TIDA-010062: How to improve iTHD at light loads?

Dear Champs,

I am asking this for our customer.

The user refers to TIDA-010062 codes on their own power boards.

So far, the iTHD at high loads seem good but that at light loads is bad.

1. The use is thinking using odd harmonic mitigation by PLL. Do you think it makes semse?

Can and how do they use 3rd harmonic and 5th harmonic to improve this?

The user wonders how to use 3rd harmonic and 5th harmonic to improve iTHD?

In spll_1ph_sogi.h, there are SPLL codes below in Line 241-, can they modify this part like theta?

If yes, would you please show us specifically? The user is not sure how to modify our PLL.

If not, do you have any suggestion?

    //
    // VCO
    //
    spll_obj->fo=spll_obj->fn+spll_obj->ylf[0];

    spll_obj->theta=spll_obj->theta + (spll_obj->fo*spll_obj->delta_t)*
                       (float32_t)(2.0*3.1415926f);

    if(spll_obj->theta>(float32_t)(2.0*3.1415926f))
    {
        spll_obj->theta=spll_obj->theta - (float32_t)(2.0*3.1415926f);
        //spll_obj->theta=0;
    }


    spll_obj->sine=(float32_t)sinf(spll_obj->theta);
    spll_obj->cosine=(float32_t)cosf(spll_obj->theta);

2. Do you have any suggestion for them to get better iTHD at light loads? From our doc, it shows about 9% at 10% loads. Would you please share some experience?

Wayne Huang