Method for operating an uninterruptible power supply, UPS, (1, N) for connecting a load to an AC source and a DC source, the UPS (1, N) comprising a first converter assembly comprising a first 3-level converter with T- or NPC-type topology, the first 3-level converter connected on a first side via three phase legs to the AC source and connected on a second side to a split DC link, the split DC link comprising two halves with a midpoint reference, wherein each phase leg of the first 3-level converter comprises a first controlled device arranged between the respective phase leg of the AC source and the respective phase leg of first 3-level converter, the first controlled device configured for connecting and disconnecting at least two phase legs of the first converter from the AC source, and wherein each phase leg further comprises an inductor arranged between respective phase leg of the first 3-level converter and the first controlled device, wherein the first converter assembly further comprises a second controlled device, configured for connecting and disconnecting the at least two phase legs of the first converter on the AC source side, wherein the second controlled device is connected on its first side between the inductor and the first controlled device of a first one of the at least two phase legs and on its second side between the inductor and the first controlled device of a second one of the at least two phase legs, a second converter assembly comprising a second converter connected on a first side to the DC link and on a second side to the load, a third converter assembly comprising a third converter connected on a first side to the DC source and on second side to the DC link, the UPS (1, N) configured for performing the steps of: Opening, in an operation mode as balancer, the three phase legs of the first controlled device, and, closing the second controlled device and operating semiconductor switches of the converter with a current path in the first 3-level converter, such that the first converter assembly transfers energy from the inductors, which are connected via the second controlled device, to the split DC link halves to maintain voltage regulation of the DC link in respect to the midpoint reference. a first converter assembly comprising a first 3-level converter with T- or NPC-type topology, the first 3-level converter connected on a first side via three phase legs to the AC source and connected on a second side to a split DC link, the split DC link comprising two halves with a midpoint reference, wherein each phase leg of the first 3-level converter comprises a first controlled device arranged between the respective phase leg of the AC source and the respective phase leg of first 3-level converter, the first controlled device configured for connecting and disconnecting at least two phase legs of the first converter from the AC source, and wherein each phase leg further comprises an inductor arranged between respective phase leg of the first 3-level converter and the first controlled device, wherein the first converter assembly further comprises a second controlled device, configured for connecting and disconnecting the at least two phase legs of the first converter on the AC source side, wherein the second controlled device is connected on its first side between the inductor and the first controlled device of a first one of the at least two phase legs and on its second side between the inductor and the first controlled device of a second one of the at least two phase legs, a second converter assembly comprising a second converter connected on a first side to the DC link and on a second side to the load, a third converter assembly comprising a third converter connected on a first side to the DC source and on second side to the DC link,