Robust PI controller design for a continuous stirred tank reactor with multiple steady-states

The paper presents a method for robust PI controller design for a system affected by parametric uncertainty. The proposed method is based on plotting the stability boundary locus in the plane of controller parameters that is called (k_p, k_i)-plane. The design approach is verified using simulations of robust stabilization and control of the chemical continuous-time stirred tank reactor (CSTR) with hydrolysis of propylene glycol. The control input is the volumetric flow rate of the reaction mixture and the controlled output is the temperature of the reacting mixture. The reactor which has three uncertain parameters is controlled into its stable and unstable steady-state. Obtained results confirm that designed robust PI controllers ensure robust stability in both steady-states.