Abstract: An AC-to-AC converter operating as a current-source between an AC input line and an AC output line connected to a load, for instance an AC motor, includes three groups of bilateral switches controlled selectively within each group so as to generate a quasi square-wave current in each output phase while establishing a DC voltage between two of the output phases at a time, the third phase being idle, the magnitude of the output voltage being controlled in relation to the firing angle of the switches and the frequency being established by controlling the duration of each square-wave alternance. The duration of such alternances is set to 120 degrees of the output wave, followed and preceded by a 60 degree zero-current period.

Abstract: A contactor includes two DC sensors within the housing which are isolated from the tripping unit, from the power supply and from each other by the combination of a transformer and photoelectric coupling, the sensed signals being pulse width modulated and demodulated on the respective sides of the photoelectric coupling barrier.

Abstract: A three-pulse UFC system uses three groups of three bilateral switches controlled according to a switch polarity pattern to generate AC currents to a load, and a deadband hysteresis having upper and lower limits is used to maintain the load current so as to match a reference current.

Abstract: In a combined cycle electrical power generator plant, the shut-down process includes a cooldown control period which is minimized before shutting down the gas turbine by detecting first whether a non-steaming condition has been reached and whether the gas turbine has been reduced to minimum load.

Abstract: To eliminate thyristor failure due to voltage imbalance across series-connected thyristors during reverse voltage recovery caused by current discontinuity under continuous pulse application to the thyristors, the continuous pulse is discontinued after a time interval of application which is a function of the control signal establishing the firing delay angle. The continuous pulse is reinstated as in a double-pulse mode, thereafter, with the same controlled duration.

Abstract: A two-pole inverter bridge has an inductor mounted between the two controlled switches in each pole and a resonant load is connected across the poles between ends of the inductors which are similarly situated relative to the terminals. In each pole one antiparallel circuit includes an auxiliary controlled switch and another antiparallel circuit includes only a diode. Fault protection is provided with an auxiliary source mounted between opposite ends of the inductors for applying reverse bias to the controlled switches of the poles whenever a fault in the inverter is detected.

Abstract: A ramp generator includes a master counter repeatedly ramping through for ramp-intersect operation of a digital pulse generator, while firing at the intersection, or when above the reference will cause a complementary digital change to define with the master counter count a ramp count on a subsequent ramp and adjacent zone below, thereby to adjust rapidly to a fast change of reference.