System-theoretic analysis of battery systems during equalization, charging, and discharging

The normal and reliable operation of the battery system in the electric vehicle plays a critical role to ensure safe and comfortable driving for users. In practice, a very common problem of battery system is charge imbalance. To solve this problem, battery equalization has been introduced as a part of the battery management system. In order to design a battery equalization system and improve its performance, it is necessary to understand its behavior and performance from the system-level based on quantitative metrics. For a battery system, the evaluation of the time to complete equalization, charging and discharging is of great importance, since many other performance metrics can be calculated from the equalization, charging, and discharging times. In this paper, mathematical model for a class of series-based battery equalization system is introduced to describe its operation under different working situations. Then, based on the mathematical model, the analytical formulas for calculating the equalization time and charging or discharging time are derived and validated by the simulations.