Variable speed generation is widely used in commercial marine Direct Current (DC) distribution systems however had been limited in Naval applications until the recent championing of the technology by both the German F126 and Belgium / Dutch Anti-Submarine Warfare (ASW) Frigate programmes and more recently programs to the Spanish Armada and Portuguese Navy.
The introduction of DC Power Distribution enables variable speed generation by simply adding a diode or thyristor rectifier at the generator output. Insulated-Gate Bipolar Transistor (IGBT) Inverters can also be used, however these come with lower efficiency and at larger powers, above 1,5 MW, a further downside in the form of size and cost. For Alternating Current (AC) distribution systems, variable speed generation would require an additional inverter stage, i.e. a full frequency converter, which is not attractive due to Size, Weight Power and Cost (SWaP-C).
This paper first addresses the design challenges of the Naval Powerplant Engineer has when balancing demands and then present thoughts how well proven solutions with variable speed operations can resolve these challenges and add benefits to a platform. By eco-driving diesels: Increased fuel efficiency and increased range of up to 27% [4] giving allowance for larger Mission systems; Extended Maintenance Intervals of up to 20%or more; Lower Noise Emissions up to 30% [4] for the benefit of crew and strict noise compliances; Increased Power Density; and Adaptability to Load Variations, especially beneficially for platforms that operate with high percentages of low loads such as loitering or Dynamic Positioning (DP) standby.
The paper will then explore further Naval advantages and the operational scenarios they benefit: Time to start up and connect the generator to the DC distribution system is much faster compared to AC distribution systems, as the generator connects to the DC system at the lower end of the speed range, e.g. 50% of the rated speed, when the generator has reached the rated voltage. No synchronization for frequency and phase is required, just voltage matching provided by the Automatic Voltage Regulator (AVR), thus synchronization is much faster and more reliable than with AC systems. Allows to tune the system to void structural resonances, vibrations, thoughts for Signature management are presented.
The paper will then summarise these benefits, discuss the challenges to overcome and utilise real world commercial examples and benchmark against simulations of naval power plants.
