Well, lets see.
You could download the service manual I linked to. It has some theory of operation type stuff in it. https://www.myfocuselectric.com/forum/v ... hp?p=33336
Ford has a course for technicians to learn about the FFE, I believe that is about $90. https://www.motorcraftservice.com/Purch ... uctID=1051
There is also a document about the electric and hybrid systems in ford vehicles at that same site for free, I believe. http://www.fordservicecontent.com/ford_ ... 01_HEV.pdf
There are 3 papers floating around this site, thermal management, braking, and I forgot the other.
The technology used in the FFE is also in other electric cars and hybrids, so any books about how they work.
The FFE was actually designed by Magna Steyr through their E-Car project. They then worked with Ford to make a mass-production vehicle.
So research into the origins of the E-Car should provide you info about the FFE.
There are some great educational teardown videos of hybrid and electric vehicles on the Weber Auto channel at youtube. https://www.youtube.com/c/WeberAuto