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I am trying to connect a Line Impedance Stabilisation Network (LISN) to a three-phase PFC rectifier simulation model as I want to simulate the common-mode and differential mode EMI. Most references on this seem to be for single phase connections where two LISN networks are used, one for power supply as well as converter reference ground like shown below: enter image description here

However, I am having a bit of trouble correlating this with a three-phase system. This reference seems to suggest placing a LISN in each of the phases and one in the neutral.

enter image description here

However my circuit(shown below) does not use the neutral terminal. Additionally, I am unable to figure out where my converter reference ground is. I have connected the LISN to each of the phases as shown below and this does not disturb my expected output, but where/how do I connect the LISN to the converter reference ground in order to obtain both common-mode and differential-mode EMI. enter image description here

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  • \$\begingroup\$ If you consider that you have two active lines in your first image and that this LISN has two branches, you can easily extrapolate to the three phase connection where you have three active branches. Whether you add a LISN on Neutral would depend on whether you use a delta or wye connection. You have delta apparently \$\endgroup\$
    – tobalt
    Apr 3, 2022 at 15:39
  • \$\begingroup\$ @tobalt and what about ground? \$\endgroup\$
    – needbrainscratched
    Apr 4, 2022 at 9:04
  • \$\begingroup\$ Look up delta 3 phase power..It doesn't have a neutral line. of course it is still earth referenced, so it makes sense to decouple both Dc+ and Dc- rails to earth potential \$\endgroup\$
    – tobalt
    Apr 4, 2022 at 9:17
  • \$\begingroup\$ @tobalt but how do I connect the LISN to ground as I would for a single phase? Since the power supply in this case does not have a return path to ground. \$\endgroup\$
    – needbrainscratched
    Apr 5, 2022 at 5:38
  • \$\begingroup\$ The LISN is only connected to earth, i.e. the PE conductor which always exists in single phase , wye and delta power schemes. The LISN isn't connected to your DUT "ground" at all. Check your first Image, which nicely explains it. \$\endgroup\$
    – tobalt
    Apr 5, 2022 at 7:35

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Sorry I can only provide a very basic answer on short term as written in comments.

The basic scheme can ne found here

On the mains side, you have one LISN branch per mains line consisting typically of:

  • C to PE
  • Series L
  • CR to PE, to couple out the emissions. You have therefore 3 of these EMI outputs. Common mode EMI is what is in phase and common to all 3 lines. And in addition, you have 3 different differential mode conducted EMIs between each of the mains lines.
  • for delta power there is no N line and thus no 4th LISN branch

After the rectifier, you end up with a DC+ rail more positive than PE and a DC- rail more negative than PE.

If you connect your load between Dc- and Dc+ at the output, you can add decoupling caps for common node noise to PE.

It also makes sense to define your functional output Ground as 0V with respect to PE..Alternatively you can use one of the Lines as output ground, but since this ground would carry an unsafe voltage, you can only use it internally with double insulation, and would anyway have to use PE for exposed metal parts.

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  • \$\begingroup\$ Can you describe the scheme or expand the answer? \$\endgroup\$
    – Voltage Spike ♦
    Apr 6, 2022 at 15:29
  • \$\begingroup\$ @VoltageSpike I can try..But I'm mobile until next week. So not really. But since noone else answered... \$\endgroup\$
    – tobalt
    Apr 6, 2022 at 16:38
  • \$\begingroup\$ Looks good, thanks \$\endgroup\$
    – Voltage Spike ♦
    Apr 6, 2022 at 17:17

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