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Advanced Medium-Voltage, High-Power Charging Converter for Pulsed Power Applications


TECHNOLOGY AREAS: Ground/Sea Vehicles, Electronics

ACQUISITION PROGRAM: PMS 320, Electric Ship Office

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports):  This topic is “ITAR Restricted”.  The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data.  Foreign Citizens may perform work under an award resulting from this topic only if they hold the “Permanent Resident Card”, or are designated as “Protected Individuals” as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop an advanced, modular, scalable, converter charger for a 250 kilo-joule (KJ) capacitor for the Electromagnetic Railgun's (EMRG's) Pulsed Power System (PPS).

DESCRIPTION: The Navy is currently developing a Pulsed Power System (PPS) to power an Electromagnetic Railgun (EMRG). The PPS uses a capacitor bank as the source of the very high current (on the order of several mega-amps) required by the EMRG for operation. EMRG requirements necessitate the use of a high power density (>1MW/m3) DC/DC converter capable of high, repetition-rate charging of capacitor banks. This capacitor bank is comprised of 250 KJ capacitor “rep-rate” modules which must recharge from the ship’s power system in no more than several seconds (equating to an average power draw of greater than 40 KW per module, or a total of greater than 8 MW for a 50 MJ system) in order to achieve the desired EMRG repetition rate. Presently, the available state-of-the-art in commercial capacitor chargers is not optimal for the anticipated high repetition-rate EMRG application. They have insufficient power ratings, with a unit size of less than 35KW, which would require that a very large number of systems be operated in parallel. They have power density of <0.2MW/m3 as single units which becomes significantly worse as units are ganged together in cabinets. They are not configured for the projected DC voltage input that they will see in this application and would require external rectifiers, further reducing power density. They are not suitable for shipboard use and would need significant modifications to meet military standards for shock, vibration, EMI, and power quality. Lastly, the volume and interior space air conditioning limits of shipboard application dictate the use of liquid cooling. Commercial chargers are nearly exclusively air cooled, which imposes a significant volume penalty and results in heat being dissipated into the interior spaces of the ship, placing a large heat burden on the air conditioning system. These shortcomings necessitate the development of a capacitor charger capable of being used to meet the more robust requirements of the EMRG pulsed power system.

This topic seeks to explore innovative approach(es) to the development of an advanced, modular, converter charger for a 250 KJ capacitor. The proposed converter charger concept must be able to: draw power from a 700-900 VDC battery bank; provide sufficient power to charge the 250 KJ capacitor to 10 kVDC within several seconds; have a repetition rate of 6 charges/minute; have a peak-to-average power ratio of no more than 1.3 over the charge cycle. As necessary, the proposed concepts should incorporate liquid cooling and other technologies (such as but not limited to: advanced power electronic devices, novel topologies, etc) for reducing the overall system size (>1MW/m^3). This system should be designed so that the devices and topologies employed will be scalable during the Phase III to the voltage and power levels (10kV and 8MW) needed for a 50+ MJ capacitor bank with 1 MJ capacitor converter chargers that can be operated separately or ganged together without compromising volume.

PHASE I: Demonstrate the feasibility of an advanced, scalable, modular converter charger for a 250 KJ capacitor.  As applicable, demonstrate the effectiveness of the solution with modeling and simulation and engineering analysis.  Establish performance goals and provide a Phase II developmental approach and schedule that contains discrete milestones for product development.

PHASE II: Develop, demonstrate and fabricate a prototype as identified in Phase I.  In a laboratory environment, demonstrate that the prototype meets the performance goals established in Phase I.  Conduct performance, integration, and risk assessments. Develop a cost benefit analysis and cost estimate for a naval shipboard unit.  Provide a Phase III installation, testing, and validation plan.  Proposer should demonstrate that the proposed components and concepts would be scaleable up to full voltage and power levels of 50 MJ.

PHASE III: Working with the Navy and Industry, as applicable, design and construct a fully functional 250 KJ charger converter capable of being scaled to 1 MJ for future use in a 50+ MJ capacitor bank.  The goal is to be able to utilize the proposed converter charger concept on the EMRG proof-of-concept demonstration and design efforts and, ultimately, in a system onboard a ship.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Technologies developed in this program are applicable utility and industrial applications requiring high density dc power conversion, especially those involving the charging of large banks of capacitors. Examples include fusion research facilities such as the National Ignition Facility (NIF) which use 100’s of megajoules of stored energy. Technologies would also be applicable to more general medium voltage power electronics applications such as High-Voltage DC transmission (HVDC) systems, medium-voltage motor drives, and systems designed to interface alternative energy supplies to the medium voltage distribution grid. 

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