Abstract: A power conversion system, including a converter for converting an AC power from a power source to a DC power, a DC capacitor for smoothing the DC power output from the converter, an inverter for converting the DC power smoothed by the DC capacitor to an AC power of an arbitrary frequency to drive and control an induction motor, a unit for detecting or computing a magnetic flux axis of the induction motor, a unit for computing a current orthogonal to the detected or computed magnetic flux axis, and a phase control unit for controlling a phase angle of an output voltage of the inverter so that a value of the current orthogonal to the detected or computed magnetic flux axis is maintained at a constant level.

Abstract: A power converter including, a converter, a three-level DC voltage source composed of a series connected capacitors connected between outputs of the converter to generate a positive, a neutral and a negative potential, a three-level NPC inverter, a chopper circuit, and a chopper control circuit. The chopper circuit includes a series circuit of a first and a second switching device connected between a positive and a negative potential points of the three-level DC voltage source, a first and a second diode connected in antiparallel with the first and second switching devices, respectively, and a reactor connected between a neutral potential point and a connecting point of the first and second switching devices.