Single-phase AC motors are what we commonly call single-phase induction motors and can be divided into asynchronous AC motors and synchronous AC motors.
When a single-phase sinusoidal current passes through the stator winding, the motor generates an alternating magnetic field, the strength and direction of which varies sinusoidally from time to time, but is fixed in spatial orientation, so it is also called an alternating pulsating rotating field.
When the rotor is stationary, these two rotating magnetic fields produce two torques of equal size and opposite direction in the rotor, making the synthetic torque zero, so the motor cannot rotate.
When we use external force to make the motor rotate in a certain direction (such as clockwise rotation), then the single-phase AC motor rotor and the instantaneous rotation direction of the rotating magnetic field between the cut magnetic line of motion becomes smaller; rotor and counterclockwise rotation direction of the electromagnetic torque will no longer be zero, the rotor will rotate up in the direction of propulsion, to make the single-phase AC motor can automatically rotate up.
Single-phase AC motors are based on the principle of phase separation:
1. Two windings that differ by 90° in space, respectively, flow into two phases of current that differ by 90° in phase, which can also produce a rotating magnetic field.
2. If the parameters of the two windings are the same, the amplitude of the two phases of current is equal, and a circular rotating magnetic field is produced.
3. The direction of the rotating magnetic field is shifted from the axis position of the winding where the current phase is ahead to the axis position of the winding where the current phase is lagging, so changing the phase relationship between the currents in the two windings can change the direction of the rotating magnetic field and therefore the direction of the motor.
