Wind power generation has three operating modes: First, independent operation mode, usually a small wind turbine provides power to one or several households, it uses a battery to store energy, to ensure the use of electricity when there is no wind; Second, wind power generation and Other power generation methods (such as diesel power generation) combine to supply electricity to a unit or a village or an island. Third, wind power is integrated into conventional power grids to provide power to large grids. It is often a dozen or even several wind farms. 100 wind turbines, which is the main direction of development of wind power.
The two main components in wind power systems are wind turbines and generators. Wind turbines are geared towards variable pitch adjustment technology and generators are moving toward variable speed constant frequency power generation technology. This is a trend in the development of wind power generation technology and is also the core technology of wind power generation today. The following is a brief introduction of these two aspects.
1/ Variable pitch adjustment of wind turbine
The wind turbine captures wind energy through the impeller and converts the wind energy into mechanical torque acting on the hub.
The variable pitch adjustment method is to change the angle between the windward surface of the blade and the longitudinal rotation axis, thereby affecting the force and resistance of the blade, limiting the increase of the output power of the fan when the wind is strong, and maintaining the output power constant. Using pitch adjustment, the fan power output curve is smooth. Below the rated wind speed, the controller sets the blade angle of attack near zero and does not change it, which is approximately equal to the fixed pitch adjustment. Above the rated wind speed, the variable pitch control structure acts to adjust the blade angle of attack and control the output power near the rated value. The start-up speed of the variable-pitch wind turbine is lower than that of the fixed-pitch wind turbine, and the transmission of impact stress during the shutdown is relatively moderate. In normal operation, power control is mainly used. In practical applications, power is proportional to the cube of wind speed. Small changes in wind speed can cause large changes in wind energy.
As the pitch adjustment wind turbine is subjected to a much smaller impact than other wind turbines, material usage can be reduced and overall weight can be reduced. The variable pitch wind turbine can maintain a good angle of attack when the wind speed is low, and has a better energy output than the stall-regulated wind turbine, so it is more suitable for installation in areas with lower average wind speed.
Another advantage of variable pitch adjustment is that, when the wind speed reaches a certain value, the stalled wind turbine must be stopped, and the variable pitch wind turbine can be gradually changed to a full-wing unfolded mode position with no load of the blade to avoid downtime and increase wind force. Machine power generation.
The disadvantage of variable pitch adjustment is that it requires sensitive response to gusts. The power pulsation caused by the wind-induced vibration of the stall-adjusted fan is relatively small, while that of the pitch-adjusting wind turbine is relatively large, especially for the constant-speed wind turbine adopting the variable pitch method, this situation is more obvious, so that the fan is not required. The response of the pitch change system to the gusts is fast enough to mitigate this phenomenon.
2/variable speed constant frequency wind generator
Variable-speed constant-frequency wind generators often use AC excitation double-fed generators, the structure shown in Figure 1. Its structure is similar to that of a wound induction motor, except that a slip ring and a brush are added to the rotor winding. Thus, the rotation speed of the rotor is related to the frequency of the excitation, so that the internal electromagnetic relationship of the double-fed generator is different. An asynchronous generator is different from a synchronous generator, but it has some characteristics of asynchronous machines and synchronous machines.
AC excited double-fed variable-speed constant-frequency wind generator can not only realize variable-speed constant-frequency control by controlling the amplitude, phase and frequency of AC excitation, but also can realize active and reactive power control, and can also make reactive compensation to the grid. effect.
AC excitation variable speed constant frequency doubly fed generator system has the following advantages:
Allows the prime mover to run at a variable speed, simplifying the adjustment device and reducing the mechanical stress during speed regulation. At the same time, the unit control is more flexible and convenient, and the unit operation efficiency is improved.
The power required for frequency conversion control is only a part of the rated capacity of the motor, so that the frequency conversion device can be reduced in size, the cost can be reduced, and the investment can be reduced.
The excitation current amplitude can be adjusted to regulate the reactive power that is issued. The phase of the excitation current can be adjusted to regulate the active power. Applying vector control can realize independent adjustment of active and reactive power.
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