Speed control of wind turbines in the stall region

This paper investigates the minimal load variations that can be achieved using a linear quadratic (LQ) controller while maintaining rated power in a stalled variable speed fixed pitch wind turbine. Analytic results can be derived for a very simple second order model. The results are confirmed with numerical analysis of higher order models with state estimation based on generator speed measurement. The characteristics derived from linear models have been verified with simulation of non-linear models. The controller is stability robust to parameter changes and significantly better than a traditional PI-controller at high wind speeds