A graphical technique of controller synthesis with desired closed-loop specifications

Abstract

A graphical technique for the design of PI/PID controllers to achieve desired closed-loop frequency-domain as well as time-domain specifications simultaneously, is proposed in this paper. Both frequency and time-domain performance measures such as gain margin, phase margin, maximum percentage overshoot and settling time can be specified before controller tuning. Simplicity of the technique is an added advantage. The concept of stability boundary locus along with gain phase margin tester (GPMT) is used to compute constant gain and phase margin boundaries in the controller parameters plane. Common area of constant gain and phase margin boundaries within the all stability region is the desired gain and phase margin region (DGPMR). A novel graphical technique using the direct synthesis approach is proposed to obtain the desired closed-loop time response. Curves corresponding to the time-domain performance measures (maximum percentage overshoot and settling time) are drawn in the controller parameters plane. Intersection of the above-said curves within the DGPMR gives the desired controller parameters. Simulation results for a nonminimum-phase third order process and hardware experimental results for a DC-DC boost converter with comparison are given to show the effectiveness of the proposed tuning strategy.