Flexible Prescribed Performance Control of Unknown Cascade Nonlinear Systems

ABSTRACT The problem of global prescribed performance control (PPC) of the cascade nonlinear systems is investigated in this paper. It is concentrated on the cases of the state‐dependent internal dynamics, inseparable state couplings, nonlinear virtual control coefficients, and totally unknown closed‐loop dynamics, which render the existing solutions infeasible. To conquer this challenge, a flexible PPC approach is put forward in this paper, which not only yields uniform performance insurance under any initial condition of the closed‐loop system but also leads to a continuous and amplitude‐reduced control input with respect to the existing solutions. Besides, it shows a striking control simplicity, with no need for parameter identification, function approximation, disturbance estimation, derivative calculation, or command filtering. A comparative simulation on a ship model illustrates the theoretical results.