Case 14953

Efficient, Reliable Energy Buffer for Grid-Interface Power Conversion with Switched Capacitor Architecture


AC-DC power conversion, DC-AC power conversion, Grid interface, line-frequency energy buffering Switched Capacitor circuits, film capacitors, high energy density/reliable power conversion



Grid interface power conversion, including power supplies, plug in hybrid vehicle chargers, motor drives, photovoltaic inverters, power supplies and many others.  Applications requiring long-term energy buffering incorporating batteries or ultracapacitors.



The majority of single-phase grid-interface power conversion systems use electrolytic capacitors to buffer the energy during the ac voltage cycle. These capacitors have high energy density and are capable of significantly reducing variation in dc bus voltage. However, they are large, can operate efficiently only over a narrow voltage voltage range at 120 Hz, and suffer from short lifetime and reliability issues. Film capacitors, on the other hand have longer lifetime and reliability, but provide lower energy density. Film capacitors, however, can be charged and discharged efficiently over a wide range of operating voltages. A buffering strategy that utilizes the ability of a capacitor to efficiently operate over a wide voltage range allows increasing the effective energy storage density to become on par with that of electrolytic capacitor. Previous switched capacitor buffering strategies have been shown to be effective in achieving high capacitor energy utilization, however, are either too complicated for practical implementation or suffer large voltage ripple ratio.



Stacked Switched Capacitor buffer architecture is composed of two series-connected blocks of switches and capacitors. The switches enable dynamic reconfiguration of both the interconnection amongst the capacitors and their connection to buffer port. The switching network is operated such that the voltage seen at the buffer port varies only over a small range as the capacitors charge and discharge over a wide range to buffer energy, thereby providing high effective energy density, as long as the capacitors can operate efficiently over a wide voltage range (e.g. as in the case of film capacitors on line-voltage time scales or ultracapacitors over longer time scales).



  • Achieve high energy storage capacity without electrolytic capacitors

  • Improved reliability, longer life and smaller size

  • Achieves extreme high efficiency over a wide range of operating voltages

  • Small number of switches and capacitors



  • Professor Steven Leeb (Department of Electrical Engineering and Computer Science, MIT)

  • Professor David Perreault (Department of Electrical Engineering and Computer Science, MIT)

  • Professor Khurram K Afridi (Department of Electrical Engineering and Computer Science, MIT)

  • Minjie Chen (Department of Electrical Engineering and Computer Science, MIT)

  • Arthur Hsu Chen Chang (Department of Electrical Engineering and Computer Science, MIT)


    Intellectual Property:

    U.S. Patent Application Serial Number 61/587308, filed on January 17, 2012

    U.S. Patent Application Serial Number 61/594990, filed on February 3, 2012



    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.

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



    Last revised:  April 3, 2013

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