Two and a half degrees of freedom LQG controller and application to wind turbines

The 2½ degrees of freedom structure considered has been used in real applications for many years but it has not been shown to follow from the solution of an H² optimal control problem. A Kucera type of polynomial solution is presented which provides a theoretical basis for the structure adopted. The proposed controller structure has the advantage that low frequency tracking properties can be achieved, as in single degree-of-freedom designs, but no constraints then apply to the high frequency tracking behaviour, since it is effectively determined by a two degrees-of-freedom structure. A wind turbine example is presented