Under normal circumstances, the rotor pole of the brushless DC motor is made of tile-type magnetic steel, the air gap magnetic density of the trapezoidal wave can be obtained through the magnetic circuit design. The stator windings are mostly concentrated integral distance windings, so the induced back electromotive force is also trapezoidal wave. The control of brushless DC motor needs position information feedback, must have position sensor use sensorless estimation technology to form a self-controlled speed regulation system. When controlling, the current of each phase is also controlled as far as possible, the output voltage of the inverter can be controlled according to the PWM method of the brushed DC motor.

In essence, the brushless DC motor is also a permanent magnet synchronous motor, the speed regulation actually belongs to the scope of variable voltage frequency regulation.

Generally, the permanent magnet synchronous motor has a stator three-phase distribution winding a permanent magnet rotor, which ensures that the induced electromotive force waveform is sine in the magnetic circuit structure winding distribution, the external stator voltage current should also be sine waves, which are generally provided by AC transformer. Permanent magnet synchronous motor control system often adopts automatic control, but also needs position feedback information, can use vector control (magnetic field orientation control) direct torque control advanced control strategy.

The difference between the two can be considered to be the difference in design concept caused by square wave sine wave control.