Adaptive output feedback event-triggered tracking control for nonlinear systems with unknown control coefficient

•A new pair of high-gain observer and output feedback controller with an improved dynamic gain are presented for a class of nonlinear systems having severe parameter uncertainty and unknown time-varying control coefficient without the precise information of their bounds.•Two kinds of adaptive output feedback event-triggered control schemes are proposed respectively based on the improved fixed threshold (time-varying) and the improved relative threshold (dynamic) strategies. The non-identification adaptive gain is used to compensate the sampling error, which simplifies the control design especially in the case of the dynamic threshold.•The global boundedness of the closed-loop system is guaranteed, while a large class of bounded time-varying reference signals can be well tracked under arbitrary preset precision. In this work, we are committed to dealing with the issue of global adaptive practical tracking for a class of uncertain nonlinear systems based on two kinds of event-triggered output feedback mechanisms. Compared with the highly relevant works, the class of nonlinear systems under investigation have not only unknown control coefficient without the precise information of its bounds, but also more general nonlinearities including any bounded disturbance. In order to deal with the relaxed restrictions, we develop a new pair of observer and output feedback controller with an improved dynamic gain, where the dynamic gain is ingeniously embedded in the backstepping design. Also, to economize communication and/or computation resources, two event-triggered control schemes via output feedback are presented with the time-varying threshold and dynamic threshold, respectively. It is worth emphasizing that the improved backstepping method can simplify the control design especially in the case of the dynamic threshold because of avoiding using hyperbolic tangent function. With the help of Barba˘lat’s lemma, it is shown that all closed-loop signals are globally bounded and system output (i.e., tracking error) will converge to the preset interval in a finite time. Finally, two examples are given to illustrate the effectiveness of the proposed control approach.