Compact, Hatchable Transformer Rectifier

Navy STTR 21.B - Topic N21B-T020
NAVAIR - Naval Air Systems Command
Opens: May 19, 2021 - Closes: June 17, 2021 (12:00pm edt)

N21B-T020 TITLE: Compact, Hatchable Transformer Rectifier

RT&L FOCUS AREA(S): General Warfighting Requirements (GWR)


OBJECTIVE: Improve transformer rectifier (T/R) maintainability via modular, portable design and/or introduction of technologies to significantly decrease footprint, volume, and weight.

DESCRIPTION: An existing transformer/rectifier (T/R) is approximately 450 ft (12.75 m) in volume and weighs nearly 40,000 lbs (18,144 kg). The transformer accounts for approximately 25% of the volume and 45% of the weight of the T/R. If the transformer fails, the entire T/R must be removed, which is a complex, expensive, and time-consuming process with a lengthy mean time to repair (MTTR).

The Navy requires a transformer/rectifier that receives 13.8 kVAC RMS, three-phase, 60 Hz power, and outputs 850 VDC nominal. The T/R must be capable of providing output power in the single-digit megawatt (MW) range continuously for tens of minutes. It must also output less than 0.5 MW for greater than one hour. It receives single-digit MW input power.

The T/R should be hatchable, that is, T/R components or line replaceable units (LRUs) must be smaller than 26" x 66" x 33" (66 x 167 x 83 cm) in order to fit through hatches. Therefore, solutions should focus on decreasing T/R size and weight and improving supportability by making components removable/replaceable/repairable within the space constraints. A hatchable T/R will improve maintainability and decrease MTTR.

LRUs, or other removable subassemblies or parts, should be of reasonable weight so that they can be lifted and carried over moderate distances through passageways, doors, and hatches. For reference, existing LRUs are 31.5" H x 9.5" W x 22" D (80 cm H x 24 cm W x 56 cm D) and weigh approximately 150 lbs (68 kg). Technologies that minimize LRU weight are encouraged and preferred as heavier loads increase injury risk and require additional personnel. MIL-STD-1472G, TABLE XXXIX [Ref 5] and similar tables may be used as a guide for one-person, two-person, and more than two-person lifting/carrying limits. Other military standards should be referenced for shock (MIL-DTL-901E [Grade A]) [Ref 2], vibration (MIL-STD-167-1A [Type 1]) [Ref 3], electromagnetic interference (MIL-STD-461G) [Ref 4], and environmental factors (MIL-STD-810H) [Ref 1] since the system must be rugged to be viable. The ability to regulate T/R temperature (i.e., thermal management) should also be considered. The T/R should remove self-generated heat to maintain acceptable component temperatures. The maximum thermal load from the transformer should be 77.5 kW at 212 F (100 C), and the maximum thermal load from the rectifier should be 2.0 kW. At the ambient temperature of 77 F (25 C), the operating temperature of control panels and controls should not exceed 120 F (49 C). Surface hot spots on accessible equipment exteriors should not exceed 140 F (60 C). The temperature of all other exposed surfaces should not be greater than 158 F (70 C).

Designs that achieve both transformation and rectification in a more reliable, maintainable (modular/portable/hatchable), and compact package are ideal as they will increase operational availability (Ao). However, solutions cannot sacrifice performance as nominal output voltages/currents must meet certain tolerances as defined by requirements in an existing specification. For example, transformer output (rectifier input) shall have a nominal output voltage of hundreds of volts RMS, +/-2%. Further information on this and other requirements will be identified to the Phase I performers.

Advances in silicon carbide (SiC) and high-frequency transformer technology, or other related innovations associated with miniaturization of power electronics, may be leveraged to achieve the goals as outlined.

PHASE I: Develop a concept for a compact and maintainable transformer/rectifier, which may consist of modular, portable, electronic building blocks, also known as LRUs. Demonstrate feasibility using modeling and power simulation tools, or other applicable design methodologies. Subscale designs are allowable at this preliminary design stage assuming the concepts are scalable. Supporting documentation that shows how a subscale system might be scaled-up to meet full power requirements will help determine if the solution will be effective, suitable, and sustainable for this application. For example, a subscale T/R that meets input/output voltage requirements but not full-scale power requirements may still be practical if it can be shown that multiple subscale T/Rs can be connected together to achieve full-scale power. The same can be said of modules that do not meet full voltage/current requirements but can be connected in series/parallel. Evaluate thermal/cooling requirements to prepare for construction of a physical prototype. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Design and build a prototype based on Phase I work. Demonstrate the technology and utilize Hardware-in-the-Loop (HIL) simulations, including Controller Hardware-in-the-Loop (CHIL) and Power Hardware-in-the-Loop (PHIL), to test and characterize performance. Validate and verify operation of the system against electrical, mechanical, and thermal requirements. If the prototype is subscale and intended for partial power, plans for how to achieve scalability and test at full rated power should be well documented.

Assuming iterative design is utilized and a larger and more capable system is developed gradually throughout this phase, consideration must be given to packaging, thermal/cooling requirements, communications, controls, and user interfaces as the effort progresses.

PHASE III DUAL USE APPLICATIONS: Design and construct a full-scale T/R based on work completed during earlier phases. Perform final testing at full-scale power via T/R test procedures and fault scenarios as defined by existing specifications and test plans. Validate and verify T/R performance. Transition after successful testing.

Transformers increase or decrease AC (alternating current) voltage, and rectifiers convert AC to DC (direct current).

Transformers and rectifiers are increasingly vital as the energy sector moves towards renewables, such as wind and solar, and the transportation industry moves towards electric vehicles (EVs). This is because T/Rs are useful for energy transmission, storage, and charging applications.

For example, to transmit energy over long distances, transformers are used to increase voltage since high-voltage energy transmission decreases energy losses over long cable runs. In addition, more so than fossil fuels, renewables utilize energy storage so that power remains available even if the sun is not shining or the wind is not blowing. Many energy storage technologies, such as batteries, accept DC voltage; however, energy is often generated as AC, so it needs to be converted by a rectifier prior to storage.

Conversion from AC to DC is also required to charge everything from cellphones to electric vehicle batteries. Therefore, for those who own an electric vehicle (EV), the AC power available in their houses must be converted to DC to charge their EVs. This functionality is often incorporated into power supplies themselves. For example, the "brick" on a phone or laptop charger converts AC power from a wall outlet to DC to charge/power the device.


  1. Department of Defense. "MIL-STD-810H. Department of Defense test method standard: environmental engineering considerations and laboratory tests." 2019, January 31.
  2. Department of Defense. "MIL-DTL-901E. Detail specification: shock tests, H. I. (high-impact) shipboard machinery, equipment, and systems, requirements for." 2017, June 20.
  3. Department of Defense. "MIL-STD-167/1A. Department of Defense test method standard: mechanical vibrations of shipboard equipment (Type I-environmental and Type II-internally excited)." 2005, November 02.
  4. Department of Defense. "MIL-STD-461G. Department of Defense interface standard: requirements for the control of electromagnetic interference characteristics of subsystems and equipment." 2015, December 11.
  5. Department of Defense. "MIL-STD-1472G. Department of Defense Design Criteria Standard: Human Engineering." 2012, January 11.

KEYWORDS: Transformer; rectifier; T/R; power; portable-electronic-building-blocks; silicon-carbide; high-frequency-transformer

TPOC-1: Sean Zabriskie

Phone: (732) 323-4708


TPOC-2: Mark Blair 

Phone: (732) 323-7310


The Navy Topic above is an "unofficial" copy from the overall DoD 21.B STTR BAA. Please see the official DoD Topic website at for any updates.

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