I enjoyed that video but it also confused me a bit. It is useful in that it clearly makes the point that what's different about the PSD is that, unlike the planetary gear system in the Ford Model T and many others, at no time is any of the three components ever locked or fixed. The sun-gear, planetary gears, and ring gear are always free to rotate, and do.
What was not clear to me was the power flow from the ICE to the wheels. It seemed as if he was saying that the only connection from the ICE to the wheels was indirect, by turning MG1 to generate current that could drive MG2 which drives the wheels. But I don't think that's the case.
I know that if I floor the pedal entering the freeway, the ICE spools up to something like 5000rpm and holds there while the car accelerates. So clearly there is a flexible connection. But is all of that mighty horsepower being transmitted by first being turned into AC in MG1, which flows to MG2, which turns it back into torque? Because that would be rather inefficient I would think.
MG1 can provide some resistance against the ICE's motion, causing part of the ICE's power to drive the ring gear instead. So in some cases, you have MG1 acting as generator (thus resisting the ICE) and driving MG2 electrically, AND you have mechanical contribution by the ICE as well.
You're right that the ICE can essentially directly drive the wheels. Take a look at the model, and think of the outer gear (connected to MG2) directly powering the wheels. Then try setting the ICE to near max, and MG2 to about the same level, so the grey line is horizontal. That should simplify the visualization. See how the ICE pulling the planetary gears around directly pulls the large gear as well? Once you grok that, you should be able to see that even if you vary the MG2 slider, the ICE is still providing torque to that outer gear.
I didn't watch the video and cannot properly explain it, but there is direct mechanical connection from ICE to wheels. AFAIK both MG1 and MG2 can work as motors and generators and spin in either direction. If you apply proper counter-torque by one of the electric motors (for planetary ring), the torque effectively flows from ICE to wheels. I'm Prius driver myself, it's a nice car for us who cannot yet drive full electric vehicle for a reason or another.
What was not clear to me was the power flow from the ICE to the wheels. It seemed as if he was saying that the only connection from the ICE to the wheels was indirect, by turning MG1 to generate current that could drive MG2 which drives the wheels. But I don't think that's the case.
I know that if I floor the pedal entering the freeway, the ICE spools up to something like 5000rpm and holds there while the car accelerates. So clearly there is a flexible connection. But is all of that mighty horsepower being transmitted by first being turned into AC in MG1, which flows to MG2, which turns it back into torque? Because that would be rather inefficient I would think.