A rotary converter is a type of electrical machine which acts as a mechanical rectifier or inverter. It was used to convert alternating current (AC) to direct current (DC), or DC to AC power, before the advent of chemical or solid state power rectification. They were commonly used to provide DC power for commercial, industrial and railway electrification from an AC power source.
Read more about Rotary Converter: Principles of Operation, Applications, Obsolescence, Self-balancing Dynamo