Research On Multi-objective Optimal Operation Of Cascade Hydropower Stations And Reservoirs In The Main Stream Of Heihe River

With the development of economy and society,since the 1960s,there has been a large number of reclamation in the middle reaches of Heihe River Basin.The increasing of agricultural water consumption and the prominent contradiction between water use in the middle and lower reaches,and the crowding-out of ecological water,resulted in the decline of desert vegetation and the rapid expansion of desertification in Ejina area in the lower reaches.On the other hand,due to the lack of regulation and storage projects,ther egulation means in Heihe River Basin is unitary,which could only meet the downstream water demand by artificially increasing the closure.To address the above issues,this research studies the multi-objective joint optimal operation of cascade hydropower stations and reservoirs of the main stream of Heihe River,aiming at improving the disharmonious contradiction of water use in the middle and lower reaches,enriching the means of river basin operation,thus to curbe the deterioration trend of ecological environment in the lower reaches and promote the sustainable development of social,economy and ecology in the whole basin.The main achievements are as follows:(1)According to the discrepancy of regulation and control means of water conservancy projects in Heihe main stream,two reservoir dispatching schemes are set up.The Scheme-1 consists of Huangzangsi and seven hydropower stations,while Scheme-2 includes Huangzangsi,Zhengyixia and seven hydropower stations..The multi-objective optimal operation model of cascade hydropower stations and reservoirs in the main stream of Heihe River is constructed with irrigation,ecology and power generation as objectives and the joint operation mode is put forward.That is,taking the Huangzangsi reservoir in the leading reservoir as the main reservoir,the downstream Zhengyixia reservoir is set as the counter-regulating reservoir,to maximize the comprehensive benefits of water supply,ecology and power generation.(2)Based on the improved NSGA-II algorithm,the multi-objective optimal scheduling model is solved and the Pareto surfaces of each scheme is obtained.The multi-objective Pareto surface graph shows that the three objectives cannot reach the theoretical optimal solution at the same time,and the non-inferior solution of the Pareto set has the equivalent weighted distance to the theoretical optimal solution.(3)The transformation relationship between different objectives is quantitatively described,and copula function is employed to explore the multi-objective competition mechanism,.Among three objectives,the impact of electricity generation on the whole Heihe River Basin is the smallest and the least significant;The recommended annual irrigation water shortage is 1271 and 1492×104 m3,and the annual ecological water shortage is 15696 and 4951 ×104 m3 of each scheme,respectively.(4)Non-inferior solution sets are optimized with the theory of fuzzy optimal decision theory,in which the optimal scheduling strategies of each scheme are No.1449 and No.1354,respectively.The optimal dispatching results show that the Huangzangsi and Zhengyixia reservoirs sacrifice their own power generation and enormously improve the power generation efficiency of the whole cascade.The participation of Zhengyixia Reservoir in regulation has increased the water supply of Dingxin irrigation area and Dongfeng field area in the lower reaches of Heihe River,which greatly improves the process of ecological water demand in the lower reaches.Finally,the results indicate that the Scheme-2 with Zhengyixia reservoir participating in regulation is better than the other.(5)The dispatching chart and scheduling function for comprehensive utilization of cascade reservoirs in Heihe River Basin are formulated respectively,which realized the operability of optimal dispatching results.The results show that the runoff compensation and reservoir capacity compensation of cascade reservoir operation are achieved with the application of operation chart.(6)Based on the optimal operation strategy,the water level variation law of cascade reservoirs in the main stream of Heihe River is reaveled.That is,the water level of Huangzangsi Reservoir frequently falls to dead water level and it is difficult to store to normal water level,which is caused by taking into account of the cascade comprehensive benefits and the operation strategy of Zhengyixia Reservoir owing to the overall water shortage in Heihe River Basin.The frequent storage of Zhengyixia Reservoir to dead water level and normal water level plays a role of anti-regulation of Huangzangsi Reservoir,which has taken account of the downstream water demand.The water level of Huangzangsi is mainly affected by inflow,which has the basic law of water storage in non-water-demand period and water discharge in water-demand period.The water level of Zhengyixia is mainly affected by water demand,and has the basic law of storaging water in non-water storage period and releasing water water demand period.Around the low water level,the water level is narrower in dry year and while near the high water level,the water level is narrower in rich year.(7)Based on the optimal operation strategy,the water intake law in the middle and lower reaches of Heihe River is revealed.In irrigation satisfacted years,there was a significant negative correlation between surface water supply and underground water supply in the middle reaches of the irrigation area;in irrigation unsatisfacted months,there was a significant positive correlation between surface water supply in the middle reaches of the irrigation area and annual runoff in Yingluoxia.Water shortage occurrs most frequently in the middle reaches of the irrigation area in April to June,and the amount of water shortage is concentrated in May to June.Dingxin irrigation district and Langxinshan are lack of water when the discharge of water under Zhengyixia is less than 7.5×108 m3,and on the contrary there is no shortage of water.The water shortage occurs frequently in the two areas in June to August and November,and concentrated in June to August.While the water shortage frequency and amount of Dongfeng field area focus in July.(8)Based on the optimal operation strategy,the cascade power generation law in the main stream of Heihe River is revealed.When the annual discharge of Huangzangsi increased by 100×104 m3,the cascade annual power generation increased by 0.0152×108 kW·h.When the discharge of Huangzangsi is greater than 98.3 mi/s,the contribution of increasing the discharge of Huangzangsi to cascade power generation is small,and when it is less than 63.9 m3/s,the space for upgrading cascade power generation is large.The farther the power stations are from Huangzangsi,the smaller the influence of Huangzangsi is and the greater the influence of local inflow is.Longshou-? and Baopinghe suffered the greatest losses as the output of Huangzang Temple decreased.