Differences in the working principles of AC servo motors and DC servo motors

Working principle of AC servo motor:

When the AC servo motor has no control voltage, there is only the pulsating magnetic field generated by the excitation winding 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 along the direction of the rotating magnetic field. When the load is constant, the speed of the motor changes with the magnitude of the control voltage. When the phase of the control voltage is opposite, the AC servo The motor will reverse. Although the working principle of the AC servo motor is similar to that of the split-phase single-phase asynchronous motor, the rotor resistance of the former is much larger than that of the latter. Therefore, compared with the single-machine asynchronous motor, the servo motor has three salient features:

1. Large starting torque

Due to the large rotor resistance, its torque characteristic curve is shown in curve 1 in Figure 3, which is obviously different from the torque characteristic curve 2 of ordinary asynchronous motors. 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, which has the characteristics of fast starting and high sensitivity.

2. Wide operating range

3. No rotation phenomenon

For a servo motor in normal operation, as long as the control voltage is lost, the motor will stop running immediately. When the servo motor loses the control voltage, it is in a single-phase operation state. Due to the large resistance of the rotor, the two torque characteristics (T1-S1, T2-S2 curves) generated by the two rotating magnetic fields rotating in opposite directions in the stator and the action of the rotor ) and synthetic torque characteristics (TS curve) The output power of the AC servo motor is generally 0.1-100W. When the power frequency is 50Hz, the voltages are 36V, 110V, 220, 380V; when the power frequency is 400Hz, the voltages are 20V, 26V, 36V, 115V and so on. The AC servo motor runs smoothly with low noise. But the control characteristic is non-linear, and because the rotor resistance is large, the loss is large, and the efficiency is low, compared with the DC servo motor of the same capacity, it is bulky and heavy, so it is only suitable for small power control systems of 0.5-100W.

Second, the difference between AC servo motor and DC servo motor:

DC servo motors are divided into brushed and brushless motors. Brushed motors are low in cost, simple in structure, large in starting torque, wide in speed regulation range, easy to control, and require maintenance, but are easy to maintain (replace carbon brushes), generate electromagnetic interference, and have requirements for the environment. Therefore, it can be used in common industrial and civil occasions that are sensitive to cost. The brushless motor is small in size, light in weight, large in output, fast in response, high in speed, small in inertia, smooth in rotation and stable in torque. The control is complicated, and it is easy to realize intelligence. Its electronic commutation method is flexible, and it can be square wave commutation or sine wave commutation. The motor is maintenance-free, has high efficiency, low operating temperature, low electromagnetic radiation, long life, and can be used in various environments.

AC servo motors are divided into synchronous and asynchronous motors. At present, synchronous motors are generally used in motion control. Its power range is large and it can achieve a large power. Large inertia, low maximum rotational speed, and decreases rapidly as power increases. Therefore, it is suitable for applications that run smoothly at low speeds.

The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase electricity controlled by the driver forms an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the encoder of the motor feeds back the signal to the driver. Values ​​are compared to adjust the angle at which the rotor turns. The accuracy of the servo motor depends on the accuracy (number of lines) of the encoder.

With the continuous advancement of industrial automation, the demand for automation software and hardware equipment remains high. Among them, the domestic industrial robot market has been growing steadily, and my country has become the world's largest demand market. At the same time, it directly drives the market demand for servo systems. At present, AC and DC servo motors with high starting torque, large torque and low inertia are widely used in industrial robots. Other motors, such as AC servo motors and stepper motors, will also be used in industrial robots according to different application requirements.

Post time: Jul-07-2023