A minimum number of levels required to output a target modulation ratio is determined. Additionally, determining a total number of voltage orders to be controlled among a voltage fundamental wave and harmonics of power converter, comparing the minimum number of levels and the total number of voltage orders to be controlled, and fixing a larger one as a number of switching times in a quarter cycle for the target modulation ratio are performed. Further, when the total number is fixed, a shape of an output voltage is determined, and based on the target modulation ratio and the number of switching times in the quarter cycle, a determination of switching phases is made, in addition to a derivation of the pulse pattern for one cycle by which each output voltage level is used according to the target modulation ratio and the output voltage shape, and the phase is determined.