Answer / sks

well, increasing D action for a controller can make a
controller random in error elimination because even for a
step change D generates a spike( means tries to compensate
for change very quickly). if its increased to its limits, D
action will overtake the process value change and this will
cause further offsets that I action wouldn't be able to
compensate due to its slow response against such a rapid error.

result is a quick overvalued offset !

Answer / david

In PID
P is Propositional means it will adjust the output propositional to the error. For example a Tacho connected to a motor, to control it's Torque and RPM at a constant level.
I is Integral means calculating the area, according to the area of the error the output is adjusted. For example, the difference between positive cycle area and negative cycle area.
D is differentiation means calculating the angle difference and driving output for example
In a 3-phase system, If the load on R-phase is more than other two phases, phase angle
difference will occur so it will calculate the angle and drive output For example Auto Power factor adjuster.

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