ZVS-ZCS High Step-Up/Step-Down Isolated Bidirectional DC-DC Converter for DC Microgrid

A soft-switched isolated bidirectional dc-dc converter is proposed for distributed generation systems. Dual coupled inductor-based flyback energy conversion circuit achieves high-voltage step-up/down ratio and high efficiency at lowered duty cycle and, attributes the galvanic isolation. Active switch-based capacitor multiplier cell appreciably reduces voltage stresses on low-voltage (LV) and high-voltage (HV) stage mosfets, thereby allowing LV rating devices (small R-ds(ON)). Active-voltage-clamping type circuit extensively suppresses the voltage spikes across LV-switches caused by leakage inductance. Indeed, this clamp circuitry is formed without any additional switches/diodes, thus, reduces clamp device count. By availing of quasi-resonance, thus, without needing the HV stage snubber, switching voltage spikes are substantially alleviated. Furthermore, this clamp along with quasi-resonance achieves zero-voltage (ZVS) and zero-current (ZCS) switching, over wide-load range, for all switches in both step-up and step-down operations. Reduced voltage stresses, minimized clamp device count, diminished conduction losses, and bidirectional soft-switching performance collectively enhances the efficiency. A 600-W laboratory built set-up working at 75 kHz verifies the viability of the design concept. Measured peak efficiencies in boost and buck stages are 96.65% and 96.58%, respectively.