Machine design and configuration of a 7000 HP hybrid electric drive for naval ship propulsion

This focuses on the electrical machine design for a 7000 HP synchronous drive system using high-field permanent magnet (PM) motors for retrofit of a hybrid electric drive to the U.S. Navy DDG-51 FLT 3 ship. A dual system is described which has each module rated at 3500 HP, 6000 rpm and connected to the output propeller shaft through a two-stage gearbox. The system is intended to operate at 12 knots or lower speed allowing the main LM-2500 gas turbine main propulsion drive to be powered down and saving 15-17% in propulsion energy. In the hybrid mode, electrical power is furnished from the ship´s 450 Volt 60 Hz electrical bus and converted to 200 Hz variable frequency through four IGCT based bi-directional converters to each drive motor. Aspects of the PM machine design which are special to this system include the use of 16-phase windings for lower harmonic content, larger damper winding arrangements and high strength rotor magnet containment. The PM stator contains a rapid internal fault detection (IFD) system for 1/4 cycle isolation of winding faults. Liquid-cooled machine designs with power density in the range of 6.0 to 12.0 kW/kg are shown. The overall system produces a total harmonic distortion of about 1.0% at the 450 Volt terminals at partial or full load in both motor and regeneration modes.