Output-Constrained Prescribed Performance Control of MIMO Nonlinear Systems With a Priori Unknown References

The problem of prescribed performance control (PPC) for the multi-input multi-output block-triangular nonlinear systems under output constraints is investigated in this article. It is focused on the scenario where the references are not known in advance. This renders the related solutions infeasible and becomes more challenging under the totally unknown and inherently nonlinear dynamics of the system. To overcome this challenge, a novel robust decoupling PPC strategy is developed in this article, in which an online boundary generation scheme and a smoothly constraint switching rule are devised and introduced. The resulting controller ensures that the system outputs evolve within their respective constraint bands and track the references with the predetermined overshoot, settling time and accuracy. Moreover, it is independent of function approximation, parameter identification, or disturbance estimation, despite the unbounded nonlinearities, unmatched disturbances and unknown dynamics. A comparative experiment on a 2-DOF serial flexible link robot is conducted to show the efficacy and superiority of our low-complexity high-performance control approach.