What are the differences between DC brushless motors and permanent magnet synchronous motors?

Many friends on the Internet often ask: DC brushless motor and permanent magnet synchronous motor what is the difference? In fact, strictly speaking, DC brushless motor is also a kind of permanent magnet synchronous motor, how to say it, let’s take a look!

Generally speaking, the physical structure of brushless DC motors and permanent magnet synchronous motors is similar, the rotor is a permanent magnet and the stator is a winding. Brushless DC motors are trapezoidal wave air gap magnetic density and phase current is trapezoidal wave.

Brushless DC motor control requires rotor position information, which is generally obtained by installing a position sensor or using a position sensorless algorithm to obtain rotor position information and phase change accordingly to achieve the rotation of the motor.

Brushless DC drives use PWM speed control to achieve motor speed regulation.

PM synchronous motors are sinusoidal wave air-gap magnetically dense, BEMF, with a series of phase currents. Permanent magnet synchronous motor control also requires rotor position information, which generally requires the installation of position sensors. In recent years, position-free control methods have made great strides and are moving toward practicality. Permanent magnet synchronous motor drive must ensure that the phase voltage, phase current is a sinusoidal wave, generally using vector control.

To sum up, the trapezoidal wave mode of DC brushless motor is characterized by high torque and low cost, but high noise and high torque pulsation. The sine wave mode of permanent magnet synchronous motor has smaller torque and higher cost, but low noise and low torque pulsation. Therefore, in general, the permanent magnet synchronous motor mode of servo motor is better than brushless DC motor, while the brushless DC motor mode of power motor is better than permanent magnet synchronous motor.

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