PI controller design with feedforward by CDM for level processes

A second-order level process controlled by PI controller designed from coefficient diagram method (CDM) can meet the desired performances both in transient and steady-state response. However, the transient response generally still has long rise time. This paper presents an additional idea to improve the speed of the system response by including a feedforward controller (FFC) in the closed-loop system. The structure of the FFC is a phase lead structure with a parameter that can be varied greater than one. The faster step response of the controlled system can be obtained while the rejection speed of the effect due to constant output disturbance is not affected by the proposed FFC.