A multilevel converter (7) comprises a plurality of converter strands (8-10),whichare connected to the phases (2-4) of a three-phase-network (1) in a star ordeltaconnection. From phase voltage values (U2-U4) and phase current values (IL2-IL4), anactive component (w) and at least two asymmetrical components (w', b') aredetermined.The phase voltage values (U2-U4) are characteristic of the phase voltagespresent at thephases (2-4), the phase current values (IL2-IL4) are characteristic of thephase currentsflowing in the phases (2-4). The active component (w) is characteristic of theoverallactive current flowing in the three-phase network (1). The at least twoasymmetricalcomponents (w', b') are characteristic of a distribution of the overallflowing active andreactive currents to the phases (2-4). The active component (w) and the atleast twoasymmetrical components (w', b') are each filtered with a filtercharacteristic. The phasevoltage values (12-U4) are multiplied with the filtered active component (w)and the atleast two filtered asymmetrical components (w', b'). The multiplied phasevoltage values(U2-U4) are multiplied with a particular weighting factor (ga-gc) and are thenadded tothe phase current values (IL2-IL4). From the asymmetrical components (w', b')and thephase voltage values (U2-U4), a zero current (10) is determined and is alsoadded to thephase current values (12-14). The zero current (10) is determined such that itsymmetrizes a potential asymmetrical active current flow of the multilevelconverter (7)that would occur without the zero current (10). From the phase current values(IL2-IL4)modified in said manner, a control state (A) for the converter strands (8-10)isdetermined. The converter strands (8-10) are actuated accordingly.
展开▼
