Aleksei

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Viewing 15 posts - 46 through 60 (of 67 total)
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  • in reply to: optimisation #888
    Aleksei
    Keymaster

    Dear Sandip,

    You are effectively bounding the parameter search space by fixing some parameters. Obviously, you will arrive at different results, because some fractional-order controller parameters yielding particular control performance will not be accessible.

    • This reply was modified 8 years, 7 months ago by Aleksei.
    in reply to: Fractional Control Basic #883
    Aleksei
    Keymaster

    In general, the Mittag-Leffler function in two parameters is a powerful generalization. It may be used to compute the (roughly speaking) fractional exponential function and thus may be employed for solving fractional-order differential equations. However, direct use of this function for real-time problems is limited. Therefore, it is not used in FOMCON for FOPID related computations.

    in reply to: Fractional PID Controller Design #875
    Aleksei
    Keymaster

    Dear Kapil,

    In case of the FOPDT model it will not be possible to obtain the feedback system comprised of the plant and FOPID controller in fotf form due to different delay terms. Only approximations are applicable. This should be taken care of automatically in fpid_optim tool.

    in reply to: Time-domain identification algorithm #868
    Aleksei
    Keymaster

    You are welcome. Should you have a feature request for the toolbox feel free to file it. I will then take it into consideration for the next release.

    in reply to: Time-domain identification algorithm #855
    Aleksei
    Keymaster

    The choice of options depends on the identification problem. Kindly consider this excerpt from the old documentation: https://fomcon.net/pub/temp_docs/fotfid_tool.pdf

    In short: What type of model would you like to obtain? You can try obtaining a model with a commensurate order, in which case the model generation panel and “fix exponents” option may be useful. You can also identify integer-order models by fixing exponents with $\alpha_k, \beta_k\in\mathbb{Z}^{+}$.

    The identification process involves constrained optimization, where the objective function is based on the model’s output error (see MATLAB’s Optimization toolbox documentation for lsqnonlin). That is, the output error is minimized in the least squares sense.

    • This reply was modified 8 years, 10 months ago by Aleksei.
    • This reply was modified 8 years, 10 months ago by Aleksei.
    • This reply was modified 8 years, 10 months ago by Aleksei.
    in reply to: Toolbox features #816
    Aleksei
    Keymaster

    Hi.

    This is indeed a valid concern. Roughly speaking, the difference is due to some constraints of the current implementation of the Gr├╝nwald-Letnikov algorithm, which is a fixed-step method. For instance, try lowering simulation step size choosing a time range of about 10-20 seconds—you can easily do this in fotf_gui, i.e. compare results with t=[0:0.01:10] and t=[0:0.001:10]. You will see that the damping ratio of the fractional-order system obtained from the undamped integer-order one will decrease with computation step size.

    I will look into this problem soon.

    in reply to: Root locus of Fractional order systems #812
    Aleksei
    Keymaster

    Hello,
    Currently the functionality that you are looking for is not yet implemented. I have, however, added this feature request to my to-do list, and will provide the implementation as soon as possible. This will probably be included in the next release of the toolbox due September.

    in reply to: Fractional PID Controller Design #808
    Aleksei
    Keymaster

    Hello Pritesh,

    This feature is not implemented yet.

    in reply to: Installing the toolbox #801
    Aleksei
    Keymaster

    Hello,
    This is the FOMCON toolbox support forum. I have no idea about the “FALCON” toolbox.

    in reply to: Fractional Control Basic #796
    Aleksei
    Keymaster

    To an extent, yes; since approximations are used, we may consider a particular fractional-order PID controller approximation to belong to a set of all possible high-order integer-order controllers for a given control problem.

    in reply to: Initial conditions #788
    Aleksei
    Keymaster

    To consider initial conditions for a fractional-order operator means to reconstruct, in terms of limited memory, the so called “past” of the operator. This feature is yet to be implemented in FOMCON.

    in reply to: Fractional PID Controller Design #786
    Aleksei
    Keymaster

    Hello Pritesh,

    1. The choice of approximation parameters ultimately depends on the application. The wider the frequency range and order, the more accurate the results. But it may become difficult to implement the system (or controller) as, e.g., an active filter or a digital IIR filter.

    2. Could you provide an example?

    in reply to: Fractional PID Controller Design #771
    Aleksei
    Keymaster

    Any proper LTI model can be used: (fractional-order) transfer function, zero-pole-gain, or state-space.

    in reply to: Fractional PID Controller Design #769
    Aleksei
    Keymaster

    Type fpid_optim in MATLAB command line to launch the tool. If you are still getting errors, please elaborate, i.e. provide the exact steps needed to reproduce the error.

    in reply to: Toolbox features #767
    Aleksei
    Keymaster

    You may use the guide tool, integrated into MATLAB, to make modifications to the GUI’s. Since FOMCON code is freely accessible, you can study the existing code.

Viewing 15 posts - 46 through 60 (of 67 total)