Highly Efficient Single-Phase Three-Level Three-Leg Converter Using SiC mosfets for AC–AC Applications

This paper proposes a highly efficient single-phase three-level three-leg converter using silicon carbide (SiC) mosfets. The proposed converter shows high efficiency and comprises two three-level T-type legs and a common leg, which operate as a rectifier and an inverter, respectively. By sharing the common leg, the power losses of the common leg are minimized. Multilevel legs offer significant benefits in terms of harmonic performance and reduced switching losses compared with two-level legs. Neutral-point-clamped type legs suffer from relatively large conduction losses. On the other hand, T-type legs incur low conduction losses and large switching losses because their outer switches block the full dc-link voltage. In the proposed converter, by replacing the outer switches in the T-type leg with SiC mosfet devices, switching losses are significantly reduced. This feature allows the switching frequency to be increased with the same power loss. The power losses of the proposed converter are theoretically analyzed in detail and comprehensively compared with those of conventional three-leg converters. Experimental results based on a 3-kW prototype show that the proposed converter provides a maximum efficiency of 99.0% and high power quality.