Abstract The main subject of this thesis is bumpless transfer. In the context of control theory this means the transfer from one controller to another as smooth as possible. The experiments with controllers and bumpless transfer is carried out on a wind turbine. The thesis is divided in two parts. A simple model for the windturbine is made in the first part. A controller is designed to control the pitch angle of the blades at wind speeds above the critical windspeed. Below the critical windspeed the pitch angle is constant. The theory of bumpless transfer is applied to make the transfer between the two controllers smooth. In the second part the model is extended. The wind turbine is now with variable speed as opposed to the simple model. A complete suite of controllers is designed for the windturbine. Each controller has its own individual goals. These are dependent on the wind speed. The goal is to make make a bumpless transfer between the controllers. When the windspeed is above the critical windspeed the controller limits the power to the rated power of the windturbine. If the wind drops below the critical windspeed the output power of the windturbine also drops . Another goal of the control strategy is to investigate the possibility of smoothing or maintaining the output power in these situations. The means by which this should be done is by extracting the kinetic energy of the rotor. In the first part a bumpless transfer was made between the two controllers. In the second part a suite of controllers was made to the windturbine. The transfer between these were smooth. Power smoothing was implemented by breaking down the rotor and thereby extracting kinetic energy from the rotor. Type Master's thesis [Academic thesis] Year 2003 Publisher Informatics and Mathematical Modelling, Technical University of Denmark, DTU Address Richard Petersens Plads, Building 321, DK-2800 Kgs. Lyngby Series IMM-THESIS-2003-11 Electronic version(s) [ps] BibTeX data [bibtex] IMM Group(s) Mathematical Statistics