Sigurd Skogestad (April 2020):
The overall goal of my work has been "to develop simple yet rigorous methods to solve problems of engineering significance". 

What are my most important achievements in terms of my research work? Hm....

1.	Probably, the most important is my book on multivariable control with Ian Postlethwaite.


2.	The second most important is probably what I have done on what I call "self-optimizing control", which really is about what we should control on a fast time scale to ensure near-optimal operation.

As Alan Foss writes in 1973 about the methanol process:
“Should one measure the concentration of carbon monoxide?  Or perhaps it is the ratio COz/CO that should be measured. Or how about the ratio CO/Hz? “
I think the idea of self-optimizing goes a long way towards answering such questions.


3.	I have always been interested in the control structure design problem, which Alan Foss stated as: “Which variables should be measured, which inputs should be manipulated, and what links should be made between these two sets?”. I have some publications on this, including: Control structure design for complete chemical plants. S Skogestad. Computers & Chemical Engineering 28 (1-2), 219-234 (464 citations on google scholar)

I'm still working on this, and I'm making steady progress on making more theory around some of the already established tools of “advanced process control”. 
More recently I have worked on systematic methods for changing between active constraints using selectors, split range controller, multiple controllers with different setpoints and so on. For example, see here:
https://folk.ntnu.no/skoge/publications/2019/reyes-lua_active-constraint-swtching_iecr2019.pdf

It's going slowly but I take comfort in what Alan Foss wrote in his famous critique paper in 1973: “There is more than a suspicion that the work of genius is needed here, for without it the control configuration problem will likely remain in a primitive, hazily stated, and wholly unmanageable form.”
See here for Foss’ 1973-paper: https://folk.ntnu.no/skoge/puublications_others/


4.	Finally, I have my work on PID control, where I still believe that my SIMC-rule is "probably the best SIMPLE PID-rule in the world". And I know a lot of people use it in practice.