Modular Switching Cell Design for High-Performance Flying Capacitor Multilevel Converter

Abstract

Multilevel topologies provide an attractive alternative to two-level converters because they enable utilization of devices with lower blocking voltage and correspondingly high figure-of-merit. The flying capacitor multilevel converter (FCML) has demonstrated both very high power density and efficiency in a variety of applications. These converters are modular in design, consisting of series-connected switching cells. As such, the optimization of this unit cell provides a framework to build up high-performance FCMLs of any level count. This work presents a novel switching cell design which uses daughterboards containing a cascaded bootstrap gate drive power supply as well as isolated signaling and gate drivers, all of which can operate up to 1000 V. The motherboard layout provides extremely low commutation loop inductance of 940 pH, the best to date for this blocking voltage, through a combined parallel hybrid and electrically thin vertical design. A 300 V, 1.3 kW, 4-level FCML prototype is fabricated to validate the proposed design, which achieves > 1 kW/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density and 98.3% peak efficiency.