Improved Control Structures and Methodologies for Linear Processes with Delay

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The aim of this thesis is to investigate various control structures and strategies for time delay processes. Time delays (dead times) appear in many processes in industry, economics, biology, communication networks etc. The presence of dead times complicates the control design and exerts severe limitations on the performance of such systems. Hence control structures that can potentially improve the performance of those processes are of central importance. Simple controllers, easy to design and tune, are very important in process industries. In this thesis, some control schemes based on a new but very simple Smith Predictor are presented. A simple modified Smith predictor control scheme with only two controllers is proposed for stable, unstable and integrating processes. The setpoint tracking controller is designed using H2 optimal control method and an optimal IMC filter structure is proposed to design a PID controller that produces an improved disturbance rejection response. The proposed scheme can, by both analysis and simulation, yield great improvement of both setpoint and load disturbance responses over existing approaches. In addition to the modified Smith predictor design for improved disturbance rejection, several cascade control structures combined with modified Smith predictor are proposed for processes with time delays. In this thesis, two series and two parallel cascade control structures are presented to improve the closed-loop performances and finally, a control structure and design method are suggested for Load frequency control of power system. A series cascade control structure with modified Smith predictor is presented for controlling open-loop unstable time delay processes. An analytical design method is derived for the disturbance rejection controllers by proposing the desired closed-loop complementary sensitivity functions. The direct synthesis method is used to design the setpoint tracking controller. The internal stability of the scheme is analyzed. For a class of integrating time delayed processes, a novel series cascade control structure to enhance the closed-loop performance is investigated. The inner loop controller is designed based on IMC approach and the primary setpoint filter is based on.
Supervisor: S. Majhi