Daily peak shaving operation of cascade hydropower stations with sensitive hydraulic connections considering water delay time

The increasing peak-valley differences pose a major threat to safe operation of the thermal-dominant power grid in China. Cascade hydropower stations, especially for one-reservoir and multi-cascade hydropower stations (OMHS), as the second largest power supply in China form an important part of peak shaving operation. However, nonconvex and nonlinear constraints have made it deeply difficult to perform the daily peak shaving operation (DPSO) of OMHS. In this paper, an improved DPSO model of OMHS considering water delay time is formulated and solved. Firstly, the confluence coefficient method (CCM) is developed to accurately describe the water delay time of OMHS. Secondly, to reduce the errors and water spillage, aggregation of nonlinear constraints, selection of the linearized area and periodic hypothesis are performed. Finally, an MIQP model integrated CCM is established by considering one-reservoir and six-cascade hydropower stations from the Hongshui River of China as a case study. The optimization results demonstrate that the proposed model can accurately simulate real-world system, and the optimized peak-valley differences on typical days in dry season and wet season reduce by 25% and 33%, respectively. Moreover, the CCM can produce more realistic and executable generation scheduling than the state-of-the-art description method of water delay time.