Spatial observer-based repetitive controller: An active disturbance rejection approach

•This work proposes a spatial repetitive controller based on a linear disturbance observer under an active disturbance rejection control approach.•The inclusion of the GPI observer transforms the nonlinear spatial system into a simplified linear one on which a linear repetitive controller can be designed.•The experimental results show that the proposed strategy is an effective option to reject the periodic disturbances operating at varying speed.•The presented scheme is simpler and does not need any adaptation or robustification mechanism.

Linear Repetitive Control has proven to be an effective strategy to compensate for periodic disturbances in mechatronic systems that operate at constant speed; however, it renders very poor performance in varying speed applications. In this work, a Repetitive Controller based on a Generalized Proportional Integral (GPI) observer under Active Disturbance Rejection approach is presented and formulated in spatial domain. The inclusion of the linear GPI observer makes possible to see the spatial non-linear system as a simplified linear one by means of an on-line estimated unified disturbance term. Experimental results show that the presented linear approach successfully rejects periodic disturbances under varying speed conditions.