Design of control for efficiency of AUV power systems

Abstract

The MIT Rapid Development Group designed and built an internal combustion hybrid recharging system for the REMUS 600 Autonomous Underwater Vehicle (AUV) in collaboration with the MIT Lincoln Laboratory. This power system will recharge the lithium ion battery pack of the REMUS 600 and allow the vehicle to travel for 40 consecutive 12-hour missions without returning to recharge. This study analyzes the optimization of time and fuel efficiency in systems of this type. First, the battery charging scheme for optimal time efficiency was investigated through theoretical simulation of the REMUS battery recharging, based on typical curves for lithium ion battery charging. Secondly, the optimal control system for optimizing fuel efficiency was found by examining behavior in several different engines and predicting behavior in MIT RDG hybrid system's engine. A system was developed to control the throttle of the engine while sensing the voltage coming out of a synchronous rectification bridge. This scheme keeps the throttle above 50% unless the power requirement of the charger drops suddenly. Finally, the control scheme was implemented in software, along with controls for engine starting and shutdown.