Medium- and long-term optimal scheduling model taking maintenance and ecological scheduling for cascade hydropower station into consideration

Abstract

A medium- and long-term optimal scheduling model taking maintenance and ecological scheduling for a cascade hydropower station into consideration. The model comprises: setting common scheduling constraints, maintenance constraints and ecological scheduling constraints, taking the maximization of cascade power generation as a goal, transforming the constraints into recognizable mathematical expressions, and establishing an optimal scheduling model for a cascade hydropower station; solving the model to generate an initial cascade power station scheduling process, calculating the average water level for time periods in the cascade power station scheduling process, using as a corridor a region that ranges from K meters above the average water level to K meters below the average water level, taking the intersection of the corridor with a normal water storage level and a dead water level, and using the intersection as a new corridor; within the range of the corridor, respectively approximating a water consumption rate and an expected output as polynomial functions, which are of degrees no greater than 2, of a reservoir-out flow, a reservoir water level and a downstream station water level, establishing a mixed-integer quadratic programming model, and executing a solution to obtain a new cascade power station scheduling process; and repeatedly performing iterative calculation until an end condition is met, and thereby obtaining a final cascade hydropower station scheduling scheme and an optimal occasion for the development of maintenance and ecological scheduling.

Description

A medium- and long-term optimal scheduling model for cascade hydropower stations considering maintenance and ecological scheduling Technical Field

[0001] The present invention belongs to the technical field of reservoir group scheduling, and more specifically, relates to a medium- and long-term optimization scheduling model for cascade hydropower stations taking maintenance and ecological scheduling into consideration. Background Art

[0002] Large hydropower stations in a river basin may not only address power generation but also multiple tasks, such as flood control, navigation, ecological conservation, and water supply. Different scheduling objectives necessitate different optimization scheduling models and algorithms. Furthermore, to ensure the safe and stable operation of the power system, annual maintenance and outsourcing maintenance are scheduled for power stations. During these maintenance periods, power station generation and outsourcing capacity are limited, impacting the overall efficiency of the power stations. With the implementation of the Yangtze River Protection Strategy and the increasing awareness and demand for environmental protection, hydropower station scheduling must also consider ecological scheduling requirements and develop scheduling plans that meet these requirements. One of the key technical challenges in hydropower station scheduling is how to automatically optimize the timing of maintenance and ecological scheduling through algorithms, minimize the adverse impacts of maintenance and ecological scheduling on power generation, and improve the comprehensive utilization of water resources.

[0003] In the area of ​​maintenance, existing research has either treated maintenance planning and power generation scheduling separately, optimizing scheduling based on a known maintenance plan; or combined maintenance planning and power generation scheduling for unified optimization. This unified optimization increases the difficulty of solving the model. Some scholars have proposed a two-level optimization model for maintenance planning and power generation scheduling, while others have simplified the calculation of hydropower station output and established a mixed-integer linear programming model. In the area of ​​ecological scheduling, existing research has mostly focused on analyzing the ecological impacts of different scheduling schemes and multi-objective scheduling of ecological power generation, with little research on ecological time optimization. Furthermore, existing research has not considered the simultaneous implementation of maintenance and ecological scheduling. In practical medium- and long-term scheduling, due to the long scheduling periods and the fact that maintenance and ecological scheduling often occur during the non-flood season, it is necessary to incorporate the relevant constraints of maintenance and ecological scheduling into the scope of optimal scheduling.

[0004] Summary of the Invention

[0005] In response to the defects of the existing technology, the present invention proposes a medium- and long-term optimal scheduling model for cascade hydropower stations that takes maintenance and ecological scheduling into consideration. The model aims to automatically provide an optimized plan for the timing of maintenance and ecological scheduling, reduce the adverse effects of maintenance and ecological scheduling on power generation of power stations, and give full play to the power generation benefits of cascade power stations.

[0006] In order to achieve the above technical features, the purpose of the present invention is achieved as follows:

[0007] A medium- and long-term optimal scheduling model for cascade hydropower stations considering maintenance and ecological scheduling is proposed, which includes the following steps:

[0008] (1) Set common scheduling constraints, maintenance constraints, and ecological scheduling constraints, take maximizing cascade power generation as the goal, and convert them into recognizable mathematical expressions to establish an optimal scheduling model for cascade hydropower stations;

[0009] (1.1) Common scheduling constraints include water balance constraints, water level range constraints, water level amplitude constraints, flow range constraints, flow amplitude constraints, and output constraints.

[0010] (1.2) Maintenance constraints include:

[0011] Maintenance start time range constraints:

[0012] Where, Indicates whether the tth period of the kth maintenance of power station i is the maintenance start period. If so, it is 1, otherwise 0; They represent the period corresponding to the earliest start time and the period corresponding to the latest start time of the k-th maintenance at power station i respectively;

[0013] Maintenance limits the output of the branch plant:

[0014] Where p i,t,f 、 They represent the output of the f-th branch in the t-th period of power station i and the maximum available output of the f-th branch due to the k-th maintenance; D i,k It indicates the duration of the kth maintenance of power station i. After the maintenance begins, i,k There should be no interruption within a period; M represents a constant, which is greater than the installed output of the power station and the maximum outflow flow of the power station;

[0015] (1.3) Ecological regulation includes ecological regulation that creates a continuous water rise process, ecological regulation that creates a stable flow process, ecological regulation that creates a flood peak process, and ecological regulation that limits the water level operation range;

[0016] (1.3.1) The constraints on ecological regulation that create a continuous flooding process include:

[0017] Time and frequency restrictions:

[0018] Constraints on the range of rising flow rate:

[0019] Constraints on daily traffic increase:

[0020] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the duration of the flood, the lower limit of the starting flow, the upper limit of the starting flow, the lower limit of the daily flow increase, and the upper limit of the daily flow increase for power station i; Q i,t represents the outflow flow of power station i in the tth period;

[0021] (1.3.2) The constraints of ecological scheduling to create a smooth flow process include:

[0022] Time and frequency restrictions:

[0023] Outbound flow range constraints:

[0024] Constraints on daily traffic fluctuations:

[0025] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the lower limit of the outflow flow during the operation period, the upper limit of the outflow flow, the duration, and the maximum daily fluctuation of the flow rate of the scheduling of power station i respectively;

[0026] (1.3.3) The constraints on ecological regulation that create peak flood processes include:

[0027] Time and frequency restrictions:

[0028] Initial flow constraint:

[0029] Constraints on duration of flooding and daily flow rate increase:

[0030] Constraints on water withdrawal duration and daily flow rate decline:

[0031] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the duration of water rise, the duration of water fall, the lower limit of daily flow increase, the upper limit of daily flow increase, the lower limit of daily flow decrease, the upper limit of daily flow decrease, the lower limit of starting flow, and the upper limit of starting flow for the scheduling of power station i respectively;

[0032] (1.3.4) Ecological regulation constraints that limit the operating range of water levels include:

[0033] Time and frequency restrictions:

[0034] Water level operation constraints:

[0035] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the operation is carried out, the lower limit of the water level, the upper limit of the water level, and the duration of the operation for power station i; Z i,t represents the final water level of the tth period at power station i;

[0036] (2) Solving the model, specifically including:

[0037] (2.1) Generate the initial cascade power station dispatch process;

[0038] (2.2) Calculate the average water level during the cascade hydropower station dispatching process, use the K meters above and below the average water level process as the corridor, and take the intersection with the normal water level and dead water level as the new corridor to keep it within the normal operating water level range;

[0039] (2.3) Within the corridor, the water consumption rate and expected output are approximated as polynomial functions of the outflow, reservoir water level, and downstream power station water level (if there is support), respectively, with a value not higher than quadratic. A mixed integer quadratic programming model is established to solve the new cascade power station scheduling process.

[0040] (2.4) Repeat steps (2.2) and (2.3) until the iterative termination conditions are met, and the final cascade hydropower station scheduling plan and the optimized timing for maintenance and ecological scheduling are obtained.

[0041] The present invention has beneficial effects:

[0042] 1. The present invention can automatically provide an optimization plan for the timing of maintenance and ecological scheduling, realize the overall optimization of maintenance, ecological scheduling and power station operation, and minimize the adverse effects of maintenance and ecological scheduling on power generation while taking into account both, so as to give full play to the economic benefits of cascade power stations.

[0043] 2. The model solving method provided by the present invention combines the idea of ​​iterative optimization by forming corridors within the solution neighborhood with mixed integer quadratic programming. This not only avoids the tediousness of layered optimization solutions for maintenance, ecological scheduling, and power station operation, but also improves the accuracy of power station output calculations. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a flow chart of a medium- and long-term optimal scheduling model for cascade hydropower stations taking into account maintenance and ecological scheduling, provided by the present invention.

[0045] FIG2 is a comparison diagram of the calculation results of the scheme of the present invention and the comparative scheme for power station A in the embodiment.

[0046] FIG3 is a comparison diagram of the calculation results of the scheme of the present invention and the comparative scheme for power station B in the embodiment.

[0047] FIG4 is a comparison diagram of the results of the calculation scheme of the present invention and the comparative scheme for power station C in the embodiment.

[0048] FIG5 is a comparison diagram of the calculation results of the scheme of the present invention and the comparative scheme for power station D in the embodiment.

[0049] FIG6 is a comparison diagram of the calculation results of the scheme of the present invention and the comparative scheme for the E power station in the embodiment.

[0050] FIG7 is a comparison diagram of the calculation results of the scheme of the present invention and the comparative scheme for the F power station in the embodiment. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Example 1:

[0053] As shown in Figure 1, a medium- and long-term optimal scheduling model for cascade hydropower stations considering maintenance and ecological scheduling includes the following steps:

[0054] (1) Set common scheduling constraints, maintenance constraints, and ecological scheduling constraints, take maximizing cascade power generation as the goal, and convert them into recognizable mathematical expressions to establish an optimal scheduling model for cascade hydropower stations;

[0055] Common scheduling constraints include water balance constraints, water level range constraints, water level variation constraints, flow range constraints, flow variation constraints, and output constraints.

[0056] The maintenance constraints include:

[0057] ① Maintenance start time range constraints:

[0058] Where, Indicates whether the tth period of the kth maintenance of power station i is the maintenance start period. If so, it is 1, otherwise 0; They represent the period corresponding to the earliest start time and the period corresponding to the latest start time of the k-th maintenance of power station i respectively.

[0059] ② Maintenance restrictions on branch plant output:

[0060] Where p i,t,f 、 They represent the output of the f-th branch in the t-th period of power station i and the maximum available output of the f-th branch due to the k-th maintenance; D i,k It indicates the duration of the kth maintenance of power station i. After the maintenance begins, i,k There should be no interruption within a period of time; M represents a constant, which is a number greater than the installed output of the power station and the maximum outflow flow of the power station.

[0061] Ecological scheduling includes ecological scheduling that creates a continuous water rise process, ecological scheduling that creates a smooth flow process, ecological scheduling that creates a flood peak process, and ecological scheduling that limits the water level operation range.

[0062] ① The constraints on ecological regulation to create a continuous flooding process include:

[0063] Time and frequency restrictions:

[0064] Constraints on the range of rising flow rate:

[0065] Constraints on daily traffic increase:

[0066] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the duration of the flood, the lower limit of the starting flow, the upper limit of the starting flow, the lower limit of the daily flow increase, and the upper limit of the daily flow increase for power station i; Q i,t represents the outflow flow of power station i in the tth period.

[0067] ② The constraints of ecological scheduling to create a smooth flow process include:

[0068] Time and frequency restrictions:

[0069] Outbound flow range constraints:

[0070] Constraints on daily traffic fluctuations:

[0071] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They respectively represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the lower limit of the outbound flow during the implementation period, the upper limit of the outbound flow, the duration, and the maximum daily fluctuation of the flow rate of the power station i.

[0072] ③ The constraints on ecological regulation that create flood peak processes include:

[0073] Time and frequency restrictions:

[0074] Initial flow constraint:

[0075] Constraints on duration of flooding and daily flow rate increase:

[0076] Constraints on water withdrawal duration and daily flow rate decline:

[0077] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They respectively represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the duration of water rise, the duration of water fall, the lower limit of daily flow increase, the upper limit of daily flow increase, the lower limit of daily flow decrease, the upper limit of daily flow decrease, the lower limit of starting flow, and the upper limit of starting flow.

[0078] ④ Constraints on ecological regulation that limit the operating range of water levels include:

[0079] Time and frequency restrictions:

[0080] Water level operation constraints:

[0081] Where, Indicates whether the t-th period of power station i is the start period of this scheduling. If so, it is 1, otherwise 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the operation is carried out, the lower limit of the water level, the upper limit of the water level, and the duration of the operation for power station i; Z i,t It represents the final water level of power station i in the tth period.

[0082] (2) Solve the model:

[0083] (2.1) Generate the initial cascade power station dispatch process;

[0084] (2.2) Calculate the average water level during the cascade hydropower station dispatching process, use the K meters above and below the average water level process as the corridor, and take the intersection with the normal water level and dead water level as the new corridor to keep it within the normal operating water level range;

[0085] (2.3) Within the corridor, the water consumption rate and expected output are approximated as polynomial functions of the outflow, reservoir water level, and downstream power station water level (if there is support), respectively, with a value not higher than quadratic. A mixed integer quadratic programming model is established to solve the new cascade power station scheduling process.

[0086] (2.4) Repeat steps (2.2) and (2.3) until the iterative termination conditions are met, and the final cascade hydropower station scheduling plan and the optimized timing for maintenance and ecological scheduling are obtained.

[0087] Example 2:

[0088] The following example, using a cascade of six hydropower stations (A, B, C, D, E, and F) as an example, further illustrates the medium- and long-term optimal scheduling model for cascade hydropower stations, which takes into account maintenance and ecological scheduling. The six stations are series-connected reservoirs, with stations A, B, C, D, E, and F, from upstream to downstream. The scheduling period is from January 1st to June 30th, with a daily scheduling scale. The maintenance constraints are shown in Table 1, and the ecological scheduling constraints are shown in Table 2.

[0089] Table 1 Maintenance constraints

[0090] Table 2 Ecological scheduling constraints

[0091] Based on the above constraints, the modeling formula and solution process in the present invention are described in detail as follows:

[0092] (1) Establishing an optimal dispatching model for cascade hydropower stations:

[0093] The scheduling target is to maximize the cascade power generation. Common scheduling constraints include water balance constraint, water level range constraint, water level amplitude constraint, flow range constraint, flow amplitude constraint, and output constraint.

[0094] Maintenance constraints:

[0095] ① Maintenance start time range constraints:

[0096] Overhaul 1:

[0097] Overhaul 2:

[0098] Overhaul 3:

[0099] ② Maintenance restrictions on branch plant output:

[0100] Overhaul 1:

[0101] Overhaul 2:

[0102] Overhaul 3:

[0103] Constraints on ecological regulation that create a continuous water rise process:

[0104] ①Constraints on time and frequency of implementation:

[0105] Power Station C:

[0106] Power Station D:

[0107] E Power Station:

[0108] ② Constraints on the range of rising flow rate:

[0109] Power Station C:

[0110] D Power Station:

[0111] E-station:

[0112] ③ Daily traffic increase constraints:

[0113] Power Station C:

[0114] D Power Station:

[0115] E-station:

[0116] Constraints on ecological scheduling to create a smooth flow process:

[0117] ①Constraints on time and frequency of implementation:

[0118] Power Station A:

[0119] Station B:

[0120] ② Constraints on outbound flow range:

[0121] Power Station A:

[0122] Power Station B:

[0123] ③ Daily traffic fluctuation constraints:

[0124] Power Station A:

[0125] Station B:

[0126] Constraints on ecological regulation that create flood peak processes:

[0127] ①Constraints on time and frequency of implementation:

[0128] Power Station A:

[0129] Station B:

[0130] ② Initial flow constraint:

[0131] Power Station A:

[0132] Station B:

[0133] ③ Constraints on duration of flooding and daily flow rate increase: Power Station A:

[0134] Power Station B:

[0135] ④ Constraints on water withdrawal duration and daily flow rate reduction:

[0136] Power Station A:

[0137] Power Station B:

[0138] Constraints on ecological regulation that limit the operating range of water levels:

[0139] ①Constraints on time and frequency of implementation:

[0140] ② Water level operation constraints:

[0141] (2) Solve the model:

[0142] (2.1) Generate the initial cascade power station dispatch process;

[0143] (2.2) Calculate the average water level during the cascade hydropower station dispatch process, use the 2 meters above and below the average water level process as a corridor, and take the intersection with the normal water level and dead water level as a new corridor to ensure that it is within the normal operating water level range;

[0144] (2.3) Within the corridor, the water consumption rate and expected output are approximated as polynomial functions of no greater than quadratic of the outflow, reservoir water level, and downstream power station water level (if there is jacking), respectively. A mixed integer quadratic programming model is established and solved to obtain a new cascade power station scheduling process. The mixed integer quadratic programming is solved using the Gurobi optimizer.

[0145] (2.4) Repeat steps (2.2) and (2.3) until the iterative termination conditions are met, and the final cascade hydropower station scheduling plan and the optimized timing for maintenance and ecological scheduling are obtained.

[0146] The optimization calculation results of the maintenance and ecological scheduling timing according to the process of the present invention are shown in Table 3.

[0147] Table 3 Timing of maintenance and ecological scheduling calculated by the present invention

[0148] Example 3:

[0149] In order to highlight the effect of the present invention, on the basis of Example 2, the maintenance start time and the ecological scheduling start time are manually set according to the maintenance constraints and ecological scheduling constraints, as shown in Table 4, and then the optimization scheduling calculation is performed to obtain three representative comparison schemes. Table 5 is a comparison of the power generation of the scheme calculated by the present invention and the comparison scheme, and Figures 2 to 7 are a comparison of the water level process of the cascade power station calculated by the present invention and the comparison scheme (in order to protect the interests of the cascade power station, the water level process is standardized and converted into a number between [0,1]). It can be seen that the method of the present invention can not only automatically provide the timing for carrying out maintenance and ecological scheduling, but also provide a scheme with greater power generation and better benefits. It not only reduces the adverse effects of maintenance and ecological scheduling on power generation of power stations, but also avoids the tediousness of repeated trial calculations for manually specifying the timing of implementation, providing convenience for dispatchers.

[0150] Table 4 Comparison of the maintenance and ecological scheduling timings set by the scheme

[0151] Table 5 Comparison of power generation calculated by the scheme of the present invention and the comparative scheme (100 million kW·h)

[0152] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any equivalent modifications made to the present invention within the scope of protection of the claims of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A medium- and long-term optimal dispatching model for cascade hydropower stations considering maintenance and ecological dispatching, characterized in that: The following steps are involved: S1, set common dispatching constraints, maintenance constraints, and ecological dispatching constraints, take the maximum cascade power generation as the goal, and convert them into recognizable mathematical expressions to establish an optimal dispatching model for cascade hydropower stations; The commonly used scheduling constraints include water balance constraints, water level range constraints, water level amplitude constraints, flow range constraints, flow amplitude constraints, and output constraints; The maintenance constraints include maintenance start time range constraints and maintenance output limit constraints on the branch plant; The ecological dispatching includes the ecological dispatching to create a continuous water rise process, the ecological dispatching to create a stable flow process, the ecological dispatching to create a flood peak process, and the ecological dispatching to limit the water level operation range; S2, solve the model, including: S2.1, generating the initial cascade power station dispatching process; S2.2, calculate the average water level of the cascade power station dispatching process, take the upper and lower K meters of the average water level process as the corridor, and take the intersection with the normal water level and dead water level as the new corridor, so that it is within the normal operating water level range; S2.3, within the corridor, the water consumption rate and expected output are approximated as polynomial functions of the outflow, reservoir water level, and downstream power station water level (if there is a top support) with a value not higher than quadratic, and a mixed integer quadratic programming model is established to solve the new cascade power station dispatching process; S2.4, repeat steps S2.2 and S2.3 until the iteration termination condition is met, and the final cascade hydropower station scheduling plan and the optimized timing of maintenance and ecological scheduling are obtained.

2. According to claim 1, a medium- and long-term optimization scheduling model for cascade hydropower stations considering maintenance and ecological scheduling is characterized in that: The maintenance start time range constraint in the maintenance constraint is: In the formula, Indicates whether the tth period of the kth maintenance of power station i is the maintenance start period, if so, it is 1, otherwise it is 0; They represent the time period corresponding to the earliest start time and the time period corresponding to the latest start time of the k-th maintenance of power station i respectively; The maintenance constraints mentioned above limit the output of the branch plant: In the formula, p i,t,f , They represent the output of the f-th branch in the t-th period of power station i and the maximum available output of the f-th branch due to the k-th maintenance; D i,k represents the duration of the kth maintenance of power station i. After the maintenance begins, i,k It cannot be interrupted within a period of time; M represents a constant, which is a number greater than the installed output of the power station and the maximum outflow flow of the power station.

3. According to claim 2, a medium- and long-term optimization scheduling model for cascade hydropower stations considering maintenance and ecological scheduling is characterized in that: The constraints on ecological regulation that create a continuous flooding process include: Time and frequency constraints: Constraints on the range of rising flow rate: Constraints on daily traffic increase: In the formula, Indicates whether the tth period of power station i is the start period of this scheduling. If yes, it is 1, otherwise it is 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the duration of the flood, the lower limit of the starting flow, the upper limit of the starting flow, the lower limit of the daily flow increase, and the upper limit of the daily flow increase of the power station i; Q i,t It represents the outflow flow of power station i in the tth period.

4. According to claim 3, a medium- and long-term optimization scheduling model for cascade hydropower stations considering maintenance and ecological scheduling is characterized in that: The constraints of ecological scheduling to create a smooth flow process include: Time and frequency constraints: Outbound flow range constraints: Constraints on daily traffic fluctuations: In the formula, Indicates whether the tth period of power station i is the start period of this scheduling. If yes, it is 1, otherwise it is 0; They respectively represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the lower limit of the outbound flow during the implementation period, the upper limit of the outbound flow, the duration, and the maximum daily fluctuation of the flow rate of the power station i.

5. According to claim 4, a medium- and long-term optimization scheduling model for cascade hydropower stations considering maintenance and ecological scheduling is characterized in that: The constraints on ecological regulation that create the peak flood process include: Time and frequency constraints: Initial flow constraint: Constraints on duration of flooding and daily flow rate increase: Constraints on water withdrawal duration and daily flow rate decline: In the formula, Indicates whether the tth period of power station i is the start period of this scheduling. If yes, it is 1, otherwise it is 0; They respectively represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the duration of water rise, the duration of water decline, the lower limit of daily flow increase, the upper limit of daily flow increase, the lower limit of daily flow decrease, the upper limit of daily flow decrease, the lower limit of starting flow, and the upper limit of starting flow.

6. A medium- and long-term optimal scheduling model for cascade hydropower stations considering maintenance and ecological scheduling according to claim 4, characterized in that: The constraints of ecological regulation that limit the operating range of water levels include: Time and frequency constraints: Water level operation constraints: In the formula, Indicates whether the tth period of power station i is the start period of this scheduling. If yes, it is 1, otherwise it is 0; They represent the earliest start time corresponding to the time period, the latest start time corresponding to the time period, the number of times the scheduling is carried out, the lower limit of the water level, the upper limit of the water level, and the duration of the scheduling of power station i; Z i,t It represents the final water level of power station i in the tth period.

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