Zero deadband reversing control

Claim 1

A zero deadband response reversible phase controlled rectifier control system comprising means for developing a control function indicative of desired load operation, timing means for developing timing functions for the controlled switch elements of said phase controlled rectifier, each timing function establishing the range of current conduction for each controlled switch element responsive thereto, the timing functions being phase displaced from one another by said timing means with periods of overlap therebetween creating common ranges of controlled switch element conduction such that during substantial satisfaction of the control function by the load, controlled switch elements capable of conducting forward load current and controlled switch elements capable of conducting reverse load current conduct nonsimultaneously during half cycles of the alternating voltage, comparing means for comparing said control function with said timing functions to obtain a time of firing indication for each controlled switch element, firing means responsive to the time of firing indications from said comparing means for triggering each controlled switch element into conduction at the time dictated by the corresponding time of firing indication, and conduction direction control means responsive to the state of conduction of the controlled switch elements to prevent conduction of forward current conducting controlled switch elements when reverse current conducting controlled switch elements are conducting and to prevent conduction of reverse current conducting controlled switch elements when forward current conducting controlled switch elements are conducting, said conduction direction control means being in an oscillatory state between forward and reverse blocking when neither forward nor reverse current conducting controlled switch elements are conducting such that substantially instantaneous conduction direction control is provided.