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Transfer function of BLDC motor -- control system

Dinesh Guleria
Intellectual 515 points


Hello TI team,

As TI team have many years of experience with BLDC Motors.
Please suggest if we have to derive the transfer function of BLDC motor (Plant) than what process do i follow ?
Do TI have any application note describing how to obtain Mathematical modeling of BLDC motor or guide me to some reference tutorial to learn this ?

one parameter of BLDC i know is :--
Time Constant = L/R.

But if i have to find the transfer function than what approach is best, please answer these questions :--
1> Find the mathematical model of BLDC motor & convert this physics into transfer function.
2> Obtain frequency response of motor by hit & trail experiments & convert bode plot response into second order transfer function ?
3> How we can calculate frequency response of motor by hit & trail experiments ? Means do i have to measure speed for various frequency of sin wave & convert this into Bode plot for gain & phase ? How exactly to plot bode plot of BLDC using experimental hit & trail method ?
4> In TI how you use to calculate the transfer function of motor means by mathematical modeling or by experimental obtained frequency response ?

I know nothing cannot be 100% accurate, but if we can approach the exact transfer function by 90% will it be fine to design my compensator as per that transfer function of plant?

Please suggest.

Regards,
Dinesh

  • 0
    TI__Mastermind 27240 points

    I would consider refering some text books authored by Pragasen Pillay and Ramu Krishnan. I have seen some papers/ publications from them on this topic and I am hoping that their book might have more insights to what you are looking for.

    Typically, we don't do the bode plot for designing the compensator. Apply a tiny step voltage and capture the motor current response in a scope. The initial slope of the current indicates the time constant while the applied voltage divided by the steady state current gives the resistance.

  • 0 in reply to Ramesh Ramamoorthy
    Intellectual 515 points

    Hello Sir,

    Thanks for your reply.

    I only found this paper from author suggested by you. It contains detailed description of the key differences between BLDC and PMSM.

    http://colgate.mech.northwestern.edu/Haptics_Course/Suggested_Readings/Pillay_1991_PermanentMagnetSynchronousAndBrushlessDCMotors.pdf

    Any other book from other author you will like to suggest.

    Regards,
    Dinesh

  • 0 in reply to Dinesh Guleria
    TI__Mastermind 27240 points

    I don't have access to a library of engineering books. I would do a search for this info online.