It is very important for utility companies and wind farms to actively control wind farm power outputs and put it into the automatic generation control（AGC） regime. This paper first discusses the active power control potential for wind farms and corresponding roles in the system AGC mode， and then proposes a three-level control model with energy storage， to achieve comprehensive goals including output limit control， AGC curve tracking， and peak regulation. The models are verified and compared with the current operation mode in terms of commercial benefits. Simulation results show that wind farms can achieve active power control with multi-goals at relatively small cost.