its basically a PWM based voltage regulator.
for smooth regulting of high voltage devices(220v).
if Duty cycle of pulse is 20 and the frequency is 50hz the voltage will be minimum and if we change it to 80% its voltage will be high and on 95% the voltage will be maximum.
Step 1: PCB of ECVR(electronically Controlled Voltage Regulator)
here is the simulated design of ECVR(electronically controlled voltage regulator) and its result.
and the PCB of ECVR.