A variable speed system for use in systems, such as, for example, wind turbines, is described. The system comprises a wound rotor induction generator, a torque controller and a proportional, integral derivative (PID) pitch controller. The torque controller controls generator torque using field oriented...http://www.google.com/patents/US6137187?utm_source=gb-gplus-sharePatent US6137187 - Variable speed wind turbine generator
