PID Controllers An Overview

PID “Actions” The PID controller has three actions. Each of these has its own purpose: 1.P-Action is infinitely sensible. The command out to the actuator is proportional to the size of the error. If the error is small, the action is a nudge. If the error is big, the action commanded is large. 2.I-Action is used to eliminate steady-state error.

PID “Actions” 3.D-Action is anticipatory. It becomes active before the error even develops. If the change-in-error is large, this action will be large before the error even develops into a significant deviation.

The PID-Controller Family There is always a P-Action, but there are four members of the PID-controller family: 1.P-only – K I and K D = 0 2.PI – K D = 0 3.PD – K I = 0 4.PID – K P, K I, K D ≠ 0

The PID adds poles and zeros to the system

PD-controller

PID-controller

Implications This leads to all sorts of strategies for “designing” PID controllers.