LQR pitch control strategy of AUVs based on the optimum of sailing resistance

When an Autonomous Underwater Vehicle(AUV) sails near the surface of the sea, it will inevitably be subjected to wave disturbance. The heave and pitch motion caused by wave disturbance not only affects the navigation attitude of the AUV, but also leads to an increase in sailing resistance. As such, its energy consumption is increased. In this paper, the six degrees of freedom model of AUVs is established and linearized in order to achieve the weighted optimization of the sailing attitude and the resistance of the AUVs. The drag force model of the AUV is derived using the theory of potential flow. The Q matrix and R matrix are determined in the controller based on research into the drag force model. The Linear Quadratic Regulator(LQR)controller of the AUV is designed using the drag force model as the performance index. The simulation results show that after adding the LQR controller, the effects of reducing heave motion and pitch motion are 46.64% and 77.62% respectively, and the increased resistance caused by the pitch motion is reduced to 1/6 of its original value. The results show that the multiple optimum of attitude and sailing resistance is realized, the energy consumption is decreased and the endurance of the AUV is increased.