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CCS: HV_1_PH_DCAC control problem in grid connected

Tong CHEN
Prodigy 105 points


Tool/software: Code Composer Studio

Dear all

 I am doing experiment by using your design HV_1_PH_DCAC as a grid-connected inverter.

I think that product is a excellent design and good for using, but I have one question now.

I notice that in the "gridconnectedinvlclfiltr.c"

The control algorithm, when you calculate the inverter' duty cycle, there goes:

"invDutyPU= (cntl2p2z_LeadLag_vars.Out + invVoInstSD)/(invVbusInst*(VDCBUS_MAX_SENSE/VDC_NOMINAL));"

I cannot understand why "invVoInstSD" appear? since the control scheme you gave in the manual did not mention about this instant grid voltage positive feedback.
If I delete it, what will happen?

Thanks for reading, looking forward to your reply.

Best regards,
Chen Tong
  • 0
    TI__Mastermind 43730 points

    Tong,

    This is the output voltage feed-forward component that helps in simplifying the current loop. However can lead to some additional phase margin loss. 

    I implemented the v1 without the voltage feedforward and v1_01_00_00 with the voltage feedforward. 

    I do agree there is some documentation missing for this part, 

    if you do not want it you can remove it, but make sure you check the build level 2 with DC and see if the control loop is still stable before you test with the AC build. 

  • 0 in reply to Manish Bhardwaj
    Prodigy 105 points

    Dear Manish Bhardwaj,

    Thanks for your response, that's a big help for me.

    My additional question is about the dc decoupling coefficient, I assume that the DC instant measured value is enough for the denominator, why after it appear some other coefficient like Vdc nominated and Vdc max mesureed value?

    Cause in modeling, the inverter act like an amplifier with the Multiply of Vdc. These two value actually will cause some unintended proportional part I think.

    Again I appreciate your design very much, this kit is really helpful for my research project.

    Best wishes,

    Tong

  • 0 in reply to Tong CHEN
    TI__Mastermind 43730 points
    Tong,

    The ratio is use to multiply is to make them come on the same scale, i.e. make the AC sense range the same ad DC bus sense range. So in PU they match for the same voltage.

    This can provide some cancellation and simplification when you derive the model. Though not completely necessary.

    regards
    Manish Bhardwaj