PID Controllers An Overview

1. PID ControllersAn Overview

2. PID “Actions” The PID controller has three actions. Each of these has its own purpose: 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. I-Action is used to eliminate steady-state error.

3. PID “Actions” 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.

4. The PID-Controller Family There is always a P-Action, but there are four members of the PID-controller family: P-only – KI and KD = 0 PI – KD = 0 PD – KI = 0 PID – KP, KI, KD ≠ 0

5. The PID adds poles and zeros to the system So with a PI-controller, you add a pole at the origin, a zero at -KI/KP, and a gain.

6. PD-controller So with a PD-controller, you add a zero at -KP/KD and a gain.

7. PID-controller So with a PID-controller, you add a pole at the origin, two zeros, and a gain.

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