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Buck converter compensation component calculation for type 2 or 2 Pole 2 Zero

VikasDabas
Prodigy 220 points
Other Parts Discussed in Thread: POWERSUITE

Dear all,

I am working on Digital power Buck converter using C2000 series controller. I have used Digital power kit as reference. The controller is C28035.

Now i have build my own hardware, it is running at frequency of 50KHz, as the power is too high. it is 450W.

Situation: I have seen Buck converter in kit, and Coefficient B2, B1, B0, A2, A1 in code.

Question: How they are calculated? Or How to calculate the resistance and capacitor values for buck type 2 feedback?

My Knowledge: I have converted the analog resistor capacitor to B2, B1.... coefficient using Discrete conversation. I have the formulas, and knowledge, how it is done.

                         Now as the components are known of kit, i cannot verify the coefficient values.

I wants to verify that the procedure of calculating the feedback component is same. Can you give me a refference to calculate Type 2 compensation for Buck also.

Vikas Dabas

India

  • 0
    TI__Genius 15555 points
    Hi Vikas,

    Thank you for your post. Your thread has been assigned to the C2000 experts and should get feedback soon.

    Best regards,
    Chen
  • 0 in reply to Chen Jiang ti
    TI__Mastermind 27200 points

    Dear Vikas,

    I believe the kit you are working on was developed for a 1-day course on digital power supply design. That course included a student lab in which the 2P2Z controller was tuned to optimise a load transient. To do this, the code emulated a PID controller and students adjusted the gains while monitoring the transient in real time. The relationship between gains and coefficients is shown in the attachment. This is not typically the way designers will tune a 2P2Z compensator - it was selected to provide a nice visual lab and to demonstrate the software.

    Normally designers use a type 3 compensator for voltage mode buck control, corresponding to a 3P3Z digital compensator. Tuning is accomplished by placing the compensator zeros at the double pole of the power stage, one pole becomes the integrator, and the two free poles at high frequencies.  Once you have selected these frequencies you perform the discrete conversion to find the control law coefficients. We have a visual tool to do all this in powerSUITE.  You are already familiar with the relationship between continuous time and discrete time transfer functions, so you will know about the phase effects of delay, sampling, and so on.

    For a general reference on power supply design, Erickson & Maksimovic "Fundamentals of Power Electronics" is widely used and well regarded. You may also find it helpful to download the 'step-by-step' description of compensator design from the Biricha website:
    https://www.biricha.com/articles/foundations-part-2b-voltage-mode-psu-compensator-design

    I hope this is helpful.

    Regards,

    Richard

    Discrete PID controller.pdf

  • 0 in reply to Richard Poley
    Prodigy 220 points

    Dear Richard,

    Richard Poley said:

    Normally designers use a type 3 compensator for voltage mode buck control, corresponding to a 3P3Z digital compensator. Tuning is accomplished by placing the compensator zeros at the double pole of the power stage, one pole becomes the integrator, and the two free poles at high frequencies


    May i know how to calculate/decide the double zero and double pole frequency for any circuit? Does it needs to have double pole and zero to be placed at some distance from each other? Or can we place them at one point?

    Richard Poley said:
    Once you have selected these frequencies you perform the discrete conversion to find the control law coefficients 


    I have seen the sheet, it uses the real component and time for sampling the circuit and find the coefficient accordingly.
    Is there a seperate way to calculate the coefficient using frequency only?

    Richard Poley said:
    We have a visual tool to do all this in powerSUITE 


    Yes you have tools for all purposes. But learning is always better than tools.

    Richard Poley said:
    You are already familiar with the relationship between continuous time and discrete time transfer functions, so you will know about the phase effects of delay, sampling, and so on 


    Yes, i have studied the relation between continuous time and discrete time transfer function, But can you help me understand other things that you have mentioned here like "Phase effect of delay, sampling" etc.

    Vikas Dabas
    India

  • 0 in reply to VikasDabas
    Prodigy 220 points
    Also,
    I wants to design using Type 3 compensation over PID loop. As it seems to be more stable.
  • 0 in reply to VikasDabas
    TI__Mastermind 27200 points

    Dear Vikas,

    The double pole in the plant comes from the RC network in CCM. You typically design the compensator such that its' double zero is at the same frequency and they cancel.

    I did not elaborate on discrete conversion because you said you were already familiar with it. If you need to review that subject I recommend watching part 4 of this seminar, which covers various methods and describes the phase effects I mentioned previously:
    https://sites.google.com/site/controltheoryseminars/home/control-theory-fundamentals-seminar

    I am also attaching a short tutorial describing 3P3Z compenstor design for a buck converter and may help you.

    Regards,

    Richard

    feedback control tutorial.pdf