Discussion
What is the purpose of the Smith predictor in control system design?
Answer: A
The Smith predictor is used to compensate for time delays in the system.
A process with dead time, \(G(s)e^{-sT}\), is hard to control because the delay adds phase lag that grows with frequency and forces the controller gain down. O. J. M. Smith's scheme (1957) runs a model of the process inside the controller. The model's output without the delay is fed back in place of the real measurement, and the difference between the real output and the delayed model output corrects for model error. The controller can then be tuned as though the delay were not in the loop.
Better transient response, less overshoot or improved frequency response can follow as consequences, but they are not the specific purpose. The predictor exists to deal with dead time.
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