Power Electronics for Future Utility Applications

Medium-voltage converters, originally developed for industrial drives (e.g. in steel and paper mills), have nowadays entered utility applications. For several years, the growing need for power quality in distribution systems in conjunction with the large scale integration of renewable energy sources has boosted the demand for new technologies. Together with communication systems, power electronics are the key enabling technology to meet these challenges. This paper addresses several utility applications for power electronics, some of which are in use already today though market penetration is still low. In the field of high power inverters, conventional 3-level hard-switching converters as presently used e.g. in wind turbines are presented alongside with soft-switching converters and their possible applications such as STATCOMs or mini-turbines. The possibility of using DC instead of AC transmission and distribution systems will be discussed. DC systems have already been used for several decades to transmit bulk power. New opportunities for the use of modern VSC-HVDC will be shown, such as DC distribution systems. For this novel application, new technologies are needed, such as multi-megawatt DC-DC converters and DC circuit breakers; possible concepts for these technologies will be addressed. Cycloconverters, a rather conventional technology, have been applied recently in innovative ways to increase the efficiencies of very high-power pumped- hydro storage systems. Due to the fact that the development of new converter systems is always strongly related to the available device technology, future high-power devices will finally be discussed.