An optimization model for joint power generation dispatching of the cascade hydropower stations on the lower reaches of Jinsha River and the Yangtze River

The Xiluodu, Xiangjiaba, Three Gorges and Gezhouba cascade hydropower stations, which located at the lower reaches of Jinsha River and the upper reaches of Yangtze River, plays a very important role in the electrical power system in China. To optimize and solve the joint power generation problem of the cascade system with highly complex constraints, hydraulic relationship and multiple dispatching objectives, this research focus on: (1) a mid-and-long term power generation optimization model for the cascade system is established, considering hydraulic and electricty connections, as well as the flood control, water supply and ecology 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 to well solving the proposed optimization model. In the optimization framework, a relative coefficient is used to calculate the coordination factor among subsystems (a single hydropower station); meanwhile, an adaptive corridor and a bias corridor are adopted to enhance convergence speed of DDDP. The optimization model is applied in the dispatching calculation of the cascade system using the 2015-2017 actual runoff conditions, respectively. The results indicate that joint optimal dispatching of the cascade system can theoretically 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 firm output guarantee rate of the system.