Nonlinear tracking controllers for actuator saturation effects mitigation

The state of the art with respect to nonlinear controller synthesis methods that address tracking control in the presence of actuator constraints is examined. Results based on the concepts of maximal output admissible sets, maximal statically admissible sets, and the linear quadratic tracking control method are reviewed. A common requirement of the first two methods is the limitation of the feasible reference signals to those that are statically admissible. Here we propose an invariance based approach that does not require static admissibility of the reference signal to obtain a BIBO stable closed-loop system with improved tracking performance. The latter is achieved since the system is driven harder without violating the actuator constraints.