Direct Control Strategy for a Three Phase Eight-Level Flying-Capacitor Inverter

Abstract

Flying-capacitor converters are a multilevel topology which provide several advantages over classic two level converters. They reduce a dv/dt phenomena and offer a better harmonic content. On the other, thanks to the series connection of commutation cells, they provide a means of increasing power and voltage. Furthermore, for certain failures, their structure can be reconfigured in order to work in degraded mode. However, all these advantages come at the price of a more complex control since it is necessary to maintain the flying capacitors voltages at their target operating levels. To overcome this problem and motivated by an industrial application in collaboration with GS Maintenance company, a direct control strategy is proposed for a three-phase eight-level flying capacitor inverter. It is showed that the control strategy is simpler than other control algorithms proposed in the literature, like for example Pulse Width Modulation (PWM) control, and leads less expensive hardware implementations. Moreover its stability is proved by means of Lyapunov theory. This approach is compared to the conventional PWM control to show its good performances during disturbances through simulation results.