Non-isolated High Step-up DC-DC Converter with Minimum Switch Voltage Stress

A new high step-up DC-DC converter topology combining a charge pump mechanism with a standard inductor-based Buck cell is here presented. Its main advantages are: minimum switch voltage stress, given by the input voltage, and reduced energy in the magnetic element compared to a conventional Boost converter designed for the same voltage gain. The proposed topology is derived through a modification of the basic voltage-doubler charge pump cell that, thanks to a coupled inductor, allows to make the flying capacitor voltages dependent on the switch duty-cycle. Both capacitor charging and discharging paths benefit from the inherent leakage inductance of the coupled inductor, with consequent soft diode turn off with no reverse recovery problems and ringing free operation. A proper design of the Buck inductance permits a quasi-square-wave operation, thus allowing a zero-voltage turn on of the switches. Suitable design criteria are proposed so as to achieve the desired converter operation mode, without need for any iterative process. Experimental results based on a 44 V to 400 V - 300 W prototype confirm the theoretical analysis and expectations, showing a quite flat efficiency curve that stays above 90% down to one tenth of the nominal power.