Nonlinear Parameters Auto-Tuning in Sliding Mode Controller for an Autonomous Underwater Vehicle Flight Control

Performance of sliding mode controller (SMC) in the autonomous underwater vehicle (AUV) is affected by the nonlinear parameters selection, which are: boundary layer thickness and switching gain. Human expertise, knowledge on disturbance amplitude and information about the bounds of system uncertainties are required to design these parameters. In order to decrease these requirements an auto-tuning SMC (AT-SMC) with optimal parameters in the nonlinear part of the controller is proposed in this article. For this purpose, a fitness function is presented and a heuristic algorithm is applied for minimizing it. The AT-SMC is implemented on an Axiomtek 84710 through the xPC Target and then the abilities of that in AUV flight control is evaluated through the processor-in-the-loop (PIL) test. By this way, the execution codes of proposed method before the harbor acceptance tests (HAT) and sea acceptance tests (SAT) are verified and so the cost of field tests are reduced in a significant manner. The results of the PIL tests in AUV flight control indicate that the AT-SMC reduces the chattering phenomenon and overshoot in comparison with the conventional SMC.