How to adjust the speed of single-phase motor?

Single-phase asynchronous motor, like three-phase asynchronous motor, is difficult to adjust speed. If variable frequency speed regulation is adopted, the equipment is complicated and the cost is high. Therefore, generally only polar coordinates are used for speed regulation, and the main speed regulation methods are as follows:

1, speed adjustment of series reactor

The reactor is connected in series with the stator winding of the motor, and the voltage applied to the stator winding of the motor is lower than the power supply voltage by using the voltage drop generated on the reactor, thus reducing the rotation speed of the motor. This speed regulation method can only be low-key from the rated speed of the motor. Mostly used for ceiling fans and table fans.

2, motor winding internal tap speed regulation

By changing the connection mode of the intermediate winding, the starting winding and the working winding through the speed regulating switch, the size of the air gap magnetic field in the motor can be changed, and the purpose of adjusting the motor speed can be achieved. There are two types of connections: L type and T type.

3, AC thyristor speed regulation

By changing the conduction angle of the thyristor, the AC voltage applied to the single-phase motor can be adjusted, so as to achieve the purpose of speed regulation. This method can realize stepless speed regulation, but there is some electromagnetic interference. Commonly used for speed regulation of electric fans.

principle of operation

When a single-phase sinusoidal current passes through the stator winding, the motor will generate an alternating magnetic field. The intensity and direction of this magnetic field change sinusoidally at any time, but it is fixed in spatial orientation, so it is also called alternating pulsating magnetic field. This alternating pulsating magnetic field can be decomposed into two rotating magnetic fields with the same rotating speed and opposite rotating directions. When the rotor is stationary, two rotating magnetic fields generate two torques with equal magnitude and opposite directions in the rotor, so that the resultant torque is zero, so the motor cannot rotate.

When we use external force to make the motor rotate in a certain direction (such as clockwise rotation), the movement of cutting magnetic lines between the rotor and the clockwise rotating magnetic field becomes smaller; The movement of cutting magnetic lines between the rotor and the rotating magnetic field in the counterclockwise direction becomes larger. In this way, the balance is broken, the total electromagnetic torque generated by the rotor is no longer zero, and the rotor will rotate in the direction of pushing.