Case 14953

Switched Capacitor Energy Buffer Architecture

Keywords:

Power conversion systems, Stacked Switched Capacitor (SSC) energy buffer, energy storage, switched capacitor, film capacitors, electrolytic capacitors

Applications:

Power conversion systems

Problem:

    Power conversion systems that interface between dc and single-phase ac need energy storage to provide buffering between the constant power desired by a dc source or load and the continuously varying power desired for a single-phase ac system. While electrolytic capacitors are generally used to provide high-density energy storage for buffering, their limited-life and reliability are a concern. Film capacitors have much longer life and higher reliability, but an order of magnitude lower peak energy density. Therefore, for long-life and compact grid-interface systems there is a strong interest in developing energy buffers based on film capacitors that provide effective energy density comparable to electrolytic capacitors.

Technology:

This patent describes the Stacked Switched Capacitor (SSC) energy buffer, which is composed of two series connected blocks of switches and capacitors. It works on the principle that while the voltages of individual capacitors can vary over a wide range, the voltage at the buffer port remains constrained to a desired narrow range. By using long-life capacitors that can be efficiently charged and discharged over a wide voltage range (e.g., film capacitors) it achieves effective energy densities comparable to electrolytic capacitors and much longer life.

Advantages:
  • High energy density because the switching network is operated such that while the voltage seen at the buffer port varies only over a small range, the voltage of the individual capacitors varies over a wide range.
  • Longer life and higher reliability because film capacitors are used instead of electrolytic capacitors.
  • High efficiency because the switching network need operate at only very low (line-scale) switching frequencies.
  • Reduce loss by taking advantage of soft charging of the energy storage capacitors.
  • High efficiency across the full operating range because the proposed buffer architecture exhibits losses that reduce as energy buffering requirements reduce.

Inventors:
  • Professor David J. Perreault (Department of Electrical Engineering and Computer Science, MIT)
  • Visiting Associate Professor Khurram K. Afridi (Department of Electrical Engineering and Computer Science, MIT)
  • Minjie Chen (Department of Electrical Engineering and Computer Science, MIT)

Intellectual Property:

PCT Patent Application Number PCT/US2013/021886, filed on January 17, 2013

PCT Patent Application Number PCT/US2013/022001, filed on January 17, 2013

PCT Patent Application Number PCT/US2013/021926, filed on January 17, 2013

PCT Patent Application Number PCT/US2013/024552, filed on February 3, 2013

Publications:

[1] M. Chen, Stacked Switched Capacitor Energy Buffer Architecture, SM Thesis, Dept. of EECS, Massachusetts Institute of Technology, Cambridge, MA, Dec. 2011.

[2] M. Chen, K. K. Afridi, and D. J. Perreault, “Stacked Switched Capacitor Energy Buffer Architecture,” Proceedings of the IEEE Applied Power Electronics Conference (APEC), Orlando, FL, Feb. 2012.

Last revised: April 30, 2013

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