The use of renewable energy source can reduce greenhouse gas emission and fossil fuel pollution. Compared with fossil fuel energy, renewable energy is not stable and cannot supply firm electrical output (i.e., it is nondispatchable). Fluctuating power from renewables may result in grid power oscillation. To reduce grid swing, energy storage is necessary to smooth output from renewable energy. Energy storage with high energy density and fast response time or high power capacity is desired for compensation of fluctuating output. Generally, superconducting magnetic energy storage (SMES) has higher power capacity than battery energy storage, while battery provides higher energy density. Thus, this research proposes a hybrid energy storage system (HESS) composed of an SMES and battery. Novel and practical synergistic control is presented for firming power fluctuation by exploiting the strong power and energy capabilities of the SMES and the battery while within the efficient operating range of (i.e., state of charges of) HESS. Comprehensive case studies demonstrate the efficacy of the proposed HESS topology and control algorithm using PSCAD/EMTDC.