Nonlinear variable structure double mode control of AUV

In order to achieve fast response and no chattering, a nonlinear variable structure double mode controller for SISO systems is presented and applied in three channels control for AUV. This controller employs the nonlinear sliding-mode control which possesses the "quasi-time-optimal-switching-surface" when the state is far from the equilibrium point, and can be automatically turned into linear sliding mode controller which possesses the integral type linear switching surface when the state is near the equilibrium one. It is believed that this controller has the following distinguishing features: 1) nearly time-optimal response speed, 2) very small overshoot, 3) no static error, and 4) no chattering.