Predicting static losses in an inverter-leg built with SiC normally-off JFETs and SiC diodes

Abstract

Predicting static losses in switches is an essential step to design a converter. This document details the methodology of a method to calculate static losses in an inverter leg built with SiC Normally-Off JFETs and diodes. Different parameters such as the temperature, the load current and the modulation ratio... are taken into account. As the JFETs can be used in reverse conduction, two strategies (using or not this capability) are described and compared. The devices are characterized and modelled, then analytical calculations are used to compute the static losses in each component. As the behaviour of the components depends on the temperature, an iterative program is used to determine the steady-state temperature of the junctions and the static losses. A good agreement is demonstrated between measurements and the proposed model with a constant current. The proposed method is applied to a three phase inverter to evaluate the benefit of using SiC devices instead of a Si power module.