1 Introduction

There are differences in capacity and internal resistance between individual batteries, coupled with the passage of time, the increase in the number of cycles, the difference in temperature and humidity, and many other factors. This makes the individual differences more obvious, especially the performance of lithium iron phosphate batteries is more prominent. If the batteries are used in series, and if the current of charging and discharging is equal, and the amount of charge and discharge is consistent, there can be a large capacity battery that is not filled or can not be fully utilized, or the small capacity of the battery overshoot or over discharge. As a result, the capacity of the battery is not fully used or the service life is greatly reduced, so the voltage of the battery must be equalized and used in series to keep all the batteries safe and to maximize the use of the battery.

Therefore, a discrete active balancing design is proposed, relying on a switching matrix and converter to construct an active balancing topology that can achieve cross-module balancing.