Peter Etter

Solid state: Thyristors on the move: New applications are seen in power converters and inverters for trains, industrial motors, and HVDC

High-power, high-frequency thyristors are playing an increasing role as basic switches in static converters and inverters that supply power to locomotives rapid-transit coaches, and variable speed motors for industry. These converters are also used in the transmission of high-voltage DC power. High-power thyristor applications are of two general types, depending on whether the thyristor equipment operates from an AC or a DC source. Thyristors operating from an AC supply function either as cycloconverters (AC/DC converters) or as AC switches (AC/AC converters). Converters are used extensively to supply variable DC voltage to control the speed of DC motors. Similar converters, designed to operate at higher power, are used in HVDC power transmission. The second type of application is operation from a DC source, such as a battery or rectified AC. These thyristor circuits feed power loads requiring a variable AC voltage (DC/AC conversion). Inverters are used primarily for driving variable-speed AC motors and for reliable sources of AC power for such critical loads as computers (uninterruptible power supplies).