Integral Sliding Mode Control: Performance, Modification, and Improvement

Sliding mode control (SMC) is attractive for nonlinear systems due to its invariance for both parametric and nonparametric uncertainties. However, the invariance of SMC is not guaranteed in a reaching phase. Integral SMC (ISMC) eliminates the reaching phase such that the invariance is achieved in an entire system response. To reduce chattering in ISMC, it was suggested that the switching element is smoothed by using a low-pass filter and an integral sliding variable is modified. This study discusses several crucial problems regarding the performance, modification, and improvement of ISMC. First, the modification of the integral sliding variable is revealed to be unnecessary as it degrades the performance of a sliding phase; second, ISMC is shown to be a kind of global SMC; third, it is manifested that a high-order ISMC design with super twisting involves a stability condition that may be infeasible in theory; finally, an efficient solution is suggested to attenuate chattering in ISMC without the degradation of tracking accuracy and the solution is extended to the case with uncertain control gain functions. Comprehensive simulation results have verified the arguments of this study.