<p> This thesis considers the problem of control of nonlinear process systems subject to input constraints and faults in the control actuators and process equipments. Faults are considered that preclude the possibility of continued operating at the nominal equilibrium point and a framework (which we call the safe-parking framework) is developed to enable efficient resumption of nominal operation upon fault-recovery. First, Lyapunov-based model predictive controllers, that allow for an explicit characterization of the stability region subject to constraints on the manipulated input, are designed. The stability region characterization is utilized in selecting 'safe-park' points from the safe-park candidates (equilibrium points subject to failed actuators). This safe-park point is chosen as a temporary operating point where process is to be operated during fault rectification. This ensures that process can be safely operated during fault rectification and the nominal operation can be resumed upon fault recovery. When multiple candidate safe-park points are available, performance considerations, such as ease of transition from and to the safe-park point and cost of running the process at the safe-park point, are quantified and utilized in choosing the optimal safe-park point. </p> <p> Next, we extend the safe-parking framework to handle practical issues such as plant-model mismatch, disturbances and unavailability of all process state measurements. \i\Te first consider the presence of constraints and uncertainty and develop a robust Lyapunov-based model predictive controller. This controller is utilized to characterize robust stability region which, subsequently, is utilized to select 'safepark' points. Then we consider the problem of availability of limited measurements. An output feedback Lyapunov-based model predictive controller, with high-gain observer to estimate unmeasured states, is formulated and its stability region explicitly characterized. An algorithm is then presented that accounts for the estimation errors in the implementation of the safe-parking framework. </p> <p> We then further extend the framework to handle faults in large scale chemical plants where multiple process units are connected via material, energy and information streams. In plant-wide setting, the safe-park point for the faulty unit is chosen such that the safe-parking has no or minimum effect on downstream units, and hence, the nominal operation in the downstream units can be continued. Next we consider the scenario where no viable safe-park point for the faulty unit exists such that its effect can be completely absorbed in the subsequent unit. A methodology is developed that allows simultaneous safe-parking of the consecutive units. The efficacy of the proposed framework is illustrated using a chemical reactor example, a styrene polymerization process and two CSTRs in series example. </p> <p> Finally, we demonstrate the efficacy of proposed Lyapunov based Model Predictive Controller and Safe-Parking framework on a polymerization reactor model to control the polymerization reactor and to handle faults that dont allow continuation of the nominal operation in the reactor. </p> / Thesis / Doctor of Philosophy (PhD)

In this thesis, attitude control of small satellites with dissimilar actuator is studied and the effects of control allocation methods on maneuvering are examined in detail. Magnetorquers and reaction wheels are considered as the actuators of a modeled remote sensing -nadir pointing- small satellite. Matlab&reg / Simulink simulation models are developed to model the satellite dynamics and the actuators on the satellite. The simulations are based on conceptual RASAT satellite, and, for verification, orbit data is taken from BILSAT satellite that is operated by TUBITAK Space Research Institute. Basic satellite control modes are developed and tested to obtain nominal control. Actuator failures are analyzed for different possible cases. A control allocation method called Blended Inverse that was originally proposed for steering CMGs is applied to select the actuators to avoid actuator saturation and singularity transition. The performance of traditional pseudo inverse method is compared with the blended inverse method and simulation results are given and discussed. The superiority of blended inverse over pseudo inverse is demonstrated.

The switched reluctance motor (SRM) is receiving attention because of its merits: high operating temperature capability, fault tolerance, inherent shoot-through preventing inverter topology, high power density, high speed operation, and small rotor inertia. Rotor position information plays a critical role in the control of the SRM. Conventionally, separate position sensors, are used to obtain this information. Position sensors add complexity and cost to the control system and reduce its reliability and flexibility. In order to overcome the drawbacks of position sensors, this dissertation proposed and investigated a position sensorless control system that meets the needs of an electric actuator application. It is capable of working from zero to high speeds. In the control system, two different control strategies are proposed, one for low speeds and one for high speeds. Each strategy utilizes a state observer to estimate rotor position and speed and is capable of 4 quadrant operation. In the low speed strategy a Luenberger observer, which has been named the inductance profile demodulator based observer, is used where a pulse voltage is applied to the SRMs idle phases generating triangle shaped phase currents. The amplitude of the phase current is modulated by the SRMs inductance. The current is demodulated and combined with the output of a state observer to produce an error input to the observer so that the observer will track the actual SRM rotor position. The strategy can determine the SRMs rotor position at standstill and low speeds with torques up to rated torque. Another observer, named the simplified flux model based observer, is used for medium and high speeds. In this case, the flux is computed using the measured current and a simplified flux model. The difference between the computed flux and the measured flux generates an error that is input to the observer so that it will track the actual SRM rotor position. Since the speed ranges of the two control stragegies overlap, the final control system is capable of working from zero to high speed by switching between the two observers according to the estimated speed. The stability and performance of the observers are verified with simulation and experiments.

This diploma thesis is focused on sensorless DC motor control based on its mathematical model. This solution will be used for Honyewell actuators (type ML5410 and N10010/N05010). The aim of this thesis is to find out if there is a possibility to use this type of motor control for future to replace the existing type of motor control using Hall sensor for measuring speed of motor.