A method for generating a combined output waveform (VOUT) in a power inverter system (100) is disclosed. The power inverter system comprises a voltage equaliser (120) having an energy storage element adapted to be charged by a combined output voltage from a plurality of switching units and to add an adjustable voltage to the combined output waveform. A voltage of the combined output waveform is measured, a difference (Δ) between the measured voltage of the output waveform and a voltage of a target waveform (UT) is determined, and a voltage (UCORR) corresponding to the determined difference is added, by the voltage equaliser, to the combined output waveform so as to improve the matching of the combined output power waveform and the target power waveform.