In many cases, no matter how the wind speed changes, the speed of the generator should be kept constant or not exceed a certain limit value. For this reason, a speed regulation or speed limit device is adopted. When the wind speed is too high, these devices are also used to limit the power output and reduce the force acting on the blades. There are various types of speed-regulating or speed-limiting devices, but in principle, there are roughly three types: one is to make the impeller deviate from the main wind direction; the other is to use aerodynamic resistance; the other is to change the pitch angle of the blade.
(1) Wind wheel side deviation speed regulation method.
The principle of side speed regulation of the wind wheel is that when the wind speed is greater than the rated wind speed, the wind wheel is forced to sideways along the wind direction by twisting the wind wheel, so that the wind wheel deviates from the wind direction and reduces the windward area of the wind wheel, thereby reducing the absorption of wind energy. When the wind speed reaches the cut-out wind speed, the rotating surface of the wind wheel is parallel to the wind direction, and the wind generator stops generating electricity. There are two ways to adjust the speed of the wind wheel.
①Flanking speed regulation method. The side wing speed regulation is to install a side wing parallel to the rotating surface of the wind wheel behind the wind wheel, and the side wing beam should be parallel to the ground. The side wing plate extends beyond the rotating diameter of the wind wheel and is parallel to the rotating surface. The windward area of the flanks is based on the standard that the wind pressure on the flanks when the wind speed reaches the speed limit is sufficient to make the wind wheel twist. It is determined through strict design and tests and cannot be changed at will. The principle of side wing speed regulation is shown in Figure 1(a). When the wind speed has not reached the speed limit wind speed, the wind wheel will be in the position facing the wind direction under the action of the tail wing, which is the working position. When the wind speed reaches or exceeds the speed limit wind speed, the wind pressure on the side wing panels is sufficient to overcome the pulling force of the spring or the counterweight, and drive the wind wheel to twist an angle along the wind direction to bring it closer to the tail (direction adjustment mechanism). At this time, due to the change of the wind-facing angle of the wind wheel, the wind-facing area becomes smaller, and the rotation speed is reduced accordingly, achieving the purpose of speed regulation. When the wind speed continues to increase and reaches the braking wind speed or exceeds the braking wind speed, the wind wheel will twist to a position that is completely close to the tail wing, that is, the position completely following the wind direction, and stop rotating to achieve the purpose of braking. The return of the wind wheel after twisting is achieved by the spring or counterweight on the side of the wing, that is, when the wind speed decreases below the speed limit, the spring or counterweight will pull the revolving body back to its original position.
Figure 1 Schematic diagram of wind wheel side wing speed regulation and eccentric speed regulation
② Eccentric speed regulation method. The so-called eccentricity refers to a certain distance between the horizontal rotation axis of the wind turbine rotor and the vertical rotation axis of the wind turbine revolving body. This distance is called the eccentricity. When the wind is strong, this eccentricity can cause the wind wheel to produce a torque that twists in the direction of the wind. The advantage of this speed regulation method is its simple structure. At present, most of the small wind turbines in our country have adopted the wind wheel eccentric speed regulation method, and its working principle is shown in Figure 1(b). There is an eccentricity e between the axis of the wind wheel and the center of rotation of the slewing body. When the wind speed acts on the wind wheel, a moment Me that forces the wind wheel to twist is produced. When the wind speed has not reached the speed limit, Me is smaller than the nose support. At this time, the wind turbine is in the working state of Figure 1 (b1). When the wind speed increases, the wind pressure acting on the wind wheel also increases, and the eccentric moment Me also increases. If M is greater than the friction When the moment Me, the wind wheel starts to sideways, as shown in Figure 1 (b2). If the wind speed is kept at a constant value at this time, the wind pressure on the wind wheel will be reduced because the wind wheel is already sideways, and the speed of the wind wheel will be reduced accordingly, so as to achieve the purpose of speed regulation. At this time, the eccentric moment Me is balanced with the friction moment Me; if the wind speed continues to increase, it is the eccentric moment M. Continue to increase, the wind wheel continues to sideways, its limit position is shown in Figure 1 (b3).
(2) The blade variable pitch speed regulation method.
The principle of blade pitch variable speed regulation is that when the wind speed is greater than the rated wind speed, a certain mechanism uses the centrifugal force of the wind turbine blade to change the pitch, reducing the wind energy utilization rate of the wind turbine, so as to achieve the effect of reducing wind energy absorption. When the wind speed is greater than the cut-out wind speed, the blades are parallel to the wind direction, and the wind generator stops generating electricity. The variable pitch speed regulation method is when the wind speed reaches the speed limit wind speed, forcing the blade to rotate an angle around the blade handle to change the angle of attack of the blade, thereby changing the lift and resistance of the blade, and achieving the purpose of speed regulation.
Figure 2 is a schematic diagram of the variable pitch speed regulation mechanism of the FD2-100 wind turbine. The spring sleeve is equipped with a starting spring and a speed regulating spring. The blades have a larger installation angle when installed, which is convenient for starting at low wind speeds. After the wind wheel rotates, under the action of centrifugal force, the blade stretches and compresses the start spring. At the same time, under the action of the screw pair, the blade twists quickly into the best angle of attack state. If the wind speed continues to increase, the centrifugal force of the blades also increases, and the speed regulating spring starts to work at this time. In the same way, under the action of centrifugal force, the blades are stretched outwards (driving the blade shaft also stretches outwards). Due to the effect of the screw pair, the blades are twisted to a negative angle of attack, and the rotor speed is significantly reduced to achieve speed regulation. the goal of. When the wind speed decreases, under the action of the spring tension, the blades return to the working position before the speed control state. In this way, the rotation speed of the wind wheel is kept within a certain range.
(3) Air brake speed regulation method.
The air brake speed regulation method uses the method of increasing the blade resistance on the blades to achieve the purpose of speed regulation. The simplest device to increase the resistance is the air brake, such as installing flaps on the blades, as shown in Figure 3. Show. The flaps are fixed on the shaft and installed on both sides of the blades. The shaft is rotated by a lever connected to a tie rod. The outer end of the tie rod is equipped with a weight. At the other end of the tie rod is a spring and a ring lever. Installed on the wind wheel shaft. At normal speed, the flaps are parallel to the airflow, so there is not much resistance. If the angular velocity of the wind wheel is greater than the normal speed, under the action of centrifugal force, the weight starts to move in the radial direction to the outer end of the blade, and the shaft of the flap is rotated by the action of the pull rod to make the plane opposite to the direction of rotation. At this time, the resistance increases to brake the wind wheel, and when the wind speed decreases, the spring turns the flap to its original position.