Automatic Voltage Regulator...?

The AVR improves load voltage by holding the voltage relatively constant, even when the load (which may draw varying amounts of current) varies. It usually does this with a feedback circuit that monitors the load voltage and raises or lowers the voltage if necessary to hold the load voltage constant.

If the loop gain is increased, the load voltage remains more steady than with a low loop gain.

Loop delay has the effect of allowing the load voltage to change briefly if the load (amount of current drawn from the regulator) changes. For example, if the load suddenly starts drawing more current, the load voltage will drop (possibly only by a small amount and for a short time, but it will usually drop). A feedback circuit then detects that the voltage has dropped and will take action to raise the voltage. If there is a longer loop delay, it will take longer for the voltage to return to its proper value.

http://www.tsipower.com/White-Papers-On-AC-Power-S...