Patent ID: 8144489

Claim:
An apparatus for conversion of an electric current, comprising: at least one DC voltage connection; at least one phase module having an AC voltage connection and a phase module branch formed between each said DC voltage connection and each said AC voltage connection, each said phase module branch having a series circuit composed of submodules each having an energy storage unit, at least one power semiconductor, and submodule sensors for detecting energy stored in said energy storage unit and obtaining energy storage unit energy values; and a regulation device for regulation of the apparatus in dependence on the energy storage unit energy values and predetermined nominal values, said regulation device having an addition unit for addition of the energy storage unit energy values resulting in branch energy actual values being obtained and means for calculation of circulating-current nominal values in dependence on the branch energy actual values, said regulation device compensating for unbalances in the branch energy actual values in dependence on the circulating-current nominal values.