A Scalable Soft-Switching Photovoltaic Inverter With Full-Range ZVS and Galvanic Isolation

Modular converters with stacked cells have an advantage of achieving higher voltage or current levels by using standard low-voltage or low-current switches. This study presents a galvanically isolated and scalable three-phase photovoltaic inverter with stacked output cells. Instead of a dc link with electrolytic capacitors, a distributed ac link composed of small ac capacitors and transformer magnetizing inductances is proposed. Due to nonappearance of a dc link, a fast dynamic response is achievable. The oscillation of the ac link provides soft-switching for all switches in the entire load range without using auxiliary snubbing switches. The transformer core is utilized symmetrically in positive and negative half cycles and the inverter operation is not affected by unequal winding leakage inductances, which makes the transformer design simple. Current symmetry among the windings and voltage symmetry among the ac capacitors is provided naturally. Analytical study, design, and experimental validation of a 750 W prototype is presented.