From Feedback Control of Computing Systems
9.4 PID CONTROL
Proportional–integral–differential control (PID control) combines the three control
actions that we have studied thus far. Figure 9.24 contains a block diagram
of the PID controller. There is one parameter for each control action: KP, KI,
and KD. Since PID controllers have more parameters, there is more flexibility in
design. However, there is more complexity as well.
Before continuing, we want to underscore the generality provided by the PID
controller. In Figure 9.24 the three control actions correspond to the three rows
of boxes in the PID controller. Observe that a proportional controller is a special
case of a PID controller in which KI = KD = 0. This is equivalent to deleting the
first and third rows of boxes inside the PID controller. Similarly, the PI controller
is constructed by having KD = 0, which corresponds to deleting the third row in
the PID controller, and the PD controller is constructed by having KI = 0, which
is obtained by deleting the first row of boxes in the PID controller.
The difference equation for a PID controller is
To find the transfer function...
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