Design method for improving reliability of mixed pumped storage lower reservoir

Abstract

The invention provides a design method for improving reliability of a reservoir under mixed pumping and storage. The design method comprises the following steps: S1, determining a water pumping working condition constraint condition; s2, establishing a lower reservoir pumping coupling hydrodynamic numerical simulation model; s3, establishing a hydrodynamic response relationship of the water pumping reliability; s4, performing technical and economic comparison to determine a proper engineering measure scheme; s5, carrying out a physical model test for verification; and S6, the water pumping reliability and the operation limiting water level of the lower reservoir are provided. According to the method, the water pumping funnel phenomenon and the hydrodynamic law of the water pumping funnel phenomenon under the water pumping working condition of the reservoir under mixed pumping and storage are disclosed, and a proper engineering measure scheme is determined through technical and economic comparison, so that the water pumping reliability of mixed pumping and storage is effectively improved, and a solid foundation is provided for mixed pumping and storage engineering design, construction and operation scheduling.

Description

Technical Field

[0001] The invention relates to the field of pumped-storage reservoir design, and in particular to a design method for improving the reliability of a hybrid pumped-storage reservoir. Background Art

[0002] Hybrid pumped storage power station (referred to as hybrid pumped storage) is a hydropower station that has both pumped storage and runoff power generation functions. It is an important component of pumped storage power stations and an ideal "high-quality long-term energy storage" method. Hybrid pumped storage has increased installed capacity, enhanced peak-shaving capacity, and long continuous power generation and pumping operation time. It can not only use the abandoned water of the hydropower station to generate electricity and improve the efficiency of water energy utilization, but also can be adjusted daily, weekly, ten-day or even seasonally. It has obvious advantages in serving new energy power generation and can better meet the needs of power systems and clean energy bases for regulation capabilities. Hybrid pumped storage does not require the construction of upper and lower reservoirs, but only requires the construction of a new water transmission and power generation system. It usually does not involve major environmentally sensitive objects, involves less land acquisition and immigration, has rich geological data accumulation, and has low operation and maintenance costs. It is easy to quickly implement construction and exert functional benefits. Under the situation of large-scale development and utilization of new power systems and new energy, hybrid pumped storage will usher in rapid development and effectively promote the development of integrated clean energy bases for water, wind, and solar storage in the basin.

[0003] Hybrid pumped storage is generally built between the upper and lower cascade hydropower stations. The inlet / outlet of the lower reservoir is generally close to the downstream of the dam of the upper reservoir and is located at the tail of the lower reservoir. Under power generation conditions, the power generation water flows downstream, forming a positive superposition effect with the power generation of the conventional units in the upper reservoir; while the pumping condition will form a reverse flow, and because the pumping flow is large and the reverse flow velocity is also large, the return water of the lower reservoir will not only not be piled up near the inlet / outlet, but will drop rapidly, thus forming a pumping funnel phenomenon. When the lower reservoir is a canyon river type reservoir, the pumping funnel effect is likely to affect the reliability of the pumping operation of the lower reservoir, and the narrower the water surface near the inlet / outlet, the larger the pumping flow, and the lower the reservoir water level, the lower the pumping reliability will be, and the more likely it is that pumping cannot be guaranteed.

[0004] When the water level of the hybrid pumped-storage reservoir power station is low and encounters unfavorable conditions such as a large pumping flow, the pumpable flow may decrease after less than 8 hours (possibly 3h to 4h) due to the narrow river channel. Continuing pumping will cause the local water level to drop rapidly. Ultimately, due to untimely water replenishment in the river channel, the pumping capacity cannot be guaranteed, which ultimately leads to inefficient and unstable operation of the unit. The pumping reliability of the hybrid pumped-storage power station will be low, and it will not be able to guarantee water intake at full pumping flow or full power pumping for energy storage. The pumping time cannot cover the 8 hours of photovoltaic power generation during the day (10:00-18:00). Therefore, it is possible to generate additional abandoned photovoltaic power that does not meet the design requirements, reduce the power generation and energy storage benefits of the project, and thus reduce the economic efficiency of the project. Summary of the invention

[0005] The main purpose of the present invention is to provide a design method for improving the reliability of a hybrid pumped storage reservoir and solve the problems in the above-mentioned background technology.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: the design method steps are as follows:

[0007] S1. Determine the constraints of pumping conditions;

[0008] S2. Establish a numerical simulation model of the pumping-coupled hydrodynamics of the lower reservoir;

[0009] S3, establish the hydrodynamic response relationship of pumping reliability;

[0010] S4. Determine the appropriate engineering measures through technical and economic comparison;

[0011] S5. Conduct physical model tests for verification;

[0012] S6. Propose the pumping reliability and operating limit water level of the lower reservoir.

[0013] Preferably, the constraints of the pumping conditions in step S1 include clarifying the pumping period, analyzing the pumping operation characteristics, sorting out the pumping conditions, and paying attention to the situation where the water head changes greatly within the year;

[0014] The water balance and the lower reservoir water level operating range restrictions should be met; the outflow flows of the upper and lower reservoirs must also meet the ecological and unit minimum downstream flow requirements. When the pumping condition begins, the initial water level of the lower reservoir is generally the normal water storage level.

[0015] Preferably, the specific steps of step S2 are as follows:

[0016] B1. Determine the research object and research period. The research object of the numerical model is the entire lower reservoir, and the research period is a single pumping cycle;

[0017] B2. Determine the theoretical formula and calculation method of the model. The model is built using the basic equations of fluid mechanics and needs to be modified for the unsteady flow under pumping simulation, including the continuity equation and momentum equation;

[0018] The model uses the numerical calculation methods of finite difference method, finite element method and finite volume method to solve the basic equations, and finally obtains the fluid velocity and pressure parameters on different grids through numerical iterative calculation;

[0019] B3. Determine the model boundary conditions. In the hydraulic simulation of the lower reservoir pumping, boundary conditions need to be defined to describe the interaction between the fluid and the solid boundary, including fixed boundary conditions, free boundary conditions and inlet / outlet boundary conditions;

[0020] The model uses the initial water level elevation as the water level at the initial moment of hydrodynamic calculation and defines three water inlet / outlet boundaries of the lower reservoir: the outflow of the upper reservoir power station in, the outflow of the lower reservoir power station out, and the outflow of the pumped flow of the hybrid pumped storage or the inflow of the power generation flow.

[0021] B4. Organize terrain data and collect surveying and mapping data of the entire reservoir. The surveying and mapping accuracy must meet the accuracy requirements for supporting hydrodynamic simulation, and organize the terrain data of the riverbed and reservoir bank;

[0022] B5. Perform grid division, determine the grid size, generate a two-dimensional grid of the water body, and divide the water body into small grid cells to represent the horizontal and vertical distribution of the water flow. The resolution and accuracy of the grid are adjusted as needed;

[0023] The non-uniform grid division method is adopted to appropriately increase the area of ​​a single grid in relatively unimportant areas, and to encrypt the grids of important local river sections near the inlet / outlet, which can coordinate the relationship between grid density, calculation time and calculation accuracy.

[0024] B6. Determine the calculation step size, select different simulation time steps to simulate the same terrain, keep other boundary conditions unchanged, and analyze the sensitivity of the simulation results; adopt a segmented simulation strategy with different calculation steps, select a larger time step when the pumping reliability is high to improve the calculation efficiency; and use a smaller time step when the pumping reliability is low to ensure the accuracy of the simulation results at critical moments;

[0025] B7. Determine the riverbed roughness. According to the relationship between the measured flow and the corresponding water surface line, the river channel of the lower reservoir is divided into multiple sections and calibrated section by section to calibrate the riverbed roughness of the hydrodynamic model.

[0026] B8. Model rationality analysis: The reliability of simulation results under different initial conditions is judged according to the hydrodynamic laws. The accuracy of simulation results is analyzed using measured data. The correlation coefficient and Nash coefficient indicators are used to judge the accuracy of the simulated water level process and the measured process. If the correlation coefficient or Nash coefficient is greater than 0.8 and the p-value is <0.05, it is considered that the results simulated by this model have a high degree of credibility.

[0027] Preferably, the specific steps of step S3 are as follows:

[0028] C1. Analysis of the hydrodynamic characteristics of the pumping condition reliability, focusing on the pumping funnel phenomenon, determining the range of the inverse proportional drop of the river water level through numerical simulation, observing the time and characteristics of the funnel, summarizing the hydrodynamic response law of the pumping condition, and judging the reliability of the hybrid pumped-storage pumping condition;

[0029] C2. The response relationship between pumping reliability and river topography, pumping conditions, engineering layout and engineering measures. Combined with the pumping simulation results under different river topography, pumping conditions, engineering layout and engineering measures, the different inlet / outlet flow patterns and hydrodynamic conditions are compared and analyzed, and the sensitive factors affecting pumping are analyzed to form the relationship between pumping reliability and topography and engineering layout.

[0030] Preferably, the specific steps of step C1 are as follows:

[0031] Apply the hydrodynamic numerical simulation model to obtain the calculation results under different typical pumping conditions, including the reservoir water surface line results, local flow velocity, flow state and water surface changes at the inlet / outlet;

[0032] Analyze the range of the reverse drop of the pumping funnel, the lowered water level, the length of the river backwater, and the minimum water depth;

[0033] Whether low-water-level pumping is reliable can be judged from multiple aspects, including the degree of guarantee of pumping time, degree of guarantee of pumping flow, depth and range of inverse proportional drop of the pumping funnel, and flow velocity at the lowest point of the funnel.

[0034] Preferably, the specific steps of step S4 are as follows:

[0035] D1. Selection of engineering measures: Based on the analysis of model results, various engineering measures to improve hydraulic conditions and water flow stability are proposed;

[0036] D2. Comparison and selection of river dredging project measures:

[0037] Initially draft different river dredging plans, including dredging river length, dredging width and depth;

[0038] Correct the riverbed topography data and re-divide the grid according to the river dredging plan, and re-conduct the hydrodynamic simulation;

[0039] Further analyze the hydrodynamic results after river dredging, conduct comparative analysis on the hydrodynamic coupling simulation results of different schemes, evaluate whether the pumping guarantee capacity of the hybrid pumped-storage project is improved, and whether the operational reliability of the pumping condition meets the requirements;

[0040] Analyze the river dredging construction methods and construction difficulty of each plan, consider the cost of measures, and calculate the engineering quantity and investment cost;

[0041] Conduct a comprehensive technical and economic comparison, comprehensively consider the effects and costs of various plans, calculate comprehensive evaluation indicators, and select the river dredging plan with the lowest cost and the best effect;

[0042] D3. Analysis of river dredging construction methods. Analysis of the river dredging scheme selection in step D2. According to the construction method, river dredging is divided into three categories: surface construction, shore construction and diversion tunnel construction;

[0043] Different construction methods are selected according to different situations to ensure that the dredging effect meets the requirements of pumping reliability.

[0044] Preferably, the specific steps of step S5 are as follows:

[0045] E1. Model design, production and verification;

[0046] E2. Working condition formulation and model test: including the working condition formulation using working conditions consistent with the numerical model simulation calculation, and conducting physical model test verification. The model terrain is based on the recommended river dredging plan, and the dredged terrain is used as the benchmark working condition for the model test. After the post-dredging working condition test is completed, the river terrain can be further restored to the pre-dredging terrain as a supplementary working condition for testing;

[0047] Model test and result analysis: set the initial water level to the normal water storage level, control the outflow of the upper reservoir, the outflow of the lower reservoir, and the pumping flow of the hybrid pumped storage according to the set operating flow, observe the water level change process of each section of the physical model test in real time, especially the water level funnel near the inlet / outlet of the lower reservoir, convert it into the actual hourly change process of the lower reservoir water surface line according to the similar scale, analyze the model test results from the indicators of the appearance time of the pumping funnel, the maximum depth, and the continuous pumping time, and finally judge the credibility of the pumping reliability results;

[0048] E3. Comparative analysis of numerical simulation and physical model results. Analysis of hydrodynamic laws is conducted by comparing the physical model test results and numerical simulation results to summarize the results.

[0049] Preferably, the specific steps of step E1 are as follows:

[0050] Model design: Based on the similarity principle, the hydraulic model of the lower reservoir is designed according to the gravity similarity criterion, using the normal model. The geometric scale is determined according to the size of the laboratory site and the need for model verification observation, and the scale of each hydraulic parameter is calculated accordingly;

[0051] Model making: The model simulation range is the whole river channel of the lower reservoir, from upstream to the corner of the dam of the upper reservoir, and from downstream to the front of the dam of the lower reservoir. The model simulation elevation is from the bottom of the lower reservoir to the normal water level plus a certain superelevation;

[0052] Verification of regulating reservoir capacity: Carry out a water filling test with a constant inflow on the model, that is, given a constant water filling flow, the water level in the model is filled from the dead water level to the normal water storage level, and the filling time is counted. It is converted into the actual total water storage according to the similarity criterion and compared with the required storage capacity of the lower reservoir river channel. The error is controlled within 3% to 5%. If the error is too large, the river channel in the model needs to be raised and narrowed or deepened and widened until the error meets the requirements;

[0053] River channel roughness correction: The calibration process is carried out according to the relationship between the measured constant flow and the corresponding water surface line. The measured constant flow is given according to the similarity criterion, and the water surface line of each section corresponding to the measurement model is compared with the measured river channel water surface line after conversion according to the similarity criterion. The roughness increase and decrease trend of each section of the river is analyzed, and the model roughness is adjusted by thickening or smoothing the cement surface, and locally increasing or decreasing pebbles. The water surface line and model roughness adjustment are repeatedly measured until the model measured water surface line is basically consistent with the measured result.

[0054] Preferably, the specific steps of step S6 are as follows:

[0055] F1. Propose the pumping reliability of hybrid pumped-storage reservoir:

[0056] From the perspective of pumping operation effect, the pumping reliability is proposed, and the pumping operation effect before and after river dredging is compared and analyzed. From the aspects of pumping time guarantee and pumping flow guarantee, the pumping reliability of hybrid pumped-storage reservoir is proposed;

[0057] The reliability is proposed from the perspective of the hydrodynamic characteristics of pumping operation, and the relevant result indicators of numerical simulation and physical model test are analyzed, including but not limited to the reservoir water surface line, local flow velocity and flow pattern of the inlet / outlet, the range of the inverse drop of the pumping funnel, the lowered water level, the river backwater length, and the minimum water depth. The hydrodynamic laws of pumping operation are summarized and refined, and on this basis, a multi-index evaluation method is used to propose the pumping reliability of the hybrid pumped-storage reservoir;

[0058] F2. Determine the pumping operation limit water level of the hybrid pumped-storage reservoir. According to the hydrodynamic laws obtained by numerical simulation and physical model test verification, analyze the reliability-related influencing factors, and summarize and propose the pumping limit water level of the lower reservoir, including the basis location and value of the limit water level.

[0059] The present invention provides a design method for improving the reliability of a hybrid pumped-storage lower reservoir, establishes a hybrid pumped-storage lower reservoir pumping-coupled hydrodynamic numerical simulation model, proposes the hydrodynamic characteristic law under the pumping condition of the lower reservoir through numerical simulation result analysis, summarizes the intrinsic relationship between pumping reliability and engineering layout and engineering measures, selects and determines targeted engineering measures, and determines a suitable river dredging plan by formulating different engineering measures (river dredging) plans and performing technical and economic comparisons. On this basis, hydraulic physical model tests are carried out to verify, and finally a quantified lower reservoir pumping reliability is proposed, as well as requirements for the lower reservoir pumping operation limit water level.

[0060] 1. The present invention adopts a coupled hydrodynamic simulation method to analyze the pumping reliability of the lower reservoir. By establishing a coupled numerical simulation model of the lower reservoir pumping operation and the hydrodynamic model, the numerical simulation results are statistically analyzed to reveal the relationship between the pumping operation of the hybrid pumped storage lower reservoir and the hydrodynamic response of the river. Hydrodynamic numerical simulation is carried out for a large number of different pumping conditions, different terrain conditions, engineering layouts and engineering measures, and the hydrodynamic laws of the lower reservoir pumping operation are summarized, and the inherent relationship between pumping reliability and pumping conditions, engineering layouts and engineering measures is summarized.

[0061] 2. The present invention combines the pumping hydrodynamic law and proposes a method for selecting effective engineering measures to improve pumping reliability. List various engineering measures to improve the water flow conditions of the lower reservoir pumping operation, including reducing the pumping flow, optimizing the inlet / outlet position and orientation, local widening of the inlet / outlet, and river dredging. Analyze the effects of different engineering measures, give priority to optimizing the inlet / outlet position and orientation, and if the improvement in pumping reliability after optimization is not enough, choose to dredge the river.

[0062] 3. The present invention adopts a multi-scheme technical and economic comparison method to determine the river dredging engineering measures. On the one hand, the proposed different river dredging schemes are subjected to hydrodynamic numerical simulation, the simulation results are summarized and the corresponding pumping effects of each scheme are quantified. On the other hand, the construction methods, construction difficulties and construction costs of different river dredging schemes are analyzed, and the corresponding cost of each scheme is quantified. The differences in the pumping effects and cost of each scheme are comprehensively compared, and the river dredging scheme with the best quantitative evaluation index is determined as the selected design scheme.

[0063] 4. The present invention carries out a full-reservoir physical model test to verify the pumping reliability of the lower reservoir. The physical model test of pumping reliability must establish a full-reservoir model, and the determination of the similarity scale should minimize the overall size of the model while giving priority to satisfying the observation accuracy of the physical model test. A certain range near the inlet / outlet of the lower reservoir where the pumping funnel phenomenon occurs should be designed as a completely similar river section. The physical model of the entire reservoir must review the regulated reservoir capacity, adopt a constant water filling method, and calibrate it by statistically analyzing the water storage capacity filled with water and the actual reservoir capacity, and make adjustments by raising, narrowing, deepening, or widening.

[0064] 5. Based on the results of hydrodynamic numerical simulation and physical model tests, the present invention proposes a method for quantitatively expressing the pumping reliability of a hybrid pumped-storage reservoir from the two perspectives of pumping operation effect and hydrodynamic characteristics of pumping operation by statistically analyzing the degree of deviation in pumping time, the degree of deviation in pumping flow, the depth, range and lowest flow velocity of the pumping funnel.

[0065] 6. The present invention has conducted a large amount of data analysis on the results of hydrodynamic numerical simulation and physical model test, and proposed a method for determining the limited water level of the lower reservoir pumping operation. The numerical simulation results of a large number of different pumping conditions are statistically analyzed, and the water level data when unreliable is screened for big data correlation analysis. The water level at the inlet / outlet of the lower reservoir is selected as the basis for judgment, and the specific value of the limited water level of pumping operation is determined.

[0066] 7. The present invention forms a complete design method for improving the pumping reliability of hybrid pumped-storage reservoirs, from the pumping-coupled hydrodynamic numerical model, to the hydrodynamic law and response relationship, to the technical and economic comparison to determine the engineering measures, to the physical model test verification, and finally to the proposal of the pumping reliability and operation limit water level of the lower reservoir. DETAILED DESCRIPTION

[0067] A design method to improve the reliability of hybrid pumped-storage reservoirs.

[0068] Step 1: Determine the constraints of the pumping condition. The constraints of the pumping condition mainly include the following:

[0069] (1) Identify the pumping period. Collect and organize the characteristics of the power system's off-peak period and the energy storage needs of complementary new energy sources to determine the scope of a single pumping cycle. For example, hybrid pumped storage based on complementary photovoltaics generally pumps water during the day when the radiation is high and the photovoltaic output is large, mainly from 10 a.m. to 5 p.m. (the photovoltaic characteristics of different regions may vary slightly, and the pumping period may be from 9 a.m. to 6 p.m.). Generally, a pumping and power generation cycle is carried out once a day.

[0070] (2) Analyze the pumping operation characteristics. Collect various engineering design parameters of hybrid pumped storage, including unit operation characteristics, pumping input characteristics, etc. The pumping condition considers an integer number of units pumping water, excluding the maintenance units. The actual pumping unit efficiency is determined according to the unit operation characteristics. The actual pumping flow is inferred from the pumping input, head and efficiency as the input condition for numerical simulation. The pumping flow calculation formula is as follows:

[0071]

[0072] H p =Z up -Z down +H ploss (Q p )

[0073] (Formula 1-2)

[0074] In the formula, Q p is the pumping flow rate, N p is the pumping input, K P is the comprehensive pumping input coefficient, H p is the pumping head, g is the acceleration due to gravity. p ) is the pumping efficiency of the water pump, and the pumping head H p η2 is the motor efficiency. Z up is the upper reservoir water level, Z down is the water level of the lower reservoir, H ploss (Q p ) is the increase in pumping head, which is related to the pumping flow rate Q p The two formulas are nested and require appropriate iterative calculations in practical applications.

[0075] (3) Sort out the pumping conditions. Sort out the various operating conditions that may occur in the hybrid pumped storage, analyze and propose typical unfavorable conditions and extremely unfavorable conditions for pumping operation. Among them, the outflow of the upper reservoir, the outflow of the lower reservoir, the continuous pumping time of the hybrid pumped storage, and the pumping flow are the four most important factors. For example, the condition where the outflow of the upper reservoir is the minimum discharge flow, the outflow of the lower reservoir is large, the continuous pumping time is long, and the full-power pumping (large pumping flow) is an extremely unfavorable condition; the condition where the outflow of the upper reservoir is appropriately increased, the outflow of the lower reservoir is appropriately reduced, the continuous pumping time is long, and the full-power pumping (large pumping flow) is a typical unfavorable condition. The formula for the sustainable pumping time and its relationship with the regulating reservoir capacity, the outflow of the upper reservoir, the outflow of the lower reservoir, and the pumping flow of the hybrid pumped storage is as follows:

[0076]

[0077] Where V tiao To regulate the storage capacity of the lower reservoir, Q p(t) is the pumping flow rate at different pumping periods (which can be calculated based on the pumping power and pumping head), Q in (t) is the inflow of the lower reservoir at different pumping periods (generally equal to the outflow of the upper reservoir plus the possible interval flow between the upper and lower reservoirs), Q out (t) is the outflow of the lower reservoir at different pumping periods, dt is the time interval between pumping periods, H max The maximum continuous pumping time.

[0078] (4) Pay attention to the situation where the water head changes greatly during the year (common in seasonal regulation reservoirs). If the drawdown depth of the upper and lower reservoirs of the hybrid pumped storage is large, the pumping flow rate under different water level heads during the year will also change accordingly. When the water level of the upper reservoir is low and the water level of the lower reservoir is high, the pumping head is small and the pumping flow rate is large, and the single pump input force is slightly greater than the single unit capacity; when the water level of the upper reservoir is high and the water level of the lower reservoir is low, the pumping head is large and the pumping flow rate is small, and the single pump input force is slightly less than the single unit capacity. The calculation formula for the maximum pumping flow rate and the minimum pumping flow rate during the year is as follows:

[0079]

[0080] In the formula, Q pmax is the maximum pumping flow in the year, N pmax is the maximum pumping input, equal to the installed capacity N capacity Multiply by the maximum pumping power coefficient R max (generally greater than 1); H pmin is the minimum pumping head, which appears in the upper reservoir as dead water level The lower reservoir is at normal water level Maximum increase in lift H ploss (Q pmax ) situation. pmin is the minimum pumping flow in the year, N pmin is the minimum pumping input, equal to the installed capacity N capacity Multiply by the minimum pumping power coefficient R min (usually less than 1); H pmax is the maximum pumping lift, which appears at the upper reservoir when the water level is normal The lower reservoir is dead water level Minimum head increase H ploss (Q pmin ) situation.

[0081] (5) Determine the pumping operation constraints. The water balance and the lower reservoir water level operating range restrictions should be met. The outflow of the upper and lower reservoirs must also meet the ecological and unit minimum discharge flow requirements. When the pumping operation starts, the initial water level of the lower reservoir is generally the normal water storage level.

[0082] Water balance constraints:

[0083] V down (t+1)=V down (t)+(Q in (t)-Q out (t)-Q p (t))*dt (Formula 1-6)

[0085] Where V down (t+1) is the water storage capacity of the lower reservoir in the next period, V down (t) is the water storage capacity of the lower reservoir in the current period, Q in (t) is the inflow flow of the lower reservoir in the current period, Q out (t) is the outflow of the lower reservoir in the current period, Q p (t) is the pumping flow rate at different pumping periods, and dt is the time interval between pumping periods.

[0086] Reservoir water level constraints:

[0087] Z min ≤Z down (t)≤Z max (Formula 1-7)

[0089] In the formula, Z down (t) is the water level of the lower reservoir in the current period, Z min is the lowest water level for pumping in the lower reservoir (if there is no pumping restriction, the lowest level can be the dead water level), Z max This is the maximum water level for pumping in the lower reservoir (if there is no pumping restriction, the maximum water level can be the normal storage level).

[0090] Ecological and unit minimum downstream flow constraints:

[0091] Q(t)≥max(Q env ,Q min ) (Formula 1-8)

[0093] Where Q(t) is the power generation flow of the upper reservoir or lower reservoir in the current period, Q env is the ecological flow that should be guaranteed by the upper or lower reservoir, Q min The minimum downstream flow required for the upper reservoir or lower reservoir unit to generate electricity.

[0094] Step 2: Establish a numerical simulation model of the lower reservoir pumping coupled hydrodynamics

[0095] The theoretical basis of hydrodynamic simulation involves continuity equation and momentum equation, basic equations of fluid mechanics, boundary conditions and initial conditions, and numerical calculation methods. The establishment of the numerical simulation model of pumping coupled hydrodynamics of the lower reservoir includes the following contents:

[0096] (1) Determine the research object and research period. The research object of the numerical model is the entire lower reservoir. The research period is a single pumping cycle.

[0097] (2) Determine the theoretical formula and calculation method of the model. The model is built using the basic equations of fluid mechanics, but needs to be modified for the unsteady flow under pumping simulation, including the continuity equation (mass conservation equation), momentum equation, etc. The following is the two-dimensional Saint-Venant equations for unsteady flow:

[0098] h=Hz

[0099] (Formula 2-1)

[0100] Where h is the water depth; H is the water level elevation; and Z is the riverbed elevation.

[0101] Considering that pumping simulation is a non-steady flow, its source and sink terms are not equal to 0, and its continuity equation is:

[0102]

[0103] Where x and y are the distance coordinates in the Cartesian rectangular coordinate system; t is the time coordinate; u and v are the flow velocities in the x and y directions respectively; and q is the source-sink vector.

[0104] Similarly, its momentum equation is expressed as follows:

[0105]

[0106] Where g is the acceleration due to gravity; v is t is the turbulent viscosity coefficient; c f is the bottom friction coefficient; f is the Coriolis coefficient.

[0107] The model uses numerical calculation methods such as finite difference method, finite element method, finite volume method, etc. to solve the basic equations, and finally obtains parameters such as fluid velocity and pressure on different grids through numerical iterative calculation.

[0108] (3) Determine the model boundary conditions. In the hydrodynamic simulation of reservoir pumping, boundary conditions need to be defined to describe the interaction between the fluid and the solid boundary, including fixed boundary conditions (such as solid wall, wall friction), free boundary conditions (such as free water surface) and inlet / outlet boundary conditions.

[0109] The model uses the initial water level elevation as the water level at the initial moment of hydrodynamic calculation and defines three water inlet / outlet boundaries of the lower reservoir: the outflow of the upper reservoir power station in, the outflow of the lower reservoir power station out, and the outflow of the pumped flow of the hybrid pumped storage or the inflow of the power generation flow.

[0110] (4) Organize terrain data. Collect surveying and mapping data of the entire reservoir. The surveying and mapping accuracy must meet the accuracy requirements for supporting hydrodynamic simulation, and organize the terrain data of the riverbed and reservoir bank. If necessary, discrete interpolation can be used to generate raster terrain data with a resolution of 1m×1m.

[0111] (5) Perform grid division and determine the grid size. Generate a two-dimensional grid of the water body. By dividing the water body into small grid units, the horizontal and vertical distribution of the water flow can be represented. The resolution and accuracy of the grid can be adjusted as needed, taking into account both the calculation accuracy and the calculation time. When modeling terrain, the denser the grid division, the higher the calculation accuracy, but the single calculation time increases exponentially.

[0112] By adopting a non-uniform grid division method, the area of ​​a single grid is appropriately increased in relatively unimportant areas, and the grid is encrypted in important local river sections near the inlet / outlet, which can coordinate the relationship between grid density, calculation time and calculation accuracy.

[0113] (6) Determine the calculation step size. The calculation time step size will affect the calculation accuracy of the hydraulic simulation of the lower reservoir pumping, especially when the pumping reliability is very low and water extraction is difficult, the model may not converge in iteration. In order to evaluate the sensitivity of the simulation results to the change of the time step size, different simulation time steps can be selected to simulate the same terrain, keep other boundary conditions unchanged, and analyze the sensitivity of the simulation results.

[0114] (7) Calibrate the riverbed roughness. Calibrate the riverbed roughness of the hydrodynamic model based on the relationship between the measured flow and the corresponding water surface line. First, measure the flow of the river section and obtain the corresponding water surface line. Then, input an assumed roughness value into the hydrodynamic simulation software and simulate according to the measured flow to obtain the water surface line of each section of the river. According to the deviation between the simulated value and the measured value of the water surface line, adjust the calculated roughness value according to the basic principles of hydrodynamics (the greater the roughness, the greater the water flow resistance and the increase in the height of the water surface line) and re-simulate. Repeat the above steps and perform repeated calculations until the simulation results are basically consistent with the measured results. At this time, it can be considered that the calibrated roughness can reflect the actual water flow resistance.

[0115] Considering that the gradient, riverbed composition, cross-sectional geometry, etc. of long-distance rivers may vary greatly, in order to ensure that the calibration results can more accurately reflect the actual terrain characteristics of the river channel, the riverbed roughness can be set in sections according to the above factors. At the same time, the calibration method can be adopted to improve the calibration efficiency.

[0116] (8) Model rationality analysis. The first step is to judge the reliability of the simulation results under different initial conditions based on the laws of hydrodynamics. For example, when other conditions remain unchanged, as the flow rate in the river increases, the water level in the river will increase, and the flow rate will also increase. The second step is to use measured data to analyze the accuracy of the simulation results, and use indicators such as correlation coefficient and Nash coefficient to judge the accuracy of the simulated water level process and the measured process. If the correlation coefficient or Nash coefficient is greater than 0.8 (and p-value < 0.05), it can be considered that the results simulated by this model have a high degree of credibility.

[0117] Step 3: Establish the hydrodynamic response relationship of pumping reliability

[0118] (1) Analysis of hydrodynamic characteristics of pumping condition reliability

[0119] Focus on the pumping funnel phenomenon, determine the range of the inverse drop of the river water level through numerical simulation, observe the time and characteristics of the funnel, summarize the hydrodynamic response law of the pumping condition, and judge the reliability of the hybrid pumped storage pumping condition. The steps are as follows:

[0120] 1) Apply the hydrodynamic numerical simulation model to obtain the calculation results under different typical pumping conditions, including the reservoir water surface curve results, local flow velocity, flow state and water surface changes at the inlet / outlet, etc.

[0121] 2) Analyze various indicators such as the range of the inverse proportional drop of the pumping funnel, the lowered water level, the river backwater length, and the minimum water depth.

[0122] 3) Determine whether low-water level pumping is reliable from multiple aspects, such as the degree of guarantee of pumping time, the degree of guarantee of pumping flow, the depth and range of the inverse proportional drop of the pumping funnel, the flow rate at the lowest point of the funnel, etc.

[0123] (2) Relationship between pumping reliability and river topography, pumping conditions, engineering layout, and engineering measures

[0124] Combining the pumping simulation results under different river topography, pumping conditions, engineering layouts and engineering measures, we compared and analyzed different inlet / outlet flow patterns and hydrodynamic conditions, analyzed the sensitive factors affecting pumping, and formed the relationship between pumping reliability and topography and engineering layout.

[0125] Summarizing the experience of numerical simulation and model tests of existing projects, the response law between the hydrodynamic conditions of pumping reliability and pumping conditions, project layout and engineering measures is as follows:

[0126] 1) The smaller the outflow of the upper reservoir, the larger the hybrid pumped storage flow, and the larger the outflow of the lower reservoir, the higher the demand for the regulating storage capacity of the lower reservoir, the more obvious the pumping funnel effect, the worse the guarantee of the pumping time, and the lower the pumping reliability.

[0127] 2) When arranging the reservoir inlet / outlet in a narrow river channel, the water flow conditions for pumping can be improved by properly optimizing the inlet / outlet position and adjusting the inlet / outlet orientation angle, and the effect of improving pumping reliability is more obvious.

[0128] 3) Pumping reliability is related to the cross-sectional area of ​​the entire reverse-flow river channel and is controlled by the bottleneck of the narrowest section. By widening and deepening the river channel, maintaining the unobstructed cross-sectional area of ​​the entire river channel and reaching a certain length range, improving the overall cross-sectional area and water replenishment capacity, it is beneficial to improve pumping reliability. However, the effect of only expanding local excavation near the inlet / outlet and increasing local storage capacity is not significant.

[0129] 4) River dredging is mainly concentrated in the areas downstream of the inlet / outlet where reverse flow may occur, while the effect of dredging in the upstream areas of the inlet / outlet is not significant.

[0130] Step 4: Technical and economic comparison to determine the appropriate engineering measures

[0131] (1) Selection of engineering measures

[0132] Combined with the analysis of model results, various engineering measures are proposed to improve hydraulic conditions and water flow stability.

[0133] The most direct solution is to reduce the scale of hybrid pumped storage, thereby reducing the pumping flow, which will effectively improve the pumping reliability. The second is to reduce the call for pumping units during operation, thereby reducing the pumping flow and extending the pumping time.

[0134] Under the condition that the scale of the project remains unchanged and the design requirements are not reduced, the optional engineering measures include optimizing the location of the inlet / outlet, adjusting the direction of the inlet / outlet, dredging the river, and partially widening the inlet / outlet.

[0135] In combination with the response law of hydrodynamic conditions of pumping reliability, the most effective measure, in addition to optimizing the water flow conditions at the inlet / outlet, is to dredge and regulate the river channel, increase the water-passing cross-sectional area, and keep the entire river channel unobstructed.

[0136] (2) Comparison and selection of river dredging project measures

[0137] Specific methods and steps for comparing river dredging project measures:

[0138] 1) Initially formulate different river dredging plans, including dredging river length, dredging width and depth, etc.

[0139] 2) According to the river dredging plan, the riverbed topography data is revised and the grid is re-divided, and the hydrodynamic simulation is re-performed.

[0140] 3) Further analyze the hydrodynamic results after river dredging, conduct comparative analysis on the hydrodynamic coupling simulation results of different schemes, evaluate whether the pumping guarantee capacity of the hybrid pumped-storage project is improved, and whether the operational reliability of the pumping conditions meets the requirements. The quantitative formula for the evaluation index of the pumping time guarantee of different dredging schemes is as follows:

[0141]

[0142] Where V ensureH is the pumping time guarantee index, including the maximum capacity satisfaction and the minimum capacity non-satisfaction penalty. The weight coefficients R1 and R2 are used to normalize the index respectively. max is the designed maximum continuous pumping time, H min is the minimum continuous pumping time that must be guaranteed in the design, and H is the continuous pumping time calculated by numerical simulation.

[0143] 4) Analyze the river dredging construction methods and construction difficulty of each scheme, consider the cost of measures, and calculate the engineering quantity and investment cost. The quantitative formula of the cost index of different dredging schemes is as follows:

[0144]

[0145] In the formula, C con is the dredging cost index, including the construction project investment cost and the construction difficulty risk. The weight coefficients R3 and R4 are used to normalize the index respectively. budget is the design of an acceptable project investment cost budget, C is the estimated construction project investment cost, R diff It is an evaluation index of the construction difficulty and construction risk of the construction method. The larger the value, the greater the difficulty and risk.

[0146] 5) Conduct a comprehensive technical and economic comparison, comprehensively consider the effects and costs of each plan, calculate the comprehensive evaluation index, and select the river dredging plan with the lowest cost and the best effect. The comprehensive evaluation quantitative formula for different dredging plans is as follows:

[0147] E sunmary =V ensure -C con

[0148] (Formula 4-3)

[0149] (3) Analysis of river dredging construction methods

[0150] Based on the analysis of step 4 of the above-mentioned river dredging scheme comparison, according to the construction method, river dredging is divided into three categories: surface construction, shore construction and diversion tunnel construction.

[0151] 1) Water surface construction. Water surface construction generally uses dredging boats, building water surface working platforms, etc. to directly carry out underwater dredging. First, a long-arm excavator is used to dig away large volumes of slag, and then a grab bucket and suction cup are used to clean up the remaining small pieces of stone and gravel. At present, there are relatively advanced grab buckets and suction cups, which have good dredging and silt removal effects. This type of method is suitable for situations where the water flow is relatively gentle and the river channel is relatively wide. It is often used for silting and sand removal in plain rivers. It is less suitable for deep mountain canyon terrain. When the water flow is turbulent, it is difficult to fix the dredging boat and the working platform, and there is a greater safety risk.

[0152] 2) Shore construction. Shore construction mainly adopts the method of alternately padding slag and retreating dredging on both sides, that is, first pad slag into the river to form a shore construction platform, then use a long-arm excavator to excavate, and then continue to retreat until the shore. After dredging on one side of the river, construction will be switched to the other side. The dredging effect is mainly subject to the maximum capacity of the construction machinery. For example, the maximum digging depth of the long-arm excavator determines the minimum depth of dredging, and the bucket volume of the long-arm excavator determines the total dredging volume and construction period. The current construction machinery is still difficult to achieve large-scale and deep river dredging, especially when the river is difficult to maintain low water level and low flow, the shore construction platform is easily flooded, and the construction effect and construction organization are difficult to guarantee.

[0153] 3) Construction of diversion tunnel. When the above two methods are difficult to solve the problem of river dredging in the hybrid pumped storage project, it can be considered to combine it with the construction of the lower reservoir inlet / outlet, and adopt a construction plan of diversion tunnel plus downstream cofferdam to provide dry land construction conditions for river dredging and removal of the rock sill reserved for the lower reservoir inlet / outlet. This method is not only convenient for the construction equipment to enter the site and achieve high-intensity excavation efficiency, but also can clean the river to form a regular and ideal river water-passing section, remove the rock sill reserved for the inlet / outlet cleanly and flatly, ensure the smooth flow of water at the inlet / outlet and the entire dredged river section, control the construction process and construction effect, and the risk of construction safety is relatively small. This method is suitable for the case where the dredged river section is not long. When encountering a curved river terrain, the length of the diversion tunnel can be shortened. If the dredging range exceeds 2km, the amount of tunnel construction will increase and the cost will be unbearable.

[0154] In summary, hybrid pumped-storage projects may encounter problems with river dredging construction downstream of the reservoir inlet / outlet. Different construction methods can be selected according to different situations to ensure that the dredging effect meets the requirements of pumping reliability.

[0155] Step 5: Conduct physical model tests for verification

[0156] A physical model test of the entire lower reservoir is established to verify the hydrodynamic characteristics and river dredging effects, so as to achieve the purpose of improving the operational reliability of the hybrid pumped-storage lower reservoir pumping conditions.

[0157] (1) Model design, production and verification

[0158] 1) Model design. The physical model test of pumping reliability must establish a full-reservoir model. Considering that the length of the whole reservoir of a river-type reservoir is relatively long (may be as long as tens of kilometers), the determination of the similarity scale should minimize the overall size of the model while giving priority to the observation accuracy of the physical model test. According to the similarity principle, the hydraulic model of the whole reservoir of the lower reservoir is designed according to the gravity similarity criterion, using the normal model. The geometric scale is determined according to the size of the laboratory site and the needs of model verification observation, and the scales of various hydraulic parameters are calculated accordingly, such as length scale, velocity scale, flow scale, time scale, sediment particle size scale, roughness scale, etc.

[0159] 2) Model making. The model simulation range is the entire river channel of the lower reservoir, from upstream to the corner of the dam of the upper reservoir, and from downstream to the front of the dam of the lower reservoir. The model simulation elevation is from the bottom of the lower reservoir to the normal water storage level plus a certain superelevation. Among them, in order to ensure the accuracy and rationality of the simulation of pumping reliability, the river section from the inlet / outlet of the lower reservoir to a distance upstream and a distance downstream is designed to be completely similar (that is, the river model terrain and direction are completely consistent with the measured terrain); the remaining river sections try to ensure that the river direction is consistent with the actual one, but considering the layout conditions of the test site, the direction can be appropriately adjusted on the premise of ensuring the similarity of the river terrain. The river terrain can be formed by the section panel method and cement mortar, and the inlet / outlet of the lower reservoir can be made of plexiglass.

[0160] 3) Verification of regulating reservoir capacity. Since the regulating reservoir capacity of the lower reservoir is closely related to the pumping reliability, the regulating reservoir capacity must be reviewed to ensure the accuracy and rationality of the model test verification results of the pumping reliability of the lower reservoir inlet / outlet. The specific method is to conduct a water filling test with a constant inflow on the model. That is, given a constant filling flow, the water level in the model starts to fill from the dead water level to the normal water storage level, the filling time is counted, and converted into the actual total water storage according to the similarity criterion, and compared with the required storage capacity for the river water storage of the lower reservoir, the error is controlled within 3% to 5%. If the error is too large, the river channel in the model needs to be raised and narrowed or deepened and widened until the error meets the requirements.

[0161] 4) Correction of river roughness. Since the river terrain is formed by artificial plastering, the roughness of the model is usually less than that of the natural river. After the model river is completed and the regulation reservoir capacity is verified, it is necessary to correct the roughness. The calibration process is based on the relationship between the measured constant flow and the corresponding water surface line. According to the similarity criterion, the measured constant flow is given, and the water surface line of each section of the model is measured. After conversion according to the similarity criterion, the error is compared with the measured river water surface line, and the roughness increase and decrease trend of each section of the river is analyzed. The model roughness is adjusted by thickening or smoothing the cement plastering, locally increasing or reducing pebbles, etc. Repeat the measurement of the water surface line and the model roughness adjustment until the model measured water surface line is basically consistent with the measured result.

[0162] (2) Working condition formulation and model test

[0163] 1) Working condition formulation. Generally, working conditions consistent with the numerical model simulation calculation can be used to conduct physical model test verification. If the flow rate input in the numerical model test fluctuates too frequently, the input flow rate needs to be continuously adjusted in the actual physical model. On the one hand, unstable flow state may be generated, affecting the accuracy of the physical model. On the other hand, the inaccurate flow adjustment operation may increase the model error, resulting in a mismatch between the numerical simulation and the physical model. Therefore, it is recommended that the model working conditions, on the basis of meeting the needs of reliability verification, ensure the long-term stability of the flow rate as much as possible and reduce frequent changes in the flow rate.

[0164] The model terrain is based on the recommended river dredging plan, and the terrain after dredging is used as the benchmark working condition for the model test. After the working condition test after dredging is completed, the river terrain can be further restored to the terrain before dredging as a supplementary working condition for testing.

[0165] 2) Model test and result analysis. Set the initial water level to the normal water storage level, control the outflow of the upper reservoir, the outflow of the lower reservoir, and the pumping flow of the hybrid pumped storage according to the set operating flow, and observe the water level changes of each section of the physical model test in real time, especially the water level funnel near the inlet / outlet of the lower reservoir, and convert it into the actual hourly change process of the lower reservoir water surface line according to the similar scale. Analyze the model test results based on indicators such as the time when the pumping funnel appears, the maximum depth, and the continuous pumping time, and finally judge the credibility of the pumping reliability results.

[0166] (3) Comparative analysis of numerical simulation and physical model results

[0167] The hydrodynamic laws were analyzed and summarized by comparing the results of physical model tests and numerical simulation results. The following laws were summarized:

[0168] 1) When the narrow river channel type lower reservoir encounters an extreme working condition with a relatively small net inflow, the hybrid pumping and storage process is affected by the insufficient hydraulic recharge capacity of the local river section, and a drop funnel will be generated within a certain range near the inlet / outlet of the lower reservoir.

[0169] 2) During the hybrid pumped-storage process, the hydraulic recharge capacity of the inlet / outlet river section further decreases as the water level of the lower reservoir decreases, which further increases the depth and range of the drop funnel generated during pumping.

[0170] 3) The results of the physical model test show that the depth and range of the drop funnel generated by the actual pumping process of the hybrid pumped storage are basically consistent with the results of the mathematical model simulation, and the physical model results are slightly smaller, which is more beneficial to the pumping reliability.

[0171] 4) By dredging the river channel at the inlet / outlet, the hydraulic recharge conditions can be improved, the depth and range of the pumping funnel can be reduced, and the reliability and guarantee rate of continuous long-term pumping can be greatly improved.

[0172] 5) When encountering extreme conditions with small net inflow, the inflow at the tail of the lower reservoir is pumped away, and there is no other inflow replenishment in the reservoir. The water body in front of the dam has no inflow replenishment and needs to continue to discharge downstream, which makes the water level in front of the dam produce a hydraulic gradient downstream, showing a non-horizontal section. The physical model can reflect this feature better than the mathematical model, and the physical model is more obvious.

[0173] Step 6: Propose the pumping reliability and operating water level of the hybrid pumped-storage reservoir

[0174] (1) Propose the reliability of pumping water in hybrid pumped-storage reservoirs

[0175] 1) Pumping reliability is proposed from the perspective of pumping operation effect.

[0176] A comparative analysis was made on the pumping operation effects before and after river dredging, and the pumping reliability of the hybrid pumped-storage reservoir was proposed from the aspects of pumping time guarantee and pumping flow guarantee.

[0177] V ensure =V ensureH +V ensureQ (Formula 6-1)

[0179] In the formula, V ensure is the pumping reliability of the lower reservoir, V ensureH is the pumping time guarantee index, see formula 18. V ensureQ For the pumping flow guarantee index, the following formula can be used:

[0180] V ensureQ =1-R5(Q(Hmin)-Q′ Hmin)-R6(Q(Hmid)-Q′ Hmid )-R7(Q(Hmax)-Q′ Hmax ) (Formula 6-2)

[0182] Where V ensureQ H is the pumping flow guarantee index, including the deviation degree of the maximum pumping time corresponding to the flow, the deviation degree of the intermediate pumping time corresponding to the flow, and the deviation degree of the minimum capacity pumping time corresponding to the flow. The weight coefficients R5, R6 and R7 are used to normalize the index respectively. The larger the deviation, the more deductions are made, and the smaller the deviation, the closer the guarantee index is to 1. max is the designed maximum continuous pumping time, H min H is the minimum continuous pumping time that must be guaranteed in the design. mid is the designed average continuous pumping time. Q′ Hmin , Q′ Hmid , Q′ Hmax They are the corresponding designed pumping flow rates corresponding to the designed continuous pumping time. Since the water level of the lower reservoir continues to drop as the pumping time continues, the pumping flow rates at different times are different. Q(Hmin), Q(Hmid), and Q(Hmax) are the simulated pumping flow rates corresponding to the designed continuous pumping time obtained by numerical simulation.

[0183] 2) Reliability is proposed from the perspective of the hydrodynamic characteristics of pumping operation.

[0184] The relevant result indicators of numerical simulation and physical model test are analyzed (including but not limited to reservoir water surface line, local flow velocity and flow state of inlet / outlet, range of inverse proportional drop of pumping funnel, lowered water level, river backwater length, minimum water depth, etc.), and the hydrodynamic laws of pumping operation are summarized and refined. On this basis, a multi-indicator evaluation method is adopted to propose the pumping reliability of hybrid pumped-storage reservoir.

[0185] V ensure =1-K1H funnel -K2L funnel -K3V funnel -…-K n X funnel

[0186] (Formula 6-3)

[0187] Where V ensure is the pumping reliability of the lower reservoir, including but not limited to the depth H of the pumping funnel inverse drop funnel 、Range L funnel , flow velocity V at the lowest point of the funnel funnel And other aspects, respectively use weight coefficients K1, K2, K3 to K nThe more obvious the pumping funnel phenomenon is, the larger the corresponding pumping funnel depth, range, flow rate and other indicators are, the more the corresponding reliability will be deducted, and the smaller the pumping funnel indicator is, the closer the reliability indicator is to 1.

[0188] (2) Determine the pumping operation limit water level of the hybrid pumped-storage reservoir.

[0189] Based on the hydrodynamic laws verified by numerical simulation and physical model tests, the reliability-related influencing factors are analyzed (such as the regulating storage capacity of the lower reservoir, pumping power or flow, outflow flow of the upper and lower reservoirs, inlet / outlet location, inlet / outlet orientation angle, length of the funnel influence zone of reverse flow, cross-sectional area of ​​the river channel in the funnel influence zone, etc.), and the lower reservoir pumping limit water level is summarized and proposed, including the basis position and value of the limit water level.

[0190] When the storage capacity of the lower reservoir is large, the water surface is wide, and the pumping funnel effect is not obvious, the location of the lower reservoir pumping operation limit water level can refer to the water level in front of the lower reservoir dam. The value is set reasonably after research and analysis. It can be the dead water level of the lower reservoir, or a water level higher than the dead water level.

[0191] When the inlet / outlet of the lower reservoir is located in a narrow and long river channel and the pumping funnel effect is more obvious, the water level at the inlet / outlet will be lower than the water level in front of the lower reservoir dam under pumping conditions. The basis for judging the unreliable pumping operation should not be the water level in front of the lower reservoir dam, nor the remaining storage capacity of the lower reservoir. Instead, the focus should be on the situation of the inlet / outlet of the lower reservoir for control. That is, the position for judging the water level limit should be selected at the water level at the inlet / outlet of the lower reservoir.

[0192] The value of the restricted water level can be determined by analyzing the results of numerical simulation. A large number of numerical simulation results corresponding to different flow conditions can be statistically analyzed. A large amount of water level data when unreliable can be analyzed for big data, and finally a reasonable restricted water level for pumping operation of the lower reservoir can be determined. If necessary, the warning water level for pumping operation of the hybrid pumped storage lower reservoir can also be determined by considering the early warning, decision-making, feedback and operation time requirements of the actual operation and scheduling.

[0193] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A design method for improving the reliability of a hybrid pumped storage reservoir, characterized by: The design method steps are as follows: S1. Determine the constraints of pumping conditions; S2. Establish a numerical simulation model of the pumping-coupled hydrodynamics of the lower reservoir; S3, establish the hydrodynamic response relationship of pumping reliability; S4. Determine the appropriate engineering measures through technical and economic comparison; S5. Conduct physical model tests for verification; S6. Propose the pumping reliability and operating limit water level of the lower reservoir.

2. A design method for improving the reliability of a hybrid pumped storage reservoir according to claim 1, characterized in that: The constraints of the pumping conditions in step S1 include clarifying the pumping period, analyzing the pumping operation characteristics, sorting out the pumping conditions, and paying attention to the situation where the water head changes greatly within the year; The water balance and the lower reservoir water level operating range restrictions should be met; the outflow flows of the upper and lower reservoirs must also meet the ecological and unit minimum downstream flow requirements. When the pumping condition begins, the initial water level of the lower reservoir is generally the normal water storage level.

3. A design method for improving the reliability of a hybrid pumped storage reservoir according to claim 1, characterized in that: The specific steps of step S2 are as follows: B1. Determine the research object and research period. The research object of the numerical model is the entire lower reservoir, and the research period is a single pumping cycle; B2. Determine the theoretical formula and calculation method of the model. The model is built using the basic equations of fluid mechanics and needs to be modified for the unsteady flow under pumping simulation, including the continuity equation and momentum equation; The model uses the numerical calculation methods of finite difference method, finite element method and finite volume method to solve the basic equations, and finally obtains the fluid velocity and pressure parameters on different grids through numerical iterative calculation; B3. Determine the model boundary conditions. In the hydraulic simulation of the lower reservoir pumping, boundary conditions need to be defined to describe the interaction between the fluid and the solid boundary, including fixed boundary conditions, free boundary conditions and inlet / outlet boundary conditions; The model uses the initial water level elevation as the water level at the initial moment of hydrodynamic calculation and defines three water inlet / outlet boundaries of the lower reservoir: inflow from the upper reservoir power station, outflow from the lower reservoir power station, and outflow or inflow from the pumped flow of the hybrid pumped storage; B4. Organize terrain data and collect surveying and mapping data of the entire reservoir. The surveying and mapping accuracy must meet the accuracy requirements for supporting hydrodynamic simulation, and organize the terrain data of the riverbed and reservoir bank; B5. Perform grid division, determine the grid size, generate a two-dimensional grid of the water body, and divide the water body into small grid cells to represent the horizontal and vertical distribution of the water flow. The resolution and accuracy of the grid are adjusted as needed; The non-uniform grid division method is adopted to appropriately increase the area of ​​a single grid in relatively unimportant areas, and to encrypt the grids of important local river sections near the inlet / outlet, which can coordinate the relationship between grid density, calculation time and calculation accuracy. B6. Determine the calculation step size, select different simulation time steps to simulate the same terrain, keep other boundary conditions unchanged, and analyze the sensitivity of the simulation results; adopt a segmented simulation strategy with different calculation steps, select a larger time step when the pumping reliability is high to improve the calculation efficiency; and use a smaller time step when the pumping reliability is low to ensure the accuracy of the simulation results at critical moments; B7. Determine the riverbed roughness. According to the relationship between the measured flow and the corresponding water surface line, the river channel of the lower reservoir is divided into multiple sections and calibrated section by section to calibrate the riverbed roughness of the hydrodynamic model. B8. Model rationality analysis: The reliability of simulation results under different initial conditions is judged according to the hydrodynamic laws. The accuracy of simulation results is analyzed using measured data. The correlation coefficient and Nash coefficient indicators are used to judge the accuracy of the simulated water level process and the measured process. If the correlation coefficient or Nash coefficient is greater than 0.8 and the p-value is <0.05, it is considered that the results simulated by this model have a high degree of credibility.

4. A design method for improving the reliability of a hybrid pumped storage reservoir according to claim 1, characterized in that: The specific steps of step S3 are as follows: C1. Analysis of the hydrodynamic characteristics of the pumping condition reliability, focusing on the pumping funnel phenomenon, determining the range of the inverse proportional drop of the river water level through numerical simulation, observing the time and characteristics of the funnel, summarizing the hydrodynamic response law of the pumping condition, and judging the reliability of the hybrid pumped-storage pumping condition; C2. The response relationship between pumping reliability and river topography, pumping conditions, engineering layout and engineering measures. Combined with the pumping simulation results under different river topography, pumping conditions, engineering layout and engineering measures, the different inlet / outlet flow patterns and hydrodynamic conditions are compared and analyzed, and the sensitive factors affecting pumping are analyzed to form the relationship between pumping reliability and topography and engineering layout.

5. A design method for improving the reliability of a hybrid pumped storage reservoir according to claim 4, characterized in that: The specific steps of step C1 are as follows: Apply the hydrodynamic numerical simulation model to obtain the calculation results under different typical pumping conditions, including the reservoir water surface line results, local flow velocity, flow state and water surface changes at the inlet / outlet; Analyze the range of the reverse drop of the pumping funnel, the lowered water level, the length of the river backwater, and the minimum water depth; Whether low-water-level pumping is reliable can be judged from multiple aspects, including the degree of guarantee of pumping time, degree of guarantee of pumping flow, depth and range of inverse proportional drop of the pumping funnel, and flow velocity at the lowest point of the funnel.

6. A design method for improving the reliability of a hybrid pumped storage reservoir according to claim 1, characterized in that: The specific steps of step S4 are as follows: D1. Selection of engineering measures: Based on the analysis of model results, various engineering measures to improve hydraulic conditions and water flow stability are proposed; D2. Comparison and selection of river dredging project measures: Initially draft different river dredging plans, including dredging river length, dredging width and depth; Correct the riverbed topography data and re-divide the grid according to the river dredging plan, and re-perform the hydrodynamic simulation; Further analyze the hydrodynamic results after river dredging, conduct comparative analysis on the hydrodynamic coupling simulation results of different schemes, evaluate whether the pumping guarantee capacity of the hybrid pumped-storage project is improved, and whether the operational reliability of the pumping condition meets the requirements; Analyze the river dredging construction methods and construction difficulty of each plan, consider the cost of measures, and calculate the engineering quantity and investment cost; Conduct a comprehensive technical and economic comparison, comprehensively consider the effects and costs of various plans, calculate comprehensive evaluation indicators, and select the river dredging plan with the lowest cost and the best effect; D3. Analysis of river dredging construction methods. Analysis of the river dredging scheme selection in step D2. According to the construction method, river dredging is divided into three categories: surface construction, shore construction and diversion tunnel construction; Different construction methods are selected according to different situations to ensure that the dredging effect meets the requirements of pumping reliability.

7. A design method for improving the reliability of a hybrid pumped storage reservoir according to claim 1, characterized in that: The specific steps of step S5 are as follows: E1. Model design, production and verification; E2. Working condition formulation and model test: including the working condition formulation using working conditions consistent with the numerical model simulation calculation, and conducting physical model test verification. The model terrain is based on the recommended river dredging plan, and the dredged terrain is used as the benchmark working condition for the model test. After the post-dredging working condition test is completed, the river terrain can be further restored to the pre-dredging terrain as a supplementary working condition for testing; Model test and result analysis: set the initial water level to the normal water storage level, control the outflow of the upper reservoir, the outflow of the lower reservoir, and the pumping flow of the hybrid pumped storage according to the set operating flow, observe the water level change process of each section of the physical model test in real time, especially the water level funnel near the inlet / outlet of the lower reservoir, convert it into the actual hourly change process of the lower reservoir water surface line according to the similar scale, analyze the model test results from the indicators of the appearance time of the pumping funnel, the maximum depth, and the continuous pumping time, and finally judge the credibility of the pumping reliability results; E3. Comparative analysis of numerical simulation and physical model results. Analysis of hydrodynamic laws is conducted by comparing the physical model test results and numerical simulation results to summarize the results.

8. A design method for improving the reliability of a hybrid pumped-storage reservoir according to claim 7, characterized in that: The specific steps of step E1 are as follows: Model design: Based on the similarity principle, the hydraulic model of the lower reservoir is designed according to the gravity similarity criterion, using the normal model. The geometric scale is determined according to the size of the laboratory site and the need for model verification observation, and the scale of each hydraulic parameter is calculated accordingly; Model making: The model simulation range is the whole river channel of the lower reservoir, from upstream to the corner of the dam of the upper reservoir, and from downstream to the front of the dam of the lower reservoir. The model simulation elevation is from the bottom of the lower reservoir to the normal water level plus a certain superelevation; Verification of regulating reservoir capacity: Carry out a water filling test with a constant inflow on the model, that is, given a constant water filling flow, the water level in the model is filled from the dead water level to the normal water storage level, and the filling time is counted. It is converted into the actual total water storage according to the similarity criterion and compared with the required storage capacity of the lower reservoir river channel. The error is controlled within 3% to 5%. If the error is too large, the river channel in the model needs to be raised and narrowed or deepened and widened until the error meets the requirements; River channel roughness correction: The calibration process is carried out according to the relationship between the measured constant flow and the corresponding water surface line. The measured constant flow is given according to the similarity criterion, and the water surface line of each section corresponding to the measurement model is compared with the measured river channel water surface line after conversion according to the similarity criterion. The roughness increase and decrease trend of each section of the river is analyzed, and the model roughness is adjusted by thickening or smoothing the cement surface, and locally increasing or decreasing pebbles. The water surface line and model roughness adjustment are repeatedly measured until the model measured water surface line is basically consistent with the measured result.

9. A design method for improving the reliability of a hybrid pumped-storage reservoir according to claim 1, characterized in that: The specific steps of step S6 are as follows: F1. Propose the pumping reliability of hybrid pumped-storage reservoir: From the perspective of pumping operation effect, the pumping reliability is proposed, and the pumping operation effect before and after river dredging is compared and analyzed. From the aspects of pumping time guarantee and pumping flow guarantee, the pumping reliability of hybrid pumped-storage reservoir is proposed; The reliability is proposed from the perspective of the hydrodynamic characteristics of pumping operation, and the relevant result indicators of numerical simulation and physical model test are analyzed, including but not limited to the reservoir water surface line, local flow velocity and flow pattern of the inlet / outlet, the range of the inverse drop of the pumping funnel, the lowered water level, the river backwater length, and the minimum water depth. The hydrodynamic laws of pumping operation are summarized and refined, and on this basis, a multi-index evaluation method is used to propose the pumping reliability of the hybrid pumped-storage reservoir; F2. Determine the pumping operation limit water level of the hybrid pumped-storage reservoir. According to the hydrodynamic laws obtained by numerical simulation and physical model test verification, analyze the reliability-related influencing factors, and summarize and propose the pumping limit water level of the lower reservoir, including the basis location and value of the limit water level.

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