Electrical/mechanical options for variable speed wind turbines

The use of variable speed wind turbines, especially in large-scale utility electricity generating systems, offers a potential improvement in the cost effectiveness of wind energy systems. This paper presents a review of the potential options (including mechanical, electrical/mechanical, electrical, and electrical/power electronic) open for variable speed wind turbine design and gives some of the advantages and disadvantages of these design options. As summarized, a major design problem is to build a system that will allow the rotor to turn at a variable speed, while the machine is feeding power of constant frequency to the load. Although many approaches have been suggested for variable speed operation, they can be grouped into two main classes: (i) discretely variable, and (ii) continuously variable. It is concluded that, based on the current state-of-the-art, the systems with the most promise appear to be those incorporating power electronics.