How to overcome the rotation of AC servo motor

The AC servo motor is a two-phase AC asynchronous motor. Its stator is equipped with two windings with a spatial difference of 90° from each other, namely: excitation winding and control winding. One is the excitation winding Rf, which is always connected to the AC voltage Uf; the other is the control winding L, which is connected to the control signal voltage Uc. Therefore, the AC servo motor can also be called two servo motors. However, when the AC motor is working, it will occasionally rotate. So how to overcome this phenomenon? Let’s find out together below!

If the parameter selection of the AC servo motor is similar to that of a general single-phase asynchronous motor, once the motor rotates, even if the control is equal to zero, the motor will continue to rotate and the motor will lose control. This phenomenon is called "rotation".

So how to overcome the "rotation" phenomenon of AC servo motors? Methods as below:

Synthetic torque characteristics of forward and reverse rotating magnetic fields: When single-phase excitation, the operating range of the motor is 0.

When the control voltage applied to the control winding is reversed (keeping the excitation voltage unchanged), the rotation direction of the rotating magnetic field changes, causing the motor rotor to reverse. When the control voltage applied to the control winding changes, the ellipticity of the rotating magnetic field generated is different, and the electromagnetic torque generated is also different, thereby changing the speed of the motor.

When the excitation voltage of an AC motor remains unchanged, as the control voltage decreases, its corresponding characteristic curve moves downward. Under the action of the same load torque, the speed of the AC servo motor decreases evenly as the control voltage decreases.

The excitation winding is connected in series with capacitor C to generate a two-phase rotating magnetic field. Appropriate selection of the size of the capacitor can make the phase difference of the current flowing into the two windings close to 90°, thereby generating the required rotating magnetic field.

The excitation winding is fixedly connected to the power supply. When the control voltage is zero, the motor has no starting torque and the rotor does not rotate. If a control voltage is applied to the control winding, and the excitation current is generated. When the current of the control winding is inconsistent with that of the control winding, a two-phase rotating magnetic field is generated. Under the action of the rotating magnetic field, the rotor rotates.