Electrochemical storage systems are increasingly used to support the electricity system thanks to their high flexibility. The demand for storage systems is growing rapidly and a substantial portion of the supply may come, in the case of stationary applications, from the reuse of vehicle batteries that are not yet at the end of their life. The so-called ‘2nd-life’ represents an important opportunity for the future, but it also poses various technological challenges. The development of balancing systems, capable of efficiently managing batteries with different performances, is of crucial importance to these applications.
In this context, Modular Multilevel Converters (MMC) will play an important role, as they can manage battery modules with uneven performances. Although this technology represents the state of the art in high voltage direct current applications, their level of development in combination with storage systems has not yet reached maturity. For this reason, we developed and analyzed in a simulation environment the balancing functions necessary to manage Storage Systems (SSs) with different charge levels and different performances installed inside an MMC. This first activity confirmed that, by means of appropriate control systems, it is possible to manage the initial charge imbalance of the modules and even use modules with different Ah capacities and/or different internal resistance. The simulations showed that this type of converter can be used in 2nd-life applications without further balancing systems; it also brings further advantages such as the possibility of excluding battery modules that have reached end of life.
Furthermore, MMC power electronics modules were designed, built and experimentally verified during the activity. This component, which is the basic element of the converter, can be used in future applications of and experiments on this type of converter applied to different use cases.31