In order to improve integration of AC grid-connected hybrid energy storage system, a single-phase, single-stage, three-port high-frequency isolated DC-AC converter is proposed. Operation principle and characteristics of the proposed converter are analyzed. The essential principle is a detailed description of the proposed converter's capability to suppress double-line-frequency ripple power. Meanwhile, PR-based control loop that realizes suppression of double-line-frequency ripple is proposed to reduce DC-side capacitance. On this basis, in order to deal with the coupling problem caused by shared AC port at control level, a system-level closed-loop control strategy is proposed to achieve separate control of the two DC ports and AC-side current. The feasibility of the proposed converter and control strategy is verified by experiments.