In order to increase the weighted efficiency of the photovoltaic micro-inverter, this paper proposes a flexible topology DC/DC converter as the former stage in the micro-inverter. The flexible converter includes two operation topology, which are improved dual-switches forward topology and full-bridge topology, respectively. The operation principles of the two topologies are introduced and the design guideline of the key parameters, such as the turns-ratio of transformer and buffering inductor, are given. The power threshold value is determined according to the analysis of switching loss, conduction loss, driving loss and core loss of the converter. A duty ratio pre-calculation control strategy combined closed-loop adjustment is proposed for good dynamic performance. The analysis is verified by the experimental results from a 300W prototype.