brushless dc motor has the following characteristics: 1, external characteristic of brushless dc motor is good, can under the low speed high torque output, makes it can provide large starting torque; 2, wide range of brushless dc motor speed, any speed can run at full power. 3, the brushless dc motor with high efficiency, strong overload capacity, makes it have excellent performance in drag system; 4, the brushless dc motor regenerative braking effect is good, because of its rotor is permanent magnetic material, brake motor can enter the generator state; 5, brushless dc motor of small size, high power density. 6, brushless dc motor without mechanical commutator, adopts fully enclosed structure, can prevent dust from entering the motor internal, high reliability; 7 than asynchronous motor, brushless dc motor drive control is simple. Working principle of the brushless dc motor, brushless dc motor stator is armature coil winding and the rotor is a permanent magnet. If only to motor with fixed dc current, the motor can only produce the constant magnetic field, the motor can't turn, only real-time detecting the rotor position, according to the position of the rotor to the motors of different mutually to corresponding current, make the rotating magnetic field of the stator produce uniform direction changes, motor can follow magnetic field rotation.