Single-switch high step-up converter with coupled-inductor and built-in transformer

In this paper, a high step-up converter with coupled-inductor and built-in transformer is proposed. Compared with other converters with coupled-inductor, the built-in transformer introduces a new control variable of the voltage gain which improves the design flexibility and conversion efficiency. Thus, low ratio of coupled-inductor can be selected. Input current ripple is reduced so that the input filter can be minimized. Secondary sides of coupled-inductor and transformer are connected in series with a capacitor functioned as a voltage multiplier to further extend the voltage gain. The reverse-recovery problem of the output diode is effectively alleviated due to the leakage inductor. Moreover, a passive regenerative snubber is utilized to recycle the energy of leakage inductor and reduce the switch voltage spike. The operating principle of the converter is discussed and the voltage gain is derived in this paper. Finally, a 200W prototype with 24–36V input and 400V output is built to verify the theoretical analysis and a maximum efficiency of 96.9% is achieved.