What Is Brushless Dc Motor

 

A brushless DC motor (BLDC) is a typical mechatronic product that consists of a motor body and a driver. It is also called a "commutator less motor" because it has no brushes and no commutator (or collector ring).

 

The history of brushless motors dates back to the nineteenth century. At that time, American inventor Nikola Tesla invented the asynchronous motor in 1887. Although some refer to the asynchronous motor as "one of the predecessors of the brushless motor," the technological limitations of the time made the development of the motor a relatively slow process. It was not until the middle of the 19th century that a breakthrough in motor technology occurred with the invention and application of the transistor. Through the use of transistor commutation circuit instead of the traditional brush and commutator, electronically commutated DC motors were officially born. This new brushless motor not only overcomes the technical defects of asynchronous motor , but also greatly improves the efficiency and reliability.

 

Nowadays, brushless DC motor is widely used in the fields of power tools, household appliances and industrial automation due to its advantages of high efficiency, low maintenance and long life.

 

 

1. Modes of speed regulation

Brushless motor can replace the traditional brushed DC motor for speed regulation, and even replace the speed regulation system of inverter + inverter motor or asynchronous motor + reducer. It does not need additional speed change equipment and directly realizes efficient speed regulation.

 

2. Carbon brush and slip ring construction

Brushed motors use carbon brushes and slip rings to realize the transmission of electrical energy, and these parts will wear out with use, increasing maintenance work. Brushless motors, on the other hand, eliminate the carbon brushes and slip ring structure, eliminating the wear and tear of these components and improving the service life and reliability of the motor.

 

3. Low-speed, high-power operation

Brushless motors can achieve high power output at low speeds and can directly drive large loads without a speed reducer, reducing the complexity and size of mechanical equipment.

 

4. Volume and weight

Brushless motors are small and lightweight, yet have a very high power output, which gives them an advantage in portable and compact devices.

 

5. Torque characteristics

The brushless motor has excellent torque characteristics, especially at low and medium speeds. Its high starting torque and low starting current make it suitable for application scenarios that require frequent starting and stopping.

 

6. Speed regulation and overload capacity

Brushless motor has stepless speed regulation function, wide range of speed regulation, and has strong overload capacity, adapting to a variety of complex working conditions.

 

7. Starting and braking characteristics

Brushless motors with good soft-start and soft-stop characteristics can eliminate the need for traditional mechanical or electromagnetic braking devices, further simplifying the complexity of the system.

 

8. Efficiency and energy conservation

Brushless motors are highly efficient because there are no carbon brushes or excitation losses. At the same time, because brushless motors eliminate the need for multi-stage speed reduction, the combined power savings can be 20% to 60% or even higher.

 

9. Reliability and stability

Brushless motors are stable, easy to repair and maintain, adaptable, and perform well in a variety of harsh environments, such as bumpy and vibrating occasions.

 

10. Noise and lifetime

Brushless motors run quieter and smoother, with less vibration and noise, and have a longer service life than brushed motors because there are no carbon brushes to wear out.

 

11. Sparks and Explosivity

Brushed motors can generate sparks due to the contact of carbon brushes, whereas brushless motors do not have this problem and are particularly suitable for locations where explosion protection is required. In addition, brushless motors can be selected with either trapezoidal or sinusoidal magnetic fields as required to further optimize performance.

 

 

After understanding the basic concepts and advantages of brushless DC motor, we should also understand how it works. Unlike traditional brush motors, it uses an electronic control system to regulate current and commutation to drive the rotor. The following is an introduction to how a brushless DC motor works and its main components.

 

1. Electronic commutation systems

The central feature of a brushless DC motor is the absence of brushes and mechanical commutators found in conventional motors. Instead, there is an electronic commutation system, which is controlled by a PCB assembly. The system switches the direction of the current according to the position of the rotor, thus enabling continuous rotation of the rotor. The position of the rotor is usually monitored by means of Hall sensors or other position detectors, and the electronic controller continuously adjusts the winding current according to the sensor signals.

 

2. Stator-rotor interaction

The stator of a brushless DC motor is fixed and consists of a stator core and windings wound around it. When current passes through the windings, a rotating magnetic field is produced. This magnetic field generated by the stator interacts with the magnets (permanent magnets) in the rotor to drive the rotor.

 

Stator: The stator windings produce an electromagnetic field that rotates with the current, which is driven by an electronic commutation controller.

 

Rotor: The rotor consists of magnets and a rotor core. When the electromagnetic field of the stator changes, the permanent magnets on the rotor are subjected to attractive and repulsive forces and begin to rotate.

 

3. Key steps in operation

Starting: When current passes through the stator windings, the magnetic field generated by the stator windings interacts with the permanent magnets on the rotor, generating a torque that starts the rotor spinning. Brushless motors have high starting torque and relatively low starting current.

 

No-load operation: In the absence of an external load, the motor operates at a high efficiency and the electronic controller adjusts the current in the windings according to the sensor feedback to keep the rotor spinning steadily.

 

Running under load: When the motor is connected to a load, the rotor will generate more torque to overcome the load. The electronic commutator automatically adjusts the current according to the load changes, ensuring that the motor runs smoothly under different loads.

 

4. Torque characteristics and speed regulation

Brushless DC motors provide excellent torque characteristics, especially at low and medium speeds. Due to the stepless speed regulation function and wide speed range, the motor is able to maintain a stable torque output at different speeds. This feature makes BLDC motors suitable for a wide range of applications requiring high-precision control, such as industrial automation and power tools.

 

5. Advantages of electronic controls

The life and efficiency of BLDC motors are greatly improved due to the electronic commutation system that replaces the carbon brushes and commutator in conventional motors. There are no brushes to wear out in the motor, reducing maintenance requirements, as well as reducing noise and electromagnetic interference. In addition, the electronic controller enables soft starting and soft stopping, resulting in smoother operation of the motor and less impact on the mechanical structure.

 

 

In the manufacturing process of a brushless dc motor, the assembly of key components is the basis for ensuring the efficient operation of the motor. The following is a typical structure and manufacturing process of one of our (VSD) internal rotor brushless dc motors.

 

Introduction to the main components

1. front end cover 2. housing 3. windings 4. stator core

5. permanent magnets 6. rotor core 7. rear winding bobbins and front winding bobbins 8. pcb assemblies

9. front bearings and rear bearings 10. rear end cover 11. shafts 12. spacers and retaining rings

 

manufacturing process

Stator assembly assembly

First, the stator core is fixed in the housing, followed by winding the windings on the stator core and using front and rear winding bobbins to fix the windings to ensure that the coils are aligned neatly and are not affected by external vibration or friction. After the winding is completed, the PCB assembly is connected to provide support for current regulation and control of the motor.

 

Rotor assembly assembly

Permanent magnets are installed on the rotor core to ensure a tight fit. The rotor core is fixed to the shaft to ensure a precise gap between the permanent magnets and the stator windings to ensure the effective action of the magnetic field.

 

Assembly of bearings and other supports

Install the front and rear bearings on the front end cap and rear end cap to support the smooth rotation of the motor shaft. Also, install the spacers and snap rings in place to ensure that the bearings and other parts are secure and not loose.

 

Complete machine assembly

Assemble the case, stator, rotor, shaft and front and rear end caps together in sequence. Ensure that each part fits tightly, especially the gap between the stator and rotor should be precisely adjusted to ensure efficient operation of the motor.

 

Testing and Debugging

After the motor is assembled, the motor is tested for operation, including no-load test, load test and torque characteristic test, to ensure that the motor meets the design requirements and operates smoothly without any abnormality.

 

 

In order to ensure proper operation and stable performance of a well-made brushless DC motor, it is necessary to check the status of the motor periodically. The following are common methods for checking a brushless dc motor:

 

1. No-load testing

The no load test is to check the operation of a brushless DC motor when no external load is connected to ensure that the motor will start and run properly. The steps are as follows:

 

Test Steps:

Connect the motor to the drive power supply, keeping no external loads.

 

Gradually increase the input voltage and observe whether the motor can start smoothly.

 

Monitors the motor speed and operating current to ensure that the motor speed and current are in the normal range for the rated voltage.

 

Checkpoints:

Does the motor run smoothly over the entire voltage range.

 

Is there any abnormal noise or overheating during startup.

 

Whether the no-load current meets the technical requirements, if the no-load current is too large, it may indicate that there is a fault in the winding or circuit.

 

2. Load testing

The load test is to check the performance of the motor under load to ensure that it can meet the design requirements. The specific operations are as follows:

 

Test Steps:

Connect the motor to external loads such as drives, equipment or test rigs.

 

Run the motor under different load conditions and record the speed, torque and current of the motor.

 

Gradually increase the load and observe the response and stability of the motor under different loads.

 

Checkpoints:

Whether the motor is capable of continuous smooth operation at rated load.

 

Does the motor current and torque change as expected when the load is increased.

 

Check for abnormal vibration, overheating, or noise, and make sure the motor is not degrading under load.

 

3. Torque characteristic test

Torque Characterization Test is to evaluate the torque output of a brushless DC motor at different speeds to ensure that the motor is able to provide sufficient power during startup and operation.

 

Test Steps:

Use torque measurement equipment to monitor the motor's torque output at different speeds and loads.

 

Test the starting torque of the motor to ensure that there is sufficient torque with a low starting current.

 

Test the torque characteristics of the motor at low and medium speed operation to check whether the design requirements are met.

 

Checkpoints:

Whether there is enough starting torque during startup to ensure that the equipment can be started smoothly.

 

Whether the torque remains stable at low and medium speeds, and whether it is suitable for the operating conditions of the motor for a long period of time.

 

Whether or not an unstable torque output occurs during the test may be related to a winding or control circuit failure.

 

Through the above three tests, you can basically get a comprehensive understanding of the performance of brushless DC motor to ensure that it can work stably and reliably under different operating conditions. Regular inspections help to time the discovery of potential problems and prolong the service life of the motor.