1 Overview Single-phase asynchronous motors are rotary resistors that are powered by a single-phase AC power source with a single-phase stator winding. When a single-phase AC power source is connected, it produces an alternating pulsating magnetic field in the air gap between the stator and the rotor. This magnetic field does not rotate in space, but the magnitude of the magnetic flux and magnetic induction varies sinusoidally with time. A pulsating magnetic field with a fixed spatial axis and a sinusoidal variation in size can be decomposed into two rotating magnetic fields of equal rotational speed and opposite directions. When the rotor is stationary, the combined electromagnetic torque generated by the two rotating magnetic fields is zero, so the single-phase asynchronous motor cannot start itself. In order to make the single-phase asynchronous motor self-starting, a rotating magnetic field is generated at startup. To this end, capacitor phase separation can be used to achieve self-start of single-phase asynchronous motor.
It is the wiring schematic diagram of the capacitive split-phase asynchronous motor.
Chen Yongli (1970-), male, lecturer, Shenzhou, Hebei Province, engaged in electrical and electronic teaching and research, research direction: PLC control and information processing; Chen Peng (1968-), male, Shijiazhuang, Hebei Province, associate professor, Engaged in electrical and electronic teaching and research work, scientific research direction: PLC control and pattern recognition; there are two windings on the stator, AX is the working winding, BY is the starting winding, BY winding is connected in series with the capacitor, and the axes of the two windings are perpendicular to each other in space. The current iB in the winding BY is advanced by 90Â° in phase than the current iA in the AX winding by appropriate selection of circuit parameters. In this way, a rotating magnetic field is generated in the stator and rotor air gaps after energization, and the single-phase asynchronous motor is started by itself. The two-phase currents iA, B are as shown, and the direction of the generated rotating magnetic field is from BY to AX, that is, the current-leading winding (BY) turns to the current-lag winding (AX), which rotates clockwise. Under the action of the rotating magnetic field, the rotor will rotate together in a clockwise direction.
2 The reversal of the motor is to reverse the single-phase asynchronous motor. The key is to change the direction of rotation of the rotating magnetic field, but it cannot be realized by replacing two power lines like a three-phase asynchronous motor. It can be seen from the analysis that the key to causing the reversal of the rotating magnetic field of the single-phase asynchronous motor is to change the relationship between lead and lag between iA and iB. If the iB is ahead of iA 90* and the single-phase asynchronous motor is rotated clockwise to forward, then the single-phase asynchronous motor should be reversed, so that iA is ahead of iB90*. after.
Capacitive split-phase asynchronous two-phase current waveform motor reverse wiring diagram Change the connection mode of the working winding and the power supply circuit As shown, the first end of the winding AX is connected to the power supply line 2, and the end X is connected to the power supply line 1. The change in the connection mode causes the phase of the current iA in the winding AX to change, that is, the iA is inverted. Then, at this time, iA changes from hysteresis iB90* to iB90*, so the rotating magnetic field is reversed, and the single-phase asynchronous motor is reversed. The two phase currents are as shown.
Capacitor split-phase asynchronous two-phase current waveform motor reverse wiring conclusion In summary, if the single-phase asynchronous motor is started by the capacitor split phase method, the serial connection position of the capacitor c can be changed, and the connection between the start branch and the power source can be changed. The way to change the connection between the working winding and the power supply is realized. The above method has been verified by experiments and is indeed feasible.
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