Control of a wind turbine equipped with a variable rotor resistance

Abstract

In this thesis the control of a wind turbine equipped with an induction generator with a variable rotor resistance was investigated. Analysis, modelling and control of the induction generator system was conducted. In particular the focus was put on the reduction of torque fluctuations, in order to reduce the stresses in the gearbox and in the mechanical structure as well as reducing the flicker emission. Different controlling methods were studied in order to find an appropriate choice. Finally, the induction machine with the variable rotor resistance controller was compared with the same induction machine without controller for the wind application, in order to study the improvement of implementing the controller. The first thing to be emphasized is that by utilising the controller the flicker contribution can be reduced between 35%‐60% compared to the uncontrolled system. It was also found that the reduction of the flicker contributions was strongly related with the turbulence intensity in the wind. The reduction in the flicker emission was stronger for more turbulent winds. Furthermore, a reduction in the magnitude of the electrical torque components for the frequencies above 1Hz was found. Those high‐frequency components are the ones that more contribute to the mechanical stresses in the gearbox and structure of the turbine, this means that by utilising the controller there will be less tear and wear on the mechanical parts of the turbine.