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LC filter connection to middle point of DC link capacitor --- CRD-25BDA6512N-K

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Sandro13
Sandro13 Contributor Level 1
edited February 20 in General

Hi,

I am design a 22kW three-phase inverter based on reference design CRD-25BDA6512N-K.

I have few questions about option to connect star point of LC filter to middle point of DC link capacitors.

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1. In the reference design, I noticed that the star point of capacitor in LC filter connect to middle point of DC link cap though a Y cap C21 value 0.1uF (in BOM).

What is the difference in term of EMI and operation if we do not connect 1 and 2 via C21?

2. Is the system still working the same if we connect point 1 to 2 directly? Mean we tie star point of LC capacitor directly to middle point of DC link capacitor.

3. If it is single phase system using 2 legs of T-type inverter, does the middle point of LC filter still able to connect to middle point of DC link cap?

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  • Forum_Moderator
    Forum_Moderator Wolfspeed Employee - Contributor Level 5
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    Thank you for your post, it has been approved and we will respond as soon as possible.

  • SGupta
    SGupta Wolfspeed Employee - Contributor Level 1
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    Hello- Thanks for your questions.

    Regarding (1), connecting star point of LC filter to mid-point of DC-link through a 2.2uF capacitor as shown in schematic improves conducted EMI substantially (up to 30dBuV). I will encourage you to check our App note on this investigation: Mitigating EMI with SiC Solutions in Renewable Energy &Grid-Connected Power Converters. For impact of connection of star point to LC filter to mid-point of DC-link, you can refer section 3.5 within this App Note.

  • TBhatia
    TBhatia Wolfspeed Admin - Contributor Level 5
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    Hello,

    (2) Electrically there is no issue with connecting the star point of LC capacitor directly to middle point of DC link. The converter will work just fine. However, the EMI performance will vary and that can be studied in the Application Note as mentioned by SGupta above.

    (3) Yes, electrically shouldn't be an issue.

    Thank you, let us know if you have anymore questions!

  • TBhatia
    TBhatia Wolfspeed Admin - Contributor Level 5
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    Hi, I hope that this answered your question. If it did, please click on "This question has been answered - Close Discussion" . If you have a follow up question, at a later date, please "Start a New Discussion"

This discussion has been closed.