Abstract: A polyphase AC/DC converter, useful as a drive for a DC motor or in a power-sharing electrical power distribution system, comprises a naturally-commutated, phase-controlled, polyphase thyristor bridge and control determining the application of firing signals to the thyristors and operable in the inversion mode of the bridge to transfer conduction of load current between phases at the conventional inversion limit defined as radians advanced from the rectification limit of the bridge, but to operate an extended control range when there is zero load current at the time when the conventional inversion limit would otherwise be applied. In a DC motor drive application, a power increase of up to 15% is obtainable by specification of a higher rated DC motor voltage, and in a power-sharing electrical power distribution system, a similar increase in power transmission may be obtainable.