Flexible topology converter used in photovoltaic micro-inverter for higher weighted-efficiency

This study proposes a pre-stage flexible DC–DC converter (PFDDC) for PV micro-inverter. The PFDDC can be operated in different modes automatically, i.e. the improved full-bridge mode when the output power is higher than the threshold value or in the improved two-transistor forward mode when the output power is lower than the threshold value. The operational principles of the PFDDC in different modes are analysed. The design of the key parameters, such as the turns ratio of transformer and buffering inductance, is presented at first. Then the loss analysis of the PFDDC in different modes is used to determine the threshold power, based on which a switch control strategy according to the threshold power value is proposed. Integration of two operational modes in a single PFDDC can effectively increase the weighted efficiency of the PV micro-inverter to easily satisfy the mandatory efficiency requirement in Europe and USA. Experimental results are presented to verify the effectiveness of the proposed PFDDC.