The project
is designed to achieve integral cycle switching, a method to remove whole
cycle, cycles or portions of cycles of an AC signal. It is a well-known and old
method of controlling AC power, especially across linear loads such as heaters
used in electric furnace. However the concept of achieving the cycle stealing
of voltage waveform by use of microcontroller can be very precise as per the
program written in assembly / C language so that the actual time-average
voltage or current experienced at the load is proportionately lower than the
whole signal if applied to the load. In place of a linear load to be used in
the output, a series motor or lamp can be used to verify the output. One side
effect of utilizing this scheme is an imbalance in the input current or voltage
waveform as the cycles are switched on and off across the load.
In this project we
are using comparator for zero crossing detection which is fed as an interrupt
to microcontroller of 8051 family. Here the microcontroller delivers the output
based on the interrupt received as the reference for generating triggering
pulses. Using these pulses, we drive the opto-isolators for triggering the TRIAC
to achieve integral cycle control as per the input switches interfaced to the
microcontroller. A lamp is provided in this project in place of a motor for
demonstration purpose.
Further this
project can be enhanced by using feedback mechanism to automatically maintain
desired output to the load by appropriate cycle stealing.
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