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Thread: advantage of proportional integral controller over pid controller .

  1. #1
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    advantage of proportional integral controller over pid controller .

    pid controller reduces the steady state error and also increases the stability .. pi controller doesn't change anything in the stability .. but now a days also pi controller selected for some ac to dc application why

  2. #2
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    Jun 2006
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    Quote Originally Posted by srinivasan View Post
    pid controller reduces the steady state error and also increases the stability .. pi controller doesn't change anything in the stability .. but now a days also pi controller selected for some ac to dc application why
    There is no advantage to a PI controller over a PID controller that I can think of other than simplicity, be it economics or otherwise.
    I'll never get there. No matter where I go, I'm always here.

  3. #3
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    Jun 2003
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    Noise: The "d" amplifies high frequency noise because it is a faster changing waveform. The higher the frequency, the faster the waveform changes, and the more the derivative function amplifies it.

    If you are going to include the "d", it can be helpful to include a low pass filter on the input, or to limit the gain on the derivative function.

  4. #4
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    D can be useful. I have not found that it is all that likely to cause instability if judiciously used.

    People tend to want to make big changes in tuning parameters rather than making little changes and seeing how well that works.

    Then they blame whatever they changed for the instability when it is really operator error.
    Bob

  5. #5
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    The "D" part of PID is derivative and it is a calculus term. Derivative is used in control loops to correct for something known as "intertgal wind up" and to prevent severe overshoots in process correction. I've found it usefull to remember that a little derivative goes a long way. Another way to look at this is that intergal (wich in calculus sets the limits of a function,and is often set in minutes per reset or resets per minute) looks at the time off of setpoint and derivative looks at how fast has the error has occured. I realize this is probably an over simplified explanation but it works in most loop tuning situations.

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