Integral Cycle Control or Principle Of On Off Control

In On-Off control, the thyristor is triggered for some input cycles, i.e, on period (Ton) and

remains un triggered for certain input cycle, i.e. off period (Tuff).

In on period, we get output same as that of input while in off period as the name indicates

we get no output or we can say zero voltage.

Such type of controls are used for temperature or other high time constant type systems

where on/off control does not cause fluctuation in system performance.

For e.g. In such applications no variation in temperature or speed will be observed if

control is obtained by connecting the load to source for on-cycles and then disconnecting

the load from source for off-cycles.

This type of power control consists of an integral number of cycles for the on-time (Ton)

and then switching off the supply for a further number of integral cycles, so it is also

referred to as integral cycle control.

Integral cycle control is also known as burst firing, zero-voltage switching, cycle selection

or cycle syncopation.

The principle of On-Off cycle control can be explained by referring to Fig as shown below.

Principle of on-off control or integral Cycle Control

In upper figure all the thyristor are triggered at the zero crossing instant of the input wave only.

When we apply gate pulse then the source get connected to the load and we get same output as like input.

The waveforms of integral Cycle Control is shown in below graph.

Waveforms of integral Cycle Control

In line current, it introduces sub harmonics, so this type of control is not popular.

Electrical Engineering