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TIDM-1000: What does ADC_PU_SCALE_FACTOR represent?

stevenh
Guru 20045 points
Part Number: TIDM-1000
Other Parts Discussed in Thread: C2000WARE, TMS320F28377D, SFRA

Hello,

Does v1Meas = 1.0 represent 120Vrms input on phase 1? 


Stephen   

  

  • 0
    TI__Mastermind 43730 points

    No, 

    refer to the ADC sense max range in the calculation sheet

    see calulcations.xls

    C:\ti\C2000Ware_DigitalPower_SDK_1_03_00_00\solutions\tidm_1000\hardware

    the ADC does not know RMS, it only knows the absolute instantaneous voltage 

    As you can see in the excel sheet pointed out above, the scale is 416V,

    Which means when you have 120*1.414 / 416 = 0.40625 pu

    -Manish

  • 0 in reply to Manish Bhardwaj
    Guru 20045 points

    I simulated the feed back circuit in TINA (see attached file).

    For a 416.917V input, the simulation gives a feedback value of 3.2Vpeak.  That is greater than what I thought was the ADC reference voltage (=3V).

    That might not be an issue if the reference voltage is 3.3V; However, that would be 0.1V off. 

    I couldn't find a TMS320F28377D control card on TI's website, so I used the F28379D control card as a reference. 

    Is there a TMS320F28377D control card?

    TestFeedback.zip

  • 0 in reply to stevenh
    Guru 20045 points

    In addition to the questions in the previous reply:

    The code has VAC_MAX_SENSE = 454.  Why Isn't the max sense = 416.917V?

    What is the factor of 2.0 in the measurement equations (i.e. iL1Meas, iL2Meas, and etc).

    Why is the the vBusPMMeas and VBusMNMeas measurement equations multiplied by VDCBUS_MAX_SENSE/VAC_MAX_SENSE?

    The SFRA functions are not included in the code.  Can they be downloaded?   Currently, I am wanting to know what SFRA_F_INJECT does.

  • 0 in reply to stevenh
    TI__Mastermind 43730 points

    1. The factor of 2 is because we are converting the sensed signal that is one positive to a bipolar value by subtracting the offset. And because we use PU we want to scale it back to +1 to -1 range. Otherwise, the range will be 0.5 to -0.5

    2. The multiplication is to make the Vac and Vbus range same from a PU perspective even though we may have a different sense gain in the hardware for best ADC performance

    VDCBUS_MAX_SENSE/VAC_MAX_SENSE;

    If you do not do that then you will need to accomodate this sense gain difference in your control code. 

  • 0 in reply to Manish Bhardwaj
    TI__Mastermind 43730 points

    For your Vac sense range question please refer to 

    https://e2e.ti.com/support/microcontrollers/c2000/f/171/p/718532/2652776#2652776

    which is the same issue for Vac sense max.

    I did TINA simulation to get the accurate sense range. Which if you do for Vac sense will be close to 454 volts as well. I do agree we need to clear up the collateral to make this more clear. It is a filed bug from the previous post I have pointed to your above. I will also link in this thread on that bug and try to prioritize this for next quarter i.e. 3Q release. 

  • 0 in reply to Manish Bhardwaj
    TI__Mastermind 43730 points

    amc1301_vac_sense.TSC

    Attached my TINA simulation file. 

    SFRA is provided as a library, we do not disclose the source code. It is based on sine sweep analysis i.e. it will inject sinusoidal frequencies in a sequence and measure the response. We prove a STB for self calibration and test. 

  • 0 in reply to stevenh
    TI__Mastermind 43730 points

    stevenh said:

    I simulated the feed back circuit in TINA (see attached file).

    For a 416.917V input, the simulation gives a feedback value of 3.2Vpeak.  That is greater than what I thought was the ADC reference voltage (=3V).

    That might not be an issue if the reference voltage is 3.3V; However, that would be 0.1V off. 

    I couldn't find a TMS320F28377D control card on TI's website, so I used the F28379D control card as a reference. 

    Is there a TMS320F28377D control card?

    TestFeedback.zip

    To answer your question, the range used on the design is 3.3 V. You are correct there is no F28377D control card, only F28379D. You can use 3.3V as refererence by mapping the VDDIO and Vref. If you are using precision vref for ADC then you will have to use 3V. Otherwise, if 3.3V VDDIO is ok , which it is in most applications, we use 3.3 of the VDDIO as vref. Note you cannot use a precision Vref at 3.3V as ADC Ref because there can be variation which can result in violating the datasheet specification for the Vref pin. There is a switch option to select this on the F28379D , please refer to the infosheet.