Optimized energy-efficient drive system for ship propulsion

Efficiency in the sense of energy saving is a main issue in ship propulsion. Optimization is achieved using an overall diesel-electric drive concept. Based on the main load, the overall structure of a Diesel-electric ship propulsion system is dimensioned. In total, gears between propellers and motors, induction motors and their inverters, two diesel engines with permanent-magnet synchronous generators, diode rectifiers feeding the common DC link and a novel reconfigurable variable-voltage DC-link structure are chosen. Based on this layout, an inverter for the auxiliary supply and a battery for feeding the auxiliaries in harbour or driving the ship at low-speed manoeuvres are designed for optimal connection to the variable-voltage DC-link structure. As a result, the diesel engines can be operated always with optimal speed according to their shell curve. Load variations are adjusted to the dynamics of the diesel engines guaranteeing smooth operation without pressing. With the highly variable DC-link voltage, the motors and inverters can be operated in a most energy-efficient way by optimized field-weakening of the induction motors. Efficiency plots prove the concept.