**2. PID controller design for performance**

Time response of the controlled variable y(t) is modifiable by tuning proportional gain K, and integrating and derivative time constants Ti and Td, respectively; the objective is to achieve a zero steady-state control error e(t) irrespective if caused by changes in the reference w(t) or the disturbance d(t). This section presents practice-oriented PID controller design methods based on various perfomance criteria. Consider the control-loop in Fig. 1 with control action u(t) generated by a PID controller (switch SW in position "1").

Fig. 1. Feedback control-loop with load disturbance d(t) and measurement noise n(t)

A controller design is a two-step procedure consisting of controller structure selection (P, PI, PD or PID) followed by tuning coefficients of the selected controller type.
