Flyback Micro Inverter for Photovoltaic Applications

Abstract-For photovoltaic applications, the flyback micro-inverter with pseudo-dc-link is popular as a simple topology but brings large transformer turns ratio and thus large leakage inductance, which would deteriorate the converter efficiency. To solve this issue, based on the non-isolated pseudo-dc-link structure, this paper proposed a hybrid boost-flyback/flyback (BF/F) micro-inverter. This new topology is operated at BF mode for the most segment of a half grid cycle and F mode for the rest. During the BF mode, high voltage gain with low voltage stress is easily available in minimized transformer turns ratio. Besides, the leakage energy is recycled and the turn-off voltage spike of main switch is clamped, as a result of a passive snubber inherently contained in this mode. Given that the BF mode is lack of step-down function, the F mode is developed to regulate the output voltage even for values lower than the input voltage. The operation and characteristic of the hybrid BF/F micro-inverter in boundary conduction mode (BCM) are analyzed in detail, and the mathematical expression of reference current is derived theoretically to guarantee high power quality. Finally, a 240W prototype was implemented to validate the theoretical analysis and the benefits of the proposed topology.