Detailed explanation of BLDC

There are mainly two kinds of DC motor: DC brush motor and BLDCM.

1. Brush DC motor

DC motor is famous for its good starting performance, speed regulation performance and other advantages. Among them, the brush DC motor, which belongs to DC motor, adopts mechanical commutator, which makes the driving method simple. Its model diagram is shown in Figure 1.2.

The motor is mainly composed of permanent magnet stator, rotor with coil winding (armature), commutator and brush. As long as a certain DC current is applied at both ends of a and B of the brush, the motor commutator will automatically change the magnetic field direction of the motor rotor, so that the DC motor rotor will continue to operate.

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It can be seen that commutator and brush play an important role in DC motor. Although it can simplify the structure of motor controller, it has its own disadvantages:

Z structure is relatively complex, which increases the manufacturing cost;

Z is easy to be affected by the environment (such as dust, etc.), reducing the reliability of the work;

Z-commutation will produce sparks, limiting the scope of use;

Z easy to damage, increased maintenance costs, etc.

2. BLDCM

The birth of BLDCM overcomes the inborn defect of BLDCM and replaces mechanical commutator with electronic commutator. Therefore, BLDCM not only has the good speed regulation performance of DC motor, but also has the advantages of simple structure, no commutation spark, reliable operation and easy maintenance.

Figure 1.3 shows the model of BLDCM, which is transformed from Figure 1.2. It is mainly composed of a rotor made of permanent magnet material, a stator with coil winding and a position sensor. It can be seen that it has a lot in common with DC motor. The structure of stator and rotor is similar (the original stator becomes rotor, the rotor becomes stator), and the wiring of winding is basically the same. However, there is an obvious difference between them in structure: there is no commutator and brush in BLDCM, instead, position sensor is used. In this way, the structure of the motor is relatively simple, reducing the manufacturing and maintenance costs of the motor, but the BLDCM can not automatically change direction (phase), the cost of sacrifice is the increase of the cost of the motor controller (such as the same three-phase DC motor, the drive bridge of the BLDCM needs 4 power tubes, and the drive bridge of the BLDCM needs 6 power tubes).

Figure 1.3 shows one kind of small power three-phase, star connected, single pair of pole to pole BLDCM, its stator is inside, the rotor is outside, and its structure is very similar to that shown in Figure 1.2. The structure of another kind of BLDCM is just the opposite of this kind. Its stator is outside and the rotor is inside. That is to say, the stator is the frame composed of coil winding, while the rotor is made of permanent magnet material.

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The BLDCM has the following characteristics:

Z-bldcm has good external characteristics and can output large torque at low speed, so it can provide large starting torque;

Z the speed range of BLDCM is wide, and it can run at full power at any speed;

Z-bldcm has high efficiency and strong overload ability, which makes it perform well in the drive system;

The regenerative braking effect of z-bldcm is good, because its rotor is made of permanent magnet, the motor can enter into the generator when braking

Motor status;

Z-bldcm has small volume and high power density;

Z no mechanical commutator for BLDCM, fully enclosed structure, which can prevent dust from entering the motor, reliable

High sex;

The drive control of z-bldcm is simpler than that of asynchronous motor.

1.2.2 working principle of BLDCM

The stator of the BLDCM is the armature of the coil winding, and the rotor is the permanent magnet. If only a fixed DC current is applied to the motor, the motor can only generate a constant magnetic field, and the motor can not rotate. Only the position of the motor rotor is detected in real time, and then the corresponding current is applied to the motor according to the position of the rotor, so that the stator can generate a rotating magnetic field with uniform direction change, the motor can rotate with the magnetic field.

As shown in Figure 1.4 is the schematic diagram of the rotating principle of the BLDCM. For the convenience of description, the central tap of the stator coil of the motor is connected to the power supply of the motor, the end points of each phase are connected to the power tube, when the position sensor is connected, the G pole of the power tube is connected to 12V, the power tube is connected, and the corresponding phase coil is powered on. As the three position sensors turn with the rotor, they will turn on in turn, making the corresponding phase coil turn on in turn, so that the direction of the magnetic field generated by the stator is constantly changing, and the motor rotor also turns with it. This is the basic principle of the rotation of the BLDCM - detecting the position of the rotor, and then electrifying each other in turn, so that the direction of the magnetic field generated by the stator is continuous and uniform Land change.

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In the following section, the driving principle of the position sensor of the BLDCM will be introduced.

For the convenience of understanding, the following contents of this document use these two symbols as the model introduction as shown in Figure 1.5. Figure a shows that the rotor and stator of the motor are on the same center point, and figure B is on different center points. It is for the convenience of explaining the internal magnetic field of the motor. See below for details.

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1.3 brushless DC