A New AC/DC Half-Bridge/String-Inverter Hybrid-Structured Isolated Bi-directional Converter

In this paper, a new bidirectional AC/DC converter based on a 5-switch string topology and an isolated CLLC resonant circuit is proposed for energy storage applications. In the battery side of the proposed circuit, one switch and two diodes are added to the conventional 4-switch string converter, reducing the output voltage ripple to half. A CLLC resonant circuit is designed to step up/down the DC voltages and to provide ZVS for all the semiconductor devices. In AC to DC mode, a hysteresis controller is used and a power factor of 0.99 is achieved. In DC to AC mode, a Second Order Generalized Integrator (SOGI) phase locked loop (PLL) is used to transfer power into the AC source. The frequency modulation technique is utilized to regulate the voltage levels in the terminals of the resonant converter. Simulation results are provided on a 1kW, 60Hz 120VAC/700VDC system to highlight the merits of the proposed converter. A 1 kW 700VDC-output experimental prototype is developed to validate the performance and feasibility of the proposed converter.