Method for operating switching elements (22, 24, 26, 28, 30, 32, 34, 36, 38, 40) of an
inverter (12) to which a
stator winding of an at least three-phase
electric machine (14) is connected, wherein the
inverter (12) has at least one series connection of the switching elements (22, 24, 26, 28, 30, 32, 34, 36, 38, 40) for each of the phases (L1, L2, L3, L4, L5) of the
electric machine (14) in order to electrically couple the
electric machine (14) to a DC link (16) connected to the
inverter (12), wherein switching signals for the switching elements are determined by
vector control and provided at a
clock rate greater than a frequency of a fundamental oscillation of the phase voltages in order to provide respective phase voltages by the inverter (12). is, wherein the switching signals are determined depending on at least one first reference pointer, which is determined bythat, for the switching states of the inverter (12) achievable by the switching elements (22, 24, 26, 28, 30, 32, 34, 36, 38, 40), first
voltage state vectors are determined in a corresponding first
space vector system using a Fortescue transformation adapted to the number of phases of the electrical
machine (14), wherein the first
reference vector is determined depending on a superposition of at least two of the first
voltage state vectors, wherein, for determining the at least one first
reference vector, at least two first
voltage state vectors are chosen, one of which is a long first voltage
state vector and the other a medium or a short first voltage
state vector, and, for superimposing a
harmonic of the phase voltage with respect to the frequency of the fundamental oscillation, the switching signals are additionally determined depending on at least one second
reference vector.which is coupled to the first reference vector depending on an
order number of the
harmonics and which is determined by determining second stress state vectors in a corresponding second
space vector system, wherein the second reference vector is determined depending on a superposition of at least two of the second stress state vectors and wherein a separate modulation level is determined for the
harmonic and a total modulation level is maximized depending on the separate modulation level.