Model-based PID tuning for high-order processes: when to approximate

In this paper different methods for the (model- based) tuning of Proportional-Integral-Derivative (PID) controllers for high-order processes are analyzed and compared. In particular, two approaches in the internal model control framework are addressed and discussed: (i) the (high-order) controller that results from considering the high-order process model is reduced through a Maclaurin series expansion in order to obtain a PID controller; (ii) the process model is first reduced in order to obtain naturally a PID controller (different techniques are considered for this purpose). Simulation results regarding different process dynamics are evaluated in order to draw general conclusions.