Prescribed performance observer-controller design for MIMO nonlinear systems with unknown control directions

In this paper, an observer-controller with performance constraints is proposed for a class of multi-input multi-output (MIMO) nonlinear systems with unknown input directions. First, a novel method for limiting estimation error is proposed in the observer design process, which is achieved by integrating the equivalent output injection approach with the prescribed performance technique. Subsequently, a controller is presented that combines the Nussbaum function with the prescribed performance control (PPC) method, which can address the issue of unknown control directions and ensure constrained tracking errors. Finally, the effectiveness of the proposed methodology is validated via a trajectory tracking control task for an unmanned surface vehicle (USV).