Electric Vehicles (EVs) have introduced a relatively new technology in the automotive industry. Presently, there are three main types of motors used in Electric Vehicles, namely: asynchronous induction motor (ASM), permanently-excited synchronous magnet motor (PSM), and electrically-excited synchronous motor (ESM).
Each motor type possesses unique advantages and disadvantages and is utilized by various significant manufacturers. There is no conclusive answer as to which motor is the best. More detailed information about the distinguishing features of these Electric Vehicle engines is discussed below.
The working mechanism of an electric motor involves two primary components: a stator and a rotor. According to Arena EV, all variations of electric motors contain these two components. Typically, the stator comprises a steel cylinder with slots and copper coils arranged in a specific pattern. When an alternating current (AC) passes through these coils, it produces a magnetic field. As the rotating magnetic field builds, it influences the rotor, which is situated within the stator, causing it to turn and ultimately drive the wheels.
One of the primary distinguishing factors between these motor types is the type of rotor they employ.
Asynchronous induction motor
The Asynchronous Induction Motor (ASM) employs a rotor that consists of a highly-conductive material, such as aluminium or copper, formed into a “squirrel cage” setup. In the “slip ring” configuration, aluminium/copper windings replace the cage bars that connect to resistors outside the rotor to perform the same function, according to EV engine specialists Oswos. In either setup, the stator’s magnetic field propels the rotor into motion, which then endeavors to keep pace with the rotating magnetic field generated by the stator. This speed difference gives the motor the name “asynchronous,” as Renault explains.
The benefits of ASM include its reliability, relatively inexpensive manufacturing cost, and minimal need for rare earth materials. However, it requires more cooling, has a relatively low power density, and exhibits lower efficiency compared to other electric motors. The Audi e-tron SUVs, Mercedes-Benz EQC, and specific VW ID cars are examples of Electric Vehicles that utilise this type of motor.
Permanently-excited synchronous magnet motor
In a Permanently-Excited Synchronous Magnet Motor (PSM), the rotor contains magnets that generate their own magnetic field instead of relying on the stator to do so. As a result, less power is necessary to set the rotor in motion, according to ThomasNet.
When a current passes through the rotor, its magnetic field matches that of the stator, producing “synchronous” rotations and almost zero slippage, resulting in superior efficiency compared to asynchronous motors.
Benefits of PSM include high efficiency, low cooling requirements, and high power density. However, it is costly to manufacture and requires rare earth materials. The Audi e-tron GT, Jaguar I-Pace, and Porsche Taycan are examples of Electric Vehicles that use this type of motor.
Electrically-excited synchronous motor
The Electrically-Excited Synchronous Motor (ESM) operates similarly to a PSM but necessitates fewer rare earth materials in its production. The rotor is excited by an electrical current from the primary battery instead of by the stator or magnets.
Instead of magnets, the ESM employs metal brushes to transport electricity from the commutator – an electric switch on the rotor that regularly reverses the direction of the incoming current – to the rotor’s electromagnetic windings, as stated by MotorTrend. This creates a magnetic field in the rotor that matches that of the stator’s rotations.
Benefits of ESM include high efficiency, lower production cost than PSMs, and minimal need for rare earth materials. However, its long-term reliability is not optimal. This type of motor is used in BMW‘s i4, iX3, and iX Electric Vehicles.
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