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TMS320F2812: Document SPRABT3, the relationship between Kp and Ki.

user5624527
Intellectual 800 points
Part Number: TMS320F2812
Other Parts Discussed in Thread: CONTROLSUITE

Hi team:

I have two questions about the document SPRABT3(Software Phase Locked Loop Design Using C2000™ Microcontrollers for Single Phase Grid Connected Inverter) and the spll_coeff_compute.xlsx(path: controlSUITE\libs\app_libs\solar).

1, In the spll_coeff_compute.xlsx and forum (https://e2e.ti.com/support/microcontrollers/c2000/f/171/p/600195/2207692?tisearch=e2e-sitesearch&keymatch=SPLL%20Kp%20Ki#2207692), Both of them said that the value of wn(the natural frequency ) should be 158.6859, but in SPRABT3, wn=119.014 (under formula 17 in SPRABT3). which one is correct?

2, I substituted the parameters (under formula 17 in SPRABT3) into spll_coeff_compute.xlsx. Which settling time as 30 ms, and the error band as 5% and damping ratio to be 0.7, the natural frequency is 119.014, 

But I got the Kp = 166.6196, the Ki = 14164.33(By formule), Not Kp =166.6 and Ki = 27755.55(By document). Then which one should be the correct one? Or is there any other ways to calculate the value of Ki?

3, Upon the figure 3 in SPRABT3(Chapter 2.2), ζ2 and ζ1 is given as 0.00001 and 0.1, How can I affirm the value of ζ2 and ζ1?

4, SPLL_1ph_init(GRID_FREQ,_IQ21((float)(1.0/ISR_FREQUENCY)) &spll1);

Whether the formule should be 0.001/ISR_FREQUENCY or not? Should the unit of ISR_FREQUENCY be KHz?

Thanks & Regards,

KK

  • 0
    TI__Genius 15935 points

    Hi K.K,

    I am not very familiar with Software Phase Locked Loop but I took a look at SPRABT3.

    Question 1,2 : The SPRABT3 has been modified and now it is wn=158.6859 which should be correct. And if you use wn=158.6859 , you should get the KP,Ki you need.

    Question 3: What do you mean by "affirm the value of ζ2 and ζ1" ? I think "ζ2 and ζ1 is given as 0.00001 and 0.1" is just to give a example to show that the notch filter can work well when ζ2 << ζ1.

    Question 4: I think (1.0/ISR_FREQUENCY) is correct and the unit is Hz. if you want to use 0.001/ISR_FREQUENCY then the unit is kHz.

    Hope that helps. Thanks!

    Chen

  • 0 in reply to Chen Jiang ti
    Intellectual 800 points
    Dear Chen:

    Thank you for your detailed reply.

    For the question 3, Are the values of ζ2 and ζ1 randomly selected? Only need to meet the condition that ζ2 << ζ1?

    Thanks & Regards,

    K.K
  • 0 in reply to user5624527
    TI__Genius 15935 points
    Hi K.K,

    It is not randomly selected. Different Q value will give different frequency response and Q is related to ζ2. And ζ1 is usually a very small value.
    The document below should give you more information about notch filter.
    www.ti.com/.../slyt235.pdf

    Thanks,
    Chen