Abstract: Aimed at addressing the daytime frequent fluctuation of power grid load and the complicated hydraulic connection existing in cascade hydropower stations, a medium-term peak shaving scheduling model for cascade reservoirs considering a piecewise flow delay strategy is developed. First, a peak-shaving multi-objective model for medium-term power grid dispatch is constructed to optimize peak shaving and maximize cascade power generation. Then, based on the principle of water balance, a medium-term piecewise time delay method is formulated to effectively describe the flow delay in calculations of the medium-term dispatching of cascade hydropower stations with a time step of one day. Finally, a comprehensive benefit calculation method to alleviate the generation deviation affected by the lag times for the scheduling period and the time lag period is presented. The method has been applied to a case study of 11 cascade hydropower stations under operation on the Lancang River mainstream. The results show it achieves a better agreement with the real operation through introducing flow delay factors, reducing the delay effects of scheduling deviation effectively. And it improves hydropower utilization benefits and has a good medium-term peak-shaving effect.

Key words: medium-term scheduling, peak-shaving, cascade reservoirs, multi-objective, delay time