MULTILEVEL CONVERTER AS REACTIVE POWER COMPENSATOR HAVING ACTIVE POWER SYMMETRIZATION

摘要

A multilevel converter (7) comprises a plurality of converter strands (8-10), which are connected to the phases (2-4) of a three-phase-network (1) in a star or delta connection. From phase voltage values (U2-U4) and phase current values (IL2-IL4), an active component (w) and at least two asymmetrical components (w", b") are determined. The phase voltage values (U2-U4) are characteristic of the phase voltages present at the phases (2-4), the phase current values (IL2-IL4) are characteristic of the phase currents flowing in the phases (2-4). The active component (w) is characteristic of the overall active current flowing in the three-phase network (1). The at least two asymmetrical components (w", b") are characteristic of a distribution of the overall flowing active and reactive currents to the phases (2-4). The active component (w) and the at least two asymmetrical components (w", b") are each filtered with a filter characteristic. The phase voltage values (I2-U4) are multiplied with the filtered active component (w) and the at least two filtered asymmetrical components (w", b"). The multiplied phase voltage values (U2-U4) are multiplied with a particular weighting factor (ga-gc) and are then added to the phase current values (IL2-IL4). From the asymmetrical components (w", b") and the phase voltage values (U2-U4), a zero current (10) is determined and is also added to the phase current values (12-14). The zero current (10) is determined such that it symmetrizes a potential asymmetrical active current flow of the multilevel converter (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) is determined. The converter strands (8-10) are actuated accordingly. FIGURE 2