Prospects and Challenges for SiC Power Devices in MMC-VSC-HVDC Applications

VSC-HVDC systems are currently implemented in silicon IGBT technology. Advocates of SiC as a high voltage technology have long suggested that SiC has the potential to enhance the performance of VSC-HVDC systems by improving the energy conversion efficiency. The topology of choice for the latest VSC-HVDC systems is modular-multilevel-converters (MMC) comprised of cascaded half or full bridge sub-modules with voltages ranging between 1.3 kV and 2.8 kV. However, the current state of the art SiC power devices are still short of the ratings required for HVDC. Furthermore, the low switching frequencies used in MMC-VSC-HVDC means that conduction losses dominate hence, the fast-switching capability of SiC power devices is not necessarily an advantage. State of the art high voltage silicon IGBTs/PiN diodes exhibit comparable if not lower losses in comparison with commercially available SiC power MOSFETs/Schottky diodes of similar ratings. This review evaluates the potential performance of SiC power devices in MMC-VSC-HVDC systems, compares them with IGBT/IGCTs and reviews the challenges ahead for SiC devices.