An improved PID control structure for unstable processes

This paper presents a novel control scheme based on modified Proportional-Integral-Derivative (PID) control structure and improved Integral-Proportional (IP) control strategy for controlling unstable, resonant and integrating processes. The newly proposed control structure, named αIP-PD, ensures a good compromise between the above two strategies by giving relatively quick dynamic response with little or no overshoot towards the step input reference. Thus, it not only offers the opportunity to move the pole locations of the controlled plant to more convenient locations, but also its zeros. On the other hand, for setting the feedforward controller gain α, a tuning method is suggested based on minimization of multidimensional rough objective functions and using Artificial Bee Colony (ABC) algorithm. Finally, some examples of different styles of case studies are given, and the simulation results demonstrate that the αIP-PD is more efficient and robust compare to the regular PI-PD controller with optimum gains. Thereby, it leads to better transient behavior, good steady state accuracy, good disturbance rejection, and small parameter sensitivity.