Brushless Motors -- Definition, Principle, and Advantages

Brushless motors are?a type?of?direct current?(DC)?motor that uses?electronic commutation to replace the mechanical commutator and brushes?found in traditional brushed motors, resulting in higher efficiency and reliability.?

Classifications of Brushless Motors

Brushless motors?are categorized?in various ways based on their structure design, phase number, drive methods, cooling methods, and whether they incorporate sensors.

1.?They?can be divided into internal and external rotor brushless motors?according to?the?motor’s?structure.

A.?Internal rotor brushless motor: The permanent magnet is sited inside the motor and fixed on the rotor, and the stator winding?is fixed?on the casing. The structure has small motor inertia, good?starting,?and braking performance, and is suitable for applications that require a quick response, such as drones, power tools,?and so on.

B.?External rotor brushless motor: The permanent magnet is located outside the motor and fixed to the housing surrounded by the stator winding, and the rotor?is located?inside the motor. The external rotor motor has?a large?torque to inertia ratio and good low-speed stability and is suitable for wind turbines, electric bicycles, washing machines, and other applications that require high torque output.

2.?They?can be divided into three-phase brushless?motors?and multi-phase brushless motors, according to phase?number.

A.?Three-phase brushless motor: It?is the most common type, with the stator winding divided into three phases.?An electronic commutation?device sequentially energizes each phase winding to form a rotating magnetic field that drives the rotor. Three-phase brushless motors operate smoothly, are highly efficient, and?are widely used?in various industrial equipment and consumer?electronic products.

B.?Multi-phase brushless motor:?In addition to?the common three-phase type, there are also brushless motors with four, five, or even more phases. Multi-phase motors typically have higher torque density, smoother operation characteristics, and?greater?reliability. They are suitable for applications that require precise control and high dynamic performance demands, such as aerospace and robotics.

3.?They can be divided into square wave brushless motors?and?sinusoidal wave brushless motors, according to the drive methods.

A.?Square wave brushless motor: The controller produces a rotary magnetic field through?change conditions of any phase winding?easily.?The square wave brushless motor is easy to control?and?cost-effective. It is suitable for applications?that do not?require?high?precision and economical requirements.

B.?Sinusoidal wave brushless motor: The controller adjusts any phase winding,?makes it change?according to a sinusoidal waveform, and?forms a smooth magnetic field. The sinusoidal wave drive operates more smoothly, with?lower noise, and has higher efficiency. It is suitable for high-drive performance requirements applications, such as High-end household appliances, precision instruments,?and so on.

4.?They?can be divided into natural cooling brushless motor, forced air-cooled brushless motor, and liquid-cooled brushless motor, according to the cooling methods.

A.?Natural cooling brushless motor: It depends on the natural convection between the surface of the motor and the surrounding air for heat dissipation. It is suitable for occasions with low power and?suitable?working environment temperature.

B.?Forced air-cooled brushless motor: It?is equipped with built-in fans or uses?external fans to force air over the motor for enhanced cooling.?The method is suitable for applications with higher power demands, long operating duration, or in environments?where the temperature is on the higher side.

C.?Liquid-cooled brushless motor: It?utilizes a liquid cooling system that circulates a coolant through the?motor?for effective heat dissipation.?The method is ideal for high-power-density applications, where high operating temperatures are?common, or in scenarios with stringent temperature control requirements, such as?in?electric vehicle drive motors.

5.?They?can be divided into sensorless brushless motor and sensored brushless motor, according to the encoder type.

A.?Sensorless brushless motor: It does not use hall sensors or encoders. Instead, it estimates the rotor position through software algorithms (such as the back EMF method, model predictive control,?and so on), simplifying the motor structure and reducing costs. It is suitable for applications that are sensitive to?cost, have space constraints, or do not require high initial positioning accuracy of the motor;

B.?Sensored brushless motor: It utilizes position sensors such as hall sensors or optical encoders to accurately detect the?rotor’s?position, providing precise motor control.?It is suitable for?applications that demand?high control precision and dynamic performance, such as servo systems and drones.

The principles of brushless motors

Brushless motors?are primarily composed of?three parts: the stator, the rotor, and the electronic commutation device (commonly known as the brushless motor controller).

1.?Stator: It contains a set of winding coils,?typically connected in a three-phase star or delta configuration, evenly distributed along the inner wall of the motor housing to form a fixed magnetic field.

2.?Rotor:?It?is built?with permanent magnets (such as neodymium-iron-boron magnetic steel), with the magnetic field direction fixed relative to the stator windings. The rotor rotates along with the motor shaft.

3.?Electronic Commutation Device:?Also known as the brushless motor controller, it detects the?rotor's?position through Hall sensors (or sensorless algorithms) and switches the current direction in the stator?windings?promptly?according to the position information.?This?maintains a state of mutual attraction between the?rotor's?magnetic?field?and?the?stator's?magnetic?field, driving the rotor to rotate continuously.

The working process?is briefly described?as follows:

1.?Hall sensors (or sensorless algorithms) monitor the?rotor's?magnetic pole position in real-time;

2.?The controller applies the appropriate current to the stator windings in sequence based on the position signal, generating a magnetic field that attracts the?rotor's?magnetic field;

3.?The rotor rotates under the force of attraction. When the position of the?rotor's?magnetic poles changes, the controller adjusts the stator current accordingly to maintain the direction of the magnetic attraction, driving the rotor to rotate continuously.

Advantages of Brushless Motors

1.?Wear-Free and Long Life:?Without brushes and mechanical commutators, they avoid wear due to friction, enhancing the?motor's?lifespan and reliability.

2.?High Efficiency:?Brushless motors lack brush resistance loss, and their magnetic field control is more precise, typically offering higher efficiency than brushed motors.

3.?Low Maintenance:?There is no need for regular brush replacement, reducing maintenance costs and downtime.

4.?Good High-Speed Performance:?They can maintain high efficiency and torque at high speeds, suitable for high-speed applications.

5.?Flexible Control:?The electronic commutation allows for precise speed control, torque control, and a wide range of speed adjustments, suitable for applications requiring?precise?control.

6.?Low Noise:?The absence of mechanical commutator friction and sparking results in lower operating noise.

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Applications of Brushless Motors

Due to their excellent performance, brushless motors?are widely used?in various devices that require precise control, energy efficiency, low noise, long life, and high reliability, including but not limited to:

1.?Power Tools:?Such as drills, saws, sanders, and gardening tools, leveraging the high efficiency and high-speed characteristics of brushless motors.

2.?Home Appliances:?Such as air conditioners, refrigerators, washing machines, and vacuum?cleaners,?utilizing their energy-saving, low-noise, and long-life features.

3.?Drones and Model Aircraft:?The lightweight, high efficiency, and quick response of brushless motors make them particularly suitable for the power systems of aerial vehicles.

4.?New Energy Vehicles:?The drive motors of electric vehicles often use brushless motors to provide efficient and reliable propulsion.

5.?Industrial Automation:?Robots, CNC machines, pumps, fans, and other equipment, taking advantage of the precise control and high efficiency of brushless motors.

6.?Medical?Devices:?Such as blood pumps and ventilators, require motors to operate smoothly, accurately, and quietly.

7.??Aerospace:?Satellite attitude control, drones, aviation electronics, and other applications with?very?high demands for motor performance and reliability.

In summary, brushless motors, with their wear-free, high-efficiency, and flexible control advantages, are gradually replacing brushed motors in many fields and have become an important direction for the development of modern motor technology.