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I have not done this measurement before, so, I would like to ask for help setting up a test to measure the boost inductance within a 3kW CCM Boost (thought I would say it again...) PFC.

Some Electrical Specs:

  • 100 - 250 VAC Input
  • 100 to 200 VAC (1.5kW max)
  • 200 to 250 VAC (3kW Max)
  • Worse Case Average Current apprx 15A (200Vac, 95% efficiency)
  • Guesstimated ripple current around 50% -> apprx 8A

enter image description here

Equipment I have:

  • GW Instek LCR 916
  • 6kW Electronic Load
  • 400V DC Source
  • 6kVA AC/DC Source
  • lots of FANS :)

The perfect answer for me would have the following information

  • Would tie in amplitude permeability and it's effects (large signal)
  • Would tie in incremental (differential) permeability (Small signal)
  • Talk about various methods of measuring
  • Pros and Cons of each method (also some gotchya's)
  • Then finishing off how I can use my equipment set up, and what I should be weary of

Cheers

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    \$\begingroup\$ What kinds of measurements? Operationally in-circuit, or for characterizing a given component out of circuit? I will suggest that, 50% sounds like a heck of a lot of ripple for a powder type core; have you given much consideration to core loss as yet? \$\endgroup\$ Jul 13, 2023 at 21:41
  • \$\begingroup\$ @TimWilliams In circuit would be to challenging I believe. I would like to characterize the inductor over half a line cycle at different points, each point having a DC bias and superimposed ripple. So, I want to see the inductance and how it changes over half a line cycle to get an understanding of it's performance. There is aggressive air cooling, I believe the ripple is actually much higher. Worse-case I saw the inductor around 70 or 80 deg C. \$\endgroup\$ Jul 14, 2023 at 16:24

1 Answer 1

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Indicating the small signal inductance, the LCR meter will get you 50% of the way there. You should definitely start with this measurement to see if theory and practice are aligned and that your inductor does indeed have the correct value at low current levels. In power electronics you also need to ensure that your inductor also behaves like an inductor at high current levels. There are at least two ways you can do this.

  1. Perform in circuit measurements using a current probe. The current during the turn on phase of the boost converter should remain linear at high current levels. This may not be feasible at the concept stage. This brings me to the second option.

  2. You can create a single boost switching cell out of a low side MOSFET and high side inductor as shown in the simplified circuit below. (You will need a low side MOSFET driver and 12V power supply to complete this). The simplest way to use this circuit is to connect it to your high voltage power supply and then using a pulse generator circuit, to give it a short narrow pulse for the worst case expected on time at that particular input voltage. Then observe the current using a current probe or sense resistor connected between the MOSFET source and ground to ensure it is linear.

The second way of using this circuit is to give it a single charge pulse to bring it to the correct operating current, then giving it a second switching pulse, observing the current before to ensure it is linear. Obviously, you will need to create some switching logic for this method.

Unfortunately there is no quick and easy way of verifying the inductance for a power electronic converter but the circuit I described is fairly simple to create and use if you don't have a converter prototype.

enter image description here

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  • \$\begingroup\$ Yes, I've seen this type of setup before. Are there any things to be wary of where the setup can influence the results? Could you please edit your answer and make it more relevant to a PFC application? \$\endgroup\$ Jul 25, 2023 at 15:42
  • \$\begingroup\$ The answer is specific to a boost converter, since the switch is between the inductor and ground. You want to adjust Vin to check the delta I at the extreme operating points of your target circuit, e.g. max line voltage at the peak. \$\endgroup\$
    – mr_js
    Jul 26, 2023 at 17:33

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