Single-Switch Forward-Flyback High Step-Up DC-DC Converter With Reduced Switching Losses

The proposed converter integrates forward and flyback modules to achieve a high voltage gain. On the primary side, the forward and flyback modules are connected in parallel, whereas on the secondary side, the flyback output capacitor is stacked with the secondary winding of the forward module to further enhance the voltage gain. During the switch-on interval, part of the input energy is directly delivered to the output capacitor through the forward module, whereas the remaining energy is stored in two DC-bus capacitors that serve as the power sources for the flyback module. In the subsequent switching cycle, this stored energy is transferred to the flyback output capacitor. To improve efficiency, a snubber circuit consisting of a diode and two DC-bus capacitors is employed to absorb the leakage energy from the flyback transformer. Moreover, by operating in critical conduction mode (CRM), the proposed converter effectively reduces switching losses. The design is implemented and experimentally validated with a 48 V input, a 400 V output, and a rated power of 200 W.