High Step-Up Boost-Fly-Back Converter with Soft Switching for Photovoltaic Applications

In this paper, a novel high step-up single switch DC-DC converter with soft switching is presented. The main application of this converter is the connection of photovoltaic (PV) system to a 400V DC-bus. The proposed converter achieves high step-up voltage gain with small duty cycle by a combined boost and fly-back topology. Also, its switch voltage stress is lower than the output voltage. Besides, in the proposed converter, any auxiliary switch or magnetic core has not been used-therefore, the number of converter components has not been increased much in comparison with the conventional boost-fly-back converter. The operation principles of the converter and its theoretical operation waveforms are presented. In order to evaluate the theoretical analysis, a prototype of the converter is designed and experimentally implemented. The practical results are presented for a 100W boost-fly-back converter with input voltage of 40V and output voltage of 400 V. Also, the output capacitor is designed to have less than 1% ripple on output voltage.