The stator has only one-phase main winding, and the rotor uses a squirrel-cage rotor. When a single-phase sinusoidal current passes through the stator winding, the motor generates an alternating magnetic field. The strength and direction of this magnetic field change sinusoidally with time. The azimuth is fixed, so this magnetic field is also called an alternating pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two or more rotating magnetic fields with the same speed and the opposite rotation direction guard. When the rotor is stationary, these two rotating magnetic fields Two equal torques are generated in the rotor in opposite directions, so that the resultant torque is zero, so the motor cannot rotate. When we use an external force to rotate the motor in a certain direction (such as clockwise), the cutting magnetic field lines between the single-phase AC motor rotor and the rotating magnetic field in the instantaneous rotation direction become smaller; the electromagnetic force between the rotor and the counterclockwise rotation direction becomes smaller. The torque will no longer be zero, and the rotor will rotate in the direction of the push, so that the single-phase AC motor can rotate automatically.