Constrained Model Predictive Control of Variable Buoyancy Device

This paper presents a design and physics-based dynamic model of an underwater depth control device based on buoyancy change. Negative buoyancy is achieved by decreasing the volume while keeping the mass constant, resulting in a higher density. The nonlinearities are discussed in the context of the operation conditions and the practically fulfilled assumptions. With reasonable considerations, the dynamic model is linearized and state-space equations are developed for such a system. The stability of such systems, when subject to constrained control input, is studied. A Model-based Predictive Control (MPC), which optimizes the control energy and output error with disturbance rejection and considers constrained control input, is then developed. The controller was simulated using MATLAB with a discrete plant model. An experimental setup was also created to test the controller. The developed MPC was then tested experimentally on the hardware which shows the validity of the dynamic model as well.