The integration of large-scale renewable energy aggravates the burden of frequency regulation for power grid

so the power system is required to be more capable of following power changes timely

that means higher demand for operational flexibility at sub-hourly time-scales. Thus this paper proposes a unit commitment(UC)model with energy storage considering operational flexibility at sub-hourly time-scales. Based on the analysis of range characteristics of the net load

the operational flexibility constraints are set according to the key scenarios of net load fluctuation. Therefore day-ahead dispatch in hourly time-scale is tied with sub-hourly operational flexibility requirements in UC. Meanwhile

the principles and restrictive factors of energy storage in different running states of charging

discharging and non-charging-and-non-discharging are discussed. Then the flexibility provided by energy storage is modeled and added to the system energy and power balance equation and operational flexibility constraints

respectively. Therefore the model of UC integrated with optimal deployment of energy storage is developed. By linearized processing

the model is reformed as a mixed integer linear programming(MILP)problem for solving. Simulations show that the proposed method can significantly improve the operational flexibility of power system at sub-hourly time-scales by using energy storage optimally.