- Current situation of small wind power in China
In order to meet the growing demand of people’s living and production power in China’s rural areas and foreign markets, China has developed small horizontal axis wind turbines with unit capacity of 100W, 200W, 300W, 500W, 1kW, 1.5KW, 2kW, 5kW, 10kW, 20kW, 30kW, 50KW and 100kW and small vertical axis wind turbines with unit capacity of 400W ~ 10kW. By the end of 2012, China had installed 500000 small wind turbines of various types, It is home to about 400000 farmers, herdsmen and fishermen in China (about 200 people provide household electricity. After using small wind turbines, the living conditions of local users have been significantly improved. At present, about 250000 small wind turbines are in operation all over China to supply power for users’ daily life. In the past five years, about 150000 small wind turbines have been exported to other countries and regions. Now, there are 200 W, 300 W, 500 W, 800 V, 1 kW, 1.5 kW and 2 W small wind turbines The unit has been widely used in agricultural and pastoral areas far away from the power grid in China; 5kW and 10kW small wind turbines have been applied in China’s agricultural and pastoral areas and communication base stations in batches; 20kW and 30kW small wind turbines have been demonstrated and applied in oil fields in China. At the same time, China’s 10kW, 20kW, 30kW and 50KW small wind turbines are exported in batches to European and American developed countries for grid connected applications. Recently, a small amount of 100W wind turbines made in China have also been exported to the markets of developed countries.
- Composition of small wind power generation system
1) Principle and structure
The principle of small wind turbine is to use the wind to drive the wind wheel of the wind turbine to rotate, and transmit the torque to the generator to drive the generator to generate electric energy. The AC power generated by the wind turbine generator is directly charged to the battery pack or supplied to the DC load after rectification; It can also supply power to AC loads (single-phase or three-phase) via converters. When there is no wind and the wind turbine generator cannot operate for power generation, the off grid wind turbine generator system shall also be equipped with battery pack in order to maintain the uninterrupted power supply of the system.
Small wind power generation system, also known as small wind turbine, has a relatively simple structure, which is usually composed of blades, wheel hubs, gearbox, generator, main frame, yaw mechanism, control device, hood and tower. For small wind power generation system, in order to simplify the structure and reduce the cost, there is generally no gearbox and active yaw mechanism.
2) Wind wheel
Wind turbine is the most critical component of wind turbine, which converts aerodynamic energy into mechanical energy. The wind turbine is generally composed of blades, hub cover plate, connecting bolt assembly and shroud.
3) Wind turbine generator
Generator is the core equipment of wind power generation. It uses electromagnetic induction to convert the mechanical energy of rotating wind turbine into elecWind turbine generatortrical energy.
Small wind turbines mainly use low-speed permanent magnet generators. This is mainly because the wind wheels of small wind turbines are directly coupled to the generator shaft, eliminating the speed raising mechanism. Therefore, the generator speed is required to be only a few hundred revolutions per minute, so low-speed generators are used. Miniature and small wind turbines with a capacity of less than 10kW adopt permanent magnet or self-excited alternator to supply power to the load and charge the battery after rectification.
4) Opposite wind device
The wind device is also known as the windward mechanism. The horizontal axis wind turbine involves the adjustment of the relative position between the rotation plane of the wind turbine blade and the air flow direction. Within the limited range of cut-in and cut-out wind speed, in order to make the wind turbine obtain the maximum energy from the flowing air, that is, to maximize the output power of the wind turbine, it is necessary to make the rotation plane of the wind turbine blade perpendicular to the air flow direction, that is, facing the wind direction. When the wind speed is high, in order to ensure the safety of the wind turbine, the wind wheel can be forced to deviate along the wind direction by twisting the wind device, so as to reduce the windward area of the wind wheel to achieve the purpose of speed regulation. When the wind speed reaches the limited wind speed, the rotation plane of the wind wheel can be parallel to the wind direction to stop the vehicle.
5) Revolving body
The rotating body is the key component of the wind turbine, the carrier of the wind wheel, generator and tail wing, and a bearing structure installed on the top of the tower. The rotating body of some wind turbines is integrated with the generator. The rotating body can rotate around the vertical axis of the tower at 360? A mechanism that rotates freely in the horizontal direction. The rotating body and tail wing are the necessary components to realize the direction (wind) and speed regulation of the wind wheel.
6) Speed regulating device
Because the wind in nature is unstable and pulsating, the wind speed is large and small, and sometimes strong wind and storm will occur. The speed of the wind turbine impeller changes with the change of wind speed. If there is no speed regulation mechanism, the speed of the wind turbine impeller will become higher and higher with the increase of wind speed. In this way, the centrifugal force generated on the blade will increase rapidly and even damage the impeller. In addition, with the increase of wind speed and impeller speed, the output power of wind turbine generator will inevitably increase, and the overload capacity of rotor coil and other electronic components of wind turbine generator has a certain limit and can not be increased at will. Therefore, in order to have a stable power output, the wind turbine must be equipped with a speed regulating mechanism.
7) Braking device
The purpose of the hand brake mechanism of small wind turbine generator is to stop the wind turbine temporarily (stop rotation). In case of severe wind, the wind turbine can be stopped urgently. In order to repair the wind turbine and stop the rotation of the wind turbine in a planned way, the wind turbine can be braked through the hand brake mechanism, or the wind turbine can be deflected parallel to the tail wing plate.
8) Tower
The main function of the tower of small wind turbine is to support the weight of the wind turbine, but also to bear the wind pressure blowing to the wind turbine and tower, as well as the dynamic load during the operation of the wind turbine.
- Composition of small wind power generation system
Small wind power generation system is composed of wind turbine, control device, energy storage device and electrical load of electric energy users. Wind turbine is the key equipment for converting wind energy into electric energy. Due to the randomness of wind energy and the change of wind power from time to time, the wind power generation system must timely adjust and control the startup, operation status (speed, voltage, frequency), shutdown, fault protection (overspeed, vibration, overload, etc.) of wind turbine through the control device according to the change of wind power and power demand, as well as the connection, adjustment and disconnection of power user load. In order to ensure that power users can continuously obtain electric energy during the period of no wind, the system also needs to be equipped with energy storage device. At the same time, when the wind energy increases sharply, the energy storage device can store excess electric energy for use in case of no wind. In order to realize uninterrupted power supply, the wind power generation system can also be equipped with inverter power supply and standby diesel generator set.
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