Power transistors in variable speed drives

Since the mid-1960s, thyristors have become established as the power control element in applications from domestic lighting and washing-machine controllers to d.c. rolling-mill drives and inverters for alternator starting, with ratings up to at least 10 MW. During this period, transistors were also evolving into types suitable for power control. Today, British-developed 500 V 300 A transistors are being applied to d.c. servo drives and inverters for multiple-unit traction drives. In application to both a.c.- and d.c.-motor drives, the fast switching capability of transistors can have advantages over thyristors, and we shall see it grow as an alternative power controller