Servo energy-saving braking equipment suppliers remind you that servo drivers are used to drive servo motors, which can be stepper motors or AC asynchronous motors. They are mainly used to achieve fast and accurate positioning, and are commonly used in situations where high precision is required for start stop operations.
A frequency converter is designed to convert AC power into a current suitable for regulating motor speed, in order to drive the motor. Nowadays, some frequency converters can also achieve servo control, which means they can drive servo motors, but servo drives and frequency converters are still different! What is the difference between servo and frequency converter? Please see the breakdown provided by the editor.
Two definitions
A frequency converter is an electrical energy control device that uses the on-off function of power semiconductor devices to convert the power frequency power supply into another frequency. It can achieve functions such as soft starting, variable frequency speed regulation, improving operating accuracy, and changing power factors for AC asynchronous motors.
The frequency converter can drive variable frequency motors and ordinary AC motors, mainly serving as a regulator of motor speed.
A frequency converter usually consists of four parts: rectifier unit, high-capacity capacitor, inverter, and controller.
A servo system is an automatic control system that enables the output controlled variables such as the position, orientation, and state of an object to follow any changes in the input target (or given value). The main task is to amplify, transform, and regulate the power according to the requirements of the control command, making the torque, speed, and position control of the driving device output very flexible and convenient.
A servo system is a feedback control system used to accurately follow or reproduce a process. Also known as a follow-up system. In many cases, a servo system specifically refers to a feedback control system where the controlled variable (system output) is mechanical displacement, displacement velocity, or acceleration. Its function is to ensure that the output mechanical displacement (or rotation angle) accurately tracks the input displacement (or rotation angle). The structural composition of servo systems is not fundamentally different from other forms of feedback control systems.
Servo systems can be divided into electromechanical servo systems, hydraulic servo systems, and pneumatic servo systems according to the type of driving components used. The most basic servo system includes servo actuators (motors, hydraulic cylinders), feedback components, and servo drivers. If you want the servo system to operate smoothly, you also need a higher-level mechanism, PLC、 And specialized motion control cards, industrial control computers+PCI cards, to send instructions to servo drives.
Working principle of both
The speed regulation principle of a frequency converter is mainly limited by four factors: the speed n of the asynchronous motor, the frequency f of the asynchronous motor, the motor slip rate s, and the number of poles p of the motor. The speed n is proportional to the frequency f, and changing the frequency f can change the speed of the motor. When the frequency f varies within the range of 0-50Hz, the range of motor speed adjustment is very wide. Variable frequency speed regulation is achieved by changing the frequency of the motor power supply to adjust the speed. The main method used is AC-DC-AC, which first converts the power frequency AC power supply into DC power supply through a rectifier, and then converts the DC power supply into AC power supply with controllable frequency and voltage to supply the motor. The circuit of a frequency converter generally consists of four parts: rectification, intermediate DC link, inverter, and control. The rectification part is a three-phase bridge uncontrolled rectifier, the inverter part is an IGBT three-phase bridge inverter, and the output is a PWM waveform. The intermediate DC link includes filtering, DC energy storage, and buffering reactive power.
The working principle of a servo system is simply based on open-loop control of an AC/DC motor, where speed and position signals are fed back to the driver through rotary encoders, rotary transformers, etc. for closed-loop negative feedback PID control. In addition, with the current closed-loop inside the driver, the accuracy and time response characteristics of the motor's output following the set value are greatly improved through these three closed-loop adjustments. The servo system is a dynamic follower system, and the steady-state balance achieved is also a dynamic balance.
The difference between the two
The technology of AC servo itself draws on and applies the technology of frequency conversion. Based on the servo control of DC motors, it imitates the control method of DC motors through the PWM method of frequency conversion. In other words, AC servo motors must have the process of frequency conversion: frequency conversion is to first rectify the AC power of 50 or 60Hz into DC power, and then invert it into a frequency adjustable waveform similar to sine and cosine pulse electricity through various controllable gate transistors (IGBT, IGCT, etc.) through carrier frequency and PWM adjustment. Due to the adjustable frequency, the speed of AC motors can be adjusted (n=60f/p, n speed, f frequency, p pole pairs).
1. Different overload capacities
Servo drives generally have a 3-fold overload capacity, which can be used to overcome the inertia moment of inertial loads at the moment of starting, while frequency converters generally allow a 1.5-fold overload.
2. Control accuracy
The control accuracy of servo systems is much higher than that of frequency converters, and the control accuracy of servo motors is usually ensured by the rotary encoder at the back end of the motor shaft. Some servo systems even have a control accuracy of 1:1000.
3. Different application scenarios
Variable frequency 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 with low performance indicators, pursuing low cost. The other is to pursue high precision, high performance, and high response.
4. Different acceleration and deceleration performance
Under no-load conditions, the servo motor can process from a stationary state to 2000r/min in no more than 20ms. The acceleration time of the motor is related to the inertia of the motor shaft and the load. Usually, the larger the inertia, the longer the acceleration time.
Market competition between servo and frequency converter
Due to the differences in performance and functionality between frequency converters and servos, their applications are not very similar, and the main competition is focused on:
1. Competition in technological content
In the same field, if the purchaser has high and complex technical requirements for machinery, they will choose servo systems. Otherwise, frequency converter products will be chosen. High tech machinery such as CNC machine tools and electronic specialized equipment will choose servo products.
2. Price competition
Most buyers are concerned about costs and often overlook technology in favor of lower priced inverters. As is well known, the price of servo systems is several times that of frequency converter products.
Although the application of servo systems is not yet widespread, especially domestic servo systems, they are rarely used in situations compared to foreign servo products. But with the acceleration of industrialization, people will gradually realize the advantages of servo systems, and servo systems will also be recognized by buyers. Similarly, domestic servo technology will not stop moving forward, whether based on lucrative profit returns or a sense of historical mission to revitalize the country. We believe that more and more manufacturers will invest in the research and development of servo systems. At that time, it will usher in the peak period of China's "servo industry".