A New Vertical Plane Motion Control Method Based on the Framework Consisting of Control Law and Control Allocation for Underwater Vehicle with Bow and Stern Elevators

To improve the vertical plane motion performance of an underwater vehicle with bow and stern elevators under actuator saturation and external disturbance conditions, a new control method is proposed in this paper. Firstly, for simplifying the analysis of the coupled kinetics equation of the underwater vehicle, virtual control variables are introduced to decompose the kinetics equation into two cascaded components. Then, a framework consisting of control law and control allocation is presented according to the cascaded components. In the aspect of control law, a double closed-loop control scheme is designed. The outer loop realizes the depth control by adjusting the expected heave velocity and pitch of the underwater vehicle with an S-plane regulator and a subsection function. Meanwhile, an Augmented Linear Quadratic Regulator (ALQR) is employed in the inner loop to control the heave velocity and pitch without steady-state error. Considering the physical constraints of elevators, a pitching-priority idea is adopted in the design of the control allocation to prioritize the pitch control requirement of the underwater vehicle. Finally, based on the framework, disturbances are estimated and compensated to enhance the anti-interference performance, as well as, auxiliary functions are constructed for reducing the adverse effect caused by saturation. Simulation results show that the new control method performs perfectly under various conditions, it is also conducive to the navigation safety of the underwater vehicle because of its superior pitch control capability.