What did you calculate?, the Control to output txfer function for a buck converter in dcm is a standard known equation, no need to calculate it, unless just for academic exercise.According to my calculated control-to-ouptut transfer function,
I am sure you know C is in Farads.
The attached shows that with your spec, you are in DCM with 100uH or 62.5uH inductor.
(vin=400v, vout=200v, pout=100w, fsw=300khz)
Did you do calcs for current mode or voltage mode?
Yes ofcourse, it should be 4.4uF. The intention is to have high inductor current ripple, but the circuit finally would be "synchronous buck". It works fine in the transient analysis, and I suspected it'd go wrong with the asynchronous averaged switch model. But it works for any other buck circuit values I input, so I got confused.
How would I write the subckt definition for the mosfet-mosfet type model ? (For synchronous buck).
What did you calculate?, the Control to output txfer function for a buck converter in dcm is a standard known equation, no need to calculate it, unless just for academic exercise.
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I have also attached for you the control to output txfer function for a Buck
Would you mind to explain where you got the behavioral converter model? I didn't check the achieved frequency response, but regarding bias point, the 400V converter is obviously operating in DCM, respectively Vout > 0.5*Vin. According to behavioral model it's an asynchronous (transistor-diode) converter, transiting between CCM and DCM depeding on load current.
I realized(pretty late) that the MATLAB plot I'd done was a CCM transfer function. I changed it referring to the DCM transfer function from Erickson-Maksimovic Fundamentals of Power Electronics book, but I'm still making a mistake somewhere because the Phase margin is not matching although the crossover frequency is close enough to Pspice. I really need some help with this, thank you.On full load, the C-to-O/p txfer function will be much the same whether synchronous Buck or non synchronous Buck.
Also, if you use current mode control, then the double pole LC at the output has a pole cancelled out, so you dont get that usual peak due to the L,C resonance.
Yes, there was a problem in the model, I fixed it now, and the Pspice simulation is I think, correct. I've added here, the pictures of that.Not clear to me which transfer functions you are comparing now. The "MATLAB" transfer function in post #1 is apparently involving hidden parasitic elements, about 10 mohm capacitor ESR, otherwise the zero at 3 MHz won't happen. Avoid comparing apples with oranges and specify all circuit parameters.
As already mentioned, the derivation of the CCM-DCM model is also unclear. In a transient simulation of the 400V switcher, I got 280 rather than 340 V output bias, thus I think, the model may be incorrect.
Thank you for your post. I have posted the model definition in my first post. In my latest post, I corrected my simulation, and got around 281 V output, which others have also corroborated. But I have a fundamental doubt as to if this circuit is operating in DCM or Forced CCM? As per what I have studied, I think DCM is when the inductor current falls to 0 A and stays there for some time which is not negligible. Also, if this was a DCM mode, then the buck output voltage would have been larger than 400 V. So I think this is not DCM, but FCCM.Can you post the spice definition of the CCM-DCM1 subcircuit? Should be fairly easy to make it operate as a synchronous converter with forced CCM.
Keep in mind, when using the CCM-DCM1 model, it has to be passed your switching frequency and inductance as parameters, and the inductance has to match the actual inductor in your circuit to get valid results. The inductance and frequency together tell the CCM-DCM1 model how to transition between CCM and DCM operation.
No it's obviously DCM. The output voltage in CCM would be 200V.But I have a fundamental doubt as to if this circuit is operating in DCM or Forced CCM? As per what I have studied, I think DCM is when the inductor current falls to 0 A and stays there for some time which is not negligible. Also, if this was a DCM mode, then the buck output voltage would have been larger than 400 V. So I think this is not DCM, but FCCM.
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