The core of a brushless DC fan is a brushless DC motor (BLDC). Its working principle is that the electronic controller (driver) switches the stator winding current in an orderly manner according to the rotor position signal to generate a rotating magnetic field, which drives the permanent magnet rotor to rotate continuously, thereby driving the fan blades to rotate.
Basic Principles:
Energy Conversion and Magnetic Field Drive: Electrical energy is converted into electromagnetic energy through the stator windings, generating a magnetic field. This magnetic field interacts (attracts or repels) with the magnetic field of the permanent magnet on the rotor, generating torque, causing the rotor to rotate, and ultimately converting mechanical energy into the fan’s kinetic energy.
Electronic Commutation: Unlike traditional brushed motors that switch current via mechanical brushes and a commutator, brushless motors achieve commutation through an electronic controller. The controller precisely controls the power switching circuit (such as a three-phase full-bridge) based on the rotor magnetic pole position signal detected by a position sensor (such as a Hall sensor), sequentially switching the energizing state of different stator windings, thereby forming a continuously changing rotating magnetic field in the stator, driving the permanent magnet rotor to rotate synchronously and continuously.
Core Components Motor Body:
Stator (Stationary Part): Typically composed of silicon steel sheets and multi-phase (commonly three-phase) coil windings wound around them, responsible for generating the electromagnetic field.
Rotor (Rotating Part): Composed of permanent magnets (such as neodymium iron boron magnets), mounted on the shaft and connected to the fan blades, rotating under the influence of the magnetic field.
Driver (Controller): Composed of power electronic devices and integrated circuits, receiving start, stop, and speed control commands as well as position sensor signals, controlling the switching of the inverter bridge power transistors to generate a continuous rotating magnetic field and torque.
Position Sensor: Typically, a Hall effect sensor is installed inside the motor to detect the position of the rotor poles in real time, providing commutation timing signals to the controller.
Control and Speed Regulation Methods
Speed Control: The driver controls the speed and torque by adjusting the average current input to the motor. The most common method is Pulse Width Modulation (PWM) control. The controller outputs a PWM pulse signal with a fixed voltage but an adjustable duty cycle. By changing the duty cycle, the average voltage applied to the motor is adjusted, thus achieving smooth, stepless speed regulation.
Closed-loop control (optional): In high-performance applications, the controller can combine speed feedback signals (such as those from Hall sensors or encoders) and PID algorithms to dynamically adjust the PWM output, achieving more precise speed or position control.