F28M36P63C2: DDSRF PLL

Srini Venkat

Part Number: F28M36P63C2

Hello,

I am using the DDSRF pll function to estimate grid angle and use that theta subsequently in the generation of my inverter's three phase output. The frequency of my three phase output is matched with that of the grid frequenxy(60 Hz). But there is a phase lag of 40deg between the grid three phase output and the three phase output of my prototype. Can this phase margin be fixed by tuning the damping factor specified in the spll_coeff_compute.pdf in solar/v1.2 directory? Any ideas or advice is greatly appreciated.

Thanks,

Srini

over 3 years ago

0 Manish Bhardwaj over 3 years ago

TI__Mastermind 43730 points

40 degree phase lag does not match expectation, please note we use cosine based transforms and hence the PLL will lock at the peak of voltage of phase A and you may see that as a 90 degree phase shift but it is expected because of the transform used.

0 Srini Venkat over 3 years ago in reply to Manish Bhardwaj

Prodigy 100 points

Thank you for your time, Manish. I am not using the cosine ramp signal functions as my grid reference, using a real three phase grid voltage as reference.

Previously i was sensing grid measurements (A,B and C) to the corresponding inverter outputs (A,B and C) and noticed close to 30-40 deg phase shift. I moved the measurements to other phases and noticed that,

there is approximately a 90 deg phase shift between,

Grid reference A phase - Inverter phase C

Grid reference B phase- Inverter phase A

Grid reference C phase- Inverter phase B

Is there a better more flexible solution i can explore other than just changing the sequence of my three phase inverter outputs from A,B,C sequencing to a C,A,B and adding the 90deg phase lag as compensation to account for the shift?

Thanks,

Srini

0 Manish Bhardwaj over 3 years ago in reply to Srini Venkat

TI__Mastermind 43730 points

Srini,

If the sense transforms and the actuating transforms are both based on cosine then they should match.

It looks like you have sequence mismatch somwhere..

-Manish

0 Srini Venkat over 3 years ago in reply to Manish Bhardwaj

Prodigy 100 points

Manish,

As you can see from attached image, Grid sense signal is a sine waveform and the generated three phase output from my prototype is a cosine. Red waveform is prototype output. Blue is the grid input.

Thanks,

Srini