Medium-voltage flexible interconnection power distribution system planning method and system oriented to flexibility improvement

Abstract

According to the medium-voltage flexible interconnection power distribution system planning method and system oriented to flexibility improvement, in a scheduling period, the ratio of the adjusting capacity of a power distribution network to the net load power variation serves as a supply and demand balance index, and the average value of the sum of the current margins of a line and a flexible interconnection switch serves as a transmission capacity index; establishing an optimization planning model of the medium-voltage flexible interconnection system, wherein the optimization planning model comprises a planning layer model taking the lowest annual comprehensive operation cost as an optimization target and an operation layer model taking the maximum difference value between a supply and demand balance index and a transmission capability index as an optimization target; and establishing a Nash equilibrium model by taking the configuration scheme of the energy storage system and the flexible interconnection switch as a decision variable of a game and taking the optimization target of the planning layer model and the optimization target of the operation layer model as game objects, and solving the Nash equilibrium model by adopting a particle swarm algorithm to obtain an optimal configuration scheme of the energy storage system and the flexible interconnection switch. And as a planning result of the medium-voltage flexible interconnection power distribution system, the problem of mutual exclusion of economy and flexibility in the planning process is solved.

Description

Technical Field

[0001] The present invention belongs to the field of electrical engineering and relates to an optimization planning technology for a flexible interconnected power distribution system, and specifically relates to an optimization planning method and system for a medium-voltage flexible interconnected power distribution system that takes into account a balance between economy and flexibility. Background Art

[0002] As the last end of the power supply, the distribution network has become the main force for accepting these flexible resources. In this context, the traditional AC radial distribution network is facing the challenges of weak power supply capacity and insufficient system flexibility. AC and DC distribution networks have received more and more attention due to their flexible power transfer capabilities. Research and demonstration projects related to the flexible interconnection of low-voltage distribution networks have been widely carried out. However, with the continuous increase in the proportion of new sources and loads, the system capacity and regulation capabilities on the low-voltage side can no longer meet the needs of flexible resource access at many points and in a wide range. In recent years, relevant research on the flexible interconnection of medium-voltage distribution networks has also been gradually carried out. However, the capacity of the medium-voltage system is large and the equipment cost is high. How to balance the flexibility requirements of the system and the economic cost of the transformation plan, and optimize the planning of the medium-voltage flexible interconnection system, is currently a highly concerned issue.

[0003] In the prior art, the flexibility evaluation method of the distribution network considering the coordinated interaction of flexible resources has constructed a flexibility evaluation index system including three aspects: coordinated regulation capability, collaborative benefit quality and grid reliability. The Gaussian mixture model has been used to construct a typical operation scenario and conduct flexibility index evaluation. A three-layer coordination planning model for improving the flexibility of new distribution systems. The upper layer aims to minimize the equal annual value investment cost, the middle layer plans to minimize the annual comprehensive operation cost of the distribution network, and the lower layer optimizes the operation with the highest daily average flexibility level as the goal. The three-layer model is solved using a hybrid optimization algorithm. However, this method solves the flexibility target as a subordinate condition of economic planning. A network-storage joint planning method considering the operational flexibility of carbon capture power plants separates the operation and planning layers, calculates the flexibility index of the planning layer using the snake optimization algorithm, and converts the model into a linear optimization model for solution. Although the prior art can solve the problem of mutual iteration of the two-layer model, it still has shortcomings in solving the problem of multi-objective solution and the mutual exclusion of objective trends. First, the traditional multi-objective conversion method based on weighted processing is difficult to determine a reasonable objective weight; second, it is difficult to select the final solution in the Pareto multi-objective solution set. Regarding the related work on medium-voltage flexible interconnection optimization planning, the following work still needs to be broken through: First, in the face of a medium-voltage flexible interconnected distribution system with flexible power transfer capabilities and containing multiple types of flexibility resources, there is a lack of methods that can accurately characterize the flexibility of the system; Second, due to the high planning and construction costs of the medium-voltage system, how to scientifically and reasonably balance the two important indicators of economy and flexibility is an issue that needs further consideration. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a medium-voltage flexible interconnected distribution system planning method and system for improving flexibility. First, a flexible interconnection switch (Soft Open Point, SOP) is used as an interconnection device to construct a typical structural form of a medium-voltage interconnected distribution system, and the power transfer constraints of the medium-voltage flexible interconnected system are given. Secondly, the main flexibility indicators of the flexible interconnected system are given from the source side, load side and grid side, and the calculation method of the flexibility indicator is given, so as to accurately characterize the flexibility of the interconnected system; then, a medium-voltage interconnected operation model considering the mutual assistance of flexible resources and a planning model that balances economy and flexibility are established.

[0005] The present invention adopts the following technical solution.

[0006] The present invention proposes a medium voltage flexible interconnected distribution system planning method for improving flexibility. The flexibility resources of the distribution network include energy storage systems and distributed power sources. The planning method includes:

[0007] Obtain the operating parameters and regulation capabilities of the energy storage system and distributed power sources, and determine the flexibility resource abundance index based on the flexibility resource regulation capability model; determine the distribution network regulation capability based on the flexibility resource abundance index and the flexible interconnection switch regulation capability, and use the ratio of the distribution network regulation capability to the net load power change within the dispatching cycle as the supply and demand balance indicator; use the average value of the sum of the line and flexible interconnection switch current margins within the dispatching cycle as the transmission capacity indicator;

[0008] Based on the two-layer model structure, an optimization planning model for the medium-voltage flexible interconnection system is established, including: a planning layer model with the lowest annual comprehensive operating cost as the optimization target, and an operation layer model with the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization target; wherein the planning layer model provides the operation layer model with the configuration scheme of the energy storage system and the flexible interconnection switch when the annual comprehensive operating cost is the lowest, and the operation layer model provides the planning layer model with the system operation loss when the difference between the supply and demand balance index and the transmission capacity index is the largest; the planning layer model updates the annual comprehensive operating cost according to the received system operation loss;

[0009] The configuration scheme of the energy storage system and the flexible interconnecting switch is used as the decision variable of the game, and the optimization objectives of the planning layer model and the operation layer model are used as the game objects. A Nash equilibrium model is established, and the particle swarm algorithm is used to solve the Nash equilibrium model. The optimal configuration scheme of the energy storage system and the flexible interconnecting switch is obtained as the planning result of the medium-voltage flexible interconnected distribution system.

[0010] Preferably, a flexibility resource regulation capability model is established; the operating parameters and regulation capabilities of the energy storage system and the distributed power source are obtained, and the flexibility resource abundance index is determined through the flexibility resource regulation capability model;

[0011] The flexibility resource adjustment capability model satisfies the following relationship:

[0012]

[0013]

[0014] In the formula, and They are the upward and downward regulation capabilities of the energy storage system at node i at time t, respectively; and They are the battery charge and discharge state quantities of the energy storage system at node i at time t, both of which are 0-1 variables; and are the active power of energy storage charging and discharging at node i at time t respectively; and are the maximum active powers of energy storage charging and discharging at node i at time t respectively;

[0015] and are the upward and downward regulation capabilities of the distributed generation at node i at time t, respectively; P DG,i,t is the active power of the distributed generation at node i at time t; P DG,i,t,max and P DG,i,t,min are the maximum and minimum active power output of the distributed power source at node i respectively; and are the upward and downward climbing power limits of the distributed generation at node i, respectively.

[0016] Preferably, the regulation capacity of the distribution network is determined based on the flexibility resource abundance index and the regulation capacity of the flexible tie switch, and the ratio of the regulation capacity of the distribution network to the change in net load power within the dispatching period is used as the supply and demand balance index;

[0017] The supply and demand balance indicator satisfies the following relationship:

[0018]

[0019]

[0020]

[0021]

[0022] In the formula, I FRis the supply and demand balance indicator, I UFR It is the sum of the ratio of the dispatchable margin of flexible resources to the change in net load when the net load increases within a dispatch cycle. DFR is the sum of the ratios of the dispatchable margin of flexible resources to the net load change when the net load decreases within a dispatch cycle, T is the total number of time periods within the dispatch cycle; F t U 、F t D are the upward and downward regulation capabilities of the distribution network at time t, which are the sum of the upward regulation capabilities of the energy storage system and distributed generation, and the sum of the downward regulation capabilities of the energy storage system and distributed generation; w t is the state variable representing the power change of net load at time t; P t nl , are the net load power at time t and time t+1 respectively; and are the installation node sets of the energy storage system and distributed generation respectively; N is the number of flexible tie switches; P ESS is the rated power of the energy storage system, and the minimum value of the rated power of the energy storage system is taken as the upward adjustment capacity of the energy storage system at node i at time t; and They are the upper and lower limits of the flexible contact switch regulation capacity at time t respectively.

[0023] Preferably, the average value of the sum of the line and flexible tie switch current margins within the scheduling period is used as the transmission capacity indicator, satisfying the following relationship:

[0024]

[0025] In the formula, I GM is the transmission capacity index, L is the total number of lines, and N is the total number of flexible tie switches; I WM,t and I SOPM,t are the current margins of the line and the flexible tie switch at time t, respectively, satisfying the following relationship:

[0026]

[0027]

[0028] In the formula, I ij,MAX I is the maximum value of the current allowed to pass through branch ij; ij,t is the current flowing through branch ij at time t; is the set of branches where the flexible tie switches are located; P SOP,MAX P is the maximum active power allowed to be transmitted by the port of the flexible tie switch; SOP,n,i,t and P SOP,n,j,tare the active powers transmitted by port i and port j of the nth flexible tie switch at time t respectively.

[0029] Preferably, the planning layer model is based on the annual comprehensive operating cost C T The minimum is the optimization goal, satisfying the following relationship:

[0030]

[0031] In the formula, They are the investment costs of flexible tie switches and energy storage systems respectively; are the operation and maintenance costs of the flexible tie switch and the energy storage system, C PL The system operation loss cost;

[0032] in,

[0033] 1) The investment cost and operation and maintenance cost of the flexible contact switch satisfy the following relationship:

[0034]

[0035]

[0036] Where, d SOP is the discount rate of the flexible contact switch, y SOP is the service life of the flexible contact switch, c SOP is the investment cost of the unit capacity flexible tie switch, η SOP is the annual operation and maintenance cost coefficient of the flexible contact switch, S SOP,i is the configuration capacity of the i-th flexible tie switch, and N is the total number of flexible tie switches;

[0037] 2) The investment cost and operation and maintenance cost of ESS satisfy the following relationship:

[0038]

[0039]

[0040] Where, d ESS is the discount rate of ESS, y ESS is the service life of ESS, and are the rated power and rated capacity of ESS respectively, c ESS,P and c ESS,E are the installation costs per unit power and per unit capacity of ESS, ξ ESS is the maintenance cost per unit capacity of ESS, Y T for the length of working hours;

[0041] 3) System operation loss cost satisfies the following relationship:

[0042]

[0043] Where η PL is the power loss cost reduction factor, and They are network operation loss and flexible tie switch loss respectively.

[0044] Preferably, the constraints for optimizing the target in the planning layer model are established, including:

[0045] 1) The capacity constraint of the flexible interconnection device satisfies the following relationship:

[0046]

[0047]

[0048] In the formula, S k,i and S k,j are the installed capacity of the kth converter at node i and node j respectively, are the active power and reactive power of the nth flexible tie switch at node i at time t, are the active power and reactive power of the nth flexible tie switch at node j at time t respectively;

[0049] 2) The capacity constraint of the energy storage system satisfies the following relationship:

[0050]

[0051] In the formula, and are the upper and lower limits of the capacity of the i-th energy storage system, is the capacity of the i-th energy storage system at time t, and They represent the charging efficiency and discharging efficiency of the i-th energy storage system respectively, and Δt is the charging time.

[0052] Preferably, the operation layer model takes the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization goal, satisfying the following relationship:

[0053] maxF DOWN =I FR,s -I GM,s

[0054] In the formula, F DOWN I is the supply and demand balance index under scenario s FR,s And the transmission capacity index I under scenario sGM,s The difference.

[0055] Preferably, the constraints for optimizing the target in the operation layer model are established, including:

[0056] 1) Node voltage constraints satisfy the following relationship:

[0057] U i,min ≤U i (t)≤U i,max

[0058] Where U i (t) is the voltage value of node i at time t, U i,min and U i,max are the lower and upper limits of the voltage at node i, respectively;

[0059] 2) Line transmission power constraints satisfy the following relationship:

[0060] P l (t)≤P l,max

[0061] Where P l (t) is the active power transmitted by line l at time t, P l,max is the maximum value of active power allowed to be transmitted by line l;

[0062] 3) The power flow balance constraint condition satisfies the following relationship:

[0063]

[0064] Where P ac,i and Q ac,i are the active power and reactive power injected at node i, respectively, G ac,ij , B ij and θ ij are the conductance, susceptance and voltage phase difference between node i and node j, respectively, U ac,i and U ac,j are the voltages at node i and node j respectively, β1 and β2 are 0-1 variables, indicating whether the node is connected to the flexible tie switch, P1 SOP,ac is the active power injected by SOP at one port, is the active power flowing out of the SOP at the other port, N ac is the total number of nodes;

[0065] 4) The power balance constraint of the flexible interconnection device satisfies the following relationship:

[0066]

[0067] In the formula, is the active power loss of SOP;

[0068] 5) ESS charging and discharging constraints satisfy the following relationship:

[0069]

[0070]

[0071] In the formula, and They are the battery charge and discharge states of the energy storage system at node i at time t, both of which are 0-1 variables. and are the maximum active power of energy storage charging and discharging at node i at time t, and are the active powers of energy storage charging and discharging at node i at time t respectively.

[0072] Preferably, the Nash equilibrium model satisfies the following relationship:

[0073] F OBF =max(F DOWN -d DOWN )(C T -d UP )

[0074] In the formula, F OBF is the Nash equilibrium model, d UP and d DOWN are the negotiation breakdown points of the planning layer model and the operation layer model respectively. In the embodiment, the specific value of the negotiation breakdown point is obtained by considering the scenario of economy and flexibility separately in the example analysis. T is the annual comprehensive operating cost, F DOWN It is the difference between the supply and demand balance index under the scenario and the transmission capacity index under the scenario.

[0075] The present invention also proposes a medium voltage flexible interconnected distribution system planning system for improving flexibility. The flexibility resources of the distribution network include energy storage systems and distributed power sources. The planning system includes:

[0076] A flexible index establishment module is used to obtain the operating parameters and regulation capabilities of the energy storage system and distributed power sources, and determine the flexibility resource abundance index based on the flexibility resource regulation capability model; determine the distribution network regulation capability based on the flexibility resource abundance index and the flexible interconnection switch regulation capability, and use the ratio of the distribution network regulation capability to the net load power change within the dispatching cycle as the supply and demand balance indicator; use the average value of the sum of the line and flexible interconnection switch current margins within the dispatching cycle as the transmission capacity indicator;

[0077] The optimization planning model establishment module is used to establish an optimization planning model for a medium-voltage flexible interconnected distribution system based on a two-layer model structure, including: a planning layer model with the lowest annual comprehensive operating cost as the optimization target, and an operation layer model with the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization target; wherein the planning layer model provides the operation layer model with the configuration scheme of the energy storage system and the flexible interconnection switch when the annual comprehensive operating cost is the lowest, and the operation layer model provides the planning layer model with the system operation loss when the difference between the supply and demand balance index and the transmission capacity index is the largest; the planning layer model updates the annual comprehensive operating cost according to the received system operation loss;

[0078] The model solving module is used to establish a Nash equilibrium model with the configuration scheme of the energy storage system and the flexible interconnection switch as the decision variables of the game, and the optimization objectives of the planning layer model and the operation layer model as the game objects. The particle swarm algorithm is used to solve the Nash equilibrium model to obtain the optimal configuration scheme of the energy storage system and the flexible interconnection switch as the planning result of the medium-voltage flexible interconnected distribution system.

[0079] A terminal comprises a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0080] A computer-readable storage medium stores a computer program, which implements the steps of the method when executed by a processor.

[0081] The beneficial effects of the present invention are that, compared with the prior art, the present invention at least includes that the present invention establishes a flexibility index system for a flexible interconnection system from three dimensions: flexibility resource abundance, supply and demand balance, and system source and load carrying capacity, and provides a calculation method for flexibility indexes to characterize the flexibility of the flexible interconnection system. In order to solve the problem of mutual exclusion between economy and flexibility in the planning process, the present invention establishes a two-layer optimization planning model based on Nash equilibrium. The upper model plans interconnection devices and energy storage with the goal of optimal balance between economy and flexibility, and the lower model optimizes the operation of the medium-voltage flexible interconnection system considering the mutual assistance of flexibility resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 It is a flow chart of a method for planning a medium voltage flexible interconnected distribution system for improving flexibility proposed by the present invention;

[0083] Figure 2 is a topological diagram of two IEEE33 nodes before transformation in an embodiment of the present invention;

[0084] Figure 3 It is a bar chart of the cost composition in various scenarios in the embodiment of the present invention. DETAILED DESCRIPTION

[0085] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0086] Flexible interconnecting switch (SOP) is a kind of interconnecting switch based on power electronic equipment. SOP can control the size and direction of active power flow, and absorb reactive power to maintain voltage. Therefore, it has been widely used in low-voltage substations in recent years to balance internal resources in the substation and improve the new source and load carrying capacity of the substation. Similarly, using SOP and medium-voltage lines to connect two substations can not only achieve flexible resource mutual assistance between substations, but also connect according to the needs and resource differences of different substations, so as to achieve the goal of coordinated planning and unified scheduling. In the topology of a typical medium-voltage flexible interconnection system, the end of one substation and the end of another substation are connected through SOP to exchange flexible resources.

[0087] Taking the SOP of back-to-back voltage source converter structure as an example, SOP connects two voltage source inverters (VSC) back-to-back through DC side capacitors to form a symmetrical structure, and the control mode is different in different operation scenarios. Among them, in the working state of closed-loop operation of the distribution network, SOP is mainly used to realize power exchange between feeders, and the flexible transfer of power needs to meet the following constraints:

[0088]

[0089] Where P1 SOP (t) and are the active power at one end of the SOP and the active power at the other end at time t, and are the reactive power at one end of the SOP and the reactive power at the other end at time t, and They are the capacity of the first VSC and the capacity of the second VSC connected to the SOP, respectively.

[0090] The present invention proposes a medium voltage flexible interconnected distribution system planning method for improving flexibility. The flexibility resources of the distribution network include energy storage systems and distributed power sources, such as Figure 1 As shown, planning methods include:

[0091] Step 1: Obtain the operating parameters and regulation capabilities of the energy storage system and distributed power sources, and determine the flexibility resource abundance index based on the flexibility resource regulation capability model; determine the distribution network regulation capability based on the flexibility resource abundance index and the flexible interconnection switch regulation capability, and use the ratio of the distribution network regulation capability to the net load power change within the dispatching cycle as the supply and demand balance indicator; use the average value of the sum of the line and flexible interconnection switch current margins within the dispatching cycle as the transmission capacity indicator.

[0092] Specifically, step 1 includes:

[0093] Step 1.1, establish a flexibility resource regulation capability model; obtain the operating parameters and regulation capabilities of the energy storage system and distributed power sources, and determine the flexibility resource abundance index through the flexibility resource regulation capability model;

[0094] The flexibility resources in the distribution network include energy storage systems (ESS) and distributed generators (DG). ESS can provide the system with upward or downward flexibility adjustment capabilities by controlling the power of battery charging and discharging; DG can provide the system with upward or downward flexibility adjustment capabilities by controlling the output. The collection of flexibility adjustment capabilities of each ES and DG in the entire substation is the flexibility resource of the substation. The flexibility resource abundance is used to characterize the amount of flexibility resources. Therefore, the operating parameters and adjustment capabilities of the energy storage system and distributed generation are obtained, and the flexibility resource abundance index is determined through the flexibility resource adjustment capability model.

[0095] Specifically, the flexibility resource adjustment capability model satisfies the following relationship:

[0096]

[0097]

[0098] In the formula, and They are the upward and downward regulation capabilities of the energy storage system at node i at time t, respectively; and They are the battery charge and discharge state quantities of the energy storage system at node i at time t, both of which are 0-1 variables; and are the active power of energy storage charging and discharging at node i at time t respectively; and are the maximum active powers of energy storage charging and discharging at node i at time t respectively;

[0099] and are the upward and downward regulation capabilities of the distributed generation at node i at time t, respectively; P DG,i,t is the active power of the distributed generation at node i at time t; P DG,i,t,max and P DG,i,t,min are the maximum and minimum active power output of the distributed power source at node i respectively; and are the upward and downward climbing power limits of the distributed generation at node i, respectively.

[0100] And the ESS charging and discharging constraints of the flexible resource regulation capability model satisfy the following relationship:

[0101]

[0102]

[0103]

[0104] In the formula, and They are the battery charge and discharge states of the energy storage system at node i at time t, both of which are 0-1 variables. and are the maximum active power of energy storage charging and discharging at node i at time t, and are the active power of energy storage charging and discharging at node i at time t

[0105] Step 1.2, based on the flexibility resource abundance index and the flexible tie switch regulation capacity, determine the distribution network regulation capacity, and use the ratio of the distribution network regulation capacity to the net load power change within the dispatching period as the supply and demand balance index;

[0106] In the embodiment, the flexibility resource abundance index is determined according to the actual operating parameters of the flexibility resources. The flexibility of the distribution network mainly comes from flexibility resources such as ESS and SOP, and the flexibility demand of the distribution network is mainly reflected in the supply and demand relationship between load and flexibility resources. Therefore, the flexibility resource abundance index provides a basis for determining the supply and demand balance index, avoiding the problem of excessive configuration results and over-investment caused by only considering the supply and demand relationship, which is conducive to improving the operating economy of the system.

[0107] Specifically, the supply and demand balance index is reflected in the adaptability of the distribution network regulation capability under the random fluctuation of net load power. Therefore, the supply and demand balance index of the distribution network satisfies the following relationship:

[0108]

[0109]

[0110]

[0111]

[0112] In the formula, I FR is the supply and demand balance indicator, I UFR It is the sum of the ratio of the dispatchable margin of flexible resources to the change in net load when the net load increases within a dispatch cycle. DFR F is the sum of the ratios of the schedulable margin of flexible resources to the net load change when the net load decreases within a scheduling cycle, T is the total number of time periods within the scheduling cycle, and in the embodiment, the scheduling cycle is 24 hours, and the interval between each time period is 1 hour; t U 、F t D are the upward adjustment capacity and downward adjustment capacity of the distribution network at time t, respectively, and are the sum of the upward adjustment capacity of the energy storage system and the distributed power source, and the sum of the downward adjustment capacity of the energy storage system and the distributed power source. In the embodiment, F is determined by the flexibility resource adjustment capacity model and the flexible tie switch adjustment capacity. t U 、F t D Therefore, the upward and downward adjustment capabilities of the distribution network are based on the flexibility resource abundance index, and the net load adaptation rate is also based on the flexibility resource abundance index; w t is the state variable representing the power change of net load at time t; P t nl , are the net load power at time t and time t+1 respectively; and are the installation node sets of the energy storage system and distributed generation respectively; N is the number of flexible tie switches; P ESS is the rated power of the energy storage system, and the minimum value of the rated power of the energy storage system is taken as the upward adjustment capacity of the energy storage system at node i at time t; and They are the upper and lower limits of the flexible contact switch regulation capacity at time t respectively.

[0113] I FR The larger the value of , the better the flexibility resources can meet the random fluctuations of net load power, indicating that the overall flexibility of the distribution network is better.

[0114] In the method proposed in the present invention, a single flexibility resource abundance index is not used as the evaluation index of the flexibility of the distribution network. Instead, on the basis of the flexibility resource abundance index, a supply and demand balance index is further determined to characterize the flexibility resource abundance of the distribution network to meet the random fluctuations of the net load power.

[0115] Step 1.3, taking the average value of the sum of the line and flexible tie switch current margins within the dispatching period as the transmission capacity indicator;

[0116] The existing technology basically describes the flexibility of the distribution network into node-type flexibility (flexibility resources) and branch-type flexibility (flexibility transmission capacity). A corresponding substation is equipped with a lot of flexibility resources. The flexibility resource abundance index and the supply and demand balance index jointly determine the upper limit of the flexibility of the distribution network. However, due to the small maximum current carrying capacity of the line, the flexibility resource abundance index and the supply and demand balance index jointly determine the distribution network dispatching task, that is, the goal of flexible operation of the distribution network cannot be achieved by relying solely on dispatchable power, resulting in a low utilization rate of flexibility resources; similarly, the maximum current carrying capacity of a substation line is very large, but there is a lack of flexibility resources in the distribution network, so the substation can only be dispatched in real time, and the source of the dispatching power can only rely on the adjustment of the upper power grid, which cannot achieve the purpose of intercommunication of flexibility resources within the substation. Therefore, the distribution network flexibility evaluation index includes a flexibility transmission capacity index that responds to the dispatch of flexibility resources;

[0117] Specifically, when the carrying capacity of the line is higher and the average current carrying capacity is lower, the ability to respond to flexible resource scheduling is stronger, that is, the flexible transmission capacity index is better. Therefore, the average value of the sum of the line and flexible tie switch current margins during the scheduling period is I GM As a flexible transmission capability indicator, the following relationship is satisfied:

[0118]

[0119] In the formula, I GM is the transmission capacity index, L is the total number of lines, and N is the total number of flexible tie switches; I WM,t and I SOPM,t are the current margins of the line and the flexible tie switch at time t, respectively, satisfying the following relationship:

[0120]

[0121]

[0122] In the formula, I ij,MAX I is the maximum value of the current allowed to pass through branch ij; ij,t is the current flowing through branch ij at time t; is the set of branches where the flexible tie switches are located; P SOP,MAX P is the maximum active power allowed to be transmitted by the port of the flexible tie switch; SOP,n,i,t and P SOP,n,j,t are the active powers transmitted by port i and port j of the nth flexible tie switch at time t respectively.

[0123] The flexibility transmission capacity index represents the flexibility transmission capacity of the distribution network to cope with random fluctuations in net load power. GM The smaller the value, the greater the current margin of each line and flexible tie switch, and the greater the flexible transmission capacity.

[0124] The present invention analyzes the flexibility resources of the medium-voltage distribution network containing SOP, defines the supply and demand balance index and transmission capacity index of the medium-voltage distribution network, and constructs a distribution network flexibility evaluation index system.

[0125] Step 2: Based on the two-layer model structure, a medium-voltage flexible interconnection system optimization planning model is established, including: a planning layer model with the lowest annual comprehensive operating cost as the optimization target, and an operation layer model with the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization target; wherein the planning layer model provides the operation layer model with the configuration plan of the energy storage system and the flexible interconnection switch when the annual comprehensive operating cost is the lowest, and the operation layer model provides the planning layer model with the system operation loss when the difference between the supply and demand balance index and the transmission capacity index is the largest; the planning layer model updates the annual comprehensive operating cost according to the received system operation loss.

[0126] Specifically, step 2 includes:

[0127] The planning model is based on the annual comprehensive operating cost C T The minimum is the optimization goal, satisfying the following relationship:

[0128]

[0129] In the formula, are the investment costs of SOP and ESS respectively; are the operation and maintenance costs of SOP and ESS, C PL The system operation loss cost.

[0130] in,

[0131] 1) The investment cost and operation and maintenance cost of SOP satisfy the following relationship:

[0132]

[0133]

[0134] Where, d SOP is the discount rate of SOP, y SOP is the service life of SOP, c SOP is the investment cost per unit capacity SOP, η SOP is the annual operation and maintenance cost coefficient of SOP, S SOP,i is the configuration capacity of the ith SOP, and N is the total number of flexible tie switches.

[0135] 2) The investment cost and operation and maintenance cost of ESS satisfy the following relationship:

[0136]

[0137]

[0138] Where, d ESS is the discount rate of ESS, y ESS is the service life of ESS, and are the rated power and rated capacity of ESS respectively, c ESS,P and c ESS,E are the installation costs per unit power and per unit capacity of ESS, ξ ESS is the maintenance cost per unit capacity of ESS, Y T For working hours.

[0139] 3) System operation loss cost satisfies the following relationship:

[0140]

[0141] Where η PL is the power loss cost reduction factor, and They are network operation loss and SOP loss respectively.

[0142] Establish the constraints of the optimization objectives in the planning layer model, including:

[0143] 1) The capacity constraint of the flexible interconnection device satisfies the following relationship:

[0144]

[0145]

[0146] In the formula, S k,i and S k,j are the installed capacity of the kth converter at node i and node j respectively, are the active power and reactive power of the nth SOP at node i at time t, are the active power and reactive power of the nth SOP at node j at time t, respectively;

[0147] 2) The capacity constraint of the energy storage system satisfies the following relationship:

[0148]

[0149]

[0150] In the formula, and are the upper and lower limits of the capacity of the i-th energy storage system, respectively. is the capacity of the i-th energy storage system at time t, and They represent the charging efficiency and discharging efficiency of the i-th energy storage system, respectively, and Δt is the charging time;

[0151] The planning layer model provides the operation layer model with the configuration plan of the energy storage system and flexible interconnecting switches when the annual comprehensive operating cost is the lowest.

[0152] The operation layer model takes the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization goal, satisfying the following relationship:

[0153] maxF DOWN =I FR,s -I GM,s

[0154] In the formula, F DOWN I is the supply and demand balance index under scenario s FR,s And the transmission capacity index I under scenario s GM,s The difference between

[0155] I FR The larger the value of I is, the more the flexible resources can meet the random fluctuations of the net load power, indicating that the overall flexibility of the distribution network is better; GM The smaller the value of is, the greater the current margin of each line and the flexible tie switch is, and the greater the flexible transmission capacity is; therefore, under a certain day scenario s, the supply and demand balance index I FR,s And the transmission capacity index I under scenario s GM,s The larger the difference, the better the flexibility of the distribution network.

[0156] Establish the constraints of the optimization objectives in the operation layer model, including:

[0157] 1) Node voltage constraints satisfy the following relationship:

[0158] U i,min ≤U i (t)≤U i,max

[0159] Where U i (t) is the voltage value of node i at time t, U i,min and U i,max are the lower and upper limits of the voltage at node i, respectively.

[0160] 2) Line transmission power constraints satisfy the following relationship:

[0161] Pl (t)≤P l,max

[0162] Where P l (t) is the active power transmitted by line l at time t, P l,max is the maximum value of active power allowed to be transmitted on line l.

[0163] 3) The power flow balance constraint condition satisfies the following relationship:

[0164]

[0165] Where P ac,i and Q ac,i are the active power and reactive power injected at node i, respectively, G ac,ij , B ij and θ ij are the conductance, susceptance and voltage phase difference between node i and node j, respectively, U ac,i and U ac,j are the voltages at node i and node j respectively, β1 and β2 are 0-1 variables, indicating whether the node is connected to the flexible tie switch, P1 SOP,ac is the active power injected by SOP at one port, is the active power flowing out of the SOP at the other port, N ac is the total number of nodes;

[0166] 4) The power balance constraint of the flexible interconnection device satisfies the following relationship:

[0167]

[0168] In the formula, is the active power loss of SOP.

[0169] 5) ESS charging and discharging constraints satisfy the following relationship:

[0170]

[0171]

[0172]

[0173] In the formula, and They are the battery charge and discharge states of the energy storage system at node i at time t, both of which are 0-1 variables. and are the maximum active power of energy storage charging and discharging at node i at time t, and are the active powers of energy storage charging and discharging at node i at time t respectively.

[0174] At the same time, the ESS charging and discharging constraints are also the constraints of the flexibility resource regulation capability model. In the process of determining the flexibility resource abundance index based on the flexibility resource regulation capability model, the ESS charging and discharging has been constrained. It is a configuration flexibility index under the premise of ensuring the safety of the energy storage system, which reflects that flexibility is a goal pursued on the basis of system safety and stability. In the process of solving the operation layer model, the ESS charging and discharging constraints are again imposed on the optimization target. At this time, since the starting basis for solving the operation layer model is that the planning layer model provides the operation layer model with the configuration plan of the energy storage system and the flexible interconnecting switch when the annual comprehensive operating cost is the lowest, the flexibility index is configured again on the premise that the operation of the energy storage system meets the system economic requirements, which reflects the pursuit of both system economy and flexibility.

[0175] The operation layer model provides the planning layer model with the system operation loss when the difference between the supply and demand balance index and the transmission capacity index is the largest; the planning layer model updates the annual comprehensive operation cost according to the received system operation loss.

[0176] Step 3: Taking the configuration scheme of the energy storage system and the flexible interconnection switch as the decision variables of the game, and the optimization objectives of the planning layer model and the operation layer model as the game objects, a Nash equilibrium model is established, and the particle swarm algorithm is used to solve the Nash equilibrium model to obtain the optimal configuration scheme of the energy storage system and the flexible interconnection switch as the planning result of the medium-voltage flexible interconnected distribution system.

[0177] Specifically, the configuration scheme of the energy storage system and the flexible interconnecting switch includes: the capacity and position of the energy storage system, and the capacity and position of the flexible interconnecting switch.

[0178] In the embodiment, the optimization target of the operation layer and the optimization target of the planning layer are used as two individuals for game, the capacity and location of the SOP and ESS are the decision variables in the game, and the established Nash equilibrium model satisfies the following relationship:

[0179] F OBF =max(F DOWN -d DOWN )(C T -d UP )

[0180] In the formula, F OBF is the Nash equilibrium model, d UP and d DOWN are the negotiation breakdown points of the planning layer model and the operation layer model respectively. In the embodiment, the specific value of the negotiation breakdown point is obtained by considering the scenario of economy and flexibility separately in the example analysis. T is the annual comprehensive operating cost, FDOWN I is the supply and demand balance index under scenario s FR,s And the transmission capacity index I under scenario s GM,s The difference.

[0181] The particle swarm algorithm is used to solve the Nash equilibrium model.

[0182] The flexible interconnection optimization and transformation of the medium-voltage distribution network has high economic costs and has high requirements for system flexibility. The present invention first considers the power regulation characteristics and source-load distribution of the flexible interconnection system, proposes a distribution network flexibility evaluation index system and a corresponding calculation method, and on this basis, proposes an optimization planning method for a medium-voltage flexible interconnection distribution system that considers the balance between economy and flexibility. A distribution network flexibility evaluation model containing SOP is established, and optimization planning is performed on the basis of a full evaluation of flexibility. The SOP capacity and the capacity and location of the ESS can be reasonably configured, while considering the operating status of the SOP and ESS to achieve a reduction in operating losses. In the process of distribution network planning, there is an exclusive relationship between investment economy and system flexibility. By introducing the Nash equilibrium method, a reasonable equilibrium solution can be obtained to achieve the comprehensive optimality of the planning scheme.

[0183] Select two IEEE33 node diagrams for flexible interconnection, and connect the two terminal areas through SOP. The topology before the transformation is as follows: Figure 2 As shown, Figure 2 The solid line in the middle is the AC line, and the dotted line is the tie switch; nodes 7 and 30 of area 1 are connected to the photovoltaic power station PV, with an installed capacity of 1.8MW; nodes 14 and 20 are connected to the wind farm WT, with an installed capacity of 1.2MW. Nodes 17 and 32 of area 2 are connected to the photovoltaic power station PV, with an installed capacity of 0.9MW; nodes 4 and 25 are connected to the wind farm, with an installed capacity of 1.5MW.

[0184] When two substations are planned to be connected end to end through SOP, a new energy storage system is planned to be added in the substation. By adjusting the capacity of SOP and ESS and adopting the method proposed in the present invention, the optimal capacity of SOP and ESS and the optimal installation position of ESS are obtained to ensure that economy and flexibility are balanced to a certain extent, and both are relatively optimal.

[0185] Compared with the weighted summation method of traditional multi-objective optimization, the Nash negotiation model combined with the intelligent algorithm can find the optimal equilibrium solution of flexibility and economy more accurately and quickly. In order to compare the advantages of Nash negotiation, the following scenarios are set for simulation calculation, as shown in Table 1.

[0186] Table 1 Scenario design table

[0187]

[0188]

[0189] In CASE3-1 and CASE3-2, the simulation results of CASE2-1 and CASE2-2 are first used to obtain the maximum and minimum values ​​of investment cost and flexibility, and then the maximum and minimum normalization method is used to standardize the upper and lower layer objective functions to eliminate the impact of different magnitudes. Among them, the cost structure under each scenario is as follows: Figure 3 shown.

[0190] The specific simulation results are shown in Table 2:

[0191] Table 2 Simulation results

[0192] CASE3-1 CASE3-2 CASE3-3 SOP capacity(MW) 0.6735 0.6992 1.0322 ESS1 capacity (MW) 1.0008 0.9231 0.5769 ESS2 capacity (MW) 0.3047 0.4562 0.953 ESS1 installation location 30 25 21 ESS2 installation location 59 65 40 Total one-time investment (10,000 yuan) 1035.1968 1088.6757 1312.1081 Total cost (ten thousand yuan) 2487.2229 2555.4235 2786.6727 Operating cost (ten thousand yuan) 1452.0260 1455.7577 1474.5646 Flexibility Index 52.2170 54.6050 66.2114

[0193] It can be seen from Table 2 that although CASE3-1 and CASE3-2 have sufficient dispatchable flexibility resources as a whole, the flexibility indicators of CASE3-1 and CASE3-2 are significantly smaller than those of CASE3-3. Specifically, the dispatchable time cannot fully respond to the flexibility requirements of the system. This is because the traditional weighting method has poor accuracy when balancing mutually exclusive and dynamic models such as economy and flexibility, and the weight calculation method is often easily affected by objective data or subjective opinions, which may cause deviations and impacts on actual projects.

[0194] The present invention also proposes a medium voltage flexible interconnected distribution system planning system for improving flexibility. The flexibility resources of the distribution network include energy storage systems and distributed power sources. The planning system includes:

[0195] A flexible index establishment module is used to obtain the operating parameters and regulation capabilities of the energy storage system and distributed power sources, and determine the flexibility resource abundance index based on the flexibility resource regulation capability model; determine the distribution network regulation capability based on the flexibility resource abundance index and the flexible interconnection switch regulation capability, and use the ratio of the distribution network regulation capability to the net load power change within the dispatching cycle as the supply and demand balance indicator; use the average value of the sum of the line and flexible interconnection switch current margins within the dispatching cycle as the transmission capacity indicator;

[0196] The optimization planning model establishment module is used to establish an optimization planning model for a medium-voltage flexible interconnected distribution system based on a two-layer model structure, including: a planning layer model with the lowest annual comprehensive operating cost as the optimization target, and an operation layer model with the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization target; wherein the planning layer model provides the operation layer model with the configuration scheme of the energy storage system and the flexible interconnection switch when the annual comprehensive operating cost is the lowest, and the operation layer model provides the planning layer model with the system operation loss when the difference between the supply and demand balance index and the transmission capacity index is the largest; the planning layer model updates the annual comprehensive operating cost according to the received system operation loss;

[0197] The model solving module is used to establish a Nash equilibrium model with the configuration scheme of the energy storage system and the flexible interconnection switch as the decision variables of the game, and the optimization objectives of the planning layer model and the operation layer model as the game objects. The particle swarm algorithm is used to solve the Nash equilibrium model to obtain the optimal configuration scheme of the energy storage system and the flexible interconnection switch as the planning result of the medium-voltage flexible interconnected distribution system.

[0198] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0199] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0200] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0201] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0202] Finally, 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 above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for planning a medium-voltage flexible interconnected distribution system for improving flexibility, wherein the flexibility resources of the distribution network include energy storage systems and distributed power sources, characterized in that: Planning methods include: Obtain the operating parameters and regulation capabilities of the energy storage system and distributed generation, and determine the flexibility resource abundance index based on the flexibility resource regulation capability model. Determine the distribution network regulation capability based on the flexibility resource abundance index and the regulation capability of the flexible interconnecting switches, using the ratio of the distribution network regulation capability to the change in net load power within the dispatching cycle as the supply and demand balance indicator. Use the average value of the sum of the line and flexible interconnecting switch current margins within the dispatching cycle as the transmission capacity indicator. Based on a two-layer model structure, an optimization planning model for a medium-voltage flexible interconnected system is established, comprising: a planning-layer model with the lowest annual comprehensive operating cost as the optimization objective, and an operating-layer model with the maximum difference between the supply-demand balance index and the transmission capacity index as the optimization objective. The planning-layer model provides the operating-layer model with the energy storage system and flexible interconnecting switch configuration plan that minimizes the annual comprehensive operating cost, while the operating-layer model provides the planning-layer model with the system operating loss plan that maximizes the difference between the supply-demand balance index and the transmission capacity index. The planning-layer model updates the annual comprehensive operating cost based on the received system operating loss plan. Taking the configuration scheme of the energy storage system and the flexible interconnecting switch as the decision variables of the game, and the optimization objectives of the planning layer model and the operation layer model as the game objects, a Nash equilibrium model is established. The particle swarm algorithm is used to solve the Nash equilibrium model, and the optimal configuration scheme of the energy storage system and the flexible interconnecting switch is obtained as the planning result of the medium-voltage flexible interconnected distribution system.

2. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 1, characterized in that: Establish a flexibility resource regulation capability model; obtain the operating parameters and regulation capabilities of the energy storage system and distributed power generation, and determine the flexibility resource abundance index through the flexibility resource regulation capability model; The flexibility resource adjustment capability model satisfies the following relationship: Where, and are the upward and downward regulation capabilities of the energy storage system at node i at time t, respectively; and are the battery charge and discharge state quantities of the energy storage system at node i at time t, both are 0-1 variables; and are the active power of energy storage charging and discharging at node i at time t; and are the maximum active powers of energy storage charging and discharging at node i at time t respectively; and are the upward and downward regulation capabilities of the distributed generation at node i at time t; P DG,i,t is the active power of the distributed generation at node i at time t; P DG,i,t,max and P DG,i,t,min are the maximum and minimum active power output of the distributed power supply at node i respectively; and are the upward and downward climbing power limits of the distributed generation at node i, respectively.

3. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 2, characterized in that: Based on the flexibility resource abundance index and the flexible tie switch regulation capacity, the distribution network regulation capacity is determined, and the ratio of the distribution network regulation capacity to the net load power change within the dispatch cycle is used as the supply and demand balance indicator; The supply and demand balance indicator satisfies the following relationship: Where, I FR is the supply and demand balance indicator, I UFR It is the sum of the ratios of the dispatchable margin of flexible resources to the change in net load when the net load increases within a dispatch period, I DFR is the sum of the ratios of the dispatchable margin of flexible resources to the net load change when the net load decreases within a dispatch cycle, T is the total number of time periods within the dispatch cycle; F t U 、F t D are the upward and downward regulation capabilities of the distribution network at time t, which are the sum of the upward regulation capabilities of the energy storage system and distributed generation, and the sum of the downward regulation capabilities of the energy storage system and distributed generation respectively; w t is the state variable representing the power change of net load at time t; P t nl 、 are the net load power at time t and time t+1 respectively; and are the installation node sets of the energy storage system and distributed power supply respectively; N is the number of flexible tie switches; P ESS is the rated power of the energy storage system, and the minimum value of the rated power of the energy storage system is taken as the upward adjustment capacity of the energy storage system at node i at time t; and are the upper and lower limits of the flexible tie switch regulation capacity at time t.

4. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 3, characterized in that: The average value of the sum of the line and flexible tie switch current margins within the dispatching period is used as the transmission capacity indicator, satisfying the following relationship: Where, I GM is the transmission capacity index, L is the total number of lines, and N is the total number of flexible tie switches; I WM,t and I SOPM,t are the current margins of the line and the flexible tie switch at time t, respectively, satisfying the following relationship: Where, I ij,MAX I is the maximum value of the current allowed to pass through branch ij; ij,t is the current flowing through branch ij at time t; is the set of branches where the flexible tie switches are located; P SOP,MAX P is the maximum active power allowed to be transmitted by the flexible tie switch port; SOP,n,i,t and P SOP,n,j,t are the active powers transmitted by port i and port j of the nth flexible tie switch at time t respectively.

5. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 1, characterized in that: The planning model is based on the annual comprehensive operating cost C T The minimum is the optimization goal, satisfying the following relationship: Where, are the investment costs of flexible tie switches and energy storage systems respectively; are the operation and maintenance costs of the flexible tie switch and the energy storage system, C PL System operation loss cost; in, 1) The investment cost and operation and maintenance cost of the flexible tie switch satisfy the following relationship: Where, d SOP is the discount rate of the flexible tie switch, y SOP is the service life of the flexible contact switch, c SOP is the investment cost of the flexible tie switch per unit capacity, η SOP is the annual operation and maintenance cost coefficient of the flexible contact switch, S SOP,i is the configuration capacity of the i-th flexible tie switch, and N is the total number of flexible tie switches; 2) The investment cost and operation and maintenance cost of ESS satisfy the following relationship: Where, d ESS is the discount rate of ESS, y ESS is the service life of ESS, and are the rated power and rated capacity of ESS respectively, c ESS,P and c ESS,E are the installation costs per unit power and per unit capacity of ESS, ξ ESS is the maintenance cost per unit capacity of ESS, Y T for working hours; 3) System operation loss cost satisfies the following relationship: Where η PL is the power loss cost conversion coefficient, and They are network operation loss and flexible tie switch loss respectively.

6. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 5, characterized in that: Establish the constraints for the optimization objectives in the planning layer model, including: 1) The capacity constraint of the flexible interconnection device satisfies the following relationship: Where S k,i and S k,j are the installed capacity of the kth converter at node i and node j respectively, are the active power and reactive power of the nth flexible tie switch at node i at time t, are the active power and reactive power of the nth flexible tie switch at node j at time t, respectively; 2) The capacity constraint of the energy storage system satisfies the following relationship: Where, and are the upper and lower limits of the capacity of the i-th energy storage system, is the capacity of the i-th energy storage system at time t, and They represent the charging efficiency and discharging efficiency of the i-th energy storage system respectively, and Δt is the charging time.

7. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 1, characterized in that: The operation layer model takes the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization goal, satisfying the following relationship: maxF DOWN =I FR,s -I GM,s Where, F DOWN I is the supply and demand balance indicator under scenario s FR,s And the transmission capacity index I under scenario s GM,s The difference.

8. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 7, characterized in that: Establish the constraints for the optimization objectives in the operational layer model, including: 1) Node voltage constraints must satisfy the following relationship: U i,min ≤U i (t)≤U i,max Where U i (t) is the voltage value of node i at time t, U i,min and U i,max are the lower and upper limits of the voltage at node i, respectively; 2) Line transmission power constraints must satisfy the following relationship: P l (t)≤P l,max Where, P l (t) is the active power transmitted by line l at time t, P l,max is the maximum value of active power allowed to be transmitted on line l; 3) The power flow balance constraint condition satisfies the following relationship: Where, P ac,i and Q ac,i are the active power and reactive power injected at node i, G ac,ij 、B ij and θ ij are the conductance, susceptance and voltage phase difference between node i and node j, respectively, U ac,i and U ac,j are the voltages at nodes i and j, respectively. β1 and β2 are 0-1 variables, indicating whether the node is connected to the flexible tie switch. P1 SOP,ac is the active power injected by SOP at one port, is the active power flowing out of the SOP at the other port, N ac is the total number of nodes; 4) The power balance constraint of the flexible interconnection device satisfies the following relationship: Where, is the active power loss of SOP; 5) ESS charging and discharging constraints must satisfy the following relationship: Where, and are the battery charge and discharge states of the energy storage system at node i at time t, both are 0-1 variables, and are the maximum active powers of energy storage charging and discharging at node i at time t, and are the active powers of energy storage charging and discharging at node i at time t, respectively.

9. The method for planning a medium voltage flexible interconnected distribution system for improving flexibility according to claim 1, characterized in that: The Nash equilibrium model satisfies the following relationship: F OBF =max(F DOWN -d DOWN )(C T -d UP ) Where, F OBF is the Nash equilibrium model, d UP and d DOWN are the negotiation breakdown points of the planning layer model and the operation layer model respectively. In the embodiment, the specific value of the negotiation breakdown point is obtained by considering the scenario of economy and flexibility separately in the case analysis. T is the annual comprehensive operating cost, F DOWN It is the difference between the supply and demand balance index under the scenario and the transmission capacity index under the scenario.

10. A medium-voltage flexible interconnected distribution system planning system for improving flexibility, wherein the flexibility resources of the distribution network include energy storage systems and distributed power sources, characterized in that: The planning system includes: A flexible index establishment module is used to obtain the operating parameters and regulation capabilities of the energy storage system and distributed generation, and determine the flexibility resource abundance index based on the flexibility resource regulation capability model. The distribution network regulation capability is determined based on the flexibility resource abundance index and the regulation capability of the flexible interconnecting switch. The ratio of the distribution network regulation capability to the net load power change within the dispatching cycle is used as the supply and demand balance indicator. The average value of the sum of the line and flexible interconnecting switch current margins within the dispatching cycle is used as the transmission capacity indicator. An optimization planning model establishment module is used to establish an optimization planning model for a medium-voltage flexible interconnected distribution system based on a two-layer model structure, including: a planning layer model with the lowest annual comprehensive operating cost as the optimization objective, and an operation layer model with the maximum difference between the supply and demand balance index and the transmission capacity index as the optimization objective. The planning layer model provides the operation layer model with the energy storage system and flexible interconnecting switch configuration plan when the annual comprehensive operating cost is lowest, and the operation layer model provides the planning layer model with the system operating loss when the difference between the supply and demand balance index and the transmission capacity index is maximized. The planning layer model updates the annual comprehensive operating cost based on the received system operating loss. The model solving module is used to establish a Nash equilibrium model using the configuration scheme of the energy storage system and the flexible interconnecting switch as the decision variables of the game, and the optimization objectives of the planning layer model and the operation layer model as the game objects. The particle swarm algorithm is used to solve the Nash equilibrium model to obtain the optimal configuration scheme of the energy storage system and the flexible interconnecting switch as the planning result of the medium-voltage flexible interconnected distribution system.

11. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 9.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 9 are implemented.

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