Joint operation of wind farm and energy storage is a vital approach to improve the wind power utilization in wind farms. Energy storage efficiency has a direct impact on the utilization effect of the combined wind power-energy storage system

but the present constant efficiency model is not that precise in depicting the efficiency characteristics of energy storage. A joint operation optimization model considering the dynamic efficiency characteristics of energy storage is established

with the target of maximizing the equivalent in-grid electricity. Changes of charging and discharging efficiency caused by power variations of storage devices are taken into account and added in the mixed integer linear programming model in the form of segmented function. Based on historical data of a wind farm

effects of constant efficiency model and dynamic efficiency model on the wind power utilization and power values are analyzed in single energy storage system and hybrid energy storage system. It is proved that the efficiency characteristics of dynamic charging and discharging have a significant impact on the utilization maximization

which means they should not be ignored in the optimal operation of combined wind power-energy storage system.