Modularized charge equalizer with switch network for lithium-ion battery in electric vehicles

Abstract

Recently, Electric vehicles (EVs) have become one of the most promising vehicles for fuel efficient and eco-friendly demands by automakers, governments, and customers. Compared to the conventional vehicle with internal combustion engines (ICE), EVs uses electric energy of the battery pack for driving electronic motors. Hence, EV batteries should be required a high-energy capacity and long-life cycle for extending the driving range. To meet these demands, lithium-ion batteries are widely used for EV applications due to their high-energy density and efficient charge properties. In lithium-ion battery system for electric vehicle (EV), necessity of the battery management system (BMS) is getting increased for the battery’s safety and life cycle. In this BMS, cell charge levels should be individually monitored by cell monitoring circuit. Moreover, charge equalizer is essential to enhance the battery life cycle and safety. However, the BMS has difficulty of individual cell balancing and cell monitoring due to the problem of size as well as the cost for a large number of battery cells. Moreover, it shows high voltage stress of electrical elements in the equalization converter due to the high voltage of battery pack. To improve these drawbacks, this paper proposes charge equalizer methods with cell switch network. These methods effectively use the cell switches for cell balancing and monitoring circuit in modularized battery system. With this switch network, it can be achieved efficient charge equalization based on the simple cell voltage monitoring. Furthermore, it leads to the great size reduction of the charge equalizer with lower cost which brings advancement of individual cell balancing in a large number of battery cells. In this paper, three types of the proposed equalizer are presented with a prototype system for lithium-ion battery cells.

1. Two-Stage Charge Equalizer with Switch Network The proposed circuit employs the two-stage DC-DC converter to reduce the...