The history of electric motors began with the discovery of electromagnetic phenomena in the early 19th century and gradually became one of the most important electronic systems of the industrial age. With technological advancements, engineers invented many types of electric motors, including direct current (DC) motors, induction motors, and synchronous motors.
As a type of permanent magnet synchronous motor (PMSM), brushless motors have a long history. However, in the early days, due to the difficulty of starting and changing speed, they were not widely used except in industrial applications with expensive control mechanisms. In recent years, however, with the improvement of powerful permanent magnets and the increasing awareness of energy conservation, brushless motors have developed rapidly in various fields.
The difference between brushed DC motors and brushless DC motors
Brushed DC motors (commonly referred to as DC motors) are the most commonly used type of motor due to their good controllability, high efficiency, and ease of miniaturization. Compared to brushed DC motors, brushless motors do not require brushes or commutators, resulting in a longer lifespan, easier maintenance, and lower operating noise. Furthermore, they not only possess the high controllability of DC motors but also offer greater structural freedom, making them easy to integrate into equipment. Thanks to these advantages, the applications of brushless motors have gradually expanded, and they are now widely used in industrial equipment, office automation equipment, and household appliances.
Figure 1. Structural differences between brushed DC motors and brushless motors
Brushless DC motors and permanent magnet synchronous motors (PMSMs) have essentially the same structure. However, brushless DC motors are both a family of motors (including PMSMs and stepper motors) and a distinct type of motor. As shown in the diagram below, they can be classified in various ways based on their rotation method.
Figure 2. Classification of DC brushless motors
Operating status of brushless motor
When a brushless motor is working, the permanent magnet is used as the rotor (rotating side), and the coil is used as the stator (fixed side). Then, the external inverter circuit controls the switching of current to the coil according to the rotation of the motor. The brushless motor works in conjunction with the inverter circuit that detects the rotor position and introduces current into the coil according to the rotor position.
There are three main methods for rotor position detection: one is current detection, which is a necessary condition for field-oriented control; the second is Hall sensor detection, which uses three Hall sensors to detect the rotor position through the rotor's magnetic field; and the third is induced voltage detection, which detects the rotor position by the change in induced voltage generated by the rotor's rotation, and is one of the position detection methods for sensorless motors.
Figure 3. Working process of a brushless DC motor
There are two basic control methods for brushless motors. In addition, there are some control methods that require complex calculations, such as vector control and weak field control.
Square wave drive
Based on the rotor's rotation angle, the switching states of the inverter circuit's power components are switched, and then the direction of the current in the stator coils is changed to make the rotor rotate.
Sine wave drive
The rotor is rotated by detecting its rotation angle, generating a 120-degree phase shift in the inverter circuit, which then changes the direction and magnitude of the current in the stator coils.
Figure 4 Brushless DC motor drive status
Brushless DC motors are currently widely used in various fields, including home appliances, automotive electronics, industrial equipment, office automation, robots, and portable consumer electronics. In the future, with the continuous advancement of motor technology, the application of brushless DC motors will have even broader development prospects.
