IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 5, MAY2014 2527 An Experimental Evaluation of SiC Switches in Soft-Switching Converters Per Ranstad, Member, IEEE, Hans-Peter Nee, Senior Member, IEEE,J¨ orgen Linn´ er, and Dimosthenis Peftitsis, Member, IEEE Abstract—Soft-switching converters equipped with insulated gate bipolar transistors (IGBTs) in silicon (Si) have to be dimen- sioned with respect to additional losses due to the dynamic con- duction losses originating from the conductivity modulation lag. Replacing the IGBTs with emerging silicon carbide (SiC) transis- tors could reduce not only the dynamic conduction losses but also other loss components of the IGBTs. In the present paper, there- fore, several types of SiC transistors are compared to a state-of- the-art 1200-V Si IGBT. First, the conduction losses with sinusoidal current at a fixed amplitude (150 A) are investigated at different frequencies up to 200 kHz. It was found that the SiC transistors showed no signs of dynamic conduction losses in the studied fre- quency range. Second, the SiC transistors were compared to the Si IGBT in a realistic soft-switching converter test system. Using a calorimetric approach, it was found that all SiC transistors showed loss reductions of more than 50%. In some cases loss reductions of 65% were achieved even if the chip area of the SiC transistor was only 11% of that of the Si IGBT. It was concluded that by increasing the chip area to a third of the Si IGBT, the SiC vertical trench junction field-effect transistor could yield a loss reduction of approximately 90%. The reverse conduction capability of the channel of unipolar devices is also identified to be an important property for loss reductions. A majority of the new SiC devices are challenging from a gate/base driver point-of-view. This aspect must also be taken into consideration when making new designs of soft-switching converters using new SiC transistors. Index Terms—Bipolar junction transistor (BJT), conductiv- ity modulation, insulated gate bipolar transistor (IGBT), junc- tion field-effect transistor (JFET), metal–oxide–semiconductor FET (MOSFET), resonant converters, silicon carbide (SiC), soft switching. I. INTRODUCTION T ECHNOLOGICAL changes resulting in material savings are key factors for reducing cost in most power electron- ics equipment. One of the most effective ways to achieve such material savings is to increase the switching frequency of the Manuscript received February 15, 2013; revised May 10, 2013; accepted May 13, 2013. Date of current version January 10, 2014. Recommended for publica- tion by Associate Editor C.-M. Zetterling. P. Ranstad (corresponding author) and J. Linner are with TS-AQCS, Alstom Power, Vaxjo 35112, Sweden (e-mail: per.ranstad@power.alstom.com; jorgen.linner@power.alstom.com). H.-P. Nee is with the Electrical Engineering Conversion Laboratory, KTH Royal Institute of Technology, Stockholm SE-10044, Sweden (e-mail: hansi@kth.se). D. Peftitsis is with the Department of Electrical Machines and Power Elec- tronics, KTH Royal Institute of Technology, Stockholm 10044, Sweden (e-mail: dimost@kth.se). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPEL.2013.2265380 Fig. 1. Circuit diagram of a series-loaded resonant converter. converter. With metal–oxide–semiconductor field-effect tran- sistors (MOSFETs), on the one hand, switching frequencies of several hundred kilohertz are possible with hard-switching con- verters [1]. In applications where the maximum voltage rating of high-performance MOSFETs is not sufficient, on the other hand, insulated gate bipolar transistors (IGBTs) are usually cho- sen, and the upper limit of the switching frequency in this case is approximately 10–20 kHz for hard-switching converters. The reason to this limitation is that the switching losses increase with the switching frequency. In the continuous trend toward ever more compact converters various soft-switching [2]–[10] technologies have, therefore, been suggested, as these technolo- gies, at least theoretically, can perform switching transitions without any significant losses. One of the most popular soft- switching converters is the series-loaded resonant (SLR) con- verter [11]–[13]. A circuit diagram of this converter is shown in Fig. 1. If this converter is operated above the resonant frequency using capacitive snubbers, soft-switching conditions should be possible to achieve at both turn ON and turn OFF. However, regardless if frequency control [11], [12], [14], phase-shift con- trol [15], or dual control [16] is used, it is never possible to eliminate the switching losses. This is partly due to the tail cur- rent [17]–[19]. Another important source of additional losses at high switching frequencies are the losses associated with the conductivity modulation lag [18], [20], [21]. These losses are simply a result of that a certain time is necessary for the device to be brought into deep saturation. At high switching frequencies, this phenomenon cannot be disregarded as the time constant of the conductivity modulation lag approaches the same order of magnitude as the cycle time. In [22], therefore, an extensive experimental investigation involving several types of IGBTs was performed. Both tail-current and conductivity-modulation- lag effects were covered. From the results, it was obvious that different types of IGBTs had very different performance with 0885-8993 © 2013 IEEE. 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