Realizing Bipolar Power Semiconductor for Highest Reliable Applications

Abstract

During the 1970s thyristors were used for the first time to realize a Line Commutated Converter (LCC) for High Voltage Direct Current (HVDC) transmission lines which decreased power losses and increased reliability. At that time thyristors with a blocking capability of 1.65 kV and a silicon diameter of 35 mm had been specially developed for this application. Nearly 43,000 thyristors were installed in this first transmission line using thyristors, Cahora Bassa, to transfer 1920 MW at ± 533 kV over 1420 km from Mozambique to South Africa. Currently there is a trend to realize HVDC transmission lines increasingly with Voltage Source Converters (VSC). This was further stimulated by the introduction of the Modular Multilevel Converter technology (MMC) which decreased system complexity greatly. Today's installations are built up to ±500 kV and 2 GW and for future projects ±800 kV with 5 GW are under discussion. Although the main semiconductor device in VSCs is the IGBT, classical bipolar devices are critical for VSC operation, too. Special developed diodes with extreme soft switching behavior are used as Free Wheeling Diodes (FWD) and antiparallel thyristors protect the IGBTs in case of surge current events. Recently Press Pack IGBT (PPI) has come into focus as an alternative realization for VSC architectures.