Application of a Mid-Long Term Optimal Operation Model for the Xiluodu-Xiangjiaba-Three Gorges-Gezhouba Cascade Reservoirs System

The cascade reservoirs system consisting of Xiluodu, Xiangjiaba, the Three Gorges and Gezhouba reservoirs, which located at the lower reaches of Jinsha River and the upper reaches of Yangtze River respectively, plays a very important role in the flood control, power generation and water supply in China. To optimize and solve the joint optimal operation problem of such a large-scale system with highly complex constraints, hydraulic relationship and multiple objectives, this paper focus on: (1) a mid-long term optimization model for the system is established when considering kinds of complex constraints, hydraulic and electricty connections, as well as the flood control and water supply objectives; (2) an improved LSSDC-DDDP hybrid optimization framework, based on the theory of large-scale system decomposition coordination (LSSDC) and the discrete differential dynamic programming (DDDP), is designed and applied to well solving the proposed optimization model. In the framework, a relative coefficient is used to calculate the coordination factor among subsystems. Meanwhile, an adaptive corridor and a bias corridor are adopted to enhance convergence speed of DDDP. Finally, the optimization model is tested on the optimization operation calculation of the cascade reservoirs system using 2015-2017 actual runoff conditions, respectively. The results indicate that joint optimal operation of the cascade reservoirs system can increase its yearly total power generation benefit about 2.73 billion yuan on average, simultaneously satisfying the requirements of downstream water supply and improving the total guarantee rate of firm power.