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TMDSSOLARCEXPKIT: PID regulator from 2P2Z

Michael Koval27
Intellectual 990 points

Part Number: TMDSSOLARCEXPKIT

Hello!  We explore SolarKit and have  found strange things during setting of Pgain, Igain, Dgain of PID regulator.

When we began  with setting of Pgain it did not have effect, system did not control voltage. But when we made Pgain =0 and set Igain =0,01 the system

became very stable and reacts very quickly and  works  very well. It is strogly confused us, becase early we used the TI PID_GRANDO and it worked as

described - main role played namely Pgain !  I tried to analize and noted, that emulating of PID from 2P2Z  (a2=0 a1=1 ) makes denominater without coefficients and

so we have only zeros in this new 2P2Z. No poles!  Is it correct? And when you set Dgain=0 we could have very interesting games with b0 = Pgain + Igain and b1= Igain -Pgain

So I ask two questions:

1. Why we can control system with Pgain=0   (in PID from 2P2Z)- is it possible or I should find error somewhere in my programm?

2. Is it possible to contrlo PID emulating from 2P2Z rigthly by setting b2,b1,b0 and what are there meanings in this sense?

Thank you.

  • 0
    TI__Mastermind 27200 points

    Michael,

    I don't have a solid explanation why adjustment of the P-term did not influence the response as you expected. However I can provide a little background information which may be helpful to you.

    I have attached the derivation of the 2P2Z compensator coefficients used in the solar explorer kit. We used a backwards Euler method for the derivative term, and Tustin for the integrator. This is not the only way, but it gave us good results.

    It is not the case that the resulting 2P2Z transfer function has no poles. The denominator is (z^2 - z), which corresponds to a unit delay and a pole at z = 1, as would be expected with an integrator.

    By using the 2P2Z controller, we are only emulating PID behaviour with an FIR structure. My view is if you want to tune for transient response then it's best to use a PID controller. The 2P2Z structure in the DP library is widely used in digital power because designers like to think in terms of pole-zero frequencies.

    BTW, I'm not sure if this will help, but there is a new floating-point digital controller library in C2000 ware which has a wider selection of controller types and hopefully some documentation you may find useful.

    Regards,

    Richard

    5344.Discrete PID controller.pdf