1. Fixed blade lift type vertical axis wind turbine
However, the wind power cannot be stabilized, and the wind turbine load will not change. When the wind speed increases rapidly, the wind turbine speed cannot be synchronized immediately, the tip speed ratio may fall below 3.5, and the wind turbine may suffer from the reverse torque. Unstable operation; this situation also occurs when the wind turbine load increases and the speed decreases to the tip speed ratio. The wind turbine will drop faster due to the load speed when the wind speed drops. This may also occur. Requiring a narrow range of wind or load variation is a major problem for fixed-blade lift-type vertical-axis wind turbines. The inability to self-start is also an important drawback of fixed-blade lift-type vertical-axis wind turbines, which imposes many limitations on applications.
2. Lifting type vertical axis wind turbine airfoil adjustment mode
In the horizontal axis wind turbine, the variable pitch angle method is adopted to adapt to the change of wind speed, adjust the relationship between wind speed and load, and the running performance can be improved by changing the airfoil in the vertical axis wind turbine. Here are some ways to analyze the airfoil and its advantages and disadvantages:
1) Change the angle of the blade according to the angle specified by the program
It is best to use a microprocessor to control the angle of the blade, but this article does not discuss the use of microprocessor control to discuss only the angle of the blade with the simplest mechanical method.
The cam angle or the eccentric wheel is used to adjust the blade angle of attack. The blade has a blade rotation axis in the longitudinal direction of the blade. The blade is mounted on the blade bracket of the wind wheel through the blade rotation shaft, and the connecting rod pulls the blade to rotate, and the connecting rod is controlled by the cam or the eccentric wheel. It is also equipped with a wind-driven device to control the cam by the wind direction. The cam is designed according to the set control law to make the blades run to different positions and turn to a predetermined angle.
This wind turbine is self-starting and can operate over a wide range of wind speeds.
The disadvantage is that since the rotation angle of the blade at each position is fixed with respect to the wind direction, regardless of the wind speed, it has high conversion efficiency only for the designed wind speed, and at other wind speeds, the blade angle of attack is not necessarily optimal, in normal The blades should not oscillate substantially during operation, so this fixed oscillating law is such that large conversion efficiencies cannot be obtained at wider wind speeds.
Structural disadvantages: complex structure, large mechanical wear, not suitable for harsh environments, and high noise.
2) Use the wind and the block to control the angle of the blade
The advantage of this approach is that the wind turbine can be self-starting and can operate at low wind speeds to high wind speeds.
The disadvantage is that when the blade is moved to an area near 90 degrees or 270 degrees, the blade swings to the position between the two sides of the bar, in a downwind position, and there is no lift and only resistance. Moreover, as the tip speed ratio increases, the blade is in the downwind area; if the blade can swing in the range of ±15 degrees, the highest tip speed ratio of the blade will not exceed 4, because the tip speed ratio exceeds 4, The blades are in the downwind position for the entire rotation of the rotor. There is no resistance to lift, and even if there is no load, the speed will not increase. Therefore, if the range of the blade swingable exceeds ±15 degrees, the wind turbine utilization efficiency of the wind turbine will be significantly reduced. If the blade swingable range is less than ±15 degrees, the wind turbine self-starting capability will be poor.
The advantages from the structural point of view are: simple structure, minimal movement pair, easy processing, installation and maintenance. The disadvantage is that frequent impact on the block is likely to cause damage to the component and noise.
3) Using the wind and centrifugal stops to control the angle of the blade
4) Using the wind and centrifugal stops to control the angle of the blade
3, using wind and centrifugal force to directly control the angle of the blade
Structurally speaking, the mechanism is simple, and the motion pair only has a blade and a wind wheel bracket connected through a bearing, which is reliable in operation, easy to process and install, easy to lubricate and seal, low in price, and basically requires no maintenance. After the wind turbine is running, the balance of the wind and the centrifugal force controls the swing angle of the blade, and does not hit the shift lever, and there is no noise.
However, this solution requires that the blade has a small moment of inertia, which requires high material selection and structural design.
to sum up
The above several simple airfoil control methods have improved the performance of the lift vertical axis wind turbine, the lower wind speed can be started, and the tip speed ratio exceeds 1 to have power output. The two schemes of controlling the angle of the blade by using the wind and the centrifugal block and the angle of directly controlling the blade by using the wind and the centrifugal force are more suitable. The former problem is that the production is complicated and the maintenance amount is large, and the latter problem is that the cost of the light blade is high.
However, these methods can not solve the problem of limiting the speed of the wind turbine when the wind speed is high. For large and medium-sized wind turbines, it is still necessary to change the airfoil to control the speed of the wind wheel, which is the final way of the lift vertical axis wind turbine.
