A PWM and PFM Hybrid Modulated Three-Port Converter for a Standalone PV/Battery Power System

A pulsewidth modulation (PWM) and pulse frequency modulation (PFM) hybrid modulated three-port converter (TPC) interfacing a photovoltaic (PV) source, a storage battery, and a load is proposed for a standalone PV/battery power system. The TPC is derived by integrating a two-phase interleaved boost circuit and a full-bridge LLC resonant circuit. Hence, it features a reduced number of switches, lower cost, and single-stage power conversion between any two of the three ports. With the PWM and PFM hybrid modulation strategy, the dc voltage gain from the PV to the load is wide, the input current ripple is small, and flexible power management among three ports can be easily achieved. Moreover, all primary switches turn ON with zero-voltage switching (ZVS), while all secondary diodes operate with zero-current switching over full operating range, which is beneficial for reducing switching losses, switch voltage stress, and electromagnetic interference. The topology derivation and power transfer analysis are presented. Depending on the resonant states, two different operation modes are identified and explored. Then, main characteristics, including the gain, input current ripple, and ZVS, are analyzed and compared. Furthermore, guidelines for parameter design and optimization are given as well. Finally, a 500-W laboratory prototype is built and tested to verify the effectiveness and advantages of all proposals.