On Controller Design for Unknown Nonlinear Systems with Prescribed Performance and Input Constraints

This paper considers the tracking control problem for an unknown control-affine nonlinear system with time-varying bounded disturbance subjected to a prescribed performance and input constraints. For such a problem, we cannot arbitrarily specify any restriction on the input. For the same, we have given a feasibility condition for prescribing input constraints. In addition, we cannot prescribe arbitrary performance constraints when input constraints are present. There is always a trade-off when performance and input constraints are specified simultaneously. To deal with such arbitrary prescription issues, we also devised a feasibility condition for prescribing performance constraints. Furthermore, considering the feasibility condition, we have proposed a low-complexity approximation-free controller, which guarantees that the tracking performance will never violate its prescribed performance and input constraints. Simulation results, including case studies, show the effectiveness of the proposed controller and support the feasibility condition by examining the failure of the tracking performance under unfeasible conditions.