# How can I remove the few peaks before the overshoot, so I only have the overshoot peak and then it directly transition into steady state?

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Samuel Pappalardo on 25 Feb 2022
Commented: Kevin Rogers on 1 Mar 2022
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
This is the output voltage graph i got:
Currently I'm manually tuning the PI to achieve an overshoot of between 10% to 20% and a settling time of 0.01 to 0.1 these are no problem but I just can't remove the oscillations following the overshoot. Also when I change the value of D it mess up the whole graph. Is it possible to remove the oscillations so the overshoot follows directly into the steady state because no matter what I change p and I to it never removes the oscillation before the overshoot and changing d mess up everything
Kevin Rogers on 1 Mar 2022
wn = 1/sqrt(LC)
2*delta * wn = 1/(RC)
For critical damping delta = 1
Therefor C = 1 / (2*wn * R).
Substitute C inot 1st equation to get L.

Pat Gipper on 26 Feb 2022
Hi Samuel. I found tuning the derivative to be difficult too. Eventually I settled in on P=3.5, I=850, D=0.01 and N=850. The default value of N was way too small. Here is the result.
Samuel Pappalardo on 26 Feb 2022
When i used your values i got this:

Dr Narayanaswamy P R Iyer on 25 Feb 2022
You have NOT mentioned anything about triangle carrier frequency. First obtain output voltage response without PI controller. Then apply Ziegler-Nicholas chart to tune PI controller. Refine this kp and ki value for desired response.
Samuel Pappalardo on 25 Feb 2022
Thanks but to apply the zieglar- Nicholas i need to know the TF. The carrier frequency would be 1Khz
would it be correct to say the Tf of my circuit would be:
If is correct i will just sub my values for R L C and Vi

Dr Narayanaswamy P R Iyer on 26 Feb 2022
TF is one method. You know the desired output voltage and duty-ratio D. Use this in the model to get open loop voltage response. Then apply Ziegler-Nicholas chart to obtain kp and ki. Then refine this PI controller parameters for desired output voltage closed loop response.
Samuel Pappalardo on 26 Feb 2022
How do i obtain open loop voltage reponse
My dersired output voltage is 8v and duty cycle should be 50%

Dr Narayanaswamy P R Iyer on 26 Feb 2022
For 8 V output, your duty-ratio should be 2/3 (0.67) for given input voltage.
Samuel Pappalardo on 26 Feb 2022
Yes you arre correct
how can i use these two values to obtain the open loop voltage
I'm unawre of the formula if there is one

Zhao Wang on 26 Feb 2022
Since you have built a Simulink model for the buck converter, you may want to consider tune the PID controller based on the actual model behavior. For a switching buck converter, you will need to conduct frequency response estimation to identify a linear system description at the desired operating point. Using the linear plant model, you can use the PID Tuner App (can be opened from the PID controller block) to tune PID controller gains to achieve the performance you want.
##### 2 CommentsShowHide 1 older comment
Zhao Wang on 26 Feb 2022
I totally understand that the linearization error message will very likely appear in a switching circuit model. This linearization error is because of the discontinuities intrinsic in such power electronics models. There is an alternative way of tuning PID controllers automatically using the Closed-Loop PID Autotuner, as shown in the example: https://www.mathworks.com/help/slcontrol/ug/tune-pid-controller-in-real-time-using-closed-loop-pid-autotuner-block.html

Pat Gipper on 26 Feb 2022
My bad. Change I to 300.
Pat Gipper on 28 Feb 2022
This is the model that was sent. It is using version R2021b Update 1. The gain constants are in the Model Workspace. Use Model Explorer to modify the constants.

Antonino Riccobono on 28 Feb 2022
Dear Samuel,
The difficulties you are encountering are understandable since when you tune a specific gain of your PID controller this will affect the other two. Therefore, manually tuning is not practical.
If you want to learn a systematic tuning workflow so that your feebback performance meets specific dynamic requirements, I invite you to consider the following training course:
Good luck,
Antonino

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