Charge Equalization Systems for Serial Valve Regulated Lead-Acid (VRLA) Connected Batteries in Hybrid Power Systems Applications

An overview of the impact of the equalization process on performance and behavior of Valve Regulated Lead-Acid (VRLA) batteries, which are a generally used in Hybrid Power Systems (HPS) is given in this paper. In order to extend the life time and runtime of batteries, an equalization process, with a good precision is required. Indeed, as mentioned in prior works, to achieve voltage equalization, the process must have a precision around 10 mV/cell. We have focused the impact of an unbalanced cells voltage on their lifetime. Typically, there are two equalization systems: While the active cell equalization processes remove charge from higher energy cell(s) and deliver it to lower energy cell(s), the passive methods, based on resistor element, remove the excess charge until the charge matches those of the lower cells in the same pack. It shows that the performance of active systems is significantly better than passive systems. Experimental results show that even for maintenance free batteries, a periodic equalization process is needed in order to extend their lifespan.