Design of decentralized PI control systems based on Nyquist stability analysis

Presents a simple but effective design method for decentralized PI control systems with guaranteed closed-loop stability. Nyquist stability conditions are analyzed for decentralized control systems. Formulas are derived that express the stability region for each PI controller in terms of the controller parameters. A detuning factor for each loop is specified based on a diagonal dominance index. Then appropriate controller settings are determined using this index and the stability region. Simulation results for a variety of 2 /spl times/ 2 and 4 /spl times/ 4 systems demonstrate that the proposed design method guarantees closed-loop stability and provides good set-point and load responses.