What is a synchronous motor

A synchronous motor is also an AC motor. It is mainly used as a generator, but also as a motor. It is generally used for production machinery with high power and no adjustment of speed, such as large water pumps, air compressors and mine fans. In recent years, due to the development of permanent magnet materials and electronic technology, miniature synchronous motors have become more and more widely used.

One of the characteristics of a synchronous motor is that there is a strict and unchanging relationship between the speed n during stable operation and the frequency f1 of the stator current, namely;

The speed n of the synchronous motor is the same as the speed n0 of the rotating magnetic field. The name "Synchronization" comes from this.

Synchronous motors run on excitation current. If there is no excitation, the motor is asynchronous. Excitation is a DC system added to the rotor. Its rotation speed and polarity are the same as those of the stator. If there is a problem with the excitation, the motor will lose step and cannot be adjusted, triggering the protection "excitation failure" motor trip

To put it more plainly, the excitation current is the current flowing in the rotor of the synchronous motor (with this current, the rotor is equivalent to an electromagnet with N poles and S poles). In normal operation, this current is externally applied to the rotor. Generated by the DC voltage. In the past, this DC voltage was supplied by a DC motor, but now it is mostly supplied by a silicon controlled rectifier. We usually call the SCR rectifier system an excitation device.

The asynchronous machine means that the speed of the rotor of the motor is inconsistent with the speed of the rotating magnetic field generated by the stator, and there is a difference (not synchronized). We call it a turnaround. The ratio of this slip to the rotation speed of the rotating magnetic field generated by the stator is called the slip rate.

The difference between the synchronous machine and the asynchronous machine is that: from the power supply aspect, the asynchronous machine only applies voltage to the stator side (there is also the voltage applied to the rotor), while the synchronous machine needs to apply voltage to both the stator and the rotor. That is to say, asynchronous motors are unilateral excitation, and synchronous motors are bilateral excitation. In terms of speed, the speed of the asynchronous machine is only related to the size of the load (of course there is a certain range), and the speed of the synchronous machine is only related to the frequency of the power grid. Structurally speaking, the structure of the rotor of a synchronous motor and an asynchronous motor is different. The rotor of an asynchronous motor is composed of a steel sheet and an aluminum bar (or a steel sheet and a coil), while a synchronous machine is generally composed of several pieces of magnetic steel and coils (there are also hidden poles that are not the same). Of course, there are many differences, such as process requirements, design issues, etc. I can't say enough, please discuss them together.