In an SCR circuit, the angle of conduction can be changed by the variation in firing angle or variation of conduction of SCR by delaying the application of gate current.
It can be done by two way:
Phase Shifting Gate control: It causes 0 to 180? delay of conduction. The phase angle of the gate voltage is changed with respect to the anode cathode voltage.
Pulse Triggering: The gate voltage can also be applied by giving pulses to the Gate terminal. The duty cycle of the pulses can be varied to provide variation in the conduction.