Developments in power electronics, electrical drives and wind turbines have allowed an increase in the power of wind systems. The need to limit mechanical stress and power disturbances has led to strong demand for variable speed systems. In wind generation systems it is necessary to decouple and control active and reactive power flow with fast response because of mains requirements. Fast and accurate control is especially important when the induction machine is designed to operate below synchronism rotational speed as a generator. This article describes a controller that can extract power from wind kinetic energy over a large speed range, at both sub- and hyper-synchronism speeds.

By Paulo Costa, António Martins and Adriano Carvalho, Portugal