Robust adaptive passivity‐based control of open‐loop unstable affine non‐linear systems subject to actuator saturation

Considering the effect of actuator saturation, a control design approach is presented for open‐loop unstable affine non‐linear systems. A feedback control law with some degrees of freedom along with a virtual output function is utilised to make the system passive. In order to achieve a fast convergence, an analytical discussion is presented to opt for the free parameters. The procedure is further developed for systems with unknown parameters, where some adaptation laws are utilised for parameter estimation. In order to enhance the convergence performance, the gains of the adaptation laws are obtained based on sensitivity analysis. Using projection technique to prevent parameter drift, it is analytically shown that the proposed scheme is robust against bounded disturbances. The effectiveness of the proposed controller is assessed through extensive simulations.