The integral cycle control (on-off control) and phase angle control are the two types of AC voltage controller.
The principle of ON-OFF control:
The on-off control is also called an integral cycle control. The on-off control is shown in the figure for single phase full wave AC voltage controller. To avoid the fluctuations at the output the turning on and off operation should be fast. The power semiconductor switches are used in integral cycle control. In integral cycle control, the switch is turned on for the certain number of complete cycle and the switch is turned off for the certain number of cycles. The integral cycle control is not very popular. Because it introduces sub-harmonics in line current. Integral cycle control is used for heating applications and speed control of AC motors.
Phase control of AC voltage controller:
Phase angle control is the type of AC voltage controller. The power flow can be control by firing angle control. In phase control, the switch is on for some period of each cycle.