Single-phase bidirectional AC-DC converters based on three-port converter (TPC) is proposed for energy storage applications. Three power interfacing ports, i.e. a DC-bus port, a DC input port and an AC port, are provided by the proposed converter. A battery, whose voltage is lower than the peak amplitude of the AC voltage, is connected to the DC input port of the TPC, with which energy exchange between the battery and grid can be achieved directly. Therefore, power processed by the down-stream DC-DC converter is reduced, which can help to reduce the power losses induced by the down-stream DC-DC converter. In addition, switching losses of the TPC can be reduced as well due to multilevel characteristic. As a result, the overall efficiency of the entire bidirectional AC-DC converter is improved significantly. Topologies, operation principles, modulation and control of the proposed TPC-based bidirectional AC-DC converter are analyzed in detail. A 2-kW prototype is built and tested to verify the effectiveness and advantages of the proposed solution.