Pack-to-Multicell Voltage Equalization of Lithium Battery String Using Switched-Capacitor in Series-Parallel Configuration
Paul Lawrence (a), Trendy Prima Wijaya (b), Edi Leksono (c), Justin Pradipta (d*), Irsyad Nashirul Haq (e)

(a,b,c,d,e) Department of Engineering Physics, Faculty of Industrial Technology, Institut Teknologi Bandung, Indonesia
(e) National Center for Sustainable Transportation Technology, Indonesia
*justinpradipta[at]itb.ac.id

Abstract

This paper proposes a novel pack-to-multicell topology to equalize the voltage distribution of a series Lithium battery pack. Several switched-capacitor converters are implemented in a series-parallel configuration to allow energy transfer from the entire pack to every cell simultaneously. Those switched capacitors not only act as an energy transfer path but also as an insulated electrical interface for each cell when the voltage balancing process occurs. The series-parallel term refers to two capacitor phases during every equalization period. In the series-connected phase, each capacitor is connected to each corresponding cell so the cell voltage and capacitors voltage would be equalized. Subsequently, in the parallel-connected phase, all capacitors are connected among each other such that they are set to desirable voltage values regulated by DC/DC converter. The experimental setup of the proposed system has been tested on 4 series-connected 3000 mAh Lithium cells, each of them has different initial voltages with a large spread (2.69-3.92 Volt). The experiment results show the convergence of the cell^s voltages without over-equalization and with a charge transfer efficiency of about 87%.

Keywords: voltage equalization, pack-to-multicell, switched-capacitor, series-parallel configuration, lithium battery

Topic: Battery Technology and Management System