Wind Turbine Technology: Components, Regulation, and Control

Posted on Mar 16, 2025 in Electromechanical Engineering

Wind Turbine Technology

Wind Rose

Gives information about the wind speed and frequency of wind blowing from various directions. The length of each spoke around the circle relates to the frequency of time that the wind blows from a particular direction. You can analyze a wind rose to determine the prevailing wind direction and frequency.

Betz Limit

The actual power that is obtainable from a wind turbine is given by:

Cp * Eg * Eb

Where:

  • Cp is the coefficient of performance.
  • Eg is the generator efficiency (a value greater than 0.8).
  • Eb is the gearbox/bearings efficiency (can be greater than 95%).

The maximum theoretical value of Cp possible is 0.593 (Betz Limit). The practical value is in the range of 0.35-0.4.

The velocity at the rotor inlet (v1) is different than at the outlet (v2). We use an average velocity to calculate the mass of the air streaming through the rotor per second:

(v1 + v2) / 2

The power extracted from the wind by the rotor using the average wind speed:

P = 0.5 * ρ * A * v^3 * Cp

The total power in the wind Po streaming through exactly the same area in the absence of the rotor:

Po = 0.5 * ρ * A * v1^3

Relation of the two powers is:

Cp = P / Po

Vertical Axis Wind Turbines (VAWTs)

Advantages:

  1. The generator and gearbox can be placed at the bottom. A tower is not needed.
  2. The turbine doesn’t need to be pointed into the wind.

Disadvantages:

  1. The pulsating torque that is produced during each revolution.
  2. Need higher turbulent air flow near the ground.
  3. Lower energy extraction efficiency.

Darrieus Wind Turbine

It’s the most common type. It requires an external power source to start rotation. Starting torque is very low.

Savonius Wind Turbine

Two half-cylinders mounted on a vertical shaft with an S-shape appearance. This drag VAWT rotates relatively slowly, but produces a high torque. Most of the area swept by the turbine is close to the ground. It is cheap and reliable.

Giromill Wind Turbine

H-bar design with straight vertical blade section attached to the central tower with horizontal supports.

Horizontal Axis Wind Turbines (HAWTs)

Advantages:

  1. Turbines are more stable than VAWTs.
  2. Tall tower allows access to stronger wind.
  3. Manufacturing cost can be less.

Disadvantages:

  1. The pieces are difficult to transport.
  2. Higher install and maintenance costs.

Parts:

  • Nacelle: Contains the key components of a wind turbine.
  • Rotor Blades: Capture the wind and transfer its power to the rotor hub.
  • Hub: Is attached to the low-speed shaft of a wind turbine.
  • Low-Speed Shaft: Connects the rotor hub to the gearbox.
  • Gearbox: Connects the low-speed shaft to the high-speed shaft and increases the rotational speed which is required to produce electricity.
  • High-Speed Shaft with its Mechanical Brake: Drives the generator and employs a disc brake to stop the rotor in emergencies.
  • Electrical Generator: Converts the mechanical energy into electrical energy.
  • Yaw Mechanism: Is used to keep the rotor facing into the wind as the wind direction changes.
  • Electronic Controller: Starts the machine at the specified wind speed.
  • Tower: Is a support structure for the wind turbine.
  • Anemometer: Measures the wind speed.
  • Wind Vane: Measures wind direction and directs the yaw drive to appropriate orientation.

Wind Turbine Speed Regulation

1. Constant Speed Wind Turbines:

Based on a gearbox and an asynchronous generator. The gearbox speeds up the rotational shaft speed from the rotor to a fixed generator speed. The generator produces electricity. Due to the lack of a frequency converter, the generator speed is dictated by the grid frequency.

2. Variable Speed Wind Turbines:

Many different options to achieve speed regulation:

  • Dual speed generators with pole switching.
  • High slip asynchronous generators for a low range of variable speed.

The power electronics used are more expensive. They are able to reduce mechanical loading and drive train fatigue and to capture more energy. They have the ability to control independently their active and reactive power.

Control Strategies

1. Passive Stall Control or Fixed Pitch:

The generator reaction torque regulates rotor speed to maximize energy capture. The power delivered by the rotor is limited at high winds. The pitch angle is fixed and tip brakes are the only part of the blade which can rotate.

2. Variable Pitch Control:

The blades regulate the power delivered by the rotor. To maintain power and rotor speed to their nominal value, the torque is held constant and the pitch is continually changed. The way to turn off the machine is turning the blade perpendicular to the wind.

3. Active Stall Control:

Is a combination of stall and pitch control. The blades are similar to stall control blades but this can be turned 90º to adjust its pitch. The blades rotated only small amounts and less frequently than in pitch control to optimize the performance of the blades.

Comparison Between Turbines

Comparing their coefficient of performance (Cp) against tip speed ratio (λ) is an important factor in designing the wind turbine. A high tip speed ratio is desirable, but there are several disadvantages:

  1. A high rotation speed can cause erosion of the blades.
  2. The level of noise and vibration increases.