The Navy’s next generation surface combatants and battle force will utilize various power systems, such as Integrated Flight Through Power (IFTP), Electric Drive (ED), and Reconfigurable Zonal Systems. New manufacturing processes and technologies can be employed to reduce the cost of producing these power systems. Utilizing advanced electronics packaging and modular concepts can reduce the overall size and weight of these integrated power systems. Finally, new interconnection materials need to be employed in high power, high temperature applications.

The Regional Electric Power Technology Integration and Leveraging Enterprise (REPTILE) Program will investigate, develop, and demonstrate new manufacturing capabilities to improve the production of naval electric power systems. Specific investigations will be centered on the design and manufacturing processes and materials for solid state power components and the integration of condition-based maintenance technologies. Applying common modular packaging and mounting fixtures for filters and magnetic components, advanced electronic packages to reduce the electronic control system’s size, and frame and partition concepts will lower the production costs. Lean Manufacturing will reduce manufacturing costs by identifying and eliminating non-value added processes and procedures in the assembly, rework and repair functions.

Phase I of the REPTILE Program was initiated in September, 2002, and completed in December, 2003. Phase I consisted of three tasks; PCM Manufacturing and Standards, High Power Switch Technology and Testing, and Engineering Studies. The first goal of Phase I was to reduce the manufacturing costs for the Power Conversion Module (PCM). The second goal developed a high power testing facility. The final goal was to perform a feasibility study on creating an electric starter for gas turbines and develop the ship secondary power specifications for alternative power sources. The Electronics Manufacturing Productivity Facility (EMPF) has been teamed with the Philadelphia Naval Surface Warfare Center (NSWC) sharing facilities and technical expertise to perform the tasks.

REPTILE Phase I
1) PCM Manufacturing and Standards:
Power Conversion Module (PCM) units are used to distribute power to various zones within a ship. The EMPF performed a series of evaluations concentrating on design optimization, alternative components, and cabinet modifications. These evaluations identified 8- 14% savings in manufacturing costs, which corresponds to $1.5M per ship set. Over the entire life of the program, from GFY-05 through GFY-10, it is estimated that $73.2M will be saved.

The EMPF also performed failure analysis on several component failures within the PCM units. In each case, the root cause of the failure was identified. For example, failures within the EMI Filters were attributed to excessive solder in the component case prior to assembly. The heat from the soldering processes melted the excessive solder, resulting in a short between the component’s lead and case. This information was given to the component supplier.

2) High Power Switch Technology and Testing:
The EMPF and NSWC-Philadelphia developed a high power test facility. The first device tested was the Generation 3 Emitter Turn-Off Thyristor (ETO). The ETO’s switching characteristics were defined, and will be used as a baseline for future Integrated Power Source (IPS) initiatives. The ETO and test fixture are shown in Figure 1-1.

3) Engineering Studies:
The EMPF created the system specifications for developing an electric starter for gas turbines and Ship Secondary Power. An electric starter is required to ignite gas turbines (Figure 1-2). A gas turbine electric starter has several advantages over current pneumatic and hydraulic starters. Gas turbine electric starters are more compact, provide better control over the gas turbine ignition process, and are more reliable. An electric starter eliminates the need for a high volume low pressure air supply for this application. The EMPF proved that the electric starter concept is feasible for naval applications and developed the system’s requirements and specifications. Secondary power is required to support mission critical systems. The EMPF developed the system requirements for alternative power sources, surveyed available alternative power source technologies, and ranked their respective capabilities to supply power to the ship zones they will support.

The output of these tasks can be applied to future naval integrated power system applications, such as those for the DD(X) Program. The DD(X) is the next-generation surface combatant ship being developed for the U.S. Navy. It will incorporate several electric ship concepts investigated by the REPTILE Program.

REPTILE Phase II
In 2004, The EMPF started several initiatives to build on the Phase I technical accomplishments. The Phase II goals are to identify opportunities to reduce the weight of the PCM units, the PCM units manufacturing production costs, and the total cost of ownership. There are four (4) areas of concentration:

1) Thermal Management:
PCM units generate much heat in operation. The EMPF’s task is to identify methods to improve heat management within the systems. If excessive heat is removed from the PCM units, the units will operate more efficiently and be more reliable. A more thermally efficient power system could have higher power densities than current units.

The EMPF tested and certified several quick disconnect fixtures to vibration requirements and mechanical shock specifications in MIL-STD 901D and MIL-STD-167 (Figure 1-3). Applying quick disconnect fixtures would improve hardware maintainability without risking coolant leaks. The EMPF is also investigating using a graphite cold plate. According to the manufacturer’s specifications, graphite cold plates are 33% more efficient in conducting heat away from heat sources. The EMPF’s task is to confirm the thermal efficiency of the graphite cold plates for PCM applications.

The Naval Research Laboratory (NRL) developed a new thermal management material technology which employs graphite fibers as a heat conductor. The NRL has shown that their Novel Cooling Technology (NCT) can conduct heat from heat sources more efficiently than conventional methods. The NRL, using an H-60 Helicopter Transformer Rectifier Unit (TRU) as a demonstration vehicle, proved that by weaving carbon sheets into the transformer windings, it was possible to remove excessive heat from the transformer. The new TRU assembly experienced a 30% weight reduction while maintaining 5Kw output power, which was required for this application.

The EMPF is considering applying NCT, and other thermal management materials, as a replacement for the thermal grease used in the PCM units. If successful in the PCM application, this technology will improve the thermal management and maintainability of PCM units in the field, where operators would have to apply new layers of thermal grease when maintenance is performed on specific units.

A concept being developed will integrate the quick disconnect fixtures, the new thermal management materials, and the graphite cold plate with the Insulated Gate Bipolar Transistors (IGBT) housing assembly. This concept will reduce the size of the IGBT housing assembly while improving its producibility and thermal management. An additional advantage will be its modularity, which will make the PCM units easier to manufacture in production and maintain in the field.

2) Fiber Optics/ Condition Based Maintenance:
The EMPF will evaluate fiber optic sensors and related networks to monitor power levels and to provide input to be utilized by a condition based maintenance system. This condition based maintenance system effort is a key element of Phase II. The thrust of the fiber optics effort will be to identify best methods used for implementation within the electric generation and distribution system of a ship.

The initial phase of the fiber optics task will focus on specification development and system design. The EMPF will concentrate their efforts on the fiber optic and sensor packaging. PCM parameters to be measured include temperature, input and output voltage, input and output current, unit resistance, transformer inductance, and output power. Optical current and voltage sensors are commercially available, and will be employed as part of the hardware monitoring strategy. The second part will involve the production and testing of a prototype system to demonstrate the feasibility of the use of fiber optic sensors in monitoring ship board power distribution unit performance.

The fiber optic condition based maintenance system will be integrated into the Navy’s Integrated Mission Support System (IMSS) and Automated Maintenance Environment System (AME). These systems have been developed, demonstrated, and deployed by the Navy.

3) Cabinet Manufacturing Analysis:
The goal of this task is to improve the producibility of PCM cabinets. A major cost driver is the cabinet design. REPTILE Phase I Manufacturing and Standards activities proved that applying a frame and partition cabinet design concept could reduce PCM cabinet manufacturing costs. The EMPF will incorporate the frame and partition concept into the new PCM unit cabinet design. Working with the 901D Company, with inputs from the PCM manufacturers, a cabinet will be developed to perform MIL-STD 901D shock testing (barge test). Components and sub-assemblies identified by the various PCM manufacturers and NSWC-Philadelphia will be tested depending upon availability. The EMPF will work with the 901D Company to design and test a small-scale cabinet.

The EMPF will review and analyze high cost components (inductors, transformers, etc), with the goal being to develop a universal mounting fixture. The EMPF will review the cold plate design for the drawer and quick disconnect/flexible hose for 901D barge test. Failure analysis of failed components from the PCM manufacturers and NSWC-Philadelphia will be performed on an as needed basis.

4) Wide Band Gap Technology:
Wide Band Gap (WBG) technology offers unique opportunities for high power applications. WBG semiconductor devices operate safely at higher temperatures, frequencies and voltages than current devices. The EMPF’s goal is to determine the best method to integrate WBG high power devices into current PCM units.

The EMPF will assess the availability of WBG power devices. WBG component manufacturers and industrial consortiums will be consulted. The output of this will be a roadmap of WBG high power devices. In parallel, the EMPF will identify high power applications and requirements from NSWC-Philadelphia and the PCM manufacturers.

Upon completion, high power WBG devices will be obtained for a demonstration test. This test will verify the capabilities of WBG devices in naval high power applications. A suitable demonstration vehicle will be developed. Testing will be tentatively performed at the high power test facility developed by the REPTILE Phase I Program at NSWC-Philadelphia.

Future Naval High Power Application Activities
The EMPF will continue to use the REPTILE Program as the vehicle to introduce advanced electronic packaging and advanced electronics manufacturing concepts to naval high power electronics. Two examples of future naval high power applications under consideration are explained below:

1) Electronic Packaging:
The EMPF has improved the packaging of the Emitter Turn-Off (ETO) device previously mentioned. The EMPF plans to leverage the packaging insights from the ETO to repackage the Insulated Gate Bipolar Transistors (IGBTs) used in the PCM units. A potential goal will be to introduce these new packaging schemes into the current PCM units.

2) Lead Free Soldering:
The EMPF plans to investigate the effects Lead Free solders have on high power devices. The European Union’s WEEE and RoHS directives require hardware to be Lead Free by July 1, 2006. Commercial components manufacturers are beginning to convert their production lines from tin-lead (SnPb) finishes to Lead Free finishes. However, there has been minimum investigation into performance of Lead Free solders and finishes when introduced into high power applications. The EMPF will investigate whether use of Lead Free solders and finishes in high power applications represents a risk to hardware reliability.

REPTILE represents the EMPF’s introduction of advanced manufacturing technologies into high power naval applications. REPTILE Phase I identified material costs reductions, hardware design improvements, and completed design requirements for specific applications. REPTILE Phase II continues power electronics technical investigative efforts for naval applications in thermal management, fiber optics and condition based maintenance, cabinet manufacturing processes, and Wide Band Gap device introduction. The results of these efforts can be applied to future power electronics endeavors on programs such as the DD(X) Program.