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

Abstract

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 low voltage rating devices(small <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>ds</i>(ON)</sub> ). 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. Further, 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.