Medium Voltage Direct Current (MVDC) Fault Detection, Localization, and Isolation
Navy STTR 2016.A - Topic N16A-T009
NAVSEA - Mr. Dean Putnam - dean.r.putnam@navy.mil
Opens: January 11, 2016 - Closes: February 17, 2016

N16A-T009 TITLE: Medium Voltage Direct Current (MVDC) Fault Detection, Localization, and Isolation

TECHNOLOGY AREA(S): Ground/Sea Vehicles

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

OBJECTIVE: Develop an affordable method for detecting, localizing, and isolating faults in a Medium Voltage Direct Current (MVDC) zonal electrical power system for naval warships.

DESCRIPTION: MVDC 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. 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 MVDC system is an affordable method to detect, localize, and isolate faults on the MVDC bus. Additional details on the overall application of MVDC to shipboard power systems are described in reference 3. One of the key technologies needed for a reasonably priced MVDC system is an affordable (equal to or less than cost of a comparable AC system), reliable method and associated hardware to detect, localize, and isolate faults on the MVDC bus while still maintaining power of the requisite Quality of Service to individual loads.

The use in MVDC power systems of traditional electromechanical circuit breakers common in AC systems is complicated by the need to extinguish the arc once the circuit breaker contactors open. In an AC circuit breaker, the natural zero crossing of the current waveform provides a mechanism for extinguishing the arc and establishing a voltage barrier to prevent the arc from re-striking. DC circuit breakers cannot take advantage of the current zero crossing. Hence, electromechanical circuit breakers are limited in the amount of DC current they can interrupt. Several manufacturers are developing hybrid DC circuit breakers that use semiconductors to shunt the current when the electro-mechanical breaker opens, thereby eliminating the arc. Although these hybrid DC circuit breakers are anticipated to work, they cost more than traditional AC breakers and will require more volume. Alternate solutions to MVDC circuit breakers (capable of interrupting greater than the rated steady-state current up to 4,000 amps with potential growth to 8,000 amps) are sought that will reduce cost by at least 20%, improve power and energy density by at least 20%, of the overall power system as compared to an equivalent AC power system. Solutions shall not have a significant negative impact on the overall power system energy efficiency.

Since power electronic rectifiers create MVDC, fault currents can be limited by controlling the power electronic rectifiers, enabling alternate strategies such as employing less expensive disconnect switches to reconfigure the plant once the power electronics have halted current flow (requiring however, zonal energy storage to power loads while the fault is cleared on the MVDC bus). The challenge confronting system designers of a MVDC system is to understand the behavior of the MVDC system when upstream rectifiers limit current and interrupt current and the rectifiersí criteria for doing so.

Localization of faults on an MVDC bus must consider the bi-directional nature of power flow of a zonal system. In AC zonal systems, a Multifunction Monitor (MFM) assists in the localization of faults. An analogous component may or may not be needed for an MVDC system.

Future MVDC systems are anticipated to operate between 6 kV and 18 kV. The grounding scheme for the MVDC system has not been established. Nominal rated bus current are anticipated to initially range up to 4,000 amps; with potential growth to 8,000 amps.

PHASE I: In Phase I, the company must provide a concept for an affordable method for fault detection, localization, and isolation on a Medium Voltage DC bus. This 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 will provide evidence that the proposed concept will likely prove more affordable and be more energy power dense than an analogous AC distribution system by 20%. The company shall demonstrate the feasibility of their concept through modeling and simulation. The company should identify technical risks of their concept. The Phase I Option, if awarded, will include the initial design layout and a capabilities description to build into Phase II.

PHASE II: Based on the results of Phase I efforts and the Phase II Phase II Statement of Work (SOW), the company shall develop a reduced scale 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 reduced scale 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 reduced scale prototype system. The reduced scale prototype system testing shall address technical risks, validate the draft specifications, and demonstrate the functionality of the overall concept in detecting, localizing, and isolating faults.

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

REFERENCES:

1. Mahajan, Nikhil Ravindra, "System Protection for Power Electronic Building Block Based DC Distribution Systems," Electrical Engineering Ph.D. Dissertation, North Carolina State University, November 2004. http://repository.lib.ncsu.edu/ir/bitstream/1840.16/5842/1/etd.pdf

2. 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

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

KEYWORDS: MVDC fault detection; MVDC fault localization; MVDC fault isolation; Power Electronics Fault Current Control; MVDC electrical distribution; zonal electrical power system

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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