Enhanced Simultaneous Automatic Synthesis (SAS) of 2-DOF QFT Based Robust PID Controller Design for Servo Systems

This article presents a simultaneous automatic synthesis (SAS) of robust controller and the pre-filter, 2-degree of freedom (DOF), involved in the quantitative feedback theory (QFT) approach to address the large setpoint tracking for the motion control problem of dc servo uncertain systems with disturbances, sensor noise and control effort constraint. The traditional QFT based 2-DOF design being manual, time consuming and tedious, involves two step design process which results in nonoptimal solution. The merits of the proposed SAS approach are: 1) formulation of the robust proportional–integral–derivative (PID) controller and the pre-filter design as a single step nonlinear optimization problem with an enhanced objective function and performance constraints; 2) inclusion of the controller and pre-filter terms in the enhanced objective function to obtain the optimal controller and pre-filter; 3) enforcing various performance constraints such as robust tracking, input disturbance rejection, control effort and robust stability constraints; 4) minimization of closed-loop system bandwidth with an inclusion of optimal pre-filter; 5) free from actuator saturation while tracking the large setpoints. The effectiveness of the proposed SAS QFT approach is demonstrated on a QUBE dc servo system. The experimental validation of the proposed scheme exhibits the fast and accurate robust tracking performance with a minimum control input.