Abstract: A modular multilevel converter having a plurality of converter modules and a controller, which is configured to individually operate at least one of the converter modules by connecting and disconnecting its battery with a frequency to selectively increase and/or decrease the temperature of its battery. Each battery in the modular multilevel converter may be controlled individually.

Abstract: A battery storage system includes a multilevel-converter and a plurality of storage sections. Each storage section includes at least one holding means configured to hold at least one battery and at least one cable with at least one connector configured to electrically connect at least one of the batteries. The multilevel-converter includes a plurality of converter modules connected in series with each other and each converter module has at least one bypass switch configured to bypass the converter module and a battery switch configured to disconnect the battery at the same time when the bypass switch is on. The battery storage system further includes a controller with means for detecting the presence of a battery in each storage section and means for configuring the switches of the plurality of converter modules based on the presence of batteries such that the plurality of converter modules provides a required voltage.