You might ask why an expensive Investor is necessary in a hybrid? The reason is that the battery is DC and the GMs are AC . If the GMs are to be DC , they would have to be at least 3 times heavier to produce the same HP & Torque.
By the way, older hybrids did not have a voltage step-up from battery voltage. That why the early batteries were 280V or so and a modern battery is about 200V but that voltage can be stepped up to about 500V when there is high power demand
For anyone interested in car mechanics, the Toyota Transaxle is an amazing mechanical/electrical unit with planetary CVT function . The oil cooling system is now external where on earlier units the water was circulated within the transaxle.
