The history of motors began with the discovery of electromagnetic phenomena in the early 19th century, and gradually became one of the most important electronic systems in the industrial age. With the development of technology, engineers and technicians have invented many types of 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 its difficulty in starting and changing speed, it has not been widely used except for industrial applications with expensive control mechanisms. However, in recent years, with the improvement of powerful permanent magnets and the enhancement of people's energy-saving awareness, brushless motors have developed rapidly in various fields.
The difference between DC brushed motors and brushless motors
The DC brushed motor (usually referred to as the DC motor) has the characteristics of good controllability, high efficiency, and easy miniaturization. It is the most commonly used type of motor. Compared with the DC brushed motor, the brushless motor does not require brushes and commutators, so it has a long service life, is easy to maintain, and has low operating noise. In addition, it not only has the high controllability of the DC motor, but also has a high degree of structural freedom and is easy to embed in the equipment. Thanks to these advantages, the application of brushless motors has gradually expanded. At present, it has been widely used in industrial equipment, office automation equipment and household appliances.
Working conditions of brushless motors
When the brushless motor is working, the permanent magnet is first 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 the current to the coil according to the rotation of the motor. The brushless motor is used in conjunction with the inverter circuit that detects the rotor position and introduces the 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 magnetic field oriented control; the second is Hall sensor detection, which uses three Hall sensors to detect the rotor position through the magnetic field of the rotor; the third is induced voltage detection, which detects the rotor position through the induced voltage change generated by the rotation of the rotor, which is one of the position detection methods of the inductive 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
According to the rotation angle of the rotor, the switching state of the power element of the inverter circuit is switched, and then the current direction of the stator coil is changed to rotate the rotor.
Sine wave drive
The rotor is rotated by detecting the rotation angle of the rotor, generating a three-phase alternating current with a phase shift of 120 degrees in the inverter circuit, and then changing the current direction and size of the stator coil.
Brushless DC motors are currently widely used in various fields, including household 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 a broader development space.
