The US Navy is developing new high power electric weapon and sensor technologies, and integration of these advanced systems poses interesting and unique challenges. Integration of high energy, high power mission systems onto future ships with fully integrated power system architectures (IPS) is currently being explored by the Navy research and development community; however, integration of these systems onto existing medium and large surface combatant platforms may also be of interest. Operation of these large pulsed systems can inject harmonics and large transient voltages and currents into the ship’s electric power distribution system. This presents interesting challenges to the ship’s power system, typically requiring some form of filtering and/or energy storage to maintain power quality and accommodate the relatively slow response of the ship’s power generation system.
As the number and magnitude of shipboard transient electric systems increases, new approaches and new technologies are needed to enable robust, flexible electric power systems capable of supporting critical mission requirements. Power generation, propulsion, and some major mission systems are well defined, but development efforts are still required in other areas of the power system to ensure robust, resilient performance. To avoid limitations on the use of current and future electric weapons and sensors, power systems must include energy storage subsystems capable of rapidly transitioning between supplying and absorbing energy at high power levels.
To address this need, CEM has designed the Combat Hybrid Power System (CHPS), an advanced dual mode generator and flywheel energy storage unit that is capable of producing 7-12 MW peak power and 3-4 MW rms power; delivers 19kW-hr energy; and capable of integrating into a range of ship power system topologies and fitting through a 26 inch hatch.
The design employs a very high density inside-out rotor topology; can provide flexible mission support for pulse power, power quality, load leveling and ride-through during power outages; can be scaled down or up; and exhibits very long cycle life. Key enablers developed in this design that also apply to a wide range of very high power density generators include the use of recent advances in composite materials; development and testing of high speed permanent magnet cartridge for the rotor; inside-out magnetic bearing technology; and use of advanced rotor-safe life design practices.
Design specifications for the CHPS machine are shown in Table 1. The CHPS machine is a fully-integrated machine with the flywheel and motor/generator sharing the same rotor. The inside-out topology puts the rotor out-board of the stator allowing an optimum air-gap diameter, an advantage in stored energy density, and an improvement in radiative cooling of the rotor even though not substantial.
Table 1: Top level CHPS specifications.
Today, the energy stored in a ship’s fuel is converted to electricity using a gas turbine and a generator, which are classed as rotating machines. While the initial tests of emerging systems have been run using batteries or capacitors for storage, rotating machines for these applications offer several potential advantages:
• Improved power and energy density
• Essentially unlimited charge/discharge cycle life
• Independent selection of charge/discharge power and energy storage
• Availability for other services to the ship’s power distribution system
Proper use of rotating electric machines to support pulsed power module concepts in the context of ship hybrid electric power system architecture can play a critical role in maximizing and optimizing naval capabilities for the full range of operations requirements. The ability to serve multiple systems minimizes overall size by maximizing energy and power density in already space constrained platforms. The vision is to have a system-level optimization of the electrical power system as opposed to developing specialized energy storage and power conversion for each individual mission system.