This paper proposes an integrated half-bridge CLLC (IHBCLLC) resonant bidirectional dc-dc converter suitable as an interface between two dc voltage buses in various applications including energy storage systems. This converter is an integration of a half-bridge CLLC resonant circuit and a buck/boost circuit. Compared with the traditional pulse frequency modulation and phase-shift controlled CLLC resonant converter, for the proposed convertor, the high voltage gain can be obtained from pulse width modulation. Synchronous pulse width modulation is adopted for the converter, and the switching frequency is equal to the resonant frequency. The CLLC resonant circuit can help MOSFETs to achieve soft switching and high voltage gain. The simulation analysis of the modulation schedule and operating principle of the proposed converter prove that the converter is able to achieve zero-voltage switching or zero-current switching. Experimental results obtained from a 1-kW converter prototype confirm the theoretical analysis and the simulation results.