According to the structure and working principle, there are three types of electric motor. They are: direct-current motor, synchronous motor and asynchronous motor.
Direct-current motor is an early product.
Direct-current motor needs routine maintenance (2-3 years)
because there are carbon brushes inside, which will wear out during the rotation.
What’s worse, spark will appear when changing direction.
Thus, direct-current motor is not recommended for electric car.
Brushless direct-current motor (BLDC motor for short) is developed on the basis of brushed direct-current motor.
Permanent magnets are stuck on the rotor and demagnetization may occur.
Furthermore, even with higher efficiency,
it does not work on harsh environment.
Usually, BLDC motor is used in e-bicycle or scooter or small power tricycle.
Synchronous motor mainly indicates permanent magnet synchronous motor (PMSM for short).
Because the structure of PMSM is more complicated,
thus, the cost is higher and there is also the possibility of magnetism-disappearing.
a. Disadvantage: Higher Price, More complicated structure, Need Liquid-cooling or water-cooling system.
b. Advantage: Higher Efficiency both in Low and high speed, Smaller Size, Lighter Weight, Higher Energy Density, Longer Mileage, Higher Peak speed(can be up to 10000rpm).
Asynchronous motor is alternating current motor (AC motor for short).
Compare with bldc motor, the efficiency of ac motor is lower, but the torque is larger at the same power, which means ac motor has better climbing ability. Besides, now the cost of ac motor is almost the same with bldc motor and it is free-maintenance and can be used in extremely harsh environment.
Normally, It is better to use BLDC motor if below 2kw, and use ac motor while 3-15kw. if beyond 15kw, PMSM will be a suitable choice.
Given that the climbing and overload ability, motor for electric car usually exceeds 3kw.
In a word, the recommended solution is:
if the total weight with full-load is 1000kg or less, 15kw AC motor controller system or below can be considered. the Max. speed will be about 90km/h.
If the total weight with full-load is from 1200kg to 5000kg, PMSM motor controller system can be considered. Its power range is from 36kw to 200kw. The max. speed can be from 90km/h to 160km/h according to different weight of vehicle.
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