This paper presents a method for harmoniously coordinating roles between generators and faster-acting energy storage systems (ESSs), e.g. batteries, to improve their frequency response and regulation services to the grid, particularly at the high wind penetration. The paper theoretically demonstrates that the proposed droop with the state of charge (SOC) feedback (DaSOF) provides a unified frequency control framework for distributed and energy-constrained ESS, seamlessly fitting the conventional primary and secondary frequency control practice. The ESS autonomously takes charge of high-frequency components of a frequency deviation and thus complements the frequency controls of the incumbent generators. By securing the SOC of the ESS at the desired level, the method provides the capability to provide other ancillary services from the energy constrained ESS. These coordinated roles are represented and validated through time and frequency domain analyses. Rigorous case studies using DIgSILENT/PowerFactory demonstrate the efficacy of the proposed method to support the high level of variable renewable energy, which should help improve the value of operating the ESS and scale up renewable energy.