Auto tuning of decentralised PID controllers for TITO system

The study presents the concept of taking the into account the higher order harmonic terms during evaluation of the ultimate gain by relay auto-tuning method. The decentralised PID control for a second order diagonally unstable system is designed. The proposed method is compared using the time integral performance and maximum singular value for the perturbated input and load. The robustness studies are conducted to interpret the process behaviour in presence of multiplicative uncertainties. The closed loop performances with less settling time and oscillatory nature is obtained. The comparison with the conventional relay auto-tuning method highlights the effect of incorporating higher order harmonic. The study is implemented on a Two Input Two output sytem with second order unstable diagonal transfer functions.