Charge equalization system for ultracapacitor series

To maximize performance and reliability, the individual ultracapacitor energy in a series connected pack must be fairly uniform. Otherwise, some cells will be damaged permanently resulting from overcharging or over-discharging. Based on the analysis of several equalization circuits, a charge equalization system is proposed. This system is consisted of double power supplies, one is the charging power supply, which is a buck converter with snubber, and the other is the equalization power supply, which is a half-bridge converter with the isolation transformer. A FPGA-based controller is used to control the whole system. This system maintains the ultracapacitor cell voltage at an equally charging/discharging level, so it can prevent ultracapacitor cell from overcharging and over-discharging and it is propitious to improve energy efficiency and enhance the cycle life of ultracapacitor.