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Talking about the Characteristics and Principle of Brushless DC Motor
- Mar 13, 2018 -

Also known as a brush motor, the series-excited motor has high torque output characteristics and is often used in power tools that do not require precise speed control, such as hand-held power drills, circular saws or bench saws, and woodworking angle saws. Sawing and so on. Mechanical commutators are used in construction to supply power to the motor rotor windings. Because contact-type mechanical structures are used to supply power to the motor rotor windings, the industry often refers to power supply contactors in commutators as “brushes.” Commonly used brushes are mostly made of graphite or copper foil.

Long-term brush friction with the rotor of the motor can cause considerable noise, vibration, electromagnetic interference (EMI), and arcing. At the same time, the worn conductive material powder can also flood the motor interior, causing some degree of electrical pollution. Therefore, no matter from the aspects of product safety, reliability, or maintenance cost, more in-depth considerations are needed. The motor speed and torque control are also more complex, generally require the use of an external angle encoder or speed generator to detect the motor running data. In addition, since the rotating windings cannot be installed with temperature protection switches or thermal fuses, it is necessary to rely on insulation materials (for example, shafts, trunking, commutator, etc.) to test various parts to evaluate whether there is a danger of electric shock and fire.

Application and Principle of Brushless DC Motor

Brushless DC motors (BLDCs) use an electronic commutation circuit to supply DC power to the rotor windings of motors. Because there are no mechanical brushes, they are called brushless DC motors. Because brushless DC motors have features such as high efficiency and precise control performance, and the ability to use electronic packaging to meet safety requirements, they are now widely used in the field of refrigeration and air conditioning under the global demand for energy conservation and carbon reduction. Common DC frequency conversion, brushless DC and other technologies, it can also be used in hybrid vehicles and some high economic value appliances such as fans and other products.

At present, the most common electronic driving method is to use a Hall effect component or back EMF to detect the mechanical angle of the motor rotor winding and the motor angle, and then accurately control the MOSFET switch to achieve continuous operation of the motor.

Taking the Hall element as an example, the Hall effect satisfies the following relationship:

Where VH is the Hall voltage, IH is the Hall current, KH/d is the Hall component electromagnetic coefficient, K is the Hall component imbalance coefficient, and B is the magnetic flux density. From the relational equation, it can be understood that the Hall voltage is proportional to the magnetic flux density (that is, the magnetic field strength at which the motor operates) and the Hall current. Therefore, when the magnetic axis of the rotor is different from that of the Hall element, the magnetic flux is small. In order to maintain a fixed Hall voltage, the Hall current must be increased so that the turn-on sequence and time of the rotor of the motor can be accurately calculated.

Brushless DC Motor Features

Hall element type brushless DC motor utilizes the Hall element to sense the excitation sequence and time. When the phase of the rotor is π/2, the stator can be turned on, thereby reducing the unnecessary waste of electric energy, and at the same time providing timely. The electromagnetic force required for the rotation of the rotor significantly increases the output torque and efficiency of the motor, which is also the greatest advantage that all brushless DC motors can provide.

In the brushless DC motor hardware, replacing the mechanical commutator and brush with an electronic circuit does not cause electrical pollution. At the same time, for the electrical signals captured by the electronic circuit, other logic circuits can also be used to amplify and compare the signals, so that the motor operation efficiency can be improved.

What is more important is that the problem that could not be solved by using an additional hardware protection device to protect the motor can be solved. The microprocessor and the software can be used on the brushless DC motor to determine the electrical signal captured by the electronic circuit and reach the motor. Blockage, underphase, overload, and other management and protection related to security functions.

In contrast, for the brushless DC motor that provides electronic protection function, since a large number of electronic devices are used to extract and process electrical signals, electromagnetic compatibility evaluation must be accepted; as for the reliability of the software, relevant risks should be taken into consideration, and Software must be managed and protected and must also be evaluated.

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