How does an electric motor work?

3 min read

An electric motor converts electrical energy into mechanical rotational motion [1]. In doing so, it utilizes the force of magnetism, which is created when electrical current flows through coils, thereby generating magnetic fields [2].

Structure and Basic Principle

At its core, an electric motor consists of two main parts: a stationary stator and a rotatable rotor [1]. Either permanent magnets or current-carrying coils that act as electromagnets are located in the stator or the rotor [1].

When current flows through the coils, they generate magnetic fields. These fields interact with each other: like poles repel each other, unlike poles attract [3]. These forces of attraction and repulsion set the rotor in motion. To prevent the rotation from stopping after half a turn, the direction of the current in the coils is regularly reversed [3].

Magnetic Fields and Lorentz Force

The physical basis of the movement is the Lorentz force: it acts on moving electrical charges, i.e., on the current in the conductors when it is located within a magnetic field [2]. The interaction between the current and the magnetic field creates a torque that drives the rotor [1].

DC and AC Motors

Direct current motors (DC) are operated with direct current. The reversal of the current in the rotor occurs mechanically via carbon brushes and a commutator [4]. This makes them easy to regulate, but also prone to wear.

Three-phase motors (AC) use alternating current, usually three-phase alternating current. The alternating current generates a rotating magnetic field in the stator, which pulls the rotor along [5]. Asynchronous AC motors do not require mechanical contacts for power supply in the rotor – the current is generated through induction. This makes them particularly robust and low-maintenance.

Brushless Motors (BLDC)

A brushless direct current motor (BLDC) does away with brushes and the commutator. Instead, the current-carrying coils are located in the fixed stator, while the rotor consists of permanent magnets. External electronics precisely control the current to the coils, creating a rotating magnetic field that pulls the rotor along.

This design is more efficient because there are no friction losses from brushes, heat can be dissipated better via the stator, and electronic control keeps the motor at its optimal operating point at all times.

Why are electric cars so efficient?

Electric cars benefit from several advantages of the electric drivetrain. Modern electric motors convert approximately 90 to 95 percent of electrical energy into motion [5]. Furthermore, they enable recuperation: during braking, the motor becomes a generator and converts kinetic energy back into electrical energy, which is stored in the battery.

When stationary, the electric motor can be switched off completely, without idling losses. The simpler drivetrain with fewer moving parts reduces additional friction losses. Together with precise power electronics and optimized thermal management, this results in a very high overall efficiency.

Which materials are used?

Various materials are required for electric motors. The windings mostly consist of copper because of its excellent conductivity. The iron cores made of electrical steel minimize magnetic losses.

Particularly powerful motors, such as permanent magnet synchronous motors, use magnets based on neodymium-iron-boron. Rare earths such as neodymium, praseodymium, dysprosium, and terbium are used to enable strong magnetic fields at high temperatures. The housing is often made of aluminum for good heat dissipation.

However, motor types without rare earths are increasingly being developed, such as asynchronous motors or synchronous reluctance motors, in order to reduce the dependency on critical raw materials.

Summary

An electric motor converts electricity into motion by flowing current through coils, generating magnetic fields, and using the Lorentz force to set a rotor in rotation. Depending on the design, DC, AC, and brushless motors differ primarily in the type of power supply and control. Thanks to high efficiencies, recuperation, and fewer moving parts, electric drives are an increasingly important technology, particularly in the automotive sector.