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2021

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11

The difference between brushed motor and brushless motor

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1. The principle of brushed motor

The brushed motor adopts mechanical commutation, the magnetic pole does not move, and the coil rotates. When the motor is working, the coil and the commutator rotate, the magnetic steel and the carbon brush do not rotate, and the alternating change of the direction of the coil current is completed by the commutator and the brush that rotate with the motor.

In a brushed motor, this process is to arrange the two power input ends of each group of coils into a ring in turn, and separate them with insulating materials to form a cylinder-like thing, which is integrated with the motor shaft. Through two small pillars (carbon brushes) made of carbon elements, under the action of spring pressure, from two specific fixed positions, press the two points on the upper coil power input annular cylinder to energize a group of coils.

As the motor rotates, different coils or different poles of the same coil are energized at different times, so that the NS poles of the magnetic field generated by the coils are close to the NS poles of the permanent magnet stator. , to generate power to push the motor to rotate. The carbon electrode slides on the coil terminal, like a brush brushing on the surface of an object, so it is called a carbon "brush".

Sliding against each other will rub the carbon brush, causing loss, and the carbon brush needs to be replaced regularly; the carbon brush and the coil terminal are alternately switched on and off, and electric sparks will occur, which will generate electromagnetic damage and interfere with electronic equipment.

2. Working principle of brushless motor

The brushless motor adopts electronic commutation, the coil does not move, and the magnetic pole rotates. The brushless motor uses a set of electronic equipment to sense the position of the poles of the permanent magnet through the Hall element. According to this perception, the electronic circuit is used to switch the direction of the current in the coil in a timely manner to generate a magnetic force in the correct direction to drive the motor. Eliminates the disadvantages of brushed motors.

These circuits are the motor controllers. The controller of the brushless motor can also realize some functions that the brushed motor cannot realize, such as adjusting the switching angle of the power supply, braking the motor, causing the motor to reverse, locking the motor, and using the brake signal to stop power supply to the motor. Now the electronic alarm lock of the battery car makes full use of these functions.

The brushless DC motor consists of a motor body and a driver, and is a typical mechatronic product. Since the brushless DC motor operates in a self-controlled manner, it does not add an additional starting winding to the rotor like a synchronous motor with heavy load under variable frequency speed regulation, nor does it cause oscillation and out of step when the load changes suddenly.

Three, the difference in speed regulation

In fact, the control of the two motors is voltage regulation, but because the brushless DC uses electronic commutation, it can only be realized with digital control, while the brushed DC is commutated through carbon brushes, using silicon controlled rectifiers, etc. Traditional analog circuits can be controlled and are relatively simple.

1、有刷马达调速过程是调整马达供电电源电压的高低。调整后的电压电流通过整流子及电刷地转换,改变电极产生的磁场强弱,达到改变转速的目的。这一过程被称之为变压调速。

2、无刷马达调速过程是马达的供电电源的电压不变,改变电调的控制信号,通过微处理器再改变大功率MOS管的开关速率,来实现转速的改变。这一过程被称之为变频调速。

四、性能差异

1、有刷电机结构简单、开发时间久、技术成熟

早在十九纪诞生电机的时候,产生的实用性电机就是无刷形式,即交流鼠笼式异步电动机,这种电动机在交流电产生以后得到了广泛的应用。但是,异步电动机有许多无法克服的缺陷,以致电机技术发展缓慢。尤其是直流无刷电机一直无法投入商业运营,伴随着电子技术的日新月异,直至近几年才慢慢投入商业运营,就其实质来说依然属于交流电机范畴。

无刷电机诞生不久,人们就发明了直流有刷电机。由于直流有刷电机机构简单,生产加工容易,维修方便,容易控制;直流电机还具有响应快速、较大的起动转矩、从空转速至额定转速具备可提供额定转矩的性能,所以一经问世就得到了广泛应用。

2、直流有刷电机响应速度快,起动扭矩大

直流有刷电机起动响应速度快,起动扭矩大,变速平稳,速度从空到几乎感觉不到振动,起动时可带动更大的负荷。无刷电机起动电阻大(感抗),所以功率因素小,起动扭矩相对较小,起动时有嗡嗡声,并伴随着强烈震动,起动时带动负荷较小。

3、直流有刷电机运行平稳,起、制动效果好

有刷电机是通过调压调速,所以起动和制动平稳,恒速运行时也平稳。无刷电机通常是数字变频控制,先将交流变成直流,直流再变成交流,通过频率变化控制转速,所以无刷电机在起动和制动时运行不平稳,振动大,只有在速度恒定时才会平稳。

4、直流有刷电机控制精度高

DC brushed motors are usually used together with gearboxes and encoders, so that the output power of the motor is greater, and the control accuracy is higher. The control accuracy can reach 0.01mm, and the moving parts can be stopped almost anywhere you want. All precision machine tools use DC motors to control precision. Because the brushless motor is not stable when starting and braking, the moving parts will stop at different positions every time, and it must be stopped at the desired position through positioning pins or stoppers.

5. DC brushed motor has low cost and easy maintenance. Due to the simple structure of the DC brush motor, low production cost, many manufacturers, and relatively mature technology, it is widely used, such as factories, processing machine tools, precision instruments, etc. If the motor fails, you only need to replace the carbon brush. Carbon brushes only cost a few dollars, very cheap. The brushless motor technology is immature, the price is high, and the application range is limited. It should be mainly used in constant-speed equipment, such as inverter air conditioners and refrigerators. If the brushless motor is damaged, it can only be replaced.

6. Brushless, low interference

The brushless motor removes the brush, and the direct change is that there is no electric spark generated when the brushed motor is running, which greatly reduces the interference of electric sparks on remote control radio equipment.

7. Low noise and smooth operation

There are no brushes in the brushless motor, the friction force is greatly reduced during operation, the operation is smooth, and the noise will be much lower. This advantage is a huge support for the stability of the model operation.

8. Long life, low maintenance cost

Without the brush, the wear of the brushless motor is mainly on the bearing. From a mechanical point of view, the brushless motor is almost a maintenance-free motor. When necessary, only some dust removal maintenance is required.