A three-phase ZVZCS DC-DC converter for fuel cell applications

In spite of having many advantages such as low switch voltage and easy implementation, the voltage-fed DC-DC converter has been suffering from problems associated with large transformer leakage inductance due to high transformer turn ratio when it is applied to low voltage high current step-up application such as fuel cells. This paper proposes a new three-phase voltage-fed DC-DC converter which is suitable for low voltage high current applications. The required transformer turn ratio is as low as that of the current-fed converter owing to Delta-Y connection. ZVZCS for all switches are achieved over wide load range without affecting effective duty cycle. A clamp circuit not only clamps the surge voltage but reduces the circulating current flowing through the high current side, resulting in significantly reduced conduction losses. The duty cycle loss can also be compensated by operation of the clamp switch. Experimental waveforms from a 1.5 kW prototype are provided.