A power conversion device including a plurality of Direct Current power sources that is configured to convert an output voltage of each of the Direct Current power sources into an Alternating Current voltage and to output the converted Alternating Current voltages in series connection to an Alternating Current motor, the device comprising: - a voltage converter connected to each of the Direct Current power sources and configured to convert the output voltage of the Direct Current power sources and having a primary circuit (Q11, Q12, Q13, Q14; T11, T12, T13, T14) and a secondary circuit (Q21, Q22, Q23, Q24; T21, T22, T23, T24) insulated from each other by a transformer; - a voltage controller that is configured to control an output voltage of each voltage converter; - an inverter circuit provided on an output side of each voltage converter and configured to convert the voltage output from the voltage converter into an Alternating Current voltage; and - voltage detectors that are each configured to detect an input voltage of a corresponding voltage converter, wherein the voltage controller, - when the input voltage detected by a voltage detector is lower than a reference input voltage, is configured to control the output voltage of the corresponding voltage converter so as to be stepped up to a reference output voltage by actively making smaller a duty ratio of switching control in the secondary circuit (Q21, Q22, Q23, Q24; T21, T22, T23, T24) of the corresponding voltage converter than a duty ratio of switching control in the primary circuit (Q11, Q12, Q13, Q14; T11, T12, T13, T114) of the corresponding voltage converter, - when the input voltage detected by a voltage detector is higher than the reference input voltage, is configured to control the output voltage of the corresponding voltage converter so as to be stepped down to the reference output voltage by actively making larger the duty ratio of the switching control in the secondary circuit (Q21, Q22, Q23, Q24; T21, T22, T23, T24) of the corresponding voltage converter than the duty ratio of the switching control in the primary circuit (Q11, Q12, Q13, Q14; T11, T12, T13, T14) of the corresponding voltage converter. - a voltage converter connected to each of the Direct Current power sources and configured to convert the output voltage of the Direct Current power sources and having a primary circuit (Q11, Q12, Q13, Q14; T11, T12, T13, T14) and a secondary circuit (Q21, Q22, Q23, Q24; T21, T22, T23, T24) insulated from each other by a transformer; - a voltage controller that is configured to control an output voltage of each voltage converter; - an inverter circuit provided on an output side of each voltage converter and configured to convert the voltage output from the voltage converter into an Alternating Current voltage; and - voltage detectors that are each configured to detect an input voltage of a corresponding voltage converter, - when the input voltage detected by a voltage detector is lower than a reference input voltage, is configured to control the output voltage of the corresponding voltage converter so as to be stepped up to a reference output voltage by actively making smaller a duty ratio of switching control in the secondary circuit (Q21, Q22, Q23, Q24; T21, T22, T23, T24) of the corresponding voltage converter than a duty ratio of switching control in the primary circuit (Q11, Q12, Q13, Q14; T11, T12, T13, T114) of the corresponding voltage converter, - when the input voltage detected by a voltage detector is higher than the reference input voltage, is configured to control the output voltage of the corresponding voltage converter so as to be stepped down to the reference output voltage by actively making larger the duty ratio of the switching control in the secondary circuit (Q21, Q22, Q23, Q24; T21, T22, T23, T24) of the corresponding voltage converter than the duty ratio of the switching control in the primary circuit (Q11, Q12, Q13, Q14; T11, T12, T13, T14) of the corresponding voltage converter.