Two-Stage Isolated Bidirectional DC–AC Converters With Three-Port Converters and Two DC Buses

A novel two-stage structure with two dc buses is proposed for isolated bidirectional dc-ac power conversion. A variable dc-link voltage plus a constant dc-link voltage operation is adopted for the proposed two-stage structure. One of the dc-link voltages is regulated adaptively according to the variation of dc-side voltage, so that the dc-dc power stage can always work at its optimized point. New families of three-port (TP) bidirectional dc-dc converters and TP bidirectional inverter/rectifier (TP-BIR) are proposed to implement the proposed two-stage dc-ac power conversion structure. A bidirectional dc-ac converter composed of a TP-CLLC resonant converter and a T-type TP-BIR is taken as an example to verify the effectiveness of the proposed structure. Operation principles of both the TP-CLLC resonant converter and the T-type TP-BIR are analyzed in detail. Modulation and control strategies are proposed for the TP-BIR to achieve voltage regulation and power distribution between the two dc buses. A 1.5-kW prototype is built and tested to verify the feasibility and advantages of the proposed solution.