kindly paraphrase this In a continued effort to reduce the cost, increase the reliability, and improve the efficiency of wind energy conversion systems (WECS), a variety of WECS configurations
have been developed. A classification of the most common configurations is given in
Figure 5-1, where the wind turbines can be generally classified into the fixed- and variable-speed turbines. The fixed-speed turbines employ a squirrel-cage induction generator (SCIG) connected directly to the grid and, thus, do not need any power converter
during normal operation.
The variable-speed wind turbines can be divided into direct- and indirect-drive turbines. In the direct-drive turbines, low-speed synchronous generators (SGs) with a
large number of poles are employed. The speed of the synchronous generators is designed to match the turbine speed such that the gearbox normally required in other
configurations is eliminated. Both wound-rotor synchronous generators (WRSGs) and
permanent-magnet synchronous generators (PMSGs) are suitable for the direct-drive
turbines, for which a full-capacity power converter system is required. The converter
system serves as an interface between the generator and the power grid.