Input saturated systems: A digital redesign approach to controller synthesis for a class of nonlinear systems

Many real world control systems are plagued by the ubiquitous problem of input saturation, resulting mainly from the limited authority of final control elements. The effects of this phenomenon on practical control systems can range from mild to potentially catastrophic for mission critical applications. While there has been a lot of research in this area, most of the research has been in the continuous-time setting. Given the current proliferation of sampled-data systems, in which digital control systems are utilized on continuous-time plant duty, this research has proposed a digital redesign solution that is applicable to both existing and new installations. A formulation for a class of nonlinear systems is proposed, in which a non Jacobian optimal linearization scheme that yields models that are truly linear and optimal at every operating point of interest is utilized in combination with a dual-rate conditioning scheme that exploits an inherent characteristic of digitally redesigned systems. The proposed system is shown capable of quickly guiding both linear and nonlinear constrained systems out of saturation.