Abstarct: Wind power is a kind of renewable energy and plays an important role in the future energy supply. Without question, the safe operation of control system which is the center of wind turbine is essential to ensure the running of the unit. However, wind turbine usually works under the bad environment. The gearbox and bearing failure and various sensor faults often occur, such as sensor bias fault, sensor constant gains and so on. Wind generators are also inaccessible since they are situated on extremely high towers, which are normally 20 m or greater in height. When fault occurs it will seriously affect the engineering quality and cause great economic losses. Consequently the use of advanced fault detection, isolation and accommodation methods could improve the reliability of the turbine, even though, for some faults. In this thesis fuzzy logic is combined with the model-baxsed method to formulate the so-called fuzzy observers. The main idea is to use the Takagi-Sugeno fuzzy model. The diagnostic signal a residual is the difference between the estimated and actual system outputs. In this thesis, the linear matrix inequality approach is used to analyze the global stability of the fuzzy observer.