Description
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The servo driver is used to drive the servo motor. The servo motor can be either a stepping motor or an AC asynchronous motor. It is mainly used to achieve fast and accurate positioning, such as in the case of stop and go and high precision requirements.
The purpose of frequency converter is to convert the power frequency alternating current into the current suitable for adjusting the motor speed to drive the motor. Now some frequency converters can also realize servo control, that is, they can drive the servo motor, but the servo driver is different from the frequency converter! What is the difference between servo and frequency converter? Please see the division for you.
Definition of both
Frequency converter is a power control device that uses the on-off function of power semiconductor devices to convert power frequency power supply to another frequency. It can realize soft start of AC asynchronous motor, variable frequency speed regulation, improving operation accuracy, changing power factor and other functions. The frequency converter can drive variable frequency motor and ordinary AC motor, mainly playing the role of adjusting motor speed. Frequency converter is usually composed of four parts: rectifier unit, high-capacity capacitor, inverter and controller.
Servo system is an automatic control system that enables the output controlled variables such as position, orientation and state of objects to follow the arbitrary change of input target (or given value). The main task is to amplify, transform and regulate the power according to the requirements of the control command, so that the torque, speed and position output by the drive device can be controlled flexibly and conveniently.
Servo system is a feedback control system used to accurately follow or reproduce a process. It is also called servo system. In many cases, the servo system specifically refers to the controlled quantity (system output) is the feedback control system of mechanical displacement or displacement speed and acceleration, which is used to make the output mechanical displacement (or angle) accurately track the input displacement (or angle). There is no difference in principle between the structure of the servo system and other forms of feedback control systems.
Servo system can be divided into electromechanical servo system, hydraulic servo system and pneumatic servo system according to the type of driving elements used. The most basic servo system includes servo actuator (motor, hydraulic cylinder), feedback component and servo driver. If you want to make the servo system run smoothly, you also need an upper mechanism, PLC, and a special motion control card, IPC+PCI card to send instructions to the servo driver.
Working principle of both
The speed regulation principle of the frequency converter is mainly subject to four factors: the speed n of the asynchronous motor, the frequency f of the asynchronous motor, the motor slip s, and the motor pole pair p. The speed n is in direct proportion to the frequency f. As long as the frequency f is changed, the speed of the motor can be changed. When the frequency f changes within the range of 0-50Hz, the speed adjustment range of the motor is very wide. Variable frequency speed regulation is to realize speed regulation by changing the power frequency of the motor. It mainly adopts AC-DC-AC mode. First, convert the power frequency AC power supply into DC power supply through rectifier, and then convert the DC power supply into AC power supply with controllable frequency and voltage for motor supply. The circuit of the frequency converter is generally composed of four parts: rectifier, intermediate DC link, inverter and control. The rectifier part is a three-phase bridge uncontrolled rectifier, and the inverter part is an IGBT three-phase bridge inverter. The output is PWM waveform, and the intermediate DC link is filtering, DC energy storage and buffered reactive power.
The working principle of the servo system is simply to say that the speed and position signals are fed back to the driver through the rotary encoder, rotary transformer, etc. on the basis of the open-loop AC/DC motor for closed-loop negative feedback PID regulation control. In addition, with the current closed loop inside the driver, the accuracy of the motor”s output following the set value and the time response characteristics are greatly improved through the adjustment of these three closed loops. The servo system is a dynamic servo system, and the steady-state balance achieved is also a dynamic balance.
Both have something in common:
The AC servo technology itself refers to and applies the technology of frequency conversion. Based on the servo control of the DC motor, it is realized by imitating the control mode of the DC motor through the PWM mode of frequency conversion. That is to say, the AC servo motor must have the link of frequency conversion: frequency conversion is to first convert the 50 Hz and 60 Hz AC power into DC power, Then, all kinds of transistors (IGBT, IGCT, etc.) that can control the gate pole are used for inversion through carrier frequency and PWM regulation to form a frequency adjustable waveform similar to the sine cosine pulse. Because the frequency is adjustable, the speed of the AC motor can be adjusted (n=60f/p, n speed, f frequency, p pole pairs).
The difference between the two is:
1. The overload capacity is different. The servo driver generally has 3 times of overload capacity, which can be used to overcome the inertia moment of inertia load at the moment of starting, while the frequency converter generally allows 1.5 times of overload.
2. Control accuracy. The control accuracy of the servo system is much higher than that of the frequency conversion. Generally, the control accuracy of the servo motor is guaranteed by the rotary encoder at the rear end of the motor shaft. The control accuracy of some servo systems even reaches 1:1000.
3. Different applications. Frequency conversion control and servo control are two categories of control. The former belongs to the field of transmission control, while the latter belongs to the field of motion control. One is to meet the requirements of general industrial applications and pursue low cost in applications with low performance requirements. The other is to pursue high precision, high performance and high response.
4. Different acceleration and deceleration performance. The processing time of servo motor from static state to 2000r/min under no-load condition will not exceed 20ms. The acceleration time of the motor is related to the inertia and load of the motor shaft. Generally, the greater the inertia, the longer the acceleration time.
1.Has been engaged in industrial control industry for a long time, with a large number of inventories.
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YOKOGAWA – Servo module, control cabinet node unit
Main products:
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