Publication Detail

Comparative Study of Various Electric Propulsion Systems and their Impact on a Nominal Ship Design

James C. Davis,
207 pp.

Synchronous, permanent magnet, and induction machines are modeled using computer programs. The computer programs incorporate an optimization algorithm which converges on lowest weight, volume, and inefficiency. Machine designs
for high and low rpms are performed, with a varying number of pole-pairs. The machine designs are analyzed to find the optimum combination of generator and motor for inclusion in
a naval ship propulsion system.

Three ships are used for the system study, a baseline mechanical transmission ship, a ship retaining the same subdivision as the baseline but with the electric machinery, and an electric transmission ship with subdivision and
machinery box arrangement chosen to benefit from the inherent arrangeability of electric transmissions.

wo generator/motor combinations are used in the final ship analysis/ Both employ a 3600 rpm, six-pole synchronous generator, which turns at the shaft speed of the prime mover. One combination uses a 180 rpm, direct-drive, 16-
pole synchronous motor, and the other uses an 1800 rpm, geared, 8-pole synchronous motor. Power converters are used in both combinations to control motor speed.

The geared combination in the rearranged ship demonstrated the best endurance speed efficiency, reducing the endurance fuel load by 18%, while maintaining the maximum and sustained speed of the baseline ship. The savings in ship volume translated to an additional twenty Tomahawk missile cells in the rearranged ship. When the fuel load was held at the tonnage of the baseline ship, endurance range increased as much as 25%.

Permanent magnet machines were not competitive in this study due to their high weight and volume, even though their individual machine efficiency was the highest of all types. Induction machines were not used as propulsion generators because of the inherent difficulties in control. The induction machine motor candidates were not competitive because of off-design-point inefficiency.

type: Full theses / dissertations

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