Energy optimal depth control for long range underwater vehicles with applications to a hybrid underwater glider

Abstract

The efficient control of a vehicle's depth is a ubiquitous need of underwater vehicles for long term deployments. Using standard hydrodynamic drag and lift formulations for a hybrid autonomous underwater glider (AUG) the performance penalty for long range underwater vehicles with a non zero buoyant force is shown to be significant. To this end, an energy optimal depth controller design methodology for a long range autonomous underwater vehicle is presented with applications to a propeller driven hybrid AUG during level flight. The method makes use of a reduced order linear model that has been validated from field data. The standard state space model is augmented with the state integral matrix and rewritten to the state error representation. The resulting representation is well suited to the computation of energy optimal gains for a linear quadratic regulator. Field demonstrations of the standard pitching depth controller and the energy optimal depth controller using the computed gains shows the reduced order model to be sufficient for the purpose of the controller design, improving on the standard pitching depth controller response, transport efficiency and ease of tuning.