Brushless DC motors do not use brushes. Brushless DC motors do not utilize commutators to regulate the current inside the coils, but instead use electronic commutators to pass the current, which produces an alternating current signal that causes the motor to drive.
A brushless DC motor works similarly to a brushed DC motor. The Lorentz force law states that as long as a current-carrying conductor is placed in a magnetic field, it experiences a force. Due to the reaction force, the magnets will experience equal and opposite forces.
When the current passes through the coil, a magnetic field will be generated. The magnetic field is driven by the magnetic poles of the stator. The same polarity repels each other and the opposite polarity attracts each other. If the direction of the current in the coil is continuously changed, the magnetic pole of the magnetic field induced by the rotor will It will also continue to change, so the rotor will continue to rotate under the action of the magnetic field.
In a BLDC motor, the current-carrying conductors (stator) are stationary while the permanent magnets (rotor) are moving.
When the stator coil gets power from the power source, it becomes an electromagnet and starts to generate a uniform magnetic field in the air gap. Although the power supply is DC, the switch still produces an AC voltage waveform with a trapezoidal shape. The rotor continues to rotate due to the interaction force between the electromagnetic stator and the permanent magnet rotor.
By switching the windings to high and low signals, the corresponding windings are excited to north and south poles. A permanent magnet rotor with south and north poles is aligned with the stator poles, causing the motor to rotate.
Brushless DC motors are available in three configurations: single-phase, two-phase and three-phase. Among them, three-phase BLDC is the most common one.
Driving method of brushless DC motor
The driving mode of the brushless direct motor can be divided into various driving modes according to different categories, and they each have their own characteristics.
According to the driving waveform: square wave driving, this driving method is convenient to realize, and it is easy to realize the control of the motor without position sensor;
Sinusoidal drive: This drive method can improve the operation effect of the motor and make the output torque uniform, but the implementation process is relatively complicated. At the same time, this method has SPWM and SVPWM (space vector PWM) two ways, the effect of SVPWM is better than SPWM.