Which trick is used to adapt the PI gains calculated in per unit to work in Simulink if the input and output to the controller are all in per unit, but the plant is in physical units?

I am trying to figure out how the gains of the PI controllers used in the Matlab examples for Voltage Source Converters have been calculated. I have tried using Modulus optimum and symmetrical optimum and doing the calculations in per unit but the gains I am getting are not close. They are too small compared to those in the examples.

Answer 1

[Sabin]

If you have a per unit controller, where input and output are in per unit. The only thing that is needed to go back to SI is the base quantity used for normalization. For example, if the output of your controller is a voltage you only need to multiply the output with the base voltage of your system. An example of per-unit control and SI plant is this in Simscape Electrical: https://www.mathworks.com/help/sps/ug/three-phase-asynchronous-drive-with-sensor-control.html

Regarding the gains for the controllers in some examples, they may have been tuned using a variety of approaches including pole placement and frequency response. Depending what specifications you have for the controllers, they may look very different from what the examples are using. I hope this helps.

[Simon]

Thank you very much for the help. This helps.