Active Disturbance Rejection Control for Nonaffined Globally Lipschitz Nonlinear Discrete-Time Systems

The design and analysis of active disturbance rejection control (ADRC) are considered for a globally Lipschitz nonlinear discrete-time system, which is nonaffine to control inputs. A local dynamic linearization is proposed to transfer the original nonaffined nonlinear system into a nonlinear system affine to control input such that the open problem of selecting a control gain in the feedback control law of ADRC is solved. Furthermore, both a parameter updating law and an adaptive extended state observer are designed to estimate control gains and total uncertainty, respectively. The stability of ADRC for nonlinear nonaffine discrete-time processes is analyzed rigorously for the first time with the aid of contraction mapping principle. The proposed adaptive feedback controller considers desired reference trajectory, parameter adaption, error feedback, and the compensation of total uncertainties caused by parameter estimation error and unknown nonlinearity simultaneously to achieve better control performance. The proposed method is nearly data driven since no other model information is needed except for the globally Lipschitz condition and the nonzero property of the partial derivative of the nonlinear system with respect to the control input. The theoretical result is verified by simulations.