As I have marked in the attached image, there is a PI controller, which is not necessarily a PI controller and could have several poles or zeroes.



I have simulated this system nearly successfully and the only thing I am struggling with is the controller parameters. I tried lots of controllers with different coefficients, but it still does not operate properly.



I have attached the output DC voltage signal, the output voltage should be 500v DC, while it is fluctuated with an undesired start-up and this is directly dependent on the controller coefficients.