A power converting apparatus comprising: a three-phase three-level inverter connectable between positive and negative terminals of a first DC power supply, one or a plurality of single-phase inverters (4, 4a) which are connected in series with an AC output line of each phase of the three-phase three-level inverter, and a control device (13, 13a), the power converting apparatus being configured such that the sums of output voltages of the three-phase three-level inverter and output voltages of the respective single-phase inverters (4, 4a) are output, wherein each single-phase inverter (4, 4a) comprises a DC capacitor for providing, as a DC input voltage for the single-phase inverter, a DC voltage which is lower than one half of the voltage of the first DC power supply; wherein the control device (13, 13a) is adapted to control the three-phase three-level inverter in such a manner that each phase of the three-phase three-level inverter outputs one pulse per half cycle of a positive or negative output voltage to a corresponding phase of the load as a primary voltage pulse (21 a), and wherein the control device (13, 13a) is adapted to control the individual single-phase inverters (4, 4a) by PWM in such a manner that each single-phase inverter (4, 4a) adds an output voltage determined by subtracting the voltage output of the corresponding phase of the three-phase three-level inverter from the phase sine wave voltage command for the corresponding phase output to the respective output of the three-phase three-level inverter, and wherein the control device (13, 13a) is adapted to control the output voltages supplied to individual phases of the load so as to form sine waves of which phases are offset by 2π/3 from one phase to another, the sine waves having the same peak value, and the output voltages supplied to the individual phases of the load being referenced to a point having a zero DC potential or a fixed DC potential with respect to a reference potential of the first DC power supply, characterized in that the control device (13, 13a) is adapted to calculate the widths of said primary voltage pulses (21 a) output by the three-phase three-level inverter in such a manner that during a half cycle or one cycle of a phase voltage, the output voltage which is determined for each single-phase inverter (4, 4a) results in the output power balance of each single individual single-phase inverter becoming zero. a three-phase three-level inverter connectable between positive and negative terminals of a first DC power supply, one or a plurality of single-phase inverters (4, 4a) which are connected in series with an AC output line of each phase of the three-phase three-level inverter, and a control device (13, 13a), the power converting apparatus being configured such that the sums of output voltages of the three-phase three-level inverter and output voltages of the respective single-phase inverters (4, 4a) are output, wherein each single-phase inverter (4, 4a) comprises a DC capacitor for providing, as a DC input voltage for the single-phase inverter, a DC voltage which is lower than one half of the voltage of the first DC power supply; wherein the control device (13, 13a) is adapted to control the three-phase three-level inverter in such a manner that each phase of the three-phase three-level inverter outputs one pulse per half cycle of a positive or negative output voltage to a corresponding phase of the load as a primary voltage pulse (21 a), and wherein the control device (13, 13a) is adapted to control the individual single-phase inverters (4, 4a) by PWM in such a manner that each single-phase inverter (4, 4a) adds an output voltage determined by subtracting the voltage output of the corresponding phase of the three-phase three-level inverter from the phase sine wave voltage command for the corresponding phase output to the respective output of the three-phase three-level inverter, and wherein the control device (13, 13a) is adapted to control the output voltages supplied to individual phases of the load so as to form sine waves of which phases are offset by 2π/3 from one phase to another, the sine waves having the same peak value, and the output voltages supplied to the individual phases of the load being referenced to a point having a zero DC potential or a fixed DC potential with respect to a reference potential of the first DC power supply, characterized in that the control device (13, 13a) is adapted to calculate the widths of said primary voltage pulses (21 a) output by the three-phase three-level inverter in such a manner that during a half cycle or one cycle of a phase voltage, the output voltage which is determined for each single-phase inverter (4, 4a) results in the output power balance of each single individual single-phase inverter becoming zero.