SiC-based Power Converters for High Temperature Applications

As commercial-grade silicon carbide (SiC) power electronics devices become available, the application of these devices at higher temperatures or frequencies has gained interest. This paper contains temperature-dependent loss models for SiC diodes and JFETs and simulations for different power converters that are useful for predicting the efficiency of these converters. Additionally, tests to characterize the static and dynamic performance of some available devices are presented to give further insight into the advantages that might be gained from using SiC devices instead of Si devices for hybrid electric vehicle applications. Introduction Increasing demand for more efficient, higher power, and higher temperature operation of power converters has led to the development of wide bandgap semiconductor power electronic devices and in particular silicon carbide (SiC) power electronics. The high temperature operation capability of these devices increases the power density of converters incorporating them because of reduced thermal management and heat sink requirements that yield reduced weight and cost. To ultimately gain full advantage of SiC power electronics devices requires high temperature packaging techniques, gate drives, and passive components [1-4]. Device and system-level temperature-dependent loss models have been developed for transportation applications and utility applications to aid in gauging the impact that these new devices might have in terms of efficiency and heat sink requirements [5-7]. Device and system loss models for SiC diodes, JFETs, and MOSFETs have shown that they will become the devices of choice once issues such as fabrication and packaging of these devices are solved. At present, SiC Schottky diodes are the only commercially available SiC devices. These diodes are used in several applications, and have proved to increase the system efficiency compared with Si device performance when used as antiparallel diodes in bridge converters [8-9]. Significant reduction in weight and size of SiC power converters with an increase in the efficiency is projected. Some applications such as hybrid electric vehicles require that devices be able to handle extreme environments that include a wide range of operating temperatures (from -40oC to 200oC). In the following sections, models and experimental tests for the static and dynamic performance of some commercially available SiC Schottky diodes and experimental samples of SiC JFETs and MOSFETs in a wide temperature range will be presented. Temperature Dependent Modeling of SiC Schottky Diodes In this section, SiC Schottky diodes are characterized by both theoretical analysis and experiments. The models for static state (forward conduction) and dynamic state (reverse recovery) will be discussed. Schottky Diode Static State. The structure of a SiC power Schottky diode and its equivalent circuit are shown in Fig. 1. VFB is the voltage drop across the Schottky barrier; RD is the resistance of the lightly doped drift region; RS and RC are the resistances of substrate and contact, respectively. Materials Science Forum Vols. 556-557 (2007) pp 965-970 online at http://www.scientific.net © (2007) Trans Tech Publications, Switzerland Online available since 2007/Sep/15 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 160.36.252.213-18/08/08,17:01:48) 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 273 323 373 423 473 523 Junction Temperature (K) R e s is ta n c e ( o h m ) Simulation Experiment CSD05120