Tuning a control loop is arranging the control parameters to their optimum values in order to
obtain desired control response. At this point, stability is the main necessity, but beyond that,
different systems leads to different behaviors and requirements and these might not be
compatible with each other. In principle, P-I-D tuning seems completely easy, consisting of
only 3 parameters, however, in practice; it is a difficult problem because the complex criteria
at the P-I-D limit should be satisfied. P-I-D tuning is mostly a heuristic concept but existence
of many objectives to be met such as short transient, high stability makes this process harder.
For example sometimes, systems might have nonlinearity problem which means that while the
parameters works properly for full load conditions, they might not work as effective for no
load conditions. Also, if the P-I-D parameters are chosen wrong, control process input might
be unstable, with or without oscillation; output diverges until it reaches to saturation or
mechanical breakage.