Type2 and PI compensator for buck converter

Altair Forum User
Altair Forum User
Altair Employee
edited August 2023 in Community Q&A

Please find the attached for a simple closed-loop buck converter design.

You can compared it between PI and type 2 from my simulation.

Type 2 compensator:

P=7 and I=285.
However this is just a simple example so the system may not be robustness, but you can tuned by your own based on its power converter transfer function.

So the output voltage regulation is converted from 24V to 12V and sudden change in the load current from (2.3A to 14.3A) by changing accordingly from the resistor value.

Hope this will help you.

Regards
John

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited August 2023

    Hi John,

    I was surprised to see such good regulation of your output voltage with a voltage loop control only, especially with just a PI control. If we look at the gating waveform we can see that your controller is far to fast and is "oscillating" which is causing your gating signal to trigger at closer to 700KHz instead of 100KHz. I needed to drop the simulation timestep down to have a look at what was going on.

    I attach a screenshot of your PI controller Vm, Vcar with the gating and you can see it bouncing during the rise. This controller needs to be completely re-designed.

    Your type 2 controller is slow, but there is not much bandwidth for speeding it up, try with c2 = 1.2n, c1 = 41.66n, R2 = 26.5k. This should give a cross frequency of 745 Hz with 30 degrees phase. You will be hard pressed to go much faster. Voltage only control of a buck is not that great, this is why average current inner with an outer voltage loop or Peak current mode control is popular for these topologies. A Type III controller will likely do better, but not as good as other control techniques.

    I used smartctrl for the control design.

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited August 2023

    Hi Albert,

    Yes, I have noticed that the Vm0 has high oscillating signal and compared with Vcarr0 triangle waveshapes

    However, the output voltage supposed to have large ripple due to its Vm0 has high oscillating signal. But I don't know why I cannot see this phenomena effect. Also, the output voltage ripple only 0.001 something.

    The reason why the response time of the power converter is so fast. It because of I set a very high P and I. Please the attachment.

    Actually, I used a smartctrl to observe the phase margin and tuned the P and I values.

    About the type2 compensator, I just posted the simulation file, try to answer someone in youtube.

    Anyway, I'm really thanks to you put comment here and discuss problem with my design.

    Best Regards,
    John

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