A new perspective on battery cell balancing: Thermal balancing and relative temperature control

Abstract

This paper introduces a new perspective on cell balancing (equalization) in a lithium-ion battery pack by proposing the thermal balancing concept of battery cells. Thermal balancing can be achieved by relative temperature control based on either conventional active cell balancing circuits or module-integrated systems. Compared to voltage/state-of-charge (SoC) balancing, relative temperature can be used as the balancing target with several advantages. First, absolute temperature directly affects the lifetime and usable capacity of battery cell. Second, the relative temperature between cells degrades the uniformity of the cells and increase the imbalance in various parameters. Third, temperature usually has a slow dynamic which makes it an ideal control target for low balancing power compared to the high charging/discharging power. Last, thermal balancing control can take over the job of the thermal management system to a certain degree. Therefore the balancing function could be potentially built into the thermal management system. In this paper, two algorithms are developed to achieve thermal balancing: direct relative temperature control and virtual heat sink temperature control. A simple battery system thermal model is developed and the proposed control algorithms are validated.