State estimation of nonlinear systems

Sammanfattning: Observer design for nonlinear systems is a popular problem in control theory that has beenstudied from many angles. Since the system state variables, in general, are not available, stateestimation is essential in many control applications, which is why the problem is so attractivefor researchers. One example of a process that has nonlinear dynamics is wood drying.In the wood drying process, there are some unmeasurable variables such as the moisturecontent at the surface and inside the wood, which are important for controlling the drying processfor the purpose of minimizing the energy consumption of the wood drying kiln. However,to the best of our knowledge, there is no straightforward observer design for the wood-dryingprocess in the current literature. In the first two research papers that compose this thesis, afterintroducing a state space realization of the wood drying process, a novel method for estimatingthe moisture content of the wood during drying is proposed.Compared to typical systems, observer design for nonlinear uncertain systems with timedelays, is significantly more complicated and thus attractive for research. In this thesis, theproblem of the observer design for a class of uncertain discrete-time nonlinear systems withunknown time delay has also been investigated. The study shows that by using upper and lowerbounds of the time delay, the time delay can be excluded in the observer structure. The thirdand fourth papers mostly focus on this topic based on an optimization approach.