Observer-based Fault Detection inNonlinear SystemsVon der Fakult¨at fu¨r Ingenieurwissenschaften derUniversit¨at Duisburg-EssenAbteilung Elektrotechnik und Informationstechnikzur Erlangung des akademischen Grades einesDoktor-Ingenieurs (Dr.-Ing.)genehmigte DissertationvonAbdul Qayyum KhanausMardan, I. R. Pakistan1. Gutachter: Prof. Dr.-Ing. Steven X. Ding2. Gutachter: Prof. Dr. Dominique SauterTag der mu¨ndlichen Pru¨fung: December 13, 2010AcknowledgeThisworkiscarriedoutduringmystayattheInstituteofAutomaticControlandComplexSystems (AKS), University of Duisburg-Essen for acquiring my Ph.D degree under thejoint grant of Higher Education Commission (HEC) of Pakistan and German AcademicExchange Program (DAAD) Germany.Besides every doctoral thesis lie years of hard work. Looking back over the last threeand half years, I can see many people who have given me support and encouragementduring this period. It is, therefore, my pleasure to thank all of them.First and foremost, I would like to express my deepest gratitude to my thesis supervisorProf. Dr.-Ing. StevenX.Ding. Hisuniqueviewoffaultdetectiontheoryandmathematicaldiscipline taught me to see nonlinear fault detection problems from a new perspectivethat enhanced my understanding of what constitutes an acceptable solution for certainfundamental issues in nonlinear fault detection. I can never thank him enough for givingmethefreedomtochoosethetheoreticalfieldsofmyinterestandhelpingmetopursuemygoals.