BASIC CONCEPTS OF WIND POWER SYSTEMS

The main components of a wind power system are illustrated in Figure 28.1, which include a turbine rotor and blades, a yaw mechanism, a gearbox, a generator, a power electronic converter system, a transformer to connect the wind power system to a power grid, and a wind turbine generator control system.

FIGURE 28.1 Main components of a wind power system.

The wind turbine converts kinetic power in wind (i.e., aerodynamic power) to mechanical power by means of rotation of turbine rotor and blades. The mechanical power is transmitted from the turbine shaft directly or through a gearbox to the generator shaft, depending on the number of poles of the generator. If the generator has a low number of poles (e.g., four poles), a gearbox is commonly used to connect the low-speed turbine shaft and the high-speed generator shaft. If a generator with a high number of poles is used, the gearbox may not be necessary. The generator converts mechanical power to electrical power, which is fed into a power grid or used to supply local loads through optional power electronic converters and a power transformer with circuit breakers. The power transformer is normally located close to the wind turbine to avoid high currents flowing in long low-voltage cables. The use of power electronic converters enables the wind turbine generator to operate at variable speed to generate the maximum power and to have many other operational benefits, such as reactive power and power factor control, reduced mechanical stresses of the drive-train system, and enhanced grid fault ride through capability. The power transformer may be mounted in the nacelle to minimize electrical losses to the grid or at the base of the tower on the foundation. Grid connection is usually made at the foundation. The yaw mechanism rotates the rotor plane of the wind turbine to be perpendicular to the wind direction in order to extract the maximum power from wind.


Wind power to electrical power conversion of the wind turbine generator is regulated by an electronic control system, which consists of the controllers for the generator and power converters, the turbine blades, and the yaw mechanism. The generator/power converter controller regulates the generator and power converters to generate a certain amount of electrical power with the voltage and frequency required by the power grid and loads. The turbine blade-angle controller optimizes the mechanical power output of the wind turbine and limits the mechanical power at the rated value during strong wind speed conditions. The power limitation may be done by stall, active stall, or pitch control. The yaw controller regulates the yaw mechanism to turn the rotor plane of the wind turbine to face the prevailing wind in order to generate the maximum power. If multiple wind turbine generators are connected to form a wind power plant, the control system of each wind turbine generator is usually coordinated by a wind plant central control system through a Supervisory Control and Data Acquisition (SCADA) System.