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UCC28180: Help for debugging, AC current distorted when the power above 5kW

Eric Bravo
Prodigy 40 points
Part Number: UCC28180
Other Parts Discussed in Thread: UCC2818

Design for a 8kW PFC, use UCC28180, but AC current distorted when the power is above 5kW,

1.CH1(yellow), AC current, 20A/div; CH3(purple), inductor current, 20A/div; CH2(green), VCOMP, 5V/div; CH4(blue), VICOMP,5V/div;

left is the wave when the power is 4kW, right is 5kW;

1)VICOMP is not distorted, VCOMP didn't have a fluctuation, but the current wave distorted.

2)when the power at 4.5kW, I found that the peak inductor current is about 40A, when the power increased, the transient average current doesn't change except the region around the max point,

the IC into a mode that is not the current  wave increased unified, that is only at the max point in order to reach the power.

3) I tried lots of group parameters of ICOMP, VCOMP, RC filtering, output CAP(4920uF now), output film cap, there is no improvement.

  • 0
    TI__Genius 9790 points
    Hi, Eric

    what is the value of current sensing resistor?
    I think you should try to reduce current sensing resistor to fix this issue.

    Regards,
    Yunsheng
  • 0 in reply to Yunsheng Qu
    Prodigy 40 points
    3.3mΩ now, I think it's small enough, it is already 130A PEAK LIMIT current. Is it into a OVP_L/SOC mode that the 4kΩ worked, so that the gain is not enough.
  • 0 in reply to Yunsheng Qu
    Prodigy 40 points

    Hi Yunsheng,

    1) You are right. I found that the current amp is saturated distortion when the power above 5kW.  So reduce the sensing resistor can fix this issue.

     But the problem is the SOC current may exceed 100A, and IPKLMT may exceed 200A, so that needs very large IGBTs.

    2) And the calculator sluc506a, the sensor calculation just consider the peak current, does not consider the max output of the current averaging amp.

    This IC is optimized of Reduced Current Sense Threshold (Minimizes Power Dissipation in Shunt), it seems it's more important to check if the sensor

    resistor meet the current averaging amp max output than the peak current. And for general use, I think the threshold of the SOC, PKLMT is a little large.

    So, according to the general use, UCC28180 may be approporiate for the use below 4kW.

    3) For single channel, larger power use, as 8kW, I think it should be better using UCC2818.

    Thank you!

    Eric