why is it impossible to use the PID tuning app when tuning a PID controller used in circuits that have PWM switchings?

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Hassan Iskandarani
Hassan Iskandarani on 8 May 2022
Edited: Antonino Riccobono on 9 May 2022
Every time I try to use the PID tuning app on MATLAB Simulink, I get error that plant cannot be linearized due to discontinuities because of switching signals, I wasted a lot of time on trial and error method, and I still can't reach the most robust PID controller, so if someone can give alternatives to tune the PID controller else than the tuning app and the trial and error I'll appreciate it, thank you.

Answers (2)

Vasco Lenzi
Vasco Lenzi on 9 May 2022
Hi Hassan
in my video series on DCDC controller development I touched on this topic in part 4 and showcase how you can retrieve a transfer function from a system with PWM switching:
It's all nicely integrated in the PID tuning app, but it does require System Identification Toolbox.
The message you are seeing is correct; the system cannot be linearized because as PWM driven system is intrinsically non-linear. From the PID tuning app, you can select "create new plant" and choose to identify it from Input/Output response. You will be prompted in picking a test case, simulate it and then you can adjust system parameters until you find a transfer function that fits well. Once you have it, you can perform tuning.
Follow the instruction in the video above (part 4) and I believe you will be successful!
Thanks
Vasco

Antonino Riccobono
Antonino Riccobono on 9 May 2022
Edited: Antonino Riccobono on 9 May 2022
Dea Hassan,
The failure in the linearization process is normal due to the discontinuities associated to switching events. This is mainly due to the fact that the linearizarion is an analytical mathematical process that requires a linear behavior of the plan model.
To tackle such a difficulty, since the linearization plant model cannot be analytically calculated for a switch-mode power electronic converter, you'd need to estimate a Linear-Time Invariant model of the plant model, that is your switching converter's control-to-output transfer function that can then be used in the tuning process.
Together with a team of experts, I have recently published a technical article where we show a systematic workflow for PID gain tuning based on frequency response estimation applied to switch-mode power electroni converters. Please, have a look at this article: https://www.mathworks.com/company/newsletters/articles/cascade-digital-pid-control-design-for-power-electronic-converters.html
Moreover, if you are interested in a training course that covers in details all these control design aspects for power electronics, please have a look at this page: https://www.mathworks.com/training-schedule/power-electronics-control-design-with-simulink-and-simscape.html
Hope this helps,
Antonino

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