Basic knowledge of Brushless DC motor

1、 Basic concept of Brushless DC motor

Brushless DC motor is a new type of mechatronic motor with the development of transistor electronic technology. It is the product of the combination of modern electronic technology (including electronic power, microelectronics technology), control theory and motor technology.

Unlike ordinary brush DC motors, which use armature winding rotation for commutation, brushless motors use electronic commutation and magnetic steel rotation. Ordinary DC motors use carbon brushes for commutation. Carbon brush commutation has great shortcomings, mainly including 1. Sparks generated by mechanical commutation cause friction between commutator and brush, electromagnetic interference, high noise and short service life. 2. The structure is complex, the reliability is poor, and there are many faults, which require frequent maintenance. 3. The existence of commutator limits the further decline of rotor inertia and affects the dynamic performance.

The name of Brushless DC motor shows the characteristics of the motor: the motor performance is similar to that of DC motor, and the motor has no carbon brush. Brushless motor achieves continuous operation through electronic commutation.

The commutation mode of brushless motor is divided into square wave drive and sine wave drive. As for its position sensor and control circuit, square wave drive is relatively simple and cheap, so it is widely used. At present, the vast majority of brushless motors are driven by square wave. At present, all model motors in the market are driven by square wave.

2、 Technological advantages and disadvantages of brushless motor

Technological advantages of brushless motor:

1. Good controllability and wide speed regulation range.

2. High reliability, long service life and no regular maintenance.

3. High power factor, high efficiency and high power density.

Similarly, brushless DC motor also has certain technological disadvantages

1. The electronic controller is required to work, which increases the complexity and cost of science and technology and reduces the reliability.

2. The permanent magnet material of the rotor limits the use environment of the motor and is not suitable for high temperature environment.

3. There is obvious torque fluctuation, which limits the application of motor in high-performance servo system and low-speed ripple system.

3、 Basic parameters of brushless motor

Naming: the naming principle of outer rotor motor varies from manufacturer to manufacturer, including the diameter and height of motor stator and the diameter and height of motor. Our motors are named after the diameter and height of motor stator. For example, 2212 motor refers to the motor stator with a diameter of 22mm and a height of 12mm.

Stator diameter: diameter of silicon steel stator

Stator height (thickness): height of silicon steel sheet stator

Number of iron core poles (slots): number of slots of stator silicon steel sheet

Number of magnetic steel poles (number of poles): the number of magnetic steel on the rotor

Turns (T): the number of turns of enameled wire wound on the stator slot of the motor. Note that the conventional turns refer to the sum of the number of coils wound in two adjacent slots, that is, 8 turns in one slot and 8 turns in the other, that is, 16t.

Kv value: the higher the running speed of the motor, the higher the speed of the motor. Motor speed =kv value * working voltage.

No load current: the working current of the motor without any load under the specified voltage

Phase resistance: the resistance value between the two contacts after the motor is connected

Maximum continuous current: the maximum safe current for the operation of the motor

Maximum continuous power: the maximum safe power of the motor during operation power = voltage * current

Motor weight: weight of motor

Shaft diameter: diameter of rotating shaft