Research

 

Piezoelectric-Resonator-Based Converters

Power converters are often the bulkiest components in the systems they serve, and the current trajectory of technology demands converters with smaller sizes, lighter weights, higher efficiencies, and lower costs. Major advances in power converter miniaturization will soon require new passive component technologies whose fundamental size and efficiency capabilities are beyond those of traditional components like magnetics. This motivates investigation of piezoelectrics, which store energy in the mechanical compliance and inertia of a piezoelectric material and have superior power density and efficiency capabilities at small scales. In this work, we have enumerated and analyzed dc-dc converter topologies and control sequences that utilize a piezoelectric resonator as the only passive component and strategically use its resonant cycle to maximize efficiency. An experimental prototype of one such converter implementation exhibits peak efficiency >99%, illustrating the promise of piezoelectric-resonator based converters for high-voltage, low-power applications.

Select Publication

  • J. D. Boles, J. J. Piel, and D. J. Perreault, "Enumeration and analysis of dc-dc converter implementations based on piezoelectric resonators," in IEEE Transactions on Power Electronics, vol. 36, no. 1, pp. 129-145, 2021. 

Awards

  • Best Paper Award: IEEE Workshop on Control and Modeling for Power Electronics (COMPEL), 2019
  • Best Poster Award: MIT Microsystems Annual Research Conference (MARC), 2020

 

 

Piezoelectric-Transformer-Based Converters

Piezoelectric transformers (i.e., multi-port piezoelectric components) exhibit the same opportunities as piezoelectric resonators but offer additional advantages for applications requiring high voltage conversion ratios and/or electrical isolation. Piezoelectric transformers have seen commercial use for driving CCFL backlights, but attempts to use them in dc-dc converters without auxiliary passives like magnetics typically results in limited efficiencies. In this work, we have enumerated both isolated and non-isolated dc-dc converter topologies and control sequences to identify those that most efficiently utilize piezoelectric transformers as their only passive components. Such converter implementations will facilitate miniaturization for applications requiring high voltage conversion ratios and/or isolation without the need for bulky magnetics.

Select Publication

  • J. D. Boles, E. Ng*, J. H. Lang, and D. J. Perreault, "Dc-dc converter implementations based on piezoelectric transformers," to appear in IEEE Journal of Emerging and Selected Topics in Power Electronics, 2022.

 

 

Piezoelectric Materials and Vibration Modes

Piezoelectric passive components offer several potential advantages to power conversion, and the converter architectures described above have been developed to most effectively utilize them. However, many questions remain about how to design the piezoelectric components themselves. In this work, we establish efficiency and power density figures of merit for piezoelectric materials and vibration modes specifically for use in power conversion. These figures of merit correspond to geometry conditions that serve as guidelines for high-efficiency, high-power-density piezoelectric resonator design. We demonstrate use of these metrics to evaluate commercially-available PZT piezoelectric materials, and we find these figures of merit to be highly representative of piezoelectric capabilities in realistic converter operation. Further, the derived efficiency and power density capabilities of piezoelectrics are shown to scale favorably for converter miniaturization. 

Select Publication

  • J. D. Boles, J. E. Bonavia*, P. L. Acosta*, Y. K. Ramadass, J. H. Lang, and D. J. Perreault, "Evaluating piezoelectric materials and vibration modes for power conversion," to appear in IEEE Transactions on Power Electronics, 2022.

 

 

Bidirectional LLC Resonant Converter

Operating at high switching frequencies can facilitate miniaturization, higher performance, and reduced cost in power electronics. The LLC resonant converter has become a popular topology for power conversion at high frequencies, but many of its advantages inherently exist only in the forward power flow direction. To extend the benefits of the LLC to bidirectional power flow applications, we have developed a LLC topology variant with operating modes that strategically utilize current circulation patterns to create LLC behavior in both directions. We experimentally demonstrated this concept in a 1 kW prototype for electric vehicle applications, and the bidirectional LLC gain characteristic proved to be vital for meeting the converter's specified operating range. 

Select Publication

  • J. D. Boles, J. A. Santiago-Gonzalez, D. M. Otten, and D. J. Perreault, "A bidirectional LLC converter enabled by common mode and differential mode operation," in Proc. IEEE Energy Conversion Congress and Exposition (ECCE), Baltimore, MD, USA, Sep. 2019.

Awards

  • Best Overall Abstract, Pitch, Poster Award: MIT MTL Annual Research Conference (MARC) Analog, RF, and Power Circuits Session, 2019

 

 

Converter-Based Emulation of Grid Battery Storage

Battery energy storage systems (BESSs) have become popular forms of grid storage in recent years - especially Lithium-ion BESSs. Power system tests for design and planning increasingly need BESS representation, but BESSs tend to be too costly, restrictive, and high-maintenance for experimental use. As a solution, we developed a BESS emulation tool (based on a three-phase inverter) to provide an inexpensive, flexible, yet representative alternative to real BESSs for grid-related tests. This emulator considers chemistry-specific battery behavior, but it also includes the BESS’s power electronics interface, control, and automatic support functions for the grid. It is now used in a hardware testbed for studying grid scenarios with up to 100% non-hydro renewable generation (ie. solar, wind) across multiple power regions in real time. 

Select Publications

  • J. D. Boles, Y. Ma, J. Wang, D. Osipov, L. M. Tolbert, and F. Wang, "Converter-based emulation of battery energy storage systems (BESS) for grid applications," in IEEE Transactions on Industry Applications, vol. 55, no. 4, pp. 4020-4032, 2019.
  • J. D. Boles, "Battery Energy Storage Emulation for Power Systems Applications," Master's Thesis, University of Tennessee, Knoxville,  Aug. 2017.

Awards

  • Outstanding Presentation Award: IEEE Applied Power Electronics Conference (APEC) Battery Systems Session, 2018
  • Outstanding Presentation Award: CURENT Industry Conference and NSF/DOE Site Visit, 2016