Direct synthesis based tuning of the parallel control structure for integrating processes

A controller tuned for servo/regulatory application gives significant performance degradation when used for regulatory/servo purpose. The degradation in the overall performance can be minimised by a two degree-of-freedom control structure. The parallel control structure reported recently decouples set-point tracking from disturbance rejection. In the present work, the two controllers of parallel control structure are designed using direct synthesis approach to achieve robust closed-loop performance for a class of integrating processes. Simulation examples show that improved servo and regulatory performances are achieved by the proposed method as compared to the recently reported strategies when the controllers are tuned to have the same degree of robustness.     

Simple Tuning Rules for Integrating Processes with Large Time Delay

In the present article, controllers of the modified Smith predictor are designed for pure integrating, integrating plus first order and double integrating processes with large time delays. The direct synthesis approach is used to tune the set point tracking controller. Suitable values of the desired closed loop time constant that satisfies both robust stability and robust performance conditions are provided based on extensive simulation studies. The PD controller, which is used for load disturbance rejection, is designed so as to achieve a specified slope (ψ) of the Nyquist curve at the gain crossover frequency. The gain crossover frequency that corresponds to a phase margin of 45 degrees is suggested for all three considered integrating processes. Furthermore, ψ is recommended as 45 degrees for double integrating processes and 90 degrees for pure integrating and integrating plus first order process models. Two simulation examples are considered to illustrate the usefulness of the proposed tuning rules.