Transformer-less high gain three-port converter with low voltage stress and reduced switches for standalone PV systems

This paper proposes a high gain transformer-less three-port converter (TPC) for standalone photovoltaic (PV) systems. The TPC is designed and developed based on a dual-inductor high gain two-port converter by utilizing one of the buffer capacitors to derive the third part for PV input. A hybrid pulse frequency modulation (PFM) scheme unified with a pulse width modulation (PWM) control strategy is adopted, which realizes the maximum power point tracking (MPPT) control, load voltage regulation, and bidirectional energy flow at the battery port. The proposed TPC offers the unique advantages of high voltage gain, continuous battery port current, reduced power semiconductors, lower voltage stresses, the common ground shared by all ports, low-cost gate driver, and small size of the rear-end inductor. The working principle, steady-state characteristics, small signal models and control method, including design conditions, are comprehensively analyzed. The correctness of the theoretical analysis is verified by developing a 300W experimental prototype, which shows the maximum efficiency is 97.7%.