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BOOSTXL-BUCKCONV: About BOOSTXL-BUCKCONV PWM frequency / Simulink ADC configuration

hassan abouobaida
Prodigy 230 points
Part Number: BOOSTXL-BUCKCONV

Hello,

I have BOOSTXL-BUCKCONV card  and Lanchpad F28379D , I want to know if I can use a frequency of 20kHz instead of 200kHz given by an example in Simulink:

the objective of minimizing the frequency is linked to the difficulty of sampling the current in the inductor, I cannot determine the traingular shape of this current.

On the other hand, if we use the 200kHz PWM frequency, how can we configure the ADC converter in Simulink to acquire the inductor current which must be triangular where in the provided example the sampling signal gives the average value only !!

  • 0
    TI__Guru 62975 points

    hassan abouobaida,

    The hardware will certainly support a slower sampling frequency of 20kHz. The averaged nature of the feedback signal probably has more to do with the signal conditioning circuitry (in other words, the RC filter) on the board rather than the sampling frequency.

    For Simulink specifics, you might get quicker answers directly from Mathworks: https://www.mathworks.com/support.html

  • 0 in reply to tlee
    Prodigy 230 points

    Hello,

    I think there is a risk of destruction of the converter inductor, if there is someone who has already used the switching frequency of 20kz please confirm us !!

    About the ADC converter setup for inductor current sampling, the signal received is the average current value and not its instantaneous value of the triangular shape, I got no response in this direction.

    Thank you for your help.

  • 0 in reply to hassan abouobaida
    TI__Guru 62975 points

    hassan abouobaida said:
    I think there is a risk of destruction of the converter inductor, if there is someone who has already used the switching frequency of 20kz please confirm us !!

    Can you elaborate on how you suspect the inductor might be damaged from a slower switching frequency?

    I doubt that anyone has tried a switching frequency as slow as 20kHz using this BoosterPack.  The typical queries are for running faster, not slower.

    hassan abouobaida said:
    About the ADC converter setup for inductor current sampling, the signal received is the average current value and not its instantaneous value of the triangular shape, I got no response in this direction.

    As mentioned in my prior post, you will need to modify the RC filter on the PCB if you want a sharper waveform.

  • 0 in reply to tlee
    Prodigy 230 points

    Hello Tlee,

    Theoretically, for a given ripple, the value of the inductance is inversely proportional to the switching frequency of the power switch, a division of the frequency by 10 implies that the value of the inductance must be multiplied by 10 to keep the same ripple current in the inductor.

    For the second point which concerns the ADC converter, the signal from the  BOOSTXL-BUCKCONV   card is triangular, I am talking about the inductance current that is sampled by the ADC block of simulink which provides me (through the COM port) the average value and not the instantaneous (traingular) signal, I am not talking about the RC filter of the BOOSTXL-BUCKCONV card.

    Thank you for your help.

  • 0 in reply to hassan abouobaida
    TI__Guru 62975 points

    hassan abouobaida said:
    Theoretically, for a given ripple, the value of the inductance is inversely proportional to the switching frequency of the power switch, a division of the frequency by 10 implies that the value of the inductance must be multiplied by 10 to keep the same ripple current in the inductor.

    Yes, I would expect the ripple to increase with the slower 20kHz switching speed. It's not clear to me how this would lead to "destruction of the converter inductor."

    hassan abouobaida said:
    For the second point which concerns the ADC converter, the signal from the  BOOSTXL-BUCKCONV   card is triangular, I am talking about the inductance current that is sampled by the ADC block of simulink which provides me (through the COM port) the average value and not the instantaneous (traingular) signal, I am not talking about the RC filter of the BOOSTXL-BUCKCONV card.

    Are you saying that you want to reconstruct the continuous current feedback signal?  If so, would it make sense to collect samples faster, closer to the Nyquist rate?

  • 0 in reply to tlee
    Prodigy 230 points 
    Hello,
My question concerns the inductor current sampling whose frequency is 200kHz, 
    how I should configure the ADC device of the DSP Launchpad F28379D and the COM port of PC Host or another transmission device to be save 
    this current in a .mat file !!
    To program the DSP, I'm using the Simulink Blocks.

    Thank you for your help.
  • 0 in reply to hassan abouobaida
    TI__Guru 62975 points

    Hassan,

    Our expertise in this forum is limited to topics related to TI-supported hardware and software.  Your question seems to be focused on software development using Simulink, which is not a TI product.  I recommend seeking Simulink support directly from Mathworks: https://www.mathworks.com/support.html

    -Tommy