What Is BLDC Motor And Its Advantages

1.Concept of Brushless DC Motors

A Brushless DC motor (BLDC), also known as a brushless motor or a synchronous DC motor, is a type of motor that does not require brushes or commutators for operation. The input to a BLDC motor is direct current (DC), but essentially it simulates alternating current (AC) by cyclically switching the main inverter switches. This creates a changing magnetic field in the coil windings, allowing the motor rotor to experience continuous torque and thus continuous rotation. BLDC motors can be configured as single-phase, two-phase, or three-phase depending on the number of stator windings. The most commonly encountered BLDC motors are three-phase motors. The diagram below illustrates the disassembly of a three-phase brushless DC motor.

2.Application of Brushless DC Motors

It is estimated that the market size of BLDC motors will reach approximately $19.76 billion by 2022. With BLDC motor technology becoming increasingly mature, BLDC motors have found extensive applications in various fields including military, aerospace, industrial, automotive, civilian control systems, and household appliances. They are commonly used in low-voltage, low-power devices such as small robots, drones, electric bicycles, vacuum cleaners, and power tools.

Below are some popular applications:

Vacuum Cleaner/Hair Dryer: When it comes to hair dryers or vacuum cleaners, the well-known brand is Dyson. The Dyson hair dryer, promoted as "next-generation black technology," features the V9 intelligent digital motor, which is smaller, lighter, and faster than traditional motors.Without the use of carbon brushes, the motor can achieve a speed of up to 110,000 revolutions per minute, and it is smaller and lighter than other motors. The motor used in Dyson's digital motor is a "single-phase brushless DC motor," essentially a type of BLDC motor.

Drones/Gimbals:

The key to motor control in drones is speed and direction control. The most popular drones are undoubtedly those from DJI. The diagram below shows the disassembly of the Spark drone, with four BLDC motors visible at each corner.

Similar applications include gimbals.

Power Tools: Common handheld power tools found in daily life include Bosch's electric wrenches, drills, and others. The energy-saving and high efficiency of brushless DC motors, coupled with the continuous reduction in the cost of handheld power tools, have led to rapid development in the use of BLDC motors in power tools. The most well-known international manufacturers, such as Bosch, Dewalt, Milwaukee, and others, are leading this trend.

3.Brushless DC Motor Construction

Stator: The stator of a BLDC motor is composed of laminated steel sheets, with windings placed in slots carved along the internal circumferential axis. The stator is similar to that of an induction motor but with a different winding distribution. Most BLDC motors have three star-connected stator windings, each consisting of multiple coils interconnected. Coils are placed in the slots and interconnected to form windings. These windings are distributed along the circumference of the stator to create evenly spaced magnetic poles.

Rotor: BLDC motors use permanent magnets as the rotor, with no coils inside. The south and north magnetic poles of the rotor are alternately arranged. Additionally, with the advancement of soft magnetic material technology and the decrease in prices, high-performance neodymium iron boron rare earth materials are increasingly used to make permanent magnet rotors. Their high magnetic energy product and stable characteristics enable BLDC motors to have better mechanical properties and dynamic response, as well as higher efficiency and speed range. Here is a schematic diagram of the rotor magnet cross-section from a principle document on BLDC by Microchip:

Hall Sensors: The most crucial aspect of BLDC motor control is rotor position identification. There are two methods for position identification: one is to use position sensors to identify the rotor's position, known as Hall sensors; the other method is sensorless, which involves identifying the rotor's position by detecting back electromotive force. For BLDC motors with sensors, most BLDC motors embed three Hall sensors in the stator. During each commutation, one winding is connected to the positive pole of the control power supply (current enters the winding), the second winding is connected to the negative pole (current flows out of it), and the third winding is in a disconnected state. The torque is generated by the interaction between the magnetic field produced by the stator coils and the permanent magnet. When the rotor magnetic pole passes near the Hall sensor, the sensor will output a high or low level signal, indicating that the south/north magnetic pole is passing through the region sensed by the Hall sensor. The phase shift between the signals output by the Hall sensors can be either 60° or 120°.