Selection of Shunting Resistance for Cell Equalization in Battery Management System

Abstract

Dissipative shunting resistor is a cheap, simple, and well-known equalizing method for resolving cell mismatch and voltage imbalance problems in a series-connected battery pack. However, seldom information reveals how to choose a good shunting resistance value for the resistor-based equalizer. Determining resistance value based on power dissipation or total equalization time alone is not an attractive solution because a trade-off exists between the two performances. In this paper, energy-time product (ETP) is proposed to be the figure-of-merit for determining the shunting resistance value. The ETP takes both power and time into account, and determines the resistance value by minimizing the ETP value. The first-order battery electrical model is applied to derive the relation between the shunting resistance and ETP, and construct a general way to quickly find the good resistance value. A resistor-based equalizer is implemented to validate the ETP equalizing results and confirms the usefulness of the proposed method. The simulation and experiment results show that the ETP error can be as low as 8.5%.