Application of SMC material in direct drive permanent magnet synchronous wind turbine
Although the SMC material has a lower relative magnetic permeability than the silicon steel sheet, the core has a large hysteresis loss. However, due to the characteristics of the direct-drive permanent magnet wind turbine itself, the relative magnetic permeability of the SMc material can be improved.
(1) In the direct drive wind energy conversion system, the running speed of the generator is low, so the SM (the high core loss of the material can be compensated for. At various rated powers and rated wind speeds, the operating frequency of the generator is usually 30 to 80 Hz. The core loss at this operating frequency is not the main source of the total loss of the direct-drive permanent magnet wind turbine. These losses are only a small part of the total loss. Especially compared with the stator copper loss, it is even more Less. Therefore, the high core loss of sMc materials is allowed in the design of permanent magnet wind turbines.
(2) In the design of permanent magnet wind turbine, since the permanent magnet is mounted on the surface of the rotor, the effective air gap is large, and the magnetic resistance of the magnetic circuit itself is large, so the design is not sensitive to the low magnetic permeability of the sMc material. Make up for the lower relative permeability of SMC materials.
(3) In the motor design, the minimum required stator yoke thickness is inversely proportional to the number of poles. Therefore, in a direct-drive permanent magnet wind turbine, the required yoke thickness is usually shorter and the magnetic circuit is shorter. Especially in an axial magnetic field motor, the magnetic flux is axially passed through a centrally located yokeless stator or rotor, and is returned through the outer or outer stator yoke to completely eliminate the yoke of the intermediate stator or rotor, which also allows the magnetic circuit to have Helps to compensate for the lack of SMC: the relative magnetic permeability of the material.
Based on SMC, an axial magnetic field (hereinafter referred to as AFPM) permanent magnet wind generator with two outer rotors and one inner stator is designed. The rated data is: 1.75kw, 210V, 28 poles. The SMC-based axial permanent magnet wind turbine was compared with the AFPM wind turbine using a silicon steel sheet stator core using the finite element method, as shown in Fig. 4. It can be seen that although the relative magnetic permeability of the SMC is low, the air gap magnetic density difference between the two different cores is not very large.
V. Conclusion
The low operating speed, high number of poles and the permanent magnets mounted on the rotor surface are beneficial for the application of SMC materials in the design of permanent magnet wind turbines. Furthermore, in the dual-rotor single-stator structure, the magnetic flux enters the stator from one rotor through the air gap and then enters the other through the air gap. The yoke of the intermediate stator can be eliminated, and the magnetic circuit can be further shortened to compensate for the SMC magnetic permeability. The lack of low rate. Although the magnetic permeability of the SMC material is low and the core loss is large, many other advantages of using SMC instead of the silicon steel core can completely compensate for this deficiency.
The pressing of SMC core components is the key, and the processing of SMC components will degrade performance, so further research is needed.
