A multilevel inverter, the multilevel inverter comprising: a phase shift transformer configured to output a voltage of predetermined phase by receiving an AC input power having a fixed frequency; and a plurality of unit power cells serially-connected and configured to output a voltage having a predetermined phase by receiving a voltage provided by the phase shift transformer; characterized in that: the multilevel inverter comprises a master controller configured to exchange data with a unit power cell controller included in each of the plurality of unit power cells, that the phase shift transformer is configured to include phase shifts of the number corresponding to the number of the plurality of unit power cells and that the unit power cell is such that three unit power cells for each phase are serially connected for 3-phase output and the phase shift transformer including nine phase shifts, and each phase value being of a difference of 60°/9, that an operation basic format for the plurality of unit power cells including output voltage command, a synchronous signal is transmitted from the master controller to the unit power cell controller via optical communication, and information including an over-voltage, an under-voltage, an arm short-circuit, a ground, a fuse open, a heat sink overheat, an abnormal H/W, open phase of output in the unit power cell, and input open phase is transmitted from the unit power cell controller to the master controller, that each of the phase value is -27°, -20°, -13°, -7°, 0°, 7°, 13°, 20° and 27°, that the master controller receives a voltage from each unit power cell, and in turn provides voltage reference information to the unit power cell, that each unit power cell generates an output voltage by receiving a DC-Link voltage, and applies the output voltage to a motor which is a load, and that a frequency of the output voltage from the unit power cell is changed to be used for controlling torque and speed of the motor. a phase shift transformer configured to output a voltage of predetermined phase by receiving an AC input power having a fixed frequency; and a plurality of unit power cells serially-connected and configured to output a voltage having a predetermined phase by receiving a voltage provided by the phase shift transformer; characterized in that: the multilevel inverter comprises a master controller configured to exchange data with a unit power cell controller included in each of the plurality of unit power cells, that the phase shift transformer is configured to include phase shifts of the number corresponding to the number of the plurality of unit power cells and that the unit power cell is such that three unit power cells for each phase are serially connected for 3-phase output and the phase shift transformer including nine phase shifts, and each phase value being of a difference of 60°/9, that an operation basic format for the plurality of unit power cells including output voltage command, a synchronous signal is transmitted from the master controller to the unit power cell controller via optical communication, and information including an over-voltage, an under-voltage, an arm short-circuit, a ground, a fuse open, a heat sink overheat, an abnormal H/W, open phase of output in the unit power cell, and input open phase is transmitted from the unit power cell controller to the master controller, that each of the phase value is -27°, -20°, -13°, -7°, 0°, 7°, 13°, 20° and 27°, that the master controller receives a voltage from each unit power cell, and in turn provides voltage reference information to the unit power cell, that each unit power cell generates an output voltage by receiving a DC-Link voltage, and applies the output voltage to a motor which is a load, and that a frequency of the output voltage from the unit power cell is changed to be used for controlling torque and speed of the motor. the multilevel inverter comprises a master controller configured to exchange data with a unit power cell controller included in each of the plurality of unit power cells, that the phase shift transformer is configured to include phase shifts of the number corresponding to the number of the plurality of unit power cells and that the unit power cell is such that three unit power cells for each phase are serially connected for 3-phase output and the phase shift transformer including nine phase shifts, and each phase value being of a difference of 60°/9, that an operation basic format for the plurality of unit power cells including output voltage command, a synchronous signal is transmitted from the master controller to the unit power cell controller via optical communication, and information including an over-voltage, an under-voltage, an arm short-circuit, a ground, a fuse open, a heat sink overheat, an abnormal H/W, open phase of output in the unit power cell, and input open phase is transmitted from the unit power cell controller to the master controller, that each of the phase value is -27°, -20°, -13°, -7°, 0°, 7°, 13°, 20° and 27°, that the master controller receives a voltage from each unit power cell, and in turn provides voltage reference information to the unit power cell, that each unit power cell generates an output voltage by receiving a DC-Link voltage, and applies the output voltage to a motor which is a load, and that a frequency of the output voltage from the unit power cell is changed to be used for controlling torque and speed of the motor.