A CONTROL SYSTEM AND A METHOD FOR VOLTAGE BALANCING OF AN ENERGY STORAGE SYSTEM

A control system for voltage balancing of an energy storage system comprises a data processing system (108) for carrying out the balancing in a hierarchical way so that an upper level of the balancing controls voltage balance of series connected energy storage racks (101-103) of the energy storage system and a lower level of the balancing controls the voltage balance of series connected energy storage modules (104-106), such as capacitor modules or cells, within each energy storage rack utilizing a rack reference value, such as a reference voltage, given by the upper level balancing to the energy storage rack. Due to the hierarchical approach, the control system is scalable to very large energy storage systems which may comprise thousands, or even tens of thousands, of energy storage cells.