RE: PID parameter tuning using Fuzzy Logic

From: P. Sarma (psarma@seas.upenn.edu)
Date: Tue Feb 26 2002 - 12:24:53 MET

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    Jayanth,

    The fuzzy logic tuning (FLT) of a crisp PID controller is relatively
    straightforward. It is a variation on Gain-Scheduling (GS) control,
    which serves to make the FLT-PID a nonlinear i/o blackbox controller.

    Let K = (P,I,D) represent the vector of gains where the PID is written
    with the controller output as

    LPID(t) = P*e(t) + I*Ie(t) + D*De(t); Ie and De are obvious. --- (1)

    This is valid for the continuous or the discrete case. To account for
    nonlinear system behaviour, each of the applicable gains (3 or less) is
    externally retuned, using an FLT as a cascade self-tuner or GS. Consider
    any one of the gains, say P.

    Then we can generate a fuzzy model of P by constructing a fuzzy
    rule-base (FRB) based on dynamic error information, namely from (e,e').
    An appropriate FRB generated from identification or domain knowledge
    will generate a nonlinear dynamically time-varying scheduled gain
    P(e(t),e'(t)) = P(t). This can be extended to K(t) as applicable,
    leading to the desired

    NPID(t) = P(t)*e(t) + I(t)*Ie(t) + D(t)*De(t); Ie and De are obvious (2)

    The selection of the FRB's for each gain like the P(e,e') is the key
    FLT-PID design issue. The selection of the FLSystem base type for the
    FLT, whether Mamdani M-FLS or TSK-FLS is a metalevel design issue.

    The great practical utility of this FLT-PID is the ability to add a
    relatively simple "fuzzy patch" FLT block (in a DCS or PLC) to an
    existing LPID block.

    For references, the Web has become a good source. A search engine run
    for "fuzzy PID tuning" is quite effective. Checking the Inspec and
    Compendex CD-R databases, and typically the IEEE Transactions on Fuzzy
    Systems, and the SMC set at the nearest large technical university's
    library would produce sufficient data.

    Pramit

    -----Original Message-----
    From: fuzzy-mail@dbai.tuwien.ac.at [mailto:fuzzy-mail@dbai.tuwien.ac.at]
    On Behalf Of g jayanth
    Sent: Wednesday, February 20, 2002 2:50 AM
    To: Multiple recipients of list
    Subject: PID parameter tuning using Fuzzy Logic

     I am doing a project on the tuning of a conventional PID controller
    using fuzzy logic when applied to a superheated steam boiler in a
    thermal power plant.However I have not found much literarture on the
    topic of fuzzy supervisory & tuning control.I want to explicitly know
    how the supervisory works and changes the K,Ti and Td constants.If you
    know of any material avilable on the net please help me.

    Thanks a lot
    JAyanth

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