Phase Control Scheme with High Accuracy and Symmetry of the Control Pulses

Very high currents and low voltages are used in some technological processes. Typical examples are galvanic processes, spot and roll welding, etc. In this case the use of a powerful transformer and control in its primary winding is strongly required. In order the saturation of the magnetic core and current surges to be avoided it is necessary the control pulses during each half-period of the supply voltage to have the same parameters with respect to the firing angle of each thyristor. In the present paper a thyristor phase control scheme satisfying the above mentioned conditions is proposed. It guarantees both high accuracy and symmetry of control pulses. This is achieved with the use of only one generator. The generator forms pulses with exactly the same parameters for each half-period of the supply voltage. These pulses are fed to the corresponding thyristor.