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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 50219 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Haeri, Mohammad
- Abstract:
- Many processes and real world systems indicate nonlinear behavior and operate either naturally in multiple regions or in a wide range of operation space. Modelling and control of these systems by nonlinear methods needs to have a deep insight. Furthermore, the nonlinear methods leads to complexity issues. To overcome these problems, multi-model methods are introduced which consist of two steps, decomposition and combination. In decomposition step, the complex system is divided into a set of simple models; in the combination step, the behavior of local models are combined. How to decompose to local models and how to combine them are two main questions in this area which not answered adequately yet. This thesis focuses on modelling and control of nonlinear systems by multi-model method. In the modelling section, considering the single path trajectory based methods, a new method is introduced to enlarge the operation space. Therefore, the presented method has more robustness when the trajectory path changes. In the control section, the gap metric is used as a powerful tool to measure the distance between the local models. To choose the best models among the local models bank, stability margin is employed to avoid the redundancy issue. In this way, the nonlinear system which the local models have a small maximum stability margin are investigated and an effective solution is introduced to modify the local models. The presented method dramatically decreases the number of the designed local controllers. Also, the local models bank selection is combined with the local controller design to avoid the redundant local controllers. Moreover, performance is added to design the local controllers and two novel methods are introduced. In the first method, robust stability and performance are integrated as an optimization problem. Also, the selection of nominal local models is added by an updating parameter in the formulated optimization problem. The main advantages of the first method are: guarantee of stability and performance, not need to experience, and avoid adding the redundant local models. In the second method, stability and performance requirements are gained in a cascade platform. In this platform, stability is guaranteed by maximizing the stability margin of local models in the first stage. In the second stage, the stabilizing controllers are employed to guarantee the performance requirements. Therefore, this method prevents the gained stability from the first stage. The second proposed method not only has the whole advantages of the first method but also is simpler
- Keywords:
- Gap Metric ; Nonlinear Systems ; Multimodel System ; Performance ; Stability ; Single Path Trojeetory Method
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