"DC Fan" brushless DC motor is a synchronous motor, which means that the rotational speed of the rotor by the stator and the rotor speed of the rotating magnetic field of the poles (P) Effect: n = 60 * f / P. In the case of a fixed number of rotor poles, changing the frequency of the stator rotating magnetic field can change the speed of the rotor. Brushless DC motor is a synchronous motor that is coupled with electronic control (drive), to control the stator rotating magnetic field and the frequency of the motor rotor speed feedback to the control center repeatedly corrected in order to achieve close to DC characteristic way. That brushless DC motor in the rated load range can still be able to control when the load changes when the motor rotor to maintain a certain speed.