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, but the magnetic steel and the carbon brush do not rotate. The alternating change of the current direction of the coil is accomplished by the commutator and brush that rotates with the motor.
In a brushed motor, the 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 columns (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 ring cylinder to energize a group of coils.
As the motor rotates, different coils or different two poles of the same coil are energized at different times, so that the N-S poles of the magnetic field generated by the coils and the N-S poles of the closest permanent magnet stator have a suitable angle difference. Repel each other, generate force, and push the motor to rotate. The carbon electrode slides on the coil terminal like a brush on the surface of the object, so it is called a carbon “brush”.
Sliding with each other will rub the carbon brushes and cause loss, and the carbon brushes need to be replaced regularly; the on-off between the carbon brushes and the coil terminals will alternate, sparks will occur, electromagnetic breakage will occur, and electronic equipment will be interfered.
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 magnetic pole 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 time to ensure that the magnetic force in the correct direction is generated 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, such as adjusting the power switching angle, braking the motor, making the motor reverse, locking the motor, and using the brake signal to stop the power supply to the motor. Now the electronic alarm lock of the battery car makes full use of these functions.
A brushless DC motor consists of a motor body and a driver, and is a typical mechatronic product. Because the brushless DC motor runs in a self-controlled manner, it will not add a starting winding to the rotor like a synchronous motor with heavy-load starting under variable frequency speed regulation, nor will it cause oscillation and loss of step when the load changes abruptly.
Three, the difference of speed regulation
In fact, the control of the two motors is voltage regulation, but because the brushless DC adopts electronic commutation, it can only be realized with digital control, while the brushed DC is commutated through carbon brushes, using thyristors, etc. Traditional analog circuits can be controlled, which is relatively simple.
1. The speed regulation process of the brushed motor is to adjust the voltage of the motor power supply. The adjusted voltage and current are converted through the commutator and the brush to change the strength of the magnetic field generated by the electrodes to achieve the purpose of changing the rotational speed. This process is called variable speed regulation.
2. The speed regulation process of the brushless motor is that the voltage of the power supply of the motor remains unchanged, the control signal of the ESC 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 variable frequency speed regulation.