The second part of the basic structure of the horizontal axis lift wind turbine
- Tower and foundation
This part includes the tower structure and supporting foundation. The towers currently in use mainly include steel tube independent towers, truss towers and concrete towers. Small wind turbines also use wire-supported towers; the height of the tower is usually 1 to 1.5 times the diameter of the wind wheel, but At least 20m high. The choice of tower is largely affected by the characteristics of the foundation. Due to the possibility of coupled vibration between the wind wheel and the tower, the rigidity of the tower is the main factor that affects the dynamic characteristics of the wind turbine system. For the wind wheel in the downwind direction, it is necessary to consider the influence of the tower shadow (that is, the wake area produced by the air flow around the tower) on the dynamic characteristics, power fluctuations, and noise of the wind turbine. For example, because of the shadow of the tower, the downwind wind turbine produces higher noise than the same upwind wind turbine. - Control
The control system of a wind turbine is very important to the operation of the machine and power generation. The control system components include:
Sensors-speed, position, flow, temperature, current, voltage, etc.;
Controller-mechanical mechanism, circuit;
Power amplifiers-switches, power amplifiers, hydraulic pumps and valves;
Actuator-motor, piston, magnet and electromagnetic coil;
Intelligent systems-computers and microprocessors.
The design of the wind turbine control system follows the traditional control engineering guidelines. However, its control system is quite special in many aspects. Wind turbine control involves the following three main aspects, and its needs should be carefully balanced:
①Set the upper limit of the torque and power that the drive chain bears, and limit it:
②To maximize the fatigue life of the drive chain rotor and other structural components, it needs to consider the alternating stress of the components during wind direction changes, wind speed changes (including gusts), turbulence changes, and wind turbine start and stop;
③ Maximize the power generation.
- Auxiliary equipment of electrical system
In addition to generators, wind turbine systems also use many electrical components, such as cables, switchgear, transformers, power electronic converters, power factor compensation capacitors, yaw and pitch angle motors. - Output power prediction
The power output of wind turbines varies with wind speed, and each wind turbine has its own unique power curve. This curve can be used to predict the starting power regardless of the technical details of other components. The power curve gives the power output as a function of the wind speed at the height of the wheel.
The performance of a given wind turbine is related to three points on the speed coordinate:
Cut-in wind speed-the minimum wind speed at which the wind turbine emits power;
Rated wind speed-the wind speed that reaches the rated power (usually the maximum output power of the generator);
Cut-out wind speed-the maximum wind speed at which the wind turbine is allowed to emit power (usually limited by engineering design and safety conditions).
The power curve of existing wind turbines is usually obtained from the manufacturer, and the power curve can also be measured on-site using standard test methods. The approximate shape of a given wind turbine power curve can be estimated. This process also includes determining the power characteristics of wind turbines and generators, gearbox transmission ratios, and component efficiencies.
The above outlines the basic structure of the horizontal-axis lift wind turbine. It is worth noting that many other structural types of wind turbines have been proposed, and some have been manufactured, but none of them are as successful as the horizontal-axis lift wind turbine. . However, it is necessary to briefly outline the concepts of other wind turbines. The closest thing to a horizontal axis wind turbine is the Darrieus vertical axis wind turbine (VAWT). This concept was widely studied in the United States and Canada in the 1970s and 1980s.
Despite its fascinating features, Darrieus wind turbines have some major reliability issues and are not comparable to the energy costs of horizontal axis wind turbines. However, this concept may provide a reference for some applications. For readers to understand the design of this vertical axis wind turbine and other vertical axis wind turbines in the past, you can refer to the literature Paraschivoiu (2002), Price (2006), and the Sandia National Laboratory Work Summary Report (SNL) (2009).
Another concept that appears from time to time is to use current collectors or diffusers to enhance wind turbines (see van Bussel, 2007). Both of these designs use a wind channel to increase the capacity of the wind turbine. The problem is that the effect is good. And the cost of the collector or diffuser that can withstand extreme wind conditions is higher than the benefit it brings.
People have also proposed some wind wheels that use resistance. One of them is the Savonius wind wheel that was used in small pumps. There are two basic problems with this type of wind wheel: (1) Inherent low efficiency (will be in the first Discussed in Chapter 3); (2) It is difficult to ensure the safety of the wind wheel under extreme wind conditions. It is questionable whether this type of wind wheel can be widely used in wind turbines.