Sensorless control of induction machines for wind energy applications

A sensorless vector control strategy for induction generators operating in variable speed wind energy conversion systems is presented. The sensorless control is based on a model reference adaptive system (MRAS observer) for estimating the rotational speed. In order to tune the MRAS observer and compensate for the parameter variation and uncertainties, a separate estimation of the speed is obtained from the rotor slot harmonics using an algorithm for spectral analysis. This algorithm can track fast dynamic changes in the rotational speed, with high accuracy. The proposed sensorless control system is applied to a grid connected wind energy conversion system and also to a power smoothing scheme based in a flywheel driven by a vector controlled induction machine. The control strategies have been experimentally verified on a 2.5 kW experimental set up with an induction generator, flywheel and a DC machine used to emulate a variable speed wind turbine. The experimental results show the high level of performance obtained with the proposed sensorless vector control method.