Sliding mode controller with improved switching face for underwater vehicles

As sliding mode (SMC) control has just a unitary switching face, the system converges slowly at the origin. An improvement was made to the linear switching surface of SMC for autonomous underwater vehicles (AUVs) in this paper. A polyline switching surface was proposed, velocity control and velocity control at appointed positions were realized. The improved switching surface was made up of the lines with different slopes, and it was smoothed at break with sigmoid functions. The slope of switching surface was set 0 to realize velocity control and the intelligent integral was introduced to reduce the steady-state error of velocity control. Finally, the simulation experiments have been carried on “XX” AUV. The results show that polyline switching surface can reduce the rise time of system and accelerate system response, the steady-state error approaches 0 at velocity control and the velocity control are realized perfectly.