Research On Optimal Regulation Of Hydropower Stations Operation Coupled With Multiple Safety Constraints

The safety accidents during hydropower station operation process are hidden trouble that seriously threaten people's lives and property in the whole world.How to prevent the trouble before it happens,prepare hydropower station countermeasures for various safety problems is the key issue to be solved.In view of this,this study aims to constrain the vibration safety problem induced by flood discharge,the hydraulic safety problem of reservoir downstream area and the safety problem of diversion and tailrace system during the hydropower stations operation period.And the optimal operation models are established respectively to give the operational strategies from the perspectives of time and space.Based on the above-mentioned optimal operational strategies,the regulation criterias for hydropower station are proposed.Regarding these as the optimization benchmark,the research on the optimal multi-objectives operation of hydropower stations coupled with multiple safety constraints is carried out and operation strategies are extracted.The main research contents and results of this paper include the following aspects:Firstly,the two-period hedging flood control optimization model coupled with flood discharge induced vibration safety constraint is constructed,and the optimal flood discharge operational strategies of Xiangjiaba hydropower station under different levels of upstream inflow and forecast uncertainty are analyzed.The conclusions can be drawn as followed:(1)The vibration safety discharge ceiling is determined according to the root mean square's upper limit of the vibration acceleration in the vertical direction under the combination of the most unfavorable gate opening degree and the reservoir water level,for Xiangjiaba hydropower station it's 13900m~3/s.(2)On the premise of not overtopping the reservoir dam,this optimization model mainly aims at the flood recession process in the face of flood peak flow at the present period and provides the operation strategy to minimize the risk of flood-induced vibration safety problem.It can reduce 6.95%of the risk of flood-induced vibration safety problem and increase 0.78%of the power generation of the hydropower station compared with the traditional flood discharge operation strategy.(3)The macro flood control strategy provided by the optimization model is as follows:when the flood scale is large(the gap between expected flood volume and vibration safety discharge capacity is smaller 660 million m~3),the operation strategy based on the“hedging theory”to ensure the marginal benefit of the GBEV for the current period objective and future period objective equal to each other is optimal;when the flood scale is small(GBEV>660 million m~3),the flood control strategy to discharge uniformly is optimal.(4)The larger the inflow forecast uncertainty is,the bigger proportion of the GBEV for current period accounts.And the average flood discharge of current period is smaller.Secondly,the safety constraint of the gate opening degree combination is extracted according to the hydraulic safety index of the downstream area.The optimal flood discharge operation model of daily regulation hydropower stations coupled with the hydraulic safety constraints is studied.It is applied to Tongzilin hydropower station and the conclusions are as follows:(1)The concept of safe flow in the open channel downstream of the floodgate is introduced to guarantee the hydraulic safety of the downstream area.In specific,when the flow rate is lower than 6000m~3/s,the flood is discharged only through the riverbed section according to the experimental suggestion;When the flow rate is higher than 6000m~3/s,after the floodgate of the open channel section shares the maximum safe flow rate,the bottom flow velocity near the guide wall of the riverbed section is controlled by the combination of the floodgate opening degree of the riverbed section.Finally,the optimal opening degree combination of the floodgate for ensuring the hydraulic safety of the downstream area is obtained.(2)In view of the large magnitude and fluctuation of the upstream inflow of the daily regulation hydropower station,for its weak regulation ability,the upstream hub reservoir is used to clip the peak of the upstream inflow.Utilizing less than 100 million m~3 of storage capacity per day can reduce flood peaks by about2000m~3/s.(3)The gate regulation workload is cut down by 60%by using the optimization model.The workload reduction of the open channel gate accounts for40%of the total workload reduction of all gates.(4)In the regulation scheme of gate workload minimization oriented optimization,the workload reduction of middle hole gate of the riverbed section accounts for 40%of the total workload reduction of all gates compared with the regulation scheme of the flood peak clipping oriented optimization.Therefore the middle hole gate is made as the main control objective to reduce the gate regulation workload.(5)The upstream hub reservior capacity's utilization rate for the minimum gate regulation workload's oriented optimal scheme is lower by 29%than the flood peak clipping oriented optimal scheme.Thirdly,the diversion and tailrace system safety constraint of the"one tunnel with two turbine units"safety operation mode and the tailrace surge chambers safety operation mode are extracted.And an optimal dispatch model of hydropower stations coupled with the diversion and tailrace system safety constraints is constructed and solved by two-hierarchical solving mode.This solving mode can reduce the dimensions(from 6480 to 270)of the decision variables and the overall solving difficulty.This model is applied to Jinping-?and Jinping-?hydropower stations and the regulation criteria of the hydropower stations is obtained by analyzing the features of reservoirs and the operational characteristics of the hydropower stations.The regulation criteria is embedded into the optimal dispatch model to obtain the operational optimal schemes covering various combinations of different grades of upstream inflow and reservior water levels.By summarizing the above schemes,the long-term and short-term operational strategies of the hydropower stations and the operational strategies for the above-mentioned safety constraints are obtained.Fouthly,a multi-objective optimal operation model is established for hydropower stations coupled with integrated safety constraints.The regulation strategy for the hydropower station's operational vibration safety and operational hydraulic flushing safety are integrated with the operational characteristics of hydropower stations,then the regulation criterias for the hydropower stations operation are extracted.The regulation mode of the“allocation after optimization”and“optimization after allocation”for the discharge water volume of hydropower stations are further proposed to optimize the model.It is applied to Jinping cascade hydropower stations and the conclusions are as followed:(1)The regulation criteria for Jinping-?hydropower station operation is to lower the reservior water level in the flood discharge period,the GBEV's allocation criteria is adjusted to using the hedging rule for all flood scale.This criteria can reduce risk of flood control,and the turbine flow upper limit can be maximized to share the flood discharge pressure.The regulation criteria for Jinping-?hydropower station operation is to operate under water level higher than 1643m in the flood discharge period.This criteria can reduce the output defeat of turbine units,the turbine flow can be maximized to share the flood discharge pressure and the discharge capacity for the reservior is higher.(2)The power generation objective for the regulation mode of“allocation after optimization”is relatively increased by 9%on the foundation of maximizing the hydropower station's operational safety degree(flood discharge induced vibration safety degree increased by 4%and downstream hydraulic anti-flush safety degree increased by 1%)compared with the regulation mode of“optimization after allocation”.(3)The operation strategy for the maximum and second large flood scale is to store the water to the normal water level at the end of flood period.On the premise of ensuring the environmental flow,the GBEV for current period is as large as possible.The operation strategy for the third and fourth large flood scale is to recover to the flood limit water level at the end of flood period.The GBEV for future period accounts for more than 57.1%of the total amount.The maximum turbine flow is determined according to the total discharge flow and hydraulic head of the hydropower station at each time interval.The heuristic optimization algorithm is utilized to gain the flood discharge series which has the minimum fluctuation degree.