This paper proposes a direct damping feedback control method. By real-time changing the power output of power electronics-interfaced resources, this method aims to control the damping ratio of a targeted oscillation mode to a desired value. It adopts a proportional-integral controller tuned for a nonlinear single-input-single-output model. The model approximates the re-al-time dynamic process of damping estimation and control for the targeted mode represented by a single-oscillator power system equivalent. The paper also proposes utilizing the zero-th order parametric resonance phenomenon to simplify the design of this new control method. The parameters of the controller are optimized considering both robustness and time performance of damping control. Tests on a single-machine-infinite-bus system and a 140-bus 48-machine Northeast Power Coordinating Council system validate the effectiveness of the proposed damping controller utilizing battery-based energy storage systems.