An important difference between servo and frequency conversion is that frequency conversion can be without encoder, while servo must have an encoder for electronic commutation.
1. What the two have in common:
The AC servo technology itself is to learn and apply the technology of frequency conversion, on the basis of the servo control of the DC motor through the PWM method of frequency conversion to imitate the control method of the DC motor to complete, that is to say, the AC servo motor must have this link of frequency conversion: frequency conversion is to rectify the power frequency of 50, 60HZ AC power into direct current, and then through various transistors (IGBT, IGCT, etc.) that can control the gate pole The waveform inverted to frequency adjustable by carrier frequency and PWM conditioning is similar to the pulsating electricity of sine and Cosine, because the frequency is adjustable, so the speed of the AC motor is adjustable (n = 60 f/p, n speed, f frequency, p pole pairs)
Second, talk about the inverter:
The abbreviated inverter can only regulate the speed of the AC motor, and at this time, it can be open-loop or closed-loop depending on the control method and the inverter, which is the traditional V/F control method. Many frequency conversion has been established through the mathematical model, the stator magnetic field UVW3 phase of the AC motor is converted into two current components that can control the motor speed and torque, most of the inverters of the first brand of torque control are selected to control the torque in this way, the output of each phase of UVW should add the current detection equipment of the Hall effect, and the PID conditioning of the current loop of the current loop that constitutes a closed-loop negative reaction after sampling reaction; ABB's inverter also proposes a direct torque control technology that is different from this method, please refer to the relevant information for details. In this way, the speed of the motor can be controlled and the torque of the motor can be controlled, and the control accuracy of the speed is better than the V/F control, and the encoder response can also be added or not, and the control accuracy and response characteristics are much better when added.
3. Talk about servo:
Driver: Under the premise of frequency conversion technology, the servo drive has carried out more advanced control technology and algorithm operation than the general frequency conversion in the current loop, speed loop and azimuth loop (the frequency converter does not have this ring) inside the drive, and it is much stronger than the traditional servo in terms of function. The speed and azimuth are controlled by the pulse train sent by the upper controller (of course, there are also some servos that integrate the control unit or directly set the parameters such as azimuth and speed in the driver through bus communication), and the algorithm inside the drive and faster and better accounting and better electronic devices make it more superior to the inverter.
Motor: the data, structure and processing technology of servo motor are much higher than that of AC motor driven by frequency converter (general AC motor or constant torque, constant power and other types of frequency conversion motors), that is to say, when the driver outputs current, voltage, frequency change quickly power supply, servo motor can produce corresponding action changes according to the power supply change, and the response characteristics and anti-overload ability are much higher than that of AC motor driven by frequency converter, and the serious difference in motor is also the root of the difference in the functions of the two. That is to say, it is not that the inverter cannot output the power signal that changes so quickly, but that the motor itself cannot respond, so the corresponding overload setting is made in order to maintain the motor when the internal algorithm of the inverter is set to punctify. Of course, even if the output ability of the inverter is not set, there are some inverters with excellent functions that can directly drive the servo motor!
Fourth, talk about AC motors:
AC motors are generally divided into synchronous and asynchronous motors
1. AC synchronous motor: that is, the rotor is composed of permanent magnet data, so after rolling, the rotor also changes the speed according to the frequency with the change of the stator rotation magnetic field of the motor, and the rotor speed = stator speed, so it is called "synchronization".
2. AC asynchronous motor: The rotor is composed of an induction coil and data. After rolling, the stator produces a rotating magnetic field, the magnetic field cuts the induction coil of the rotor, the rotor coil produces an induced current, and then the rotor produces an induced magnetic field, and the induced magnetic field follows the change of the rotating magnetic field of the stator, but the magnetic field change of the rotor is always less than the change of the stator, once it is equal to the magnetic field that has not been changed, the induction coil of the rotor is cut open, and there is no induced current in the rotor coil, the rotor magnetic field disappears, and the rotor stalls and the stator generates a speed difference and obtains the induced current from the beginning. Therefore, in AC asynchronous motors, there is a key parameter is the slip rate, which is the ratio of the speed difference between the rotor and the stator.
3. The corresponding AC synchronous and asynchronous motors have corresponding synchronous inverters and asynchronous inverters, and the servo motors also have AC synchronous servos and AC asynchronous servos.
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