] In C1: the commutation switch location planning model is modeled as a mixed integer non-convex programming problem, and linearized and convexly relaxed;

[0092] In C2: The site selection planning of phase-changing switches for three-phase imbalance control in the substation is realized by solving the problem.

[0093] It should be noted that the established method for phase-changing switch location planning for three-phase imbalance management in the substation is a mixed integer non-convex programming problem, which has nonlinear expressions and non-convex constraints, and contains many integer variables, has NP-hard problem characteristics, and is not easy to solve. Therefore, this embodiment linearizes and convexly relaxes the problem, converting it into a mixed integer second-order cone programming problem that is easy to solve.

[0094] In a feasible implementation, the linearization processing includes three-phase imbalance linearization processing and phase constraint linearization processing, wherein the three-phase imbalance linearization processing is to replace the real-time three-phase current average value of the denominator in the three-phase imbalance calculation with the three-phase current average value before treatment, and the phase constraint linearization processing is to use the big M method to convert the logical constraints into linear inequalities.

[0095] Specifically, the calculation of three-phase imbalance involves the division of continuous variables, which results in a nonlinear expression. In normal grid operation, for three-phase loads of the same size, the average three-phase current when the three-phase load is balanced is roughly the same as when the three-phase load is unbalanced. Therefore, the real-time three-phase current average value of the denominator in the three-phase imbalance calculation formula is replaced by the three-phase current average value before treatment, that is:

[0096]

[0097] Among them, I av It is the average value of three-phase current before treatment.

[0098] Specifically, the user phase constraint is a logical constraint, which is equivalent to the following form:

[0099]

[0100] It can be seen that there is a nonlinear expression A for multiplication of integer variables in the formula n,t s h , A h,t s h Therefore, the Big M method is used to convert the above equation into the following linear inequality:

[0101]

[0102] Among them, M0 is a sufficiently large positive number.

[0103] In a feasible implementation, the convex relaxation process includes: performing variable replacement on the power flow constraint of the distribution station area after phase angle relaxation; using the second-order cone relaxation technology to relax the equation constraint after transformation and replacement into a second-order cone, and rewriting it into a standard second-order cone form to obtain the power flow constraint after convex relaxation; when there is a situation of disconnecting the branch line, introducing the large M method to improve the power flow constraint after convex relaxation;

[0104] Specifically, the power flow constraint of the distribution station area after phase angle relaxation is still a non-convex constraint. Consider the following variable replacement:

[0105]

[0106] When the objective function is L ij,t Under the conditions that the active and reactive loads connected to the node have no upper bound, the second-order cone relaxation technique is used to relax the second equality constraint in the above formula into a second-order cone, and further rewrite it into the following standard second-order cone form:

[0107] ||[2P ij,t 2Q ij,t L ij,t -U i,t ] T ||2≤L ij,t +U i,t

[0108] The power flow constraint after convex relaxation is further obtained:

[0109]

[0110] For a distribution substation with radial constraints, when there is a disconnected branch, the third term of the above equation will make the voltage amplitudes at both ends of the branch equal, which is unreasonable. Therefore, the large M method is introduced to improve the power flow constraint as follows:

[0111]

[0112] Among them, M1 is a sufficiently large positive number.

[0113] In a feasible implementation, the relaxed model is transformed from a mixed integer non-convex programming problem to a mixed integer second-order cone programming problem, and the mixed integer second-order cone programming problem is solved by a CPLEX solver to achieve the location planning of the phase-changing switch for the three-phase unbalance management in the substation area;

[0114] Specifically, the reconstructed commutation switch location planning model is as follows:

[0115] minC=min(C new +C sw +C loss +C unb )

[0116]

[0117] Compared with the original model, the relaxed model is transformed from a mixed integer non-convex programming problem to a mixed integer second-order cone programming problem, which can be directly solved by commercial solvers such as CPLEX and GUROBI with good computational efficiency.

[0118] It should be noted that the above step S300 not only reduces the computational difficulty and improves the solution efficiency by linearizing and convexly relaxing the model, but also ensures the feasibility and effectiveness of the obtained solution in practical applications, thereby improving the operating efficiency and stability of the power system.

[0119] The above is a schematic scheme of the phase-changing switch site selection and planning method for three-phase imbalance management in the present embodiment. It should be noted that the technical scheme of the phase-changing switch site selection and planning system for three-phase imbalance management in the substation and the technical scheme of the phase-changing switch site selection and planning method for three-phase imbalance management in the substation belong to the same concept. The details not described in detail in the technical scheme of the phase-changing switch site selection and planning system for three-phase imbalance management in the present embodiment can be found in the description of the technical scheme of the phase-changing switch site selection and planning method for three-phase imbalance management in the substation.

[0120] This embodiment provides a phase-changing switch site selection and planning system for three-phase unbalance management in a transformer area, including:

[0121] A decision variable determination module, used to determine the decision variables for the phase-changing switch site selection planning;

[0122] A model building module is used to build a commutation switch location planning model based on decision variables with the minimum comprehensive cost of the substation as the objective function;

[0123] The planning and solving module is used to model the phase-changing switch site selection planning model as a mixed integer non-convex planning problem, and perform linearization and convex relaxation processing, so as to realize the phase-changing switch site selection planning for three-phase imbalance control in the substation area by solving the problem.

[0124] The above-mentioned unit modules may be embedded in or independent of the processor in the computer device in the form of hardware, or may be stored in the memory in the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above-mentioned modules.

[0125] This embodiment also provides an electronic device, which includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be implemented through WIFI, an operator network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, a phase-changing switch site selection planning method for three-phase unbalanced management of the substation area is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a button, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse.

[0126] This embodiment also provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the method proposed in the above embodiment is implemented.

[0127] The storage medium proposed in this embodiment and the method proposed in the above embodiment belong to the same inventive concept. The technical details not fully described in this embodiment can be referred to the above embodiment, and this embodiment has the same beneficial effects as the above embodiment.

[0128] Through the above description of the implementation methods, the technicians in the relevant field can clearly understand that the present invention can be implemented by means of software and necessary general hardware, and of course can also be implemented by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ReadOnly, Memory, ROM), random access memory (RandomAccess Memory, RAM), flash memory (FLASH), hard disk or optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform the methods of various embodiments of the present invention.

[0129] Example 2

[0130] Reference Figure 2 to Figure 4 Based on the previous embodiment, this embodiment provides an application example of a phase-changing switch site selection planning method and system for three-phase imbalance management in a transformer substation, in order to verify and illustrate the technical effects adopted in this method.

[0131] In order to verify the effectiveness of the proposed phase-changing switch site selection and planning method, this embodiment takes a certain distribution substation as an example for simulation analysis. The substation capacity of the distribution substation is 200kVA, the voltage level is 380 / 220V, there are 11 A-phase loads, 11 B-phase loads, and 12 C-phase loads. Figure 2 The model parameter settings are shown in Table 1.

[0132] Table 1: Model parameter settings.

[0133]

[0134] To demonstrate the superiority of the method of the present invention, the present invention has developed the following three comparison scenarios:

[0135] (1) Scenario 1: No three-phase imbalance control is performed and no phase-changing switch is planned.

[0136] (2) Scenario 2: Phase-changing switches are used for nodes with large load deviations.

[0137] (3) Scenario 3: planning the phase-changing switches according to the method of the present invention.

[0138] Figure 2The configuration results of the phase-changing switches after planning by the method of the present invention are given. The rectangle in the figure represents the phase-changing switch, and the node connected to it represents the single-phase load controlled by it. The planning results show that 5 type I phase-changing switches should be installed at nodes 3, 25, 28, 30 and 31. Table 2 gives a comparison of the comprehensive costs of the substations in each scenario. Among them, in scenario 2, phase-changing switches are put into use at nodes 18, 19, 26, 31 and 32 with large load deviations.

[0139] Table 2: Comprehensive cost of each scenario area.

[0140] Cost / 10,000 yuan Scenario 1 Scenario 2 Scene 3 Investment cost 0 0.54 0.45 Action Cost 0 0.03 0.08 Network loss cost 13.96 13.59 12.64 Imbalance Cost 12.05 6.97 0 Comprehensive cost 26.01 21.13 13.16

[0141] As can be seen from Table 2, the phase-changing switch site selection planning method proposed in the present invention can significantly reduce the comprehensive cost of the substation. Compared with Scenario 1, the comprehensive cost of the substation in Scenario 3 is reduced by about 49.4%. The comprehensive cost of the substation in Scenario 1 is mainly the network loss cost and the penalty cost of three-phase imbalance. Although Scenario 3 increases the investment cost of the phase-changing switch system and the phase-changing switch operation cost, the network loss cost and the penalty cost of three-phase imbalance are significantly reduced, so the total cost is lower. Compared with Scenario 2, although the number of phase-changing switches configured in Scenario 3 is the same, the investment cost is lower. Since the installation location is more reasonable, the comprehensive cost of the substation is optimized to be lower.

[0142] Figure 3 and Figure 4 The three-phase current curve and three-phase imbalance comparison of the low-voltage side of the distribution transformer in each scenario are given respectively. It can be seen that the maximum three-phase imbalance of the substation is as high as 47.1%, and the average three-phase imbalance is as high as 27.5%. Compared with scenario 1, the maximum three-phase imbalance of scenario 3 is reduced from 47.1% to 2.98%, and the average three-phase imbalance is reduced from 27.5% to 2.53%, with an average reduction of up to 90.8%. Compared with scenario 2, the phase-changing switch planning strategy of scenario 3 fully considers the power flow distribution of the substation. Therefore, under the same number of phase-changing switch configurations, the three-phase imbalance can be optimized to a lower level, and the role of the phase-changing switch can be maximized.

[0143] Therefore, it can be seen from the above that the present invention comprehensively considers the investment and operation costs of the phase-changing switches and the power flow distribution in the substation, and can obtain the optimal installation position and the optimal phase-changing strategy of the phase-changing switches. When the number of installed phase-changing switches and the number of operations are small, the three-phase imbalance can be effectively controlled while achieving the best economy; the present invention can not only plan the optimal installation number and installation position for the substation with uncertain installation number and position of the phase-changing switches, but also provide the optimal installation position for the substation with determined installation number of the phase-changing switches, and has strong versatility; in addition, the phase-changing switch site selection planning method proposed in the present invention is a mixed integer second-order cone programming model, which can directly use the solver to solve and obtain the global optimal solution, without the need to write a solution algorithm, and has high computational efficiency.

[0144] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0145] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0146] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0147] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0148] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0149] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0150] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for site selection and planning of phase-changing switches for three-phase unbalance management in a transformer area, characterized in that: include: Determine the decision variables for commutation switch site planning; Based on the decision variables, a phase-changing switch location planning model is constructed with the minimum comprehensive cost of the substation area as the objective function; The phase-changing switch location planning model is modeled as a mixed integer non-convex programming problem, and linearization and convex relaxation are performed. By solving the problem, the phase-changing switch location planning for three-phase imbalance management in the substation area is realized.

2. The method for site selection and planning of phase-changing switches for three-phase unbalance management in a transformer area according to claim 1, characterized in that: The decision variables for determining the location planning of the commutation switch include: Consider treating users connected to the same root node as equivalent, and use equivalent users as candidate locations for phase-changing switch construction. If a root node contains users who cannot install phase-changing switches, this root node cannot be selected as a candidate location for phase-changing switch construction. Based on this, the phase-changing switch location matrix S and the user phase matrix Λ are defined; The phase-changing switch location matrix S and the user phase matrix Λ constitute decision variables of the phase-changing switch location planning model, wherein the phase-changing switch location matrix S determines the optimal phase-changing switch installation position, and the user phase matrix Λ determines the optimal phase-changing strategy.

3. The method for site selection and planning of phase-changing switches for three-phase unbalance management in a transformer area as claimed in claim 2, characterized in that: The objective function of the phase-changing switch location planning model is: minC=min(C new +C sw +C loss +C unb ) C sw =365c s D s Among them, C is the comprehensive cost of the area, C new is the phase-changing switch system investment cost, C sw is the switching cost, C loss is the network loss cost of the area, C unb is the penalty cost of three-phase imbalance in the transformer area, c e is the investment cost of the commutation master controller, Ω T It is a collection of various phase-changing switch models. is the installation cost of the ω-type phase-changing switch, is the number of ω-type phase-changing switches installed, w is the service life of the phase-changing switches, r is the cash flow discount rate, c s is the cost of one phase-changing switch action, D s is the sum of the number of operations of all phase-changing switches in the transformer area, c p is the network loss cost coefficient, I l,t is the current flowing through line l at time t, r l is the line resistance, Ω l is the line set, c u is the three-phase unbalance penalty coefficient, γ t is the three-phase imbalance degree exceeding the standard in the substation at time t, and ε is the three-phase imbalance penalty threshold.

4. The method for site selection and planning of phase-changing switches for three-phase imbalance control in a transformer area as claimed in claim 3, characterized in that: The constraint conditions of the phase-changing switch site selection planning model include phase-changing switch constraints, user phase constraints, and distribution station area constraints.

5. The method for site selection and planning of phase-changing switches for three-phase unbalance management in a transformer area as claimed in claim 4, characterized in that: Modeling the phase-changing switch location planning model as a mixed integer non-convex programming problem and performing linearization processing includes: The linearization processing includes three-phase imbalance linearization processing and phase constraint linearization processing. The three-phase imbalance linearization processing is to replace the real-time three-phase current average value of the denominator in the three-phase imbalance calculation with the three-phase current average value before treatment. The phase constraint linearization processing is to use the big M method to convert the logical constraint equivalent into a linear inequality.

6. The method for site selection and planning of phase-changing switches for three-phase unbalance management in a transformer area as claimed in claim 5, characterized in that: Modeling the phase-changing switch location planning model as a mixed integer non-convex programming problem and performing convex relaxation processing includes: Perform variable replacement on the power flow constraints of the distribution station area after phase angle relaxation; The transformed equality constraint is relaxed into a second-order cone by using a second-order cone relaxation technique, and rewritten into a standard second-order cone form to obtain a convexly relaxed power flow constraint; When there is a situation of disconnected branch circuit, the large M method is introduced to improve the power flow constraint after convex relaxation.

7. The method for site selection and planning of phase-changing switches for three-phase unbalance management in a transformer area according to claim 6, characterized in that: The phase-changing switch site selection planning for achieving three-phase unbalance management in the substation area by solving the problem includes: After relaxation, the model is transformed from a mixed integer non-convex programming problem into a mixed integer second-order cone programming problem, which is solved by the CPLEX solver to realize the site selection planning of phase-changing switches for three-phase imbalance control in the substation.

8. A system using the phase-changing switch site selection and planning method for three-phase unbalance management in a transformer area as claimed in any one of claims 1 to 7, characterized in that: include: A decision variable determination module, used to determine the decision variables for the phase-changing switch site selection planning; A model building module, used to build a phase-changing switch location planning model with the minimum comprehensive cost of the substation as the objective function based on the decision variables; The planning and solving module is used to model the phase-changing switch site selection planning model as a mixed integer non-convex planning problem, and perform linearization and convex relaxation processing, so as to realize the phase-changing switch site selection planning for three-phase imbalance management in the substation area by solving the problem.

9. An electronic device, comprising: Memory and processor; The memory is used to store computer executable instructions, and the processor is used to execute the computer executable instructions. When the computer executable instructions are executed by the processor, the steps of the phase-changing switch site selection planning method for three-phase imbalance control in a substation are implemented as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the phase-changing switch site selection planning method for three-phase imbalance control in a substation as described in any one of claims 1 to 7.

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