Modeling of the electrical impact of the tower flexion in a wind turbine

The aim of this work is to study the bending effect of the tower of a variable speed wind turbine system on its production of electrical energy and how this production is related to the structural fatigue of the tower. The research is built using a simulator based on Matlab / Simulink software. The model of variable speed energy conversion system, has an aerodynamic stage described according to unsteady blade element (BEM) theory, an electromechanical stage with a double fed induction generator (DFIG) and the structural stage described by a cantilever beam with the first oscillation mode, considering that the DFIG uses stator voltage orientation control (SVOC) and PID controller. The SCEVV is a Hammerstein model, linear time variant, with two feedback loops towards the aerodynamic stage, one is the velocity ratio at the tip of the blade and another is the angle of the tower flexion. The feedback of the flexion angle generates variations in the pitch angle of the blades and this develops on the operation of the SCEVV two significant effects, on the one hand generates a force from the turbine to the tower increasing the fatigue of the material and on the other hand the electric power production is affected by variations in the pitch angle, then three conclusions are obtained, first, the vibration of the tower causes an electric power variation of the order of 40% with respect to the nominal and second, if the SCEVV operates in the maximum power peack tracking (MPPT), then the structural stress is maximum consequently the fatigue also and third, to propose that the relationship generated electric power and the tower fatigue is described as an optimization problem where the optimum of operation of the system is defined by the compromise between the maximization of energy conversion and the minimization of fatigue to mechanics, through the control input that determines the structural fatigue of the tower, considering that the MPPT concept and fatigue are restrictions to impose on the optimal operation of the SCEVV.