A Modified Dual-input LLC Converter for Standalone PV/Battery Power System

This paper proposes a modified dual-input LLC resonant converter that interfaces with one PV panel and one battery energy storage system (BESS). The topology is a dual half-bridge LLC circuit with four active switches. This topology allows the two sources to share the same resonant tank for transferring energy to the load without the need for additional circuit components. Back-to-back switches are used to short the resonant capacitor and transformer in battery charging scenario; therefore, the converter is operating as a boost circuit. A phase-shift pulse width modulation (PWM) control is employed to implement maximum power point tracking (MPPT) for PV panel. The converter voltage gain is controlled by varying the operating frequency as in a typical LLC resonant converter. Zero-voltage-switching (ZVS) is realized in half-bridge circuit switches over the entire range of source voltage and load conditions in battery discharging scenario and single-input scenario. A 350-W prototype was built to validate the performance of the proposed topology. The input voltage range of the PV source was selected to be 25 V to 45 V and the nominal input voltage of battery was 55 V with an output voltage regulated at 200 V DC. Experimental results show that the proposed converter can achieve the peak efficiency of 93.695% while maintaining a wide input voltage range.