Here is an excellent explanation about how the powersplit device in a hybrid works. The difference between the FFH & Fusion Energi is that the MG1 is larger in the Energi which allows it to reach a higher speed in EV mode (85 MPH vs 62 MPH). This is exactly how our cars work, the difference being that the gear ratio is different because of different size MG1, MG2 and engine.
Toyota and Ford both use this design for their hybrids and this technology is why the Ford & Toyota hybrids are superior to hybrids made by Honda, Kia, Hyundai, Volkswagen or GM. All the other manufacturers place an electric motor sandwiched between the engine and the automatic transmission. That is a less efficient design than what Ford & Toyota have done. The other hybrids are "one motor" hybrids, whereas the Ford & Toyota hybrids are "two motor" hybrids as they have 2 electric motor/generators as shown in the video. The next gen Honda Accord Hybrid and Plug-in Hybrid introduces a two motor hybrid system for Honda, their first. It will be interesting to see if it is engineered the same as I believe Toyota and Ford own the patents for this design.