What do servo drives and frequency converters have in common? For this question, I believe many people want to know, what is the difference between the servo drive and the frequency converter?
1. Definition of servo driver:
Servo drive: Under the premise of the development of frequency conversion technology, the current loop, speed loop and position loop (the frequency converter does not have the loop) inside the servo drive are more accurate control technology and algorithm calculation than the general frequency conversion, and the function is much more powerful than the traditional servo, the main point can be accurate position control. The speed and position are controlled by the pulse sequence sent by the upper controller (of course, some servos are also integrated with the control unit or directly set the position and speed parameters in the servo drive through the bus communication). The internal algorithm of the servo drive, faster and more accurate calculation and better performance of electronic devices make it more superior to the frequency converter.
Motor: The material, structure and processing technology of the servo motor are much higher than that of the AC motor driven by the frequency converter (general AC motor or variable frequency motor with constant torque and constant power, etc.). That is to say, when the servo driver outputs the power supply with rapid changes in current, voltage and frequency, the servo motor can produce action changes in response to the power supply changes. The response characteristics and anti-overload capability are much higher than that of inverter driven AC motor, and the serious differences in the motor are also the fundamental differences in the performance of the two. That is to say, it is not that the frequency converter can not output the power signal that changes so fast, but that the motor itself can not react, so in order to protect the motor when the internal algorithm of frequency conversion is set, the corresponding overload setting is made. Of course, even if the output capacity of the frequency converter is not set, some good performance of the frequency converter can be directly driven!
2. Definition of frequency converter:
Simple frequency converter can only adjust the speed of AC motor, then can open loop or closed loop depending on the control mode and frequency converter, this is the traditional sense of V/F control mode. Many frequency converters have converted the stator magnetic field UVW3 phase of AC motor into two current components that can control the motor speed and torque through the establishment of mathematical models. Most of the famous brand frequency converters capable of torque control adopt this way to control the torque. The output of each UVW phase requires a current detection device with Hall effect. The PID adjustment of the current loop with negative feedback after sampling feedback; ABB frequency conversion also puts forward a direct torque control technology which is different from this method. Please refer to relevant materials for details. In this way, both the motor speed and the motor torque can be controlled, and the speed control accuracy is better than v/f control. The encoder feedback can be added or not, and the control accuracy and response characteristics are much better when added.
Common points between servo drive and inverter:
The technology of AC servo itself refers to and applies the technology of frequency conversion. Based on the servo control of DC motor, it is realized by imitating the control mode of DC motor through the PWM mode of frequency conversion. That is to say, AC servo drive must have the link of frequency conversion: Frequency conversion is the power frequency of 50, 60HZ AC first rectifier into DC, and then through the control gate of all kinds of transistors (IGBT, IGCT, etc.) through the carrier frequency and PWM regulation inverter frequency adjustable waveform similar to sine and cosine pulse electricity, because the frequency is adjustable, so the speed of the AC motor can be adjusted (n=60f/p, n rotational speed, f frequency, p pole logarithm).