The mission of the Laboratory for Electromagnetic and Electronic Systems (LEES) is 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 to the molecular 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 10 faculty from EECS, one Senior Lecturer, 2 Senior Research Engineers, 6 research staff, 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 ME, CE, MS&E and NE are collaborators in many of the laboratory's programs, and there are extensive joint activities with the Microsystems Technology Laboratory (MTL) and the Energy Laboratory. LEES is also an active participant in the Leaders for Manufacturing Program, and the Technology and Policy Program (TPP). During the past year the laboratory has experienced a continued expansion of its automotive related research, demonstrated a 1/5 scale Maglev test facility for high temperature superconductors, and created a consortium on Transmission Provision and Pricing Under Open Access.
AUTOMOTIVE ELECTRONICS AND ELECTRICAL SYSTEMS
Professor John G. Kassakian and Dr. Thomas M. Jahns 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. Four new members were added to the consortium in the past year, bringing the membership to 13. The consortium held four two-day meetings and organized a major industry wide workshop to promote the adoption of 42 volts as a standard for future automotive electrical systems. The laboratory has also engaged in a strategic alliance with Ford to accelerate the adoption of this standard. Under the auspices of the consortium, the multi-attribute trade-off analysis tool MAESTrO has been upgraded to near commercial quality by an outside software developer. Professors James L. Kirtley and Jeffrey H. Lang, Dr. Jahns and graduate student Edward Lovelace have been investigating the designs of high power starter/alternators for future cars. Permanent magnet, induction, switched reluctance, hybrid induction and Lundell machines have been considered. A prototype of the most promising design will be built and tested during the next year.
Under sponsorship from Daimler-Benz, Dr. Jahns and graduate students Khurram Afridi and Isaac Trefz have adapted MAESTrO for application to the electrical systems of trucks and buses. This work has been very favorably received by Daimler-Benz.
With graduate student Deron Jackson, Professor Steven B. Leeb has continued development of a 3 kW prototype of a battery charging system for electric vehicles employing a non-ohmic, magnetically-coupled connector system. A bi-directional version of the charger has been completed that permits both carefully controlled battery charging from the utility, and also controlled discharging of the battery back into the utility. This bi-directional capability is essential for ensuring maximum battery life. Other applications for non-ohmic power transfer are under investigation, including incorporation into marine refrigeration units and hinged, fire-resistant power couplings for doors.
HIGH SPEED AND AUTOMATED TRANSPORTATION SYSTEMS
Professor Richard D. Thornton and graduate students Marc Thompson, Brian Perreault and Scott Macgreggor completed three projects concerned with applying magnetics and computers to automated transportation systems.
Mr. Thompson completed his Ph.D. thesis with the design, test and analysis of a 1/5 scale magnetically levitated (Maglev) train test facility suitable for high-temperature superconductors. A new low cost multiple loop guideway was built and tested, and resultant electrodynamic forces were measured at actual Maglev train operating speeds. The results were compared to predictions based on simple circuit models, with close correlation. The test fixture was also used to validate the concept of lift generation at zero velocity by ac excitation of the main magnet coils. In further tests, a novel magnetic active secondary suspension was tested. Results show that it may be possible to actively control ride quality by varying the high temperature superconducting coil currents, removing the requirement for a mechanical suspension for ride control.
Mr. Perreault completed his Ph.D. thesis on position sensing and communication between guided vehicles operating under automatic control. The system allows vehicles to keep accurate track of the position of other vehicles and to communicate messages between vehicles and from a vehicle to a central control. The system does not make use of radio waves and is suitable for use with almost any type of guidance and propulsion system.
Mr. Macgreggor completed his M.Eng. thesis on fault tolerant control for automated transportation. He demonstrated a multiprocessor system that can sense when any one processor fails and take corrective action to eliminate any accident that might occur without fault tolerant protection.
MODELING, MONITORING AND CONTROL OF POWER SYSTEMS
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.
Modeling and Control
Professor Bernard Lesieutre and graduate student James Hockenberry have developed a nonlinear thermostatic load model as part of Professor Lesieutre's ongoing research on power system dynamic load modeling sponsored by the NSF. In previous work the importance of proper load models has been demonstrated, an improved probabilistic aggregate model of a cluster of induction motors was developed, and common lighting and power electronic loads were investigated. The new thermostatic load model captures important characteristics that are lacking in traditional "voltage recovery" and linear system models. Professor Lesieutre has also begun new research in the area of uncertainty analysis in large scale power system simulations.
A great deal of power system practice is dependent on transient simulators, but these are often used uncritically and without insight. Professors Lesieutre and George C. Verghese have initiated work on intelligent simulation aids for power system transient simulators. They are also continuing their studies of new approaches to reduction of large power system dynamic models, with a view to reducing simulation times.
Professor Verghese and graduate student Ben Leong, in collaboration with Dr. Joseph Thottuvelil of Lucent Technologies, have been conducting pioneering studies of the interesting dynamic properties of broadband power networks that are being put into place to power coax/optical fiber communication networks. The loads on these networks are regulated power electronic supplies, which are activated once the voltage across their input exceeds some threshold. The results obtained thus far describe the dynamic and steady-state properties of these nonlinear networks, provide guidance on what choice of threshold voltage will ensure that the network settles into a desirable steady state, and also suggest simple approximate calculations that provide rapid yet accurate numerical results.
Dr. Marija Ilic, in collaboration with Professor Francisco Galiana of McGill University and the Energy Laboratory's Electric Utility Program, has created the Consortium on Transmission Provision and Pricing Under Open Access. The consortium is studying issues related to the operational stability of the regional power grid in the face of the relaxed control over individual generators implied by the deregulation of the electric utility industry.
Professor Lesieutre, Dr. Ilic and Professor Verghese were the organizers and hosts of the North American Power Symposium held at MIT in October 1996. The Symposium included a session on challenges under deregulation and a plenary talk on the major summer blackouts of 1995. It drew world-wide participation and was highly successful.
Adaptive Monitoring of Transformers
Research Engineer Wayne Hagman and graduate students Mary Jane Boyd and Paul Barrett have completed the design for the next generation of software for the MIT Adaptive Transformer Monitoring System, including enhanced intra-system inter-process communication of data information. Mr. Hagman has also trained a number of Boston Edison employees in the use and maintenance of the MIT systems that are monitoring five of Boston Edison's large substation transformers. Ms Boyd has also developed artificial intelligence methods for the integration of spatial and temporal information in the detection of anomalies, and knowledge elicitation and structuring in the context of on-line power apparatus monitoring.
Principal Research Engineer Chathan Cooke has demonstrated, on an energized 500 kV power transformer at Consolidated Edison, a system capable of on-line detection of defects that induce internal partial discharges (PDs) in large power transformers. The system uses advanced time and frequency domain signal processing to identify and locate PD events. A tear-down of the transformer showed excellent correlation between the measured PD signals and actual tracking damage of the internal winding. Dr. Cooke is now making the measurement system robust enough for field application.
Professor Lesieutre and graduate student Reza Olfati-Saber have developed a neural state space model (NSSM) for describing the relations between temperature and measured dissolved gas content in transformer oil. The advantage of the NSSM approach is that the unknown functional form for the components of a traditional nonlinear state space model can be approximated by neural networks and estimated from measured data. The NSSM model should significantly improve the transformer thermal model and facilitate the detection and diagnosis of certain problems, and allow better evaluation of the present condition for purposes of dynamic loading.
The laboratory's efforts to team with an appropriate company to produce and market a transformer monitoring system based on the technology developed in LEES appears to have been successful. It is expected that by August, 1997, an agreement will be in place that both licenses the technology and provides funding for continued research.
Non-Intrusive Load Monitoring
Professor Leeb, in collaboration with Professor Leslie K. Norford of the Department of Architecture, and with graduate student Steven R. Shaw, have demonstrated techniques that extend the capabilities of the Nonintrusive Load Monitor (NILM) to the determination of power quality, i.e., current waveform shape, anywhere in a monitored building. Also, diagnostic techniques have been developed that permit the NILM to determine the parameters of models describing important loads, e.g., induction motors, solely from partial electrical measurements made at the utility service entrance. A second patent on the NILM technology will be awarded in 1997. A field portable platform capable of implementing not only the NILM algorithm but also the power quality and diagnostic techniques will be completed this year and tested in on-campus buildings and off-campus manufacturing operations.
The Novice Design Assistant (NDA), a computer aided tool for designing three-phase induction motors developed by Professor Kirtley and graduate student Ujjwal Sinha, has been enhanced by the development of a technique based on multi-dimensional adaptive regressive splines for adapting the design space for use with an NDA design synthesis. Work is progressing to build the NDA into the production design software of Magnetek, the sponsor of this research.
Gel Polymer Actuators
Professor Leeb, in collaboration with Professor Toyoichi Tanaka of the Center for Materials Science and Engineering, and with graduate students Ahmed Mitwalli, Deron Jackson and Tim Dennison, continue to explore applications of polymer gels as actuators and sensors. Building on last year's demonstration of a thermo-optical gel sensor for metal ion detection, a new multi-sensor apparatus has been constructed that estimates, in real time, the transition temperature at a number of positions in a long gel. This sensor is being used to explore the possibility of identifying the components of a mixture by using the gel as a chromatogram. For example, if the constituents of a given mixture exhibit different mobilities in the gel, the gel could serve as a chromatographic or electrophoretic medium for separating the mix. As the mix separates, different regions of the gel exhibit different phase transition temperatures, which correspond to the local concentrations of the constituents. Optical sensors, placed along the length of the gel to scan the different phase transition temperatures in different regions of the gel, could be used to identify the components of the mix.
Work is also underway to develop new imaging techniques for "soft" materials like gels. Professor Leeb and Mr. Dennison are working to use the Faraday effect to develop tomographic imaging techniques for optically translucent materials with differing Verdet constants. These new imaging technologies might ultimately be used to develop more sophisticated approaches for examining spatial separation in phase transition chromatography experiments.
Professor Martha Gray and her group have made important strides in their work on the use of magnetic resonance (MR) methods for measuring the composition and functional integrity of cartilage. Specifically, they have demonstrated that a method designed to measure the fixed charge density of cartilage corresponds quantitatively to destructive biochemical measures of charge and qualitatively to histological measures. Moreover, they have established that their methods are feasible in a clinical setting with pilot studies revealing information not available with traditional MRI scans. This method offers the potential to monitor cartilage disease progression and therapeutic efficacy with a specificity and sensitivity not previously available.
Professor Kassakian, with graduate students David Perreault and Kenji Sato, have completed the construction and testing of a prototype 6 kW unity power factor rectifier designed using the cellular architecture that they have been studying for several years. A new single-wire, but robust, current sharing and interleaving scheme has also been incorporated in the prototype. This highly reliable, and potentially very economical, power electronic architecture is currently being applied to advanced automotive applications where the cost and reliability of power electronics has been a major obstacle to its penetration of the automotive market.
Professor Verghese, with Dr. Joseph Thottuvelil of Lucent Technologies and David Perreault have developed and tested the first precise criteria for stability of paralleled power converters under active current sharing. These results are already being applied by designers at Lucent and elsewhere.
Professor Verghese in collaboration with Professor Aleksandar Stankovic of Northeastern University, Professor Paolo Mattavelli of the University of Padova, Italy, and graduate students Vahe Caliskan and Chalee Asavathiratham, have continued - with support from the NSF - to demonstrate the efficacy of harmonic averaging methods in constructing frequency-selective dynamic models for power electronic components. These models permit the user to focus on the behavior of interest, while suppressing irrelevant detail. they are well matched to the phasor representations used in power system applications, lead to much faster simulations and more tractable starting points for control design, and are more accurate than those obtained by traditional averaging methods.
Professor Anantha Chandrakasan with graduate students Rajeevan Amirtharajah, Abram Dancy and Vadim Gutnik have developed embedded power techniques for portable electronic systems. They have shown that providing a feedback path from the digital signal processor to the power supply module can reduce the power dissipation of the processor. Rather than designing a feedback system around the power converter to fix the output voltage, it is better to allow the voltage to vary such that the timing constraints are just met at any given temperature and operating conditions. They have also developed a variety of techniques for achieving high efficiency at low voltages and power levels which include delay line based pulse width modulation, low resolution feedback, voltage quantization, etc. Mr. Amirtharajah extended this work to develop a self-power system where the energy required by the electronics is derived from the environment (e.g., motion). Such techniques will be critical for future battery operated wireless sensors. This work was recently reported in a Nikkie Times article in Japan.
HIGH VOLTAGE AND INSULATION RESEARCH
Professor Lesieutre and Professor Markus Zahn, with graduate students Alexander Mamishev and Yanqing Du, have redesigned the MIT-developed three-wavelength dielectrometry sensor to maximize its signal to noise ratio and to minimize cross-coupling effects between wavelengths. They have also conducted experiments to study the diffusion process of moisture between oil and pressboard to better understand and quantify the flow electrification problem in transformers, which can lead to a transformer failure when a cold transformer is energized.
Professor Zahn and graduate student Afsin Üstündag have extended their mathematical formulation that allows reconstruction of an applied electric field from light intensity measurements using electric field induced birefringence (Kerr effect) even when the magnitude and direction of the electric field varies along the light path. Using an "onion-peeling" method it is possible to calculate from light intensity measurements the magnitude and direction of an applied electric field. This methodology is being used to research the effects of charge injection on electrical conduction and breakdown behavior in high field stressed dielectrics. Graduate student Tza-Jing Gung has performed numerous confirming experiments using needle-to-plane electrodes stressed by high voltages.
Dr. Cooke and graduate student Robert Lyons have enhanced their ultrasound method for detecting charges and defects within XLPE polymer power cables. They have increased the resolution of the measurement system and applied it to the detection of localized space-charge phenomena at high applied stresses, and have observed distinct charge processes just prior to the electrical treeing breakdown failure. An improved system to observe charge conditions prior to tree inception is under construction. This will allow direct observation of the details of the micro-processes and to compare the results with theory.
In cooperation with Tokyo Electric Power Company's research laboratory (TEPCO), Dr. Cooke has established an internet link to exchange data from ultrasound charge measurement experiments at TEPCO and MIT. This link allows daily cooperative communication, including audio, video, and file sharing between groups, and direct viewing of the remote experiments. The link is used to compare experimental results and models for charge transport in XLPE polymer power cables.
Mr. Paul Warren, a longtime Research Engineer in LEES left the laboratory to join the research activities of the Gas Turbine Laboratory. Mrs. Barbara Connolly and Mrs. Kathleen McCue both retired from MIT during the last year.
Dr. Thomas M. Jahns, on a two year sabbatical leave from General Electric's Corporate Research and Development Laboratory, has joined LEES as Senior Lecturer and is working closely with Professor Kassakian. Ms Karin Janson-Strasswimmer and Ms Sara Wolfson have joined the laboratory as Senior Secretaries.
John G. Kassakian
MIT Reports to the President 1996-97