Transient Behavior of an 800 kHz Nine Level Single-Phase Flying Capacitor GaN Multilevel Inverter

The volume of industrial three-phase grid connected inverters often suffers from large EMI filters which harm the overall power density. In recent publications the flying capacitor inverter is seen as a possible approach to reduce this filter effort and increase the efficiency. This paper presents a prototype of a nine level GaN single-phase flying capacitor inverter with a switching frequency of 800 kHz and a peak efficiency of 99.2 %. The steady state of such a flying capacitor inverter is already tested with some prototypes. In contrast the transient behavior of the flying capacitor natural voltage balancing is mainly theoretically investigated with no EMI filter and some simplifications to derive a linear system. Especially the impact of typical industrial operation conditions for flying capacitor inverters with very high switching frequencies is not tested right now. This paper should fill this gap and present measurements of the flying capacitor voltages at a DC voltage step. Additionally the effect of rapid changes in the modulation signal and the impact on the flying capacitor voltages is presented and compared to a simulation. These results should lead to a three phase industrial 24 kW grid connected prototype with a volume of approximately four liters.