Y_Po wrote:I will repeat, wires in transformer are insulated and AC motors have no advantage over DC motors, in fact they are heavier and less efficient at low speed
Perhaps you're right-- that a DC motor at low speed can be made slightly more efficient than an AC motor. The advantage of the properly engineered AC motor is that it can achieve high efficiency over a wide range of speeds-- which the DC motor can't. That's why a DC motor used to propel an EV needs a transmission, while a properly designed AC motor doesn't.
Now, as I've said, this applies only to inboard motors. For in-wheel motors, physical constraints require different engineering, and therefore different types of motors. It's my understanding that DC *can* compete, or may even be superior, for those applications.
But in-wheel motors are considerably more expensive, at least currently. Will we ever see an affordable "family sedan" driven by in-wheel motors? Only time will tell.
At present, for highway-capable EVs, AC rules.
Sigh you are both right or both wrong depending on your point of view.
Quick motor type overview
Series wound DC
+ Inexpensive, rugged. Very, very common in electric vehicles.
- Uses brushes
- Regen very difficult, electrical braking usually done via plugging.
+ Common in smaller vehicles
+ Easy to speed control
+ Regen is easy
- Doesn't scale well
- Can be sensitive to temperature and shock, something that has improved with newer magnets.
+ Doesn't need to generate a field so usually more efficient
- Fixed field strength
Shunt wound DC, uses a separate low current winding for the field.
+ Control can be as simple as that for PM DC along with all its benefits
+ Scales better than PM
+ Currently replacing series wound motors in electric vehicles as the motor of choice.
+ Because field is generated it can be strengthened to increase torque or weakened to increase speed. A wider variety of speed torque charaqcteristics are available at run time
+ Very rugged
- Speed control needs to be a lot more sophisticated to match drive frequency with motor speed
+ Like shunt wound motors the two interacting fields of the motor are generated independently allowing wide selection of torque speed curves.
PM AC AKA Synchronous AC AKA BLDC AKA ECPM Motor. Note that these are definitely AC motors, not DC motors
+ Similar to PM DC motor in performance characteristic but requires slighty more complex control.
+ Very Very rugged
- Even more complex to control
Currently, shunt wound motors are replacing series wound in EVs, with AC motors replacing shunt wound motors. European EVs appear to have largely skipped the shunt wound motors, moving to AC earlier than North America.
BLDC hasn't seen much use in EV except in automobile because the present controllers and especially motors have too high a premium. Also by the time you have the power electronics for a PM AC you have all the power electronics to support induction AC, you just need the sophisticated control to use the cheaper, more flexible, more rugged motor.
There's not a lot to choose between the motors on efficiency grounds although the PM motors will be more efficient.