1. Number of blades
According to the number of wind turbine blades, it is divided into few blades and multi-blade types. Generally, if the number of blades is less than or equal to 4, it is called a few-blade wind turbine. Few-blade wind turbines are the mainstream models of current wind turbines. Its high speed, light wind turbine, compact structure, high wind energy utilization coefficient when wind speed is high, so it is mostly used in areas with high average annual wind speed. At present, the commonly used horizontal axis wind turbines are mostly three blades. Multi-blade wind turbines generally have 5 to 24 blades, which are characterized by larger starting torque and lower starting wind speed. When the wind speed is low, the wind turbine has a higher wind energy utilization coefficient, so it is mostly used in areas where the average annual wind speed is lower than 3~4m/s. It is suitable for directly driving agricultural and animal husbandry machinery and equipment, such as windmills to take water. Figure 1 shows a wind turbine with different blades.
2. How the blade works
According to the working principle of the blades, wind turbines can be divided into lift-type and drag-type wind turbines. The use of the lift of the wind turbine blade airfoil to realize the operation of the wind turbine is called a lift-type wind turbine, and the force on the impeller is perpendicular to the relative wind speed on the blade;
The use of aerodynamic resistance to achieve the work of the wind turbine is called a resistance wind turbine. Figure 2 shows a schematic diagram of the lift and drag generated by the wind turbine blade airfoil.
For horizontal-axis wind turbines, when the lift-type blades are used, the rotation speed is fast, and the resistance-type blades rotate at a slow speed. For vertical axis wind turbines, the force can also be divided into lift type and drag type. The wind wheel torque of a lift-type vertical axis wind turbine is provided by the lift of the blades, such as a Darrie (commonly known as an egg beater) fan. The resistance torque of the wind wheel is formed by the different resistance of the two sides. Wind wheels made of flat plates and cups are all resistance-type fans. There is also an S-type fan, which has partial lift and mainly relies on resistance to rotate. The three fan types are shown in Figure 3. Because the aerodynamic efficiency of the resistance type wind turbine is much lower than that of the lift type, and for a given wind turbine quality and cost, the lift type wind turbine has a higher power output. Therefore, lift-type wind turbines are the mainstream of current wind turbines.
3. Wind turbine capacity
According to the classification of the output capacity of wind turbines, wind turbines are usually divided into three types: small (below 100kW), medium (100~1000kW) and large (above 1000kW). In China, there are four types: micro (below 1kW), small (1-10kW), medium (10-100kW), and large (above 100kW). There are also four types of wind turbines above 1,000kW as giant wind turbines.
4. Power adjustment method
According to the power adjustment method, it can be divided into fixed pitch type and variable pitch type. The blades of the fixed-pitch stall type wind turbine are fixedly connected with the hub. When the wind speed changes, the blade pitch angle cannot change accordingly. Rely on the action of the spoiler at the blade airfoil or blade tip to limit the output torque and power. The structure is simple, the performance is reliable, the cost is low, and the maintenance is low, but the blade structure is more complicated and the molding process is difficult. At high wind speeds, the variable pitch type can limit the output torque and power by changing the pitch angle. Its power output is stable and the wind energy utilization factor is high, but the wheel hub structure is complex, the manufacturing and maintenance costs are high, and the reliability is poor.
5. Wind wheel speed
According to the speed of the wind wheel, the wind turbine can be divided into a fixed speed type and a variable speed type. The fixed-speed wind wheel has a constant speed and low wind energy utilization. The variable speed type also has a continuous speed type and a two-speed type. The speed of the continuously variable wind wheel is continuously adjustable and the efficiency is the highest. The two-speed type can run at two set speeds, adapt to low wind speed and high wind speed respectively, and improve the utilization rate of wind energy.
6. Other categories
According to whether there is a gearbox, it can be divided into direct drive type and speed-up type. The direct-drive type directly connects the low-speed wind turbine and the low-speed generator. The speed-up type uses a gearbox to connect a low-speed wind turbine with a high-speed generator.
According to the generator type, it can be divided into asynchronous generator type and synchronous generator type. As long as a suitable converter device is selected, it can be applied to variable-speed wind power generation systems.
According to the voltage of the output terminal, it can be divided into high-voltage wind turbine and low-voltage wind turbine. Low-voltage wind turbines are mainly used in distributed power generation systems.