Flying Capacitor Converter Using Low-Voltage GaN-FETs for Grid-Connected Applications

This paper investigates the adoption of low voltage GaN FETs (150V) in a multilevel flying capacitor converter for grid-connected applications. When compared to similar voltage class Si-based FET switches, the GaN technology enables much higher switching frequencies in hard switched topologies due to their lower dynamic losses. The flying capacitor topology profits from the increased switching frequency because of the reduced capacitance requirements. Furthermore, due to the small voltage steps of the multilevel topology, the AC filtering effort can be reduced. Analysis presented herein provide insight in the modulation method and the design of a flying capacitor converter implementing a voltage balancer passive circuit based on a RLC trap-filter. Additionally, the concept of low cost gate drivers based on bootstrap circuit is discussed. A prototype of a single-phase 5-level flying capacitor converter has been designed and implemented, where experimental measurements are shown verifying the operation of the studied system.