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The impeller of the doubly-fed wind turbine drives the generator through a multi-stage gearbox. The main structure includes the wind wheel, transmission device, generator, converter system, control system, etc.The doubly-fed wind turbine system converts the mechanical energy transmitted from the gearbox to the generator main shaft into electrical energy, and transmits it to the grid through the generator stator and rotor.
The doubly-fed wind turbine has the advantages of mature technology, reliable quality, high efficiency, excellent cost performance, good maintainability, good power quality, and strong low voltage ride through capability. However, the gearbox is a component with a high failure rate and is installed in a small space on the top of the tower. Once a failure occurs, it is very difficult to repair it.

The direct-drive permanent magnet wind turbine eliminates the heavy speed-increasing gearbox. The generator shaft is directly connected to the impeller shaft. The speed of the rotor changes with the wind speed, and the frequency of its alternating current also changes. The power electronic converter rectifies alternating current with variable frequency into direct current, and then inverts it into alternating current output with the same frequency as the grid.Its main components include: impeller blades, hub, pitch system, generator rotor, generator stator, yaw system, wind measurement system, bottom plate, tower, etc. Its advantages include strong grid compatibility, low maintenance cost, low noise, etc., but it is difficult to transport and hoist.

The concept of semi-direct drive came into being when the direct drive and doubly-fed wind turbines were developing towards large-scale development, taking into account the characteristics of both. From the structural point of view, semi-direct drive and double-fed are relatively similar, with the characteristics of various layout forms, but the appearance is similar to that of direct drive. Semi-direct drive and double-fed and direct-drive fans are different. One is that the transmission ratio of the semi-direct-drive gearbox is lower than that of the double-fed model, the other is that the semi-direct-drive generator is with higher speed compared with the direct-drive model. This determines that on the one hand, the semi-direct drive can improve the reliability and service life of the gearbox, and at the same time, compared with the direct drive generator, it can take into account the corresponding generator design and improve the design and manufacturing conditions of the high-power direct drive generator.