Small Signal/Impulse Response Analysis (Open Loop Response - Buck PWM converter)

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Hello,

I am trying to extract the open-loop response (control to output bode plot) of a Buck PWM converter from PLECS Simulation Environment and I run into a ‘problem’ when displaying the waveforms.The switching frequency of the converter is 200kHz.The ‘problem’ is in the frequency range of the Inpulse Response Analysis.I will attach a pdf file with some pictures for this purpose. When the frequency range is larger then the simulation result for the high-frequency values is not so good or accurate.How can the display result of this ‘problem be solved or improved’?Also, I tried from the menu: Steady-State Options - to increase the value of some parameters (meaning to make: Number of init. cycles or Max. number of iterations bigger than 0 or 20) but without success in displaying a more accurate graph. (I am using PLECS Standalone 4.1)Thank you.

Small_Signal_Analysis_Impulse_Response_Open_Loop_Buck_PWM_Converter.pdf (379 KB)

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You are trying to derive a small signal transfer function well above the switching frequency of your converter. If you consider what you are asking the program to do, it should be clear that above the switching frequency the small signal results will not be meaningful (both for PLECS and analytical models based on averaging). Therefore you’ll notice up to about 200 kHz the results seem reasonable, but are incorrect above that point, as expected.