Non-isolated high step-up three-port converter with single magnetic element for photovoltaic systems

A new non-isolated high-voltage gain three-port converter for standalone photovoltaic systems is proposed. The magnetic element of this converter is only one coupled inductor. The primary winding of the coupled inductor is shared between battery charger circuit and main converter. Leakage inductance energy of the coupled inductor is either transferred to battery or is regenerated via the passive-clamp circuit. Using switched capacitor and voltage lift techniques, the voltage gain is significantly increased for both low-voltage ports. Single magnetic element, high-voltage gain with reasonable duty cycle, low-voltage stress on the switches, low winding turn ratio of coupled inductor and high efficiency are the merits of this converter. The operation principles and the steady-state analysis are described for the three modes of: single-input single-output, single-input dual-output and dual-input single-output. To verify the theoretical analysis, a laboratory prototype with 28V input, 48V battery voltage and 380V output voltage is implemented and tested.