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CRD-30DD12N-K reference design : the three-phase current measurement strategy

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gkim
gkim Contributor Level 3
edited October 2022 in General

Hello,

With respect to the reference design of CRD-30DD12N-K, I have a few questions on the three-phase current measurement strategy.

Let me describe it with the phase C current as an example.

The current measurement circuit for phase C on the main board is uploaded as below.

CS_C-main.png

The phase C current is measured by the 1:200 current transformer and it is full-wave rectified by the diode bridge circuit.

The current measurement circuit for phase C on the control board is uploaded as below.

CS_C-control.png

The current signal is converted into the voltage signal by this circuit.

Now I have a few questions on these phase current measurement circuits as follows:

(1) When the current signal is full-wave rectified as aforementioned, how can the DSP know the direction of the alternating current signal?

(2) Why are two signals of C_ADC and C_ADC1 input to the DSP? It seems that C_ADC1 is just a filtered signal of C_ADC.

Meanwhile, for phase B, only the B_ADC signal is input to the DSP. There is no B_ADC1 signal as uploaded below.

What is the reason?

CS_B-control.png

Thank you for your consideration.

With regards,

GKIM

Comments

  • TBhatia
    TBhatia Wolfspeed Admin - Contributor Level 5
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    Hello, thank you for your message. A member of our technical team is looking into your questions and we will respond shortly. 

  • FrankWei
    FrankWei Wolfspeed Employee - Contributor Level 2
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    Hello GKIM,

    They are for current sensing and peak current protection. please note that the filtered signal for B phase is also on the board. thanks

    Regards,

    Frank

  • gkim
    gkim Contributor Level 3
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    Hi FrankWei,

    Thank you for your review.

    That is right! I have found out that the filtered signal for B phase is also on the board.

    I still need to ask a few questions as follows:

    (1) Is the C_ADC1 signal for the current sensing and is the C_ADC signal for he peak current protection? Or else is it the opposite way?

    (2) The question of how the DSP can know the direction of the alternating current signal when  the current signal is full-wave rectified has not been answered yet. Otherwise the DC-DC control strategy does not have to know the direction of the alternating current signal?

    Thank you for your consideration.

    With regards,

    GKIM

  • FrankWei
    FrankWei Wolfspeed Employee - Contributor Level 2
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    Hi GKIM,

    Thank you. Yes. the C_ADC1 signal for the average current sensing. It can be used for current sharing control. C_ADC signal is for the peak current protection. we don't need to know the direction of the alternating current signal for protection. thank you

    Regards,

    Frank

  • gkim
    gkim Contributor Level 3
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    Hi FrankWei,

    Thank you for your review.

    There might be no direction information of the alternating current signal for the C_ADC1 signal.

    The current sharing control does not have to know the direction information of the alternating current signal such as the C_ADC1 signal?

    Thank you for your consideration.

    With regards,

    GKIM

  • FrankWei
    FrankWei Wolfspeed Employee - Contributor Level 2
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    Hi GKIM,

    Yes, in this design, we don't need the direction information of the alternating current signal for the control. Thanks

    Regards,

    Frank

This discussion has been closed.