An optimization framework for multi-timescale operations of pumped storage systems: Balancing stability and economy

Pumped storage hydropower system (PSHS) has multi-timescale operating characteristics which are divided into hour scale short-term scheduling and second scale power regulation with the objectives of minimizing water consumption and optimizing power regulation characteristics, respectively. However, the operating characteristics of these two scales are often analyzed independently, preventing decision makers from obtaining a strategy with optimal multi-timescale operating characteristics. This paper proposes a novel optimization framework by coupling the second scale model with the hour scale model which balances the stability (power regulation characteristics) with the economy (water consumption). Firstly, the power regulation characteristics of the unit under different operating conditions are summarized in terms of the integrated time and absolute error (ITAE) and maximum deviation of the rotational speed (ntd_max) based on a refined PSHS model. And a novel short-term scheduling model is developed which couples the power regulation characteristics. Secondly, with the novel model, the Pareto solution sets are obtained based on the non-dominated sorting genetic algorithm-III (NSGA-III) with the objective of minimizing the water consumption and ITAE/ntd_max. Finally, by the technique for order preference by similarity to an ideal solution (TOPSIS), the Pareto solution sets are further evaluated to obtain an operating strategy with optimal power regulation characteristics and water consumption. Compared to the traditional solution aiming for the minimum water consumption, this strategy results in a significant improvement in the stability (65.03 % reduction in ITAE and 68.43 % reduction in ntd_max) at the expense of a smaller economic behavior (0.0295 % increase in water consumption). The strategy outstands existing operating rules and innovatively introduces power regulation characteristics to obtain a short-term scheduling strategy that balances stability with economy. It provides a theoretical basis for the multi-timescale operation of PSHS.