1. Classification of wind turbines
The wind turbine is mainly composed of two parts:
The wind turbine part – it converts wind energy into Mechanical energy;
The generator part – which converts mechanical energy into electrical energy.
According to the different types of structures adopted by the two major parts of the wind turbine, the different characteristics of the technical solutions adopted by them, and their different combinations, wind turbines can be classified into various categories.
1. According to the direction of the rotating main shaft of the fan (that is, the relative position of the main shaft and the ground), it can be divided into:
“Horizontal axis fan”— ―The rotating shaft is parallel to the ground, and the impeller needs to be adjusted with the change of the wind direction;
“Vertical shaft fan”―The rotating shaft is perpendicular to the ground, the design is relatively simple, and the impeller does not need to be adjusted with the change of the wind direction direction.
2. According to the force of the blades, it can be divided into “lift type fan” or “drag type fan”.
3. According to the number of blades, it can be divided into “single-blade”, “double-blade”, “three-blade” and “multi-blade” fans.
The number of blades is determined by many factors, including aerodynamic efficiency, complexity, cost, noise, aesthetic requirements, and more.
Large wind turbines can be constructed with 1, 2 or 3 blades.
Wind generators with fewer blades generally require higher rotational speeds to extract energy from the wind, and are therefore louder. And if there are too many blades, they will interact with each other and reduce the efficiency of the system. At present, 3-blade wind turbines are the mainstream. From an aesthetic point of view, the 3-blade wind turbine looks more balanced and beautiful.
4. According to the direction in which the fan receives the wind, there are “upwind type” – the front of the impeller faces the wind direction (that is, it rotates in front of the tower) and “downwind type” ——The back of the impeller is along the wind direction, there are two types.
Upwind fans generally require some sort of directional control to keep the impeller facing the wind.
The downwind fan can automatically align with the wind direction, thus eliminating the need for a directional device. However, for the downwind fan, since a part of the air passes through the tower and then blows to the impeller, the tower interferes with the airflow passing through the blades and forms the so-called tower shadow effect, which reduces the performance.
5. According to the different mechanical connection methods of power transmission, it can be divided into “fan with gearbox” and “direct-drive fan” without gearbox .
The blade of the fan with gearbox transmits the torque to the drive shaft of the generator through the gearbox and its high-speed shaft and the universal elastic coupling. The characteristics of absorbing damping and vibration can absorb the right amount of radial, axial and angular deflection, and the coupling can prevent the overload of the mechanical device.
The direct-drive fan takes a different approach and adopts a number of advanced technologies. The torque of the blade can be directly transmitted to the drive shaft of the generator without increasing the speed of the gearbox, so that the electric energy generated by the fan can be generated. The output can also be connected to the grid. Such a design simplifies the structure of the device, reduces the probability of failure, and has many advantages, and is now mostly used in large-scale units.
6. According to the power adjustment method of receiving wind energy according to the blade, it can be divided into:
“fixed pitch (stall type) unit” – propeller The connection of the blade to the hub is fixed. When the wind speed changes, the windward angle of the blades cannot be changed accordingly. Due to the simple structure and reliable performance of fixed-pitch (stall type) units, they have been dominant in the development and utilization of wind energy for 20 years.
“Variable pitch unit”——The blade can rotate around the central axis of the blade, so that the angle of attack of the blade can be adjusted and changed within a certain range (generally 0-90 degrees), and its performance is higher than that of the fixed pitch type Many, but the structure also tends to be complex, and now they are mostly used in large units.
7. According to whether the impeller speed is constant or not, it can be divided into:
“Constant speed wind turbine” – simple and reliable design, low cost and maintenance The disadvantages are: low aerodynamic efficiency, high structural load, causing grid fluctuations to the grid, and absorbing reactive power from the grid.
“Variable speed wind turbine” – high aerodynamic efficiency, low mechanical stress, small power fluctuation, high cost efficiency, light support structure. The disadvantages are: the power is sensitive to voltage drop, the price of electrical equipment is high, and the maintenance is large. It is now commonly used in large-capacity main models.
8. According to the classification of wind turbine generator types, it can be divided into two categories: “Asynchronous generator type” “Synchronous generator type”
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All of them can be used for variable speed fans as long as the appropriate converters are used.
Asynchronous generators can be divided into:
(a) squirrel-cage asynchronous generators – the rotor is squirrel-cage. Because of its simple and reliable structure, low cost and easy access to the power grid, it is widely used in small and medium-sized units.
(b) Wire-wound doubly-fed asynchronous generators—the rotor is of wire-wound type. The stator is directly connected to the grid to transmit electric energy, and the wound rotor is also controlled by the inverter to transmit active or reactive power to the grid.
Synchronous generators can be divided into:
(a) Electric excitation synchronous generators – the rotor is a wire-wound salient pole type , which is excited by an external DC current to generate a magnetic field.
(b) Permanent magnet synchronous generator – the rotor is a permanent magnet pole made of ferrite material, usually a low-speed multi-pole type, without external excitation, which simplifies the generator structure, so it has a variety of Advantage.
9. According to the level of the output voltage of the wind turbine, it can be generally divided into:
“High-voltage wind turbine” – wind turbine output The terminal voltage is 10~20kV, or even 40kV, which can save the booster transformer of the fan and directly connect to the grid. It is an overall scheme of synchronous generator composed of direct drive type and permanent magnet magnetic pole structure, which is a promising type of wind generator at present.
“Low-voltage wind turbine” – the output voltage is below 1kV, and most of these models are currently on the market.
10. According to the rated power of the fan, it can be generally divided into:
Microcomputer: below 10 kW
Small Machines: 10 kW to 100 kW
Medium Machines: 100 kW to 1000 kW
Large Machines: Above 1000 kW (MW Class Fans)
2. The difference between vertical axis wind turbine and horizontal axis
1. Different generators: vertical axis generators generally use ironless permanent disk motors or external rotor motors. The torque is small, and it can be started in a breeze, which is quite suitable for use in cities or areas with low wind speed such as southern China; horizontal axis generators generally use low-cost iron-core generators, and the starting torque is often large, which is not suitable for urban roads, And the use of low wind speed such as southern China.
2. The structure of the wind blades is different: the wind turbine with the vertical axis is a vertical structure that receives the wind in all directions. Regardless of the incoming wind in any direction, it keeps rotating in the same direction, making better use of the wind energy; The horizontal axis wind turbine has a tail specially used to adjust the wind direction of the wind turbine. Every time the wind comes, the wind direction of the fan must be adjusted first, which not only wastes wind energy, but also the horizontal wind turbine. A transmission bearing has to be installed between the flange supporting the motor. If the bearing is driven too much, it will cause mechanical fatigue and cause the fan to break or fall off easily.
3. Under the same wind speed conditions, the vertical axis power generation efficiency is higher than that of the horizontal type, especially in low wind speed areas.
4. In high wind speed areas, vertical axis wind turbines are safer and more stable than horizontal wind turbines; in addition, a large number of cases at home and abroad have proved that horizontal wind turbines often do not rotate in urban areas. In the high wind speed areas such as the north and northwest, problems such as breaking and falling off of fans are often prone to occur, causing dangerous accidents such as pedestrians and vehicles on the road.
5. Wind energy utilization rate, China Aerodynamics Research and Development Center has conducted wind tunnel experiments on related horizontal axis wind turbines, and the measured utilization rate is about 23%-29%. Experiments by the China Aerodynamics Research and Development Center show that the wind energy utilization rate of the vertical axis is above 40%. In addition, in the actual environment, the wind direction changes frequently, and the windward side of the horizontal axis wind rotor cannot always face the wind, which causes “wind loss”, while the vertical axis wind rotor does not have this problem. Therefore, considering After taking into account the wind loss, the wind energy utilization rate of the vertical axis wind rotor completely exceeds that of the horizontal axis wind rotor.
From the perspective of various factors, the vertical axis wind turbine is the development direction of wind power in the future. Since the horizontal axis wind turbine has been produced and developed in China for nearly 20 years, the development and production of Years, so as its advantages appear, it will gradually become popular like a horizontal axis.
