A DISCRETE-TIME GLOBAL QUASI-SLIDING MODE CONTROL SCHEME WITH BOUNDED EXTERNAL DISTURBANCE REJECTION

A global quasi-sliding mode control (GQSMC) scheme is introduced to ensure zigzag motion with a smaller bound than that offered by Gao's method and to provide disturbance rejection throughout the entire response in discrete time. The design of an augmented forcing function is followed by three conditions in discrete time extended from global sliding mode control (GSMC) in continuous time. Furthermore, we adopt a switching gain, which is auto-tuned as a function of sliding surface s(k), such that chattering phenomena can be considerably alleviated during the steady-state, significantly reducing switching control applied to the plant. The proposed GQSMC scheme can provide more advantages such as an even distribution of the control input throughout the entire response and an improvement in the accuracy and speed of the desired performance, guaranteeing a quasi-sliding mode throughout the entire response. In addition, we also consider the input disturbance rejection according to the norm-bounded exogenous signal. Results from both the simulation and the experiments are reported. The results further verify that we can use the global sliding surface to curtail reaching the phase stage.