Switched Capacitor Balancing Time Estimation and Dependency

Balancing/equalization plays a key role in lithium battery management systems. Dissipative techniques are commonly used to balance batteries for vehicles. The main advantages are the low complexity and the hardware simplicity. But the system has a worth efficiency, only works during the main charge process and takes a long time. Capacitive balancing structures are a special case of active balancing techniques which allow precise balancing, no sensing and whose process can be performed separately, or continuously during battery operation. This paper describes a way to estimate the balancing time of a switched-capacitor system, an appreciated low-cost capacitive structure. This balancing technique can offer a good trade-off between electronic complexity, cost and performance, but strongly depends on the open voltage lithium cell characteristic. A mathematical formulation of the balancing dynamic is presented the balancing time is expressed as a function of capacitors, resistances, clock frequency and cell open circuit voltage.