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Original question:

UCC28180: Input Current Shape

UCC28180: UCC28180 Input current distortion

CHIENHAO LIN
Prodigy 110 points

Part Number: UCC28180

Hi,

Based on the support team's recommendation, the inductance was doubled, but the results show the input current is still distorted, as shown in the figure below. I cannot overcome this by adjusting the inductor value. The current distortion results in non-compliance with the IEEE-519 (2022 rev) current distortion requirements and the PF is too low.

Is the cause of this current distortion an issue with the input capacitor or the component values on the ISENSE PIN?

This seems to be a distortion caused by a specific condition, as it occurs right after the zero-crossing. 

Thanks.

pfc bigL--00004.jpgH3390009.BMPH3390005.BMP

 

  • 0
    TI__Intellectual 1475 points

    Hi Chienhao,

    Can you please share the schematic and design calculator for this design? Also, Can you please try capture the same waveforms but only for 2-3 line cycles? Inductor current ripple is not getting captured properly. 
    Thanks

    Sanchayan

  • 0 in reply to Sanchayan Das
    Prodigy 110 points

    Hi Sanchayan,

    The circuit diagram and design tools are attached. Additionally, I've provided the current curve reference for the larger PFC choke.

    For this test, I modified the CIN from the original 3.3uF to 1uF. This seems to have improved the skipping distortion issue, but the current waveform is still not a sine wave.

    Thanks.

    /cfs-file/__key/communityserver-discussions-components-files/196/7331.5HP.xls

  • 0 in reply to CHIENHAO LIN
    TI__Intellectual 1475 points

    Hi Chienhao,

    Please share the PFC inductor current waveform.
    Thanks
    Sanchayan

  • 0 in reply to Sanchayan Das
    Prodigy 110 points

    Hi 

    Please see the waveform shown above.

    CH1=VIN

    CH2=IN

    CH3=IL

    CH4=DC Vbus

    tks.

  • 0 in reply to CHIENHAO LIN
    TI__Intellectual 1475 points

    Hi Chienhao,
    Can you try to capture it at a higher bandwidth the inductor ripple is not visible? Try to capture 2-3 line cycle waveforms and don't put any noise filter on the waveforms.
    Thanks
    Sanchayan

  • 0 in reply to Sanchayan Das
    Prodigy 110 points

    Hi Sanchayan,

    As shown in the attached figures, I have captured 2-3 line cycle waveforms on the oscilloscope and turned off the noise filter.

    Regarding the previous suggestion to increase the switching frequency, the design uses an IGBT, which is not suitable for excessively high switching frequencies. Therefore, we can only focus on increasing the inductance.

    The current test condition is CIN=1uF. Since the IGBT module has a built-in R-shunt of 5m ohm, we added DR262 = 220 ohm for voltage division based on calculations. Will this impact the current waveform?

    Thanks.

  • 0 in reply to CHIENHAO LIN
    Prodigy 110 points

    Hi  Sanchayan & Support Team,

    Have any suggestions for me?

    Thanks

  • 0 in reply to CHIENHAO LIN
    TI__Intellectual 1475 points

    Hi Chienhao,

    Can you please share the Icomp pin voltage and inductor current waveforms along with the input current and input voltage?
    Thanks
    Sanchayan

  • 0 in reply to Sanchayan Das
    Prodigy 110 points

    Hi  Sanchayan,

    The board fried during testing, so I can't get any readings for ICOMP right now.

    Testing was conducted with two inductors in series.

    Setup: CIN=1uF, C_ISENSE=4400pF,DR262=220ohm(IGBT internal shunt=5m ohm)

    Looking at the filtered scope shot, there's a flat plateau during zero-crossing, then a spike and another plateau before the PWM stabilizes. This seems to be why the THD performance is so bad.

    CH1=VIN,CH2=Iin,CH3=IL,CH4=Vbus

    Thanks

  • 0 in reply to CHIENHAO LIN
    TI__Intellectual 1475 points

    Hi Chienhao,

    The ICOMP pin should give the average current of the inductor which should translate to duty internally in the IC. I wanted to check the icomp signal is coming properly once. Yes, you are correct THD is high because the current shape is getting distorted around the zero crossing of ac input. Form the waveforms it seems to go into DCM but from the waveforms it is not much clear. If the current is in CCM, it should regulate the duty properly.
    Thanks
    Sanchayan

  • 0 in reply to Sanchayan Das
    Prodigy 110 points

    Hi  Sanchayan,

    Thank you for your idea. Since the board is currently under repair, I am unable to capture the ICOMP waveform at this moment.

    Based on the design tool, the calculated value for Cicomp is 3900~8200pF. I would like to consult you on the following:

    • To further improve THD, what is the typical trend when fine-tuning Cicomp Would increasing or decreasing its value yield better results for zero-crossing performance?

    • Besides Cicomp, are there any other parameters or pins you would recommend reviewing that might influence the current shape near the zero-crossing area?

    Thanks

  • 0 in reply to CHIENHAO LIN
    TI__Intellectual 1475 points

    Hi Chienhao,
    The CICOMP capacitor is used more for the inductor current averaging if the inductor current is correct, it should work properly. We have to observe the inductor current and VICOMP properly to see what is happening at zero crossing area. Also, after the board is fixed can you also try to plot the gate duty just to see how it is varying around the zero-crossing area.
    Thanks
    Sanchayan