The Power Electronics Teaching Factory (PETF), is designed to meet the needs of the growing power electronics industry. From manufacturing process development to customized training, the PETF assists in the advancement of power electronics technology and applications. Currently, the PETF is involved in a variety of power electronics projects that will provide substantial benefit to its partners, both military and commercial, and will continue to facilitate the development of high-power semiconductor- based devices and systems.

What Are Power Electronics?
The term "power electronics" loosely refers to high-power components and systems that use semiconductor devices (usually silicon-based) as the primary switching devices. However, the power semiconductors comprise only a portion of most power electronic systems. Supporting devices, in the form of sensors, passive filters, fault protectors, and microelectronic logic controllers, are also present in all but the simplest power electronic systems. Power electronics typically provide two main services: power conversion and power distribution control. In a power conversion application, the power electronics are called upon to convert electric power from one form to another. Electric power exists in two forms which are known as direct current (DC) power and alternating current (AC) power. A power conversion system will convert electric power in one of four possible fashions: AC to AC, AC to DC (rectification), DC to DC, and DC to AC (inversion). In a power distribution control application, the power electronics are used to monitor the levels of electric current flow within a distribution grid, and can either interrupt or enable the flow of electric current according to the operational requirements of the grid. In this case, the power electronics are used as intelligent circuit breakers that can be tripped and reset automatically using basic controls. High-power silicon semiconductors have progressed to the point where they are now capable of controlling thousands of amperes of electric current and thousands of volts of electric potential energy. There are a variety of power semiconductor devices available, including Gate Turn-Off Thyristors (GTOs), Insulated Gate Bipolar Transistors (IGBTs), MOSControlled Thyristors (MCTs), Silicon Controlled Rectifiers (SCRs), and Emitter Turn-Off Thyristors (ETOs). Typically, the selection of the device is dependent upon which system design parameter is more crucial, either electric current capability or switching speed. High electric current capability enables the designer to use fewer components in the design of the conversion system, where fast switching speeds promote cleaner output waveforms and require smaller passive filtering components. As the technology of power silicon devices has matured, devices are evolving that offer the designer high current capability and faster switching speeds.

Industry's Use of the PETF
The PETF serves the industry as a design, modeling, manufacturing, testing, and training center that specializes in high-power semiconductor-based components and systems. By partnering with universities and commercial facilities that are involved in the development of power electronic devices and systems, the PETF is able to leverage the collective knowledge of the industry and transfer those technologies to its commercial and military partners. The PETF is equipped to provide substantial industry benefit in the areas of manufacturing, reliability analysis, and training. Advanced manufacturing equipment and environmental screening chambers allow the PETF to serve as the process development and prototyping facility for emerging power devices and systems. Customized training courses, developed in partnership with leading universities and commercial facilities, will help to shed some light on the increasingly complex power devices and systems which are being developed every day.

PETF: Solving Real Problems
The PETF is currently involved in a variety of projects which provide real solutions in the area of power electronics for its commercial and military partners. Some of these projects are described below.

PowerElectronics Application for the U.S. Army
The U.S. Army has discovered a vital need for power electronic systems in the maintenance and operation of many of its vehicles and aircraft. The Army is currently investigating the integration of power electronics into their helicopters as the interface between the aircraft's alternator and its various electronic systems. The alternator produces AC power at a frequency of approximately 1000 Hz, while many of the aircraft's electronic aviation and navigation systems require AC power at a frequency of 400 Hz.

The PETF is developing a power conversion system that can be mounted directly to the alternator housing. This system will be smaller and lighter than the legacy power conversion systems, while providing for all of the helicopter's electric power requirements.

ETO Thyristor Development
One of the emerging high-power semiconductor devices that holds great promise for military and utility applications is the Emitter Turn-Off (ETO) Thyristor. The ETO thyristor was developed at Virginia Tech under a program directed by Sandia National Labs. The ETO Thyristor was initially developed as an extremely high-power switching device to be used in power conversion systems within electric utility grids. However, the ETO Thyristor has properties which also make it an attractive option for other high-power applications, such as large multi-megawatt electric motor drive controllers. The ETO Thyristors are capable of switching up to 4,000 amps of electric current and 6,000 volts of electric potential. Currently, the ETO Thyristors are assembled by hand in a laboratory, which can take up to one full day for a single device. In order to transition this promising new technology to real world applications, the PETF is developing an automated manufacturing process for these devices, performing a series of reliability tests, and producing a series of prototype devices which will be used in a power conversion demonstration system.

Advanced Semiconductor Packaging Techniques
Power semiconductors are only as good as their connections to the rest of the system. Poorly-crafted wirebond and solder joints can produce "hot spots" which conduct the bulk of electric current within unacceptably small cross-sections of the connection. These hot spots will severely reduce the performance and reliability of the power semiconductors and can eventually lead to system failure. In addition, wirebonded power semiconductors can have unacceptable levels of inductance in their leads, which can produce damaging levels of voltage within the semiconductor as it switches the electric current on and off. New packaging technologies, such as the "thinPak" developed by Silicon Power Corporation (SPCO), eliminate wirebond technology and allow electric current to flow through much larger cross-sectional areas and reduces the appearance of hot spots. The thinPak packaging technology, which has been adapted to IGBTs, MCTs, and diodes, requires the use of large-area soldering techniques. The PETF is developing an automated thinPak manufacturing line which is capable of meeting the expected commercial demand for these devices once they are made available to the public.

The PETF and Future Power Technologies
The PETF will continue to expand its services and capabilities to meet the needs of a growing industry. It will serve as a vital link between power electronics R&D projects and real world systems through the use of manufacturing process development and the transfer of technology. Additional training courses, expanded manufacturing and testing capabilities, and increased design & modeling capabilities are just some of the improvements that can be expected over the next several years. Some of the exciting areas in which the PETF will be involved in the future are presented below.

Integrated Power Systems and Electric Propulsion
The U.S. Navy has embraced electric drive as the architecture of choice for its future surface and submarine vessels. Large gas turbines and diesel engines, which have provided the horsepower to propel the ship through the water, will be replaced with advanced electric motors. Electric motors are more efficient and powerdense than turbines or diesels, and emerging technologies such as superconductivity and permanent magnet configurations will continue to improve the torque and power ratings of large electric motors. Future Naval vessels are expected to require more than 60 MW of electric power for the propulsion motors, weapons systems, communication systems, surveillance systems, and standard ship services (the combination of all these systems comprises an Integrated Power System). Since these systems all require different types of AC and DC power, power conversion systems will be necessary to supply all of the machinery and loads with the necessary forms of power. As a result, power electronics will comprise a significant portion of any electric ship, and the PETF will be there to provide solutions and training for the U.S. Navy as it begins to revolutionize its fleet.

Emerging Power Semiconductors
New power semiconducting materials that have the potential to replace silicon as the material of choice in the future are beginning to emerge. For instance, Silicon Carbide (SiC) holds great promise as a power semiconducting material because it is capable of operating at much higher temperatures than standard silicon. As a result, SiC systems will require less cooling and can be assembled using a smaller footprint. Further down the road are diamond- based semiconductors. Diamonds have a number of properties that make them extremely attractive as the foundation of a semiconducting device. Diamond is the best conductor of heat known to man, and yet it has extremely high electrical resistance. New manufacturing techniques such as Carbon Vapor Deposition (CVD) allow synthetic diamonds to be produced at a reasonable cost, though these costs can be expected to drop as the technology matures. It is estimated that a diamond semiconductor could withstand temperatures of up to 5000°C without degradation of performance, which makes them an interesting alternative to silicon semiconductors once they become available.

Aircraft Power Conversion and Control Systems
Electric actuators and activators provide an excellent alternative to traditional hydraulic systems. Hydraulic systems require a great deal of maintenance to operate properly, and can cause quite a mess if one of the lines should burst or otherwise fail. Electric actuators and activators, since they are fluidless, do not pose the same environmental issues as hydraulic systems, and are also much easier to maintain and control. Reliable power electronics will serve as the controllers for these actuators and activators, and will be critical in upgrading the existing hydraulic systems with superior electrical systems. For more information about the Power Electronics Teaching Factory, contact the EMPF Helpline at (610)362-1320.