Electric vehicles can use seven types of motors. What are they? What are their characteristics? This video will provide the answers.
There are seven types of motors used in electric vehicles: brushed DC motors, brushless DC motors, permanent magnet synchronous motors, induction motors, switched reluctance motors, synchronous reluctance motors, and coreless permanent magnet motors with axial flux.
Brushed DC motors are the simplest type of DC motor. They use brushes to mechanically commutate and transfer current to the motor windings. The armature or rotor is an electromagnet, and the magnetic field is a permanent magnet. This type of motor does not require a controller to operate or change speed, and it provides maximum torque at low speeds. Its disadvantages include a bulky structure, low efficiency, and the brushes generating heat that further contributes to inefficiency; the heat is concentrated in the center of the rotor and difficult to dissipate. Therefore, brushed DC motors are no longer used in electric vehicles.
Brushless DC motors, equipped with permanent magnets, are called brushless because they lack commutators and brushes. They employ electronic commutation, are maintenance-free, and feature high starting torque and traction characteristics with efficiencies as high as 95%-98%, making them suitable for high power density designs. These traction characteristics make brushless DC motors widely used in electric vehicles, suitable for small cars with a maximum power of 60 kW. Disadvantages include a limited constant power range, torque decreasing with increasing speed, and high cost due to the permanent magnets. The Toyota Prius uses a brushless DC motor.
Permanent magnet synchronous motors (PMSMs) have permanent magnets on their rotors, offering high power density and efficient traction characteristics. They can be used at higher rated power, making them more expensive than other motors. These motors can operate across a wide speed range without a gear system. They are efficient and compact, suitable for hub applications, and provide high torque even at low speeds. A drawback is significant iron loss during high-speed hub operation. Currently, PMSMs are widely used in hybrid and electric vehicles, such as the Chevrolet Bolt, Ford Focus, Nissan Leaf, and BMW i3.
Unlike DC motors, induction motors cannot generate high starting torque at a fixed voltage and frequency. However, this can be altered using various control methods, such as vector control or field-oriented control. These methods allow for the acquisition of the maximum torque required for traction during motor startup. Squirrel-cage induction motors require less maintenance, have a long service life, and can achieve a design efficiency of 92%-95%. Their disadvantages include the need for complex inverter circuits and difficulties in motor control. Due to their low cost, induction motors have become the preferred choice for high-performance electric vehicles. The Tesla Model S is a prime example of the high performance of induction motors. The Toyota RAV4 and GM EV1 also use this type of motor.
Switched reluctance motors are a type of variable reluctance motor with dual advantages: simple and robust structure, with the rotor being a single stacked steel sheet without windings or permanent magnets. This reduces rotor inertia, contributing to increased acceleration. Their robustness makes them suitable for high-speed applications and allows for high power density. Their disadvantages include complex control and the addition of switching circuitry, which introduces noise. Synchronous reluctance motors are synchronous motors with reluctance properties; torque is generated by the difference in reluctance between the direct and quadrature axes of the rotor, without excitation windings or permanent magnets. These motors are increasingly popular in electric and hybrid vehicles due to their simple and robust structure. Their advantages include no rotor losses and the ability to provide higher permanent torque than an induction motor of the same size.
The coreless permanent magnet motor with axial flux is currently the most advanced motor for electric vehicles. Its outer rotor is slotless, thus eliminating the need for a core. It also lacks a stator core, resulting in lighter weight. The radial component of the air gap magnetic field provides higher power density. The rotor of this motor can be mounted on the wheel side, while the stator windings are placed on the shaft. The slotless design results in lower copper losses, higher efficiency, and more usable space. The Renault Coupe uses this type of motor.
