A non-isolated high gain DC-DC converter with coupled-inductor and built-in transformer for grid-connected photovoltaic systems

A non-isolated high gain DC-DC converter based on coupled-inductor (CI) and built-in transformer (BT) with voltage multiplier cell (VMC) is presented for renewable energy applications, especially solar photovoltaic (PV) sources. In this circuit, the BT used in addition to the coupled inductor improves the design flexibility. It enhances the voltage gain with the simultaneous action of CI and BT, compared to converters that include BT or CI. Also, the formation of voltage multiplier cell with the series combination of secondary windings of the CI and BT, switched capacitors and the diodes give an extra voltage gain to the converter. This converter structure adds the turns ratios in voltage gain expression and does not entail a reverse recovery issue with the leakage energy. The active clamped circuit recycles this leakage energy to alleviate the switching stresses. Consequently, active clamping provides add-on features like improved converter efficiency with ZVS operation and further voltage gain. The converter principle of operation and the design procedure of all components are presented. Finally, a 400 W laboratory prototype with input voltage range 24-40 V and output 400 V is developed and illustrated the effectiveness of the converter at a switching frequency of 100 kHz.