Last updated: Feb 2020 by Narasimhan Santhanam
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t is a part of EV Next’s EV Perspectives.
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Introduction
The rapid development in the field of Power electronics and control techniques has created a space for various types of electric motors to be used in Electric Vehicles. The electric motors used for automotive applications should have characteristics like high starting torque, high power density, good efficiency, etc.
Electric car can use AC or DC motor
If the motor is a DC motor, then it may run on anything from 96 to 192 volts. Many of the DC motors used in electric cars come from the electric forklift industry.
If it is an AC motor, then it probably is a three-phase AC motor running at 240 volts AC with a 300 volt battery pack.
DC installations tend to be simpler and less expensive. DC motors also have the nice feature that one can overdrive them (up to a factor of 10-to-1) for short periods of time. That is, a 20 kW motor will accept 100 kW for a short period of time and deliver 5 times its rated horsepower. This is great for short bursts of acceleration. The only limitation is heat build-up in the motor. Too much overdriving makes the motor heated up to the point where it self-destructs. AC installations allow the use of almost any industrial three-phase AC motor, which can make finding a motor with a specific size, shape or power rating easier. AC motors and controllers often have a regen feature. During braking, the motor turns into a generator and delivers power back to the batteries.
DC Motors
DC motors are a natural choice because they are cheap to build. The components are readily available off-the-shelf; for example, a large generator from a jet engine can be quickly adapted for use as a motor. And because DC motors use the battery power directly, the control circuitry is much simpler. From an operating standpoint, DC motors generate more torque (starting power), so it is not unusual for a DC electric car to have no transmission—another cost-cutting aspect. And brushless DC motors generate less heat than an AC induction motor, meaning less energy is wasted.
AC Motors
AC motors are more complicated. Because the DC power of batteries must be converted to AC, the car needs a voltage inverter. The speed control circuitry is more involved, and the entire system is more expensive simply because the electric vehicle industry has not yet developed the necessary infrastructure to drive prices down. But AC motors have important advantages in electric vehicles. As motors get larger and performance becomes a consideration, AC can really show off– for example, the Tesla zips from 0 to 60 MPH in a mere 3.9 seconds. And while the circuitry is more complex, AC systems are actually simpler to install and safer. DC systems can short-circuit the entire battery pack, possibly causing the motor to catch fire, while a blown AC inverter simply fails and the car stops.
Motors used by Major EV Companies
| Company | Motor Type |
| Tata | 3 phase AC Induction Electric Motor |
| Mahindra | 3 phase AC Induction Electric Motor |
| Tesla Roadster | Permanent Magnet and 3 phase 4 pole AC Induction Motor |
| Chevy Volt | 200 hp (150 kW) Permanent Magnet Motor |
Learn more on the key components of the Powertrain: Transmission Systems | EV Motors | AC-DC Motors | Component Suppliers to Major EVs |
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See also the blog posts
- Electric Vehicle Transmission System – EV Transmission, Gears, Powertrain
- Motors used in EVs – BLDC, Induction, SRM, Permanent Magnet Motors for Electric Vehicles
- Electric Vehicles Supply Chain in India – Components for E-scooters, Electric Cars, E-rickshaws
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