Hydropower reversible transformation layout optimization planning method and system

Abstract

This invention belongs to the technical field of electrical engineering and discloses a method and system for optimizing the layout of reversible hydropower retrofits. The method includes: for candidate reservoir pairs, constructing a stochastic programming model with the construction parameters of the water conveyance path between the upper and lower reservoirs and the operating parameters of the reversible generating units as decision variables to be optimized. The objective function of this model is to minimize the total cost, including investment and operating costs. The constraints include water level variation constraints, head and water level variation coupling constraints, flow and water level coupling constraints, power constraints, and water balance constraints. The stochastic programming model is then solved to obtain the decision variables as the optimal retrofit scheme for the candidate reservoir pairs. This stochastic programming model is more comprehensive, not only limiting the range of key retrofit parameters but also providing the coupling relationships between different parameters, and using the lowest cost as the optimization objective, thereby improving the feasibility of reversible hydropower retrofit layout planning and reducing retrofit costs.

Description

Technical Field

[0001] This invention belongs to the technical field of electrical engineering, and more specifically, relates to a method and system for optimizing the layout of hydropower reversible retrofit. Background Technology

[0002] The primary function of a pumped-storage hydroelectric power station (reversible hydroelectric power station) is energy storage and peak shaving for the power grid. It mainly employs reversible hydroelectric technology, using surplus electricity from the grid during off-peak hours (such as at night) to pump water from the lower reservoir to the upper reservoir, converting the electrical energy into the potential energy of the water for storage. During peak hours, the water is released to generate electricity, supplementing the grid. Therefore, a pumped-storage power station must have two reservoirs, an upper and a lower one, and reversible pump-turbine units (capable of both pumping water and generating electricity). In areas where several conventional hydroelectric power stations already exist, existing conventional hydroelectric power stations can be reversibly converted. This involves utilizing the existing reservoirs, constructing new water conveyance systems and underground powerhouses, and installing reversible pump-turbine units to transform the conventional hydroelectric power stations into pumped-storage power stations. Compared to building entirely new pumped-storage power stations, this method can save on construction costs.

[0003] However, current hydropower reversible retrofit layout optimization planning models usually mainly consider constraints such as unit power, water head, and reservoir capacity. The factors considered are relatively one-sided, and they cannot output a feasible and cost-optimal water transmission-unit combination scheme.

[0004] Therefore, improving the feasibility of hydropower reversible retrofit layout planning and reducing retrofit costs are urgent technical problems that need to be solved. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method and system for optimizing the layout of hydropower reversible retrofit, the purpose of which is to improve the feasibility of hydropower reversible retrofit layout planning and reduce retrofit costs.

[0006] To achieve the above objectives, this invention is proposed.

[0007] According to a first aspect of the present invention, a method for optimizing the layout of reversible hydropower retrofitting is provided, comprising: Two reservoirs were selected as candidate reservoir pairs, one of which was the upper reservoir and the other was the lower reservoir. Using the construction parameters of the water conveyance path between the upper and lower reservoirs and the operating parameters of the reversible generator units as decision variables to be optimized, a stochastic programming model is constructed. The construction parameters of the water conveyance path include the number of water conveyance paths, the diameter of the water conveyance tunnels and the diameter of the pressure pipelines on the water conveyance path, and the number and single-unit capacity of the newly added reversible generator units. The operating parameters of the reversible generator units include the power generation and pumping power of the reversible generator units. The model includes an objective function and constraints. The objective function is to minimize the total cost, including investment cost and operating cost. The investment cost is the investment cost for constructing the water conveyance path, and the operating cost is the operating cost of the reversible generator units. The constraints include water level fluctuation constraints, head and water level fluctuation coupling constraints, flow rate and water level coupling constraints, power constraints, and water balance constraints. The water level fluctuation constraint is to impose an upper limit constraint on the daily water level fluctuation of each reservoir and to impose upper and lower limit constraints on the water level of each reservoir. The coupling constraint between water head and water level variation is to establish the coupling relationship between water head and water level and to impose upper and lower limits on water head. The flow rate and water level coupling constraint is used to establish the coupling relationship between flow rate and water level; The power constraint is to establish the coupling relationship between the pumping power of the reversible unit and the head and the power generation flow of the reversible unit, and to impose upper and lower limit constraints on the pumping power and power generation of the reversible unit. The water balance constraint establishes a coupling relationship between the reservoir water volume and the reservoir water surface area, and constrains the reservoir water volume at the next moment to be equal to the sum of the reservoir water volume at the previous moment and the net increase in reservoir water volume.

[0008] Solve the stochastic programming model to obtain the optimal modification scheme for the candidate reservoir pair as the decision variables.

[0009] According to a second aspect of the present invention, a hydropower reversible retrofit layout optimization planning system is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method described above.

[0010] Overall, compared with the prior art, the technical solutions conceived in this invention have the following beneficial effects.

[0011] 1. The proposed hydropower reversible retrofit layout optimization planning scheme, for candidate reservoir pairs, derives the corresponding optimal retrofit scheme through a stochastic programming model. The objective function of the stochastic programming model simultaneously considers investment costs and operating costs. The constraints include water level fluctuation constraints, head and water level fluctuation coupling constraints, flow and water level coupling constraints, power constraints, and water balance constraints. The above stochastic programming model comprehensively considers the impact of water conveyance path construction and the operating parameters of reversible units on water level, water level fluctuation, head, flow, and water volume. This stochastic programming model is more comprehensive, not only limiting the range of key retrofit parameters but also providing the coupling relationships between different parameters. Based on the above stochastic programming model, with the lowest cost as the optimization objective, decisions are made on water conveyance path construction parameters and reversible unit operating parameters. That is, this scheme simultaneously considers water conveyance path construction and reservoir scheduling, thereby improving the feasibility of hydropower reversible retrofit layout planning and reducing retrofit costs.

[0012] 2. Optionally, in some embodiments, an ecological baseflow constraint is also added. By adding this ecological baseflow constraint, the safe and stable operation of the original watershed can be ensured without affecting the downstream ecology.

[0013] 3. Optionally, in some embodiments, the unit operating costs under different water inflow scenarios are considered during modeling, so that the transformation and operation benefits under different natural conditions can be fully considered.

[0014] 4. Optionally, in some embodiments, a candidate reservoir pair set is first constructed, and then each reservoir pair is planned and the planning schemes of each reservoir pair are compared. In this way, the best reservoir pair can be selected from the target area for reversible reservoir transformation. Attached Figure Description

[0015] Figure 1 This is a flowchart of the steps in the hydropower reversible retrofit layout optimization planning method according to an embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of a reversible hydroelectric power station in one embodiment. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] Example 1 like Figure 1The diagram shown is a flowchart of the steps in the hydropower reversible retrofit layout optimization planning method according to an embodiment of the present invention. The following is a summary of the steps. Figure 1 The method is described in detail.

[0019] The main parameters involved in this invention include: Unit power P, water flow rate Q, reservoir water level Z, head H, reservoir capacity V, planned time period T.

[0020] To facilitate differentiation, different superscripts and subscripts are set, where upper and lower represent the upper and lower reservoirs respectively, and gen and pump represent the power generation and pumping operations respectively.

[0021] S1. Select two reservoirs as candidate reservoir pairs, one of which is the upper reservoir and the other is the lower reservoir.

[0022] Specifically, such as Figure 2 The diagram shows a reversible hydropower station in one embodiment. Two reservoirs are selected as candidate reservoir pairs. The addresses of the upper and lower reservoirs are known. The construction parameters of the water conveyance path between the two reservoirs and the operating parameters of the reversible generating units need to be planned. Specifically, each water conveyance path is connected to a reservoir at both ends via water conveyance tunnels, with a pressure pipeline connecting them in the middle. Reversible generating units are installed along the water conveyance path, operating in both power generation and pumping modes. During power generation, water flows from the upper reservoir to the lower reservoir via the water conveyance path; during pumping, water flows from the lower reservoir to the upper reservoir via the water conveyance path.

[0023] S2. Using the construction parameters of the water conveyance path between the upper and lower reservoirs and the operating parameters of the reversible units as decision variables to be optimized, a stochastic programming model is constructed. The construction parameters of the water conveyance path include the number of water conveyance paths, the diameter of the water conveyance tunnels and the diameter of the pressure pipelines on the water conveyance path, and the number of newly added reversible units and their individual capacities. The operating parameters of the reversible units include the power generation and pumping power of the reversible units. The model includes an objective function and constraints. The objective function is to minimize the total cost, including investment cost and operating cost. The investment cost is the investment cost for constructing the water conveyance path, and the operating cost is the operating cost of the reversible units. The constraints include water level fluctuation constraints, head and water level fluctuation coupling constraints, flow rate and water level coupling constraints, power constraints, and water balance constraints.

[0024] First, identify the decision variables to be planned, which can be categorized into the following two types: Investment decision variables related to water conveyance route construction parameters: ; Operational decision variables for reversible units: ; in, The diameter of the water conveyance tunnel. Where is the diameter of the pressure pipe. The number of water conveyance paths. This refers to the number of reversible generator units. This refers to the single-unit capacity of a reversible generator set. These represent the power generation and pumping power of the reversible unit at time t, respectively.

[0025] In one embodiment, the planning period is the whole year and the scheduling time is the hour, i.e., T=8760.

[0026] Subsequently, based on the above decision variables, a stochastic programming model related to them is constructed.

[0027] The objective function of the model is to minimize the total cost, which includes investment cost and operating cost. Investment cost is the investment cost for constructing the water conveyance route (related to decision variable x), and operating cost is the operating cost of the reversible unit (related to decision variable y).

[0028] In one embodiment, the objective function can be expressed as: ; In the formula, This indicates the investment cost of constructing the water conveyance route. This indicates the operating cost of a reversible generator unit.

[0029] In one embodiment, investment cost This mainly includes the construction cost of the water conveyance path between the upper and lower reservoirs, as well as the cost of the reversible turbine units put into operation. The specific calculation formula can be: ; In the formula, , Represents the cost fitting parameters. , These refer to the lengths of the water conveyance tunnel and the pressure pipeline within the same water conveyance route. , , These represent the cost per unit of water conveyance tunnel, the cost per unit of pressure pipeline, and the cost per unit of reversible generator unit, respectively.

[0030] In one embodiment, unit operating costs This mainly includes the operating costs of reversible units. The specific calculation formula is as follows: ; In the formula, The unit operating cost of the reversible unit, This represents the total operating power of the reversible unit at time t. If it is in pumping mode, then this represents the pumping power. If in power generation mode, then it is the power generation capacity. .

[0031] In this invention, the following model constraints are constructed by comprehensively considering the influence of various factors such as water level, water level fluctuation, water head, flow rate, and water volume.

[0032] (1) Water level fluctuation constraints.

[0033] The water level fluctuation constraint is to impose an upper limit constraint on the daily water level fluctuation of each reservoir, and to impose upper and lower limit constraints on the water level of each reservoir separately.

[0034] In one embodiment, the constraint on the water level fluctuation of the upper reservoir can be expressed as: ; ; ; In the formula, These are the daily water level fluctuations and their set upper limits for the upper reservoir. These are the maximum daily pumping water flow and the maximum power generation water flow, respectively. This represents the daily operating time of the reversible unit; it is a set value and is generally greater than 6 hours. The upper reservoir is the area of ​​the reservoir surface as the water level changes (reservoirs are usually tiered, and the area shrinks as the water level drops). Let t be the water level in the upper reservoir at time t. These are the upper and lower threshold values ​​for the upper reservoir water level, respectively. , These are the dead water level and rated water level of the upper reservoir, respectively. These are the safe water level threshold and flood level of the upper reservoir, respectively.

[0035] In one embodiment, the constraint on the water level fluctuation of the lower reservoir can be expressed as: ; ; ; In the formula, These are the daily water level fluctuations in the lower reservoir and their set upper limits. The lower reservoir is the water surface area that varies with water level. Let t be the water level at time t in the lower reservoir. These are the upper and lower threshold values ​​for the lower reservoir water level, respectively. , , These are the dead water level and the rated water level of the lower reservoir, respectively.

[0036] (2) Coupling constraint between head and water level variation.

[0037] The coupling constraint between head and water level variation is to establish the coupling relationship between head and water level and to impose upper and lower limits on the head.

[0038] In one embodiment, the coupling constraint between head and water level variation can be expressed as: ; In the formula, This represents the water head between the upper and lower reservoirs at time t. The values ​​represent the head losses at time t for the water conveyance tunnel and the pressure pipeline, respectively. These are the upper and lower threshold values ​​for the water head, respectively.

[0039] Among them, the head loss of the water conveyance tunnel and head loss in pressure pipelines It can be represented as: ; ; In the formula, Let be the water flow rate generated by the reversible unit at time t. If the reversible unit is in pumping mode, then it is the water flow rate pumped by the reversible unit. If in power generation mode, it is the reversible generator water flow rate. , The friction coefficient of the water conveyance tunnel can be taken as 130. The friction coefficient of the pressure pipeline can be taken as 140.

[0040] (3) Flow rate and water level coupling constraints.

[0041] The flow rate and water level coupling constraint is used to establish the coupling relationship between flow rate and water level.

[0042] In one embodiment, the flow rate and water level coupling constraint can be expressed as: ; ; ; ; In the formula, These represent the natural inflow of water into the upper and lower reservoirs, respectively, and can be predicted in advance. These represent the outbound flow rates of the upper and lower warehouses, respectively. Let be the power generation capacity of the reversible unit at time t. This refers to the power generation efficiency of reversible generator units. The power generation duration of the reversible generator unit; Let be the pumping power of the reversible unit at time t. The pumping efficiency of the reversible unit. This refers to the pumping time of the reversible unit. This is the acceleration due to gravity.

[0043] Among them, the outbound flow of Shangku The calculation formula is: ; In the formula, These are the original water conveyance flow rate of the upper reservoir unit, the power generation water flow rate of the reversible unit, and its pumping water flow rate, respectively. Outbound flow of the warehouse The calculation formula is: ; In the formula, This refers to the water flow rate of the original unit in the lower reservoir.

[0044] Under this constraint, the water flow rate during reversible unit operation is selected as the minimum value between the conventional reversible power generation flow rate and the reservoir capacity flow rate, which can improve the observability of the operating flow rate.

[0045] (4) Power constraints.

[0046] The power constraint is to establish the coupling relationship between the pumping power of the reversible unit and the head and the power generation flow of the reversible unit, and to impose upper and lower limits on the pumping power and power generation of the reversible unit.

[0047] In one embodiment, the power constraint can be expressed as: ; ; ; In the formula, This is the lower limit threshold for the power generation capacity of reversible generator units. To set the coefficient, usually Greater than 1 and less than 2.

[0048] (5) Water balance constraints.

[0049] The water balance constraint establishes a coupling relationship between the reservoir water volume and the reservoir surface area, and constrains the reservoir water volume at the next moment to be equal to the sum of the reservoir water volume at the previous moment and the net increase in reservoir water volume.

[0050] In one embodiment, the water balance constraint can be expressed as: ; ; ; ; In the formula, These represent the water volume in the upper and lower reservoirs at time t, respectively.

[0051] (6) Ecological base flow constraints.

[0052] The ecological baseflow constraint limits the outflow from the upper reservoir to a threshold that does not fall below the ecological flow demand. The outflow from the upper reservoir is the sum of the external water output from the original generating units and the external water output from the reversible generating units. The ecological flow is the flow required by the downstream ecosystem (such as downstream water supply and fish in the river). If the reversible generating units are in pumping mode, their external water output is the negative of their pumping flow; if they are in power generation mode, their external water output is their power generation flow.

[0053] In one embodiment, the ecological baseflow constraint can be expressed as: ; In the formula, To minimize ecological flow, This is the ecological sensitivity coefficient, reflecting the impact of water level changes on the downstream ecosystem. It's understandable that a reversible unit is either in pumping or generating mode at any given time. If it's in pumping mode, the water flow for power generation is zero; if it's in power generation mode, the water flow for pumping is zero.

[0054] Under this constraint, the outflow from the upper reservoir is greater than the maximum value of the set minimum ecological flow and water level change sensitivity, thus allowing for consideration of the lower limit of sensitivity for different watersheds.

[0055] (7) Minimum extreme water level duration constraint.

[0056] The minimum extreme water level duration constraint is an upper limit constraint on the duration of water shortage in the lower reservoir.

[0057] In one embodiment, the minimum extreme water level duration constraint can be expressed as: ; In the formula, To ensure a safety margin for the lower warehouse, express Duration, Set an upper limit for the duration of water shortage.

[0058] S3. Solve the stochastic programming model to obtain the decision variables as the optimal modification scheme for the candidate reservoir pair.

[0059] After defining the constraints and optimization objective of the stochastic programming model, the optimal solution for the decision variables can be obtained using existing commercial solvers such as Gurobi.

[0060] Solving this system yields the investment decision variables: and the operational decision variables of reversible units In addition, other related runtime variables will be obtained during model solving, such as wait.

[0061] In one embodiment, for a candidate reservoir pair, S inflow scenarios are constructed based on historical runoff data, and the probability of occurrence of each inflow scenario s is determined. The decision-making process for the operating parameters of a reversible unit based on a stochastic programming model involves determining the operating parameters of the reversible unit under each inflow scenario s. The operating cost used in the model's objective function is specifically a weighted sum of the operating costs of the reversible unit under different inflow scenarios, with the weight of each inflow scenario s being its probability of occurrence. The constraints in the model are specifically designed for each water inflow scenario s.

[0062] Specifically, for the reservoir pairs to be renovated, based on long-term historical runoff data, K-means clustering and scenario reduction techniques are used to construct a data structure that includes high-water, normal-water, low-water, and extreme inflow conditions. A set of water inflow scenarios, each scenario is assigned a probability weight. ,satisfy .

[0063] At this point, the objective function of the model is to minimize the total cost, including investment and operating costs. The investment cost is the investment cost for the reversible hydropower reservoir renovation, which is independent of the inflow scenario. The operating cost is the weighted sum of the operating costs of the reversible unit under different inflow scenarios, where the inflow time sequence varies under different inflow scenarios s. They are different, in terms of water inflow sequence. Let represent the observed natural water inflow time series under inflow scenario s. The weighted average of each inflow scenario s is its probability of occurrence. Correspondingly, the objective function can be expressed as: ; In the formula, This represents the operating cost of the reversible unit under the incoming water scenario s.

[0064] The above embodiments consider the weighted summation of unit operating costs under different water inflow scenarios, thus taking into account the actual operating benefits under different water inflow conditions.

[0065] In one embodiment, the method further includes: First, select all reservoir pairs that satisfy the spatial nearest neighbor constraint, gross head constraint, and reservoir capacity threshold constraint from the existing reservoir set in the target area of ​​the reversible hydropower station to be built, forming a candidate reservoir pair set. The spatial nearest neighbor constraint is that the spatial distance between the two reservoirs that make up the reservoir pair is less than a preset distance threshold. The gross head constraint is that the gross head of the two reservoirs that make up the reservoir pair meets a preset range. The reservoir capacity threshold constraint is that the reservoir capacity threshold of each reservoir that makes up the reservoir pair is not lower than a preset reservoir capacity threshold. Then, for each candidate reservoir pair, a stochastic programming model is constructed and the corresponding optimal modification scheme is solved. Evaluation indicators are determined, and the evaluation indicators of the optimal modification scheme of each candidate reservoir pair are compared. Based on the evaluation indicators, the optimal candidate reservoir pair is selected as the reservoir pair for reversible modification.

[0066] When constructing a set of candidate reservoir pairs, spatial nearest neighbor constraints, gross head constraints, and reservoir capacity threshold constraints are selected as constraints for screening.

[0067] Specifically, the spatial nearest neighbor constraint requires that the spatial distance between the two reservoirs forming a reservoir pair is less than a preset distance threshold. In practice, the minimum distance between the boundaries of the two reservoirs can be used as their spatial distance. For example, a fixed number of boundary sampling points can be extracted from the boundary of each reservoir i. The spatial distance between reservoir i and reservoir j can be approximated as: ; The spatial nearest neighbor constraint, which requires the spatial distance between the two reservoirs forming a reservoir pair to be less than a preset distance threshold, can be expressed as: ; In the formula, Let i be the spatial distance between reservoir i and reservoir j. This is a preset distance threshold.

[0068] Specifically, the formula for calculating the gross head between reservoir i and reservoir j is: ; The gross head constraint, which requires the gross heads of the two reservoirs constituting a reservoir pair to meet a preset range, can be expressed as:

[0069] In the formula, and The water levels of reservoirs i and j are respectively. The gross head between reservoir i and reservoir j , These are the preset lower and upper limits for gross water head, respectively.

[0070] Specifically, the reservoir capacity threshold constraint ensures that the reservoir capacity threshold of each reservoir in a reservoir pair is not lower than a preset reservoir capacity threshold. This is used to exclude reservoirs without effective regulation capacity, and can be expressed as: ; Let be the reservoir capacity threshold for any reservoir i in the reservoir pair. This is the preset storage capacity threshold.

[0071] In one embodiment, reservoir pairs that satisfy the spatial nearest neighbor constraint can be obtained from the reservoir set based on the spatial nearest neighbor constraint using the KD number spatial indexing technique to form a preliminary set of candidate reservoir pairs; then, reservoir pairs that satisfy the constraints can be selected from the preliminary set of candidate reservoir pairs based on the gross head constraint and the reservoir capacity threshold constraint to obtain a set of candidate reservoir pairs.

[0072] Specifically, evaluation indicators may include one or more of the following: water reuse rate, investment per kilowatt, expected annual net income, system cost per kilowatt-hour, and capital recovery factor.

[0073] Water reuse rate : ; In the formula, These represent the annual cumulative pumping volume and the annual runoff of the upper reservoir, respectively.

[0074] Investment per kilowatt : .

[0075] Expected annual net income : ; ; in and These represent the electricity price when the reversible generator is generating electricity and the electricity price when it is pumping water, respectively. For revenue generated from electricity generation.

[0076] Levelized Cost of Electricity (LCOS): ; ; Wherein, CRF is the capital recovery factor. For the system's energy storage capacity, The number of cycles per year. The project's lifespan. Let r be the round-trip efficiency, and r be the discount rate.

[0077] Example 2 This invention also relates to a hydropower reversible retrofit layout optimization planning system, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of the method described above.

[0078] This system can be installed on electronic devices, such as desktop computers, laptops, handheld computers, and cloud servers. The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The memory can be used to store computer programs and / or modules. The processor implements various functions of the electronic device by running or executing the computer programs and / or modules stored in the memory, and by accessing data stored in the memory.

[0079] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. It should be noted that the terms "in one embodiment," "for example," and "again" are intended to illustrate the present invention and are not intended to limit the present invention.

[0080] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for optimizing the layout of reversible hydropower retrofits, characterized in that, include: Two reservoirs were selected as candidate reservoir pairs, one of which was the upper reservoir and the other was the lower reservoir. Using the construction parameters of the water conveyance path between the upper and lower reservoirs and the operating parameters of the reversible generator units as decision variables to be optimized, a stochastic programming model is constructed. The construction parameters of the water conveyance path include the number of water conveyance paths, the diameter of the water conveyance tunnels and the diameter of the pressure pipelines on the water conveyance path, and the number and single-unit capacity of the newly added reversible generator units. The operating parameters of the reversible generator units include the power generation and pumping power of the reversible generator units. The model includes an objective function and constraints. The objective function is to minimize the total cost, including investment cost and operating cost. The investment cost is the investment cost for constructing the water conveyance path, and the operating cost is the operating cost of the reversible generator units. The constraints include water level fluctuation constraints, head and water level fluctuation coupling constraints, flow rate and water level coupling constraints, power constraints, and water balance constraints. The water level fluctuation constraint is to impose an upper limit constraint on the daily water level fluctuation of each reservoir and to impose upper and lower limit constraints on the water level of each reservoir. The coupling constraint between water head and water level variation is to establish the coupling relationship between water head and water level and to impose upper and lower limits on water head. The flow rate and water level coupling constraint is used to establish the coupling relationship between flow rate and water level; The power constraint is to establish the coupling relationship between the pumping power of the reversible unit and the head and the power generation flow of the reversible unit, and to impose upper and lower limit constraints on the pumping power and power generation of the reversible unit. The water balance constraint establishes a coupling relationship between the reservoir water volume and the reservoir water surface area, and constrains the reservoir water volume at the next moment to be equal to the sum of the reservoir water volume at the previous moment and the net increase in reservoir water volume. Solve the stochastic programming model to obtain the optimal modification scheme for the candidate reservoir pair as the decision variables.

2. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, The water level fluctuation constraint includes: The constraint on water level variation in the upper reservoir is expressed as follows: ； ； ； In the formula, These are the daily water level fluctuations and their set upper limits for the upper reservoir. These are the maximum daily pumping water flow and the maximum power generation water flow, respectively. This represents the daily operating time of the reversible unit; it is a set value. The upper reservoir is the water surface area of ​​the reservoir according to water level changes. Let t be the water level in the upper reservoir at time t. These are the upper and lower threshold values ​​for the water level in the upper reservoir, respectively. The constraint on water level variation in the lower reservoir is expressed as follows: ； ； ； In the formula, These are the daily water level fluctuations in the lower reservoir and their set upper limits. The lower reservoir is the water surface area that varies with water level. Let t be the water level at time t in the lower reservoir. These are the upper and lower threshold values ​​for the water level in the lower reservoir, respectively.

3. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, The coupling constraint between the head and water level variation is expressed as follows: ； In the formula, This represents the water head between the upper and lower reservoirs at time t. Let t be the water level in the upper reservoir at time t. Let t be the water level at time t in the lower reservoir. The values ​​represent the head losses at time t for the water conveyance tunnel and the pressure pipeline, respectively. These are the upper and lower threshold values ​​for the water head, respectively.

4. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, The flow rate and water level coupling constraint is expressed as follows: ； ； ； ； In the formula, These represent the water levels of the upper and lower reservoirs at time t, respectively. These represent the natural inflow of water into the upper and lower reservoirs at time t, respectively. The natural inflow was predicted in advance. These represent the outbound flow rates of the upper and lower warehouses, respectively. These refer to the surface area of ​​the upper and lower reservoirs, respectively, based on their respective water level changes. The power generation water flow rate and the pumping water flow rate are respectively at time t. These represent the power generation and pumping power of the reversible unit at time t, respectively. These refer to the power generation efficiency and pumping efficiency of the reversible unit, respectively. These are the single power generation time and single pumping time of the reversible unit, respectively; This is the acceleration due to gravity.

5. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, The power constraint is represented as follows: ； ； ； In the formula, These represent the power generation and pumping power of the reversible unit at time t, respectively. Let t be the water flow rate for power generation. This represents the water head between the upper and lower reservoirs at time t. It is the acceleration due to gravity. These refer to the power generation efficiency of reversible generator units. This is the lower limit threshold for the power generation capacity of reversible generator units. This refers to the number of reversible generator units. This refers to the single-unit capacity of a reversible generator set. The set coefficient has a value greater than 1 and less than 2.

6. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, The water balance constraint is expressed as follows: ； ； ； ； In the formula, Let be the water volume in the upper and lower reservoirs at time t, respectively. These are the dead water levels of the upper and lower reservoirs, respectively. Let t represent the water levels at time t in the upper and lower reservoirs. These refer to the surface area of ​​the upper and lower reservoirs, respectively, based on their respective water level changes. These represent the natural inflow of water into the upper and lower reservoirs at time t, respectively. The natural inflow was predicted in advance. These represent the outflow from the upper and lower warehouses, respectively.

7. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, The constraints also include ecological baseflow constraints, which limit the outflow from the upper reservoir to not be lower than the ecological flow demand threshold. Ecological flow refers to the flow required by the downstream ecosystem, and its form is as follows: ； In the formula, Let be the outbound flow of the upper warehouse at time t. To minimize ecological flow, Ecological sensitivity coefficient, Let be the water level of the upper reservoir at time t. Let t be the water level in the upper reservoir at time t.

8. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, For candidate reservoir pairs, S inflow scenarios are constructed based on historical runoff data, and the probability of occurrence of each inflow scenario s is determined. The decision-making process for the operating parameters of a reversible unit based on a stochastic programming model involves determining the operating parameters of the reversible unit under each inflow scenario s. The operating cost used in the model's objective function is specifically a weighted sum of the operating costs of the reversible unit under different inflow scenarios, with the weight of each inflow scenario s being its probability of occurrence. The constraints in the model are specifically designed for each water inflow scenario s.

9. The hydropower reversible retrofit layout optimization planning method as described in claim 1, characterized in that, The method further includes: First, select all reservoir pairs that satisfy spatial proximity constraints, gross head constraints, and reservoir capacity threshold constraints from the existing reservoir set in the target area where the reversible hydropower station is to be built, forming a candidate reservoir pair set. The spatial proximity constraint is that the spatial distance between the two reservoirs that make up the reservoir pair is less than a preset distance threshold. The gross head constraint is that the gross head of the two reservoirs that make up the reservoir pair meets a preset range. The reservoir capacity threshold constraint is that the reservoir capacity threshold of each reservoir that makes up the reservoir pair is not lower than a preset reservoir capacity threshold. Then, for each candidate reservoir pair, a stochastic programming model is constructed and the corresponding optimal modification scheme is solved. Evaluation indicators are determined, and the evaluation indicators of the optimal modification scheme of each candidate reservoir pair are compared. Based on the evaluation indicators, the optimal candidate reservoir pair is selected as the reservoir pair for reversible modification.

10. A hydropower reversible retrofit layout optimization planning system, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1 to 9.

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