Introduction：Brushless DC motor is a typical mechatronics product, which is composed of motor body and driver. Brushless motor refers to the motor without brush and commutator (or collector ring), also known as commutator free motor. As early as the birth of the motor in the 19th century, the practical motor produced is a brushless form, that is, the AC squirrel cage asynchronous motor, which has been widely used. However, the asynchronous motor has many insurmountable defects, so that the development of motor technology is slow. The transistor was born in the middle of last century, so the brushless DC motor using transistor commutator circuit instead of brush and commutator came into being. This new brushless motor is called electronically commutated DC motor, which overcomes the shortcomings of the first generation of brushless motors.

BLDC motor The motor uses a permanent magnet as a rotor, and there is no coil in the rotor. Since there are no coils in the rotor, commutators and brushes for electrification are not required. Instead, the coil serves as the stator.   

The rotor of a BLDC motor is a permanent magnet that rotates by changing the direction of the magnetic field generated by the surrounding coil. The rotation of the rotor is controlled by controlling the direction and magnitude of the current to the coil.

Brushless motor structure 

A single brushless motor is not a complete power system, brushless basically must be controlled by a brushless controller, that is, electrical regulation, in order to achieve continuous operation. The ordinary carbon brush motor rotates the winding, while the brushless motor rotates the magnet regardless of the external or internal rotor structure. Therefore, any motor is composed of a stator and a rotor. The stator of the brushless motor is a part of the rotating magnetic field, which can support the rotor to rotate. It is mainly composed of silicon steel sheet, enameled wire, bearing and supporting parts. The rotor is a magnet, rotating parts in the stator rotating magnetic field, mainly composed of rotating shaft, magnet, support parts. In addition, the number of magnetic poles composed of the stator and rotor also affects the speed and torque of the motor.

The front cover, middle cover and rear cover of a brushless motor are mainly integral structural components, which play a role in constructing the overall structure of the motor. However, the outer shell of an outer rotor brushless motor is also the magnetic circuit path of the magnet, so the outer shell must be made of magnetic conductive material. The outer shell of an inner rotor motor is only a structural component, so there is no restriction on the material. However, an inner rotor motor has one more rotor core than an outer rotor motor, and the function of this rotor core is also to serve as a magnetic circuit path.

Magnet: It is installed on the rotor and is an important component of a brushless motor. Most of the performance parameters of a brushless motor are related to the magnet, including power, speed, torque, etc.

Silicon steel sheet: It is an important component of a slotted brushless motor. Of course, a slotless brushless motor does not have silicon steel sheets, but currently the vast majority of brushless motors are slotted. Its main role in the entire system is to reduce magnetic resistance and participate in the magnetic circuit operation.

Shaft: It is the direct force-bearing part of the motor rotor, and the hardness of the shaft must be able to meet the requirements of high-speed rotation of the rotor.

Bearing: It ensures the smooth operation of the motor. Bearings can be divided into sliding bearings and rolling bearings, and rolling bearings can be further classified into ten categories such as deep groove ball bearings, needle roller bearings and angular contact bearings. Currently, most brushless motors use deep groove ball bearings.

Summary

In general, compared with traditional brushed motors and induction motors, brushless motors have excellent characteristics such as high speed/torque ratio, good dynamic performance, high efficiency, long life, low noise, wide speed range and easy manufacturing. Especially the power output per unit volume characteristic makes it suitable for applications where size and weight are sensitive. These excellent characteristics make BLDC widely used in industrial control, automotive industry, aerospace and other fields.