What is a brushless DC motor

Brushless DC motor

In this article we would like to give you a first insight into the subject of brushless DC motors. We show its structure and also explain how it works.

It's best to have a look at ours Video purely to understand the topic even better.

Brushless DC motor simply explained

A brushless DC motor, also known as a BLDC (Brushless Motor or Brushless DC) or EC (Electronical Commutated) motor, is less of a DC motor. It is more like a synchronous machine. The idea is to “commutate” the motor by means of an electrical circuit in such a way that we no longer need brushes. The rotor is therefore permanently excited and the stator consists of coils. The coils are controlled in such a way that a rotating excitation field (rotating magnetic field) is created.

The reason for the development of a torque is the force that arises as an interaction between two magnetic fields. The permanently excited rotor is thus pulled along by the excitation field.

Structure of the brushless DC motor

The excitation windings are usually connected to three phases, i.e. three power connections with different phase relationships. The excitation windings are each housed in the stator of the motor, offset by 120 degrees. A motor with three coils arranged in this way has a number of pole pairs of 1. If you were to insert three additional coils between the existing ones, the motor would have a number of pole pairs of 2, etc. In general, the structure is similar to that of a synchronous machine. Most motors have their rotor in the inside of the stator. They are known as inner runners. A brushless DC motor can also have its rotor on the outside. This is called an external runner.

Brushless DC motor commutation

Although the structure is the same as that of a synchronous motor, a brushless DC motor can also be operated with direct current. The commutation, i.e. the energization and reversal of the current direction, then takes place via control electronics. This switches the coils on and off one after the other. The voltage of the individual phases is therefore a type of pulsating DC voltage.

One coil is always off, while two others are on. So that the motor control knows where the rotor is, three Hall sensors are distributed around the circumference. A circuit consisting of three half bridges is used to switch the coils on and off. The switches of the half bridges are often designed either as MOS-FETs or IGBTs.