Abstract: A method and an apparatus for reducing harmonics mains-power-supply perturbations of a self-commutated multilevel inverter which is clocked at the fundamental frequency and has capacitive storage devices. On one hand, when a predetermined operating point of the multilevel inverter is left, angular values for turn-on and turn-off instants of individual voltage levels of the multilevel inverter are calculated for a newly determined operating point. On the other hand, a terminal voltage of the multilevel inverter is matched to an altered fundamental amplitude of the inverter output voltage. Consequently, the harmonics mains-power-supply perturbations of a multilevel inverter can be kept to a minimum at any time.

Abstract: A switch-off method for a three-phase solid state reactive power compensator for a rotary three phase power system has first and second thyristor valves receiving respective first and second firing signals, and three capacitors. The firing signals are suppressed to a point in time for first turning off the second firing thyristor valve in immediately successive phases in direction of rotation of the three-phase power system.