1. Systems Engineering Fundamentals
http://www.dau.mil/pubs/pdf/SEFGuide%2001-01.pdf
This is a large Department of Defense document that has extensive amount of coverage on Systems Engineering, with fundamental explanations in simple language leading to an in - depth understanding of all the concepts involved.
2. Tech Online webcasts and resources
http://www.techonline.com/community/ed_resource
When you choose engineering, you must visit this website from time to time and update yourself with the latest and coolest in technology!
3. How PID Controllers work
http://www.manufacturing.net/ctl/article/CA189611
A good starting point, helps you understand how PID controllers work.