AC DRIVES MOVE INTO dc TERRITORY.

AC motors surpass conventional dc types on many counts. But until recently, dc was preferred for most adjustable-speed drives because it usually involves less initial cost and often provides more precise control than ac. But economics and technology are changing, with the cost of ac drives falling and with new solid-state circuits making ac suitable for applications once limited to dc or hydraulic motors. Moreover, so-called brushless motors and the high-speed switching processes developed for ac drives combine to provide the best features of both ac and dc systems.