A Battery Management System based on Indirect Voltage Detection

Lithium-ion battery cells like the 18650 are commonly installed in energy storage and electric vehicle applications. In a battery cell array with series and parallel connections, the charging voltage of each cell is different, and the charging current concentrates in the cell with the lowest voltage. During discharge, however, the current is concentrated in the cell with the highest voltage. During charge, the current is concentrated in the cell with the lowest voltage, and during discharge, the current is conentrated in the cell with the highest voltage. In prior battery cell balancing studies, the balancing technique has involved a very complicated control method. This paper proposes a battery management system (BMS) for cell balancing that uses indirect voltage detection. The proposed BMS can set the lowest voltage for cell current balancing and can perform over-voltage blocking in a very simple structure that allows stable charging and discharging. In this study, a BMS for three parallel models of 65 Wh lithium-ion batteries was tested to verify its voltage controlling, current balancing, and charging/discharging abilities.