Browsing by Subject "State estimation"
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Item Advanced tabulation techniques for faster dynamic simulation, state estimation and flowsheet optimization(2009-08) Abrol, Sidharth; Edgar, Thomas F.Large-scale processes that are modeled using differential algebraic equations based on mass and energy balance calculations at times require excessive computation time to simulate. Depending on the complexity of the model, these simulations may require many iterations to converge and in some cases they may not converge at all. Application of a storage and retrieval technique, named in situ adaptive tabulation or ISAT is proposed for faster convergence of process simulation models. Comparison with neural networks is performed, and better performance using ISAT for extrapolation is shown. In particular, the requirement of real-time dynamic simulation is discussed for operating training simulators (OTS). Integration of ISAT to a process simulator (CHEMCAD®) using the input-output data only is shown. A regression technique based on partial least squares (PLS) is suggested to approximate the sensitivity without accessing the first-principles model. Different record distribution strategies to build an ISAT database are proposed and better performance using the suggested techniques is shown for different case studies. A modified ISAT algorithm (mISAT) is described to improve the retrieval rate, and its performance is compared with the original approach in a case study. State estimation is a key requirement of many process control and monitoring strategies. Different nonlinear state estimation techniques studied in the past are discussed with their relative advantages/disadvantages. A robust state estimation technique like moving horizon estimation (MHE) has a trade-off between accuracy of state estimates and the computational cost. Implementation of MHE based ISAT is shown for faster state estimation, with an accuracy same as that of MHE. Flowsheet optimization aims to optimize an objective or cost function by changing various independent process variables, subject to design and model constraints. Depending on the nonlinearity of the process units, an optimization routine can make a number of calls for flowsheet (simulation) convergence, thereby making the computation time prohibitive. Storage and retrieval of the simulation trajectories can speed-up process optimization, which is shown using a CHEMCAD® flowsheet. Online integration of an ISAT database to solve the simulation problem along with an outer-loop consisting of the optimization routine is shown using the sequential-modular approach.Item Optimal monitoring and visualization of steady state power system operation(2009-06-02) Xu, BeiPower system operation requires accurate monitoring of electrical quantities and a reliable database of the power system. As the power system operation becomes more competitive, the secure operation becomes highly important and the role of state estimation becomes more critical. Recently, due to the development of new technology in high power electronics, new control and monitoring devices are becoming more popular in power systems. It is therefore necessary to investigate their models and integrate them into the existing state estimation applications. This dissertation is dedicated to exploiting the newly appeared controlling and monitoring devices, such as Flexible AC Transmission System (FACTS) devices and (Phasor Measurement Units) PMUs, and developing new algorithms to include them into power system analysis applications. Another goal is to develop a 3D visualization tool to help power system operators gain an in-depth image of the system operation state and to identify limit violations in a quick and intuitive manner. An algorithm of state estimation of a power system with embedded FACTS devices is developed first. This estimator can be used to estimate the system state quantities and Unified Power Flow Controller (UPFC) controller parameters. Furthermore, it can also to be used to determine the required controller setting to maintain a desired power flow through a given line. In the second part of this dissertation, two methods to determine the optimal locations of PMUs are derived. One is numerical and the other one is topological. The numerical method is more effective when there are very few existing measurements while the topology-based method is more applicable for a system, which has lots of measurements forming several observable islands. To guard against unexpected failures of PMUs, the numerical method is extended to account for single PMU loss. In the last part of this dissertation, a 3D graphic user interface for power system analysis is developed. It supports two basic application functions, power flow analysis and state estimation. Different visualization techniques are used to represent different kinds of system information.