Turn-off control means for an ac-to-dc electric power converter

Abstract From the Canadian patent

In the propulsion system of an electric locomotive, a-c wayside power is converted to direct current for the traction motors by a plurality of phase-controlled rectifying circuits having serially connected outputs. To improve power factor, forced commutation means is provided for turning off the controllable valves in one of the circuits at a desired "extinction angle." This angle is varied with motor speed, but its effective range of variation is restricted so as to avoid undesired leading power factor at low speeds to optimize power factor when the locomotive is running at full power, and to prevent misoperation when the level of load current is low.