Servo drives use digital signal processor (DSP) as the control core, which can implement more complex control algorithms to achieve digitization, network and
intelligence; power devices generally use drive circuits designed with intelligent power module (IPM) as the core. The IPM integrates a drive circuit and has
over-voltage, over-current, over-heat, and under-voltage fault detection and protection circuits. A soft-start circuit is also added to the main circuit to reduce
the impact on the driver during the startup process.
Today, I will introduce the working principle of the servo driver.
I. Working principle of servo driver
First, the power drive unit rectifies the input three-phase power or mains power through a three-phase full-bridge rectifier circuit to obtain corresponding
DC power. After rectifying the three-phase power or the city power, the three-phase sinusoidal PWM voltage inverter is used to drive the AC servo motor.
The entire process of the power drive unit can be simply referred to as the AC-DC-AC process. The main topology circuit of the rectifier unit (AC-DC) is
a three-phase full-bridge uncontrolled rectifier circuit.
Two, servo drives generally have three control methods
Position control mode, torque control mode, speed control mode.
Position control Position control mode generally determines the rotation speed by the frequency of the externally input pulses, and determines the rotation
angle by the number of pulses. Some servos can directly assign speed and displacement through communication methods. Due to the position mode It can
control the speed and position very strictly, so it is generally used in positioning devices.
Torque control The torque control mode is to set the external output torque of the motor shaft through external analog input or direct address assignment.
You can change the set torque by changing the analog setting in real time. You can also change the value of the corresponding address through communication.
The application is mainly used in winding and unwinding devices that have strict requirements on the material's force, such as winding devices or fiber optic
equipment. The torque setting should be changed at any time according to the change of the winding radius to ensure that the material's force is not affected.
Will change as the winding radius changes.
The speed control mode can control the rotation speed through the analog input or the frequency of the pulse. The speed mode can also perform positioning
when the outer loop PID control of the host control device is used, but the position signal of the motor or the load must be directly loaded. The position signal
is fed back to the upper level for calculation. The position mode also supports the direct detection of the outer load position signal. At this time, the encoder at
the motor shaft end only detects the motor speed, and the position signal is provided by the direct final load end detection device. This has the advantage that
it can reduce the intermediate transmission process. The error increases the positioning accuracy of the entire system.
1) If there is no requirement for the speed and position of the motor, just output a constant torque and use the torque mode.
2) If there is a certain accuracy requirement for position and speed, but not very concerned about real-time torque, it is not convenient to use torque mode,
it is better to use speed or position mode.
3) If the higher-level controller has a better closed-loop control function, the speed control effect will be better. If the requirements are not very high, or there are
basically no real-time requirements, the position control method is used. Requirements for servo feed systems
Fourth, PID controller
1) PID controller (Proportional-Integral-Derivative Controller) is a common feedback loop component in industrial control applications. It consists of proportional
unit P, integral unit I and differential unit D.
2) The basis of PID control is proportional control;
Integral control can eliminate steady-state errors, but may increase overshoot; differential control can speed up the response of large inertial systems and reduce
the tendency of overshoot.
In short, the servo driver is a kind of controller used to control the servo motor. Its function is similar to that of the inverter on ordinary AC motors. It belongs
to the servo system and is mainly used in high-precision positioning systems. Generally, the servo motor is controlled by three methods of position, speed and
torque to achieve high-precision positioning of the transmission system. It is currently a high-end product of transmission technology.