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PSpice Gain/phase model for S/H and quantization in software loop(digital SMPS)

Discussion in 'Electronic Design' started by Klaus Kragelund, Nov 15, 2012.

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  1. Hi

    I have implemented a digital SMPS in a Cortex M3 controller. The feedback of the SMPS is done using the TL431 and opto coupler feedback.

    The feedback is sampled by the ADC at 10kSa and the sampled values controls the duty-cycle of the SMPS.

    It is stable, but I would like to simulate the loop in PSPice. The ADC has sample and hold along with quantiziation that affects the gain/phase. The timer generating the PWM has finite number of different dutycycles and that has a small scale effect also.

    I would like to have a model both for transient and ac sweeps.

    The ac sweep can be modelled by a sinc function, but how to model the quantization and PWM stage (discrete duty cycles)?

    Also, for the transient simulation, the ADC can be modelled simple by a S/H. The quantization can be modelled by a floor function, and for the PWM I need another floor function and a couple of ABMs to model the PWM. But, is there a better method for this?

    Thanks

    Klaus
     
  2. Yes, that makes sense. Thats what I'm seeing on the scope, it really can never as opposed to an analog controller regulate to the exact target value.
    Good insights, thanks :)
    I just may need to buy that book ;-)
    My code supports sigma delta, but have not tried it yet, since I want to remove that from the closed loop analysis


    Regards

    Klaus
     
  3. Mark

    Mark Guest

    you can approximate the phase (time delay) using a pspice transmission
    line with a delay of 1/2 the sampling period

    Mark
     
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