The servo drive is used to drive the servo motor. The servo motor can be a stepper motor or an AC asynchronous motor. It is mainly used for fast and precise positioning. It is used in many occasions where the stop and stop and high precision are required. .
The inverter is to convert the power frequency AC power into a current suitable for adjusting the speed of the motor to drive the motor. Now some inverters can also realize servo control, that is, the servo motor can be driven, but the servo driver and the inverter are still different. of! What is the difference between servo and inverter? Please see the small series for your decomposition.
Definition of both
The frequency converter is a power control device that converts the power frequency power source into another frequency by using the on/off function of the power semiconductor device, and can realize functions such as soft start of the AC asynchronous motor, frequency conversion speed regulation, improvement of operation precision, and change of power factor.
The frequency converter can drive the variable frequency motor and the common AC motor, mainly as the role of adjusting the motor speed.
The frequency converter is usually composed of a rectifying unit, a high-capacity capacitor, an inverter and a controller.
The servo system is an automatic control system that enables an output controlled amount of an object to follow an arbitrary change of an input target (or a given value). The main task is to enlarge, transform and control the power according to the requirements of the control command, so that the torque, speed and position control of the drive device are very flexible and convenient.
A servo system is a feedback control system used to accurately follow or reproduce a process. Also known as the follow-up system. In many cases, the servo system refers to a feedback control system in which the controlled amount (output of the system) is mechanical displacement or displacement velocity and acceleration, and its function is to make the mechanical displacement (or rotation angle) of the output accurately track the displacement of the input ( Or corner). There is no principle difference between the structural composition of the servo system and other forms of feedback control systems.
The servo system can be divided into electromechanical servo system, hydraulic servo system and pneumatic servo system according to the type of drive components used. The most basic servo systems include servo actuators (motors, hydraulic cylinders), feedback components, and servo drives. If you want the servo system to run smoothly, you need a higher-level mechanism, PLC, and a special motion control card, industrial computer + PCI card, in order to send instructions to the servo drive.
The speed regulation principle of the frequency converter is mainly subject to the four factors of the speed n of the asynchronous motor, the frequency f of the asynchronous motor, the motor slip ratio s, and the motor pole pair number p. The rotational speed n is proportional to the frequency f. The rotational speed of the motor can be changed by changing the frequency f. When the frequency f is varied within the range of 0-50 Hz, the motor rotational speed adjustment range is very wide. Frequency control is to adjust the speed of the motor by changing the frequency of the motor. Mainly adopting the AC-DC-AC method, the power frequency AC power supply is first converted into a DC power source through a rectifier, and then the DC power source is converted into an AC power source whose frequency and voltage can be controlled to supply the motor. The circuit of the inverter is generally composed of four parts: rectification, intermediate DC link, inverter and control. The rectification part is a three-phase bridge type uncontrollable rectifier, the inverter part is an IGBT three-phase bridge inverter, and the output is a PWM waveform, and the intermediate DC link is filtering, DC energy storage and buffer reactive power.
The working principle of the servo system is simply that the speed and position signals are fed back to the driver through the rotary encoder, the resolver, etc. on the basis of the open-loop controlled AC-DC motor to perform closed-loop negative feedback PID adjustment control. In addition to the current loop inside the drive, these three closed-loop adjustments improve the accuracy and time response characteristics of the motor's output to setpoints. The servo system is a dynamic follow-up system, and the steady state balance achieved is also a dynamic balance.
The difference between the two:
The technology of AC servo itself is a technology that draws on and applies frequency conversion. It is realized by the PWM method of DC motor to simulate the control mode of DC motor based on the servo control of DC motor. That is to say, AC servo motor must have frequency conversion. Link: The frequency conversion is to rectify the AC frequency of 50, 60HZ of the power frequency into DC power, and then adjust the inverter to the frequency adjustable waveform through the carrier frequency and PWM through various types of transistors (IGBT, IGCT, etc.) that can control the gate. The sinusoidal pulsating power, because the frequency is adjustable, the speed of the AC motor can be adjusted (n=60f/p, n speed, f frequency, p pole logarithm).
The difference between the two is:1. Different overload capabilities.
The servo drive generally has 3 times overload capability, which can be used to overcome the inertia moment of the inertia load at the moment of starting, and the inverter generally allows 1.5 times overload.
2. Control accuracy.
The control accuracy of the servo system is much higher than 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. Some servo systems have a control accuracy of even 1:1000.
3. The application is different.
Variable frequency control and servo control are two categories of control. The former belongs to the field of transmission control, and the latter belongs to the field of motion control. One is to meet the requirements of general industrial applications, and the application requirements are not high, and the pursuit of low cost. The other is the pursuit of high precision, high performance, and high response.
4. Acceleration and deceleration performance is different.
In the case of no-load, the servo motor is processed from a standstill to 2000r/min, and it will not exceed 20ms. The acceleration time of the motor is related to the inertia of the motor shaft and the load. Generally, the larger the inertia, the longer the acceleration time.
Domestic servo and inverter market conditions
Although the servo technology in our country started late, the servo system consisting of servo motor, feedback device and controller has only passed 50 years. However, it is undeniable that Chinese manufacturing industry has gradually realized that servo systems play an increasingly important role in improving product competitiveness. The strong market demand for servo systems is beginning to emerge. I believe that in the near future, the new round of growth in servo systems will continue to write the history of another "China inverter". The main reasons for the analysis are as follows:
First, with the development of the overall form of China's economy, many servo-critical application industries such as machine tools, electronic special equipment, medical equipment, hybrid vehicles, and new energy industries have recovered more than people's expectations due to economic and political reasons. The development of these industries has directly led to strong demand in the servo market, which has led to the rise of many domestic servo brands. With the acceleration of the industrialization process, industrial upgrading and import substitution have also promoted the massive use of servo products, and the effects of energy saving and production increase have become increasingly apparent. It is worth mentioning that the initial maturity of servo application technology in the wind power industry implies that the business opportunities of energy saving and carbon reduction to servo are no less than the opportunities brought by energy saving and emission reduction to high voltage inverters.
Secondly, in the high-end field, the most important factors that users value in the process of use, such as stability, responsiveness and accuracy, are the advantages of the servo system. In today's increasingly demanding technology, whoever has the highest performance, who can get the favor of users, the price is no longer the decisive factor hindering the development of servo. The high-end market is undoubtedly occupied by the servos. The inverter only plays a role in some relatively low-end simple areas.
According to incomplete statistics, there are almost more than 20 manufacturers of servo products in China. For a long time, the entry barrier in the servo field is higher than that in the low-voltage inverter field. Many manufacturers are still developing based on the inverter technology. Enterprises such as the domestic manufacturer Huichuan have already begun to taste the actual reality brought by the servo industry. benefit. Huichuan's original R&D strength provides effective support for its servo field, and its brand influence, capacity release and segmentation industry extension will make its position in the servo market increase year by year. In 2010, its servo sales will reach 1 More than 100 million yuan. Investigating the final reason for its turn to servo products, the national servo development policy is good enough to break the mystery. Among the seven strategic emerging industries, the machinery industry accounts for two high-end equipment manufacturing and new energy vehicles, and the other five strategic emerging industries also need the support of the machinery industry. From this point of view, the development of manufacturing will also bring new opportunities for servo development.
Market competition between servo and inverter
Due to the difference in performance and function between the inverter and the servo, the application is not the same. The main competition is concentrated on:
Technical content competition. In the same field, if the purchaser has higher technical requirements and is more complicated, the servo system will be selected. Otherwise, the inverter product will be selected. For example, some high-tech machines such as CNC machine tools and electronic special equipment will be the first choice for servo products.
price competition. Most purchasers will be concerned about the cost, often ignoring the technology and prefer the lower cost inverter. As we all know, the price of the servo system is almost several times that of the inverter product.
Although the application of servo systems has not yet been popularized, especially in domestic servo systems, there are very few applications compared to foreign servo products. However, with the acceleration of the industrialization process, people will gradually realize the advantages of the servo system, and the servo system will also be recognized by the purchaser. Similarly, domestic servo technology will not stop, whether based on rich profit returns or revitalizing the country's historical mission, I believe more and more manufacturers will invest in the research and development of servo systems. It will usher in the heyday of China's "servo industry".
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