Medium Voltage Direct Current (MVDC) Grounding System
Navy STTR 2016.A - Topic N16A-T012
NAVSEA - Mr. Dean Putnam - dean.r.putnam@navy.mil
Opens: January 11, 2016 - Closes: February 17, 2016

N16A-T012 TITLE: Medium Voltage Direct Current (MVDC) Grounding System

TECHNOLOGY AREA(S): Ground/Sea Vehicles

ACQUISITION PROGRAM: FNC Efficient and Power Dense Architecture and Components; PMS 320 Electric

OBJECTIVE: Develop an affordable, general method for grounding Medium Voltage Direct Current (MVDC) zonal electrical power systems for naval warships.

DESCRIPTION: MVDC zonal electrical distribution systems are being considered for future naval combatants to affordably achieve power and energy density sufficient to successfully integrate advanced high power electric weapon systems and electric propulsion. Details on the overall application of MVDC to shipboard power systems are described in references 1 and 2. One of the key technologies needed for an MVDC system is an affordable, reliable method as compared to current systems in use and associated hardware to provide a ground reference for an MVDC shipboard power system. The goal for reliability should be a mean time between operational failure of the ground reference system in excess of 30,000 hours. This grounding method must account for multiple sources of MVDC power on the bus; these sources may or may not be online at any one time. These sources will have a power electronics interface with the MVDC bus. The sources of power may include AC generators, transformers, batteries, capacitors, flywheels, and fuel cells.

Desirable attributes of the grounding system include the ability to continue operation with one line to ground fault, the ability to detect and locate line to ground faults, minimizing currents in the hull, and avoiding high line to ground voltages that can stress and reduce the service life of cable insulation. Previous research on grounding systems include those documented in references 4 and 5. To date, of the many possible ways of grounding an MVDC system, a preferred solution for MVDC system grounding has not been established; the Navy has not previously funded industry to develop an MVDC grounding system for a shipboard power system. None of the known existing ways is ideal for the prospective application.

By reducing the amount of power conversion and energy storage required as compared to an AC system, MVDC systems offer the opportunity to incorporate electric weapons and high power sensors in surface combatants under 10,000 MT. Since the surface combatant following the DDG 51 class is anticipated to be below 10,000 MT, MVDC will enable these ships to have potentially game changing military capability by employing advanced electric weapons and high power sensors. An important enabler to an affordable MVDC system is an affordable method to ground the MVDC bus.

PHASE I: In Phase I, the company must provide a concept for the development of a general grounding system for MVDC zonal systems. The grounding system must account for multiple sources of MVDC power on the bus; these sources may or may not be online at any one time. All sources have a power electronics interface with the MVDC bus. The sources of power may include AC generators, transformers, batteries, capacitors, flywheels, and/or fuel cells. The grounding system concept should include the ability to continue operation with one line to ground fault, the ability to detect and locate line to ground faults, minimizing currents in the hull, and avoiding high line to ground voltages that can stress and reduce the service life of cable insulation.

The grounding system concept must include a description of the allocation of functionality among power conversion equipment, power distribution equipment, system controls, and other power system elements. The company must provide evidence that the proposed concept will likely prove more affordable than alternate feasible concepts that the company has considered but not selected. The company shall demonstrate the feasibility of their concept through modeling and simulation. The company shall identify technical risks of their concept. The Phase I Option, if awarded, should include an initial design layout and capabilities description to build a grounding system for MVDC zonal systems prototype in Phase II.

PHASE II: Based on the results of Phase I efforts and the Phase II Statement of Work (SOW), the company shall develop a grounding system for MVDC zonal systems prototype system to address the technical risks of their concepts. The company shall develop draft specifications for the different elements of the concept. At a minimum, the prototype system shall consist of multiple MVDC sources of power, at least one MVDC load, and multiple ship service zones. The company shall conduct testing of the prototype system. Testing shall address the technical risks of the system. The prototype system testing shall validate the draft specifications, and the effectiveness of the grounding system in meeting objectives. The prototype should be delivered at the end of Phase II.

PHASE III DUAL USE APPLICATIONS: The company shall support the Navy in transitioning and integrating the grounding system for MVDC zonal systems technology to Navy use. The company shall develop specifications and first articles for concept unique elements and specifications for other concept elements (such as power conversion equipment and generator rectifiers) which must have specific functionality to implement the grounding system concept. The technology will be installed on future surface combatants following the end of production of the DDG 51 class. An affordable grounding system for MVDC systems has many potential commercial applications to include commercial ships, industrial facilities, server farms, photovoltaic farms and wind farms.

REFERENCES:

1. Doerry, CAPT Norbert USN and Dr. John Amy, "Functional Decomposition of a Medium Voltage DC Integrated Power System," http://doerry.org/norbert/papers/MVDC-Functional-Decomp.pdf

2. Electric Ships Office, "Naval Power Systems Technology Development Roadmap," PMS 320, April 29, 2013. http://www.defenseinnovationmarketplace.mil/resources/NavalPowerSystemsTechnologyRoadmap.pdf

3. Graber, L., S. Pekarek, M. Mazzola, "Grounding of Shipboard Power Systems - Results from Research an Preliminary Guidelines for the Shipbuilding Industry," ESRDC Technical Report, Contract N0014-08-1-0080, February 2014. https://www.esrdc.com/library/?q=system/files/ESRDC%20Technical%20Report_Grounding%20Guidelines_FINAL.pdf

4. Jacobson, Boris, and John Walker, "Grounding Considerations for DC and Mixed DC and AC Power Systems," Naval Engineers Journal, Volume 119, Number 2, 1 October 2007, pp. 49-62. http://onlinelibrary.wiley.com/doi/10.1111/j.0028-1425.2007.00019.x/abstra

KEYWORDS: MVDC grounding system; MVDC circulating currents; MVDC power systems; MVDC ground fault; MVDC ground fault detection; MVDC ground fault localization

TPOC-1: Norbert Doerry

Phone: 202-781-2520

Email: norbert.doerry@navy.mil

TPOC-2: John Amy

Phone: 202-781-0714

Email: john.amy@navy.mil

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