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Bilevel Equalizer Drivers for Large Lithium-Ion Batteries

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2019, Master of Science, University of Toledo, Electrical Engineering.
The market for electric and hybrid electric vehicles is continually growing. Li-ion batteries are the heart of electric vehicles as they have high energy and power density. The Li-ion battery cells in a pack become mismatched with ageing as they undergo continuous charge and discharge cycles. All large Li-ion batteries use an electronic equalizer (EQU) to balance the cell voltages. Generally, Passive Equalizers (PEQs) are used, which connect a resistor across each of the series connected cells which are drained to match the lowest cell voltage in the pack. There are also active equalizers (AEQs) which balance the cell voltage by transferring charge between cells, but their use is limited due to high cost. A new type of hybrid equalizer called the Bilevel Equalizer (BEQ) developed during previous research [1][5][6][16][17], mitigates the weak cell issue, is low cost and works effectively. However, the BEQ has a possible open line problem when one of its lines connecting to the battery is opened. Also, the previous Open Loop (OL) system has high peak to average ratio, higher conduction losses in the inductor and its equalization current varies with the cell voltages. This makes it more difficult to predict the performance and reliability of the system. Further, the design parameters for the component needs to be at higher end incorporating the fluctuation of equalization current at various voltage levels which increases the cost of the system. This research proposes solutions to these problems, i.e. an open line protection circuit and a Closed Loop (CL) controller. This study also tested the charge transfer efficiency between sections of a battery pack for both OL and CL drivers. It was found that the OL and CL drivers have almost the same charge transfer efficiency. While the CL circuit was designed to achieve high charge transfer efficiency, the switching losses are much higher than those in the open loop. Therefore, although the peak current in the OL driver is much higher than the CL driver, the OL with open line protection is probably the most suitable driver in terms of efficiency, cost and simplicity.
Ngalula Mubenga (Committee Chair)
Thomas Stuart (Committee Member)
Richard Molyet (Committee Member)
80 p.

Recommended Citations

Citations

  • Sharma, K. (2019). Bilevel Equalizer Drivers for Large Lithium-Ion Batteries [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564677943667852

    APA Style (7th edition)

  • Sharma, Kripa. Bilevel Equalizer Drivers for Large Lithium-Ion Batteries. 2019. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564677943667852.

    MLA Style (8th edition)

  • Sharma, Kripa. "Bilevel Equalizer Drivers for Large Lithium-Ion Batteries." Master's thesis, University of Toledo, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564677943667852

    Chicago Manual of Style (17th edition)