AC servo driver working principle and control method

Servo drives are used in digital signal processor (DSP) as the control, It can achieve more complex control algorithms and develop for digital, networked and smart. Power Module widely used in intelligent power module (IPM) as the core design of the drive circuit. At the same time have over-voltage, over current, overheating, undervoltage protection circuit fault detection. The main circuit also joined the soft-start circuit to reduce the impact on startup drive

First, the power drive unit via a three-phase full bridge rectifier circuit or three-phase mains input is rectified to get relative DC. After a good three-phase power rectifier or mains, and then to variable frequency AC servo motor driven by three-phase sinusoidal PWM voltage source inverter. The whole process of the power drive unit can simply say that AC-DC-AC process of rectifying unit (AC-DC) is the main circuit topology of three-phase full-bridge controlled rectifier circuit

General servo has three control modes: position control mode, torque control mode, speed control mode.

1, the position control: Position control mode is generally through an external input frequency pulses to determine the size of the rotational speed. To determine the angle of rotation by the number of pulses. Some servo velocity and Position can be assigned directly through communication. Since the position of method can have very strict control over the speed and position, it is generally used in the positioning application.

2.Torque control: That is set servo motor output torque by analog or assignments at the address. It can change the torque by change analog real-time. Also can be performed by change the value at the relative address by communication

Application for materials are mainly under the strict requirements of winding and unwinding device, for example winding device or pull fiber optic equipment, torque is set according to the change in the winding radius change at any time to ensure that the material will be discontinuity with changes winding radius change

3, the speed mode: The speed can be changed by analog input and pulse. And when host controller outer loop PID speed control mode also can be fixed position. But it must be the position signal of the motor or the load position signal directly to the host to do the operation with feedback. Position mode is also supported load outer position signal detection. At this point the motor shaft encoder only detect the motor speed, the position signal is provided directly by the end of the final load detection device. This has the advantage that it can reduce errors during the intermediate transmission. Increasing the positioning accuracy of the entire system.

If the speed of the motor and position are not required, as long as a constant torque output, of course, it is the torque mode.

If there is a accuracy requirements, and no concern torque so much. for the position and speed mode is better.

If the host controller has a better closed-loop control functions, with the speed control effect will be better, if itself is not very high, or substantially no real-time requirements, using the position control mode.