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• attractive cost/performance enabling a measureable system advantage • volume production capability • product definition driven by system understanding During the last years, intensive studies have been carried out mainly in order to understand the system benefits of SiC. The increase of switching frequency for a converter using unipolar SiC transistors can result in dramatically reduced volume and weight of the magnetic components. From an analysis carried out by Infineon, a converter built on SiC devices is a third of the size and 25 percent of the weight compared to a current Si based reference solution. Thanks to the significant reduction in volume and weight, the system costs can also bereduced by more than 20 percent. Figure 2: Benefits of SiC depending on use in arenas and applications. Over the next few years, SiC solutions will expand into other application fields such as industrial or traction drives. The reasons for this are the market forces pushing for loss reduction, not only for the sake of improved efficiency but also for smaller packages – resulting from reduced heat sink requirements. As shown in figure 2, SiC is already being used for high end and niche solutions. Today’s designs use these benefits to reduce system cost in specific application areas. In the future, more and more applications will benefit from the overall loss reduction made possible by implementing SiC solutions. In this regards, the next major step forward will be the introduction of SiC switches. Figure 3: Material property comparison of silicon vs. silicon carbide. To understand the differences between Si and SiC solutions, it has to be made clear that silicon carbide devices belong to the so-called wide band gap semiconductors. A comparison of Si vs. SiC material properties is shown in figure 3. The voltage range for fast and unipolar Schottky diodes as well as field effect based SiC switches (MOSFET, JFET) can be extended to over1000V. This is possible because of inherent properties of the SiC material: The low leakage current in high voltage Schottky-diodes is possible because of the metal-semiconductor barrier which is two times higher than inSi Schottky diodes. The very attractive, specific on-resistance of unipolar transistors compared to Si is achieved because of the breakdown field strength which is approximately ten times higher. Figure 4 shows the minimum specific on-resistance of different semiconductors versus the desired blocking voltage (only the drift region is used here, any substrate contribution to the resistivity is neglected). The end points of each line symbolize the usable voltage range of the specific semiconductor in a unipolar configuration excluding Super-Junction MOSFETS. Figure 4: Comparison of on-resistance and blocking voltage of SiC and Si. SOLAR POWER SiC transistors are about to become an attractive alternative to today’s established IGBT technologies in industrial power electronics. The dedicated material properties of SiC enable the design of minority carrier free unipolar devices instead of the charge modulated IGBT devices at high blocking voltages. This is based mainly on the high critical field which is provided by the wide bandgap. The loss restrictions of IGBTs are caused by the dynamics of minority carriers. In MOSFETs those minority carriers are eliminated. As an example, extremely high dv/dt slopes in the range above 100kV/μs have been measured for SiC MOSFETs. In the beginning, the superior dynamic performance of SiC based transistors compared to IGBTs in the area of 1200V and higher was seen as the most important advantage. However, recent results indicate a significant future potential in the IGBT technologies, as shown by Infineon’s TRENCHSTOP™5 technologies. Taking the long term view, however, the fundamental differences between the IGBT and the unipolar SiC switch will increasingly attract attention. With the two major differences being: first, the linear, threshold free I-V curve of the output characteristic, second, the ability to integrate a body diode with the option of synchronous rectification. Based on these properties, the device offers thresholdfree conduction behavior in synchronous rectification mode. In addition, the number of necessary components is reduced by half. This leads toa significant reduction of the required power module footprint. On system level, the feature of threshold free conduction behavior offers a significant potential for loss reduction. Many systems are operated for a large portion of their lives under partial load conditions and conduction losses are considerably lower compared to the competing standard IGBT technologies. Even at very low frequencies of less than 5 kHz and unchanged dv/dt slopes it can be seen that a threshold-free switch with integrated body diode, in synchronous rectification mode, offers a potential of 50 percent total loss reduction compared to a commercial GBT solution available today. The comparison in losses can be seen in figure 5. 23 energetica INDIA · MAY | JUN16


energetica-india-57_asiapowerweek
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