The U.S. Navy wants to move to all-electric ships because they are more efficient and require less maintenance than traditional fuel-propelled ships. They also reduce pollution and greenhouse gas emissions.
Producing smaller, more agile ships that have increased electrical capacity is another of the Navy’s priorities. Doing that means increasing the voltage levels of shipboard energy systems through more compact equipment.
Putting in more electrical equipment and producing more power on a smaller footprint is currently a time-consuming challenge for ship designers, requiring painstaking trade-offs between physical aspects of the electrical system and its capability, and the ship’s objectives.
To ease the process, Robert Cuzner, professor, electrical engineering, has received a five-year, $1.2 million grant from the Office of Naval Research, in collaboration with Arizona State University, to continue development of a virtual prototyping process.
Space isn’t the only concern
Next-generation all-electric ships operate high-voltage electrical systems that use more power electronics for distribution and control than traditional ships.
The modeling tool Cuzner is working on will help naval architects make choices in an environment where the physical space needs of the electrical systems aren’t the only concern.
Many architectural and environmental considerations will affect a ship’s design in ways that are difficult to predict, he said, such as voltage levels, thermal management, fault protection philosophy, placement and amount of energy storage, and the introduction of new power semiconductor technology.
For example, the impact of voltage stresses brought on by power electronics are poorly understood.
“The model will help us better scale the size and weight of this equipment given the unique nature of the voltage stresses,” he said.
Air insulation
When operating system voltages range from 6,000 to 24,000, Cuzner said, designers must consider the spacing of air-insulated power conversion equipment.
The research team is also investigating variables that pertain to insulation. Currently air is the insulator, so designers must provide enough clearance between energized parts of the system. And they are testing an advanced insulating material, called electret, that can be used to significantly reduce this spacing.
The model will help quantify the impact of applying this insulation material to shape the electric fields and reduce stresses on equipment.
“We are applying a machine-learning approach to the significant amounts of experimental data we are collecting,” Cuzner said. “This will enable correlation of experimental data at the limits of operation to a physics-based model, resulting in a usable model that will help designers come up with compact designs that are reliable.”
The research will accelerate the development of multi-disciplinary, multi-level modeling tools to another area vital to the future: green energy. Renewable sources feeding the power grid fluctuate, requiring energy storage to keep the flow of electricity on the grid in balance. Use of power electronics in similarly complex system configurations will enable that.
Cuzner has been involved in the Navy’s quest for creating the next-generation, all-electric ships for the last decade, through multiple grants from the Office of Naval Research and Naval Sea Command.