Abstract: In an apparatus for controlling a power converter, which is adapted to control, in accordance with a PWM system, a voltage-type inverter for system interconnection interposed between a d.c. power source and an a.c. system to interchange power therebetween, a scheme is employed to switch voltage amplitude adjustment signals of respective phases depending upon an output voltage phase signal provide a phase voltage amplitude. Energization periods of respective controllable rectifier elements of the power converter are determined on the basis of the phase voltage amplitude and the output voltage phase signal. Employment of such a scheme makes it possible to independently control the output voltage of the inverter every phase or with respect to both positive and negative sides of the phases, respectively.