A Dual-Current-Path State-Based Multistep Soft-Switching Modulation Scheme for Hybrid Device Multilevel Converters

In recent years, wide bandgap (WBG) devices such as silicon carbide (SiC) MOSFET have shown a promising future for achieving high-power-density design in power electronic converters. However, its wide applications are still constrained by the high cost. The SiC and Si hybrid multilevel converter is a high-performance and cost-effective solution. However, these hybrid device converters have limited control degree of freedom for other control objectives such as dc bus capacitor voltage balancing. In this article, a multistep soft-switching modulation scheme is proposed for hybrid device multilevel converters. It utilizes dual-current-path (DCP) state and other intermediate states to create soft-switching conditions for all Si devices during the switching between multiple voltage levels. As a result, without adding huge additional switching losses, all switches in the hybrid device converters can operate in high frequency (HF). The proposed modulation scheme is applied to a hybrid four-level (4L) converter and realizes the capacitor voltage balancing over the entire operation operating range but also guarantees the soft-switching of all Si devices. The modulation scheme and the control effects for 4L hybrid converters are verified by experiments.