Servo Drive Basics & Working Principle
Servo drive basics
What is a servo drive? The servo drive is a kind of controller to control the servo system. Its function is similar to the frequency effect on ordinary AC motor, which belongs to a part of the servo system and is mainly applied in high-accuracy positioning system. Generally, the servo motor is controlled by three ways, location, speed and torque, so as to realize high precision positioning of transmission system.
Servo drive woking principle
How does a servo drive work? The servo driver adopts digital signal processor (DSP) as the control core, an realize the complex control algorithm, digitization, networking and intelligentialization. The power device generally adopts intelligent power module (IPM) as the driving circuit of the core design. IPM integrated drive circuit with over-voltage and over-current, overheating, undervoltage fault detection and protection circuit. The soft start circuit is also added in the major loop, so as to reduce the impact on thedrive in the start-up process.
First, the power drive unit is rectified by the three-phase full bridge rectifier circuit to input the three-phase electric or municipal power, and the corresponding DC power is obtained. The three-phase power or electric supply after rectifying can drive the AC servo motor through three-phase sine PWM voltage source inverter frequency conversion. The whole process of the power drive unit can be simply described as the process of AC-DC-AC. The main topology of the rectifier unit (AC-DC) is the three-phase full bridge uncontrolled rectifier circuit.
Control methods of servo drive
Servo drive generally has three control methods: position control mode, torque control mode and speed control method.
- The position control mode can determine the rotational speed generally through the external input pulse frequency and the rotation angle by the number of pulses. Some servo systems can assign velocity and displacement directly by means of communication. Because the position mode can control the speed and position strictly, it is generally used in the positioning device.
- Torque control mode is assigned by the external analog input or direct address to set the external output torque of motor shaft. The torque can be changed by changing the setting of the analog immediately and the corresponding address value can be realized by the change of communication mode. The main application has strict requirement for the material on stress in the winding and unwinding device, such as winding device or fiber optic equipment. The setting of the torque should be changed at any time according to the radius of the winding so as to ensure that the force of the material does not change with the change of the winding radius.
- Speed mode can have control for the rotation speed through the input of the analog quantity or the pulse frequency. The outer loop PID with the upper control device can be positioned. But the position signal of the motor or the position signal of the direct load should be sent to the upper feedback for calculation. The position mode also supports direct load loop detection position signal. At this moment, the coder at the motor shaft end can only detect the motor speed and the position signal is provided by the detection device directly of the final load end. The advantage of this method is that it can reduce the error in the intermediate transmission process and increase the positioning accuracy in the whole system.