The permanent magnet synchronous motor has the characteristics of high power, simple structure, small size and low noise, which we have introduced in detail before. And the selection of materials for permanent magnet synchronous motors is very important. There are several categories of materials. Everyone should be careful when choosing. So what are the excitation methods of permanent magnet synchronous motors? What are the characteristics of each excitation method? The following is a detailed introduction around these two issues.
The excitation method of the permanent magnet synchronous motor is as follows:
1. Excitation method of DC generator power supply
The generator with this excitation method has a dedicated DC generator. This dedicated DC generator is called a DC exciter. The exciter is generally coaxial with the generator. The excitation winding of the generator passes through a slip ring mounted on the large shaft. and fixed brushes draw DC current from the exciter. This excitation method has the advantages of independent excitation current, relatively reliable operation and reduced self-consumption of electricity. It has been the main excitation method of generators in the past few decades and has relatively mature operating experience. Its shortcomings are: the excitation adjustment speed is slow and the protection workload is large, so it is ly used in units above 10MW.
2. Excitation method of AC exciter power supply
Some modern large-capacity generators use AC exciters to provide corresponding excitation current. The AC exciter is also installed on the large shaft of the generator. The AC current it outputs is rectified to provide excitation for the generator rotor. At this time, the excitation method of the generator belongs to other excitation methods. Since a static rectifier device is used, it is It is called separately excited static excitation, and the AC auxiliary exciter supplies the excitation current.
The AC auxiliary exciter can be a permanent magnet measuring device or an alternator with self-excited constant voltage equipment. In order to increase the excitation conditioning speed, the AC exciter generally uses a 100-200Hz intermediate frequency generator, while the AC auxiliary exciter uses a 400-500Hz intermediate frequency generator. The DC excitation winding and three-phase AC winding of this kind of generator are wound in the stator slots. The rotor only has teeth and slots without windings, like a gear. Therefore, it does not have brushes, slip rings and other rolling contact parts, and is reliable in operation. It has the advantages of simple structure and convenient production process. Its disadvantages are: its noise is larger, and the harmonic weight of the AC potential is also larger.
3. Excitation method without exciter
In the excitation mode, there is no special exciter, but the excitation power is obtained from the generator itself, and then supplied with the generator's own excitation after rectification, which is called self-excited static excitation.
Self-excited static excitation can be divided into two methods: self-shunt excitation and self-re-excitation. The self-shunt excitation method obtains the excitation current through a rectifier transformer connected to the generator outlet, and supplies the generator excitation after rectification. This excitation method has the advantages of simple structure, less equipment, less investment cost and less maintenance work. In addition to the rectifier transformer, the self-re-excitation method also has a high-power current transformer connected in series with the stator circuit of the generator.
The function of this transformer is to provide a larger excitation current to the generator in the permanent magnet synchronous motor to compensate for the lack of output of the rectifier transformer when a short circuit occurs. This excitation method has two excitation power sources, a voltage power source obtained through a rectifier transformer and a current source obtained through a series transformer.
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