METHOD TO OPERATE A SYSTEM COMPRISING AN ENERGY STORAGE SYSTEM

There is disclosed herein a method to operate a system comprising an energy storage system (ESS) and a converter. The ESS being connected to the converter such that a DC-side of the converter forms DC terminals between which at least one string of modules of the ESS is connected. The method comprises receiving a bypass request to bypass at least one module in the ESS, based on a total number of modules to be bypassed exceeding a number of redundant modules, controlling the converter to reduce the terminal voltage of the ESS; and after reducing the terminal voltage of the ESS, bypassing the module. There is further disclosed herein a system comprising a central controller performing said method.