How does a DC brushless motor operate

With the rapid development of motor technology and the widespread adoption of various high-power electronic devices, this desire has gradually been realized. The structure of DC brushless motors has advantages such as reliable operation, simple structure, and easy maintenance. Due to its speed being no longer limited by mechanical commutation, if high-speed bearings are used, it can also operate at speeds of up to hundreds of thousands of revolutions per minute.

The main advantages of DC brushless motors are good speed regulation and starting characteristics, large locked rotor torque, and wide application in various driving devices and servo systems. However, DC brushless motors have brushes and commutators, and the sliding mechanical contact formed between them seriously affects the performance, accuracy, and reliability of the motor. The sparks generated can cause radio interference, shorten the lifespan of the motor, and the commutator brush device makes the structure of DC motors complex, difficult to maintain, and noisy. For a long time, people have been seeking DC motors that do not require brushes and commutator devices.

The overall structure of a brushless DC motor mainly includes a rotor, stator, and sensors. The rotor is composed of permanent magnets, which can be flat, disc-shaped, or cylindrical in shape. The stator is composed of a winding and an iron core, and the winding is composed of several turns of coils. There are several excitation poles distributed on the coils. The sensors are used to detect the speed and position of the rotor and provide feedback to the control system, so that the motor can work according to requirements. During the rotation of the rotor, the sensor continuously detects the position and speed of the rotor, and adjusts the energization of the stator winding through the control system to ensure that the motor operates as required.

When the number of rotor stages is fixed, changing the frequency of the stator's rotating magnetic field can change the rotor's speed. A DC brushless motor not only adds electronic control (driver) to the synchronous motor, controls the frequency of the stator's rotating magnetic field, and sends the motor rotor's speed back to the control center for repeated correction, in order to achieve a way close to the characteristics of a DC motor. In other words, a DC brushless motor can still control the motor rotor to maintain a certain speed when the load changes within the rated load range.

Brushless motors generally hope to use speed control that can stabilize at the set value without significant changes when the load changes. Therefore, the motor is equipped with a Hall sensor that can sense the magnetic field as a closed loop control for speed and also as a basis for phase sequence control. However, this is only used for speed control and cannot be used for positioning control.

The working principle of a DC motor is to use the magnetic field interaction between the rotor permanent magnet and the stator coil to generate torque. During the operation of the motor, the stator winding is energized with current to generate a rotating magnetic field. The permanent magnet on the rotor interacts with the stator magnetic field due to rotation, generating torque and causing the rotor to start rotating.