Brush motor and brushless motor principle, and differences

In such an advanced age of automation, there is one thing that cannot be separated from the motor.Today we're going to talk about how motors work.

A, brush motor working principle

Brush motor is the first kind of motor we contact, the introduction of the motor in the physics class in middle school is to show it as a model.

The main structure of brush-motor:

stator + rotor + brush, which generates torque through the rotating magnetic field and outputs kinetic energy.The brush is constantly in contact with the commutator to conduct electricity and change phase in rotation.

Brush motor USES mechanical commutation, magnetic pole does not move, coil rotation.

When the motor works, the coil and the commutator rotate, while the magnetic steel and carbon brush do not. The alternating change of coil current direction is accomplished by the commutator and the brush which rotate with the motor.

In a brush motor, this process is to group the two power input end of the coil, in turn, arranged in a ring, separated with insulating materials between each other, forming a anything like cylinder, become an organic whole repeatedly with the motor shaft, the power supply through the two small pillar made of carbon (carbon brush), under the action of spring pressure, from the two specific fixed position, the pressure on the power input, two points of circular cylindrical coil to coil of a set of electricity.

As the motor rotates, different coils or different poles of the same coil are energized at different times, so that there is a suitable Angle difference between the n-s pole of the coil generating magnetic field and the n-s pole of the nearest permanent magnet stator. Magnetic fields attract each other and repel each other, generating force and pushing the motor to rotate.The carbon electrode slides on the wire head like a brush on the surface of an object, hence the name "brush".

Sliding with each other will cause friction and loss of carbon brushes, which need to be replaced regularly.Alternating on and off between the carbon brush and the wire head of the coil can cause electric spark, electromagnetic break and interfere with electronic equipment.

B, brushless motor working principle

In a brushless motor, the commutation is performed by the control circuit in the controller (generally hall sensor + controller, and more advanced technology is magnetic encoder).

Brushless motor USES electronic commutator, coil does not move, magnetic pole rotates.

An electronic device is used to induce the position of the magnetic pole of permanent magnet through the hall element. According to this induction, an electronic circuit is used to switch the direction of coil current at the right time, so as to ensure the right direction of magnetic force is generated to drive the motor, eliminating the disadvantages of brush-motor.

The controller of the brushless motor can realize some functions that cannot be realized by the brushless motor, such as adjusting the power switching Angle, braking motor, making the motor reverse, locking the motor, and using the brake signal to stop the power supply to the motor.Now battery car electronic alarm lock, on the full use of these functions.

Brushless dc motor is a typical mechatronics product, which is composed of the motor body and the driver.Since brushless dc motor is operated in automatic control mode, it will not add a starting winding to the rotor like the synchronous motor with variable frequency speed regulation and heavy load start, and it will not cause oscillation and step out when the load changes.

C, brush motor and brushless motor speed difference

In fact, the control of brushless and brushless motor is through voltage regulation, but brushless dc USES electronic commutator, so digital control can be achieved, while brushless dc is through carbon brush commutator, using silicon controlled circuit.

1. The speed regulation process of brush motor is to adjust the voltage of the power supply of the motor.After adjustment, the voltage and current are converted by commutator and brush to change the strength of the magnetic field generated by the electrode to achieve the purpose of changing the speed.This process is known as pressure regulation.

2. The speed regulation process of brushless motor is that the voltage of the power supply of the motor remains unchanged, the control signal of the electrical adjustment is changed, and the switching rate of the high-power MOS tube is changed by the microprocessor to realize the change of the speed.This process is called frequency conversion.

D. Performance differences

1. Brush motor has simple structure and mature technology

Back in the 19th century, when the motor was born, the practical motor was the brushless form, namely the ac squirrel-cage asynchronous motor, which was widely used after the generation of alternating current.However, asynchronous motor has many insurmountable defects, so that the development of motor technology is slow.In particular, brushless dc motor has been unable to be put into commercial operation. With the rapid development of electronic technology, it has been slowly put into commercial operation until recent years. In essence, it still belongs to the category of ac motor.

Brushless motor was born not long ago, people invented the brushless dc motor.Because the dc brush motor mechanism is simple, easy to produce and process, easy to maintain, easy to control;Dc motor also has fast response, large starting torque, and can provide rated torque performance from zero speed to rated speed, so it has been widely used once it comes out.

2. The brushless dc motor has fast response speed and large starting torque

Dc brushless motor has fast starting response, large starting torque, stable speed change, almost no vibration is felt from zero to the maximum speed, and can drive larger load when starting.Brushless motor has a large starting resistance (inductive reactance), so the power factor is small, the starting torque is relatively small, the starting sound is buzzing, accompanied by strong vibration, and the driving load is small when starting.

3. The brushless dc motor runs smoothly and has good braking effect

The brushless motor is regulated by voltage regulation, so the starting and braking are stable, and the constant speed operation is also stable.Brushless motor is usually controlled by digital frequency conversion, which first changes the ac to dc, and then dc to ac, and controls the speed through frequency change. Therefore, the brushless motor does not run smoothly when starting and braking, with large vibration, and will only be stable when the speed is constant.

4, dc brush motor control precision is high

The brushless dc motor is usually used together with speed reducer and decoder, which makes the output power of the motor larger and the control precision higher. The control precision can reach 0.01 mm, and the moving parts can stop at almost any place they want.All precision machine tools are dc motor control accuracy.Since the brushless motor is not stable during starting and braking, the moving parts will stop at different positions each time, and the desired position can only be stopped by positioning pin or position limiter.

5, dc brush motor use cost is low, easy maintenance

Due to the simple structure of brushless dc motor, low production cost, many manufacturers, mature technology, so it is widely used, such as factories, processing machine tools, precision instruments, etc., if the motor failure, just replace the carbon brush, each carbon brush only need a few dollars, very cheap.Brushless motor technology is not mature, the price is higher, the application scope is limited, mainly should be in constant speed equipment, such as frequency conversion air conditioning, refrigerator, etc., brushless motor damage can only be replaced.

6, no brush, low interference

Brushless motors remove the brush, the most direct change is the absence of the brush motor running spark, thus greatly reducing the electrical spark interference to remote radio equipment.

7. Low noise and smooth operation

Without brushes, brushless motor will have much less friction during operation, smooth operation and much lower noise, which is a great support for the stability of model operation.

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Post time: Sep-10-2019
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