A Coupled Inductor Based High Step-Up Converter for DC Microgrid Applications

A high gain nonisolated dc-dc converter is proposed for the distributed generation systems. High voltage gain is achieved by integrating different methods with reduced duty ratio. Inductive voltage spikes across MOSFETs are alleviated and stress is reduced with inclusion of a passive-clamp circuit. Thus, lower voltage rating (small R-ds(ON)) active devices can be adopted. Using this clamp, zero-voltage switching over wide load range is achieved for both the MOSFETs. In addition, leakage energy of the coupled inductor is recycled without using auxiliary switch and thus, the gain get further improved. Zero-current switching is obtained for all the diodes using quasi - resonance principle, which diminishes voltage spikes across the diode caused by the parasitic ringing between leakage inductance and diode's stray capacitance. Therefore, snubbers are not necessary to protect the diodes and to mitigate reverse-recovery losses. Overall efficiency improves because of lower switching and conduction losses of the semiconductor devices. A 600 W prototype working at 75 kHz is built in the laboratory to verify the performance. The peak efficiency is nearly 96.5% and is above 95% for wide load range.