1. Field of Invention
The invention relates to wind turbines and, more particularly, to a small horizontal axis wind turbine having an automatic blade pitch angle control mechanism including lateral torsion bars fastening a hub and each blade together so that a rotational torque, as a result of blade rotation, can change blade pitch angle automatically, with the wind turbine being adapted to activate under low speed wind, to have a high CP (power coefficient) under high speed wind, and to protect the blades under strong gusts.
2. Description of Related Art
A typical small wind turbine has blades secured directly to a hub (i.e., fixed pitch blades). It is desired that the wind turbine can be activated under low speed wind and have a large CP under high speed wind. The two goals are difficult to achieve at the same time for wind turbines with fixed pitch blades.
Another type of typical wind turbine has blades capable of being temporarily deformed in response to wind speed to increase efficiency of harnessing the wind power. However, its fabrication is very complicated and costly due to technological difficulties. Furthermore, the strength of such blades can be greatly weakened by the repeating deformations. Consequently, their lifetime is shortened significantly.
As for the protection of the blades in strong winds, the side-furling mechanism is mostly used. The mechanism turns the wind turbine away from the strong wind and returns it back to the calming wind. The advantage of the mechanism is its simplicity in principle. Its disadvantages are twofold: 1. Even though the turbine outputs power when it slightly furls, the power reduces greatly due to the highly sensitive nature of horizontal axis wind turbines to the yaw angle; and 2. In response to strong gusts, returning from furling takes time and consequently reduces the overall efficiency. Thus, the need for improvement still exists.