Frequency conversion can have no encoder, but servo must have an encoder for electronic commutation. The AC servo technology itself borrows and applies the frequency conversion technology. On the basis of the servo control of the DC motor, it imitates the control mode of the DC motor through the PWM method of frequency conversion. The M-adjustable inverter becomes a frequency-adjustable waveform similar to sine-cosine pulsating electricity. Since the frequency is adjustable, the speed of the AC motor can be adjusted (n=60f/2p, n speed, f frequency, p pole pairs)

Talk about inverter

A simple inverter can only adjust the speed of the AC motor. At this time, it can be open-loop or closed-loop, depending on the control method and the inverter. This is the traditional V/F control method. Now many frequency conversions have established mathematical models to convert the stator magnetic field UVW3 phase of the AC motor into two current components that can control the motor speed and torque. Now most of the famous brand inverters capable of torque control use this method to control the torque. The output of each phase of UVW needs to add a current detection device with Moore effect, and the PID adjustment of the current loop that forms a closed-loop negative feedback after sampling feedback; In this way, both the speed of the motor and the torque of the motor can be controlled, and the speed control accuracy is better than v/f control, and the encoder feedback can be added or not, and the control accuracy and response characteristics are much better when added.

Talk about servo motor

Drive: On the premise of the development of frequency conversion technology, the servo drive has carried out more accurate control technology and algorithm calculation than ordinary frequency conversion in the current loop, speed loop and position loop (the frequency converter does not have this loop) inside the drive. It is also much more powerful than the traditional servo in terms of function. The main point is that it can perform precise position control. The speed and position are controlled by the pulse sequence sent by the upper controller (of course, some servos have integrated control units inside or directly set parameters such as position and speed in the drive through bus communication), and the internal algorithms, faster and more accurate calculations of the drive and electronic devices with better performance make it superior to the frequency converter.

Motor: The material, structure and processing technology of the servo motor are much higher than those of the AC motor driven by the inverter (general AC motor or constant torque, constant power and other variable frequency motors), that is to say, when the driver outputs a power supply with rapid changes in current, voltage, and frequency, the servo motor can respond to changes in power supply. The response characteristics and anti-overload capacity are much higher than the AC motor driven by the inverter. That is to say, it is not that the frequency conversion cannot output the power signal that changes so fast, but that the motor itself cannot respond, so the corresponding overload setting is made to protect the motor when setting the internal algorithm of the frequency conversion. Of course, even if the output capacity of the inverter is not set, it is still limited, and some inverters with excellent performance can directly drive the servo motor!!!

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Talk about AC motors

AC motors are generally divided into synchronous and asynchronous motors

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1. AC synchronous motor: the rotor is composed of permanent magnet materials, so after rotation, with the change of the rotating magnetic field of the stator of the motor, the rotor also responds to frequency changes, and the rotor speed = stator speed, so it is called "synchronous".

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2. AC asynchronous motor: the rotor is composed of induction coils and materials. After rotation, the stator generates a rotating magnetic field, which cuts the induction coil of the stator. The rotor coil generates an induced current, and then the rotor generates an induced magnetic field. The induced magnetic field follows the change of the stator's rotating magnetic field, but the change of the rotor's magnetic field is always smaller than that of the stator. . . Therefore, a key parameter in the AC asynchronous motor is the slip rate, which is the ratio of the speed difference between the rotor and the stator.

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3. Corresponding to AC synchronous and asynchronous motor inverters, there are corresponding synchronous inverters and asynchronous inverters. Servo motors also have AC synchronous servos and AC asynchronous servos. Of course, AC asynchronous frequency conversion is common in inverters, and AC synchronous servos are common in servos.