A nonlinear optimal control approach for DFIG wind power generators

A nonlinear optimal (H-infinity) control method is proposed for a wind power generation system which consists of two-mass drivetrain and a DFIG. With reference to the 6-th order dynamic model of the DFIG, the state-space model of the considered power generation unit is extended by including in it the dynamics of the drivetrain. At a first stage, the dynamic model of the power generation unit undergoes approximate linearization around a temporary operating point which is recomputed at each time-step of the control algorithm. The linearization procedure makes use of Taylor series expansion and of the computation of the associated Jacobian matrices. At a second stage an H-infinity controller is developed for the linearized state-space description of the power unit. This provides the solution of the optimal control problem for the wind power system under model uncertainty and external perturbations. For the computation of the controller's feedback gain an algebraic Riccati equation is repetitively solved at each iteration of the control method. Finally, the global asymptotic stability of the control scheme is proven with the use of Lyapunov analysis.