Brushless DC Motor (BLDC) is a type of motor commonly used for high efficiency and precision control. Unlike conventional brushed DC motors, BLDC motors have no brush or commutator, resulting in higher reliability and longer service life. BLDC motors are widely used in computer hard drives, fans, drones, power tools, electric vehicles and other fields.

1. Basic structure of BLDC motor
    The main structure of the BLDC motor compared with the traditional brush DC motor, there are some significant differences, mainly including:
    Stator: The stator of a BLDC motor generally consists of multiple electromagnetic coils that generate a rotating magnetic field through an electric current. Unlike the rotor of a brush motor, the stator is fixed and does not move.
    Rotors: Rotors are generally made of permanent magnet materials (such as rare earth permanent magnets). The magnetic field of the rotor interacts with the stator and generates torque through external current control to drive the rotor to rotate. The polarity of the rotor changes according to the current switching of the stator coil.
    Electronic Commutator: Because there are no brushes or mechanical commutators, BLDC motors need to switch from electric current to electronic commutators, changing the polarity of the stator electromagnetic coil and thus controlling the rotor rotation. Hall sensors are usually used to detect the position of the rotor and achieve commutation.

2. Working principle of BLDC motor
    The working principle of BLDC motors is based on the law of electromagnetic induction. Through the electronic control system, the current is switched in the stator windings, creating a rotating magnetic field that drives the rotor to rotate.
    Commutation: In BLDC motors, commutation is done by an electronic controller (usually a PWM governor). The electronic controller controls the movement direction of the rotor by changing the direction of the current in the stator coil. The commutation process is real-time and is usually determined by detecting the rotor position with a Hall sensor or position encoder.
    Stator magnetic field: The stator's electromagnetic coil generates a rotating magnetic field. The electronic controller adjusts the current according to the position and speed of the rotor, ensuring that the rotation of the magnetic field always corresponds to the rotor polarity, so that the rotor is constantly rotating.
    Hall sensors: Hall sensors are used to detect the position of the rotor and feed the position back to an electronic controller to control the switching of current. Common BLDC motors use three Hall sensors that each detect the current in the stator windings, providing real-time data on the rotor position.

3. Advantages of BLDC motor
    Compared to brushed DC motors, BLDC motors have the following major advantages:
    High efficiency and high power density: Since there is no friction from brushes and commutators, the efficiency of BLDC motors is generally higher, especially at high speeds. Lower energy loss and higher output power density.
    Long service life: There are no brushes, so mechanical wear is reduced, and the life of BLDC motors is generally long and maintenance costs are low.
    Low noise: The BLDC motor runs without brush friction, so the running noise is low, suitable for applications requiring low noise.
    Precision control: BLDC motors achieve speed and position control through electronically controlled commutators for high-precision and complex applications.
     High reliability: there is no brush and commutator, so the failure rate is low and the reliability is high.

4. Disadvantages of BLDC motor
    Despite the many advantages of BLDC motors, there are some limitations:
    Higher cost: The manufacturing cost of BLDC motors is usually higher, especially requiring the use of high-quality permanent magnet materials (such as rare earth materials), as well as complex electronic controllers.
    Complex drive control: BLDC motors require a dedicated electronic controller (usually a PWM controller) to drive, which adds complexity to the system design.
    High power requirements: The electronic drive part of the BLDC motor requires a certain power supply, especially in high-power applications, which may require a strong power supply and cooling system.

5. Type of BLDC motor
    There are two main types of BLDC motors:
    Internal rotor (Inrunner) : The rotor of the internal rotor motor is located inside the motor, and the stator rotates around the rotor. Internal rotor motors typically have a higher speed and higher power density and are suitable for applications that require high-speed operation.
    Outer rotor (Outrunner) : The rotor of the outer rotor motor is located on the outside of the motor, and the stator is located on the inner ring of the motor. External rotor motors typically have larger torques and lower rotational speeds, making them suitable for applications where larger torques are required.

6. Application of BLDC motor
    BLDC motors are widely used in the following fields:
    Power tools: such as electric screwdrivers, electric drilling RIGS, etc., because BLDC motors have high efficiency and long life, they are very popular in power tools.
    Drones: BLDC motors become the power systems of drones because of their high efficiency, low noise and long service life.
    Electric vehicles (EVs) : In electric vehicles, BLDC motors are widely used in drive systems with higher power output and higher energy efficiency.
    Computer hard drives and fans: BLDC motors are commonly used in computer hard drives and cooling fans due to their ability to provide high precision control.
    Home appliances: such as air conditioners, washing machines, refrigerators, etc., BLDC motors can provide efficient power output and reduce energy consumption.
    Robots and automation equipment: BLDC motors are also widely used in robots and automation equipment with high precision control requirements.

7. BLDC motor control mode
    BLDC motor control methods usually have the following:
    Six-step commutation: Six-step commutation is a method of commutation based on sequence switching of the stator windings. It is suitable for applications where very little control is required and is often used for systems with low cost or simple control.
    Sinusoidal control: Sinusoidal control is a method of smoothing commutation by adjusting the current waveform. It provides smoother operation, reduces noise and vibration, and is commonly used in high-performance applications.
    Field-oriented control (FOC) : Vector control is a complex control method that realizes the control of motor speed and torque by controlling the direction and amplitude of stator current in real time. It is suitable for applications that require high control accuracy, such as robots and unmanned systems.

8. Drive circuit of BLDC motor
    Driving a BLDC motor requires a specialized drive circuit, which usually includes the following parts:
    Power supply: Provides the power required by the motor, generally DC power supply or through the DC-DC converter to provide a stable voltage.
    Motor controller: responsible for controlling the motor's commutation, speed, torque, etc. PWM (pulse width modulation) control technology is usually used to regulate the current.
    Hall sensor or encoder: Used to detect the position of the rotor and provide feedback signals to the controller to achieve reversing control.
    Power switching devices, such as MOSFETs or IGBTs, are responsible for controlling the on-off of the current to drive the motor.