Adaptive fuzzy sliding control enhanced by compensation for explicitly unidentified aspects

Reality shows that 1) the effectiveness of compensators for uncertainty and disturbance (UAD) depends deeply on UAD's time varying rate (TVR), and 2) controlling a system over a network introduces different constraints and conditions, in which some of these are variable delays in control signal, packet losses, data quantization, safety, and security. This paper presents a new design of fuzzy sliding mode control (FSMC) enhanced by compensation for UAD using a disturbance observer (DO), named DO-FSMC, for a class of nonlinear systems subjected to UAD. First, in order to weaken partly the negative influence of TVR of UAD on the compensation effectiveness, we separate explicitly unidentified aspects into two groups, one related to the model error while the other coming from external disturbances, to distinctly consider. To stamp out the chattering status and reduce calculating cost, we propose an adaptive gain updated directly based on the sliding surface convergence status, to which two new control laws, one for the FSMC and the other for the DO-FSMC, are given via Lyapunov stability analysis. In order to evaluate the DO-FSMC, simulations as well as surveys based on a real semi-active suspension system using a Magnetorheological damper (MRD) with measured datasets are performed. The results obtained from the surveys coincide with the theoretical analysis which show that the competence to stamp out vibration is the advantage of the proposed method compared with the other published methods.