Enhanced Two-Degrees-of-Freedom Control Strategy for Second-Order Unstable Processes with Time Delay

Using the direct synthesis method, a proportional-integral-derivative (PID) controller in series with a lead-lag compensator is designed for control of the open-loop unstable second order plus time delay processes with/without a zero. Set-point weighting is considered for reducing the overshoot. The method has two tuning parameters, and guidelines are provided for selecting the two tuning parameters. The method gives significant improvement in load disturbance rejection performances. The designed controller is also robust for uncertainties in the process parameters. Illustrative examples are considered to show the performances of the proposed method. Significant improvement is obtained when compared to recently reported methods.