Prius "eCVT" is a special planetary gearset that all gears are powered. ICE is connected to the planets, input and output has the alternator and traction motors. Difference in resistance between two motors is imparted to the ICE, achieving power mix and generation control.
It's a really simple and clever solution. So much so that brain hurts to think about
It's a really simple and clever solution. So much so that brain hurts to think about