What does a PD controller do?
A PD controller is a proportional-derivative controller. A PD controller is essentially a controller which responds to the rate of change of the process error. Properly designed PD controllers can affect the performance of a control system in the following ways: * Improve damping and reduce maximum overshoot * Reduce rise and settling time * Increase bandwidth * Improvement of gain and phase margin However, PD controllers do have a few caveats * PD controllers are not suited for use with with lightly damped or initially unstable systems. * PD controllers accentuate noise at higher frequencies * The setpoint to a PD controller (in most cases) will require insertion of a lag. In an industrial plant, a PD controller is applied in applications where overshoot cannot be tolerated, such as batch pH neutralization. I have also seen PD controllers applied in some positioning applications.
