By John Haystead
In an age of ever-more sophisticated military and aerospace systems and platforms, the technology of power switches, converters, controllers, and other power-management devices may seem less than exciting. But in fact, these devices are mission-critical components of every electrically powered, military system and subsystem, and the technology behind them is undergoing an equally dramatic transformation.
As military leaders move steadily to convert the mechanical systems in their ground vehicles, ships, and aircraft to power electronics-based systems, the need to make these devices smaller, lighter, cheaper, more capable, and in ever-greater numbers is driving radical changes in the entire power-products manufacturing community.
The worldwide market for power semiconductors and modules will grow by an average rate of 19 percent per year, from $1.2 billion in 1998 to $2.8 billion in 2003, according to a study by Allied Business Intelligence of Oyster Bay, N.Y. In fact, power-semiconductor 'macroprocessors' will replace electromechanical switches, just as microprocessors and other silicon circuits replaced vacuum tubes, predicts Harshad Mehta, president and chief executive officer of Silicon Power Corp. in Cypress, Calif.
The common driver behind advances in power technology is the need for more-efficient, faster, and ubiquitous control of power distribution and consumption, than power electronics manufacturers can supply today: in other words, "smart power."
What is smart power?
Unfortunately, the term "smart power" is neither ubiquitous nor clearly defined. While the benefits of smart power are clear, many questions remain as to where this intelligence should reside. Possibilities range from individual DC-DC converters and switches, to operating system software, to standard microprocessor logic, to specially designed power-management ICs or modules, to all of the above.
One central initiative addressing this problem is the Office of Naval Research's (ONR) Power Electronics Building Blocks Program (PEBB). PEBBs are universal power processors capable of changing any electrical power input to any desired form of voltage, current, and frequency output. PEBBs sense what they are plugged into and automatically perform the required electrical conversion, for example, matching a ship's high-power electrical source to its electric propulsion drive system.
While the term smart power has evolved into a catch-phrase for a whole class of technologies, it does not accurately capture the essence of the military's objectives and initiatives, says Albert Tucker, ONR Division Director, Mechanical & Electrical Systems Division. "We're also beginning to see the term 'smart-power chip' emerge, but in fact, there is no single smart-power chip," Tucker says. "Instead, smart power results from building up and combining standard components into complex, hierarchical management systems."
In cooperation with the Joint-Service Dual-Use Science and Technology Program, ONR's $17 million core PEBB program has taken a form, fit, and function approach to the smart-power challenge. Already, experts involved with the PEBB program have demonstrated that one power device, modified only in software, can function as a universal power-management component, performing as an AC or DC motor controller, inverter, converter, or actuator.
Based on PEBB efforts, Silicon Power engineers have developed intelligent, integrated power processor modules consisting of a power semiconductor switch, control microprocessor, and packaging for thermal management. Silicon Power acquired all of the Harris Semiconductor PEBB technology in November 1998.
Researchers are developing a standard-cell approach to product and manufacturing processes that involves new power semiconductor switches and diodes, power assembly techniques, and power switches, a prototype of a new approach to substrate bonding and high performance thermal management, and a prototype AC-AC matrix power converter.
Tucker lauds advances in new core technologies such as power metal-oxide semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), and complementary metal oxide semiconductors (CMOS). Still, he says these technologies "don't focus on the broad middle where people have to build specific power devices like converters, inverters, and motor controllers," Tucker notes.
As a result, the power community is suffering from an inability to apply high-volume manufacturing techniques, points out Terry Ericsen, program officer at the ONR Mechanical & Electrical Systems Division. "To address this, we've tried to partition the problem all the way from systems to chips and break it into blocks that will enable greater levels of integration," Ericsen says. This is where the concept of smart-power systems begins to evolve, when you can build these hierarchies of systems."
Ericsen points out that as more mechanical systems convert to all-electric control, systems designers must address an increasingly wide range of power distribution and power management requirements. For example, as Navy leaders move toward all-electric drives for their ships, designers must address a whole new class of systems ranging from electric systems to launch and arrest aircraft to electric servicing stations. In parallel, designers need to look into a requirement to automate and integrate these devices. "Unless we can get the size, weight, and cost of the necessary power management down to reasonable levels, we won't be able to do it and unless we can build the infrastructure necessary to provide the higher levels of integration, we can't reach those goals," Tucker says.
Commercial challenges
Military and aerospace systems designers are not alone in this dilemma, however. The target cost goal for power devices in commercial applications operating in the 50-to-100-kilowatt range is less than 1 cent per switching watt, while current prices are closer to 25 cents per switching watt, Tucker says.
Individual device manufacturers are unable to see a clear path to reducing costs while still maintaining an acceptable profit, so there is not a lot of enthusiasm in the commercial industry to work toward the necessary standards, modularization, and packaging solutions.
Ultimately, the solution will require the power industry to pursue a different business and investment strategy, Ericsen says. "We can point out ways to pound the price down on each little piece, but the individual companies that manufacture the power chips or packaging won't realize the kinds of net profit needed to justify the investment."
To reach the next step in reducing size, weight, and cost, Ericsen says consortiums must form to give companies control of enough of the elements to justify the necessary level of investment. "The biggest changes are coming by the large companies realizing that they are up against the wall unless they can increase the number of products they can put out."
Applied technology
ONR officials recently signed an agreement with Rockwell Corp. to develop a standard cell-based design and manufacturing approach for solid-state motor drives and extremely high efficiency DC-DC power converters.
The Rockwell Science Center in Thousand Oaks, Calif., will lead the $8 million, two-year development effort together with the Rockwell Automation/Power Systems division in Greenville, S.C; Rockwell Collins in Cedar Rapids, Iowa; Lambda Electronics Inc. in Melville, N.Y.; and the U.S. Department of Energy Oak Ridge National Laboratory in Oak Ridge, Tenn. The effort aims to achieve 50 percent increases in motor drive power density, and DC-DC power converters that are one cubic inch in volume and 90 percent efficient.
In addition, the Science Center will work with the Rockwell Collins Advanced Technology Center and Boeing's Phantom Works in St. Louis to create a new multi-function power converter for distributed power systems in aircraft. The converter is intended to handle conversion and regulation of all aircraft power services including variable-frequency AC to variable or constant-frequency AC power conversion while achieving 50 percent reductions in power-conversion system size and weight with significant increases in efficiency and power.
Rockwell's efforts in the PEBB program are primarily concerned with improving power density and efficiency, and with creating new capabilities for power conversion, points out Hank Marcy, director of program development and customer alliance at the Rockwell Science Center. "When we talk about smart power, we typically mean incorporating overcurrent/overvoltage/overtemperature protection functions and/or providing signals to be used by external control loops without adding additional circuitry external to the device," Marcy says.
To take advantage of these devices, engineers must develop a new system-level power-distribution solution. Marcy notes that some commercial aircraft platforms are beginning to implement such systems.
For motor drives, Rockwell's strategy is to take a building-block approach. They will develop pre-engineered standard functional cells that designers can combine and scale to meet different levels of requirements.
Engineers are already implementing some of these concepts in Rockwell Automation's "PowerFlex" family of drives based on "six-pack" modules of 6.5-kilovolt Symmetrical Gate Commutated Thyristors (SGCT). By stacking modules, designers can apply the drives to loads ranging from five to 200 horsepower. "Ultimately, the goal is to deliver economies of scale by turning this building block approach into a defacto standard that multiple suppliers can build to and compete according to the merits of their total solutions and cost," Marcy says.
DC-DC converters
Rockwell Collins engineers, who are working on new 100-watt 3.3-volt and 1.5-volt DC-DC power converters, are focusing primarily on overall power efficiency and cost effectiveness. They say they expect the power module itself to have very limited intelligence.
"Although it will incorporate feedback circuitry linked to an intelligent power distribution system, the amount of data and the manner in which it is used will be system specific and unique, and we want to leave this to the system designer to implement at the system level," says George Schoneman, Collins project engineer for power conversion research & development.
He points out that engineers can achieve significant cost savings in only one way: experts must implement the stage at which they convert aircraft primary power to the requirements of individual systems by standard items. "There are clearly different power-monitoring and recording requirements for mission-critical systems vs. in-flight entertainment systems and designers don't want to pay for bits they don't need. At 600 seats/aircraft, each incremental increase can add up to considerable overhead costs."
The program is currently in the conceptual phase of topology selection and detailed electrical design, says Dan Jenkins, senior manager of the Collins advanced technology center power conversion group. Collins officials say they expect to implement MOSFET technology in the devices. Although researchers have considered using gallium arsenide (GaAs) and silicon carbide, Jenkins says there is still concern about the maturity level of silicon carbide technology. "We're also dealing with relatively low-voltage inputs and outputs, and although silicon carbide has excellent temperature characteristics, it seems better suited for higher-voltage devices," he says.
Jenkins says packaging, particularly thermal constraints, pose particular challenges. "It's really more of a mechanical packaging than electrical design issue. We're also interfacing with magnetics people to control parasitics although we believe we can do this with commercially available magnetics materials." Jenkins says he also expects radiation-hardening requirements to be handled externally according to the requirements of each application. "We haven't seen that much requirement for radiation-hardening in the areas we're targeting, but that doesn't mean it won't be required in certain weapon systems and platforms."
With an overall cost goal of $1 per watt, the 3-cubic-inch 100-watt module would come in right around $100.00 providing major cost savings to the military as well as making it viable for the commercial avionics market. At least in the prototype phase, there will be two separate piece parts for the 3.3- and 1.5-volt modules. The next major milestone is delivery and certification of the 3.3-volt module prototype, which is expected, roughly a year from now, followed by the 1.5-volt device.
Overall the ONR/Rockwell strategy aims at providing standard industrial-level electronic components that designers can further package in ruggedized and hardened enclosers at the system level to deal with shock, vibration, temperature, and other environmental factors. "It's just far too expensive to implement mil-spec parts across the board, and while the approach won't work for everything, it's perfectly applicable for the great majority of mil-aero environments," Marcy says.
Software smart
Clearly, designers implement smart-power not only in silicon and connecting hardware but in software as well. In fact, software is ultimately the key to interoperability and multifunctionality of smart power devices. Functional integration will provide the next level at which integrators can achieve significant price reductions, ONR's Tucker notes. "We're really at the limit of the components in terms of cost with each component almost at commodity price these days."
Tucker says engineers have much to do on the software side, and says they must do it in manageable steps. "Ultimately, we need to get to the point where we have an operating system for power," he says. "We've started working on hierarchical control with blocks nested at various stages that come together in a plug-and-play fashion, but we also need a basic I/O system with resident software in the various elements that let them know where they fit when the power comes up."
Regardless of the ultimate solution, designers will implement power management via a multilevel software architecture, with some software running at the device and some at the microprocessor level. Tucker notes that while continuing advances in microelectronic technology and materials make it increasingly feasible to bring microprocessors down to the individual switch level, "we're really still trying to find out what the best partition is. We don't want you to have to be an expert in device physics to plug a semiconductor switch into a system. Instead, each different layer needs to be plug-and-play taking us more into system and away from component engineering."
Ericsen adds that there are still issues over how much control should be in software vs. hardware. "Right now, we have to have hybrid approaches because of the speed requirements associated with some functions."
Rockwell's Marcy says most of the software his engineers are currently developing, particularly in the multi-function power converter, is primarily at the embedded firmware level running power-conversion algorithms. "It is a critical element of the device since we're controlling and manipulating variable frequency and variable voltage sources on the input and output side," he says.
The next exit
ONR's Ericsen says the PEBB program is focusing on high power applications of 1 megawatt and above such as aircraft launch and recovery systems. "Each break point represents a different technology of manufacture and for high power the primary technology has been silicon carbide, but we're also looking at other technologies such as fast turnoff devices (FTOs), emitter turnoff devices (ETOs), and IGBTs."
Silicon Power's high-power components business focuses on the development of a family of MOS-controlled Thyristors (MCTs).
"Anything that is based on a current — rather than a voltage-fit topology such as power-factor correction or fly-back power supplies — are potential applications," Donegan says, adding that smart munitions will be a key application for MCTs replacing the vacuum switches in electrical safety arming systems.
Another potential market for smart-power based on MCTs is the smart varistor, which combines a low-voltage metal oxide varistor (MOV) and an MCT in series. "Normally people have to select MOVs with a much higher voltage than needed so that the leakage current is low enough to prevent self-heating," Donegan says. "This means the clipping voltage is also higher than desired, however, whereas the use of an MCT in series eliminates this requirement."
ONR officials say they expect to have system demonstrations of their very high-energy technologies in 2003. Ericsen emphasizes however, that while they are investigating a wide range of device types, they are also trying to move closer to the foundry to develop a basic power-device manufacturing capability.
"To solve all the problems, we need to get under the individual devices and into the core manufacturing base," Ericsen says.
"We know we may have to pay something extra, but we're trying to minimize these extra costs to the military by investing in ways to meet these requirements in the upfront design of products," ONR's Tucker says. "There will always be military-unique requirements, but the goal is to make these a small part of the unit cost. We can't afford the whole freeway, but we can afford the next exit."
Eagle-Picher develops test equipment for smart batteries
Eagle-Picher Technologies LLC of Joplin, Mo., and Neptune Sciences Inc. of Slidell, La., are working on Phase II of the U.S. Navy's Universal Battery Charger/Analyzer Equipment (BCAE) program. This project uses commercial off-the-shelf (COTS) components wherever possible.
The BCAE will replace the Navy's current battery maintenance equipment and is to improve significantly the service's battery maintenance processes while reducing manpower requirements. "The projected yearly savings to the Navy are expected to be $35 million with a 22 to 1 return on investment over a 10-year period." says Patricia Sanders, Eagle-Picher director of test, systems engineering, and evaluation.
As opposed to several pieces of equipment that service one or a few battery systems, the BCAE will be able to service any battery that has similar voltage and current characteristics and termination criteria. This includes lead acid, nickel-cadmium, and silver-zinc secondary batteries, as well as lithium sulfur dioxide, lithium magnesium dioxide, and alkaline primary batteries.
The BCAE will incorporate several different diagnostic methods including analysis of the open circuit, dynamic resistance, and pulse test.
The pulse test applies a series of sequential charge and discharge pulses to the battery while recording the voltage response. Experts then analyze the data and compare it to a diagnostic model to determine the state of charge (SOC) of the battery.
A core feature of the BCAE is its battery database which links individual batteries to their maintenance profiles and historical data, says Steve Girard, manager of Eagle-Picher's electronic systems group. "This provides a local logistical system for tracking batteries and their data, while providing for seamless application across multiple chargers," he says.
Eagle-Picher engineers are developing Advanced Development Models for a depot level system and a portable unit. Meanwhile, Neptune Sciences engineers are developing new diagnostic technology for integration in the systems will include battery capacity, state-of-charge, and condition-based caution indicators.
The portable version of the BCAE will be enclosed in a case specified to a maximum size of 12 by 26 by 24 inches and a maximum weight of 60 pounds and will be able to accommodate 2-, 6-, 12-, 24-, and 36-volt batteries.
The units will be capable of a maximum 20 amps charge current and a maximum of 20 amps discharge current. The four-channel depot version will be capable of operating four simultaneous charge, discharge and diagnostic functions at once. Advanced Development Models for Phase II are scheduled for delivery in early 2001. — J.H.
