Buy Innovation in Wind Turbine Design. Wind turbine design - Wikipedia, the free encyclopedia. An example of a wind turbine, this 3 bladed turbine is the classic design of modern wind turbines. Wind turbine components : 1- Foundation, 2- Connection to the electric grid, 3- Tower, 4- Access ladder, 5- Wind orientation control (Yaw control), 6- Nacelle, 7- Generator, 8- Anemometer, 9- Electric or Mechanical Brake, 1. Gearbox, 1. 1- Rotor blade, 1. Blade pitch control, 1. Rotor hub. Wind turbine design is the process of defining the form and specifications of a wind turbine to extract energy from the wind. Catalogue Innovation in wind turbine design. Innovation in wind turbine design.
This Betz' law limit can be approached by modern turbine designs which may reach 7. In addition to aerodynamic design of the blades, design of a complete wind power system must also address design of the hub, controls, generator, supporting structure and foundation. Further design questions arise when integrating wind turbines into electrical power grids. Aerodynamics. The air flow at the blades is not the same as the airflow far away from the turbine. The very nature of the way in which energy is extracted from the air also causes air to be deflected by the turbine. In addition the aerodynamics of a wind turbine at the rotor surface exhibit phenomena that are rarely seen in other aerodynamic fields. In 1. 91. 9 the physicist Albert Betz showed that for a hypothetical ideal wind- energy extraction machine, the fundamental laws of conservation of mass and energy allowed no more than 1. This Betz' law limit can be approached by modern turbine designs which may reach 7. Power control. The centrifugal force on the spinning blades increases as the square of the rotation speed, which makes this structure sensitive to overspeed. Because the power of the wind increases as the cube of the wind speed, turbines have to be built to survive much higher wind loads (such as gusts of wind) than those from which they can practically generate power. Wind turbines have ways of reducing torque in high winds. A wind turbine is designed to produce power over a range of wind speeds. All wind turbines are designed for a maximum wind speed, called the survival speed, above which they will be damaged. The survival speed of commercial wind turbines is in the range of 4. MPH) to 7. 2 m/s (2. MPH). The most common survival speed is 6. MPH). If the rated wind speed is exceeded the power has to be limited. There are various ways to achieve this. A control system involves three basic elements: sensors to measure process variables, actuators to manipulate energy capture and component loading, and control algorithms to coordinate the actuators based on information gathered by the sensors. Stalling is simple because it can be made to happen passively (it increases automatically when the winds speed up), but it increases the cross- section of the blade face- on to the wind, and thus the ordinary drag. A fully stalled turbine blade, when stopped, has the flat side of the blade facing directly into the wind. A fixed- speed HAWT (Horizontal Axis Wind Turbine) inherently increases its angle of attack at higher wind speed as the blades speed up. A natural strategy, then, is to allow the blade to stall when the wind speed increases. This technique was successfully used on many early HAWTs. However, on some of these blade sets, it was observed that the degree of blade pitch tended to increase audible noise levels. Vortex generators may be used to control the lift characteristics of the blade. The VGs are placed on the airfoil to enhance the lift if they are placed on the lower (flatter) surface or limit the maximum lift if placed on the upper (higher camber) surface. One major problem in designing wind turbines is getting the blades to stall or furl quickly enough should a gust of wind cause sudden acceleration. A fully furled turbine blade, when stopped, has the edge of the blade facing into the wind. Loads can be reduced by making a structural system softer or more flexible. These systems will be nonlinear and will couple the structure to the flow field - thus, design tools must evolve to model these nonlinearities. Standard modern turbines all furl the blades in high winds. Since furling requires acting against the torque on the blade, it requires some form of pitch angle control, which is achieved with a slewing drive. This drive precisely angles the blade while withstanding high torque loads. In addition, many turbines use hydraulic systems. These systems are usually spring- loaded, so that if hydraulic power fails, the blades automatically furl. Other turbines use an electric servomotor for every rotor blade. They have a small battery- reserve in case of an electric- grid breakdown. Small wind turbines (under 5. W) with variable- pitching generally use systems operated by centrifugal force, either by flyweights or geometric design, and employ no electric or hydraulic controls. Fundamental gaps exist in pitch control, limiting the reduction of energy costs, according to a report from a coalition of researchers from universities, industry, and government, supported by the Atkinson Center for a Sustainable Future. Load reduction is currently focused on full- span blade pitch control, since individual pitch motors are the actuators currently available on commercial turbines. Significant load mitigation has been demonstrated in simulations for blades, tower, and drive train. However, there is still research needed, the methods for realization of full- span blade pitch control need to be developed in order to increase energy capture and mitigate fatigue loads. A control technique applied to the pitch angle is done by comparing the current active power of the engine with the value of active power at the rated engine speed (active power reference, Ps reference). Control of the pitch angle in this case is done with a PI controller controls. However, in order to have a realistic response to the control system of the pitch angle, the actuator uses the time constant Tservo, an integrator and limiters so as the pitch angle to be from 0. The reference pitch angle, which comes from the PI controller, goes through a limiter. Restrictions on limits are very important to maintain the pitch angle in real term. Limiting the rate of change is very important especially during faults in the network. The importance is due to the fact that the controller decides how quickly it can reduce the aerodynamic energy to avoid acceleration during errors. When the wind speed is below rated, generator torque is used to control the rotor speed in order to capture as much power as possible. The most power is captured when the tip speed ratio is held constant at its optimum value (typically 6 or 7). This means that as wind speed increases, rotor speed should increase proportionally. The difference between the aerodynamic torque captured by the blades and the applied generator torque controls the rotor speed. If the generator torque is lower, the rotor accelerates, and if the generator torque is higher, the rotor slows down. Below rated wind speed, the generator torque control is active while the blade pitch is typically held at the constant angle that captures the most power, fairly flat to the wind. Above rated wind speed, the generator torque is typically held constant while the blade pitch is active. One technique to control a permanent magnet synchronous motor is Field Oriented Control. Field Oriented Control is a closed loop strategy composed of two current controllers (an inner loop and outer loop cascade design) necessary for controlling the torque, and one speed controller. Constant torque angle control. In this control strategy the d axis current is kept zero, while the vector current is align with the q axis in order to maintain the torque angle equal with 9. This is one of the most used control strategy because of the simplicity, by controlling only the Iqs current. So, now the electromagnetic torque equation of the permanent magnet synchronous generator is simply a linear equation depend on the Iqs current only. So, the electromagnetic torque for Ids = 0 (we can achieve that with the d- axis controller) is now: Te= 3/2 p (. In that we have the control inputs, which are the duty rations mds and mqs, of the PWM- regulated converter. Also, we can see the control scheme for the wind turbine in the machine side and simultaneously how we keep the Ids zero (the electromagnetic torque equation is linear). By minimizing the yaw angle (the misalignment between wind and turbine pointing direction), the power output is maximized and non- symmetrical loads minimized. However, since the wind direction varies quickly the turbine will not strictly follow the direction and will have a small yaw angle on average. The power output losses can simply be approximated to fall with (cos(yaw angle))3. Particularly at low- to- medium wind speeds, yawing can make a significant reduction in turbine output, with wind direction variations of . At high wind speeds, the wind direction is less variable. Electrical braking. This method is useful if the kinetic load on the generator is suddenly reduced or is too small to keep the turbine speed within its allowed limit. Cyclically braking causes the blades to slow down, which increases the stalling effect, reducing the efficiency of the blades. This way, the turbine's rotation can be kept at a safe speed in faster winds while maintaining (nominal) power output. This method is usually not applied on large grid- connected wind turbines. Mechanical braking. This brake is a secondary means to hold the turbine at rest for maintenance, with a rotor lock system as primary means. Such brakes are usually applied only after blade furling and electromagnetic braking have reduced the turbine speed generally 1 or 2 rotor RPM, as the mechanical brakes can create a fire inside the nacelle if used to stop the turbine from full speed. The load on the turbine increases if the brake is applied at rated RPM. Mechanical brakes are driven by hydraulic systems and are connected to main control box.
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