Design and Control of a GaN-Based, 13-Level, Flying Capacitor Multilevel Inverter

Abstract

Multilevel topologies are an appealing method to achieve higher power density converters for both mobile and stationary systems. This article discusses the design and high-performance hardware implementation of a 13-level, flying capacitor multilevel (FCML) inverter. Derivation of flying capacitor sizing for ac output voltages (for an arbitrary level FCML) is provided. Operating from an 800- $V_{\text {dc}}$ bus, this hardware prototype utilizes switch modules with 100-V rating. Moreover, a 120-kHz switching frequency is enabled through the use of gallium nitride (GaN) FETs and the development of custom-integrated switching cells, which reduce commutation loop inductance and allow for a modular design. The frequency multiplication effect of FCML inverters allows the output inductor of the inverter to be made exceptionally small ( $4.7~\mu \text{H}$ ) while maintaining a 0.7% total harmonic distortion (THD) due to the 1.44-MHz effective inductor ripple frequency.