Unified ship power grids with alternators and DC power distribution

Nowadays, diesel and turbo-generator sets operated with a constant speed are most widely used as marine power sources. Advantages of standard generator sets include a relatively high efficiency. When generator set is operated as a part of the unified electric power grids with an electric propulsion system and load varying within a wide range, efficiency and reliability of a standard generator set are greatly reduced. A solution for this problem is the use of an alternator consisting of a generator set and semiconductor converters. This alternator is operated with a variable speed optimal for fuel consumption, while a semiconductor converter maintains constant parameters in the power supply network. Modern electric propulsion systems apply frequency converters with a DC link for propulsion motor speed control and power distribution within the unified power grid. The paper describes the design and operation principles of the alternators as well as provides block diagrams of the ship unified power grids with DC power distribution.