| Most plants in thermal process are two-input and two-output (TITO) systems, characterized by large inertia, strong coupling and difficulty to set up accurate models, etc. So it is complicated to design multivariable PID controllers for plants of this kind. Combined with simulation experiments, applications of GB approach, refined GB approach and DCP approach are studied in this thesis to design appropriate controllers for the following plants: the boiler-turbine coordinated control system in BTG unit, the Circulating Fluidized Bed (CFB) Boiler combustion system, and the binary distillation column control system.The principles of GB approach and DCP approach are analyzed respectively. The former is based on diagonal dominance and Nyquist stability, while the latter is deducted by relay feedback identification. Analytic expressions of intersections of real axis and Gershgorin Band of diagonal element can be obtained by means of equations of envelope. Then refined GB approach and DCP approach are used to control first-order plus delay plant and high order plant as well.By utilizing the precompensator, multivariable PID controllers are designed for the boiler-turbine coordinated control system in BTG unit. Simulation experiments are performed in comparison with principal gain method.According to the procedure of refined GB approach, the multi-loop PID control system of the Circulating Fluidized Bed (CFB) Boiler combustion process is developed. Simulation results in step response are compared with those obtained by the strategy with neural network decoupling and the one without it.Compared with O-R approach and Inversed-Based (I-B) approach, the binary distillation column control system designed by DCP approach is under investigation in the folloing aspects: set-point response, load disturbance and performance parameters. The design methods mentioned above provide good disturbance rejection, performance robustness as well as satisfactory set-point tracking for simulation examples. |
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