A Three-Port Bidirectional LLC Resonant Converter for PV/Battery Applications

This paper proposes a three-port bidirectional LLC resonant converter that interfaces with one PV panel and one battery energy storage system (BESS). The topology is a combination of a half-bridge and a full-bridge LLC circuit with six active switches on the primary and a full-bridge rectifier composed of four switches on the secondary. The back-to-back switches are used to short the resonant capacitor and transformer when the battery is charged by the PV source. This topology allows the two sources to share the same resonant tank for transferring energy to the load and allows to store the extra energy from the load into the battery without additional circuit components. In the forward operation, a phase-shift pulse width modulation (PWM) control is employed to implement independent maximum power point tracking (MPPT) for PV panel and the converter voltage gain is controlled by varying the operating frequency as in a typical LLC resonant converter. In the backward operation, the switching frequency is fixed at resonant frequency. Soft switching is realized in all switches over the entire range of source voltage and load conditions. A simulation study was carried out in LTspice software to validate the operating principles of the proposed topology. The PV input voltage range is selected to be 25 V to 45 V and the battery nominal voltage is 50 V with an output voltage regulated at 200 V DC.