Laboratory for Electromagnetic and Electronic Systems
The mission of the Laboratory for Electromagnetic and Electronic Systems (LEES) is to be the focus for research and teaching in electric energy from its production through its processing to its utilization, and in electromechanics from the macroscopic through the microscopic levels. Electric energy and electromechanics are defined broadly to include power systems monitoring and operation; automatic control; power electronics; high voltage engineering; and conventional, continuum and biological electromechanics. Much of the work of the laboratory is experimental, and industrial sponsorship represents a large fraction of the laboratory's support. The laboratory's professional staff consists of seven faculty members from EECS, one principal research engineer and two research scientists, and approximately 50 graduate students. The laboratory faculty and most of the staff are heavily involved in both undergraduate and graduate teaching. Faculty from the departments of Mechanical Engineering, Chemical Engineering, Materials Science and Engineering, and Nuclear Engineering are collaborators in many of the laboratory's programs, and there are extensive joint activities with the Microsystems Technology Laboratory, the Gas Turbine Laboratory, and the Laboratory for Information and Decision Systems.
Professor John G. Kassakian, principal research scientist Dr. Thomas A. Keim, and assistant professor David Perreault lead the laboratory's work in automotive electrical and electronic systems. This work is sponsored primarily through the laboratory's Consortium on Advanced Automotive Electrical and Electronic Components and Systems. The consortium, representing almost all of the world's major automobile manufacturers and component suppliers, is truly global, with more Asian-based member companies than North American companies, and a substantial European representation. The consortium has facilitated international working groups addressing issues of safety, battery/connector design, and arcing faults—all challenges that must be met for the deployment of advanced 42-volt electrical systems. This year the laboratory's work through the consortium has manifested itself in the first production vehicle containing a 42V electrical system, the Toyota Crown. The Crown is a luxury vehicle marketed in Japan.
Professor Perreault, Dr. Keim, and graduate student Juan Rivas have continued to investigate low-cost methods to improve the output of automotive alternators at idle speed. Professor Perreault and graduate student Gimba Hassan are demonstrating the ability to control the flow of alternator output power to buses at two different voltages, again using a very low-cost circuit. Professor Perreault and visiting engineer Dr. S.C. Tang are working on packaging these improvements in automotive alternator packages. All this work complements the work in earlier years by Professor Perreault and former graduate student Vahe Caliskan to improve alternator output at cruising speed. This work has great potential to facilitate high-power electric systems in future automobiles. This year a patent was issued for the Perreault/Caliskan work, and a filing was made for the Perreault/Keim work.
Professor Kassakian, Dr. Keim, and graduate students Woo Sok Chang and Tushar Parlikar continue to develop an innovative electromagnetic drive for engine valves. This new design uses a non-linear mechanical element to minimize electric power requirements and provides soft landing as an inherent feature of the design, rather than as an objective to be achieved by control system action. The superior behavior of this valve system design has been verified by detailed simulation, and a laboratory prototype is presently under construction. A number of car manufacturers and suppliers have expressed strong interest in this work, which is currently supported by internal funds. A patent filing describing this design has been made this year.
Professors Kassakian and Perreault, Dr. Keim and graduate student Ivan Celanovic are investigating the rmophotovoltaic converters for automotive electricity production. Multilayer dielectric stacks functioning as selective bandwidth filters show great potential to enhance the performance of such systems. This work has experienced increasing interest from consortium members as auto companies begin to introduce vehicles whose engines turn off when the vehicle is stopped, as in the Toyota Crown.
Professor Perreault and graduate student Gimba Hassan have developed a new alternator design that simultaneously regulates two outputs at different voltages. This new dual-output alternator can supply power to both outputs while maintaining optimal load-matched power generation capability and providing tight transient control of both outputs. The high performance of the approach, which incorporates a dual-output switched-mode rectifier, has been demonstrated experimentally. It is anticipated that this new approach will facilitate the rapid introduction of dual-voltage electrical systems in automobiles.
Professor Jeffrey Lang, Dr. Keim and graduate student David Wentzloff are completing the experimental characterization of an integrated starter generator for future automobiles. Such a machine can perform both the functions of the present starter and of the present generator, and can generate at higher power for future automotive loads.
The consortium completed a year-long strategic planning process. In response, several investigations were successfully concluded, and four new studies were initiated. The new studies are advanced automotive power electronics, automotive applications of ultra-capacitors, battery modeling, and heat driven air conditioning.
The consortium held meetings in Los Angeles, California and Kyoto, Japan in the past year. Registration at both meetings was strong, with Kyoto, having almost 400 attendees, representing the largest registration of any consortium meeting to date. A third meeting scheduled for October 2001 had to be canceled because of the September 11 attacks.
The work of the consortium has been featured in numerous trade publications, including a feature article in Mechanical Engineering, the mass membership publication of the American Society of Mechanical Engineers.
Utility industry restructuring has placed an intense focus on achieving economically optimal system operation by employing new and more sophisticated control and monitoring strategies. LEES has been making significant contributions to the solutions of problems of power system modeling, economic control, and apparatus monitoring.
Monitoring of Power Apparatus and Systems
Professor Steven Leeb, in collaboration with Professor Les Norford in the architecture department, continues the aggressive load monitoring program in California to identify conservation opportunities that could mitigate problems with the state's electric energy supply. This year they completed a field upgrade of all monitoring sites. For example, in Los Angeles county, a county courthouse and several other municipal buildings were instrumented not only with NILMs but also with additional hardware to record detailed environmental conditions in the buildings. This equipment records "fine grain" temperature information in the buildings, sunlight on the surfaces of the buildings, and other environmental data that impacts the operation of the HVAC plant in these buildings. Doctoral students are using these data to test the hypothesis that information from the NILM, with no other sensors, can be used to estimate the mechanical state (temperatures, air flow, etc.) in the building. The installed sensors will be used for measuring these quantities to compare the actual building behavior with predictions from the NILM. If this system works, it will be possible to predict the environmental conditions in a building with very few sensors, and use this information to minimize the energy needed to preserve occupant comfort.
Under a project sponsored by Entergy Services Inc., Dr. Chathan Cooke and his graduate student Timothy Cargol (now graduated) developed the technology for in-service measurement of key oil indicators in high voltage electric power system apparatus. They have achieved the first operating in-service oil dielectric strength integrity (DSi) monitor which solves a problem which has been a reliability bottleneck for over 40 years. Oil dielectric breakdown strength is an important factor in the health and routine maintenance of virtually all oil filled electric power apparatus. Before the DSi project, breakdown strength could only be measured via extracted oil samples due to the destructive nature of all industry standard tests. In contrast, the DSi system employs a new non-destructive breakdown measurement technology that enables in-service measurements and automatic operation. Oil dielectric integrity is now reported to authorized users at any secure web-connected location without travel to the apparatus site. Problems in the LTC compartment are known to account for approximately 50 percent of the troubles experienced by transformers so this new system can greatly improve reliability while also reducing costs.
The in-service demonstration DSi system has provided excellent results and has worked continuously for one year. Importantly, the demonstration system detected a low-strength alert condition of the LTC oil early in its operation. Confirmed by laboratory tests, the degradation was traced to an unexpected high-level of water contamination. Thanks to the DSi system a high-risk situation was averted by need-based maintenance. The DSi system is now in the process of being commercialized.
Modeling and Control of Power Systems
Professors Bernard Lesieutre (now at Cornell University) and George Verghese, with their doctoral student Ernst Scholtz, have developed innovative ideas for control of electromechanical disturbances in power systems by studying the traveling wave nature of these disturbances. This is in contrast to the conventional view, which treats the disturbances in terms of superpositions of swing modes. With the traveling wave viewpoint, a natural control approach is to regulate the generators at the boundaries so that they extinguish reflections. Preliminary studies, presented at the Power Systems Computation Conference in Seville, Spain, in June 2002, show promising results with this approach.
These researchers, together with masters student Paisarn Sonthikorn, have also developed observer methods for estimating the states of a swing model of a power system, from a limited set of measurements. Such estimation is of increasing interest, with the deployment of so-called phasor measurement units in the field, and the desire to obtain more comprehensive and global real-time assessments of system state, for both monitoring and control purposes. This research stands in contrast to what currently goes under the rubric of "state estimation" in power systems, namely the estimation of static power flow variables (bus angles and voltages) from generally redundant measurements. The observer work is to be presented at the North American power symposium in October 2002.
In other work, Professors Verghese and Lesieutre, with their doctoral student Sandip Roy and masters student Carlos Gomez, have been extending the scope and application of the "influence model" for networked Markov chains. This rich yet tractable model was recently introduced in the doctoral thesis of Chalee Asavathiratham (done in LEES under Professor Verghese) as an abstract representation of networks whose nodes can be in one of several states, for example, "Normal" or "Alert" or "Failed." A paper on this material appeared in the IEEE Control Systems Magazine in December 2001, in an issue devoted to complex systems. The paper presents an interesting example to suggest that as the nodes in a network become more reliable, and assuming local repair resources are commensurately reduced, one can arrive at a network that displays only small local failures or massive failures of the entire network, but nothing in between.
Relatives of the influence model have been developed for stochastic flow networks, and Sandip Roy has had some success with applying these and related ideas to air traffic modeling and control, during the course of a summer internship at NASA Ames. Other work is directed at solving various estimation problems related to the influence model—for instance, inferring states at hidden nodes from observations of state sequences at certain nodes in the network. The results of this research have the potential to generalize the results that are known for "hidden Markov models," a class of models that is widely used in speech processing, bioinformatics and elsewhere.
Over the last two years, Professor David Perreault and graduate students Joshua Phinney and Timothy Neugebauer have been developing novel inductance cancellation techniques for power filters and filter components. These techniques have been employed in the design of discrete filters using conventional components and in the design of new integrated filter elements having extremely high performance. Factors of up to 30 improvement in filtering performance have been demonstrated this year, in both discrete filters and integrated filter elements. The work to date has resulted in a US patent filing, and licensing negotiations with a major capacitor manufacturer have commenced.
Professor Perreault and graduate student Albert Chow have focused on the development of active ripple filters that greatly reduce the size of filter capacitors needed in many power electronic systems. Previously, they developed a high performance feedforward/feedback ripple filtering technique that is well suited to aerospace applications, where capacitor type and size is a critical consideration. In the past year they have developed a feedback ripple filtering technique suitable for a broad range of motor drive applications. This approach has been experimentally verified in an automotive motor drive filter, where significant cost improvements have been demonstrated as compared to a production filter design.
Professor Leeb and his students are developing a tunable vibration damper that utilizes a thermothickening gel material to reduce vibrations over a user-specified frequency range. Such a damper could solve the problem of damping vibrations in structures that encounter disturbances over a wide frequency range, automobiles for instance. The tunable gel damper is based on the idea that a variable viscosity material can be used to alter the moment of inertia associated with a rotating auxiliary mass. The thermothickening gel consists of a crosslinked network of polymers suspended in a solvent and exhibits large reversible changes in volume when thermally stimulated. Below a certain temperature threshold the polymer network is "swollen," effectively trapping the solvent within the polymer matrix. The resulting gel mixture has a considerably higher viscosity and approximates a solid mass. Above the temperature threshold, the gel undergoes a sharp decrease in volume as the polymer network "shrinks," thereby releasing the solvent and decreasing the overall viscosity of the gel mixture. This reduction in viscosity translates into an effective reduction in the moment of inertia thereby increasing the damper's resonant frequency. Structuring the damper by linking gel compartments whose transitions can be individually controlled permits control of the damping frequency.
Thermal activation of each gel-filled compartment is accomplished using a noncontact induction heating method. In order to distinguish between chambers, each compartment contains an induction target that has been designed to exhibit preferential heating at a unique frequency. This is achieved by infusing the gel with powders of metal alloys having varying conductivities. In addition to these magnetically linear alloys, the possibility of making custom powdered targets comprised of both ferrous metals and controlled amounts of resistive (but magnetically linear) materials is also being explored. A novel multilevel inverter circuit has been designed to efficiently induction heat any combinations of gel compartments by generating a sum of sinewaves signal for each frequency needed.
Professor Lang and graduate student Hur Koser, in collaboration with Professor Mark Allen and his students at the Georgia Institute of Technology, have completed testing the micro-scale magnetic induction motors whose fabrication was first reported last year. The torque produced by these first-generation motors is already comparable to that which has been produced by some of the best micro-scale electric induction motors. The measured torque has also been compared to the theoretical torque predicted by a numerical model that accounts for the presence of eddy currents and saturation throughout the solid-core motors. The match between experiment and theory was excellent, and so the numerical model was used to design laminated-core motors that should perform better still. These second-generation motors have now been fabricated, and testing will begin shortly.
Dr. Carol Livermore, Dr. Stephen Umans, and Professor Jeffrey Lang, in collaboration with the many other students, staff and faculty, both on campus and at the MIT Lincoln Laboratory, who participate in the MIT Micro Gas Turbine Engine Project, have recently demonstrated the operation of a micro-scale electric induction motor that produces a 40-fold improvement in motoring torque and power in comparison to all earlier micro-scale electric motors. This performance is consistent with theoretical predictions, and those predictions indicate that much higher torques and powers can yet be achieved. Following this analysis, a new generation of motors has been designed, and those motors are currently under fabrication.
Graduate students Jian Li and Jin Qiu, and Professor Lang, in collaboration with Professor Alex Slocum of Mechanical Engineering, have recently demonstrated the design, fabrication and operation of a new electrically-actuated mechanically-bistable micro-scale relay. The actuation mechanism is particularly successful in that it permits the low-voltage actuation of a relay having a relatively large contact force and stroke. They are currently working to develop this relay for use in low-voltage residential and commercial applications.
Professor Markus Zahn has developed an extensive theory and completed measurements as part of an NSF sponsored research program to develop magnetic field based MEMS and microfluidic technologies using sub-micron size magnetic particles in a carrier fluid. This research has resulted for the first time in a "negative" viscosity measurement in a ferrofluid stressed by a rotating magnetic field. Such "negative" viscosity effects have been paradoxical and an active research area for electrohydrodynamic and ferrohydrodynamic researchers because these effects seem to violate the second law of thermodynamics. However, the research has shown that there is no violation but that the decrease and sign reversal in effective magnetoviscosity is due to magnetic body torques as the magnetization and magnetic field are not collinear in alternating magnetic fields. This effect can have many useful applications in magnetic field driven micro-fluidics sensors and actuator devices.
Professor Zahn concluded service as a member of the National Academies Naval Studies Board Committee for Mine Warfare Assessment, Professor Leeb became a senior member of the IEEE this year, and Mr. Wayne Hagman, a staff engineer in LEES for many years, has left MIT for a position at NStar.
Administrative Secretary Vivian Mizuno received a School of Engineering Infinite Mile award for her dedicated and generous service to LEES, especially its students.
Professor Perreault has received a US Office of Naval Research young investigator award.
Professor James Kirtley received the IEEE's 2002 Nikola Tesla award.
For more information on the Laboratory for Electromagnetic and Electronic Systems, see http://web.mit.edu/lees-lab/www/.