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

In recent years, wide-band-gap (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 & 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 paper, a multi-step 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. The proposed modulation scheme is applied to a hybrid four-level 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 four-level hybrid converters are verified by experiments.