Comparison of AC servo motor selection

AC servo motor
      The configuration of the AC servo motor stator is basically similar to that of a capacitive split phase single-phase asynchronous motor. The stator is provided with two windings with a position difference of 90°, one is the field winding Rf, which is always connected to the AC voltage Uf; the other It is the control winding L, which is connected to the control signal voltage Uc. Therefore, the AC servo motor is also called two servo motors.
      The rotor of the AC servo motor is usually made into a squirrel-cage type, but in order to make the servo motor have a wide speed range, linear mechanical characteristics, no "rotation" phenomenon and fast response performance, it should have compared with the ordinary motor. Two characteristics of large rotor resistance and small moment of inertia. At present, there are two types of rotor structures that are widely used: one is a squirrel-cage rotor made of a high-resistivity conductive material made of a high-resistivity conductive material, and the rotor is made slender in order to reduce the moment of inertia of the rotor; One is a hollow cup rotor made of aluminum alloy, the cup wall is very thin, only 0.2-0.3mm. In order to reduce the magnetic resistance of the magnetic circuit, a fixed inner stator is placed in the hollow cup rotor. The rotor has a large moment of inertia, a fast response, and a smooth operation, so it is widely used.
When there is no control voltage in the AC servo motor, only the pulsating magnetic field generated by the field winding is present in the stator, and the rotor is stationary. When there is a control voltage, a rotating magnetic field is generated in the stator, and the rotor rotates in the direction of the rotating magnetic field. When the load is constant, the rotational speed of the motor varies with the magnitude of the control voltage. When the phase of the control voltage is opposite, the servo motor Will reverse.
Permanent magnet AC servo motor
      Since the 1980s, with the development of integrated circuits, power electronics technology and AC variable speed drive technology, permanent magnet AC servo drive technology has developed prominently. Famous electric manufacturers from all over the world have successively launched their own AC servo motor and servo drive series. The product is constantly being refined and updated. AC servo system has become the main development direction of modern high-performance servo system, which makes the original DC servo face the crisis of being eliminated. After the 1990s, the AC servo system that has been commercialized in various countries around the world is a sinusoidal motor servo drive with full digital control. The development of AC servo drives in the field of transmission is changing with each passing day.
      Compared with DC servo motors, permanent magnet AC servo motors have the following main advantages:
(1) No brushes and commutators, so reliable operation and low maintenance and maintenance requirements.
(2) The stator winding heat dissipation is convenient.
(3) The inertia is small, which is easy to improve the rapidity of the system.
(4) Adapted to high speed and large torque working conditions.
(5) Smaller volume and weight at the same power.
Comparison between servo motor and single-phase asynchronous motor
The working principle of the AC servo motor is similar to that of the split-phase single-phase asynchronous motor, but the rotor resistance of the former is much larger than the latter, so the servo motor has three remarkable characteristics compared with the single-machine asynchronous motor:
1, the starting torque is large
Due to the large rotor resistance, there is a significant difference compared to the torque characteristic curve of a conventional asynchronous motor. It can make the critical slip rate S0>1, which not only makes the torque characteristic (mechanical characteristic) closer to linear, but also has a larger starting torque. Therefore, when the stator has a control voltage, the rotor rotates immediately, that is, it has the characteristics of quick start and high sensitivity.
2, a wider range of operation
3, no rotation phenomenon
      In the normal operation of the servo motor, the motor stops running as soon as the control voltage is lost. When the servo motor loses the control voltage, it is in single-phase operation. Due to the large rotor resistance, the two rotating torques in the opposite direction of the stator and the two torque characteristics generated by the rotor (T1-S1, T2-S2 curves) And synthetic torque characteristics (T-S curve)
The output power of the AC servo motor is generally 0.1-100W. When the power frequency is 50Hz, the voltage is 36V, 110V, 220, 380V; when the power frequency is 400Hz, the voltage is 20V, 26V, 36V, 115V and so on.
The AC servo motor runs smoothly and has low noise. However, the control characteristics are non-linear, and because of the large rotor resistance, large loss, and low efficiency, it is bulky and heavy compared with the same capacity DC servo motor, so it is only suitable for small power control systems of 0.5-100W.