Three-phase power control and phase shifter therefor

Claim 1

A three phase control circuit of the type having three input power lines carrying alternating current with respect to a neutral line, an output line corresponding to each input line, and a pair of silicon controlled rectifiers each having a control electrode and each connected between one of said input lines and the corresponding output line with their respective anodes and cathodes in mutually opposite orientation, and a trigger pulse forming means for initiating conductivity of each associated pair of said silicon controlled rectifiers during selected portions of alternate voltage cycles on an associated of said supply lines, said circuit characterized by the improvement comprising: first, second, and third potentiometer means for deriving a voltage signal which is proportional to the voltage on the associated input line; first, second, and third wave squaring means coupled to the wipers of said first, second, and third potentiometer means, for providing first, second, and third trains of alternating square wave having voltage phase differing from that of the alternating current of the respective input lines; first, second, and third differentiating means coupled to said first, second, and third squaring means, respectively, for forming first, second, and third trains of alternating, spiked waves; first, second, and third emitter follower means coupled to said first, second, and third differentiating means respectively; a diode connected to Each of said control electrodes; first, second, and third transformer means for coupling said first, second, and third emitter follower means through said diodes to said first, second, and third silicon controlled rectifier pairs to bias said rectifier pairs to pass only a selected portion each of a half-cycle of electrical current from each input to the respective output line.