Abstract: A new and improved control subassembly for HVDC power converters and method of its use during transient faults affecting the A. C. system employed in the HVDC power transmission system to assure the presence of adequate firing and commutating voltages across the respective HVDC thyristor valves during selected intervals of the alternating current periods of the respective phases. The HVDC power converters used in the system include gating circuits for gating-on respective ones of the thyristor valves during selected intervals of the alternating current periods of the respective phases. The gating circuits include equidistant-spaced gate firing pulse generating circuits for supplying equidistant-spaced gating-on firing pulses to the gate drives for the respective HVDC thyristor valves of the HVDC bridge power converter during normal operation of the converter in the presence of symetrically-shaped A. C. system voltage waveforms.

Abstract: An HVDC electric power delivery system having a floating current order current control subsystem is described. The system is comprised by power converters at each end of an HVDC power conductor link each of which includes a plurality of controllable electric valves connected between alternating current and the direct current electric power conductors together with means for cyclically firing the valves in a predetermined sequence and at firing angles measured with respect to the alternating voltage that can be varied to control the flow of power between the alternating current system and the direct current system. Each of the power converters further includes a regulator for comparing a plurality of input control signals which respectively represent different predetermined operating characteristics of the HVDC system during operation and for deriving an output error control signal that controls the firing angles of the valves.