DEVICE FOR REGULATING THREE-PHASE VOLTAGE

In a three phase static voltage regulator comprising a set of parallel-connected thyristor and diode between each phase R, S and T of a three phase supply source and the corresponding phase of a three phase load, a pulse is produced in response to each single phase source voltage passing by a zero amplitude where the voltage amplitude changes from a negative to a positive value. A pulse is also produced in response to each such passage by a zero amplitude of the difference voltage between the phases R and S, which pulses are counted and digital-to-analog converted to produce a sawtooth signal of period To. During each period To, the sawtooth signal is compared with a reference signal to produce a control pulse. At the beginning of each control pulse, the pulses obtained from the difference voltage are applied to the gate of the thyristor interposed between the phase R and the corresponding phase of the load to turn the same on whereby a voltage is applied to the load. After the latter voltage is detected, the pulses obtained from the single phase voltage of each phase R, S and T are transmitted to the gate of the thyristor connected to this phase to turn the thyristors on and supply the load with power, until the control pulse ends. In operation, the electric power supplied to the three phase load is adjusted by adjusting the width of the control pulses through adjustment of the amplitude of the reference signal.