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 skill of communication servo itself is to learn and apply the skill 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 communication servo motor must have this link of frequency conversion: frequency conversion is to rectify the communication power of the power frequency of 50 and 60HZ into direct current, and then pass through various transistors (IGBT, IGCT, etc.) that can control the gate pole After carrier frequency and PWM conditioning, the waveform is inverted into a frequency-adjustable waveform similar to the pulsating electricity of sine and Cosine, because the frequency is adjustable, so the speed of the communication motor is adjustable (n=60f/p, n-speed, f-frequency, p-pole pairs)
Second, talk about the inverter:
A simple inverter can only regulate the speed of the communication motor, and whether it can open the loop or close the loop depends on the control method and the inverter, which is the traditional V/F control method. Many frequency converters have now been established by mathematical models, the stator magnetic field UVW3 phase of the communication motor is converted into the weight of the two currents that can control the speed and torque of the motor, most of the inverters of the first brand that can be used for torque control are controlled in this way, the output of each phase of UVW should add the current detection device of the Hall effect, and the PID conditioning of the current loop of the closed-loop negative feedback after sampling feedback; 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, both the speed of the motor and the torque of the motor can be controlled, and the control accuracy of the speed is better than that of V/F control, and the encoder feedback can also be added or not, and the control accuracy and echo characteristics are much better when added.
3. Talk about servo:
Driver: Under the premise of carrying out frequency conversion skills, the servo drive has carried out more advanced control skills and algorithm operations than general frequency conversion in the current loop, speed loop and position loop inside the drive (the frequency converter does not have the ring), and it is also much more powerful than the traditional servo in terms of function, and the main point is that it can be controlled by the best position. The speed and position are controlled through 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 position and speed in the driver through bus communication), and the algorithm inside the drive and faster and better calculations and better electronic devices make it superior to the inverter.
Motor: the material, structure and processing technology of servo motor are much higher than that of the communication motor driven by the inverter (general communication motor or constant torque, constant power and other types of variable frequency motors), that is to say, when the driver outputs the current, voltage, frequency of the power supply that changes quickly, the servo motor can respond to the action change according to the change of the power supply, and the echo characteristics and anti-overload can be much higher than the communication motor driven by the inverter, and the serious difference in the motor is also the basis for the different 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 protect the motor when the internal algorithm of the frequency conversion is set to be punctual. Of course, even if the output capacity of the inverter is not set, there are some inverters with excellent functions that can directly drive the servo motor!
Fourth, talk about the communication motor:
Communication motors are generally divided into synchronous and asynchronous motors
1. Communication synchronous motor: that is, the rotor is composed of permanent magnet materials, so after rolling, with the change of the stator rotation magnetic field of the motor, the rotor also responds to the speed change of the frequency, and the rotor speed = stator speed, so it is called "synchronization".
2. Communication asynchronous motor: The rotor is composed of an induction coil and a material. After rolling, the stator rotates the magnetic field, the magnetic field cuts the induction coil of the rotor, the rotor coil induces the current, and then the rotor induces the magnetic field, and the induced magnetic field follows the change of the stator rotating magnetic field, 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 changed cuts the induction coil of the rotor, there is no induced current in the rotor coil, the rotor magnetic field disappears, and the rotor stalls and the stator occurs the speed difference and obtains the induced current from the beginning. Therefore, in the communication asynchronous motor, 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 communication synchronous and asynchronous motors have corresponding synchronous inverters and asynchronous inverters, and the servo motors also have communication synchronous servos and communication asynchronous servos.
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