I-PD controller design for integrating processes and identification of asymmetrical systems by relay feedback

Within the scope of this thesis, studies were carried out on the control of integrating processes and relay feedback identification and control of asymmetrical heating and cooling systems. Integrating processes, that is, processes containing one or more integrators in their transfer functions, are frequently encountered in the industry. In this thesis, analytical expressions are derived for controlling integrating first order plus dead time (IFOPDT) and double integrating first order plus dead time (DIFOPDT) processes that allow optimal calculation of integral-proportional derivative (I-PD) controller parameters for both setpoint tracking and rejecting input load disturbance. Optimal tuning formulas for setpoint tracking and rejecting input load disturbance were achieved by minimizing of time moment weighted integral performance criteria. The resulting I-PD tuning formulas are in terms of the transfer function parameters of the process, i.e., gain, time delay and time constant. Simulation examples are given to demonstrate the use of the proposed method. In order to demonstrate the superior closed-loop performance of the proposed approach compared to the existing proportional-integral-derivative (PID) and I-PD controller design methods, comparisons are made with some studies in the literature, and the practical application of the proposed design method is demonstrated by controlling the position of a cart on an experimental setup. Another study conducted in this thesis on integrating processes focuses on the control of such processes based on maximum sensitivity (Ms). In this study, I-PD controllers for pure integrating plus dead time (PIPDT), double integrating plus dead time (DIPDT) and IFOPDT processes are designed using direct synthesis approach. The proposed design method is based on the comparison of the characteristic equation of the closed-loop system, which involves an integrating process and an I-PD controller with a phase lead/lag filter, with the looked-for characteristic equation. In the study, simple and analytical tuning rules are derived to determine the parameters of the I-PD controller and the phase lead/lag filter according to the desired robustness, represented by Ms. The resulting formulas contain the process transfer function parameters and a tuning parameter used to set the desired Ms. Again, the benefits of the proposed method are demonstrated with simulation examples and a practical application of cart position control in an experimental setup, and comparisons with some PID and I-PD design methods in the literature are provided to clearly demonstrate the advantages of the proposed method. In this thesis study, besides, xxii asymmetrical heating and cooling systems are identified by relay feedback and controlled by proportional integral-proportional derivative (PI-PD) controllers. Asymmetrical heating and cooling systems are a type of nonlinear system common in the process industry. These systems consist of two operating phases, heating and cooling modes, and each operating mode has a different dynamic characteristic. In the identification process, relay feedback identification method based on state-space approach was used to obtain two first order plus dead time (FOPDT) process models. After the system was identified, two sets of PI-PD controller parameters were gained in accordance with the gain and phase margin specifications selected by the user, and the system was controlled in a gain-scheduled PI-PD control strategy. Again, some simulation examples are given to demonstrate the use and benefits of the proposed identification and control methods, and comparisons are made with a similar study to clearly reveal the advantages of the proposed techniques for both the identification and control method.