SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  N113-181 (Navy)
Title:  Advanced Medium-Voltage, High-Power Charging Converter for Pulsed Power Applications
Research & Technical Areas:  Ground/Sea Vehicles, Electronics

Acquisition Program:  PMS 320, Electric Ship Office
 RESTRICTION ON PERFORMANCE BY FOREIGN NATIONALS: 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 nationals 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 national who is not in one of the above two categories, the proposal may 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.

  References:   1. Gully, J. H., “Power Supply Technology for Electric Guns”, Magnetics, IEEE Transactions on, Volume: 27 Issue: 1, Jan 1991, Page(s): 329 -334. 2. Elwell, R.; Cherry, J.; Fagan, S.; Fish, S.; “Current And Voltage Controlled Capacitor Charging Schemes”, Magnetics, IEEE Transactions on, Volume: 31, Issue: 1, Jan 1995, Pages: 38 – 42. 3. Bernardes, J. S.; Sturmborg, M. F.; Jean, T. E., “Analysis of a Capacitor-Based Pulsed-Power System for Driving Long-Range EM Guns”, Magnetics, IEEE Transactions on, Volume: 39, Issue: 1, Jan. 2003 Pages: 486 - 490. 4. Grater, G.F.; Doyle, T.J.; “Propulsion Powered Electric Guns-A Comparison Of Power System Architectures”, Magnetics, IEEE Transactions on, Volume: 29, Issue: 1, Jan 1993 Pages: 963 – 968.

Keywords:  electromagnetic; capacitors; pulsed-power; converter; power electronics; EMRG

Questions and Answers:
Q: 1. Do you have a datasheet or additional information for the capacitors that need to be charged (such as ESR, ESL, rms current limit, cut-off frequency, etc.)?

2. Is it possible to charge multiple capacitors in parallel to a lower voltage level and then stack them in series to achieve 10 kV?

3. Could the output voltage be +/- 5kV instead of 10 kV (i.e. is a mid-point connection in the capacitor bank available to connect a transformer midpoint to)?
A: 1. The ESR for the capacitor is ~ 5 milliohms. The ESL for the capacitor is ~ 300 nanohenries.

2. No, the capacitor a single unit.

3. No, the current topology calls for one side of the capacitor to be referenced to ground.
Q: 1. Multiple capacitors with each of 250KJ/10KV are to be charged, correct?

2. Do you prefer to have a DC-DC converter (40KW) for each capacitor or a single DC-DC converter (8MW) for all capacitors (50MJ/10KV)?
A: 1. That is correct. Early prototypes should be sized for this level.

2. We prefer a 40kW converter for early prototype testing. We are still somewhat open as to the final topology but it should be scaled up from the prototype, either by paralleling numerous smaller converters or by using concepts developed and demonstrated at lower power to build a larger converter. Tell us your recommended approach.
Q: 1. How do you define " peak-to-average power ratio of no more than 1.3 over the charge cycle". E.g, if you deliver 250kJoules in 5 seconds during charge, this would represent 50 kW average power, but how would you define the peak power?

2. What source impedance (reactance and resistance) can be assumed for the battery bank?
A: 1. The peak power is the maximum instantaneous power drawn at any time during the charge cycle. The purpose of this parameter is to encourage the contractors to develop their controls to enable a charge profile that resembles a constant power charger rather than a constant current charger. Many commercial systems use a constant current charge methodology resulting in a power profile that looks like a sawtooth, having a peak-to-average ratio of 2 at a minimum. In a system connected to a power generator, this may be unacceptable for such a large load. We will entertain ratios of greater than 1.3 in the proposals but want to avoid constant current profiles.

2. The battery system has yet to be developed. Contractors can assume notional values of 5 milli-ohms and 50 nano-henries for the time being.

Please let me know if you have any questions or comments.

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