SiC versus Si Freewheeling Diodes: A Comparative Study of their Impact on IGBT VCE Overshoot in 3-level T-type Power Converters

Abstract

Using SiC freewheeling diodes with Si IGBTs is a typical cost-effective alternative to full-SiC power electronics. The benefit of SiC JBS diodes in switching losses reduction, due to zero reverse recovery, has been widely reported in literature. The lack of reverse recovery losses is a key enabler for high efficiency and high frequency power converters. Another important advantage of SiC diodes is absence of forward recovery, critical from the perspective of reduced energy losses and voltage overshoots. The excessive voltage overshoots, likely during overloading conditions of power converters, can lead to destruction of semiconductors or impact their reliability. In this paper, 3-level silicon IGBT based T-type rectifier topologies with Si and SiC diodes have been investigated. The T-type topologies present a distinct scenario where the horizontal/ T-switches are ideally rated for 50% voltage of the DC bus, and the vertical/ outer switches are rated for 100%. In rectifier operation, the T-switches need to endure reverse/ forward recovery from diodes of the higher voltage outer switches. The objective of this paper is to present a detailed experimental evaluation of SiC and Si diodes in these topologies, with emphasis on T-switch IGBT V CE overshoot.