Nonlinear PI controller for systems with state constraint requirements

PI control is widely applied in industrial applications to guarantee a desired regulation for both linear and nonlinear systems. However, when a state constraint requirement is needed for the plant, conventional PI controllers fail to guarantee a desired upper bound for the system states of a generic nonlinear plant at all times. In this paper, a novel nonlinear PI controller is proposed to achieve regulation with state constraint satisfaction for a class of nonlinear systems with constant disturbances. An upper bound for the desired closed-loop system states is guaranteed based on nonlinear ultimate boundedness theory and closed-loop stability is analytically proven for the desired equilibrium point. In addition, a detailed analysis is presented for the appropriate design of the proportional and integral gains of the proposed controller. A practical example of a dc/dc power converter is investigated and simulation results demonstrate the effectiveness of the proposed nonlinear PI control compared to the conventional approach.