A method for controlling an inverter of a control apparatus controlling the inverter, the method comprising: calculating a maximum current from an output current of each phase of the inverter; determining a variable level upper limit by performing a DQ conversion for the output current of each phase of the inverter and adding a change allowable value to the DQ converted output current; wherein the determining of the variable level upper limit further comprises determining a variable level lower limit by subtracting a variable level band from the variable level upper limit, the method further comprising: determining an output frequency of the inverter by controlling the output frequency of the inverter differently for each of four sections comprising a first section, a second section, a third section, and a fourth section, wherein the determining of the output frequency of the inverter further comprises: in the first section in which the output current of the inverter enters the variable level lower limit, fixing the output frequency of the inverter; in the second section in which the output current of the inverter enters the variable level upper limit, attenuating the output current of the inverter by attenuating the output frequency of the inverter based on the difference between the maximum current for each phase and the variable level upper limit; in the third section in which the output current of the inverter is reduced from the variable level upper limit to the variable level lower limit or less, increasing the output frequency of the inverter up to a target frequency level and fixing the output frequency to the target frequency level in the fourth section in which the output current of the inverter maintains or enters the variable level lower limit. calculating a maximum current from an output current of each phase of the inverter; determining a variable level upper limit by performing a DQ conversion for the output current of each phase of the inverter and adding a change allowable value to the DQ converted output current; wherein the determining of the variable level upper limit further comprises determining a variable level lower limit by subtracting a variable level band from the variable level upper limit, the method further comprising: determining an output frequency of the inverter by controlling the output frequency of the inverter differently for each of four sections comprising a first section, a second section, a third section, and a fourth section, wherein the determining of the output frequency of the inverter further comprises: in the first section in which the output current of the inverter enters the variable level lower limit, fixing the output frequency of the inverter; in the second section in which the output current of the inverter enters the variable level upper limit, attenuating the output current of the inverter by attenuating the output frequency of the inverter based on the difference between the maximum current for each phase and the variable level upper limit; in the third section in which the output current of the inverter is reduced from the variable level upper limit to the variable level lower limit or less, increasing the output frequency of the inverter up to a target frequency level and fixing the output frequency to the target frequency level in the fourth section in which the output current of the inverter maintains or enters the variable level lower limit. determining an output frequency of the inverter by controlling the output frequency of the inverter differently for each of four sections comprising a first section, a second section, a third section, and a fourth section, wherein the determining of the output frequency of the inverter further comprises: in the first section in which the output current of the inverter enters the variable level lower limit, fixing the output frequency of the inverter; in the second section in which the output current of the inverter enters the variable level upper limit, attenuating the output current of the inverter by attenuating the output frequency of the inverter based on the difference between the maximum current for each phase and the variable level upper limit; in the third section in which the output current of the inverter is reduced from the variable level upper limit to the variable level lower limit or less, increasing the output frequency of the inverter up to a target frequency level and fixing the output frequency to the target frequency level in the fourth section in which the output current of the inverter maintains or enters the variable level lower limit. in the first section in which the output current of the inverter enters the variable level lower limit, fixing the output frequency of the inverter; in the second section in which the output current of the inverter enters the variable level upper limit, attenuating the output current of the inverter by attenuating the output frequency of the inverter based on the difference between the maximum current for each phase and the variable level upper limit; in the third section in which the output current of the inverter is reduced from the variable level upper limit to the variable level lower limit or less, increasing the output frequency of the inverter up to a target frequency level and fixing the output frequency to the target frequency level in the fourth section in which the output current of the inverter maintains or enters the variable level lower limit.