The Rotary Era, Part 1: Early ac-to-dc Power Conversion [History]
Thomas J. Blalock · IEEE Power and Energy Magazine · 2013
During the early 20TH Century, machines known as synchronous converters, or rotary converters, were mainly responsible for the successful transition from early Edison direct current (dc) power distribution to alternating current (ac) distribution. Rotary converters were the most efficient means of converting ac power into dc power so as to be able to continue supplying established dc motor loads.