Control system performance and efficiency for a mid-depth Lagrangian profiling float

This paper presents the development of a new mid-depth Lagrangian profiling float with a primary emphasis on the control system performance and efficiency. While deep water floats have demonstrated much success in open ocean environments, many are not suited for the additional challenges associated with coastal regions. To study these regions, which are often subject to varying bathymetry within the operating range and higher variations in water density, a more advanced system is required. This new design utilizes pressure and altitude feedback to drive a high volume auto-ballasting system (ABS). The main operating modes of this float include step inputs to park and drift at constant depths, profiling inputs with adjustable rates and adaptable limits, and constant altitude bottom tracking. To handle these tasks, a state-space feedback control system, which uses feedback linearization to account for the nonlinear drag force acting on the moving float, was designed and simulated. Additionally, the development of the control system was coupled with empirical motor efficiency data to study the tradeoffs between efficiency and performance.