Due to its simple structure, no need for excitation windings and high efficiency, permanent magnet synchronous generators are widely used in small and medium-sized wind turbines. With the improvement of high-performance permanent magnet materials manufacturing technology, large-capacity wind power generation systems also tend to use Permanent magnet synchronous generator. Permanent magnet wind turbines are commonly used in variable speed constant frequency wind power generation systems. Wind turbine rotors are directly dragged by wind turbines, so the speed is very low. Since the speed-increasing gearbox is removed, the reliability and life of the unit are increased; the magnetic pole is composed of many high-performance permanent magnets, unlike the electric excitation synchronous motor, which requires a complicated and bulky field winding, which improves the air gap. Magnetic density and power density reduce the motor volume at the same power level.
The permanent magnet synchronous generator is divided into an outer rotor and an inner rotor.
For a typical outer rotor permanent magnet synchronous generator structure, the inner rotor has a magnetic pole formed by a high magnetic energy product permanent magnet material, and the inner stator is embedded with a three-phase winding. The outer rotor design enables more space to be placed on the permanent magnet poles, and the centrifugal force when the rotor rotates makes the poles more secure.
Since the rotor is directly exposed to the outside, the cooling condition of the rotor is better. The problem with the outer rotor is the cooling of the stator of the main heat generating component and the transportation of the large size motor.
The inner rotor permanent magnet synchronous generator is a rotor with a permanent magnet pole and a wind turbine, and the outside is a stator core. In addition to the advantages of the conventional permanent magnet motor, the inner rotor permanent magnet synchronous motor can utilize the natural wind conditions outside the frame to effectively improve the cooling conditions of the stator core and the winding. A certain cooling effect. In addition, if the outer diameter of the motor is greater than 4m, it will often bring some difficulties to transportation. Many wind farms are designed in remote areas. From the factory to the installation site, it is likely to pass through some bridges and culverts. If the outer diameter of the motor is too large, it will not pass smoothly. The inner rotor structure reduces the size of the motor and often facilitates transportation.
In the inner rotor permanent magnet synchronous generator, there are four types of rotor magnetic circuits, which are radial, tangential, and axial. Compared with other rotor magnetic circuit structures, the radial magnetization structure has a small magnetic flux leakage coefficient because the magnetic pole directly faces the air gap, and the yoke is a monolithic magnet, which is convenient to implement; and in the radial magnetization structure, The air gap magnetic induction intensity is close to the magnetic induction intensity of the working point of the permanent magnet. Although there is no air gap magnetic density as large as the tangential structure, it is not too low, so the radial structure has obvious superiority and is also in the design of large wind turbines. Apply more rotor magnetic circuit structure.
