The control system of AFPT (Air Flow Pressure and Temperature) pilot plant has been used successfully to demonstrate the design of some controllers such as PID, cascade PID and fuzzy logic controller. It is important to develop a gas density control system in the AFPT pilot plant since gas density is one of the gas properties which need to be set precisely in few processes. The control system is designed based on Internal Model Control (IMC) structure. Internal Model Control (IMC) yields very good performance for set point tracking, but gives sluggish response for disturbance rejection problem. Feedback/feedforward controller and cascade control configuration have been widely used to overcome the disturbance rejection. However, feedback/feedforward IMC is suffering with the difficulty of measuring disturbance and/or making disturbance model in real plant due to the possibility of more than one disturbances. The present study has developed a controller for disturbance rejection based on feedback/feedforward IMC structure and combined with cascade control. The proposed controller is also implemented to a long time delay process i.e. Semino and Brambilla proces model. The controller structure could give a good performance compared to standard IDOF IMC.
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