An apparatus for supplying a polyphase alternating current motor with driving voltages, comprising: conversion means arranged to be coupled to phases of the polyphase AC motor, the conversion means including a plurality of switching means and including, in at least one phase: first switching means between a bus of an AC power supply and an output terminal; second switching means between a bus of a DC power supply and the output terminal; and third switching means between a common bus for the AC power supply and the DC power supply and the output terminal; and control means operable to generate driving voltages for the polyphase AC motor by selecting a voltage from among voltages having potential values corresponding to the AC power supply and the DC power supply and operable to use the selected voltage to operate a switch of the plurality of switching means characterized in that the control means are operable to generate a first modulation factor command value for the AC power supply from a first voltage value and an AC voltage command value of the AC power supply; generate a second modulation factor command value for the DC power supply from a second voltage value and a DC voltage command value of the DC power supply, wherein the DC voltage command value and the AC voltage command value are generated from a motor current command value dependent on a motor torque command value, a distribution ratio command value representing targeted distribution of power of the AC power supply and power of the DC power supply, and output voltage values of the AC power supply and the DC power supply; generate pulse-width-modulation pulses based on the first modulation factor command value and the second modulation factor command value; and generate ON/OFF signals for the conversion means from a first pulse-width-modulation pulse signal corresponding to the DC power supply, a second pulse-width-modulation pulse signal corresponding to the AC power supply, a signal for selecting one of the AC power supply and the DC power supply, and an AC voltage sign. conversion means arranged to be coupled to phases of the polyphase AC motor, the conversion means including a plurality of switching means and including, in at least one phase: first switching means between a bus of an AC power supply and an output terminal; second switching means between a bus of a DC power supply and the output terminal; and third switching means between a common bus for the AC power supply and the DC power supply and the output terminal; and first switching means between a bus of an AC power supply and an output terminal; second switching means between a bus of a DC power supply and the output terminal; and third switching means between a common bus for the AC power supply and the DC power supply and the output terminal; and control means operable to generate driving voltages for the polyphase AC motor by selecting a voltage from among voltages having potential values corresponding to the AC power supply and the DC power supply and operable to use the selected voltage to operate a switch of the plurality of switching means characterized in that the control means are operable to generate a first modulation factor command value for the AC power supply from a first voltage value and an AC voltage command value of the AC power supply; generate a second modulation factor command value for the DC power supply from a second voltage value and a DC voltage command value of the DC power supply, wherein the DC voltage command value and the AC voltage command value are generated from a motor current command value dependent on a motor torque command value, a distribution ratio command value representing targeted distribution of power of the AC power supply and power of the DC power supply, and output voltage values of the AC power supply and the DC power supply; generate pulse-width-modulation pulses based on the first modulation factor command value and the second modulation factor command value; and generate ON/OFF signals for the conversion means from a first pulse-width-modulation pulse signal corresponding to the DC power supply, a second pulse-width-modulation pulse signal corresponding to the AC power supply, a signal for selecting one of the AC power supply and the DC power supply, and an AC voltage sign. generate a first modulation factor command value for the AC power supply from a first voltage value and an AC voltage command value of the AC power supply; generate a second modulation factor command value for the DC power supply from a second voltage value and a DC voltage command value of the DC power supply, wherein the DC voltage command value and the AC voltage command value are generated from a motor current command value dependent on a motor torque command value, a distribution ratio command value representing targeted distribution of power of the AC power supply and power of the DC power supply, and output voltage values of the AC power supply and the DC power supply; generate pulse-width-modulation pulses based on the first modulation factor command value and the second modulation factor command value; and generate ON/OFF signals for the conversion means from a first pulse-width-modulation pulse signal corresponding to the DC power supply, a second pulse-width-modulation pulse signal corresponding to the AC power supply, a signal for selecting one of the AC power supply and the DC power supply, and an AC voltage sign.