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TMS320F280049: SPLL_1PH_SOGI park transform

Part Number: TMS320F280049
Other Parts Discussed in Thread: TIDA-01606

Hi team,

here is a confusing item about our C2K code library: SPLL_1PH_SOGI

And they is a step park transform in :https://www.ti.com/lit/an/sprabt3a/sprabt3a.pdf 

And from my knowledge,  the park transform formula should be 

So if we assue:

ia=osg_u(1); ib=osg_qu(1); then after park transform,

then u_D(1)= cosine*osg_u(1)+sine*osg_qu(1);

so it's not U_Q(1) shown in the above formula; seems here is a mistake between D value and Q value?

Or if anything other point that I am missing?

Thanks

Best regards

Mia Ma

  • MIa, 

    This code was developed long time back, the adjustment to the transform was done to make the PLL angle zero at the grid zero crossing. 

    If you use the above transform you will get the PLL angle to be cosine based and the angle will be 90 degrees at the grid zero crossings. In the three phase systems we do indeed using cosine based transform 

    v->d = v->alpha * cosine_val + v->beta * sine_val;
    v->q = -v->alpha * sine_val + v->beta * cosine_val;

    For the single phase we wanted to keep grid angle zero at the zero crossing, and hence the adjustment was done.

    by contrast see the output of the three phase PLL module in TIDA-01606, the angle crosses pi/2 when ac value crosses zero for phase A

    Hope this clears the issue. 

  • Hi Manish,

    If you use the above transform you will get the PLL angle to be cosine based

    I am little confusing here, why we follow the basic transform, we don't get a sine but a cosine?

    any special process will lead to this result? Or from my understanding v->q value will bring us a sine result, and then a angle info:

    Thanks

    Best regards

    Mia Ma

  • MIa,

    In SOGI we create our own orthogonal signal, you can do the classical transform but you will need to change a few more things for the PLL to work. 

    1. YOu will need to run the PLL on the D component and not the Q component

    2. Your angle will be 90 degree off from the expected. 

    We have the matlab script included in the app-note, i will encourage you to experiment with it and see it for your-self.

    -Manish  

  • Hi Manish,

    Got it, and thanks.

    Best regard

    Mia Ma