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Why is the settling value of my TF so high when compared to my output value? How can I resolve this?

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I built a buck converter ( circuit will be below):
The parameters are:
Vi = 12V, L = 33e-3, the R next to L =0.5, C = 680e-6 , R next to C= 5e-3, R = 10
For the switching frequency I set the time value off the repeating sequence to 2e^-4
This is the output I'm getting:
This is the TF fomrula I have used:
This is the TF i obtained:
However, when I place the transfer function block in the circuit and attach it to the output of the PID when I view the scope this is what I'm seeing:
The shape is quite similar to the output voltage
They both have the same settling time
However, the peak of the TF is too high it overshoots too around 90V and settles around 86.3V.
Could you please have a look my what I've done and to suggest any amendments I could make as I'm unsure on how to resolve this error?

Answers (2)

Pemendra Kumar Pardhi
Pemendra Kumar Pardhi on 1 Mar 2022
Hello Samuel Pappalardo Firstly, form your second order characteristics experience in standard form S^2+ 2*zeta*w+ w^2=0 For reducing the overshoot zeta should be nearer one But not one for practical system. Therefore i suggest to select the proper value of passive elements in your buck converter model. Because value of zera would be function of passive elements

Antonino Riccobono
Antonino Riccobono on 2 Mar 2022
Dear Samuel, the discrepancy you're getting may be explained by the presence of other nonidealities you model with Simscape Electrical - Specialized Power Systems components. More specifically, please have a look at the idealswitch and diode. The ideal switch may have nonzero resisteive elements, and the diode may have nonzero resisteive element as well as nonzero forward voltage. The transfer function you are using includes only capacitor and inductor's ESRs.
One more tip for you. When comparing results, you may want to use the same scope block with two muxed signals.
Hope this helps!


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