Ok I just got finished reading a thread entitled "Hybrids aren't electric cars" the OP explains that electric motors have more torque than gas so when using the electric at the start in a hybrid then allowing the gas motor to take over at higher speeds results in greater efficiency and better mileage. This got me to thinking has anyone at all used a combination of AC and DC motors in a full electric conversion? Since AC I have heard uses much less amperage at the very start then you could switch over to the DC motor for top speed. Could an already converted car using a DC motor be retrofitted with a small AC assist motor like the prius to achieve greater efficiencies?
I think it is important to keep in mind the real advantages and disadvantages of AC vs DC.
1) Power is power. When looking at power there is not a significant efficiency advantage between AC and DC.
2) AC makes it easier to regen power
3) AC can maintain a constant top speed while voltage decreases. It is the phase difference that controls speed not voltage.. A DC motor's top speed is directly proportional to the voltage, so as voltage drops so does the DC motors top speed.
If you have done the heavy lifting (paid the $) of installing a AC controller, then I see no benefit of adding a DC motor with the AC motor.
Then add in the fact you have twice the controller weight, twice the leakage current, twice the motor weight, and worse yet half the mean time between failures.. Yikes.
One of my pet peeves with hybrids is the increased complexity and reduced mean time between failures.
But to build on your idea....
What if you wanted 4 wheel direct drive EV? In that case maybe it would make a little sense to have AC on the front two wheels and DC on the rear to wheels to make the vehicle a little less expensive while getting most of the benefits of AC. (Kind of like putting rotors on the front and drums on the rear).
Wow this just made me realize something..... I am doing and AC EV and the car is rear wheel drive.. dang. I would get a lot better regen out of the AC motor if it were a front wheel drive vehicle. Oh well too late to change know.