Diving control of autonomous underwater vehicles via fuzzy sliding mode technique

In this paper we address the design and implementation of a fuzzy sliding mode control (FSMC) scheme for depth control of autonomous underwater vehicles (AUV´s). The proposed scheme is compared with classical sliding mode control (SMC). At first we examine the response of sliding mode control based on ackermann formula for diving model. SMC is adequate for controlling depth of AUV´s, since it offers robustness in the presence of uncertainties parameters and environmental disturbances. However the main drawback is the chattering effect that stimulates high frequency vibration that can damage the actuators. An SMC can give good transient response, however the steady state performance is poor due to the presence of discontinuous control which causes chattering hence we focus on designing of FSMC for controlling depth maneuver. Next we describe the design scheme of FSMC in which mamdani type fuzzy inference system is employed. The proposed control method enhances the ability of fuzzy logic control (FLC) so that the minimal number of fuzzy inference rule is systematically obtained even the plant parameters are unknown. Comparative study between the both control laws is presented through numerical simulation. An illustrative example shows that good transient and steady state response can be obtained by applying proposed control strategy.