Enhanced delay compensator based parallel cascade control scheme

Conventional parallel cascade control structure (PCCS) does not yield satisfactory closed-loop performance for processes with large time delay. To overcome this limitation, this manuscript presents a modified Smith delay compensator based PCCS. Stable, integrating and unstable processes with dead time are considered in this work. The proposed PCCS consists of a secondary disturbance rejection controller, a stabilizing controller, a setpoint tracking controller, a setpoint filter and a lag filter for the predicted disturbance. Settings of the primary setpoint filter and setpoint tracking controller are obtained using direct synthesis approach whereas the secondary disturbance rejection controller is designed using internal model control approach. Routh-Hurwitz stability criterion is used to design the stabilizing controller. Moreover, the method of choosing primary and secondary closed-loop time constants is discussed. Simulation studies show that the proposed scheme results in enhanced regulatory performance which is very much essential in process industries.