A hybrid variable structure control scheme for nonlinear systems

This paper presents a hybrid variable structure control scheme for nonlinear systems. A hard variable structure control is constructed firstly for achieving uniform ultimate boundedness control. Then, a soft variable structure control using fuzzy logic is incorporated to help improve dynamic responses when trajectories enter into the ultimate bound. For practical consideration, we added a GA-based alpha-beta filter in front of the fuzzy controller to suppress noise and obtain smooth input signals. The performance of the control scheme was examined not only by a simulative example of an inverted pendulum but also by an experimental PC-based magnetic levitation system. The simulation and experimental results strongly suggest the newly proposed control scheme is encouraging for practical applications.