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TMS320F28069: DPLib Controller Coefficients Calculation

user4921965
Prodigy 40 points
Part Number: TMS320F28069


I have built a buck converter based on the TMS320F28069 MCU as its controller, I've implemented the 3P3Z module, calculated the control coefficients and inserted them into my code and got the converter stable, but when measuring the loop using the Bode 100 I find that the system has a very different frequency response than calculated, for example a 1KHz crossover frequency when it should be 5KHz. the control coefficients are correctly calculated and the I've implemented a compensation factor for the feedback and ADC effects.

is there a certain factor that should be inserted to the system for it to behave as expected?

  • 0
    TI__Genius 11975 points

    Please review the TI reference design below. It explains how a DC/DC voltage control loop is designed using C2000 MCU

    https://www.ti.com/tool/TIDM-DC-DC-BUCK

    Shamim

  • 0
    Prodigy 40 points

    I've already gone through this design guide, it does not explain how to work with your calculated coefficients. the thing is once the coefficients are calculated they must be multiplied by a factor determined by the feedback loop gains and the way the code is written. I've restudied the code and did some work around and found that the required coefficient is the to divide by the feed back gain divided by the ADC voltage reference. but since my output voltage is much higher than the ADC reference I get a large number which makes my coefficients larger than the Q26 limit (31.999999). and this limits my crossover frequency to 1KHz.

    is there a workaround to this (IQ26 range limitation in DPLib)?

  • 0 in reply to user4921965
    TI__Genius 11975 points

    I responded to this same question on a different post from you. Please see that response.

    Shamim